WO2018037774A1 - Cathode, electrolysis cell for producing organic hydride, and organic hydride production method - Google Patents
Cathode, electrolysis cell for producing organic hydride, and organic hydride production method Download PDFInfo
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- WO2018037774A1 WO2018037774A1 PCT/JP2017/025984 JP2017025984W WO2018037774A1 WO 2018037774 A1 WO2018037774 A1 WO 2018037774A1 JP 2017025984 W JP2017025984 W JP 2017025984W WO 2018037774 A1 WO2018037774 A1 WO 2018037774A1
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- B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
- B01J23/00—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00
- B01J23/38—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of noble metals
- B01J23/40—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of noble metals of the platinum group metals
- B01J23/42—Platinum
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
- B01J23/00—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00
- B01J23/38—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of noble metals
- B01J23/40—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of noble metals of the platinum group metals
- B01J23/46—Ruthenium, rhodium, osmium or iridium
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- C—CHEMISTRY; METALLURGY
- C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
- C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
- C25B11/00—Electrodes; Manufacture thereof not otherwise provided for
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- C25B11/03—Electrodes; Manufacture thereof not otherwise provided for characterised by shape or form perforated or foraminous
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- C—CHEMISTRY; METALLURGY
- C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
- C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
- C25B3/00—Electrolytic production of organic compounds
- C25B3/20—Processes
- C25B3/25—Reduction
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- C—CHEMISTRY; METALLURGY
- C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
- C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
- C25B9/00—Cells or assemblies of cells; Constructional parts of cells; Assemblies of constructional parts, e.g. electrode-diaphragm assemblies; Process-related cell features
Definitions
- the present invention relates to a cathode, an electrolytic cell for producing organic hydride, and a method for producing organic hydride.
- the present invention relates to a cathode used in an electrolysis cell for electrochemically hydrogenating a hydride to produce an organic hydride, an electrolysis cell for producing an organic hydride comprising the cathode, and an organic hydride using the electrolysis cell. It relates to a manufacturing method.
- renewable energy obtained from solar, wind, hydropower, geothermal power, etc.
- renewable energy is required to mitigate output fluctuations, particularly output fluctuations in a medium to long cycle.
- renewable energy is relatively difficult to transport on a large scale.
- it is effective to convert electric power obtained from renewable energy into chemical energy.
- An example of a process for converting electric power directly into chemical energy is an electrochemical system.
- a secondary battery which is an example of an electrochemical system, a so-called storage battery, is a device that converts electric power into chemical energy and stores it, and is widely used.
- organic hydride organic chemical hydride
- organic hydride organic chemical hydride
- examples of the organic hydride include cyclic organic compounds such as cyclohexane, methylcyclohexane, and decalin.
- Organic hydride is easy to handle because it is generally liquid at normal temperature and pressure.
- Organic hydrides can also be electrochemically hydrogenated and dehydrogenated. For this reason, if organic hydride is used as an energy carrier, it can be transported and stored more easily than liquid hydrogen.
- a liquid with properties similar to petroleum is selected as the organic hydride, it is excellent in affinity with a relatively large-scale energy supply system, so that it can be easily delivered to the end of the energy supply system.
- Patent Document 1 discloses an electrolytic cell including an oxidation electrode that generates protons from water and a reduction electrode that hydrogenates an organic compound having an unsaturated bond. .
- the present invention has been made in view of such circumstances, and an object thereof is to provide a technique for improving the production efficiency of organic hydride.
- An embodiment of the present invention is a cathode of an electrolytic cell for producing an organic hydride.
- the cathode includes a cathode catalyst layer containing a first catalyst for hydrogenating a hydride with protons to produce an organic hydride, a cathode chamber containing the cathode catalyst layer, and a region excluding the cathode catalyst layer in the cathode chamber.
- a second catalyst that promotes a chemical reaction between a hydrogen gas that is a product of a side reaction at the cathode and an unreacted hydride.
- Another aspect of the present invention is an electrolytic cell for producing an organic hydride.
- the electrolytic cell is provided with an electrolyte membrane having proton conductivity, a cathode according to the above aspect provided on one side of the electrolyte membrane, and a side opposite to one side of the electrolyte membrane, and oxidizes water to generate protons.
- an anode having an anode chamber for housing the anode catalyst layer.
- Still another embodiment of the present invention is a method for producing an organic hydride.
- the manufacturing method includes supplying water to an anode included in an electrolytic cell for manufacturing an organic hydride, electrolyzing the water to generate protons, and supplying a hydride to a cathode included in the electrolytic cell for manufacturing an organic hydride.
- a step of producing an organic hydride by a chemical reaction is supplying water to an anode included in an electrolytic cell for manufacturing an organic hydride, electrolyzing the water to generate protons, and supplying a hydride to a cathode included in the electrolytic cell for manufacturing an organic hydride.
- the production efficiency of organic hydride can be improved.
- FIG. 4A is a graph showing the relationship between the current density and the electrode potential in the electrolytic cells of Example 1 and Comparative Example 1.
- FIG. 4B is a graph showing the relationship between current density and current efficiency in the electrolytic cells of Example 1 and Comparative Example 1.
- FIG. 5A is a graph showing the relationship between the current density and the cell voltage in the electrolytic cells of Example 2 and Comparative Example 2.
- FIG. 5B is a graph showing the relationship between current density and current efficiency in the electrolytic cells of Example 2 and Comparative Example 2.
- An electrolytic cell for producing an organic hydride is provided on one surface of a solid polymer electrolyte membrane having proton conductivity and a solid polymer electrolyte membrane, A cathode catalyst layer that generates a hydride by reducing the hydride with protons, a cathode chamber that contains the cathode catalyst layer and is supplied with the hydride, and is provided on the other surface of the solid polymer electrolyte membrane; An anode catalyst layer that oxidizes water to generate protons, and an anode chamber that accommodates the anode catalyst layer and is supplied with an electrolytic solution.
- a cathode catalyst layer In the cathode chamber, as viewed from the solid polymer electrolyte membrane side, a cathode catalyst layer, a microporous layer, a diffusion layer, and a hydride channel portion that also functions as a cathode support are provided.
- the cathode chamber is provided with a cathode chamber outlet from which organic hydride is discharged.
- a catalyst made of Pt or the like or an alloy containing Pt or the like (multi-element metal) is disposed in a region excluding the cathode catalyst layer.
- FIG. 1 is a schematic diagram of an organic hydride production apparatus (electrochemical reduction apparatus) including an organic hydride production electrolytic cell according to an embodiment.
- an organic hydride production apparatus electrochemical reduction apparatus
- FIG. 1 illustration of the separator with which an electrolysis cell is provided is abbreviate
- the organic hydride manufacturing apparatus 10 is an apparatus that hydrogenates a hydride that is a dehydrogenated form of an organic hydride by an electrochemical reduction reaction.
- a catholyte storage tank 30, a separation tank 36, an anolyte storage tank 40, and a control unit 60 are provided.
- the power control unit 20 is, for example, a DC / DC converter that converts the output voltage of the power source into a predetermined voltage.
- the positive output terminal of the power control unit 20 is connected to the anode 150 (oxygen generating electrode) of the electrolysis cell 100.
- the negative output terminal of the power control unit 20 is connected to the cathode 120 (reduction electrode) of the electrolysis cell 100. Thereby, a predetermined voltage is applied between the anode 150 and the cathode 120 of the electrolytic cell 100.
- the power control unit 20 may be provided with a reference electrode for the purpose of detecting positive and negative potentials.
- the reference electrode input terminal is connected to a reference electrode (not shown) provided on the electrolyte membrane 110 of the electrolytic cell 100.
- the reference electrode is electrically isolated from the cathode 120 and the anode 150.
- the reference electrode is held at the reference electrode potential.
- a current flowing between the cathode 120 and the anode 150 is detected by a current detection unit (not shown).
- the current value detected by the current detection unit is input to the control unit 60 and used for controlling the power control unit 20 by the control unit 60.
- the potential difference between the reference electrode and the cathode 120 is detected by a voltage detector (not shown).
- the value of the potential difference detected by the voltage detection unit is input to the control unit 60 and used for control of the power control unit 20 by the control unit 60.
- the control unit 60 controls the output of the positive output terminal and the negative output terminal of the power control unit 20 so that the potential of the anode 150 or the cathode 120 becomes a desired potential.
- the power source is preferably renewable energy obtained by sunlight, wind power, hydropower, geothermal power generation, or the like, but is not particularly limited thereto.
- the catholyte storage tank 30 stores a hydride to be hydrogenated by an electrochemical reduction reaction in the electrolytic cell 100.
- the organic hydride used in the present embodiment is not particularly limited as long as it is an organic compound capable of adding / eliminating hydrogen by reversibly causing hydrogenation / dehydrogenation reaction.
- Acetone-isopropanol, benzoquinone- A hydroquinone type, an aromatic hydrocarbon type, etc. can be used widely.
- an aromatic hydrocarbon system typified by a toluene-methylcyclohexane system is preferable.
- An aromatic hydrocarbon compound used as a dehydrogenated form of organic hydride is a compound containing at least one aromatic ring, and examples thereof include benzene, alkylbenzene, naphthalene, alkylnaphthalene, anthracene, and diphenylethane.
- Alkylbenzene includes compounds in which 1 to 4 hydrogen atoms of an aromatic ring are substituted with a linear or branched alkyl group having 1 to 6 carbon atoms, such as toluene, xylene, mesitylene, ethylbenzene, diethylbenzene and the like. Can be mentioned.
- Alkylnaphthalene includes compounds in which 1 to 4 hydrogen atoms of an aromatic ring are substituted with a linear or branched alkyl group having 1 to 6 carbon atoms, and examples thereof include methylnaphthalene. These may be used alone or in combination.
- the aromatic hydrocarbon compound is preferably at least one of toluene and benzene.
- Nitrogen-containing heterocyclic aromatic compounds such as pyridine, pyrimidine, pyrazine, quinoline, isoquinoline, N-alkylpyrrole, N-alkylindole and N-alkyldibenzopyrrole can also be used as dehydrogenated products.
- the organic hydride dehydrogenated product that is, the hydride
- the hydride can be supplied to the electrolytic cell 100 in a liquid state without performing treatment such as heating or pressurization. Thereby, simplification of the structure of the organic hydride manufacturing apparatus 10 can be achieved.
- the liquid stored in the catholyte storage tank 30 is referred to as “catholyte” as appropriate.
- the hydride stored in the catholyte storage tank 30 is supplied to the cathode 120 of the electrolysis cell 100 by the first liquid supply device 32.
- the first liquid supply device 32 for example, various pumps such as a gear pump or a cylinder pump, a natural flow-down device, or the like can be used.
- a circulation path 34 is provided between the cathode 120 and the catholyte storage tank 30.
- the hydride nucleated by the electrolysis cell 100 that is, the organic hydride and the unreacted hydride reach the separation tank 36 via the circulation path 34.
- hydrogen gas and the like are separated from the mixture of the organic hydride and the hydride.
- the separated gas is discharged out of the system through the cracking catalyst 38. Thereafter, the organic hydride and the hydride are returned to the catholyte storage tank 30.
- anolyte storage tank 40 for example, ion exchange water, pure water, or an aqueous solution obtained by adding an acid such as sulfuric acid, phosphoric acid, nitric acid, hydrochloric acid or the like (hereinafter referred to as “anolyte” as appropriate) is stored. .
- the ionic conductivity measured at 20 ° C. of the anolyte is preferably 0.01 S / cm or more. By making the ionic conductivity of the anolyte 0.01 S / cm or more, an industrially sufficient electrochemical reaction can be caused.
- the anolyte stored in the anolyte storage tank 40 is supplied to the anode 150 of the electrolysis cell 100 by the second liquid supply device 42.
- the second liquid supply device 42 for example, various pumps such as a gear pump or a cylinder pump, a natural flow-down device, or the like can be used.
- a circulation path 44 is provided between the anode 150 and the anolyte storage tank 40. The unreacted anolyte in the electrolytic cell 100 is returned to the anolyte storage tank 40 via the circulation path 44.
- the anolyte storage tank 40 is provided with a steam / water separator (not shown), and gas such as oxygen generated by electrolysis of the anolyte in the electrolysis cell 100 is separated from the anolyte by the steam / water separator and decomposed. It is discharged out of the system through the catalyst 46.
- FIG. 2 is a cross-sectional view showing a schematic structure of an electrolytic cell for producing an organic hydride according to an embodiment.
- FIG. 3 is an enlarged schematic view showing a part of the cathode catalyst layer and the microporous layer.
- the electrolytic cell 100 includes a membrane electrode assembly 102 and a pair of separators 170 a and 170 b that sandwich the membrane electrode assembly 102.
- the membrane electrode assembly 102 includes an electrolyte membrane 110, a cathode 120, and an anode 150.
- the electrolyte membrane 110 is formed of a material (ionomer) having proton conductivity.
- the electrolyte membrane 110 selectively conducts protons, while suppressing the mixing and diffusion of substances between the cathode 120 and the anode 150.
- Examples of the material having proton conductivity include perfluorosulfonic acid polymers such as Nafion (registered trademark) and Flemion (registered trademark).
- the thickness of the electrolyte membrane 110 is not particularly limited, but is preferably 5 to 300 ⁇ m, more preferably 10 to 150 ⁇ m, and further preferably 20 to 100 ⁇ m.
- the thickness of the electrolyte membrane 110 By setting the thickness of the electrolyte membrane 110 to 5 ⁇ m or more, the barrier property of the electrolyte membrane 110 can be secured, and the occurrence of cross leaks such as hydride and oxygen can be more reliably suppressed. Further, by setting the thickness of the electrolyte membrane 110 to 300 ⁇ m or less, it is possible to suppress the ion migration resistance from becoming excessive.
- the area resistance of the electrolyte membrane 110 that is, the ion transfer resistance per geometric area is not particularly limited, but is preferably 2000 m ⁇ ⁇ cm 2 or less, more preferably 1000 m ⁇ ⁇ cm 2 or less, and further preferably 500 m ⁇ ⁇ cm 2. It is as follows. By setting the area resistance of the electrolyte membrane 110 to 2000 m ⁇ ⁇ cm 2 or less, the possibility of insufficient proton conductivity can be avoided more reliably.
- the ion exchange capacity (IEC) of the cation exchange type ionomer is not particularly limited, but is preferably 0.7 to 2 meq / g, more preferably 1 to 1.3 meq / g.
- the ion exchange capacity of the cation exchange ionomer By setting the ion exchange capacity of the cation exchange ionomer to 0.7 meq / g or more, it is possible to more reliably avoid the possibility that the ion conductivity is insufficient. On the other hand, by setting the ion exchange capacity to 2 meq / g or less, it is possible to more reliably avoid the possibility that the solubility of the ionomer in the anolyte or hydride increases and the strength of the electrolyte membrane 110 becomes insufficient. it can.
- the electrolyte membrane 110 may be mixed with a reinforcing material such as porous PTFE (polytetrafluoroethylene).
- a reinforcing material such as porous PTFE (polytetrafluoroethylene).
- the cathode 120 is provided on one side of the electrolyte membrane 110. In the present embodiment, cathode 120 is provided in contact with one main surface of electrolyte membrane 110.
- the cathode 120 includes a cathode catalyst layer 122 and a cathode chamber 124 that houses the cathode catalyst layer 122.
- the cathode 120 includes a spacer 126, a microporous layer 128, a diffusion layer 130, a flow path portion 132, a cathode chamber inlet 134, and a cathode chamber outlet 136.
- the cathode catalyst layer 122 is in contact with one main surface of the electrolyte membrane 110 in the cathode chamber 124. As shown in FIG. 3, the cathode catalyst layer 122 includes a reduction catalyst 122a as a first catalyst for hydrogenating a hydride with protons to generate an organic hydride.
- the reduction catalyst 122a for example, metal particles selected from the group consisting of Pt, Ru, Pd, Ir, and an alloy containing at least one of them can be used.
- a commercially available product may be used, or a catalyst synthesized according to a known method may be used.
- the reduction catalyst 122a includes a first catalytic metal (noble metal) made of at least one of Pt, Ru, Pd, and Ir, and Cr, Mn, Fe, Co, Ni, Cu, Zn, Mo, Ru, Sn, You may be comprised with the metal composition containing 1 type, or 2 or more types of 2nd catalyst metals selected from W, Re, Pb, Bi.
- examples of the form of the metal composition include an alloy of the first catalyst metal and the second catalyst metal, or an intermetallic compound composed of the first catalyst metal and the second catalyst metal.
- the average particle diameter of the reduction catalyst 122a is preferably 1 nm to 1 ⁇ m, and more preferably 1 nm to 5 nm.
- the surface area (reaction area) per catalyst weight can be increased. Moreover, it can suppress more reliably that aggregation of catalyst particles advances and durability falls by making the average particle diameter of the reduction catalyst 122a 1 nm or more.
- the reduction catalyst 122a is supported by a catalyst carrier 122b made of an electron conductive material.
- the electron conductivity of the electron conductive material used for the catalyst carrier 122b is preferably 1.0 ⁇ 10 ⁇ 2 S / cm or more, more preferably 3.0 ⁇ 10 ⁇ 2 S / cm or more, Preferably it is 1.0 ⁇ 10 ⁇ 1 S / cm or more.
- Examples of the catalyst carrier 122b include an electron conductive material containing as a main component any one of porous carbon (such as mesoporous carbon), porous metal, and porous metal oxide.
- Examples of the porous carbon include carbon black such as ketjen black (registered trademark), acetylene black, furnace black, and Vulcan (registered trademark).
- BET specific surface area of the porous carbon as measured by nitrogen adsorption method is preferably 50m 2 / g ⁇ 1500m 2 / g, more preferably 500m 2 / g ⁇ 1300m 2 / g, more preferably from 700 meters 2 / g to 1000 m 2 / g.
- the catalyst carrier 122b is liable to be deteriorated during the reaction of the hydride or when the organic hydride production apparatus 10 is started or stopped. Can be avoided. Thereby, sufficient durability can be imparted to the catalyst carrier 122b.
- the average particle size of carbon fine particles such as carbon black used as the catalyst carrier 122b is preferably 0.01 ⁇ m to 1 ⁇ m.
- porous metal examples include Pt black, Pd black, and Pt metal deposited in a fractal shape.
- porous metal oxide include Ti, Zr, Nb, Mo, Hf, Ta, and W oxides.
- the catalyst support 122b includes porous metals such as nitrides, carbides, oxynitrides, carbonitrides, partially oxidized carbonitrides of metals such as Ti, Zr, Nb, Mo, Hf, Ta, and W.
- a compound hereinafter referred to as a porous metal carbonitride as appropriate
- a porous metal carbonitride can also be used.
- the BET specific surface areas of the porous metal, porous metal oxide and porous metal carbonitride measured by the nitrogen adsorption method are preferably 1 m 2 / g or more, more preferably 3 m 2 / g or more, More preferably, it is 10 m 2 / g or more.
- the catalyst carrier 122b carrying the reduction catalyst 122a is coated with an ionomer 122c.
- the ion conductivity of the cathode 120 can be improved.
- the ionomer 122c include perfluorosulfonic acid polymers such as Nafion (registered trademark) and Flemion (registered trademark).
- the ion exchange capacity (IEC) of the ionomer 122c is preferably 0.7 to 3 meq / g, more preferably 1 to 2.5 meq / g, and further preferably 1.2 to 2 meq / g.
- the ionomer (I) / catalyst carrier (C) mass ratio I / C is preferably 0.1 to 2, more preferably 0.2 to 1.5. More preferably, it is 0.3 to 1.1.
- the mass ratio I / C is 0.1 or more, sufficient ion conductivity can be obtained more reliably.
- the mass ratio I / C is 2 or less, it is possible to suppress an excessive increase in the coating thickness of the ionomer 122c with respect to the reduction catalyst 122a and to inhibit contact of the hydride with the catalyst active point. It can be avoided.
- the ionomer 122c included in the cathode catalyst layer 122 preferably partially covers the reduction catalyst 122a. According to this, three elements (hydrogenated product, proton, electron) necessary for the electrochemical reaction in the cathode catalyst layer 122 can be efficiently supplied to the reaction field.
- the thickness of the cathode catalyst layer 122 is preferably 1 to 100 ⁇ m, more preferably 5 to 30 ⁇ m. As the thickness of the cathode catalyst layer 122 increases, not only the proton transfer resistance increases, but also the diffusibility of the hydride decreases. For this reason, it is desirable to adjust the thickness of the cathode catalyst layer 122 within the above-described range.
- the cathode catalyst layer 122 can be produced, for example, by the following method. That is, first, a catalyst component powder, a hydrophobic resin (fluorine component) as a gas permeable material, water, a solvent such as naphtha, and an ionomer (for example, Nafion (registered trademark) dispersion DE521 (manufactured by DuPont)) And mix.
- the addition amount of the ionomer is preferably such that the ratio of the mass of the ionomer after drying to the mass of carbon in the catalyst component powder is 1:10 to 10: 1.
- the hydrophobic resin is in the form of a powder, and the particle size is preferably 0.005 to 10 ⁇ m.
- a solvent is appropriately added to the obtained mixture to prepare a catalyst ink.
- the obtained catalyst ink is applied to the microporous layer 128, dried, and then hot pressed to fix the cathode catalyst layer 122 to the microporous layer 128. It is preferable to perform hot pressing after performing the above-described application and drying in a plurality of times. Thereby, a more uniform cathode catalyst layer 122 can be obtained.
