JP5823587B2 - Electrolytic device, refrigerator, operating method of electrolytic device, and operating method of refrigerator - Google Patents

Description

  The present invention relates to an electrolyzer, an electrolyzer, a refrigerator, an electrolyzer operation method, and a refrigerator operation method.

  2. Description of the Related Art Conventionally, development of devices using an oxygen reduction reaction by electrolysis for a dehumidifying device, an oxygen concentrating device, a deoxygenating device, a salt electrolysis device, a gas sensor, a humidity sensor, and the like has been advanced. A catalyst of platinum, lead, oxide, iridium composite oxide or ruthenium composite oxide is used for the anode of the electrolysis cell that performs this electrolysis, and a platinum-based catalyst is used for the cathode.

  However, in the oxygen reduction reaction, when the voltage applied to the cathode exceeds the theoretical hydrogen generation potential, hydrogen is generated on the cathode side. For example, when the deoxygenation device is used in a refrigerator, the hydrogenation reaction proceeds and the power efficiency is deteriorated. This is because Pt has a very high catalytic ability, so that a hydrogenation reaction easily occurs and is parallel to the oxygen reduction reaction. Further, when the electrolysis voltage is lowered, a large current cannot be taken out, so that there is a problem that deoxidation efficiency is not good.

JP-A-1-148327

  An object of the present invention is to provide an electrolytic device and a refrigerator in which hydrogenation reaction is suppressed and efficiency is high.

An electrolysis device according to an embodiment includes an electrolysis cell having a membrane electrode assembly including an anode, a cathode having a carbon alloy catalyst into which nitrogen is introduced, an electrolyte disposed between the anode and the cathode, and an anode side. An electrolysis apparatus comprising a container for sealing the space of the cathode or the cathode side, a power source for applying a voltage to the anode and the cathode, and a control unit for controlling the power source , wherein the carbon alloy catalyst is a pyridine type nitrogen substitution, pyrrole -It has at least one of pyridone type nitrogen substitution and N oxide type nitrogen substitution , and the electrolyte is either acidic, neutral or alkaline, and when the electrolyte is acidic, the hydrogen generation potential is -0.2 to -0.7 V vs. In the RHE , the control unit controls the power supply so that the cathode potential is higher than the hydrogen generation potential in the operation of the electrolysis apparatus, or when the electrolyte is neutral or alkaline, the hydrogen generation potential is -0.2 to -0.9V vs. In the RHE , the control unit controls the power supply so that the potential of the cathode is higher than the generation potential of hydrogen in the operation of the electrolysis apparatus .

2 is a structural formula showing an example of nitrogen-substituted carbon of the embodiment. It is a conceptual diagram of the cathode of embodiment. It is a conceptual diagram of the electrolyzer of embodiment. It is a conceptual diagram of the soda electrolysis apparatus provided with the gas diffusion electrode of embodiment. It is a conceptual diagram of the apparatus provided with the electrolyzer of embodiment. It is a conceptual diagram of the apparatus provided with the electrolyzer of embodiment. It is a conceptual diagram of the deoxygenation apparatus of embodiment. It is a conceptual diagram of the refrigerator of embodiment. It is a conceptual diagram of the 3 pole type rotation ring disk electrode cell of embodiment. 6 is a graph showing the XPS measurement results of Example 1. 6 is a graph showing the XPS measurement results of Example 1.

  An electrolysis apparatus according to an embodiment includes an electrolytic cell having an anode, a cathode having a carbon alloy catalyst into which nitrogen is introduced, and a membrane electrode assembly including the anode and an electrolyte disposed between the cathodes. At least, a voltage is applied to the anode and the cathode.

  The electrolyzer cell performs electrolysis of water on the anode side with a power source to which a voltage is applied to the anode and the cathode, and performs oxygen reduction reaction on the cathode side using the generated protons. Generally, Pt is used for the oxygen reduction catalyst for electrolysis, but the cathode of the electrolysis cell of the embodiment does not include Pt having a high oxygen reduction starting potential. When Pt is contained in the cathode, the oxygen reduction starting potential is high, and thus an oxygen reduction reaction is likely to occur. Specifically, the oxygen reduction standard electrode potential of 1.23 V vs. standard hydrogen electrode potential (NHE) standard. 0.95 to 1.0 V vs. NHE. It becomes about NHE. However, since the cathode containing Pt, which is also an excellent hydrogen generation catalyst, has a high hydrogen generation potential, the difference between the oxygen reduction start potential and the hydrogen generation potential is small, so that a hydrogenation reaction at the cathode is likely to occur. Specifically, the hydrogen generation standard potential in acidity is 0 V vs. NHE, the cathode is 0 V vs. As soon as NHE is reached, hydrogen is generated. Considering the application of the electrolysis cell of the embodiment that is not for fuel cells, high hydrogen generation capacity is not an advantage.

  In the case of a dehumidifier, deoxygenator, etc., a voltage is applied from the outside. Therefore, if the power consumption is increased to some extent, a catalyst that generates less hydrogen under electrolysis conditions than the oxygen reduction performance comparable to Pt is better. Have advantages. In particular, when the potential of each electrode of the anode and cathode is not monitored, the overvoltage ratio of each electrode is determined by the catalyst performance at the anode and the cathode and the diffusion rate of the substance, so it is not easy to know the applied voltage. It cannot be judged whether hydrogen is generated only by (applied voltage). In that case, a catalyst that is less likely to generate hydrogen can set a higher limit applied voltage, and thus the oxygen reduction reaction proceeds efficiently.

  The oxygen reduction initiation potential of nitrogen-free carbon (for example, KetjenBlack (registered trademark) or Vulcan (registered trademark) XC72R) is 0.7 to 0.6 V vs. reversible hydrogen electrode potential (RHE). Since it is about RHE, oxygen reduction ability is not high. The hydrogen generation potential is about −0.1 to −0.2 Vvs. RHE and hydrogen generation ability is not low. Therefore, the operating potential window ([oxygen reduction start potential] − [hydrogen generation potential]) is about 0.8 to 0.9 V, and neither the oxygen reduction ability nor the hydrogen generation ability is suitable as the cathode catalyst of the embodiment.

