JP2023128449A - Cathode, membrane electrode assembly and organic hydride production device - Google Patents

Abstract

To provide a cathode of an organic hydride production device capable of producing an organic hydride with high power efficiency.SOLUTION: A cathode 20 of an organic hydride production device comprises: a cathode catalytic layer 21; a microporous layer 22; and a diffusion layer 23 from the side of an electrolyte membrane 10 in this order. The microporous layer 22 comprises a hydrophilic porous oxide 22a.SELECTED DRAWING: Figure 1

Description

The present invention relates to a cathode for an organic hydride manufacturing device, a membrane electrode assembly, and an organic hydride manufacturing device.

In order to curb global warming, efforts to use renewable energies such as solar and wind power, which do not emit greenhouse gases, are gaining momentum. Since solar energy and wind energy have relatively large output fluctuations, there is a need for advances in technology for storing the obtained energy and extracting it when needed.
Furthermore, hydrogen energy is expected to be a next-generation energy because it does not emit greenhouse gases, and research and development are actively being conducted on hydrogen production, hydrogen storage, transportation, and hydrogen utilization. Here, if renewable energy is used for hydrogen production and hydrogen storage, there will be great synergy effects.

Regarding the method of storing and transporting hydrogen, there is a method using organic hydride, that is, hydrogenation reaction of hydrogen gas with an aromatic hydrocarbon such as toluene to obtain a cyclic saturated hydrocarbon such as methylcyclohexane. There is a method in which hydrogen is stored and transported in the form of hydrogen, and hydrogen is generated from the cyclic saturated hydrocarbon at the point of consumption through a catalytic dehydrogenation reaction. If organic hydride is used, hydrogen can be transported in the form of an organic hydride, specifically a liquid cyclic saturated hydrocarbon such as methylcyclohexane, at room temperature and pressure, making it easy to handle and suitable for mass transportation and supply. It is expected that this will become possible.

To produce organic hydride, instead of using hydrogen obtained by electrolyzing water as a raw material, water is used as a raw material, and aromatic hydrocarbons such as toluene are hydrogenated through an electrochemical reaction with water to produce products such as methylcyclohexane. A technique for obtaining cyclic saturated hydrocarbons has been developed. The organic compound hydrogenation equipment used in this technology consists of an oxidation tank that contains water containing an electrolyte, a reduction tank that contains organic compounds with unsaturated bonds, and a proton conductive tank that separates the oxidation tank and reduction tank. It is equipped with an electrolyte membrane, an oxidizing electrode placed in an oxidizing tank to generate protons from water, and a reducing electrode placed in a reducing tank to hydrogenate organic compounds having unsaturated bonds (for example, Patent Document 1 ).

In recent years, an organic hydride production apparatus has been proposed which is an improved version of the hydrogenation apparatus described above. Such an organic hydride production apparatus includes a proton-conducting electrolyte membrane, a cathode (reducing electrode) provided on one side of the electrolyte membrane that hydrogenates a substance to be hydrided with protons to generate an organic hydride, and this electrolyte membrane. A membrane electrode assembly (MEA) is now being used in which an anode (oxidation electrode) is provided on the other side of the membrane electrode and which oxidizes water to generate protons.
Regarding the cathode of an organic hydride production apparatus, there is one that includes a cathode catalyst layer, a microporous layer, and a diffusion layer in that order from the electrolyte membrane side (Patent Document 2).

International Publication No. 2012/091128 Japanese Patent Application Publication No. 2018-31046

There is a constant demand for improved power efficiency in organic hydride production equipment, and it is required to produce organic hydride with higher power efficiency than ever before.

The present invention has been made in response to the above requirements, and provides a cathode for an organic hydride production device that can produce organic hydride with high power efficiency, a membrane electrode assembly equipped with the cathode, and an organic hydride production device. With the goal.

In order to achieve the above object, the cathode of the present invention is a cathode for an organic hydride production apparatus, and includes a cathode catalyst layer, a microporous layer, and a diffusion layer in that order from the electrolyte membrane side, and the microporous layer is a hydrophilic layer. It is characterized by containing a porous oxide.
In the cathode of the present invention, the hydrophilic porous oxide may include diatomaceous earth.
The membrane electrode assembly of the present invention is characterized by comprising an electrolyte membrane having proton conductivity and the cathode provided on one side of the electrolyte membrane.
The organic hydride production apparatus of the present invention is characterized by comprising the cathode or the membrane electrode assembly.

According to the cathode of the present invention, organic hydride can be manufactured with high power efficiency in an organic hydride manufacturing apparatus.

FIG. 1 is a schematic diagram showing main parts of an organic hydride production apparatus of the present invention. It is a figure explaining the effect of the cathode of this invention. FIG. 2 is a schematic diagram showing an organic hydride manufacturing apparatus used in the experiment. It is a graph showing the relationship between current density and cell voltage. It is a graph showing the relationship between current density and cell voltage. It is a graph showing the relationship between current density and the amount of associated water. It is a graph showing the relationship between current density and current efficiency.

EMBODIMENT OF THE INVENTION Hereinafter, embodiments of a cathode, a membrane electrode assembly, and an organic hydride manufacturing apparatus of the present invention will be described based on the drawings.