- the cathode catalyst layer 122 can be produced.
- the cathode catalyst layer 122 may be formed on the electrolyte membrane 110.
- a composite of the cathode catalyst layer 122 and the electrolyte membrane 110 can be produced by applying a catalyst ink to one main surface of the electrolyte membrane 110 using a bar coater.
- the composite of the cathode catalyst layer 122 and the electrolyte membrane 110 can be produced by spraying the catalyst ink on one main surface of the electrolyte membrane 110 by spray coating and drying the solvent component in the catalyst ink.
- the catalyst ink is preferably applied so that the mass of the reduction catalyst 122a in the cathode catalyst layer 122 is 0.5 mg / cm 2 per electrode area.
- the cathode chamber 124 is defined by an electrolyte membrane 110, a separator 170a, and a frame-shaped spacer 126 disposed between the electrolyte membrane 110 and the separator 170a.
- the cathode chamber 124 not only the cathode catalyst layer 122 but also the microporous layer 128, the diffusion layer 130, and the flow path portion 132 are accommodated.
- the spacer 126 is provided with a cathode chamber inlet 134 and a cathode chamber outlet 136 that communicate the inside and the outside of the cathode chamber 124.
- the microporous layer 128 is disposed adjacent to the cathode catalyst layer 122. More specifically, the microporous layer 128 is provided so as to be in contact with the main surface of the cathode catalyst layer 122 opposite to the electrolyte membrane 110.
- the diffusion layer 130 is disposed adjacent to the microporous layer 128. More specifically, the diffusion layer 130 is provided so as to contact the main surface of the microporous layer 128 opposite to the cathode catalyst layer 122.
- the diffusion layer 130 has a function of uniformly diffusing the liquid hydride supplied from the flow path portion 132 into the cathode catalyst layer 122.
- the material constituting the diffusion layer 130 preferably has a high affinity for the hydride.
- Examples of the material constituting the diffusion layer 130 include a porous conductive base material and a fiber sintered body. These are preferable because they have porosity suitable for supply and removal of gas and liquid and can maintain sufficient electrical conductivity.
- the diffusion layer 130 preferably has a thickness of 10 to 5000 ⁇ m, a porosity of 30 to 95%, and a typical pore size of 1 to 1000 ⁇ m.
- the electronic conductivity of the material constituting the diffusion layer 130 is preferably 10 ⁇ 2 S / cm or more.
- the material constituting the diffusion layer 130 include carbon woven fabric (carbon cloth), carbon non-woven fabric, and carbon paper.
- the carbon cloth is a bundle of hundreds of thin carbon fibers having a diameter of several ⁇ m, and this bundle is a woven fabric.
- the carbon paper is obtained by sintering a carbon raw material fiber as a thin film precursor by a paper manufacturing method.
- the microporous layer 128 has a function of promoting the diffusion of liquid hydride and organic hydride in the surface direction of the cathode catalyst layer 122.
- the microporous layer 128 can be formed, for example, by applying a paste-like kneaded material obtained by kneading a conductive powder and a water repellent to the surface of the diffusion layer 130 and drying it.
- a paste-like kneaded material obtained by kneading a conductive powder and a water repellent to the surface of the diffusion layer 130 and drying it.
- the conductive powder for example, conductive carbon such as Vulcan (registered trademark) can be used.
- As the water repellent a fluorine-based resin such as tetrafluoroethylene resin (PTFE) can be used.
- PTFE tetrafluoroethylene resin
- the ratio between the conductive powder and the water repellent is appropriately determined within a range where desired conductivity and water repellency can be obtained.
- the mass ratio Vulcan: PTFE
- the microporous layer 128 can be made of carbon cloth, carbon paper, or the like, similarly to the diffusion layer 130.
- the average flow pore size (dm) of the microporous layer 128 is preferably 100 nm to 20 ⁇ m, more preferably 500 nm to 5 ⁇ m after hot pressing.
- the average flow pore size of the microporous layer 128 can be measured with a mercury porosimeter or the like.
- the thickness of the microporous layer 128 is preferably 1 to 50 ⁇ m, more preferably 2 to 20 ⁇ m.
- the average thickness of the microporous layer 128 itself including the portion hidden in the diffusion layer 130 is calculated. It is defined as the thickness of the microporous layer 128.
- a metal component may coexist on the surface of the microporous layer 128. Thereby, the electron conductivity of the microporous layer 128 is improved, and the current can be made uniform.
- the microporous layer 128 and the diffusion layer 130 are used in a state where pressure is applied in the thickness direction. Therefore, it is not preferable that the electrical conductivity in each thickness direction changes due to the pressurization in the thickness direction during use. For this reason, it is preferable that the microporous layer 128 and the diffusion layer 130 are pre-pressed. Thereby, since the carbon material of each layer is compressed, the conductivity in the thickness direction of each layer can be increased and stabilized. In addition, the cathode 120 having a stable filling rate of 20 to 50% can be realized.
- improving the degree of bonding between the cathode catalyst layer 122 and the microporous layer 128 also contributes to improving the conductivity of the cathode 120. Moreover, the supply capability of the raw material and the removal capability of the generated material are improved by improving the degree of joining.
- a known apparatus such as a hot press or a hot roller can be used.
- the pressing conditions are preferably temperature: room temperature to 360 ° C. and pressure: 0.1 to 5 MPa.
- the flow path portion 132 is disposed adjacent to the diffusion layer 130. More specifically, the channel portion 132 is provided so as to be in contact with the main surface of the diffusion layer 130 on the side opposite to the microporous layer 128.
- the flow path portion 132 has a structure in which a groove 132b is provided on the main surface of the plate-like main body portion 132a.
- the groove 132b constitutes a flow path for the hydride.
- the main body 132a is made of a conductive material.
- the channel portion 132 also functions as a cathode support that positions the cathode catalyst layer 122, the microporous layer 128, and the diffusion layer 130 in the cathode chamber 124.
- the cathode chamber inlet 134 is disposed below the cathode chamber 124 in the vertical direction. One end of the cathode chamber inlet 134 is connected to the flow path of the flow path portion 132, and the other end is connected to the first liquid supply device 32.
- the hydride supplied from the outside of the cathode chamber 124 is introduced into the cathode chamber 124 through the cathode chamber inlet 134.
- the hydride introduced into the cathode chamber 124 is supplied to the cathode catalyst layer 122 via the groove 132b of the flow path portion 132, the diffusion layer 130, and the microporous layer 128.
- the cathode chamber outlet 136 is disposed vertically above the cathode chamber 124.
- the cathode chamber outlet 136 has one end connected to the flow path of the flow path portion 132 and the other end connected to the circulation path 34.
- the organic hydride and unreacted hydride in the cathode chamber 124 are discharged to the outside of the cathode chamber 124 via the cathode chamber outlet 136.
- the separator 170a is disposed on the cathode 120 side in the electrolytic cell 100.
- separator 170a is laminated on the main surface of flow path portion 132 on the side opposite to diffusion layer 130.
- the cathode 120 includes a second catalyst 138 disposed in a region excluding the cathode catalyst layer 122 in the cathode chamber 124.
- the second catalyst 138 is disposed in the microporous layer 128 as an example. The second catalyst 138 will be described in detail later.
- the anode 150 is provided on the side opposite to one side of the electrolyte membrane 110, that is, on the side opposite to the cathode 120. In the present embodiment, anode 150 is provided in contact with the other main surface of electrolyte membrane 110.
- the anode 150 includes an anode catalyst layer 152 and an anode chamber 154 that accommodates the anode catalyst layer 152.
- the anode 150 includes a spacer 156, a supporting elastic body 158, an anode chamber inlet 160, and an anode chamber outlet 162.
- the anode catalyst layer 152 is in contact with the other main surface of the electrolyte membrane 110 in the anode chamber 154.
- the anode catalyst layer 152 is a layer containing a catalyst for oxidizing protons in the anolyte to generate protons.
- a catalyst for oxidizing protons in the anolyte to generate protons As the catalyst contained in the anode catalyst layer 152, for example, metal particles selected from the group consisting of Ru, Rh, Pd, Ir, Pt, and an alloy containing at least one of them can be used.
- the catalyst may be dispersedly supported or coated on a metal substrate having electronic conductivity.
- a metal substrate is composed of a metal such as Ti, Cr, Mn, Fe, Co, Ni, Cu, Zn, Nb, Mo, Ta, W, or an alloy containing these as a main component. Examples thereof include metal fibers (fiber diameter: for example, 10 to 30 ⁇ m), mesh (mesh diameter: for example, 500 to 1000 ⁇ m), sintered metal porous bodies, foamed molded bodies (foam), expanded metals, and the like.
- the base material used for the anode catalyst layer 152 has a thickness of 0.1 to 0.1 because of the necessity of having sufficient electric conductivity for flowing current necessary for electrolysis and the necessity of the mechanical strength of the electrolysis cell 100.
- a 2 mm plate material is preferred.
- the substrate is preferably a porous body and excellent in corrosion resistance to the anolyte in order to avoid the increase in resistance due to bubbles and promote the supply of the anolyte.
- an expanded mesh made of titanium is widely used.
- the expanded mesh preferably has a center distance in the short direction of 0.1 to 4 mm, a center distance in the long direction of preferably 0.1 to 4 mm, and an opening ratio of preferably about 30 to 70%. .
- the anode chamber 154 is defined by the electrolyte membrane 110, the separator 170b, and a frame-shaped spacer 156 disposed between the electrolyte membrane 110 and the separator 170b.
- the anode chamber 154 accommodates not only the anode catalyst layer 152 but also the supporting elastic body 158.
- the spacer 156 is provided with an anode chamber inlet 160 and an anode chamber outlet 162 that communicate the inside and the outside of the anode chamber 154.
- the supporting elastic body 158 is disposed adjacent to the anode catalyst layer 152. More specifically, the supporting elastic body 158 is provided so as to contact the main surface of the anode catalyst layer 152 opposite to the electrolyte membrane 110.
- the supporting elastic body 158 has a function of urging the anode catalyst layer 152 toward the electrolyte membrane 110. By pressing the anode catalyst layer 152 against the electrolyte membrane 110 by the supporting elastic body 158, the electrolytic characteristics of the electrolytic cell 100 can be improved.
- the supporting elastic body 158 is formed of a conductive member having an elastic body structure such as a leaf spring structure or a coil structure.
- the supporting elastic body 158 preferably has acid resistance. Examples of the material constituting the supporting elastic body 158 include titanium or a titanium alloy. Specific examples of the elastic body structure include a V-shaped spring, an X cross spring, a cushion coil, an assembly of chatter fibers, and the like.
- the anode chamber inlet 160 is disposed below the anode chamber 154 in the vertical direction.
- the anode chamber inlet 160 has one end connected to the anode chamber 154 and the other end connected to the second liquid supply device 42.
- the anolyte supplied from outside the anode chamber 154 is introduced into the anode chamber 154 through the anode chamber inlet 160.
- the anolyte introduced into the anode chamber 154 is supplied to the anode catalyst layer 152 directly or via the supporting elastic body 158.
- the anode chamber outlet 162 is disposed above the anode chamber 154 in the vertical direction.
- the anode chamber outlet 162 has one end connected to the anode chamber 154 and the other end connected to the circulation path 44.
- the oxygen gas in the anode chamber 154 and the unreacted anolyte are discharged to the outside of the anode chamber 154 via the anode chamber outlet 162.
- the separator 170b is disposed on the anode 150 side in the electrolytic cell 100.
- the separator 170b is laminated on the main surface of the supporting elastic body 158 opposite to the anode catalyst layer 152.
- the reaction that occurs when toluene (TL) is used as an example of the hydride is as follows.
- the resulting organic hydride is methylcyclohexane (MCH).
- MCH methylcyclohexane
- the electrode reaction at the anode 150 and the electrode reaction at the cathode 120 proceed in parallel. Then, protons (H + ) generated by water electrolysis at the anode 150 are supplied to the cathode 120 through the electrolyte membrane 110. The proton supplied to the cathode 120 is used for nuclear hydrogenation of the hydride at the cathode 120. Thereby, toluene is hydrogenated and methylcyclohexane is produced. Therefore, according to the organic hydride manufacturing apparatus 10 according to the present embodiment, water electrolysis and hydrogenation reaction of the hydride can be performed in one step.
- the cathode 120 further includes a second catalyst 138 disposed in a region excluding the cathode catalyst layer 122 in the cathode chamber 124.
- the second catalyst 138 is a catalyst for promoting a chemical reaction between hydrogen gas that is a product of a side reaction at the cathode 120 and an unreacted hydride.
- the chemical reaction between the hydrogen gas, which is a by-product in the cathode 120, and the unreacted hydride can be promoted, and the hydrogen gas can be reduced. Thereby, it can suppress that the movement to the reaction field of a hydride is inhibited. Moreover, the current efficiency of the electrolytic cell 100 can be increased.
- the chemical reaction between hydrogen gas and unreacted hydride is as follows. ⁇ Chemical reaction at the cathode> TL + 3H 2 ⁇ MCH
- the current efficiency of the organic hydride manufacturing apparatus 10 is preferably 80% or more obtained by an electrolytic reaction, 20% or less by a chemical reaction, 90% or more by an electrolytic reaction, and 10% or less by a chemical reaction. More preferably, 95% or more is obtained by electrolytic reaction, and 5% or less is more preferably obtained by chemical reaction.
- the second catalyst 138 is disposed in the microporous layer 128.
- the present invention is not particularly limited to this configuration, and the second catalyst 138 may be disposed in a region other than the microporous layer 128 in the cathode chamber 124 (excluding the cathode catalyst layer 122).
- the diffusion layer 130, the flow path portion 132, the cathode chamber outlet 136, and the like are exemplified. That is, the second catalyst 138 is preferably disposed in at least one of the microporous layer 128, the diffusion layer 130, the flow path portion 132, and the cathode chamber outlet 136.
- the region where the second catalyst 138 is disposed constitutes a chemical reaction part of the hydride.
- the region where the reduction catalyst 122a is disposed that is, the cathode catalyst layer 122 constitutes an electrolytic reaction part of the hydride.
- the second catalyst 138 is preferably disposed in a region close to the reaction field, that is, in at least one of the microporous layer 128 and the diffusion layer 130. Thereby, the movement inhibition of the hydride by hydrogen gas can be suppressed more reliably.
- the second catalyst 138 is disposed more on the downstream side than on the upstream side in the flow of the hydride and the organic hydride in the cathode chamber 124.
- the concentration of the hydride decreases due to the conversion of the hydride to the organic hydride, so that hydrogen gas is more easily generated.
- the second catalyst 138 By disposing the second catalyst 138 more on the downstream side than on the upstream side, effective hydrogen gas removal can be realized at a lower cost.
- the area of the region where the second catalyst 138 is installed with respect to the total area of the electrode is preferably 1/100 to 1/2 of the downstream region, more preferably the downstream region.
- the second catalyst 138 is supported on the carbon fiber 128a of the microporous layer 128 as an example.
- the second catalyst 138 can be supported on the carbon fibers of the diffusion layer 130.
- the support of the second catalyst 138 on the microporous layer 128 and the diffusion layer 130 is realized by, for example, immersing each layer in a catalyst-containing solution and then performing a liquid phase reduction process using a reducing agent. It can also be realized by immersing each layer in a catalyst-containing solution and then performing a reduction treatment by heating.
- the average particle diameter of the 2nd catalyst 138 can be made small compared with heat processing reduction.
- the second catalyst 138 When the second catalyst 138 is disposed at the flow path portion 132 and the cathode chamber outlet 136, the second catalyst 138 is applied to the groove 132 b of the flow path portion 132, the wall surface of the cathode chamber outlet 136, etc. with the second catalyst 138 supported on the carrier.
- the carrier for example, inorganic particles such as alumina and zeolite can be used.
- the size and shape of the inorganic particle carrier are not particularly limited. However, when the inorganic particles are not particularly fixed to the wall surface or the like, the size of the inorganic particle carrier is preferably 100 ⁇ m or more. Thereby, it can suppress that an inorganic particle support
- the second catalyst 138 is preferably selected from the group consisting of Pt, Ni, Re, Pd and alloys containing at least one of these metals.
- a commercially available product may be used, or one synthesized according to a known method may be used. For example, a method of immersing Pt ions in an aqueous solution and performing heat treatment under an inert atmosphere, a method such as a liquid phase reduction method, an emulsion method, or a micelle method can be employed.
- the second catalyst 138 is preferably primary particles having an average particle diameter of 1 nm to 1 ⁇ m.
- the “average particle diameter” is defined as an average value of the diameters of a plurality of particles obtained from a photographed image obtained by photographing the second catalyst 138 to be used with an electron microscope. If the particle is not a perfect circle, the area of the particle is measured and defined as the diameter of the circle corresponding to that area.
- the average particle diameter is desirably obtained as an average value of 100 or more particles by photographing with an electron microscope at a plurality of locations.
- the average particle diameter can be determined more easily by binarizing the electron microscope image using image processing software (for example, WinROOF manufactured by Mitani Corporation) and counting the particles.
- the average particle diameter of the reduction catalyst 122a is defined in the same manner.
- the supported amount of the second catalyst 138 is preferably 0.01 to 0.5 mg / cm 2 .
- the second catalyst 138 is not covered with the ionomer 122c.
- the ionomer 122c is composed of a strongly acidic polymer such as a perfluorosulfonic acid polymer.
- the reduction catalyst 122a at least partially covered with the ionomer 122c is limited to noble metals and metal oxide species that can withstand strong acids. Further, even if a noble metal such as Pt is used as the reduction catalyst 122a, degradation such as dissolution may occur gradually due to continuous use.
- a material used as the second catalyst 138 can be selected from a wide range of catalysts.
- the second catalyst 138 when a noble metal catalyst is used as the second catalyst 138, deterioration can be significantly suppressed, so that the amount of noble metal used can be reduced.
- the second catalyst 138 and the reduction catalyst 122a can be distinguished based on whether or not the ionomer 122c is coated.
- an anolyte containing water is supplied to the anode 150 provided in the above-described electrolysis cell 100.
- water is electrolyzed to generate protons.
- the generated protons pass through the electrolyte membrane 110 provided in the electrolytic cell 100 and move to the cathode 120 side.
- the hydride is supplied to the cathode 120 provided in the electrolytic cell 100.
- the cathode catalyst layer 122 the hydride is hydrogenated by protons that have passed through the electrolyte membrane 110, and organic hydride is generated.
- the cathode 120 includes the cathode catalyst layer 122 that hydrogenates a hydride with protons to generate an organic hydride, the cathode chamber 124 that houses the cathode catalyst layer 122, and the cathode chamber. And a second catalyst 138 that is disposed in a region excluding the cathode catalyst layer 122 in 124 and promotes a chemical reaction between hydrogen gas as a by-product in the cathode and an unreacted hydride.
- the hydrogen gas as a by-product is reduced. be able to.
- the movement inhibition of the hydride by hydrogen gas can be suppressed.
- the reduction reaction of the hydride can be advanced with high current efficiency and a small electric power unit.
- the organic hydride is generated using hydrogen gas, which is a byproduct, the apparent current efficiency of the electrolytic cell 100 can be improved. From the above, the production efficiency of organic hydride can be improved.
- the decrease in current efficiency due to side reactions becomes more significant as the hydride concentration in the catholyte decreases.
- the viewpoint of transport efficiency of organic hydride there is a demand to reduce the ratio of hydride as much as possible.
- current efficiency can be maintained even at a low hydride concentration. Therefore, the organic hydride manufacturing apparatus 10 with higher performance can be provided.
- Carbon paper carrying Pt was produced by a liquid phase reduction method.
- This carbon paper corresponds to the diffusion layer 130 and the microporous layer 128 containing the second catalyst 138.
- a H 2 PtCl 6 ⁇ 6H 2 O Wako Pure Chemical Industries, Ltd.
- Amount of H 2 PtCl 6 ⁇ 6H 2 O is supported amount of Pt to carbon paper was adjusted to 0.5 mg / cm 2.
- Carbon paper (GDL 35BC, manufactured by SGL Carbon) was immersed in the obtained mixed solution. This carbon paper is GDL (gas diffusion layer) with MPL (microporous layer).
- the carbon paper was completely dried under an N 2 gas atmosphere at 60 ° C.
- NaBH 4 manufactured by Wako Pure Chemical Industries, Ltd.
- pure water were added to the carbon paper and subjected to a reduction treatment for several minutes.
- the addition amount of NaBH 4 the molar ratio of H 2 PtCl 6 ⁇ 6H 2 O and NaBH 4 was 1: 1.5 and qs.
- the carbon paper was immersed in pure water overnight and washed. Thereafter, the carbon paper was dried at 60 ° C. for 60 minutes to obtain carbon paper carrying Pt.
- the electrolytic cell was produced using the obtained carbon paper.
- Nafion (registered trademark) dispersion DE521 manufactured by DuPont
- PtRu / C catalyst TEC61E54E Pt23 mass%, Ru27 mass%, manufactured by Tanaka Kikinzoku Kogyo Co., Ltd.
- catalyst ink is appropriately used using a solvent.
- the amount of Nafion (registered trademark) dispersion was added so that the ratio of the mass of Nafion after drying to the mass of carbon in the catalyst was 4: 5.
- the obtained catalyst ink was applied to the main surface on the MPL side of the carbon paper carrying Pt with a bar coater.
