JP2018031046A - Cathode, electrolysis cell for organic hydride production, and method for producing organic hydrides - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve production efficiency of organic hydrides.SOLUTION: A cathode 120 of an electrolysis cell 100 for organic hydride production comprises: a cathode catalyst layer 122 containing a first catalyst for organic hydride production by hydrogenation of a material to be hydrogenated with a proton; a cathode chamber 124 which houses the cathode catalyst layer 122; and a second catalyst, which is arranged in a region except the cathode catalyst layer 122 in the cathode chamber 124 and which facilitates a chemical reaction of hydrogen gas, which is a product of a side reaction at a cathode 120, and an unreacted material to be hydrogenated.SELECTED DRAWING: Figure 2

Description

  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.

  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.

  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.

  Under such circumstances, organic hydride (organic chemical hydride) has attracted attention as an energy carrier that can 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.

  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.

  On the other hand, according to the electrolytic synthesis method, hydrogen can be directly added to the hydride, so that the manufacturing process of the organic hydride 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. .

International Publication No. 12/091128 Pamphlet

  As a result of intensive studies on the above-described technology for producing the organic hydride, the present inventors have come to recognize that there is room for improving the production efficiency of the organic hydride in the conventional technology.

  This invention is made | formed in view of such a condition, The objective is to provide the technique which improves the manufacturing efficiency of an organic hydride.

  One 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.

  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.

  Yet 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.

  According to the present invention, the production efficiency of organic hydride can be improved.

It is a schematic diagram of an organic hydride manufacturing apparatus provided with the electrolytic cell for organic hydride manufacture which concerns on embodiment. It is sectional drawing which shows schematic structure of the electrolytic cell for organic hydride manufacture which concerns on embodiment. It is a schematic diagram which expands and shows a part of cathode catalyst layer and a microporous layer. 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. 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.

  The present invention will be described below 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.

  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.

  Hereinafter, an electrolytic cell according to an embodiment and a method for producing an 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. The main structure includes an electrolytic cell 100 for manufacturing an organic hydride, a power control unit 20, and the like. 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 positive and negative potential detection. 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.

  The control unit 60 controls the outputs 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. 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 represented by a toluene-methylcyclohexane system is preferable.

  The 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, diphenylethane and the like. 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 a compound in which 1 to 4 hydrogen atoms of an aromatic ring are substituted with a linear alkyl group having 1 to 6 carbon atoms or a branched alkyl group, 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 the dehydrogenated product.

  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.

  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.

  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.

  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.

  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.

[Electrolyte membrane]
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). Although the thickness of the electrolyte membrane 110 is not specifically limited, Preferably it is 5-300 micrometers, More preferably, it is 10-150 micrometers, More preferably, it is 20-100 micrometers. 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.

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 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.

  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.

[Cathode]
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. 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.

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.

  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), a porous metal, and a 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. 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 diameter of carbon fine particles such as carbon black used as the catalyst carrier 122b is preferably 0.01 μm to 1 μm.

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.

  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 support 122b is porous carbon, the ionomer (I) / catalyst support (C) mass ratio I / C is preferably 0.1 to 2, more preferably 0.2 to 1.5. Yes, more preferably 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.

  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.

  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.

  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 amount of ionomer added 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 a powder form, 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.

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.

  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.

  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 μm, a porosity of 30 to 95%, and a typical pore size of 1 to 1000 μm. The electronic conductivity of the material constituting the diffusion layer 130 is preferably 10 ⁻² S / cm or more.

  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.

  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, the mass ratio (Vulcan: PTFE) when Vulcan (registered trademark) is used as the conductive powder and PTFE is used as the water repellent 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.

  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. In addition, 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. Further, 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.

  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.

  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. As pressing conditions, temperature: room temperature to 360 ° C. and pressure: 0.1 to 5 MPa are preferable.

  The flow path part 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 above the cathode chamber 124 in the vertical direction. 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. 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.

  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.

[anode]
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. 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. 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), a sintered body of a metal porous body, a foamed molded body (foam), an expanded metal, and the like. As a base material used for the anode catalyst layer 152, a thickness of 0.1 to 0.1 is necessary because of the necessity of having sufficient electric conductivity for flowing a 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%. .

  The anode chamber 154 is defined by the electrolyte membrane 110, the separator 170b, and a frame-like 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 vertically above the anode chamber 154. 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. 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.

In the electrolytic 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

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.

However, the following side reactions can occur at the cathode 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 the cathode 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.

On the other hand, as shown in FIG. 3, the cathode 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

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.

  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.

  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 likely to be 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. 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.

  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.

  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.

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. Moreover, the loading amount of the second catalyst 138 is preferably 0.01 to 0.5 mg / cm ² .

  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.

[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 anode 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.

  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.

  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.

  Moreover, the reduction in current efficiency due to side reactions becomes more prominent 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.

  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.

  Examples of the present invention will be described below. However, these examples are merely examples for suitably explaining the present invention, and do not limit the present invention.

Example 1
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. _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).

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.

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.

  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.

  Subsequently, a carbon-based structure in which carbon / epoxy resin was molded 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.

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.

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 .

(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 1)
An electrolytic cell was obtained in the same manner as in Example 1 except that Pt was not supported on carbon paper.

(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 .

(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.

  Further, the negative electrode of the constant voltage power source was connected to the cathode, and the positive electrode was connected to the anode. And the output voltage of the constant voltage power supply was changed in the voltage range of 1.3-5.0V by 0.2V space | interval, and it applied to the electrolysis cell of each Example and each comparative example.

  And about the electrolytic cell of Example 1 and the comparative example 1, the current density of the electrolytic cell, the electric 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.

  As shown in FIG. 4A, 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.

  Further, as shown in FIG. 4B, the current efficiency of the electrolytic cell of Example 1 is higher than that of the electrolytic 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.

  Moreover, about the electrolytic cell of Example 2 and Comparative Example 2, the current density (i) of the electrolytic cell, the cell voltage (U), and the current efficiency (ε) 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.

  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.

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 .

  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. Therefore, 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.

  DESCRIPTION OF SYMBOLS 10 Organic hydride manufacturing apparatus, 100 electrolytic cell, 110 electrolyte membrane, 120 cathode, 122 cathode catalyst layer, 124 cathode chamber, 128 microporous layer, 130 diffusion layer, 132 flow path part, 136 cathode chamber outlet, 138 2nd catalyst, 150 anode, 152 anode catalyst layer, 154 anode chamber.

Claims (6)

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: 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.   The cathode according to claim 2, wherein the second catalyst is disposed in at least one of the microporous layer and the diffusion layer.   4. The cathode according to claim 1, 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. 5. 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: 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.