  The catalyst used for the cathode of the electrolytic cell of the embodiment is one that performs an oxygen reduction reaction at a relatively fast reaction rate and has a high hydrogen generation suppression effect.

  The carbon alloy catalyst according to the embodiment is a compound mainly composed of an aggregate of carbon atoms, and a part of the carbon atoms is substituted with a nitrogen atom. The catalyst as a whole has conductivity and high specific surface area, so amorphous and sp3 carbon are included. However, nitrogen is pyridine type (A), pyrrole / pyridone type in the skeleton of sp2 carbon as shown in the structural formula of FIG. (B), N oxide type (C), and the three-coordinate type (D) include those in which a carbon atom is substituted with a nitrogen atom in at least one form. 1A to 1D show examples of forms of nitrogen substitution, and the structural formula of FIG. 1 does not show the carbon alloy catalyst of the embodiment itself.

  The nitrogen substitution amount of the carbon alloy catalyst of the embodiment is 0.1 atom% or more and 30 atom% or less with respect to the surface element amount of the carbon alloy catalyst. If the amount of nitrogen substitution is less than this lower limit, the effect of nitrogen substitution is not sufficient, which is not preferable. Moreover, when there is more nitrogen substitution amount than this upper limit, it is unpreferable that a structure will be disturb | confused and electroconductivity will fall. The nitrogen substitution amount is more preferably 0.1 atm% or more and 10 atom% or less from the viewpoint of conductivity. Use of a carbon alloy catalyst as the cathode catalyst is preferred because the hydrogen generation potential decreases depending on the amount of nitrogen substitution, and the operating potential window exceeds 1V. Specifically, as a carbon alloy catalyst, an oxygen reduction starting potential of 0.84 V vs. RHE, hydrogen oxidation voltage −0.46V, and potential window of about 1.3V are observed, and the potential window is wider than Pt.

  In addition, the definition of the carbon alloy catalyst in the text represents a carbon in which a part of carbon in which sp 2 hybridized orbits are substituted with nitrogen.

  In the carbon alloy catalyst of the embodiment, the active point of the catalyst increases in proportion to the amount of carbon into which nitrogen is introduced. In addition, the carbon catalyst of the embodiment preferably has a large specific surface area because the active site contributing to the oxygen reduction current increases as the surface area increases.

Moreover, when the specific surface area of a carbon alloy catalyst becomes large too much, the ratio of the micropore of a 10 nm diameter or less will increase on the surface of a carbon alloy catalyst. This micropore is not preferable because the diffusion rate of oxygen gas necessary for the oxygen reduction reaction becomes extremely slow. Therefore, it is preferable that the ratio of the fine pores is small, and most of the pores (60% or more) of the carbon alloy catalyst have a diameter of 20 nm or more. From the above, it is preferable that the specific surface area of the carbon alloy catalyst is 100 m ² / g or more and 1200 m ² / g or less.

The amount of nitrogen atom substitution is the ratio (C / N ratio) of nitrogen (N) substitution to carbon (C) that can be measured by X-ray photoelectron spectroscopy (XPS). The C / N ratio can be calculated from the signal in the vicinity of 290 eV of the carbon atom C1s and the signal intensity ratio in the vicinity of 400 eV of the nitrogen atom N1s. For the calculation of the C / N ratio, a compound having a clear composition ratio such as C ₃ N ₄ can be used as a standard substance and can be calculated based on this.

The measurement sample can be prepared by scraping from the cathode of the electrolytic cell.
However, in XPS measurement, non-substituted nitrogen such as amine is detected in addition to nitrogen substituted with sp2 carbon. Therefore, in order to exclude the influence of these non-substituted nitrogen, the produced sample was baked at 800 ° C. for 1 hour in an argon atmosphere, the non-substituted nitrogen was decomposed, and then the XPS measurement was performed. Is lost.
Here, it is also possible to further separate the substitution forms. Separating the signal near 400 eV of nitrogen atom N1s into 398.5 eV-pyridine type, 400.5 eV-pyrrole / pyridone type, 401.2 eV-3 coordination type, 402.9 eV-N oxide type The substitution form and amount of nitrogen can be clarified.
In order to specify the amount of nitrogen substitution, it is effective to divide a batch of prepared sample into four equal parts by mass and measure the surface condition with XPS in consideration of unevenness in heating and mixing of the sample. Yes, this is effective for quality inspection.

[Method for producing carbon alloy catalyst]
Although the manufacturing method of the carbon alloy catalyst of embodiment is illustrated below, it is not limited to these. The carbon alloy catalyst can be produced by known production methods including those exemplified below.

  The carbon alloy catalyst of the embodiment is manufactured by heat treating and carbonizing a resin containing nitrogen and a compound containing metal under an inert gas atmosphere (nitrogen, argon, etc.), and treating the carbonized acid.

  A compound containing a resin and a metal is heat-treated in a nitrogen-existing atmosphere for carbonization, and the carbonized product is acid-treated to produce the carbon alloy catalyst of the embodiment. Instead of the compound containing a resin and a metal, a resin containing a metal may be used.

  Nitrogen plasma treatment is performed on carbon to produce the carbon alloy catalyst of the embodiment.

  The carbon alloy catalyst of the embodiment is manufactured by chemical vapor deposition from a material containing a carbon source and a nitrogen source.

  Examples of the nitrogen-containing resin include resins such as nitrogen-containing phenol resin, imide resin, melamine resin, benzoguanamine resin, epoxy acrylate, urea resin, bismaleimide aniline, and benzoxazine.

  Examples of the metal include iron and cobalt.

  Examples of the metal-containing compound include compounds such as iron phthalocyanine, cobalt phthalocyanine, iron sulfate, cobalt sulfate, iron chloride, cobalt chloride, cobalt sulfate, iron nitrate, potassium hexacyanoiron, cobalt nitrate, and cobalt acetate.

  Examples of the substance containing a carbon source include methane, ethane, acetylene, ethylene, ethanol, methanol and the like.

  Examples of the target containing a nitrogen source include ammonia, nitrogen trifluoride, hydrazine, and the like.