- the catalyst ink was applied so that the total mass of Pt and Ru was 0.5 mg / cm 2 per electrode area. Thereafter, the carbon paper was dried at 70 ° C. to remove the solvent component in the catalyst ink, thereby obtaining a laminate of the carbon paper and the cathode catalyst layer.
- the obtained laminate and an electrolyte membrane (Nafion (registered trademark) 117, manufactured by DuPont) were laminated and pressurized for 1 minute under conditions of a temperature of 120 ° C. and a pressure of 1 MPa. As a result, a composite of carbon paper, cathode catalyst layer and electrolyte membrane was obtained.
- a carbon-based structure obtained by molding carbon / epoxy resin was prepared.
- This carbon-based structure corresponds to a joined body of the flow path portion 132, the spacer 126, and the separator 170a.
- the carbon-based structure is provided with a serpentine channel (width 1 mm, depth 0.5 mm) on the surface corresponding to the channel portion 132.
- a liquid supply header is provided at one end of the serpentine flow path, and a liquid discharge header is provided at the other end of the serpentine flow path.
- an expanded mesh having a thickness of 1.0 mm, a distance between centers in the short direction of 3.5 mm, and a distance between centers in the long direction of 6.0 mm was prepared as the anode base material. Then, the surface of the anode base material was subjected to a dry blast process, and then a cleaning process in a 20% aqueous sulfuric acid solution. Thereafter, a film having a thickness of 2 ⁇ m was formed on the surface of the anode base material using an arc ion plating apparatus and a titanium-tantalum alloy plate under the conditions of a base material temperature of 150 ° C. and a vacuum degree of 1.3 Pa.
- a mixed aqueous solution of iridium tetrachloride / tantalum pentachloride was applied to the anode substrate provided with the coating. Thereafter, the anode base material was put into an electric furnace and subjected to a heat treatment at 550 ° C.
- the anode catalyst layer containing iridium oxide and tantalum oxide as a catalyst was formed by repeating application of the solution and heat treatment a plurality of times.
- the amount of catalyst supported was 12 g / m 2 per electrode area in terms of the amount of Ir metal.
- the prepared carbon-based structure, composite, and anode catalyst layer were laminated in this order.
- the carbon-based structure was disposed so that the flow path extends in the vertical direction in the organic hydride manufacturing apparatus, and was fixed to the surface on the diffusion layer side of the composite. Further, a catholyte supply and discharge path was connected to the serpentine channel via a header.
- the anode catalyst layer was fixed to the surface of the composite on the electrolyte membrane side.
- a spacer and a separator arranged on the anode side were prepared. And the separator was fixed to the electrolyte membrane side of the composite via a spacer. A gap constituting an anode chamber was provided between the anode catalyst layer and the separator.
- the electrolytic cell of Example 1 was obtained by the above process.
- the electrode area of the electrolysis cell was 16 cm 2 .
- Example 2 An electrolytic cell was obtained in the same manner as in Example 1 except that the electrode area was 100 cm 2 .
- Comparative Example 2 An electrolytic cell was obtained in the same manner as in Comparative Example 1 except that the electrode area was 100 cm 2 .
- a catholyte having a toluene concentration of 10% (that is, a catholyte having 10 mol% of toluene and 90 mol% of methylcyclohexane with respect to the total amount of the catholyte) is allowed to flow through the cathode chamber of the electrolysis cell of each example and each comparative example. It was.
- the catholyte was circulated from the lower side in the vertical direction to the upper side using a riser.
- a 5% aqueous sulfuric acid solution as an anolyte was circulated through the anode chamber using a riser.
- the circulation flow rate of the catholyte was 5 mL / min.
- the circulation flow rate of the anolyte was 10 mL / min.
- the negative electrode of the constant voltage power source was connected to the cathode, and the positive electrode was connected to the anode. Then, the output voltage of the constant voltage power source was changed at a voltage range of 1.3 to 5.0 V at intervals of 0.2 V and applied to the electrolysis cells of the examples and the comparative examples.
- Example 1 And about the electrolytic cell of Example 1 and Comparative Example 1, the current density of the electrolytic cell, the potential of each electrode, and the current efficiency were measured.
- 4A is a graph showing the relationship between the current density and the electrode potential in the electrolytic cells of Example 1 and Comparative Example 1.
- FIG. 4B is a graph showing the relationship between current density and current efficiency in the electrolytic cells of Example 1 and Comparative Example 1.
- the upper stage is the anode potential
- the lower stage is the cathode potential.
- the results of Example 1 are shown as square plots
- the results of Comparative Example 1 are shown as triangular plots.
- Example 1 As shown in FIG. 4 (A), a sharp drop in cathode potential was observed in the electrolysis cell of Comparative Example 1, whereas no such potential drop was observed in the electrolysis cell of Example 1.
- the hydrogen gas generated on the cathode side chemically reacted with toluene on the Pt catalyst, so that the inhibition of the movement of toluene by the hydrogen gas was suppressed, thereby increasing the overvoltage accompanying the inhibition of the movement of toluene. It is considered that no potential drop occurred as a result. Therefore, in Example 1, it was confirmed that the current density can be increased in the entire electrolytic cell.
- the electrolysis cell of Example 1 has a higher current efficiency than the electrolysis cell of Comparative Example 1.
- FIG. 5A is a graph showing the relationship between the current density and the cell voltage in the electrolytic cells of Example 2 and Comparative Example 2.
- FIG. 5B is a graph showing the relationship between current density and current efficiency in the electrolytic cells of Example 2 and Comparative Example 2. In each graph, the result of Example 2 is indicated by a broken line, and the result of Comparative Example 2 is indicated by a one-dot chain line.
- the cell voltage of the electrolytic cell of Example 2 is lower than that of the electrolytic cell of Comparative Example 2. That is, in the electrolysis cell of Example 2, the electrolysis characteristics were improved by reducing the overvoltage. In the electrolytic cell of Example 2, it is considered that hydrogen gas generated on the cathode side chemically reacted with toluene on the Pt catalyst to generate methylcyclohexane.
- the current efficiency of the electrolytic cell of Example 2 is higher than that of the electrolytic cell of Comparative Example 2.
- the current at which hydrogen generation was started was improved from about 0.05 Acm ⁇ 2 to about 0.1 Acm ⁇ 2 .
- Organic hydride production equipment 100 electrolysis cell, 110 electrolyte membrane, 120 cathode, 122 cathode catalyst layer, 124 cathode chamber, 128 microporous layer, 130 diffusion layer, 132 flow channel, 136 cathode chamber outlet, 138 second catalyst, 150 anode, 152 anode catalyst layer, 154 anode chamber.
- the present invention can be used for a cathode, an electrolytic cell for producing organic hydride, and a method for producing organic hydride.
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Abstract
A cathode 120 of an electrolysis cell 100 for producing an organic hydride is provided with: a cathode catalyst layer 122 comprising a first catalyst for hydrogenating a substance to be hydrogenated with protons and generating an organic hydride; a cathode chamber 124 for housing the cathode catalyst layer 122; and a second catalyst that is disposed in an area in the cathode chamber 124 excluding the cathode catalyst layer 122 and that promotes a chemical reaction of hydrogen gas, which is a product of a side reaction in the cathode 120, with unreacted substance to be hydrogenated.
Description
本発明は、カソード、有機ハイドライド製造用電解セル及び有機ハイドライドの製造方法に関する。特に本発明は、被水素化物を電気化学的に水素化して有機ハイドライドを生成する電解セルに用いられるカソードと、当該カソードを備える有機ハイドライド製造用電解セルと、当該電解セルを用いた有機ハイドライドの製造方法に関する。
The present invention relates to a cathode, an electrolytic cell for producing organic hydride, and a method for producing organic hydride. In particular, the present invention relates to a cathode used in an electrolysis cell for electrochemically hydrogenating a hydride to produce an organic hydride, an electrolysis cell for producing an organic hydride comprising the cathode, and an organic hydride using the electrolysis cell. It relates to a manufacturing method.
近年、火力発電で得られるエネルギーに比べて生成過程での二酸化炭素排出量を抑制することができる新エネルギーとして、太陽光、風力、水力、地熱発電等で得られる再生可能エネルギーの普及が望まれている。しかしながら、再生可能エネルギーは、その出力変動、特に中長周期での出力変動の緩和が求められる。また、再生可能エネルギーは、大規模輸送が比較的困難である。これに対し、再生可能エネルギーから得られる電力を化学エネルギーに変換することが有効である。電力を直接化学エネルギーに変換するプロセスとしては、電気化学システムが挙げられる。電気化学システムの一例である二次電池、いわゆる蓄電池は、電力を化学エネルギーに変換して貯蔵するデバイスであり、広く用いられている。
In recent years, the spread of renewable energy obtained from solar, wind, hydropower, geothermal power, etc. is desired as a new energy that can reduce carbon dioxide emissions during the production process compared to the energy obtained from thermal power generation. ing. However, renewable energy is required to mitigate output fluctuations, particularly output fluctuations in a medium to long cycle. In addition, renewable energy is relatively difficult to transport on a large scale. On the other hand, it is effective to convert electric power obtained from renewable energy into chemical energy. An example of a process for converting electric power directly into chemical energy is an electrochemical system. A secondary battery, which is an example of an electrochemical system, a so-called storage battery, is a device that converts electric power into chemical energy and stores it, and is widely used.
再生可能エネルギーを基盤とする電気化学システムとしては、大規模な太陽光発電システムや風力発電システムを世界の適地に設置し、これにより得られる再生可能エネルギーを、輸送に適したエネルギーキャリアに変換して国内に輸送し、国内でエネルギーを消費するシステムが有望である。エネルギーキャリアとしては、液体水素が考えられる。しかしながら、水素は常温常圧で気体であるため、輸送や貯蔵には特殊なタンカーが必要となる。
As an electrochemical system based on renewable energy, large-scale solar power generation systems and wind power generation systems are installed in appropriate locations around the world, and the resulting renewable energy is converted into energy carriers suitable for transportation. Therefore, a system that transports and consumes energy in the country is promising. As the energy carrier, liquid hydrogen can be considered. However, since hydrogen is a gas at normal temperature and pressure, a special tanker is required for transportation and storage.
このような状況の中、液体水素に代わるエネルギーキャリアとして、有機ハイドライド(有機ケミカルハイドライド)が注目されている。有機ハイドライドとしては、シクロヘキサンやメチルシクロヘキサン、デカリン等の環式有機化合物が挙げられる。有機ハイドライドは、一般に常温常圧で液体であるため、取り扱いが容易である。また、有機ハイドライドは、電気化学的に水素付加及び脱水素することができる。このため、有機ハイドライドをエネルギーキャリアとして用いれば、液体水素に比べて簡単に輸送、貯蔵することができる。特に、石油と似た性状の液体を有機ハイドライドとして選択した場合には、比較的大規模なエネルギー供給システムとの親和性に優れるため、エネルギー供給システムの末端にまで容易に配送することができるという利点がある。
Under such circumstances, organic hydride (organic chemical hydride) has been attracting attention as an energy carrier to replace liquid hydrogen. Examples of the organic hydride include cyclic organic compounds such as cyclohexane, methylcyclohexane, and decalin. Organic hydride is easy to handle because it is generally liquid at normal temperature and pressure. Organic hydrides can also be electrochemically hydrogenated and dehydrogenated. For this reason, if organic hydride is used as an energy carrier, it can be transported and stored more easily than liquid hydrogen. In particular, when a liquid with properties similar to petroleum is selected as the organic hydride, it is excellent in affinity with a relatively large-scale energy supply system, so that it can be easily delivered to the end of the energy supply system. There are advantages.
従来、有機ハイドライドの製造方法としては、再生可能エネルギーでの水電解により水素を製造し、水素化反応器中で被水素化物(有機ハイドライドの脱水素化体)に水素を付加して有機ハイドライドを製造する方法が知られている。
Conventionally, as a method for producing organic hydride, hydrogen is produced by water electrolysis with renewable energy, and hydrogen is added to a hydride (dehydride of organic hydride) in a hydrogenation reactor to produce organic hydride. Manufacturing methods are known.
これに対し、電解合成法によれば、被水素化物に直接水素を付加することができるため、有機ハイドライドの製造工程を簡略化することができる。また、規模によらず効率損失が少なく、さらに有機ハイドライド製造装置の起動停止に対する追従性にも優れる。このような有機ハイドライドの製造技術に関して、例えば特許文献1には、水からプロトンを生成する酸化極と、不飽和結合を有する有機化合物を水素化する還元極とを備える電解セルが開示されている。
On the other hand, according to the electrolytic synthesis method, hydrogen can be directly added to the hydride, so that the organic hydride manufacturing process can be simplified. In addition, the efficiency loss is small regardless of the scale, and the followability to start / stop of the organic hydride manufacturing apparatus is also excellent. Regarding such an organic hydride manufacturing technique, for example, Patent Document 1 discloses an electrolytic cell including an oxidation electrode that generates protons from water and a reduction electrode that hydrogenates an organic compound having an unsaturated bond. .
本発明者らは、上述した有機ハイドライドを製造する技術について鋭意検討を重ねた結果、従来の技術には、有機ハイドライドの製造効率を向上させる余地があることを認識するに至った。
As a result of intensive studies on the above-described technology for producing organic hydride, the present inventors have come to recognize that there is room for improving the production efficiency of organic hydride in the conventional technology.
本発明はこうした状況に鑑みてなされたものであり、その目的は、有機ハイドライドの製造効率を向上させる技術を提供することにある。
The present invention has been made in view of such circumstances, and an object thereof is to provide a technique for improving the production efficiency of organic hydride.
本発明のある態様は、有機ハイドライド製造用電解セルのカソードである。当該カソードは、プロトンで被水素化物を水素化して有機ハイドライドを生成するための第1触媒を含むカソード触媒層と、カソード触媒層を収容するカソード室と、カソード室におけるカソード触媒層を除く領域に配置され、カソードにおける副反応の生成物である水素ガスと、未反応の被水素化物との化学反応を促進させる第2触媒と、を備える。
An embodiment of the present invention is a cathode of an electrolytic cell for producing an organic hydride. The cathode includes a cathode catalyst layer containing a first catalyst for hydrogenating a hydride with protons to produce an organic hydride, a cathode chamber containing the cathode catalyst layer, and a region excluding the cathode catalyst layer in the cathode chamber. And a second catalyst that promotes a chemical reaction between a hydrogen gas that is a product of a side reaction at the cathode and an unreacted hydride.
本発明の他の態様は、有機ハイドライド製造用電解セルである。当該電解セルは、プロトン伝導性を有する電解質膜と、電解質膜の一方の側に設けられる上記態様のカソードと、電解質膜の一方の側とは反対側に設けられ、水を酸化してプロトンを生成するためのアノード触媒層、及びアノード触媒層を収容するアノード室を有するアノードと、を備える。
Another aspect of the present invention is an electrolytic cell for producing an organic hydride. The electrolytic cell is provided with an electrolyte membrane having proton conductivity, a cathode according to the above aspect provided on one side of the electrolyte membrane, and a side opposite to one side of the electrolyte membrane, and oxidizes water to generate protons. And an anode having an anode chamber for housing the anode catalyst layer.
本発明のさらに他の態様は、有機ハイドライドの製造方法である。当該製造方法は、有機ハイドライド製造用電解セルが備えるアノードに水を供給し、当該水を電気分解してプロトンを生成する工程と、有機ハイドライド製造用電解セルが備えるカソードに被水素化物を供給し、有機ハイドライド製造用電解セルが備える電解質膜を通過したプロトンで被水素化物を水素化して有機ハイドライドを生成する工程と、カソードにおける副反応の生成物である水素ガスと、未反応の被水素化物とを化学反応させて有機ハイドライドを生成する工程と、を含む。
Still another embodiment of the present invention is a method for producing an organic hydride. The manufacturing method includes supplying water to an anode included in an electrolytic cell for manufacturing an organic hydride, electrolyzing the water to generate protons, and supplying a hydride to a cathode included in the electrolytic cell for manufacturing an organic hydride. , A step of hydrogenating a hydride with protons that have passed through an electrolyte membrane included in an electrolytic cell for producing an organic hydride to produce an organic hydride, a hydrogen gas that is a product of a side reaction at the cathode, and an unreacted hydride And a step of producing an organic hydride by a chemical reaction.
本発明によれば、有機ハイドライドの製造効率を向上させることができる。
According to the present invention, the production efficiency of organic hydride can be improved.
以下、本発明を好適な実施の形態をもとに図面を参照しながら説明する。実施の形態は、発明を限定するものではなく例示であって、実施の形態に記述されるすべての特徴やその組み合わせは、必ずしも発明の本質的なものであるとは限らない。各図面に示される同一または同等の構成要素、部材、処理には、同一の符号を付するものとし、適宜重複した説明は省略する。また、各図に示す各部の縮尺や形状は、説明を容易にするために便宜的に設定されており、特に言及がない限り限定的に解釈されるものではない。また、本明細書または請求項中に「第1」、「第2」等の用語が用いられる場合には、特に言及がない限り、いかなる順序や重要度を表すものでもなく、ある構成と他の構成とを区別するためのものである。
Hereinafter, the present invention will be described based on preferred embodiments with reference to the drawings. The embodiments do not limit the invention but are exemplifications, and all features and combinations described in the embodiments are not necessarily essential to the invention. The same or equivalent components, members, and processes shown in the drawings are denoted by the same reference numerals, and repeated descriptions are omitted as appropriate. In addition, the scale and shape of each part shown in each drawing are set for convenience in order to facilitate the explanation, and are not limitedly interpreted unless otherwise specified. In addition, when terms such as “first” and “second” are used in the present specification or claims, they do not represent any order or importance unless otherwise specified. It is for distinguishing from the structure of.
実施の形態に係る有機ハイドライド製造用電解セル(以下では適宜、単に「電解セル」という)は、プロトン伝導性を有する固体高分子電解質膜と、固体高分子電解質膜の一方の面に設けられ、プロトンで被水素化物を還元して水素化物を生成するカソード触媒層と、カソード触媒層を収容し、被水素化物が供給されるカソード室と、固体高分子電解質膜の他方の面に設けられ、水を酸化してプロトンを生成するアノード触媒層と、アノード触媒層を収容し、電解液が供給されるアノード室とを備える。カソード室には、固体高分子電解質膜側から見て、カソード触媒層、マイクロポーラス層、拡散層、及びカソード支持体としても機能する被水素化物の流路部が設けられる。また、カソード室には、有機ハイドライドが排出されるカソード室出口が設けられる。さらに、カソード室には、カソード触媒層を除く領域に、Pt等もしくはPt等を含む合金(多元金属)からなる触媒が配置される。
An electrolytic cell for producing an organic hydride according to an embodiment (hereinafter simply referred to as “electrolytic cell” as appropriate) is provided on one surface of a solid polymer electrolyte membrane having proton conductivity and a solid polymer electrolyte membrane, A cathode catalyst layer that generates a hydride by reducing the hydride with protons, a cathode chamber that contains the cathode catalyst layer and is supplied with the hydride, and is provided on the other surface of the solid polymer electrolyte membrane; An anode catalyst layer that oxidizes water to generate protons, and an anode chamber that accommodates the anode catalyst layer and is supplied with an electrolytic solution. In the cathode chamber, as viewed from the solid polymer electrolyte membrane side, a cathode catalyst layer, a microporous layer, a diffusion layer, and a hydride channel portion that also functions as a cathode support are provided. The cathode chamber is provided with a cathode chamber outlet from which organic hydride is discharged. Further, in the cathode chamber, a catalyst made of Pt or the like or an alloy containing Pt or the like (multi-element metal) is disposed in a region excluding the cathode catalyst layer.
以下、実施の形態に係る電解セルと、有機ハイドライドの製造方法とについて、図面を参照しながら詳細に説明する。図1は、実施の形態に係る有機ハイドライド製造用電解セルを備える有機ハイドライド製造装置(電気化学還元装置)の模式図である。なお、図1では、電解セルが備えるセパレータの図示を省略し、膜電極接合体の構造を簡略化している。有機ハイドライド製造装置10は、有機ハイドライドの脱水素化体である被水素化物を電気化学還元反応により水素化する装置であり、主な構成として、有機ハイドライド製造用電解セル100、電力制御部20、カソード液貯蔵槽30、分離槽36、アノード液貯蔵槽40及び制御部60を備える。
Hereinafter, the electrolytic cell according to the embodiment and the method for producing the organic hydride will be described in detail with reference to the drawings. FIG. 1 is a schematic diagram of an organic hydride production apparatus (electrochemical reduction apparatus) including an organic hydride production electrolytic cell according to an embodiment. In addition, in FIG. 1, illustration of the separator with which an electrolysis cell is provided is abbreviate | omitted, and the structure of a membrane electrode assembly is simplified. The organic hydride manufacturing apparatus 10 is an apparatus that hydrogenates a hydride that is a dehydrogenated form of an organic hydride by an electrochemical reduction reaction. A catholyte storage tank 30, a separation tank 36, an anolyte storage tank 40, and a control unit 60 are provided.
電力制御部20は、例えば、電力源の出力電圧を所定の電圧に変換するDC/DCコンバータである。電力制御部20の正極出力端子は、電解セル100のアノード150(酸素発生用電極)に接続される。電力制御部20の負極出力端子は、電解セル100のカソード120(還元電極)に接続される。これにより、電解セル100のアノード150とカソード120との間に所定の電圧が印加される。
The power control unit 20 is, for example, a DC / DC converter that converts the output voltage of the power source into a predetermined voltage. The positive output terminal of the power control unit 20 is connected to the anode 150 (oxygen generating electrode) of the electrolysis cell 100. The negative output terminal of the power control unit 20 is connected to the cathode 120 (reduction electrode) of the electrolysis cell 100. Thereby, a predetermined voltage is applied between the anode 150 and the cathode 120 of the electrolytic cell 100.
なお、電力制御部20には、正及び負極の電位検知の目的で参照極が設けられていてもよい。この場合、参照極入力端子は、電解セル100の電解質膜110に設けられる参照電極(図示せず)に接続される。参照電極は、カソード120及びアノード150から電気的に隔離されている。参照電極は、参照電極電位に保持される。本願における参照電極電位は、可逆水素電極(RHE)に対する電位を意味するものとする(参照電極電位=0V)。なお、参照電極電位は、Ag/AgCl電極に対する電位であってもよい(参照電極電位=0.199V)。カソード120とアノード150との間を流れる電流は、電流検出部(図示せず)によって検出される。電流検出部で検出された電流値は、制御部60に入力され、制御部60による電力制御部20の制御に用いられる。参照電極とカソード120との間の電位差は、電圧検出部(図示せず)によって検出される。電圧検出部で検出された電位差の値は制御部60に入力され、制御部60による電力制御部20の制御に用いられる。
The power control unit 20 may be provided with a reference electrode for the purpose of detecting positive and negative potentials. In this case, the reference electrode input terminal is connected to a reference electrode (not shown) provided on the electrolyte membrane 110 of the electrolytic cell 100. The reference electrode is electrically isolated from the cathode 120 and the anode 150. The reference electrode is held at the reference electrode potential. The reference electrode potential in the present application means a potential with respect to the reversible hydrogen electrode (RHE) (reference electrode potential = 0 V). The reference electrode potential may be a potential with respect to the Ag / AgCl electrode (reference electrode potential = 0.199V). A current flowing between the cathode 120 and the anode 150 is detected by a current detection unit (not shown). The current value detected by the current detection unit is input to the control unit 60 and used for controlling the power control unit 20 by the control unit 60. The potential difference between the reference electrode and the cathode 120 is detected by a voltage detector (not shown). The value of the potential difference detected by the voltage detection unit is input to the control unit 60 and used for control of the power control unit 20 by the control unit 60.
制御部60は、アノード150又はカソード120の電位が所望の電位となるように、電力制御部20の正極出力端子及び負極出力端子の出力を制御する。なお、電力源は、好ましくは太陽光、風力、水力、地熱発電等で得られる再生可能エネルギーであるが、特にこれに限定されない。
The control unit 60 controls the output of the positive output terminal and the negative output terminal of the power control unit 20 so that the potential of the anode 150 or the cathode 120 becomes a desired potential. The power source is preferably renewable energy obtained by sunlight, wind power, hydropower, geothermal power generation, or the like, but is not particularly limited thereto.
カソード液貯蔵槽30には、電解セル100での電気化学還元反応により水素化される被水素化物が貯蔵される。本実施の形態において用いられる有機ハイドライドは、水素化反応/脱水素反応を可逆的に起こすことにより、水素を添加/脱離できる有機化合物であれば特に限定されず、アセトン-イソプロパノール系、ベンゾキノン-ヒドロキノン系、芳香族炭化水素系等広く用いることができる。これらの中で、エネルギー輸送時の運搬性、毒性、安全性、保存安定性等の観点から、また、体積あるいは質量当たりに輸送できる水素量、水素添加及び脱水素反応の容易性、Gibbs自由エネルギー変化が著しく大きくない等のエネルギー変換効率の観点から、トルエン-メチルシクロヘキサン系に代表される芳香族炭化水素系が好ましい。
The catholyte storage tank 30 stores a hydride to be hydrogenated by an electrochemical reduction reaction in the electrolytic cell 100. The organic hydride used in the present embodiment is not particularly limited as long as it is an organic compound capable of adding / eliminating hydrogen by reversibly causing hydrogenation / dehydrogenation reaction. Acetone-isopropanol, benzoquinone- A hydroquinone type, an aromatic hydrocarbon type, etc. can be used widely. Among these, from the viewpoint of transportability during energy transportation, toxicity, safety, storage stability, etc., the amount of hydrogen that can be transported per volume or mass, the ease of hydrogenation and dehydrogenation reactions, Gibbs free energy From the viewpoint of energy conversion efficiency such that the change is not significantly large, an aromatic hydrocarbon system typified by a toluene-methylcyclohexane system is preferable.
有機ハイドライドの脱水素化体として用いられる芳香族炭化水素化合物は、少なくとも1つの芳香環を含む化合物であり、例えば、ベンゼン、アルキルベンゼン、ナフタレン、アルキルナフタレン、アントラセン、ジフェニルエタン等が挙げられる。アルキルベンゼンには、芳香環の1~4の水素原子が炭素数1~6の直鎖アルキル基又は分岐アルキル基で置換された化合物が含まれ、例えば、トルエン、キシレン、メシチレン、エチルベンゼン、ジエチルベンゼン等が挙げられる。アルキルナフタレンには、芳香環の1~4の水素原子が炭素数1~6の直鎖アルキル基又は分岐アルキル基で置換された化合物が含まれ、例えばメチルナフタレン等が挙げられる。これらは単独で用いられても、組み合わせて用いられてもよい。芳香族炭化水素化合物は、好ましくはトルエン及びベンゼンの少なくとも一方である。なお、ピリジン、ピリミジン、ピラジン、キノリン、イソキノリン、N-アルキルピロール、N-アルキルインドール、N-アルキルジベンゾピロール等の含窒素複素環式芳香族化合物も、脱水素化体として用いることができる。
An aromatic hydrocarbon compound used as a dehydrogenated form of organic hydride is a compound containing at least one aromatic ring, and examples thereof include benzene, alkylbenzene, naphthalene, alkylnaphthalene, anthracene, and diphenylethane. Alkylbenzene includes compounds in which 1 to 4 hydrogen atoms of an aromatic ring are substituted with a linear or branched alkyl group having 1 to 6 carbon atoms, such as toluene, xylene, mesitylene, ethylbenzene, diethylbenzene and the like. Can be mentioned. Alkylnaphthalene includes compounds in which 1 to 4 hydrogen atoms of an aromatic ring are substituted with a linear or branched alkyl group having 1 to 6 carbon atoms, and examples thereof include methylnaphthalene. These may be used alone or in combination. The aromatic hydrocarbon compound is preferably at least one of toluene and benzene. Nitrogen-containing heterocyclic aromatic compounds such as pyridine, pyrimidine, pyrazine, quinoline, isoquinoline, N-alkylpyrrole, N-alkylindole and N-alkyldibenzopyrrole can also be used as dehydrogenated products.
有機ハイドライドの脱水素化体、すなわち被水素化物は、常温で液体であることが好ましい。また、上述の芳香族炭化水素化合物及び/又は含窒素複素環式芳香族化合物の複数種を混合したものを用いる場合は、混合物として液体であればよい。被水素化物が常温で液体である場合、加熱や加圧などの処理を行うことなく、液体の状態で被水素化物を電解セル100に供給することができる。これにより、有機ハイドライド製造装置10の構成の簡素化を図ることができる。以下では適宜、カソード液貯蔵槽30に貯蔵される液体を「カソード液」という。
The organic hydride dehydrogenated product, that is, the hydride, is preferably liquid at room temperature. Moreover, what is necessary is just to be a liquid as a mixture, when using what mixed multiple types of the above-mentioned aromatic hydrocarbon compound and / or nitrogen-containing heterocyclic aromatic compound. When the hydride is liquid at room temperature, the hydride can be supplied to the electrolytic cell 100 in a liquid state without performing treatment such as heating or pressurization. Thereby, simplification of the structure of the organic hydride manufacturing apparatus 10 can be achieved. Hereinafter, the liquid stored in the catholyte storage tank 30 is referred to as “catholyte” as appropriate.
カソード液貯蔵槽30に貯蔵された被水素化物は、第1液体供給装置32によって電解セル100のカソード120に供給される。第1液体供給装置32としては、例えば、ギアポンプあるいはシリンダーポンプ等の各種ポンプ、または自然流下式装置等を用いることができる。カソード120とカソード液貯蔵槽30との間には、循環経路34が設けられる。電解セル100により核水素化された被水素化物、すなわち有機ハイドライドと、未反応の被水素化物とは、循環経路34を経て分離槽36に到達する。分離槽36において、有機ハイドライド及び被水素化物の混合物から、水素ガス等が分離される。分離されたガスは、分解触媒38を経て系外に排出される。その後、有機ハイドライド及び被水素化物は、カソード液貯蔵槽30に戻される。
The hydride stored in the catholyte storage tank 30 is supplied to the cathode 120 of the electrolysis cell 100 by the first liquid supply device 32. As the first liquid supply device 32, for example, various pumps such as a gear pump or a cylinder pump, a natural flow-down device, or the like can be used. A circulation path 34 is provided between the cathode 120 and the catholyte storage tank 30. The hydride nucleated by the electrolysis cell 100, that is, the organic hydride and the unreacted hydride reach the separation tank 36 via the circulation path 34. In the separation tank 36, hydrogen gas and the like are separated from the mixture of the organic hydride and the hydride. The separated gas is discharged out of the system through the cracking catalyst 38. Thereafter, the organic hydride and the hydride are returned to the catholyte storage tank 30.
アノード液貯蔵槽40には、例えばイオン交換水、純水、あるいはこれらに硫酸、リン酸、硝酸、塩酸等の酸を加えた水溶液等(以下では適宜、「アノード液」という)が貯蔵される。アノード液の20℃で測定したイオン伝導度は、好ましくは0.01S/cm以上である。アノード液のイオン伝導度を0.01S/cm以上とすることで、工業的に十分な電気化学反応を起こさせることができる。
In the anolyte storage tank 40, for example, ion exchange water, pure water, or an aqueous solution obtained by adding an acid such as sulfuric acid, phosphoric acid, nitric acid, hydrochloric acid or the like (hereinafter referred to as “anolyte” as appropriate) is stored. . The ionic conductivity measured at 20 ° C. of the anolyte is preferably 0.01 S / cm or more. By making the ionic conductivity of the anolyte 0.01 S / cm or more, an industrially sufficient electrochemical reaction can be caused.
アノード液貯蔵槽40に貯蔵されたアノード液は、第2液体供給装置42によって電解セル100のアノード150に供給される。第2液体供給装置42としては、例えばギアポンプあるいはシリンダーポンプ等の各種ポンプ、または自然流下式装置等を用いることができる。アノード150とアノード液貯蔵槽40との間には、循環経路44が設けられる。電解セル100において未反応のアノード液は、循環経路44を経てアノード液貯蔵槽40に戻される。アノード液貯蔵槽40には気水分離部(図示せず)が設けられ、電解セル100におけるアノード液の電気分解によって生じる酸素等のガスは、気水分離部によってアノード液から分離されて、分解触媒46を経て系外に排出される。
The anolyte stored in the anolyte storage tank 40 is supplied to the anode 150 of the electrolysis cell 100 by the second liquid supply device 42. As the second liquid supply device 42, for example, various pumps such as a gear pump or a cylinder pump, a natural flow-down device, or the like can be used. A circulation path 44 is provided between the anode 150 and the anolyte storage tank 40. The unreacted anolyte in the electrolytic cell 100 is returned to the anolyte storage tank 40 via the circulation path 44. The anolyte storage tank 40 is provided with a steam / water separator (not shown), and gas such as oxygen generated by electrolysis of the anolyte in the electrolysis cell 100 is separated from the anolyte by the steam / water separator and decomposed. It is discharged out of the system through the catalyst 46.
図2は、実施の形態に係る有機ハイドライド製造用電解セルの概略構造を示す断面図である。図3は、カソード触媒層及びマイクロポーラス層の一部を拡大して示す模式図である。図2に示すように、電解セル100は、膜電極接合体102と、膜電極接合体102を挟む一対のセパレータ170a,170bと、を備える。膜電極接合体102は、電解質膜110、カソード120、及びアノード150を有する。
FIG. 2 is a cross-sectional view showing a schematic structure of an electrolytic cell for producing an organic hydride according to an embodiment. FIG. 3 is an enlarged schematic view showing a part of the cathode catalyst layer and the microporous layer. As shown in FIG. 2, the electrolytic cell 100 includes a membrane electrode assembly 102 and a pair of separators 170 a and 170 b that sandwich the membrane electrode assembly 102. The membrane electrode assembly 102 includes an electrolyte membrane 110, a cathode 120, and an anode 150.
[電解質膜]
電解質膜110は、プロトン伝導性を有する材料(アイオノマー)で形成される。電解質膜110は、プロトンを選択的に伝導する一方で、カソード120とアノード150との間で物質が混合したり拡散したりすることを抑制する。プロトン伝導性を有する材料としては、ナフィオン(登録商標)、フレミオン(登録商標)などのパーフルオロスルホン酸ポリマーが挙げられる。電解質膜110の厚さは、特に限定されないが、好ましくは5~300μmであり、より好ましくは10~150μmであり、さらに好ましくは20~100μmである。電解質膜110の厚さを5μm以上とすることで、電解質膜110のバリア性を確保して、被水素化物や酸素等のクロスリークの発生をより確実に抑制することができる。また、電解質膜110の厚さを300μm以下とすることで、イオン移動抵抗が過大になることを抑制することができる。 [Electrolyte membrane]
Theelectrolyte membrane 110 is formed of a material (ionomer) having proton conductivity. The electrolyte membrane 110 selectively conducts protons, while suppressing the mixing and diffusion of substances between the cathode 120 and the anode 150. Examples of the material having proton conductivity include perfluorosulfonic acid polymers such as Nafion (registered trademark) and Flemion (registered trademark). The thickness of the electrolyte membrane 110 is not particularly limited, but is preferably 5 to 300 μm, more preferably 10 to 150 μm, and further preferably 20 to 100 μm. By setting the thickness of the electrolyte membrane 110 to 5 μm or more, the barrier property of the electrolyte membrane 110 can be secured, and the occurrence of cross leaks such as hydride and oxygen can be more reliably suppressed. Further, by setting the thickness of the electrolyte membrane 110 to 300 μm or less, it is possible to suppress the ion migration resistance from becoming excessive.
電解質膜110は、プロトン伝導性を有する材料(アイオノマー)で形成される。電解質膜110は、プロトンを選択的に伝導する一方で、カソード120とアノード150との間で物質が混合したり拡散したりすることを抑制する。プロトン伝導性を有する材料としては、ナフィオン(登録商標)、フレミオン(登録商標)などのパーフルオロスルホン酸ポリマーが挙げられる。電解質膜110の厚さは、特に限定されないが、好ましくは5~300μmであり、より好ましくは10~150μmであり、さらに好ましくは20~100μmである。電解質膜110の厚さを5μm以上とすることで、電解質膜110のバリア性を確保して、被水素化物や酸素等のクロスリークの発生をより確実に抑制することができる。また、電解質膜110の厚さを300μm以下とすることで、イオン移動抵抗が過大になることを抑制することができる。 [Electrolyte membrane]
The
電解質膜110の面積抵抗、即ち幾何面積当たりのイオン移動抵抗は、特に限定されないが、好ましくは2000mΩ・cm2以下であり、より好ましくは1000mΩ・cm2以下であり、さらに好ましくは500mΩ・cm2以下である。電解質膜110の面積抵抗を2000mΩ・cm2以下とすることで、プロトン伝導性が不足するおそれをより確実に回避することができる。カチオン交換型のアイオノマーのイオン交換容量(IEC)は、特に限定されないが、好ましくは0.7~2meq/gであり、より好ましくは1~1.3meq/gである。カチオン交換型のアイオノマーのイオン交換容量を0.7meq/g以上とすることで、イオン伝導性が不十分となるおそれをより確実に回避することができる。一方、当該イオン交換容量を2meq/g以下とすることで、アイオノマーのアノード液や被水素化物への溶解度が増大して電解質膜110の強度が不十分となるおそれをより確実に回避することができる。
The area resistance of the electrolyte membrane 110, that is, the ion transfer resistance per geometric area is not particularly limited, but is preferably 2000 mΩ · cm 2 or less, more preferably 1000 mΩ · cm 2 or less, and further preferably 500 mΩ · cm 2. It is as follows. By setting the area resistance of the electrolyte membrane 110 to 2000 mΩ · cm 2 or less, the possibility of insufficient proton conductivity can be avoided more reliably. The ion exchange capacity (IEC) of the cation exchange type ionomer is not particularly limited, but is preferably 0.7 to 2 meq / g, more preferably 1 to 1.3 meq / g. By setting the ion exchange capacity of the cation exchange ionomer to 0.7 meq / g or more, it is possible to more reliably avoid the possibility that the ion conductivity is insufficient. On the other hand, by setting the ion exchange capacity to 2 meq / g or less, it is possible to more reliably avoid the possibility that the solubility of the ionomer in the anolyte or hydride increases and the strength of the electrolyte membrane 110 becomes insufficient. it can.
電解質膜110には、多孔性のPTFE(ポリテトラフルオロエチレン)等の補強材が混合されてもよい。補強材を導入することで、イオン交換容量の増加に伴う電解質膜110の寸法安定性の低下を抑制することができる。これにより、電解質膜110の耐久性を向上させることができる。また、被水素化物や酸素のクロスオーバーを抑制することができる。
The electrolyte membrane 110 may be mixed with a reinforcing material such as porous PTFE (polytetrafluoroethylene). By introducing the reinforcing material, it is possible to suppress a decrease in dimensional stability of the electrolyte membrane 110 accompanying an increase in ion exchange capacity. Thereby, the durability of the electrolyte membrane 110 can be improved. Further, crossover of hydride and oxygen can be suppressed.
[カソード]
カソード120は、電解質膜110の一方の側に設けられる。本実施の形態では、カソード120は電解質膜110の一方の主表面に接するように設けられている。カソード120は、カソード触媒層122と、カソード触媒層122を収容するカソード室124とを備える。また、カソード120は、スペーサ126、マイクロポーラス層128、拡散層130、流路部132、カソード室入口134及びカソード室出口136を備える。 [Cathode]
Thecathode 120 is provided on one side of the electrolyte membrane 110. In the present embodiment, cathode 120 is provided in contact with one main surface of electrolyte membrane 110. The cathode 120 includes a cathode catalyst layer 122 and a cathode chamber 124 that houses the cathode catalyst layer 122. The cathode 120 includes a spacer 126, a microporous layer 128, a diffusion layer 130, a flow path portion 132, a cathode chamber inlet 134, and a cathode chamber outlet 136.
カソード120は、電解質膜110の一方の側に設けられる。本実施の形態では、カソード120は電解質膜110の一方の主表面に接するように設けられている。カソード120は、カソード触媒層122と、カソード触媒層122を収容するカソード室124とを備える。また、カソード120は、スペーサ126、マイクロポーラス層128、拡散層130、流路部132、カソード室入口134及びカソード室出口136を備える。 [Cathode]
The
カソード触媒層122は、カソード室124内で電解質膜110の一方の主表面に接している。図3に示すように、カソード触媒層122は、プロトンで被水素化物を水素化して有機ハイドライドを生成するための第1触媒としての還元触媒122aを含む。還元触媒122aとしては、例えばPt、Ru、Pd、Ir及びこれらの少なくとも1つを含む合金からなる群から選択される金属粒子を用いることができる。還元触媒122aは、市販品を用いてもよいし、公知の方法に従って合成したものを用いてもよい。また、還元触媒122aは、Pt、Ru、Pd、Irの少なくとも1つからなる第1の触媒金属(貴金属)と、Cr、Mn、Fe、Co、Ni、Cu、Zn、Mo、Ru、Sn、W、Re、Pb、Biから選択される1種又は2種以上の第2の触媒金属とを含む金属組成物で構成されてもよい。この場合、当該金属組成物の形態としては、第1の触媒金属と第2の触媒金属との合金、あるいは第1の触媒金属と第2の触媒金属からなる金属間化合物などが挙げられる。還元触媒122aの平均粒径は、好ましくは1nm~1μmであり、より好ましくは1nm~5nmである。還元触媒122aの平均粒径を1μm以下とすることで、触媒重量当たりの表面積(反応面積)を増加させることができる。また、還元触媒122aの平均粒径を1nm以上とすることで、触媒粒子同士の凝集が進んで耐久性が低下することをより確実に抑制することができる。
The cathode catalyst layer 122 is in contact with one main surface of the electrolyte membrane 110 in the cathode chamber 124. As shown in FIG. 3, the cathode catalyst layer 122 includes a reduction catalyst 122a as a first catalyst for hydrogenating a hydride with protons to generate an organic hydride. As the reduction catalyst 122a, for example, metal particles selected from the group consisting of Pt, Ru, Pd, Ir, and an alloy containing at least one of them can be used. As the reduction catalyst 122a, a commercially available product may be used, or a catalyst synthesized according to a known method may be used. The reduction catalyst 122a includes a first catalytic metal (noble metal) made of at least one of Pt, Ru, Pd, and Ir, and Cr, Mn, Fe, Co, Ni, Cu, Zn, Mo, Ru, Sn, You may be comprised with the metal composition containing 1 type, or 2 or more types of 2nd catalyst metals selected from W, Re, Pb, Bi. In this case, examples of the form of the metal composition include an alloy of the first catalyst metal and the second catalyst metal, or an intermetallic compound composed of the first catalyst metal and the second catalyst metal. The average particle diameter of the reduction catalyst 122a is preferably 1 nm to 1 μm, and more preferably 1 nm to 5 nm. By setting the average particle diameter of the reduction catalyst 122a to 1 μm or less, the surface area (reaction area) per catalyst weight can be increased. Moreover, it can suppress more reliably that aggregation of catalyst particles advances and durability falls by making the average particle diameter of the reduction catalyst 122a 1 nm or more.