Moreover, when the surface area and conductivity of these carbon alloy catalysts are low, the catalyst can be supported on a carrier or mixed.
As a carrier, carbonized organic materials containing carbon such as KetjenBlack (registered trademark), Vulcan XC72R (registered trademark), VGCF (registered trademark), and carbon such as phenol, conductive properties such as RuO ₂ and IrO ₂ An oxide can be used.

  Examples of a method of mixing a resin containing nitrogen or a metal and a resin containing nitrogen and a compound containing a metal or a metal include wet and dry mixing using a ball mill or a stirrer.

  When nitrogen is introduced into carbon by carbonization, a material such as a resin is fired in a nitrogen-containing gas atmosphere. When it is not necessary to introduce nitrogen into carbon due to carbonization, a material such as a resin may be fired in an inert gas atmosphere. The carbonization temperature is, for example, 600 ° C. or more and 1200 ° C. or less for several minutes to several hours.

  Nitrogen can also be introduced into carbon by performing nitrogen plasma treatment on carbon. Carbon may be further introduced by performing a nitrogen plasma treatment on the carbon alloy catalyst.

In addition, after preparation by the above method, when a metal compound is contained, it is removed by treatment with an acid. Examples of the acid used for the acid treatment include hydrochloric acid, sulfuric acid, and nitric acid, although depending on the metal used.
In the acid treatment, an example of treatment is to immerse in a solution (0.1 to 10 M) diluted with pure water for 30 to 20 hours, then filter and wash with pure water, and repeat this three or more times.

[cathode]
The cathode of the embodiment is composed of, for example, an electrode support material 3 and a carbon alloy catalyst 1 fixed on the electrode support material 3 with an ion conductive binder 2 as shown in the conceptual diagram of FIG. The structure of the cathode is not particularly limited as long as the carbon alloy catalyst is fixed to the electrode support material.

The carbon alloy catalyst of the embodiment can be prepared by dispersing the slurry in a solvent, applying the prepared slurry to an electrode support material, and preparing a cathode electrode by a process such as drying or firing. You may perform both drying and baking. It is preferable to drop or apply the ion conductive binder before or after baking or drying. The ion conductive binder may be mixed in the slurry. The steps of coating, drying and baking may be performed a plurality of times.
In the case of an acidic electrolyte, a proton conductive binder such as Nafion (registered trademark) is preferably used, and in the case of a neutral / alkaline electrolyte, an alkali conductive binder is preferably used.

Examples of the electrode support material include porous materials similar to gas diffusion layers (for example, porous materials such as carbon paper) held in various electrolyte membranes, fuel cells, etc., titanium mesh, SUS mesh, nickel mesh, and the like. .
Examples of the solvent used for the preparation of the slurry include those used when preparing an electrode catalyst for a fuel cell. Specific examples include water, ethanol, isopropyl alcohol, butanol, toluene, xylene, methyl ethyl ketone, and acetone.
Examples of the ion conductive binder include a fluorine-based or hydrocarbon-based ionomer as a proton conductor, and an ionomer having an ammonium base as a hydroxide ion conductor. The ion conductive binder should be dissolved in a solvent such as ethanol. Is preferred.

[anode]
The anode of the embodiment can be produced by the same material and method as the cathode using an anode for the catalyst. Examples of the catalyst used for the anode include platinum, lead oxide, iridium composite oxide, and ruthenium composite oxide. Examples of methods for producing these catalysts include a thermal decomposition method, a sol-gel method, and a complex polymerization method.

  The oxide composite metal includes at least one of Ti, Nb, V, Cr, Mn, Co, Zn, Zr, Mo, Ta, W, Tl, Ru, and Ir. Examples of the electrode supporting element of these catalysts include valve metals such as Ta and Ti.

[Electrolytes]
As the electrolyte of the embodiment, a liquid electrolyte, a cation exchange membrane, an anion exchange membrane, or the like can be used. Examples of the liquid electrolyte include sulfuric acid, nitric acid, hydrochloric acid, aqueous sodium hydroxide, aqueous potassium hydroxide, aqueous potassium chloride, and the like. Examples of the cation exchange membrane include Nafion (registered trademark) 112, 115, 117, Flemion (registered trademark), Aciplex (registered trademark), and Gore Select (registered trademark). Examples of the anion exchange membrane include A201 manufactured by Tokuyama Corporation. A hydrocarbon membrane system can also be used as the electrolyte.

[Electrolytic reaction]
When an acidic electrolyte is used, the following reaction (reaction formula 1-2) occurs at the anode and cathode when a voltage is applied to the electrode.

Anode 2H ₂ O → O ₂ + 4H ⁺ + 4e ⁻ (Reaction Formula 1)
Cathode O ₂ + 4H ⁺ + 4e ⁻ → 2H ₂ O (Reaction Formula 2)

  Also, if the supply of oxygen becomes insufficient because the surface of the cathode is covered with water and the applied voltage exceeds a certain value (hydrogen generation potential), the following reaction (reaction formula 3) is performed in parallel at the cathode. Occur.

2H ⁺ + 2e ⁻ → H ₂ (Scheme 3)

  When a neutral or alkaline electrolyte is used as the electrolyte (electrolytic solution), the following reaction (reaction formula 4-5) occurs at the anode and cathode when a voltage is applied to the electrode.

Cathode O ₂ + 2H ₂ O + 4e ⁻ → 4OH ⁻ (Reaction Formula 4)
Anode 4OH ⁻ → O ₂ + 2H ₂ O + 4e ⁻ (Reaction Formula 5)

  In addition, when the supply of oxygen becomes insufficient because the surface of the cathode is covered with water and the applied voltage exceeds a certain value (hydrogen generation potential), the following reaction (reaction formula 6) is performed in parallel at the cathode. Occur.

2OH ⁻ → O ₂ + H ₂ + 2e ⁻ (Scheme 6)

[Membrane electrode assembly]
In the membrane electrode assembly 19 of the embodiment, a solid polymer electrolyte 13 is formed between an anode 12 and a cathode 14 as shown in a part of the conceptual diagram of the electrolytic cell of FIG. The membrane electrode assembly 19 can be brought into close contact with the solid polymer electrolyte 2 by double-side hot pressing or direct application.