還元触媒122aは、電子伝導性材料で構成される触媒担体122bによって担持される。還元触媒122aを触媒担体122bに担持させることで、カソード触媒層122の表面積を拡大することができる。また、還元触媒122aの凝集を抑制することができる。触媒担体122bに用いられる電子伝導性材料の電子伝導度は、好ましくは1.0×10-2S/cm以上であり、より好ましくは3.0×10-2S/cm以上であり、さらに好ましくは1.0×10-1S/cm以上である。電子伝導性材料の電子伝導度を1.0×10-2S/cm以上とすることで、カソード触媒層122に対してより確実に電子伝導性を付与することができる。
The reduction catalyst 122a is supported by a catalyst carrier 122b made of an electron conductive material. By carrying the reduction catalyst 122a on the catalyst carrier 122b, the surface area of the cathode catalyst layer 122 can be increased. Further, aggregation of the reduction catalyst 122a can be suppressed. The electron conductivity of the electron conductive material used for the catalyst carrier 122b is preferably 1.0 × 10 −2 S / cm or more, more preferably 3.0 × 10 −2 S / cm or more, Preferably it is 1.0 × 10 −1 S / cm or more. By setting the electron conductivity of the electron conductive material to 1.0 × 10 −2 S / cm or more, electron conductivity can be more reliably imparted to the cathode catalyst layer 122.
触媒担体122bとしては、例えば多孔性カーボン(メソポーラスカーボンなど)、多孔性金属、多孔性金属酸化物のいずれかを主成分として含有する電子伝導性材料を挙げることができる。多孔性カーボンとしては、例えばケッチェンブラック(登録商標)、アセチレンブラック、ファーネスブラック、バルカン(登録商標)などのカーボンブラックが挙げられる。
Examples of the catalyst carrier 122b include an electron conductive material containing as a main component any one of porous carbon (such as mesoporous carbon), porous metal, and porous metal oxide. Examples of the porous carbon include carbon black such as ketjen black (registered trademark), acetylene black, furnace black, and Vulcan (registered trademark).
窒素吸着法で測定した多孔性カーボンのBET比表面積は、好ましくは50m2/g~1500m2/gであり、より好ましくは500m2/g~1300m2/gであり、さらに好ましくは700m2/g~1000m2/gである。多孔性カーボンのBET比表面積を50m2/g以上とすることで、還元触媒122aを均一に担持させやすくすることができる。また、被水素化物の拡散性をより確実に担保することができる。また、多孔性カーボンのBET比表面積を1500m2/g以下とすることで、被水素化物の反応時や、有機ハイドライド製造装置10の起動時あるいは停止時に、触媒担体122bの劣化が生じやすくなることを回避することができる。これにより、触媒担体122bに十分な耐久性を付与することができる。また、触媒担体122bとして用いられるカーボンブラック等の炭素微粒子の平均粒径は、好ましくは0.01μm~1μmである。
BET specific surface area of the porous carbon as measured by nitrogen adsorption method is preferably 50m 2 / g ~ 1500m 2 / g, more preferably 500m 2 / g ~ 1300m 2 / g, more preferably from 700 meters 2 / g to 1000 m 2 / g. By setting the BET specific surface area of the porous carbon to 50 m 2 / g or more, the reduction catalyst 122a can be easily supported uniformly. Moreover, the diffusibility of the hydride can be ensured more reliably. Further, by setting the BET specific surface area of the porous carbon to 1500 m 2 / g or less, the catalyst carrier 122b is liable to be deteriorated during the reaction of the hydride or when the organic hydride production apparatus 10 is started or stopped. Can be avoided. Thereby, sufficient durability can be imparted to the catalyst carrier 122b. The average particle size of carbon fine particles such as carbon black used as the catalyst carrier 122b is preferably 0.01 μm to 1 μm.
多孔性金属としては、例えばPtブラック、Pdブラック、フラクタル状に析出させたPt金属などが挙げられる。多孔性金属酸化物としては、例えばTi、Zr、Nb、Mo、Hf、Ta、Wの酸化物が挙げられる。また、触媒担体122bには、Ti、Zr、Nb、Mo、Hf、Ta、Wなどの金属の窒化物、炭化物、酸窒化物、炭窒化物、部分酸化した炭窒化物といった、多孔性の金属化合物(以下では適宜、多孔性金属炭窒化物等と呼ぶ)も用いることができる。窒素吸着法で測定した多孔性金属、多孔性金属酸化物及び多孔性金属炭窒化物等のBET比表面積は、好ましくは1m2/g以上であり、より好ましくは3m2/g以上であり、さらに好ましくは10m2/g以上である。多孔性金属、多孔性金属酸化物及び多孔性金属炭窒化物等のBET比表面積を1m2/g以上とすることで、還元触媒122aを均一に担持させやすくすることができる。
Examples of the porous metal include Pt black, Pd black, and Pt metal deposited in a fractal shape. Examples of the porous metal oxide include Ti, Zr, Nb, Mo, Hf, Ta, and W oxides. Further, the catalyst support 122b includes porous metals such as nitrides, carbides, oxynitrides, carbonitrides, partially oxidized carbonitrides of metals such as Ti, Zr, Nb, Mo, Hf, Ta, and W. A compound (hereinafter referred to as a porous metal carbonitride as appropriate) can also be used. The BET specific surface areas of the porous metal, porous metal oxide and porous metal carbonitride measured by the nitrogen adsorption method are preferably 1 m 2 / g or more, more preferably 3 m 2 / g or more, More preferably, it is 10 m 2 / g or more. By setting the BET specific surface area of the porous metal, the porous metal oxide, the porous metal carbonitride and the like to 1 m 2 / g or more, the reduction catalyst 122a can be easily supported uniformly.
還元触媒122aを担持した状態の触媒担体122bは、アイオノマー122cで被覆される。これにより、カソード120のイオン伝導性を向上させることができる。アイオノマー122cとしては、例えばナフィオン(登録商標)、フレミオン(登録商標)などのパーフルオロスルホン酸ポリマー等を挙げることができる。アイオノマー122cのイオン交換容量(IEC)は、好ましくは0.7~3meq/gであり、より好ましくは1~2.5meq/gであり、さらに好ましくは1.2~2meq/gである。触媒担体122bが多孔性カーボンである場合、アイオノマー(I)/触媒担体(C)の質量比I/Cは、好ましくは0.1~2であり、より好ましくは0.2~1.5であり、さらに好ましくは0.3~1.1である。質量比I/Cを0.1以上とすることで、十分なイオン伝導性をより確実に得ることができる。一方、質量比I/Cを2以下とすることで、還元触媒122aに対するアイオノマー122cの被覆厚みが過剰になることを抑制して、被水素化物の触媒活性点への接触が阻害されることを回避することができる。
The catalyst carrier 122b carrying the reduction catalyst 122a is coated with an ionomer 122c. Thereby, the ion conductivity of the cathode 120 can be improved. Examples of the ionomer 122c include perfluorosulfonic acid polymers such as Nafion (registered trademark) and Flemion (registered trademark). The ion exchange capacity (IEC) of the ionomer 122c is preferably 0.7 to 3 meq / g, more preferably 1 to 2.5 meq / g, and further preferably 1.2 to 2 meq / g. When the catalyst carrier 122b is porous carbon, the ionomer (I) / catalyst carrier (C) mass ratio I / C is preferably 0.1 to 2, more preferably 0.2 to 1.5. More preferably, it is 0.3 to 1.1. By setting the mass ratio I / C to be 0.1 or more, sufficient ion conductivity can be obtained more reliably. On the other hand, by setting the mass ratio I / C to 2 or less, it is possible to suppress an excessive increase in the coating thickness of the ionomer 122c with respect to the reduction catalyst 122a and to inhibit contact of the hydride with the catalyst active point. It can be avoided.
なお、カソード触媒層122に含まれるアイオノマー122cは、還元触媒122aを部分的に被覆していることが好ましい。これによれば、カソード触媒層122における電気化学反応に必要な3要素(被水素化物、プロトン、電子)を効率的に反応場に供給することができる。
Note that the ionomer 122c included in the cathode catalyst layer 122 preferably partially covers the reduction catalyst 122a. According to this, three elements (hydrogenated product, proton, electron) necessary for the electrochemical reaction in the cathode catalyst layer 122 can be efficiently supplied to the reaction field.
カソード触媒層122の厚さは、好ましくは1~100μmであり、より好ましくは5~30μmである。カソード触媒層122の厚さが増加すると、プロトンの移動抵抗が増大するだけでなく、被水素化物の拡散性も低下する。このため、カソード触媒層122の厚さは、上述した範囲で調整することが望ましい。
The thickness of the cathode catalyst layer 122 is preferably 1 to 100 μm, more preferably 5 to 30 μm. As the thickness of the cathode catalyst layer 122 increases, not only the proton transfer resistance increases, but also the diffusibility of the hydride decreases. For this reason, it is desirable to adjust the thickness of the cathode catalyst layer 122 within the above-described range.
カソード触媒層122は、例えば以下の方法により作製することができる。すなわち、まず、触媒成分粉末と、ガス透過性材料である疎水性樹脂(フッ素成分)と、水と、ナフサ等の溶剤と、アイオノマー(例えばナフィオン(登録商標)分散液DE521(デュポン社製))とを混合する。アイオノマーの添加量は、乾燥後のアイオノマーの質量と触媒成分粉末中のカーボン質量との比率が1:10~10:1となる量であることが好ましい。疎水性樹脂は粉末状であり、その粒径は好ましくは0.005~10μmである。得られた混合物に適宜溶媒を添加して、触媒インクを調製する。
The cathode catalyst layer 122 can be produced, for example, by the following method. That is, first, a catalyst component powder, a hydrophobic resin (fluorine component) as a gas permeable material, water, a solvent such as naphtha, and an ionomer (for example, Nafion (registered trademark) dispersion DE521 (manufactured by DuPont)) And mix. The addition amount of the ionomer is preferably such that the ratio of the mass of the ionomer after drying to the mass of carbon in the catalyst component powder is 1:10 to 10: 1. The hydrophobic resin is in the form of a powder, and the particle size is preferably 0.005 to 10 μm. A solvent is appropriately added to the obtained mixture to prepare a catalyst ink.
続いて、得られた触媒インクを、マイクロポーラス層128に塗布し、乾燥させた後にホットプレスして、カソード触媒層122をマイクロポーラス層128に固着させる。上述の塗布及び乾燥を複数回に分けて行った後に、ホットプレスを実施することが好ましい。これにより、より均質なカソード触媒層122を得ることができる。以上の工程により、カソード触媒層122を作製することができる。なお、カソード触媒層122は、電解質膜110上に形成してもよい。例えば、バーコーターを用いて電解質膜110の一方の主表面に触媒インクを塗布することで、カソード触媒層122と電解質膜110の複合体を作製することができる。また、スプレー塗布により電解質膜110の一方の主表面に触媒インクを吹き付け、触媒インク中の溶剤成分を乾燥させることで、カソード触媒層122と電解質膜110の複合体を作製することができる。触媒インクは、カソード触媒層122中の還元触媒122aの質量が、電極面積あたり0.5mg/cm2となるように塗布することが好ましい。
Subsequently, the obtained catalyst ink is applied to the microporous layer 128, dried, and then hot pressed to fix the cathode catalyst layer 122 to the microporous layer 128. It is preferable to perform hot pressing after performing the above-described application and drying in a plurality of times. Thereby, a more uniform cathode catalyst layer 122 can be obtained. Through the above steps, the cathode catalyst layer 122 can be produced. Note that the cathode catalyst layer 122 may be formed on the electrolyte membrane 110. For example, a composite of the cathode catalyst layer 122 and the electrolyte membrane 110 can be produced by applying a catalyst ink to one main surface of the electrolyte membrane 110 using a bar coater. Moreover, the composite of the cathode catalyst layer 122 and the electrolyte membrane 110 can be produced by spraying the catalyst ink on one main surface of the electrolyte membrane 110 by spray coating and drying the solvent component in the catalyst ink. The catalyst ink is preferably applied so that the mass of the reduction catalyst 122a in the cathode catalyst layer 122 is 0.5 mg / cm 2 per electrode area.
図2に示すように、カソード室124は、電解質膜110と、セパレータ170aと、電解質膜110及びセパレータ170aの間に配置される枠状のスペーサ126とで画成される。カソード室124には、カソード触媒層122だけでなく、マイクロポーラス層128、拡散層130、及び流路部132が収容される。また、スペーサ126には、カソード室124の内部と外部とを連通する、カソード室入口134及びカソード室出口136が配置される。
As shown in FIG. 2, the cathode chamber 124 is defined by an electrolyte membrane 110, a separator 170a, and a frame-shaped spacer 126 disposed between the electrolyte membrane 110 and the separator 170a. In the cathode chamber 124, not only the cathode catalyst layer 122 but also the microporous layer 128, the diffusion layer 130, and the flow path portion 132 are accommodated. The spacer 126 is provided with a cathode chamber inlet 134 and a cathode chamber outlet 136 that communicate the inside and the outside of the cathode chamber 124.
マイクロポーラス層128は、カソード触媒層122に隣接して配置される。より具体的には、マイクロポーラス層128は、カソード触媒層122の電解質膜110とは反対側の主表面に接するように設けられている。拡散層130は、マイクロポーラス層128に隣接して配置される。より具体的には、拡散層130は、マイクロポーラス層128のカソード触媒層122とは反対側の主表面に接するように設けられている。
The microporous layer 128 is disposed adjacent to the cathode catalyst layer 122. More specifically, the microporous layer 128 is provided so as to be in contact with the main surface of the cathode catalyst layer 122 opposite to the electrolyte membrane 110. The diffusion layer 130 is disposed adjacent to the microporous layer 128. More specifically, the diffusion layer 130 is provided so as to contact the main surface of the microporous layer 128 opposite to the cathode catalyst layer 122.
拡散層130は、流路部132から供給される液状の被水素化物をカソード触媒層122に均一に拡散させる機能を担う。拡散層130を構成する材料は、被水素化物に対して親和性が高いことが好ましい。拡散層130を構成する材料としては、例えば多孔性導電基材や繊維焼結体等が例示される。これらは、ガス及び液の供給や除去に適した多孔性を有し、且つ十分な電導性を保つことができるため好ましい。拡散層130は、好ましくは厚さが10~5000μmであり、空隙率が30~95%であり、代表的孔径が1~1000μmである。また、拡散層130を構成する材料の電子伝導度は、好ましくは10-2S/cm以上である。
The diffusion layer 130 has a function of uniformly diffusing the liquid hydride supplied from the flow path portion 132 into the cathode catalyst layer 122. The material constituting the diffusion layer 130 preferably has a high affinity for the hydride. Examples of the material constituting the diffusion layer 130 include a porous conductive base material and a fiber sintered body. These are preferable because they have porosity suitable for supply and removal of gas and liquid and can maintain sufficient electrical conductivity. The diffusion layer 130 preferably has a thickness of 10 to 5000 μm, a porosity of 30 to 95%, and a typical pore size of 1 to 1000 μm. Further, the electronic conductivity of the material constituting the diffusion layer 130 is preferably 10 −2 S / cm or more.
拡散層130を構成する材料のより具体的な例としては、カーボンの織布(カーボンクロス)、カーボンの不織布、カーボンペーパー等を挙げることができる。カーボンクロスは、数μmの径の細いカーボン繊維を数百本の束とし、この束を織布としたものである。また、カーボンペーパーは、カーボン原料繊維を製紙法にて薄膜の前駆体とし、これを焼結したものである。
More specific examples of the material constituting the diffusion layer 130 include carbon woven fabric (carbon cloth), carbon non-woven fabric, and carbon paper. The carbon cloth is a bundle of hundreds of thin carbon fibers having a diameter of several μm, and this bundle is a woven fabric. The carbon paper is obtained by sintering a carbon raw material fiber as a thin film precursor by a paper manufacturing method.
マイクロポーラス層128は、液体の被水素化物及び有機ハイドライドの、カソード触媒層122の面方向への拡散を促す機能を有する。マイクロポーラス層128は、例えば導電性粉末と撥水剤とを混練して得られるペースト状の混練物を、拡散層130の表面に塗布し、乾燥させることで形成することができる。導電性粉末としては、例えばバルカン(登録商標)等の導電性カーボンを用いることができる。撥水剤としては、例えば四フッ化エチレン樹脂(PTFE)などのフッ素系樹脂を用いることができる。導電性粉末と撥水剤の割合は、所望の導電性及び撥水性が得られる範囲内で適宜定められる。一例として、導電性粉末としてバルカン(登録商標)を用い、撥水剤としてPTFEを用いた場合の質量比(バルカン:PTFE)は、例えば4:1~1:1である。なお、マイクロポーラス層128は、拡散層130と同様にカーボンクロスやカーボンペーパー等で構成することもできる。
The microporous layer 128 has a function of promoting the diffusion of liquid hydride and organic hydride in the surface direction of the cathode catalyst layer 122. The microporous layer 128 can be formed, for example, by applying a paste-like kneaded material obtained by kneading a conductive powder and a water repellent to the surface of the diffusion layer 130 and drying it. As the conductive powder, for example, conductive carbon such as Vulcan (registered trademark) can be used. As the water repellent, a fluorine-based resin such as tetrafluoroethylene resin (PTFE) can be used. The ratio between the conductive powder and the water repellent is appropriately determined within a range where desired conductivity and water repellency can be obtained. As an example, when Vulcan (registered trademark) is used as the conductive powder and PTFE is used as the water repellent, the mass ratio (Vulcan: PTFE) is, for example, 4: 1 to 1: 1. Note that the microporous layer 128 can be made of carbon cloth, carbon paper, or the like, similarly to the diffusion layer 130.
マイクロポーラス層128の平均流量細孔径(dm)は、ホットプレス後において、好ましくは100nm~20μmであり、より好ましくは500nm~5μmである。マイクロポーラス層128の平均流量細孔径は、水銀ポロシメーター等で測定することができる。平均流量細孔径を100nm以上とすることで、細孔の壁面と液体の被水素化物及び有機ハイドライドの接触面積が過大となって拡散抵抗が増加することをより確実に抑制することができる。また、平均流量細孔径を20μm以下とすることで、毛管現象による液体の被水素化物及び有機ハイドライドの吸引が小さくなって流動性が低下することをより確実に抑制することができる。また、平均流量細孔径を100nm~20μmとすることで、毛管現象により液体の被水素化物及び有機ハイドライドをスムーズに吸引、排出することができる。また、マイクロポーラス層128の厚さは、好ましくは1~50μmであり、より好ましくは2~20μmである。なお、マイクロポーラス層128が拡散層130の表面よりも内部に落ち込むように形成されている場合には、拡散層130に潜っている部分を含めて、マイクロポーラス層128自体の膜厚の平均をマイクロポーラス層128の厚さと定義する。マイクロポーラス層128の表面には、金属成分を共存させてもよい。これにより、マイクロポーラス層128の電子伝導性が向上し、電流の均一化を図ることができる。
The average flow pore size (dm) of the microporous layer 128 is preferably 100 nm to 20 μm, more preferably 500 nm to 5 μm after hot pressing. The average flow pore size of the microporous layer 128 can be measured with a mercury porosimeter or the like. By setting the average flow pore size to 100 nm or more, it is possible to more reliably suppress an increase in diffusion resistance due to an excessive contact area between the pore walls and the liquid hydride and organic hydride. In addition, by setting the average flow pore size to 20 μm or less, it is possible to more reliably suppress a decrease in fluidity due to a decrease in suction of liquid hydride and organic hydride due to capillary action. Further, by setting the average flow pore size to 100 nm to 20 μm, liquid hydride and organic hydride can be smoothly sucked and discharged by capillary action. The thickness of the microporous layer 128 is preferably 1 to 50 μm, more preferably 2 to 20 μm. In the case where the microporous layer 128 is formed so as to drop inward from the surface of the diffusion layer 130, the average thickness of the microporous layer 128 itself including the portion hidden in the diffusion layer 130 is calculated. It is defined as the thickness of the microporous layer 128. A metal component may coexist on the surface of the microporous layer 128. Thereby, the electron conductivity of the microporous layer 128 is improved, and the current can be made uniform.
なお、マイクロポーラス層128と拡散層130とは、それぞれ厚さ方向に圧力が加えられた状態で使用される。したがって、使用時の厚さ方向への加圧によって、それぞれの厚さ方向における導電性が変化することは好ましくない。このため、マイクロポーラス層128及び拡散層130は、予めプレス加工が施されることが好ましい。これにより、各層の炭素材料が圧縮されるため、各層の厚さ方向における導電性を高め、且つ安定させることができる。また、20~50%の充填率を安定的に有するカソード120を実現できる。
The microporous layer 128 and the diffusion layer 130 are used in a state where pressure is applied in the thickness direction. Therefore, it is not preferable that the electrical conductivity in each thickness direction changes due to the pressurization in the thickness direction during use. For this reason, it is preferable that the microporous layer 128 and the diffusion layer 130 are pre-pressed. Thereby, since the carbon material of each layer is compressed, the conductivity in the thickness direction of each layer can be increased and stabilized. In addition, the cathode 120 having a stable filling rate of 20 to 50% can be realized.
また、カソード触媒層122とマイクロポーラス層128との接合度を向上させることも、カソード120の導電性向上に寄与する。また、当該接合度の向上によって、原料物質の供給能力と生成物質の除去能力とが向上する。プレス加工装置としては、ホットプレス、ホットローラー等の公知の装置を利用することができる。また、プレス条件としては、温度:室温~360℃、圧力:0.1~5MPaが好ましい。
Further, improving the degree of bonding between the cathode catalyst layer 122 and the microporous layer 128 also contributes to improving the conductivity of the cathode 120. Moreover, the supply capability of the raw material and the removal capability of the generated material are improved by improving the degree of joining. As the press working apparatus, a known apparatus such as a hot press or a hot roller can be used. The pressing conditions are preferably temperature: room temperature to 360 ° C. and pressure: 0.1 to 5 MPa.
流路部132は、拡散層130に隣接して配置される。より具体的には、流路部132は、拡散層130のマイクロポーラス層128とは反対側の主表面に接するように設けられている。流路部132は、板状の本体部132aの主表面に溝132bが設けられた構造を有する。溝132bは、被水素化物の流路を構成する。本体部132aは、導電性材料からなる。流路部132は、カソード室124内において、カソード触媒層122、マイクロポーラス層128及び拡散層130の位置決めをするカソード支持体としても機能する。
The flow path portion 132 is disposed adjacent to the diffusion layer 130. More specifically, the channel portion 132 is provided so as to be in contact with the main surface of the diffusion layer 130 on the side opposite to the microporous layer 128. The flow path portion 132 has a structure in which a groove 132b is provided on the main surface of the plate-like main body portion 132a. The groove 132b constitutes a flow path for the hydride. The main body 132a is made of a conductive material. The channel portion 132 also functions as a cathode support that positions the cathode catalyst layer 122, the microporous layer 128, and the diffusion layer 130 in the cathode chamber 124.
カソード室入口134は、カソード室124の鉛直方向下方に配置される。カソード室入口134は、一端が流路部132の流路に接続され、他端が第1液体供給装置32に接続される。カソード室124の外部から供給される被水素化物は、カソード室入口134を介してカソード室124内に導入される。カソード室124に導入された被水素化物は、流路部132の溝132b、拡散層130及びマイクロポーラス層128を経由してカソード触媒層122に供給される。
The cathode chamber inlet 134 is disposed below the cathode chamber 124 in the vertical direction. One end of the cathode chamber inlet 134 is connected to the flow path of the flow path portion 132, and the other end is connected to the first liquid supply device 32. The hydride supplied from the outside of the cathode chamber 124 is introduced into the cathode chamber 124 through the cathode chamber inlet 134. The hydride introduced into the cathode chamber 124 is supplied to the cathode catalyst layer 122 via the groove 132b of the flow path portion 132, the diffusion layer 130, and the microporous layer 128.
カソード室出口136は、カソード室124の鉛直方向上方に配置される。カソード室出口136は、一端が流路部132の流路に接続され、他端が循環経路34に接続される。カソード室124内の有機ハイドライドと未反応の被水素化物とは、カソード室出口136を介してカソード室124の外部に排出される。
The cathode chamber outlet 136 is disposed vertically above the cathode chamber 124. The cathode chamber outlet 136 has one end connected to the flow path of the flow path portion 132 and the other end connected to the circulation path 34. The organic hydride and unreacted hydride in the cathode chamber 124 are discharged to the outside of the cathode chamber 124 via the cathode chamber outlet 136.
セパレータ170aは、電解セル100においてカソード120側に配置される。本実施の形態では、セパレータ170aは、流路部132の拡散層130とは反対側の主表面に積層されている。
The separator 170a is disposed on the cathode 120 side in the electrolytic cell 100. In the present embodiment, separator 170a is laminated on the main surface of flow path portion 132 on the side opposite to diffusion layer 130.
図3に示すように、カソード120は、カソード室124におけるカソード触媒層122を除く領域に配置される第2触媒138を備える。本実施の形態では、一例としてマイクロポーラス層128に第2触媒138が配置されている。第2触媒138については、後に詳細に説明する。
As shown in FIG. 3, the cathode 120 includes a second catalyst 138 disposed in a region excluding the cathode catalyst layer 122 in the cathode chamber 124. In the present embodiment, the second catalyst 138 is disposed in the microporous layer 128 as an example. The second catalyst 138 will be described in detail later.
[アノード]
アノード150は、電解質膜110の一方の側とは反対側、すなわちカソード120とは反対側に設けられる。本実施の形態では、アノード150は電解質膜110の他方の主表面に接するように設けられている。アノード150は、アノード触媒層152と、アノード触媒層152を収容するアノード室154とを備える。また、アノード150は、スペーサ156、支持用弾性体158、アノード室入口160及びアノード室出口162を備える。 [anode]
Theanode 150 is provided on the side opposite to one side of the electrolyte membrane 110, that is, on the side opposite to the cathode 120. In the present embodiment, anode 150 is provided in contact with the other main surface of electrolyte membrane 110. The anode 150 includes an anode catalyst layer 152 and an anode chamber 154 that accommodates the anode catalyst layer 152. The anode 150 includes a spacer 156, a supporting elastic body 158, an anode chamber inlet 160, and an anode chamber outlet 162.
アノード150は、電解質膜110の一方の側とは反対側、すなわちカソード120とは反対側に設けられる。本実施の形態では、アノード150は電解質膜110の他方の主表面に接するように設けられている。アノード150は、アノード触媒層152と、アノード触媒層152を収容するアノード室154とを備える。また、アノード150は、スペーサ156、支持用弾性体158、アノード室入口160及びアノード室出口162を備える。 [anode]
The
アノード触媒層152は、アノード室154内において、電解質膜110の他方の主表面に接している。アノード触媒層152は、アノード液中の水を酸化してプロトンを生成するための触媒を含む層である。アノード触媒層152に含まれる触媒としては、例えばRu、Rh、Pd、Ir、Pt及びこれらの少なくとも1つを含む合金からなる群から選択される金属粒子を用いることができる。
The anode catalyst layer 152 is in contact with the other main surface of the electrolyte membrane 110 in the anode chamber 154. The anode catalyst layer 152 is a layer containing a catalyst for oxidizing protons in the anolyte to generate protons. As the catalyst contained in the anode catalyst layer 152, for example, metal particles selected from the group consisting of Ru, Rh, Pd, Ir, Pt, and an alloy containing at least one of them can be used.
触媒は、電子伝導性を有する金属基材に分散担持、又はコーティングされてもよい。このような金属基材としては、Ti、Cr、Mn、Fe、Co、Ni、Cu、Zn、Nb、Mo、Ta、Wなどの金属、あるいはこれらを主成分とする合金などで構成される、金属繊維(繊維径:例えば10~30μm)、メッシュ(メッシュ径:例えば500~1000μm)、金属多孔体の焼結体、発泡成型体(フォーム)、エキスパンドメタル等を挙げることができる。アノード触媒層152に用いる基材としては、電解に必要な電流を流すための十分な電気伝導性を有する必要性と、電解セル100の機械的強度の必要性とから、厚さ0.1~2mmの板状材料が好ましい。また、基材は、気泡による抵抗の増大を避けてアノード液の供給を促進するために、多孔体であるとともにアノード液に対する耐食性に優れることが好ましい。このような基材としては、チタン製のエキスパンドメッシュが汎用されている。エキスパンドメッシュは、短目方向中心間距離が好ましくは0.1~4mmであり、長目方向中心間距離が好ましくは0.1~4mmであり、開口率が好ましくは30~70%程度である。
The catalyst may be dispersedly supported or coated on a metal substrate having electronic conductivity. Such a metal substrate is composed of a metal such as Ti, Cr, Mn, Fe, Co, Ni, Cu, Zn, Nb, Mo, Ta, W, or an alloy containing these as a main component. Examples thereof include metal fibers (fiber diameter: for example, 10 to 30 μm), mesh (mesh diameter: for example, 500 to 1000 μm), sintered metal porous bodies, foamed molded bodies (foam), expanded metals, and the like. The base material used for the anode catalyst layer 152 has a thickness of 0.1 to 0.1 because of the necessity of having sufficient electric conductivity for flowing current necessary for electrolysis and the necessity of the mechanical strength of the electrolysis cell 100. A 2 mm plate material is preferred. The substrate is preferably a porous body and excellent in corrosion resistance to the anolyte in order to avoid the increase in resistance due to bubbles and promote the supply of the anolyte. As such a base material, an expanded mesh made of titanium is widely used. The expanded mesh preferably has a center distance in the short direction of 0.1 to 4 mm, a center distance in the long direction of preferably 0.1 to 4 mm, and an opening ratio of preferably about 30 to 70%. .
アノード室154は、電解質膜110と、セパレータ170bと、電解質膜110及びセパレータ170bの間に配置される枠状のスペーサ156とで画成される。アノード室154には、アノード触媒層152だけでなく、支持用弾性体158が収容される。また、スペーサ156には、アノード室154の内部と外部とを連通する、アノード室入口160及びアノード室出口162が配置される。
The anode chamber 154 is defined by the electrolyte membrane 110, the separator 170b, and a frame-shaped spacer 156 disposed between the electrolyte membrane 110 and the separator 170b. The anode chamber 154 accommodates not only the anode catalyst layer 152 but also the supporting elastic body 158. The spacer 156 is provided with an anode chamber inlet 160 and an anode chamber outlet 162 that communicate the inside and the outside of the anode chamber 154.
支持用弾性体158は、アノード触媒層152に隣接して配置される。より具体的には、支持用弾性体158は、アノード触媒層152の電解質膜110とは反対側の主表面に接するように設けられている。支持用弾性体158は、アノード触媒層152を電解質膜110に付勢する機能を有する。支持用弾性体158によりアノード触媒層152を電解質膜110に押し付けることで、電解セル100の電解特性を向上させることができる。支持用弾性体158は、例えば板ばね構造やコイル構造等の弾性体構造を有する導電性部材で構成される。また、支持用弾性体158は、耐酸性を有することが好ましい。支持用弾性体158を構成する材料としては、例えばチタンまたはチタン合金が挙げられる。弾性体構造の具体例としては、V字型スプリング、Xクロススプリング、クッションコイル、ビビリ繊維の集合体等が挙げられる。
The supporting elastic body 158 is disposed adjacent to the anode catalyst layer 152. More specifically, the supporting elastic body 158 is provided so as to contact the main surface of the anode catalyst layer 152 opposite to the electrolyte membrane 110. The supporting elastic body 158 has a function of urging the anode catalyst layer 152 toward the electrolyte membrane 110. By pressing the anode catalyst layer 152 against the electrolyte membrane 110 by the supporting elastic body 158, the electrolytic characteristics of the electrolytic cell 100 can be improved. The supporting elastic body 158 is formed of a conductive member having an elastic body structure such as a leaf spring structure or a coil structure. The supporting elastic body 158 preferably has acid resistance. Examples of the material constituting the supporting elastic body 158 include titanium or a titanium alloy. Specific examples of the elastic body structure include a V-shaped spring, an X cross spring, a cushion coil, an assembly of chatter fibers, and the like.
アノード室入口160は、アノード室154の鉛直方向下方に配置される。アノード室入口160は、一端がアノード室154内に接続され、他端が第2液体供給装置42に接続される。アノード室154の外部から供給されるアノード液は、アノード室入口160を介してアノード室154内に導入される。アノード室154に導入されたアノード液は、直に又は支持用弾性体158を介してアノード触媒層152に供給される。
The anode chamber inlet 160 is disposed below the anode chamber 154 in the vertical direction. The anode chamber inlet 160 has one end connected to the anode chamber 154 and the other end connected to the second liquid supply device 42. The anolyte supplied from outside the anode chamber 154 is introduced into the anode chamber 154 through the anode chamber inlet 160. The anolyte introduced into the anode chamber 154 is supplied to the anode catalyst layer 152 directly or via the supporting elastic body 158.
アノード室出口162は、アノード室154の鉛直方向上方に配置される。アノード室出口162は、一端がアノード室154内に接続され、他端が循環経路44に接続される。アノード室154内の酸素ガスと未反応のアノード液とは、アノード室出口162を介してアノード室154の外部に排出される。
The anode chamber outlet 162 is disposed above the anode chamber 154 in the vertical direction. The anode chamber outlet 162 has one end connected to the anode chamber 154 and the other end connected to the circulation path 44. The oxygen gas in the anode chamber 154 and the unreacted anolyte are discharged to the outside of the anode chamber 154 via the anode chamber outlet 162.
セパレータ170bは、電解セル100においてアノード150側に配置される。本実施の形態では、セパレータ170bは、支持用弾性体158のアノード触媒層152とは反対側の主表面に積層される。
The separator 170b is disposed on the anode 150 side in the electrolytic cell 100. In the present embodiment, the separator 170b is laminated on the main surface of the supporting elastic body 158 opposite to the anode catalyst layer 152.
上述した構造を備える電解セル100において、被水素化物の一例としてトルエン(TL)を用いた場合に起こる反応は、以下の通りである。被水素化物としてトルエンを用いた場合、得られる有機ハイドライドはメチルシクロヘキサン(MCH)である。
<アノードでの電極反応>
2H2O→O2+4H++4e-:E0>1.23V
<カソードでの電極反応>
TL+6H++6e-→MCH:E0<0.15V
<全反応>
2TL+6H2O→2MCH+3O2 In theelectrolytic cell 100 having the above-described structure, the reaction that occurs when toluene (TL) is used as an example of the hydride is as follows. When toluene is used as the hydride, the resulting organic hydride is methylcyclohexane (MCH).
<Electrode reaction at the anode>
2H 2 O → O 2 + 4H + + 4e − : E 0 > 1.23V
<Electrode reaction at the cathode>
TL + 6H + + 6e − → MCH: E 0 <0.15V
<All reactions>
2TL + 6H 2 O → 2MCH + 3O 2
<アノードでの電極反応>
2H2O→O2+4H++4e-:E0>1.23V
<カソードでの電極反応>
TL+6H++6e-→MCH:E0<0.15V
<全反応>
2TL+6H2O→2MCH+3O2 In the
<Electrode reaction at the anode>
2H 2 O → O 2 + 4H + + 4e − : E 0 > 1.23V
<Electrode reaction at the cathode>
TL + 6H + + 6e − → MCH: E 0 <0.15V
<All reactions>
2TL + 6H 2 O → 2MCH + 3O 2
すなわち、アノード150での電極反応と、カソード120での電極反応とが並行して進行する。そして、アノード150における水の電気分解により生じたプロトン(H+)が、電解質膜110を介してカソード120に供給される。カソード120に供給されたプロトンは、カソード120において被水素化物の核水素化に用いられる。これにより、トルエンが水素化されて、メチルシクロヘキサンが生成される。したがって、本実施の形態に係る有機ハイドライド製造装置10によれば、水の電気分解と被水素化物の水添反応とを1ステップで行うことができる。
That is, the electrode reaction at the anode 150 and the electrode reaction at the cathode 120 proceed in parallel. Then, protons (H + ) generated by water electrolysis at the anode 150 are supplied to the cathode 120 through the electrolyte membrane 110. The proton supplied to the cathode 120 is used for nuclear hydrogenation of the hydride at the cathode 120. Thereby, toluene is hydrogenated and methylcyclohexane is produced. Therefore, according to the organic hydride manufacturing apparatus 10 according to the present embodiment, water electrolysis and hydrogenation reaction of the hydride can be performed in one step.
しかしながら、カソード120では、以下に示す副反応が生じ得る。
<カソードでの副反応>
2H++2e-→H2
この副反応は、カソード120に供給されるカソード液中の被水素化物の濃度が低下するにつれて、カソードでの電極反応に対する比率が増大する。副反応によって水素ガスが生成されると、水素ガスの気泡により被水素化物の反応場への移動が阻害され、有機ハイドライドの生成が阻害されるおそれがある。有機ハイドライドの生成が阻害されると、電解セル100の電流効率は低下する。 However, the following side reactions can occur at thecathode 120.
<Side reaction at cathode>
2H + + 2e − → H 2
The ratio of this side reaction to the electrode reaction at the cathode increases as the concentration of the hydride in the catholyte supplied to thecathode 120 decreases. When hydrogen gas is generated by the side reaction, movement of the hydride to the reaction field is hindered by bubbles of hydrogen gas, and the production of organic hydride may be hindered. When the production of organic hydride is inhibited, the current efficiency of the electrolysis cell 100 decreases.
<カソードでの副反応>
2H++2e-→H2
この副反応は、カソード120に供給されるカソード液中の被水素化物の濃度が低下するにつれて、カソードでの電極反応に対する比率が増大する。副反応によって水素ガスが生成されると、水素ガスの気泡により被水素化物の反応場への移動が阻害され、有機ハイドライドの生成が阻害されるおそれがある。有機ハイドライドの生成が阻害されると、電解セル100の電流効率は低下する。 However, the following side reactions can occur at the
<Side reaction at cathode>
2H + + 2e − → H 2
The ratio of this side reaction to the electrode reaction at the cathode increases as the concentration of the hydride in the catholyte supplied to the
これに対し、図3に示すように、本実施の形態に係るカソード120は、カソード室124におけるカソード触媒層122を除く領域に配置される第2触媒138をさらに備える。第2触媒138は、カソード120における副反応の生成物である水素ガスと、未反応の被水素化物との化学反応を促進させるための触媒である。第2触媒138を設けることで、カソード120における副生成物である水素ガスと未反応の被水素化物との化学反応を促進させて、水素ガスを減少させることができる。これにより、被水素化物の反応場への移動が阻害されることを抑制することができる。また、電解セル100の電流効率を増大させることができる。水素ガスと未反応の被水素化物との化学反応は、以下のとおりである。
<カソードでの化学反応>
TL+3H2→MCH On the other hand, as shown in FIG. 3, thecathode 120 according to the present embodiment further includes a second catalyst 138 disposed in a region excluding the cathode catalyst layer 122 in the cathode chamber 124. The second catalyst 138 is a catalyst for promoting a chemical reaction between hydrogen gas that is a product of a side reaction at the cathode 120 and an unreacted hydride. By providing the second catalyst 138, the chemical reaction between the hydrogen gas, which is a by-product in the cathode 120, and the unreacted hydride can be promoted, and the hydrogen gas can be reduced. Thereby, it can suppress that the movement to the reaction field of a hydride is inhibited. Moreover, the current efficiency of the electrolytic cell 100 can be increased. The chemical reaction between hydrogen gas and unreacted hydride is as follows.
<Chemical reaction at the cathode>
TL + 3H 2 → MCH
<カソードでの化学反応>
TL+3H2→MCH On the other hand, as shown in FIG. 3, the
<Chemical reaction at the cathode>
TL + 3H 2 → MCH
有機ハイドライド製造装置10の電流効率は、80%以上が電解反応によって得られ、20%以下が化学反応によって得られることが好ましく、90%以上が電解反応によって得られ、10%以下が化学反応によって得られることがより好ましく、95%以上が電解反応によって得られ、5%以下が化学反応によって得られることがさらに好ましい。プロトンの還元による水素発生の標準電極電位(E0)は0Vであり、上述したトルエンの還元反応(E0=約0.15V)よりも低い。したがって、水素の発生にはトルエンの電解還元反応よりも多くのエネルギーが必要である。このため、水素発生量が多くなるほど、すなわち電流効率が低くなるほど、有機ハイドライド製造に要するエネルギー量(電力量)が増加する。トルエンの電解反応による電流効率を80%以上とすることで、水電解により製造した水素を用いて化学反応によりトルエンを水素化する場合に比べて、本装置の優位性をより確実に得ることができる。トルエン以外の被水素化物についても同様である。
The current efficiency of the organic hydride manufacturing apparatus 10 is preferably 80% or more obtained by an electrolytic reaction, 20% or less by a chemical reaction, 90% or more by an electrolytic reaction, and 10% or less by a chemical reaction. More preferably, 95% or more is obtained by electrolytic reaction, and 5% or less is more preferably obtained by chemical reaction. The standard electrode potential (E 0 ) for hydrogen generation by proton reduction is 0V, which is lower than the above-described reduction reaction of toluene (E 0 = about 0.15V). Therefore, the generation of hydrogen requires more energy than the electrolytic reduction reaction of toluene. For this reason, as the amount of hydrogen generation increases, that is, as the current efficiency decreases, the amount of energy (electric power) required for organic hydride production increases. By setting the current efficiency due to the electrolytic reaction of toluene to 80% or more, the superiority of the present apparatus can be obtained more reliably than in the case where toluene is hydrogenated by a chemical reaction using hydrogen produced by water electrolysis. it can. The same applies to hydrides other than toluene.