[Electrolysis cell, electrolysis equipment]
As shown in the conceptual diagram of FIG. 3, the electrolytic device 10-1 of the embodiment includes the membrane electrode assembly 19, the water supply pipe 15, the water discharge pipe 16, the supply air introduction pipe 17 and the air discharge pipe 18 described above. A power source (DC power source) 11 for applying a voltage to both electrodes of the electrolytic cell and the membrane electrode assembly 19 is provided. The water supply pipe 15, the water discharge pipe 16, the supply air introduction pipe 17 and the air discharge pipe 18 are members for supplying the gas and water (aqueous solution) necessary for the above reaction. Any configuration can be used depending on the purpose and application. A voltage is applied to the electrolysis cell to advance the reaction.

The carbon alloy catalyst of the embodiment can be used as an oxygen reduction catalyst having an effect of suppressing hydrogen generation, and its use is not limited to a deoxidizing element, a humidifying element, and a dehumidifying element. For example, it can be used as a cathode for soda electrolysis.
Other examples of the electrolysis apparatus of the embodiment include a soda electrolysis apparatus 10-2 and an apparatus for generating chlorine as shown in the conceptual diagram of FIG. A slurry obtained by mixing a carbon alloy catalyst and a binder (PTFE) in ethanol is applied to a titanium mesh, and a gas diffusion electrode obtained by firing the slurry at 300 degrees in Ar is used as a cathode 14. At this time, the anode 12 uses a carbon electrode or the like, the electrolytic solution is a NaCl aqueous solution, and the cathode 14 and the anode 12 are separated by the ion exchange membrane 13. The cathode side of the apparatus of FIG. 4 is configured to supply oxygen or air through the gas supply pipe 17C, water through the water supply pipe 15C, discharge caustic soda through the liquid discharge pipe 16C, and discharge exhaust gas through the gas discharge pipe 18C. ing. The anode side of the apparatus of FIG. 4 is configured to supply a sodium chloride aqueous solution through a liquid supply pipe 15A and discharge chlorine gas through a gas discharge pipe 18A. When a voltage is applied between the electrodes with the external power source 11 using such an apparatus, chlorine gas is generated at the anode and sodium hydroxide is generated at the cathode. At this time, generation of hydrogen can be suppressed by applying nitrogen-substituted carbon when a high voltage is applied as compared with other catalysts. This is effective because the treatment of the generated hydrogen and the introduction of a safety device are unnecessary or reduced, and even when the extreme potential is not monitored, the current can be taken out efficiently.

[Electrolysis apparatus equipped with membrane electrode assembly]
By providing the container with the membrane electrode assembly to which the power source of the embodiment is connected, an oxygen reduction device, an oxygen concentration device, a humidification device, and a dehumidification device can be obtained.
As shown in the conceptual diagram of the apparatus 20-1 in FIG. 5, the membrane electrode assembly 19 is fixed so that the space of the container 22 is divided into the anode side and the cathode side of the membrane electrode assembly 19. A power supply 11 is connected to the membrane electrode assembly 19 so that a voltage can be applied to both electrodes of the membrane electrode assembly. The membrane electrode assembly is fixed with a sealant 21 so that the reaction system space on each electrode side can be separated. Moreover, the container 22 may be attached to either the anode side or the cathode side of the membrane electrode assembly as in the conceptual diagram of the device 20-2 of FIG. In the devices 20-1 and 20-2, the container 22 and the membrane electrode assembly 19 may be semi-fixed so as to be detachable.

  In the space on the anode side of the membrane electrode assembly using an acidic electrolyte, a reaction for decomposing water into oxygen and protons occurs, and thus functions as an oxygen concentration or dehumidification device. On the other hand, the space on the cathode side of the electrolytic cell using an acidic electrolyte functions as a device for reducing or humidifying because water is generated from oxygen and protons generated at the anode. When a neutral or alkaline electrolyte is used, water is consumed at the cathode and water is generated at the anode, and the reverse function is obtained when an acidic electrolyte is used. In the case of an apparatus intended for humidification or dehumidification, the container 22 may be used as a water supply container or a water storage container.

  FIG. 7 shows a conceptual diagram of an example of an oxygen reduction device 20-3 using a membrane electrode assembly. The electrolyte of the oxygen reduction device 20-3 is acidic. In the oxygen reduction device 20-3, a container 22 is fixed to the cathode side of the membrane electrode assembly 19 and a water tank 24 is fixed to the anode side by a sealant 21. The container 22 is provided with a door 23 through which an object to be placed under reduced oxygen can be taken in and out. On the water tank 24 side, a water supply pipe 25 and an oxygen discharge pipe 26 are provided.

  The container 22 may be provided with a member for supplying and discharging a gas, a liquid, or a substance such as a door through which an object can be taken in and out, an intake pipe, an exhaust pipe, a water supply pipe, a drain pipe, and the like. These doors and tubes can be of any shape and function depending on the purpose and application of the apparatus.

  In addition, a device equipped with a membrane electrode assembly is controlled by a control unit (not shown) to switch between intake / exhaust, water supply / drainage, sealed area, etc., and perform any operation of oxygen reduction, oxygen concentration, dehumidification and humidification. May be. An oxygen concentration meter or a hygrometer may be provided so that the effect of the operation of the apparatus can be easily confirmed. Moreover, you may control so that it may become arbitrary oxygen concentration or humidity. These controls may be controlled electronically using a programmable IC such as a microcomputer or FPGA (Field-Programmable Gate Array), or may be controlled manually.

[Refrigerator with oxygen reduction device]
FIG. 8 is a conceptual diagram of a refrigerator 30 provided with a device 20 ′ having a membrane electrode assembly. When performing oxygen reduction, apparatus 20 'which has a membrane electrode assembly has the aspect which uses the door 23 of the oxygen reduction apparatus 20-3 of FIG. 8, for example as the door of a refrigerator. In the case of performing oxygen reduction, in the refrigerator 30 of FIG. 8, one room of the refrigerator is an oxygen reduction device, but a configuration in which the oxygen reduction device is arranged in a part of the one room may be used, You may arrange in a position. When the oxygen-reducing operation is performed in the storage room for storing fresh food, the oxidation of the food can be suppressed. In the refrigerator 30, a humidifier or a dehumidifier provided with a membrane electrode assembly may be used instead of the device 20 ′ having a membrane electrode assembly.