本実施の形態では、第2触媒138は、マイクロポーラス層128に配置されている。しかしながら、特にこの構成に限定されず、第2触媒138は、カソード室124におけるマイクロポーラス層128以外の領域(カソード触媒層122は除く)に配置されてもよい。第2触媒138が配置される領域の好ましい例としては、マイクロポーラス層128に加えて、拡散層130、流路部132、及びカソード室出口136等が例示される。すなわち、第2触媒138は、マイクロポーラス層128、拡散層130、流路部132及びカソード室出口136の少なくとも1つに配置されることが好ましい。第2触媒138が配置された領域は、被水素化物の化学反応部を構成する。還元触媒122aが配置された領域、すなわちカソード触媒層122は、被水素化物の電解反応部を構成する。なお、第2触媒138は、反応場に近い領域、すなわちマイクロポーラス層128及び拡散層130の少なくとも一方に配置されることが好ましい。これにより、水素ガスによる被水素化物の移動阻害を、より確実に抑制することができる。
In the present embodiment, the second catalyst 138 is disposed in the microporous layer 128. However, the present invention is not particularly limited to this configuration, and the second catalyst 138 may be disposed in a region other than the microporous layer 128 in the cathode chamber 124 (excluding the cathode catalyst layer 122). As a preferable example of the region where the second catalyst 138 is disposed, in addition to the microporous layer 128, the diffusion layer 130, the flow path portion 132, the cathode chamber outlet 136, and the like are exemplified. That is, the second catalyst 138 is preferably disposed in at least one of the microporous layer 128, the diffusion layer 130, the flow path portion 132, and the cathode chamber outlet 136. The region where the second catalyst 138 is disposed constitutes a chemical reaction part of the hydride. The region where the reduction catalyst 122a is disposed, that is, the cathode catalyst layer 122 constitutes an electrolytic reaction part of the hydride. The second catalyst 138 is preferably disposed in a region close to the reaction field, that is, in at least one of the microporous layer 128 and the diffusion layer 130. Thereby, the movement inhibition of the hydride by hydrogen gas can be suppressed more reliably.
また、第2触媒138は、カソード室124内での被水素化物及び有機ハイドライドの流れにおいて、上流側よりも下流側に多く配置されることがより好ましい。カソード室124内の下流側では、被水素化物の有機ハイドライドへの変換によって被水素化物の濃度が減少するため、水素ガスがより発生しやすい。上流側よりも下流側に多く第2触媒138を配置することで、より低コストで効果的な水素ガス除去を実現することができる。下流側のみに第2触媒138を配置する場合、電極の全面積に対する第2触媒138を設置する領域の面積は、好ましくは下流域の1/100~1/2であり、より好ましくは下流域の1/10~1/3である。第2触媒138を設置する領域の面積を電極全体の1/100以上とすることで、水素ガスによる被水素化物の移動阻害をより確実に抑制することができる。また、第2触媒138を設置する領域の面積を電極全体の1/2以下とすることで、第2触媒138が過剰量となることを抑制してコストアップを抑えることができる。これにより、第2触媒138の設置に起因する製造プロセスの増加によるコストアップを考慮しても、有機ハイドライド製造装置10全体でコストメリットを得ることができる。
In addition, it is more preferable that the second catalyst 138 is disposed more on the downstream side than on the upstream side in the flow of the hydride and the organic hydride in the cathode chamber 124. On the downstream side in the cathode chamber 124, the concentration of the hydride decreases due to the conversion of the hydride to the organic hydride, so that hydrogen gas is more easily generated. By disposing the second catalyst 138 more on the downstream side than on the upstream side, effective hydrogen gas removal can be realized at a lower cost. When the second catalyst 138 is disposed only on the downstream side, the area of the region where the second catalyst 138 is installed with respect to the total area of the electrode is preferably 1/100 to 1/2 of the downstream region, more preferably the downstream region. 1/10 to 1/3 of the above. By setting the area of the region where the second catalyst 138 is installed to be 1/100 or more of the entire electrode, it is possible to more reliably suppress inhibition of movement of the hydride due to hydrogen gas. In addition, by setting the area of the region where the second catalyst 138 is installed to be ½ or less of the entire electrode, it is possible to suppress the second catalyst 138 from becoming an excessive amount and suppress cost increase. Thereby, even if it considers the cost increase by the increase in the manufacturing process resulting from installation of the 2nd catalyst 138, the cost merit can be acquired in the organic hydride manufacturing apparatus 10 whole.
また本実施の形態では、第2触媒138は、一例としてマイクロポーラス層128のカーボン繊維128aに担持されている。第2触媒138が拡散層130に配置される場合も同様に、拡散層130のカーボン繊維に第2触媒138を担持させることができる。マイクロポーラス層128及び拡散層130への第2触媒138の担持は、例えば、各層を触媒含有溶液に浸漬した後、還元剤を用いた液相還元処理を施すことで実現される。また、各層を触媒含有溶液に浸漬した後、加熱による還元処理を施すことでも実現され得る。なお、液相還元によれば、熱処理還元に比べて第2触媒138の平均粒径を小さくすることができる。
In the present embodiment, the second catalyst 138 is supported on the carbon fiber 128a of the microporous layer 128 as an example. Similarly, when the second catalyst 138 is disposed in the diffusion layer 130, the second catalyst 138 can be supported on the carbon fibers of the diffusion layer 130. The support of the second catalyst 138 on the microporous layer 128 and the diffusion layer 130 is realized by, for example, immersing each layer in a catalyst-containing solution and then performing a liquid phase reduction process using a reducing agent. It can also be realized by immersing each layer in a catalyst-containing solution and then performing a reduction treatment by heating. In addition, according to liquid phase reduction, the average particle diameter of the 2nd catalyst 138 can be made small compared with heat processing reduction.
第2触媒138を流路部132及びカソード室出口136に配置する場合は、第2触媒138を担体に担持した状態で、流路部132の溝132bやカソード室出口136の壁面等に塗布することが好ましい。担体としては、例えば、アルミナやゼオライト等の無機粒子を用いることができる。第2触媒138を担体に担持させることで、上述した化学反応が生じる領域の面積を拡大することができる。また、第2触媒138の凝集を抑制することができる。無機粒子担体の大きさ及び形状は、特に限定されない。しかしながら、無機粒子を壁面等に対して特に固定しない場合には、無機粒子担体の大きさは100μm以上であることが好ましい。これにより、無機粒子担体が系外に流出することを抑制することができる。
When the second catalyst 138 is disposed at the flow path portion 132 and the cathode chamber outlet 136, the second catalyst 138 is applied to the groove 132 b of the flow path portion 132, the wall surface of the cathode chamber outlet 136, etc. with the second catalyst 138 supported on the carrier. It is preferable. As the carrier, for example, inorganic particles such as alumina and zeolite can be used. By supporting the second catalyst 138 on the carrier, the area of the region where the above-described chemical reaction occurs can be expanded. Further, aggregation of the second catalyst 138 can be suppressed. The size and shape of the inorganic particle carrier are not particularly limited. However, when the inorganic particles are not particularly fixed to the wall surface or the like, the size of the inorganic particle carrier is preferably 100 μm or more. Thereby, it can suppress that an inorganic particle support | carrier flows out out of a system.
第2触媒138は、好ましくはPt、Ni、Re、Pd及びこれらの金属の少なくとも1種を含む合金からなる群から選択される。第2触媒138は、市販品を用いてもよいし、公知の方法に従って合成したものを用いてもよい。例えば、Ptイオンを水溶液に浸し、不活性雰囲気下で熱処理を施す方式や、液相還元法、エマルジョン法、ミセル法等の方式を採用することができる。第2触媒138は、好ましくは平均粒径が1nm~1μmの一次粒子である。前記「平均粒径」は、使用する第2触媒138を電子顕微鏡で撮影し、その撮影像から得られる複数粒子の直径の平均値として定義される。粒子が真円でない場合は、粒子の面積を測定し、その面積に対応する円の直径として定義する。平均粒径は、複数個所で電子顕微鏡撮影を行い、100個以上の粒子の平均値として求めることが望ましい。電子顕微鏡像を画像処理ソフト(例えば、三谷商事株式会社製WinROOF)を用いて二値化し、粒子をカウントすることで、より簡便に平均粒径を求めることができる。なお、還元触媒122aの平均粒径についても同様に定義される。また、第2触媒138の担持量は、好ましくは0.01~0.5mg/cm2である。
The second catalyst 138 is preferably selected from the group consisting of Pt, Ni, Re, Pd and alloys containing at least one of these metals. As the second catalyst 138, a commercially available product may be used, or one synthesized according to a known method may be used. For example, a method of immersing Pt ions in an aqueous solution and performing heat treatment under an inert atmosphere, a method such as a liquid phase reduction method, an emulsion method, or a micelle method can be employed. The second catalyst 138 is preferably primary particles having an average particle diameter of 1 nm to 1 μm. The “average particle diameter” is defined as an average value of the diameters of a plurality of particles obtained from a photographed image obtained by photographing the second catalyst 138 to be used with an electron microscope. If the particle is not a perfect circle, the area of the particle is measured and defined as the diameter of the circle corresponding to that area. The average particle diameter is desirably obtained as an average value of 100 or more particles by photographing with an electron microscope at a plurality of locations. The average particle diameter can be determined more easily by binarizing the electron microscope image using image processing software (for example, WinROOF manufactured by Mitani Corporation) and counting the particles. The average particle diameter of the reduction catalyst 122a is defined in the same manner. The supported amount of the second catalyst 138 is preferably 0.01 to 0.5 mg / cm 2 .
なお、第2触媒138は、還元触媒122aとは異なりアイオノマー122cで被覆されていない。通常、アイオノマー122cは、パーフルオロスルホン酸ポリマー等の強酸性のポリマーで構成される。このため、少なくとも一部がアイオノマー122cで被覆される還元触媒122aは、強酸に耐えられる貴金属、金属酸化物種に限定される。また、還元触媒122aとしてPt等の貴金属を用いたとしても、連続使用により徐々に溶解等の劣化が生じ得る。一方で、第2触媒138はアイオノマー122cに被覆されないため、幅広い触媒群から第2触媒138として用いる材料を選択することができる。また、第2触媒138として貴金属触媒を用いた場合には、劣化を大幅に抑制することができるため、使用する貴金属量を削減することができる。第2触媒138と還元触媒122aとは、アイオノマー122cの被覆の有無に基づいて区別することができる。
Note that, unlike the reduction catalyst 122a, the second catalyst 138 is not covered with the ionomer 122c. Usually, the ionomer 122c is composed of a strongly acidic polymer such as a perfluorosulfonic acid polymer. For this reason, the reduction catalyst 122a at least partially covered with the ionomer 122c is limited to noble metals and metal oxide species that can withstand strong acids. Further, even if a noble metal such as Pt is used as the reduction catalyst 122a, degradation such as dissolution may occur gradually due to continuous use. On the other hand, since the second catalyst 138 is not coated with the ionomer 122c, a material used as the second catalyst 138 can be selected from a wide range of catalysts. In addition, when a noble metal catalyst is used as the second catalyst 138, deterioration can be significantly suppressed, so that the amount of noble metal used can be reduced. The second catalyst 138 and the reduction catalyst 122a can be distinguished based on whether or not the ionomer 122c is coated.
[有機ハイドライドの製造方法]
本実施の形態に係る有機ハイドライドの製造方法では、上述した電解セル100が備えるアノード150に、水を含むアノード液が供給される。そして、アノード触媒層152において、水が電気分解されてプロトンが生成される。生成されたプロトンは、電解セル100が備える電解質膜110を通過して、カソード120側に移動する。また、電解セル100が備えるカソード120に被水素化物が供給される。そして、カソード触媒層122において、電解質膜110を通過したプロトンで被水素化物が水素化されて、有機ハイドライドが生成される。また、この有機ハイドライドの生成と並行して、カソード120における副反応の生成物である水素ガスと、未反応の被水素化物とが、第2触媒138の作用によって化学反応を起こし、有機ハイドライドが生成される。プロトンの生成工程と、電解還元反応による有機ハイドライドの生成工程と、水素ガスとの化学反応による有機ハイドライドの生成工程とは、少なくとも一時において並行して起こる。 [Method for producing organic hydride]
In the method for manufacturing an organic hydride according to the present embodiment, an anolyte containing water is supplied to theanode 150 provided in the above-described electrolysis cell 100. Then, in the anode catalyst layer 152, water is electrolyzed to generate protons. The generated protons pass through the electrolyte membrane 110 provided in the electrolytic cell 100 and move to the cathode 120 side. Further, the hydride is supplied to the cathode 120 provided in the electrolytic cell 100. In the cathode catalyst layer 122, the hydride is hydrogenated by protons that have passed through the electrolyte membrane 110, and organic hydride is generated. In parallel with the generation of the organic hydride, hydrogen gas, which is a product of a side reaction at the cathode 120, and an unreacted hydride cause a chemical reaction by the action of the second catalyst 138, and the organic hydride is converted. Generated. The proton generation step, the organic hydride generation step by an electrolytic reduction reaction, and the organic hydride generation step by a chemical reaction with hydrogen gas occur in parallel at least temporarily.
本実施の形態に係る有機ハイドライドの製造方法では、上述した電解セル100が備えるアノード150に、水を含むアノード液が供給される。そして、アノード触媒層152において、水が電気分解されてプロトンが生成される。生成されたプロトンは、電解セル100が備える電解質膜110を通過して、カソード120側に移動する。また、電解セル100が備えるカソード120に被水素化物が供給される。そして、カソード触媒層122において、電解質膜110を通過したプロトンで被水素化物が水素化されて、有機ハイドライドが生成される。また、この有機ハイドライドの生成と並行して、カソード120における副反応の生成物である水素ガスと、未反応の被水素化物とが、第2触媒138の作用によって化学反応を起こし、有機ハイドライドが生成される。プロトンの生成工程と、電解還元反応による有機ハイドライドの生成工程と、水素ガスとの化学反応による有機ハイドライドの生成工程とは、少なくとも一時において並行して起こる。 [Method for producing organic hydride]
In the method for manufacturing an organic hydride according to the present embodiment, an anolyte containing water is supplied to the
以上説明したように、本実施の形態に係るカソード120は、プロトンで被水素化物を水素化して有機ハイドライドを生成するカソード触媒層122と、カソード触媒層122を収容するカソード室124と、カソード室124におけるカソード触媒層122を除く領域に配置され、カソードにおける副生成物である水素ガスと、未反応の被水素化物との化学反応を促進させる第2触媒138とを備える。
As described above, the cathode 120 according to the present embodiment includes the cathode catalyst layer 122 that hydrogenates a hydride with protons to generate an organic hydride, the cathode chamber 124 that houses the cathode catalyst layer 122, and the cathode chamber. And a second catalyst 138 that is disposed in a region excluding the cathode catalyst layer 122 in 124 and promotes a chemical reaction between hydrogen gas as a by-product in the cathode and an unreacted hydride.
このように、被水素化物の還元反応を促進する第1触媒(還元触媒122a)が設けられる部位とは異なる部位に、第2触媒138を設けることで、副生成物である水素ガスを減少させることができる。これにより、水素ガスによる被水素化物の移動阻害を抑制することができる。このため、被水素化物の還元反応を高い電流効率で、且つ小さい電力原単位にて進行させることができる。また、副生成物である水素ガスを用いて有機ハイドライドを生成しているため、電解セル100の見かけ上の電流効率を向上させることもできる。以上より、有機ハイドライドの製造効率を向上させることができる。
In this way, by providing the second catalyst 138 at a site different from the site where the first catalyst (reduction catalyst 122a) for promoting the reduction reaction of the hydride is provided, the hydrogen gas as a by-product is reduced. be able to. Thereby, the movement inhibition of the hydride by hydrogen gas can be suppressed. For this reason, the reduction reaction of the hydride can be advanced with high current efficiency and a small electric power unit. In addition, since the organic hydride is generated using hydrogen gas, which is a byproduct, the apparent current efficiency of the electrolytic cell 100 can be improved. From the above, the production efficiency of organic hydride can be improved.
また、副反応による電流効率の低下は、カソード液中の被水素化物濃度が低下するにつれて顕著になる。一方で、有機ハイドライドの運搬効率の観点から、被水素化物の割合は極力減らしたいという要求がある。これに対し、本実施の形態によれば、低被水素化物濃度時においても電流効率を維持することができる。したがって、より性能の高い有機ハイドライド製造装置10を提供することができる。
Also, the decrease in current efficiency due to side reactions becomes more significant as the hydride concentration in the catholyte decreases. On the other hand, from the viewpoint of transport efficiency of organic hydride, there is a demand to reduce the ratio of hydride as much as possible. On the other hand, according to the present embodiment, current efficiency can be maintained even at a low hydride concentration. Therefore, the organic hydride manufacturing apparatus 10 with higher performance can be provided.
本発明は、上述の実施の形態に限定されるものではなく、当業者の知識に基づいて各種の設計変更等の変形を加えることも可能であり、そのような変形が加えられた実施の形態も本発明の範囲に含まれうるものである。
The present invention is not limited to the above-described embodiments, and various modifications such as design changes can be added based on the knowledge of those skilled in the art. Embodiments to which such modifications are added Can also be included in the scope of the present invention.
以下、本発明の実施例を説明するが、これら実施例は、本発明を好適に説明するための例示に過ぎず、なんら本発明を限定するものではない。
Hereinafter, examples of the present invention will be described. However, these examples are merely examples for suitably explaining the present invention, and do not limit the present invention.
(実施例1)
液相還元法によりPtを担持したカーボンペーパーを作製した。このカーボンペーパーは、第2触媒138を含有する拡散層130及びマイクロポーラス層128に相当する。まず、H2PtCl6・6H2O(和光純薬工業社製)と、20mlのイソプロパノールとを混合して混合溶液を作製した。H2PtCl6・6H2Oの添加量は、カーボンペーパーへのPtの担持量が0.5mg/cm2となるように調整した。得られた混合溶液に、カーボンペーパー(GDL 35BC、SGL Carbon社製)を浸漬した。このカーボンペーパーは、MPL(マイクロポーラス層)付きGDL(ガス拡散層)である。 (Example 1)
Carbon paper carrying Pt was produced by a liquid phase reduction method. This carbon paper corresponds to thediffusion layer 130 and the microporous layer 128 containing the second catalyst 138. First, a H 2 PtCl 6 · 6H 2 O ( Wako Pure Chemical Industries, Ltd.) to prepare a mixed solution by mixing a isopropanol 20 ml. Amount of H 2 PtCl 6 · 6H 2 O is supported amount of Pt to carbon paper was adjusted to 0.5 mg / cm 2. Carbon paper (GDL 35BC, manufactured by SGL Carbon) was immersed in the obtained mixed solution. This carbon paper is GDL (gas diffusion layer) with MPL (microporous layer).
液相還元法によりPtを担持したカーボンペーパーを作製した。このカーボンペーパーは、第2触媒138を含有する拡散層130及びマイクロポーラス層128に相当する。まず、H2PtCl6・6H2O(和光純薬工業社製)と、20mlのイソプロパノールとを混合して混合溶液を作製した。H2PtCl6・6H2Oの添加量は、カーボンペーパーへのPtの担持量が0.5mg/cm2となるように調整した。得られた混合溶液に、カーボンペーパー(GDL 35BC、SGL Carbon社製)を浸漬した。このカーボンペーパーは、MPL(マイクロポーラス層)付きGDL(ガス拡散層)である。 (Example 1)
Carbon paper carrying Pt was produced by a liquid phase reduction method. This carbon paper corresponds to the
その後、60℃のN2ガス雰囲気下でカーボンペーパーを完全に乾燥させた。続いて、NaBH4(和光純薬工業社製)及び純水をカーボンペーパーに添加し、数分間の還元処理を施した。なお、NaBH4の添加量は、H2PtCl6・6H2OとNaBH4のモル比が1:1.5となる量とした。還元処理の後、カーボンペーパーを純水に一晩漬け込んで洗浄した。その後、カーボンペーパーを60℃で60分間乾燥させて、Ptを担持したカーボンペーパーを得た。
Thereafter, the carbon paper was completely dried under an N 2 gas atmosphere at 60 ° C. Subsequently, NaBH 4 (manufactured by Wako Pure Chemical Industries, Ltd.) and pure water were added to the carbon paper and subjected to a reduction treatment for several minutes. The addition amount of NaBH 4, the molar ratio of H 2 PtCl 6 · 6H 2 O and NaBH 4 was 1: 1.5 and qs. After the reduction treatment, the carbon paper was immersed in pure water overnight and washed. Thereafter, the carbon paper was dried at 60 ° C. for 60 minutes to obtain carbon paper carrying Pt.
続いて、得られたカーボンペーパーを用いて電解セルを作製した。まず、PtRu/C触媒TEC61E54E(Pt23質量%、Ru27質量%、田中貴金属工業社製)の粉末に、ナフィオン(登録商標)分散液DE521(デュポン社製)を添加し、適宜溶媒を用いて触媒インクを調製した。ナフィオン(登録商標)分散液の添加量は、乾燥後のナフィオンの質量と触媒中のカーボンの質量との比率が4:5となるように添加した。得られた触媒インクを、Ptを担持したカーボンペーパーにおけるMPL側の主表面にバーコーターで塗布した。触媒インクは、Pt及びRuの合計質量が電極面積あたり0.5mg/cm2となるように塗布した。その後、カーボンペーパーを70℃で乾燥させて触媒インク中の溶媒成分を除去し、カーボンペーパー及びカソード触媒層の積層体を得た。
Then, the electrolytic cell was produced using the obtained carbon paper. First, Nafion (registered trademark) dispersion DE521 (manufactured by DuPont) is added to a powder of PtRu / C catalyst TEC61E54E (Pt23 mass%, Ru27 mass%, manufactured by Tanaka Kikinzoku Kogyo Co., Ltd.), and catalyst ink is appropriately used using a solvent. Was prepared. The amount of Nafion (registered trademark) dispersion was added so that the ratio of the mass of Nafion after drying to the mass of carbon in the catalyst was 4: 5. The obtained catalyst ink was applied to the main surface on the MPL side of the carbon paper carrying Pt with a bar coater. The catalyst ink was applied so that the total mass of Pt and Ru was 0.5 mg / cm 2 per electrode area. Thereafter, the carbon paper was dried at 70 ° C. to remove the solvent component in the catalyst ink, thereby obtaining a laminate of the carbon paper and the cathode catalyst layer.