  In addition to the oxygen reduction device 20 ′, a device that can be controlled to perform any one of the operations of oxygen reduction, dehumidification and humidification by switching the intake / exhaust, water supply / drainage, sealed area, etc. by a control unit (not shown). Also good. An oxygen concentration meter or a hygrometer may be provided so that the effect of the operation of the apparatus can be easily confirmed. Moreover, you may control so that it may become arbitrary oxygen concentration or humidity. These controls may be controlled electronically using a programmable IC such as a microcomputer or FPGA, or may be controlled manually.

[Electrode activity test for oxygen reduction and hydrogen generation]
As a method for evaluating the oxygen reduction characteristics and hydrogen generation characteristics of a single catalyst, electrode potential scanning can be mentioned as a simple method. Electrode activity related to oxygen reduction and hydrogen generation is measured by scanning the potential using a tripolar rotating ring disk electrode cell shown in the conceptual diagram of FIG. Specifically, a working electrode 41 in the center of FIG. 9, a reference electrode (Ag / AgCl) 42 on the left side of the drawing, and a counter electrode (carbon felt) 43 on the right side of the drawing are provided. The working electrode 41 has a disk electrode made of glass fiber at the center, and a catalyst formed by applying, baking and drying the catalyst ink on the outer periphery of the disk electrode. The catalyst is covered with a polymer insulator, and an Au ring electrode covers the periphery of the catalyst. Furthermore, the periphery of the ring electrode is covered with a polymer insulator. As the electrolytic solution 44, an acidic aqueous solution (0.5 MH ₂ SO ₄ aq.) Bubbling nitrogen or oxygen or an alkaline aqueous solution (0.1 M KOH aq.) Was used.
A potential scan is performed at 10 mV / s using a potentiostat in the apparatus of the form described in the schematic diagram of FIG. The rotation speed was fixed at 2000 rpm, and the potential range was 1.2 to -0.7 V vs.. RHE.

(1) Oxidation reduction starting potential In the electrode activity test, a difference is taken from the voltammogram obtained by performing potential scanning using an electrolyte purged with nitrogen and oxygen, and the potential at which a negative current begins to flow is defined as the oxygen reduction starting potential. .

(2) Hydrogen generation start potential An accurate hydrogen generation start potential cannot be estimated due to the fact that hydrogen is generated even in an electrolyte purged with nitrogen, and the hydrogen adsorption current flows. Therefore, a potential at which a current of −5 mA / cm ² or more flows below the standard electrode potential is defined as a hydrogen generation start potential.

(3) Hydrogen peroxide production rate In the case of an acidic electrolytic solution, the reaction of Reaction Formula 2 may stop halfway, and the reaction of Reaction Formula 7 may produce hydrogen peroxide instead of water. Therefore, a voltage is applied to the gold electrode 27 of the working electrode 21 to cause the reaction of reaction formula 8, and the hydrogen peroxide production rate is obtained from the reaction current at that time.
Similarly, in the case of a neutral / alkaline electrolyte, the reaction of Reaction Formula 5 may stop halfway, and the reaction of Reaction Formula 9 may generate hydrogen peroxide instead of water. Therefore, the reaction of reaction formula 10 is caused to similarly determine the hydrogen peroxide production rate.

O ₂ + 2H ⁺ + 2e ⁻ → H ₂ O ₂ (Scheme 7)
H ₂ O ₂ → O ₂ + 2H ⁺ + 2e ⁻ (Reaction Formula 8)
1.5O ₂ + H ₂ O + 2e ⁻ → 2HO ₂ ⁻ (Scheme 9)
^{_{2HO 2 - → 1.5O 2 + H}} 2 O + 2e - ( Scheme 10)
Specifically, 1.2 V vs. RHE is applied to the gold ring electrode, and the hydrogen peroxide production rate is obtained from the current value during potential scanning.
The derivation formula (formula 1) of the hydrogen peroxide production rate x is as follows.

... Formula 1
x: Hydrogen peroxide production rate (%)
I _R: ring current (A)
_ID : Disc current (A)
N: Supplementary rate (-)

The capture rate (N) is defined as the ratio of the absolute value of the ring current and the disk current, and this time, N = 0.4.
The collection efficiency N is calculated by the following formula (formula 2): N = | I _D | / | I _R |

Hereinafter, the electrolytic cell, the apparatus, and the refrigerator according to the embodiment will be specifically described by way of examples.
Note that the hydrogen generation detection in the MEA was calculated from the exhaust gas from the pump and the hydrogen concentration in the sealed container using a hydrogen gas detector.
The theoretical oxygen consumption (N _O2 ) was obtained from the following equation (Equation 3).

... Formula 3
N _O2 : Theoretical oxygen consumption (CCM)
I: Applied current (A)
n: number of reaction electrons F: Faraday constant T: temperature (K)

Example 1
8 g of benzguanamine resin containing nitrogen, 1 g of ferric chloride and 5 g of KetjenBlack® EC300J as a carrier are mixed with 150 ml of THF (tetrahydrofuran). After mixing, the mixture is refluxed at 80 ° C. for 2 hours while stirring at a stirrer of 300 rpm. The refluxed solution is dried by an evaporator using a 45 ° C. hot water bath, and the dried material is fired in an argon atmosphere at 800 ° C. for 1 hour. After calcination, the calcined product was washed with 2M hydrochloric acid to produce a carbon alloy catalyst. The prepared sample is packed in a stainless steel pan (diameter: 1 mm, depth: 30 μm), and XPS (Quantum-200 X-ray source / output / analysis region manufactured by PHI): Elemental analysis of catalyst surface by single crystal spectroscopy AlKα ray / 40 W / φ200 μm As a result of 4-point measurement, it was confirmed that the nitrogen substitution amount was 1.3 to 1.8%. FIG. 10 shows the N1s spectrum (1 sample among 4 measured samples) at this time. Since the spectrum of FIG. 10 includes at least a pyridine type (A), a pyrrole / pyridone type (B), an N oxide type (C), and a tricoordinate type (D), these peaks are shown in FIG. Shown separated. It can be seen that the intensity of the pyridine type (A) is the strongest when this peak is separated (FIG. 11).

  10 mg of the produced carbon alloy catalyst was added to 1 ml of a dispersion medium in which water and ethanol were adjusted to have a mass ratio of 1: 1. The dispersion medium to which the carbon alloy catalyst was added was dispersed by ultrasonic waves for 30 minutes to produce a catalyst ink. 1 μl was taken with a micropipettor, dropped onto glassy carbon (registered trademark) with a diameter of 3 mm, and dried in a thermostatic chamber at 60 ° C. for 30 minutes. After drying, 3 μl of 0.05 wt% Nafion (registered trademark) ionomer was dropped and dried again to produce a working electrode.

Using the manufactured working electrode, the above electrode activity tests on oxygen reduction and hydrogen generation were performed. Unless otherwise specified, the electrode activity test was performed under the conditions described above.
In the electrode activity test of Example 1, 0.5 M sulfuric acid aqueous solution was used as the electrolytic solution, and the scanning speed was set to 10 mV / s.

From the measurement results, the reduction initiation potential of oxygen in Example 1 was about 0.84 V vs. RHE. The generation potential of hydrogen - 0.46Vvs. RHE. The operating potential window from oxygen reduction to hydrogen generation is 1.3V. The hydrogen peroxide production rate at this time is 2 to 50%.

(Comparative Example 1)
The same as Example 1 except that an electrode activity test was performed using an electrode using Pt / C (TEK10E70TPM manufactured by Tanaka Kikinzoku) as the catalyst instead of the carbon alloy catalyst.

  From the measurement results, the reduction initiation potential of oxygen in Comparative Example 1 was about 0.98 V vs. RHE. The hydrogen generation start potential is -0.012 V vs. RHE. The operating potential window from oxygen reduction to hydrogen generation is 0.992V. The hydrogen peroxide production rate at this time is 2 to 15%.

  When the carbon alloy catalyst of Example 1 was used as compared with Pt of Comparative Example 1, the oxygen reduction starting potential was lower, but the hydrogen generation starting potential was lower, indicating that the generation of hydrogen was suppressed. Further, the potential range from the oxygen reduction start potential to the hydrogen generation start potential, that is, the potential range where only the oxygen reduction reaction occurs, was expanded as compared with the case where Pt of Comparative Example 1 was used as a catalyst. For this reason, the membrane electrode assembly using the carbon alloy catalyst of Example 1 as a cathode electrode catalyst can apply a higher voltage than the membrane electrode assembly using Pt as a catalyst, while suppressing hydrogen generation. It has the potential to pass a high current.

(Comparative Example 2)
Example 1 is the same as Example 1 except that an electrode activity test was performed with an electrode using carbon (KetjenBlack (registered trademark) EC300J) containing no nitrogen as a catalyst instead of a carbon alloy catalyst.

  The reduction start potential of oxygen in Comparative Example 2 was about 0.7 V vs. RHE. The hydrogen generation start potential was -0.07 V vs. RHE. The operating potential window from oxygen reduction to hydrogen generation is 0.77V. The hydrogen peroxide production rate at this time is 50 to 100%. It can be seen that a carbon alloy catalyst is indispensable for the cathode in the reduction reaction from oxygen to water.

(Example 2)
In Example 2, an electrode activity evaluation test was performed using an alkaline solution as the electrolytic solution. Example 1 was the same as Example 1 except that the electrode was prepared without using an ionomer when the working electrode was prepared, and a 0.1 M KOH aqueous solution was used as the electrolytic solution. Since the electrode was prepared without using an ionomer, the working electrode was carefully immersed so that the catalyst was not peeled off. Since the size of the cyclic voltammogram did not change before and after the electrode activity evaluation test, it is considered that there was no desorption of the catalyst into the electrolyte solution.

  The reduction initiation potential of oxygen in Example 2 was about 0.95 V vs. RHE. The generation start potential of hydrogen is −0.61 V vs. RHE. The operating potential window from oxygen reduction to hydrogen generation is 1.56V. The hydrogen peroxide production rate at this time is 2 to 50%.

(Comparative Example 3)
Example 2 is the same as Example 2 except that an electrode activity test was performed with an electrode using Pt / C (TEK10E70TPM manufactured by Tanaka Kikinzoku) as a catalyst instead of the carbon alloy catalyst.

  The reduction initiation potential of oxygen in Comparative Example 3 was about 0.99 V vs. RHE. The generation start potential of hydrogen is −0.096 V vs. RHE. The operating potential window from oxygen reduction to hydrogen generation is 1.08V. The hydrogen peroxide production rate at this time is 2 to 15%.

(Comparative Example 4)
This example is the same as Example 2 except that an electrode activity test was performed using an electrode using carbon (KetjenBlack (registered trademark) EC300J) containing no nitrogen as a catalyst instead of the carbon alloy catalyst.

  The reduction start potential of oxygen in Comparative Example 4 was about 0.93 V vs. RHE. The hydrogen generation start potential is -0.58 V vs. RHE. The operating potential window from oxygen reduction to hydrogen generation is 1.41V. The hydrogen peroxide production rate at this time is 50 to 100%. The operating potential window is similar to that in Example 2, but the hydrogen peroxide production rate is very high. Therefore, it is understood that the carbon alloy catalyst of the embodiment containing nitrogen has sufficient reduction performance from oxygen to water.

In the embodiment, the carbon alloy catalyst used as the oxygen reduction catalyst is not limited to the raw materials shown in Examples 1 and 2. For example, nitrogen-containing carbon precursors include nitrogen-containing phenol resins, imide resins, melamine resins, benzoguanamine resins, etc., and metal compounds such as iron phthalocyanine, cobalt phthalocyanine, iron sulfate, cobalt sulfate, iron chloride, cobalt chloride , Cobalt sulfate, iron nitrate, potassium hexacyanoiron, cobalt nitrate, and cobalt acetate. These materials were mixed with 8 g of each resin, 1 g of a metal precursor, and 5 g of KetjenBlack (registered trademark) EC300J as a carrier with 150 ml of THF (tetrahydrofuran). After mixing, the mixture is refluxed at 80 ° C. for 2 hours while stirring at a stirrer of 300 rpm. The refluxed solution is dried by an evaporator using a 45 ° C. hot water bath, and the dried material is fired in an argon atmosphere at 800 ° C. for 1 hour. After calcination, the calcined product was washed with 2M hydrochloric acid to produce various carbon alloy catalysts. These produced catalysts have a surface nitrogen substitution rate of 10% by XPS.