得られた積層体と電解質膜(ナフィオン(登録商標)117、デュポン社製)とを積層し、温度120℃、圧力1MPaの条件で1分間加圧した。これにより、カーボンペーパー、カソード触媒層及び電解質膜の複合体を得た。
The obtained laminate and an electrolyte membrane (Nafion (registered trademark) 117, manufactured by DuPont) were laminated and pressurized for 1 minute under conditions of a temperature of 120 ° C. and a pressure of 1 MPa. As a result, a composite of carbon paper, cathode catalyst layer and electrolyte membrane was obtained.
続いて、カーボン/エポキシ樹脂をモールド成型したカーボン系構造体を用意した。このカーボン系構造体は、流路部132と、スペーサ126と、セパレータ170aとの接合体に相当する。カーボン系構造体は、流路部132に相当する側の表面に、サーペンタイン流路(幅1mm、深さ0.5mm)が設けられている。サーペンタイン流路の一端には液体供給用ヘッダーが設けられ、サーペンタイン流路の他端には液体排出用ヘッダーが設けられている。
Subsequently, a carbon-based structure obtained by molding carbon / epoxy resin was prepared. This carbon-based structure corresponds to a joined body of the flow path portion 132, the spacer 126, and the separator 170a. The carbon-based structure is provided with a serpentine channel (width 1 mm, depth 0.5 mm) on the surface corresponding to the channel portion 132. A liquid supply header is provided at one end of the serpentine flow path, and a liquid discharge header is provided at the other end of the serpentine flow path.
また、アノード基材として、厚さ1.0mm、短目方向中心間距離3.5mm、長目方向中心間距離6.0mmのエキスパンドメッシュを用意した。そして、アノード基材の表面に、乾式ブラスト処理を施し、ついで20%硫酸水溶液中での洗浄処理を施した。その後、アークイオンプレーティング装置とチタン-タンタル合金板を用い、基材温度150℃、真空度1.3Paの条件で、アノード基材の表面に厚さ2μmの被膜を形成した。被膜を設けたアノード基材に対して、四塩化イリジウム/五塩化タンタルの混合水溶液を塗布した。その後、アノード基材を電気炉に投入して、550℃の熱処理を施した。溶液の塗布と熱処理とを複数回繰り返すことにより、触媒として酸化イリジウムと酸化タンタルとを含有するアノード触媒層を形成した。触媒の担持量は、Ir金属量換算で電極面積あたり12g/m2とした。
Further, an expanded mesh having a thickness of 1.0 mm, a distance between centers in the short direction of 3.5 mm, and a distance between centers in the long direction of 6.0 mm was prepared as the anode base material. Then, the surface of the anode base material was subjected to a dry blast process, and then a cleaning process in a 20% aqueous sulfuric acid solution. Thereafter, a film having a thickness of 2 μm was formed on the surface of the anode base material using an arc ion plating apparatus and a titanium-tantalum alloy plate under the conditions of a base material temperature of 150 ° C. and a vacuum degree of 1.3 Pa. A mixed aqueous solution of iridium tetrachloride / tantalum pentachloride was applied to the anode substrate provided with the coating. Thereafter, the anode base material was put into an electric furnace and subjected to a heat treatment at 550 ° C. The anode catalyst layer containing iridium oxide and tantalum oxide as a catalyst was formed by repeating application of the solution and heat treatment a plurality of times. The amount of catalyst supported was 12 g / m 2 per electrode area in terms of the amount of Ir metal.
用意したカーボン系構造体、複合体及びアノード触媒層を、この順に積層した。カーボン系構造体は、有機ハイドライド製造装置における鉛直方向に流路が延びるように配置して、複合体の拡散層側の面に固定した。また、サーペンタイン流路には、ヘッダーを介してカソード液の供給及び排出用の経路を接続した。また、アノード触媒層は、複合体の電解質膜側の面に固定した。さらに、アノード側に配置するスペーサ及びセパレータを用意した。そして、スペーサを介してセパレータを複合体の電解質膜側に固定した。アノード触媒層とセパレータとの間には、アノード室を構成する空隙を設けた。以上の工程により、実施例1の電解セルを得た。電解セルの電極面積は、16cm2とした。
The prepared carbon-based structure, composite, and anode catalyst layer were laminated in this order. The carbon-based structure was disposed so that the flow path extends in the vertical direction in the organic hydride manufacturing apparatus, and was fixed to the surface on the diffusion layer side of the composite. Further, a catholyte supply and discharge path was connected to the serpentine channel via a header. The anode catalyst layer was fixed to the surface of the composite on the electrolyte membrane side. Furthermore, a spacer and a separator arranged on the anode side were prepared. And the separator was fixed to the electrolyte membrane side of the composite via a spacer. A gap constituting an anode chamber was provided between the anode catalyst layer and the separator. The electrolytic cell of Example 1 was obtained by the above process. The electrode area of the electrolysis cell was 16 cm 2 .
(実施例2)
電極面積を100cm2としたことを除いて、実施例1と同様にして電解セルを得た。 (Example 2)
An electrolytic cell was obtained in the same manner as in Example 1 except that the electrode area was 100 cm 2 .
電極面積を100cm2としたことを除いて、実施例1と同様にして電解セルを得た。 (Example 2)
An electrolytic cell was obtained in the same manner as in Example 1 except that the electrode area was 100 cm 2 .
(比較例1)
カーボンペーパーにPtを担持させなかったことを除いて、実施例1と同様にして電解セルを得た。 (Comparative Example 1)
An electrolytic cell was obtained in the same manner as in Example 1 except that Pt was not supported on carbon paper.
カーボンペーパーにPtを担持させなかったことを除いて、実施例1と同様にして電解セルを得た。 (Comparative Example 1)
An electrolytic cell was obtained in the same manner as in Example 1 except that Pt was not supported on carbon paper.
(比較例2)
電極面積を100cm2としたことを除いて、比較例1と同様にして電解セルを得た。 (Comparative Example 2)
An electrolytic cell was obtained in the same manner as in Comparative Example 1 except that the electrode area was 100 cm 2 .
電極面積を100cm2としたことを除いて、比較例1と同様にして電解セルを得た。 (Comparative Example 2)
An electrolytic cell was obtained in the same manner as in Comparative Example 1 except that the electrode area was 100 cm 2 .
(性能評価)
各実施例及び各比較例の電解セルのカソード室に、トルエン濃度10%のカソード液(すなわち、カソード液の総量に対してトルエンが10mol%、メチルシクロヘキサンが90mol%であるカソード液)を流通させた。カソード液は、ライザーを用いて鉛直方向下側から上側に流通させた。また、アノード液としての5%硫酸水溶液を、ライザーを用いてアノード室に流通させた。カソード液の循環流量は、5mL/分とした。アノード液の循環流量は、10mL/分とした。 (Performance evaluation)
A catholyte having a toluene concentration of 10% (that is, a catholyte having 10 mol% of toluene and 90 mol% of methylcyclohexane with respect to the total amount of the catholyte) is allowed to flow through the cathode chamber of the electrolysis cell of each example and each comparative example. It was. The catholyte was circulated from the lower side in the vertical direction to the upper side using a riser. A 5% aqueous sulfuric acid solution as an anolyte was circulated through the anode chamber using a riser. The circulation flow rate of the catholyte was 5 mL / min. The circulation flow rate of the anolyte was 10 mL / min.
各実施例及び各比較例の電解セルのカソード室に、トルエン濃度10%のカソード液(すなわち、カソード液の総量に対してトルエンが10mol%、メチルシクロヘキサンが90mol%であるカソード液)を流通させた。カソード液は、ライザーを用いて鉛直方向下側から上側に流通させた。また、アノード液としての5%硫酸水溶液を、ライザーを用いてアノード室に流通させた。カソード液の循環流量は、5mL/分とした。アノード液の循環流量は、10mL/分とした。 (Performance evaluation)
A catholyte having a toluene concentration of 10% (that is, a catholyte having 10 mol% of toluene and 90 mol% of methylcyclohexane with respect to the total amount of the catholyte) is allowed to flow through the cathode chamber of the electrolysis cell of each example and each comparative example. It was. The catholyte was circulated from the lower side in the vertical direction to the upper side using a riser. A 5% aqueous sulfuric acid solution as an anolyte was circulated through the anode chamber using a riser. The circulation flow rate of the catholyte was 5 mL / min. The circulation flow rate of the anolyte was 10 mL / min.
また、定電圧電源の負極をカソードに、正極をアノードにそれぞれ接続した。そして、定電圧電源の出力電圧を、0.2V間隔で且つ1.3~5.0Vの電圧範囲で変化させて、各実施例及び各比較例の電解セルに印加した。
Also, the negative electrode of the constant voltage power source was connected to the cathode, and the positive electrode was connected to the anode. Then, the output voltage of the constant voltage power source was changed at a voltage range of 1.3 to 5.0 V at intervals of 0.2 V and applied to the electrolysis cells of the examples and the comparative examples.
そして、実施例1及び比較例1の電解セルについて、電解セルの電流密度と、各電極の電位と、電流効率とを計測した。図4(A)は、実施例1及び比較例1の電解セルにおける電流密度と電極電位との関係を示すグラフである。図4(B)は、実施例1及び比較例1の電解セルにおける電流密度と電流効率との関係を示すグラフである。図4(A)において、上段はアノード電位であり、下段はカソード電位である。また、図4(A)及び図4(B)において、実施例1の結果は四角形のプロットで示し、比較例1の結果は三角形のプロットで示す。
And about the electrolytic cell of Example 1 and Comparative Example 1, the current density of the electrolytic cell, the potential of each electrode, and the current efficiency were measured. 4A is a graph showing the relationship between the current density and the electrode potential in the electrolytic cells of Example 1 and Comparative Example 1. FIG. FIG. 4B is a graph showing the relationship between current density and current efficiency in the electrolytic cells of Example 1 and Comparative Example 1. In FIG. 4A, the upper stage is the anode potential, and the lower stage is the cathode potential. 4A and 4B, the results of Example 1 are shown as square plots, and the results of Comparative Example 1 are shown as triangular plots.
図4(A)に示すように、比較例1の電解セルではカソード電位の急激な降下が見られたのに対し、実施例1の電解セルではこのような電位降下は見られなかった。実施例1の電解セルでは、カソード側で発生する水素ガスがPt触媒上でトルエンと化学反応したことで水素ガスによるトルエンの移動阻害が抑制され、これにより、トルエンの移動阻害にともなう過電圧の上昇が生じず、結果として電位降下が起こらなかったと考えられる。したがって、実施例1では、電解槽全体で電流密度を増大できることが確認された。
As shown in FIG. 4 (A), a sharp drop in cathode potential was observed in the electrolysis cell of Comparative Example 1, whereas no such potential drop was observed in the electrolysis cell of Example 1. In the electrolysis cell of Example 1, the hydrogen gas generated on the cathode side chemically reacted with toluene on the Pt catalyst, so that the inhibition of the movement of toluene by the hydrogen gas was suppressed, thereby increasing the overvoltage accompanying the inhibition of the movement of toluene. It is considered that no potential drop occurred as a result. Therefore, in Example 1, it was confirmed that the current density can be increased in the entire electrolytic cell.
また、図4(B)に示すように、実施例1の電解セルは、比較例1の電解セルに比べて電流効率が上昇している。実施例1の電解セルでは、カソード側で発生する水素ガスがPt触媒上でトルエンと化学反応したことでメチルシクロヘキサンが生成され、その結果として見かけ上の電流効率が上昇したと考えられる。
Further, as shown in FIG. 4B, the electrolysis cell of Example 1 has a higher current efficiency than the electrolysis cell of Comparative Example 1. In the electrolysis cell of Example 1, it is considered that methylcyclohexane was generated by the hydrogen gas generated on the cathode side chemically reacting with toluene on the Pt catalyst, and as a result, the apparent current efficiency was increased.
また、実施例2及び比較例2の電解セルについて、電解セルの電流密度(i)と、セル電圧(U)と、電流効率(ε)とを計測した。図5(A)は、実施例2及び比較例2の電解セルにおける電流密度とセル電圧との関係を示すグラフである。図5(B)は、実施例2及び比較例2の電解セルにおける電流密度と電流効率との関係を示すグラフである。各グラフにおいて、実施例2の結果は破線で示し、比較例2の結果は一点鎖線で示す。
Further, for the electrolytic cells of Example 2 and Comparative Example 2, the current density (i), cell voltage (U), and current efficiency (ε) of the electrolytic cell were measured. FIG. 5A is a graph showing the relationship between the current density and the cell voltage in the electrolytic cells of Example 2 and Comparative Example 2. FIG. 5B is a graph showing the relationship between current density and current efficiency in the electrolytic cells of Example 2 and Comparative Example 2. In each graph, the result of Example 2 is indicated by a broken line, and the result of Comparative Example 2 is indicated by a one-dot chain line.
図5(A)に示すように、実施例2の電解セルは、比較例2の電解セルに比べてセル電圧が低下している。すなわち、実施例2の電解セルでは、過電圧の減少による電解特性の向上が見られた。実施例2の電解セルでは、カソード側で発生する水素ガスがPt触媒上でトルエンと化学反応してメチルシクロヘキサンが生成されたためと考えられる。
As shown in FIG. 5A, the cell voltage of the electrolytic cell of Example 2 is lower than that of the electrolytic cell of Comparative Example 2. That is, in the electrolysis cell of Example 2, the electrolysis characteristics were improved by reducing the overvoltage. In the electrolytic cell of Example 2, it is considered that hydrogen gas generated on the cathode side chemically reacted with toluene on the Pt catalyst to generate methylcyclohexane.
また、図5(B)に示すように、実施例2の電解セルは、比較例2の電解セルに比べて電流効率が上昇している。実施例2の電解セルでは、カソード側で発生する水素ガスがPt触媒上でトルエンと化学反応してメチルシクロヘキサンが生成されたためと考えられる。また、実施例2では、水素発生が開始される電流が約0.05Acm-2から約0.1Acm-2へと改善された。
Further, as shown in FIG. 5B, the current efficiency of the electrolytic cell of Example 2 is higher than that of the electrolytic cell of Comparative Example 2. In the electrolytic cell of Example 2, it is considered that hydrogen gas generated on the cathode side chemically reacted with toluene on the Pt catalyst to generate methylcyclohexane. In Example 2, the current at which hydrogen generation was started was improved from about 0.05 Acm −2 to about 0.1 Acm −2 .
ベンゼン、アルキルベンゼン、ナフタレン、アルキルナフタレン、アントラセン、ジフェニルエタン、トルエン、キシレン、メシチレン、エチルベンゼン、ジエチルベンゼン、ピリジン、ピリミジン、ピラジン、キノリン、イソキノリン、N-アルキルピロール、N-アルキルインドール、N-アルキルジベンゾピロールについても、実施例2と同様の電解還元試験を行い、電流効率を見積もった。この結果、いずれの化合物についても上述のトルエンと同様に、水素発生が開始される電流や電流効率が改善されることが確認された。したがって、少なくとも1つの芳香環を含む化合物、芳香環の1~4の水素原子が炭素数1~6の直鎖アルキル基又は分岐アルキル基で置換された化合物、含窒素複素環式芳香族化合物に対して、本手法が有効であることが分かった。
About benzene, alkylbenzene, naphthalene, alkylnaphthalene, anthracene, diphenylethane, toluene, xylene, mesitylene, ethylbenzene, diethylbenzene, pyridine, pyrimidine, pyrazine, quinoline, isoquinoline, N-alkylindole, N-alkylindole, N-alkyldibenzopyrrole In addition, the same electrolytic reduction test as in Example 2 was performed to estimate the current efficiency. As a result, it was confirmed that the current at which hydrogen generation was started and the current efficiency were improved for all the compounds as in the case of toluene described above. Accordingly, a compound containing at least one aromatic ring, a compound in which 1 to 4 hydrogen atoms of the aromatic ring are substituted with a linear alkyl group having 1 to 6 carbon atoms or a branched alkyl group, and a nitrogen-containing heterocyclic aromatic compound On the other hand, it was found that this method is effective.
10 有機ハイドライド製造装置、 100 電解セル、 110 電解質膜、 120 カソード、 122 カソード触媒層、 124 カソード室、 128 マイクロポーラス層、 130 拡散層、 132 流路部、 136 カソード室出口、 138 第2触媒、 150 アノード、 152 アノード触媒層、 154 アノード室。
10 Organic hydride production equipment, 100 electrolysis cell, 110 electrolyte membrane, 120 cathode, 122 cathode catalyst layer, 124 cathode chamber, 128 microporous layer, 130 diffusion layer, 132 flow channel, 136 cathode chamber outlet, 138 second catalyst, 150 anode, 152 anode catalyst layer, 154 anode chamber.
本発明は、カソード、有機ハイドライド製造用電解セル及び有機ハイドライドの製造方法に利用することができる。
The present invention can be used for a cathode, an electrolytic cell for producing organic hydride, and a method for producing organic hydride.
Claims (6)
- 有機ハイドライド製造用電解セルのカソードであって、
前記カソードは、
プロトンで被水素化物を水素化して有機ハイドライドを生成するための第1触媒を含むカソード触媒層と、
前記カソード触媒層を収容するカソード室と、
前記カソード室における前記カソード触媒層を除く領域に配置され、カソードにおける副反応の生成物である水素ガスと、未反応の前記被水素化物との化学反応を促進させる第2触媒と、
を備えることを特徴とするカソード。 A cathode of an electrolytic cell for producing organic hydride,
The cathode is
A cathode catalyst layer comprising a first catalyst for hydrogenating a hydride with protons to produce an organic hydride;
A cathode chamber containing the cathode catalyst layer;
A second catalyst disposed in a region excluding the cathode catalyst layer in the cathode chamber and accelerating a chemical reaction between hydrogen gas, which is a product of a side reaction at the cathode, and the unreacted hydride;
A cathode comprising: - 前記カソード触媒層に隣接して配置されるマイクロポーラス層、前記マイクロポーラス層に隣接して配置される拡散層、及び拡散層に隣接して配置される前記被水素化物の流路部、及び前記有機ハイドライドを前記カソード室の外部に排出するカソード室出口をさらに備え、
前記第2触媒は、前記マイクロポーラス層、前記拡散層、前記流路部及び前記カソード室出口の少なくとも1つに配置される請求項1に記載のカソード。 A microporous layer disposed adjacent to the cathode catalyst layer, a diffusion layer disposed adjacent to the microporous layer, a channel portion of the hydride disposed adjacent to the diffusion layer, and the A cathode chamber outlet for discharging organic hydride to the outside of the cathode chamber;
2. The cathode according to claim 1, wherein the second catalyst is disposed in at least one of the microporous layer, the diffusion layer, the flow path portion, and the cathode chamber outlet. - 前記第2触媒は、前記マイクロポーラス層及び前記拡散層の少なくとも一方に配置される請求項2に記載のカソード。 The cathode according to claim 2, wherein the second catalyst is disposed in at least one of the microporous layer and the diffusion layer.
- 前記第2触媒は、Pt、Ni、Re、Pd及びこれらの金属の少なくとも一種を含む合金からなる群から選択される請求項1乃至3のいずれか1項に記載のカソード。 The cathode according to any one of claims 1 to 3, wherein the second catalyst is selected from the group consisting of Pt, Ni, Re, Pd, and an alloy containing at least one of these metals.
- プロトン伝導性を有する電解質膜と、
前記電解質膜の一方の側に設けられる請求項1乃至4のいずれか1項に記載のカソードと、
前記電解質膜の前記一方の側とは反対側に設けられ、水を酸化してプロトンを生成するためのアノード触媒層、及び前記アノード触媒層を収容するアノード室を有するアノードと、
を備えることを特徴とする有機ハイドライド製造用電解セル。 An electrolyte membrane having proton conductivity;
The cathode according to any one of claims 1 to 4, provided on one side of the electrolyte membrane;
An anode catalyst layer provided on the opposite side of the electrolyte membrane to oxidize water to generate protons, and an anode having an anode chamber containing the anode catalyst layer;
An electrolytic cell for producing an organic hydride, comprising: - 有機ハイドライド製造用電解セルが備えるアノードに水を供給し、当該水を電気分解してプロトンを生成する工程と、
前記有機ハイドライド製造用電解セルが備えるカソードに被水素化物を供給し、前記有機ハイドライド製造用電解セルが備える電解質膜を通過した前記プロトンで前記被水素化物を水素化して有機ハイドライドを生成する工程と、
前記カソードにおける副反応の生成物である水素ガスと、未反応の前記被水素化物とを化学反応させて有機ハイドライドを生成する工程と、
を含むことを特徴とする有機ハイドライドの製造方法。 Supplying water to an anode included in an electrolytic cell for producing organic hydride, and electrolyzing the water to generate protons;
Supplying a hydride to a cathode included in the electrolytic cell for producing the organic hydride, and hydrogenating the hydride with the proton passing through an electrolyte membrane provided in the electrolytic cell for producing the organic hydride to generate an organic hydride; ,
A step of chemically reacting hydrogen gas, which is a product of a side reaction at the cathode, and the unreacted hydride to generate an organic hydride;
The manufacturing method of the organic hydride characterized by including this.
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