This catalyst is converted into an electrode as in the first embodiment. When evaluating oxygen reduction properties,
In the acidic electrolyte, the reduction initiation potential of oxygen is about 0.88 to 0.75 V vs. RHE, and the hydrogen generation potential is -0.2 to -0.7 V vs.. In RHE and alkaline / neutral electrolytes, the reduction initiation potential of oxygen is about 0.94 to 0.87 V vs. RHE, the generation potential of hydrogen is −0.2 to −0.9 V vs. RHE. The hydrogen peroxide production rate at this time is 1 to 50%.

(Example 3)
The electrolysis apparatus 10-1 shown in the conceptual diagram of FIG. 3 was created and the electrolysis test was conducted.
The anode of Example 3 was prepared by adding a solution prepared by adding 1-butanol to 0.25 M (Ir) to iridium chloride (IrCl ₃ · nH ₂ O) in advance in an aqueous 10 wt% oxalic acid solution for 80 hours. It is applied to a titanium mesh (0.1 t × LW0.2 × SW0.1) etched at a degree. Then, it was dried (10 minutes, 80 ° C.) and fired (10 minutes, 450 ° C.). Coating, drying and firing were repeated 5 times to produce an anode.

In the cathode of Example 3, 60 mg of the catalyst obtained in Example 1 is dispersed in 50 cc of water. The liquid is stirred and suspended while boiling. The suspension was poured onto water-repellent-treated (20 wt%) carbon paper (TPG-H-090 manufactured by Toray, thickness 0.28 mm, area 12 cm ² ), and suction filtered until the filtrate became transparent at 0.09 MPa. Repeat and then dry. A 2 wt% Nafion (registered trademark) solution dissolved in ethanol is dropped into the dried product by a reduced pressure dropping method (0.09 MPa), and then impregnated in a 4 wt% Nafion (registered trademark) solution dissolved in ethanol. The impregnated product is boiled in pure water for 1 hour to form a cathode.

  The membrane / electrode assembly of Example 3 was obtained by sandwiching the prepared anode and cathode on both sides of a polymer electrolyte Nafion (registered trademark) 112 (50 μm) and hot pressing at 125 ° C. for 5 minutes at 0.36 MPa. Assume a joined body.

A water supply pipe 15, a water discharge pipe 16, a supply air introduction pipe 17 and an air discharge pipe 18 are attached to the membrane electrode assembly, an external DC voltage is applied to the produced electrolytic cell, and a flowing current (A) and supply The flow rate (1 CCM = 1.667 × 10 ⁻⁸ m ³ / s) and the oxygen concentration (vol%) of the air introduction pipe 17 and the air discharge pipe 18 were measured.

  When the amount of air in the supply air introduction pipe 17 was 100 CCM (21% oxygen), the air in the air discharge pipe 18 was 96.5 CCM and the oxygen concentration was 18.1% with an applied current of 1A. When the applied current was 2 A, the air in the air exhaust pipe 18 was 93 CCM and the oxygen concentration was 15.1%. In all results, almost theoretical results were obtained, and no hydrogen production was observed. It was also confirmed that water was generated on the cathode surface during voltage application.

(Comparative Example 5)
Example 3 is the same as Example 3 except that Pt / C was used as the cathode catalyst.

  When the amount of air in the supply air introduction pipe 17 was 100 CCM (21% oxygen), the air in the air discharge pipe 18 was 96.5 CCM and the oxygen concentration was 18.1% with an applied current of 1A. When the applied current was 2 A, the air in the air exhaust pipe 18 was 93 CCM and the oxygen concentration was 15.1%. Since Pt / C was used for the catalyst of Comparative Example 5, the hydrogen generation rate at an applied voltage of 1.7 V was estimated to be 1 to 50%. In Comparative Example 5, not only the oxygen reduction reaction does not occur, but also wasteful power is consumed for the hydrogen generation reaction.

Example 4
A hypoxic device in which the membrane / electrode assembly produced in Example 3 was attached to an openable / closable sealed container like the hypoxic device 20-3 in FIG. 7 was prepared. When a current was supplied from the power source 11 attached to the membrane electrode assembly, it was confirmed that the oxygen concentration decreased theoretically with respect to the current, and the concentration decreased from about 20% to about 5%. Further, even when the voltage applied to the membrane electrode assembly was 1.7 V, no generation of hydrogen was observed.

(Comparative Example 6)
Example 4 is the same as Example 4 except that Pt / C was used as the cathode catalyst. When a current was supplied from the power supply 11 attached to the membrane electrode assembly, the oxygen concentration decreased. However, when the applied voltage to the membrane electrode assembly was 1.7 V, 1 to 20% of the reaction at the cathode was hydrogen. It was a reaction to be generated.

  When Example 4 and Comparative Example 6 were compared, there was a difference in suppressing hydrogen generation as an actual device. In Comparative Example 6, the oxygen reduction reaction does not occur by the amount of the hydrogen generation reaction, and wasteful power is consumed.

(Example 5)
For example, the oxygen-reduced device of Example 4 is attached to the refrigerator, so that the oxygen-reduced space can be provided in the refrigerator. It was confirmed that when the oxygen reduction device was operated, the oxygen concentration decreased theoretically with respect to the current, and the concentration decreased from about 21% to about 10%. Since the oxygen concentration in the refrigerator can be reduced when the refrigerator is closed, corrosion due to oxidation can be suppressed and the shelf life of the food can be extended.

  Although several embodiments of the present invention have been described, these embodiments are presented by way of example and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the scope of the invention. These embodiments and modifications thereof are included in the scope and gist of the invention, and are included in the invention described in the claims and the equivalents thereof. Some of the elements in the specification and the drawings are described with element symbols.

DESCRIPTION OF SYMBOLS 1 ... Carbon alloy catalyst 2 ... Ion electroconductive binder 3 ... Electrode support material 10 ... Electrolyzer, soda electrolyzer 11 ... Power source 12 ... Anode 13 ... Electrolyte, ion-exchange membrane 14 ... Cathode 15 ... Liquid (water) supply pipe 16 ... Liquid (water) discharge pipe 17 ... Gas (air) supply pipe 18 ... Gas (air) discharge pipe 19 ... Membrane electrode assembly 20 ... Electrolyzer (oxygen reduction device, oxygen concentrator, humidifier, dehumidifier)
DESCRIPTION OF SYMBOLS 21 ... Sealant 22 ... Container 23 ... Door 24 ... Water tank 25 ... Water supply pipe 26 ... Air discharge pipe 30 ... Refrigerator 41 ... Working electrode 42 ... Reference electrode 43 ... Counter electrode 44 ... Electrolyte

Claims (17)

An electrolytic cell having a membrane electrode assembly composed of an anode, a cathode having a carbon alloy catalyst into which nitrogen is introduced, and an electrolyte disposed between the anode and the cathode ;
A container that separates the space on the anode side and the space on the cathode side;
A power source for applying a voltage to the anode and the cathode;
An electrolysis apparatus comprising a control unit for controlling the power source ,
The carbon alloy catalyst has at least one of pyridine type nitrogen substitution, pyrrole / pyridone type nitrogen substitution, and N oxide type nitrogen substitution,
The electrolyte is either acidic, neutral or alkaline,
When the electrolyte is acidic, the hydrogen generation potential is -0.2 to -0.7 V vs. RHE , wherein the control unit controls the power supply so that a potential of the cathode is higher than a generation potential of the hydrogen in the operation of the electrolyzer, or
When the electrolyte is neutral or alkaline, the hydrogen generation potential is -0.2 to -0.9 V vs. The electrolysis apparatus according to claim 1, wherein the control unit controls the power supply so that a potential of the cathode is higher than a generation potential of the hydrogen during operation of the electrolysis apparatus. In the electrolyte,
When the electrolyte is acidic, the reduction initiation potential of oxygen is 0.88 to 0.75 Vvs. RHE , wherein the control unit controls the power supply so that the potential of the cathode is lower than the reduction start potential of the oxygen in the operation of the electrolysis apparatus, or
When the electrolyte is neutral or alkaline, the reduction initiation potential of oxygen is 0.94 to 0.87 Vvs. 2. The electrolysis according to claim 1 , wherein the control unit controls the power supply so that a potential of the cathode is lower than a reduction start potential of the oxygen during operation of the electrolysis apparatus. apparatus.   3. The electrolysis apparatus according to claim 1, wherein the electrolyte of the membrane electrode assembly is an acidic cation exchange membrane. 4.   4. The electrolytic device according to claim 1, wherein the electrolyte of the membrane electrode assembly is a neutral or alkaline membrane and is an anion exchange membrane. 5.   The electrolysis apparatus according to claim 1, wherein the electrolysis cell is provided in a sealable container.   6. The carbon alloy catalyst according to claim 1, wherein 0.1 atm% or more and 30 atm% or less of the surface alloy amount is nitrogen-substituted from carbon. Electrolytic device.   7. The carbon alloy catalyst according to claim 1, wherein 0.1 atm% or more and 10 atm% or less of the surface element amount is nitrogen-substituted from carbon. Electrolytic device.   The electrolysis apparatus according to any one of claims 1 to 7, wherein in the carbon alloy catalyst, a part of carbon in which carbons form an Sp2 hybrid orbital is substituted with nitrogen. When the electrolyte is acidic, the control unit controls the power supply so that the potential of the cathode becomes −0.012 V vs. RHE or less during operation of the electrolysis apparatus, or
When the electrolyte is neutral or alkaline, the control unit controls the power supply so that the potential of the cathode becomes −0.096 V vs. RHE or less in the operation of the electrolysis apparatus. The electrolyzer according to any one of claims 1 to 8.   The electrolysis apparatus according to any one of claims 1 to 9, wherein the carbon alloy catalyst has pores, and 60% or more of the pores have a diameter of 20 nm or more. 11. The electrolyzer according to claim 1, wherein the carbon alloy catalyst has a specific surface area of 100 m ² / g or more and 1200 m ² / g or less.   A refrigerator comprising the electrolyzer according to any one of claims 1 to 11. When the electrolyte is acidic, the hydrogen generation potential is -0.2 to -0.7 V vs. RHE , wherein the control unit operates the power supply so that a potential of the cathode is higher than a generation potential of the hydrogen, or
When the electrolyte is neutral or alkaline, the hydrogen generation potential is -0.2 to -0.9 V vs. 12. The electrolysis apparatus according to claim 1, wherein the control unit operates the power supply so that a potential of the cathode is higher than a generation potential of the hydrogen. Driving method . In the electrolyte,
When the electrolyte is acidic, the reduction initiation potential of oxygen is 0.88 to 0.75 Vvs. RHE , the control unit operates the power supply so that the potential of the cathode is lower than the reduction start potential of the oxygen ,
When the electrolyte is neutral or alkaline, the reduction initiation potential of oxygen is 0.94 to 0.87 Vvs. 14. The operating method according to claim 13 , wherein the control unit operates the power supply so that the potential of the cathode is lower than the reduction start potential of the oxygen .   The method for operating an electrolysis apparatus according to claim 13 or 14, wherein the hydrogen peroxide production rate is 1 to 50%. When the electrolyte is acidic, the control unit operates the power supply so that the potential of the cathode becomes −0.012 V vs. RHE or less, or
  16. When the electrolyte is neutral or alkaline, the control unit operates the power supply so that the potential of the cathode becomes −0.096 V vs. RHE or less. The operating method of the electrolyzer of any one of these. The operating method of the refrigerator which drives the electrolyzer which the refrigerator of Claim 12 has by the method of any one of Claim 13 thru | or 16 .