FIG. 1 shows a schematic diagram of the main parts of the organic hydride production apparatus of the present invention. In FIG. 1, an electrolytic cell 1 includes an electrolyte membrane 10 having proton conductivity, a cathode 20 provided in contact with the electrolyte membrane 10 on one side of the electrolyte membrane 10, and a cathode 20 on the other side of the electrolyte membrane 10. and an anode 30 provided in contact with the electrolyte membrane 10. A positive electrode of a DC power source (not shown) is electrically connected to a terminal (not shown) of the anode 30, and a negative electrode of the DC power source is electrically connected to a terminal (not shown) of the cathode 20. A predetermined voltage is applied between the cathode 20 and the cathode 20. A reference electrode for power adjustment may be connected to the electrolyte membrane 10.

Water containing an electrolyte is passed through the anode 30 through a channel 34 (arrows in the figure indicate the direction of water flow), and the water is electrochemically oxidized to generate protons. The generated protons move to the cathode 20 through the electrolyte membrane 10. A hydrogenated substance to be hydrogenated in the electrolytic cell 1, specifically an organic compound having an unsaturated bond (toluene in FIG. (indicates the direction of flow), is electrochemically reduced and hydrogenated by protons that have moved through the electrolyte membrane 10.

[Cathode]
The cathode 20 includes a cathode catalyst layer 21, a microporous layer 22, and a diffusion layer 23 in this order from the side in contact with the electrolyte membrane 10, and a flow path 24 connected to the diffusion layer 23 is provided. The present invention includes a hydrophilic porous oxide in the microporous layer 22. The cathode catalyst layer 21, microporous layer 22, and diffusion layer 23 of the cathode 20 will be explained below.

The cathode catalyst layer 21 includes a reduction catalyst for hydrogenating a hydride with protons transferred from the electrolyte membrane 10 to generate an organic hydride. In FIG. 1, the reference numeral 21a indicates a reduction catalyst. As the reduction catalyst, particles selected from the group consisting of, for example, Pt, Ru, Pd, Ir, and alloys containing at least one of these metals can be used. As the reduction catalyst, a commercially available product may be used, or one synthesized according to a known method may be used. Further, the reduction catalyst includes at least one noble metal selected from the above-mentioned Pt, Ru, Pd, and Ir, and Cr, Mn, Fe, Co, Ni, Cu, Zn, Mo, Ru, Sn, W, Re, and Pb. It is also possible to use particles made of an alloy or an intermetallic compound with at least one selected from , Bi, and the like. The average particle size of the reduction catalyst is preferably 1 nm to 1 μm, more preferably 1 nm to 5 nm. By setting the average particle size of the reduction catalyst to 1 μm or less, the surface area per weight of the catalyst can be increased and the reaction can be improved. Further, by setting the average particle size of the reduction catalyst to 1 nm or more, it is possible to suppress a decrease in durability due to aggregation of catalyst particles.

The reduction catalyst is supported by a catalyst carrier made of an electron-conductive material. By supporting the reduction catalyst on the catalyst carrier, the surface area of the cathode catalyst layer 21 can be expanded, and aggregation of the reduction catalyst can be suppressed. The electron conductivity of the catalyst support material is preferably 1.0×10 ⁻² 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 21.

Examples of the catalyst carrier include an electron conductive material containing as a main component any one of porous carbon (such as mesoporous carbon), porous metal, and porous metal oxide. Examples of porous carbon include carbon blacks such as Ketjenblack (registered trademark), acetylene black, furnace black, and Vulcan (registered trademark).

The BET specific surface area of the porous carbon measured by the nitrogen adsorption method is preferably 50 m ² /g to 1500 m 2 /g, more preferably 500 m ^{2 /} g to 1300 m ² /g, and even more preferably 700 m ² /g to 1000m ² /g. When the BET specific surface area of the porous carbon is 50 m ² /g or more, the reduction catalyst can be easily supported uniformly, and the hydrogenated product can be more reliably diffused. In addition, since the BET specific surface area of the porous carbon is 1500 m ² /g or less, deterioration of the catalyst carrier can be suppressed during the reaction of the hydride or when starting or stopping the organic hydride production equipment. As a result, the catalyst carrier will have sufficient durability. The average particle size of carbon fine particles such as carbon black used as a catalyst carrier is preferably 0.01 μm to 1 μm.

Porous metals include, for example, Pt black, Pd black, and fractal-precipitated Pt metal. Examples of porous metal oxides include oxides of Ti, Zr, Nb, Mo, Hf, Ta, and W. Furthermore, porous metal compounds (hereinafter, as appropriate, Porous metal carbonitrides, etc.) can also be used. The BET specific surface area of the porous metal, porous metal oxide, porous metal carbonitride, etc. measured by a nitrogen adsorption method is preferably 1 m ² /g or more, more preferably 3 m ² /g or more. , more preferably 10 m ² /g or more. By setting the BET specific surface area of the porous metal, porous metal oxide, porous metal carbonitride, etc. to 1 m ² /g or more, the reduction catalyst can be easily supported uniformly.

The catalyst carrier supporting the reduction catalyst is usually coated with an ionomer. Thereby, the ionic conductivity of the cathode 20 can be improved. Examples of the ionomer include perfluorosulfonic acid polymers such as Nafion (registered trademark) and Flemion (registered trademark). The ion exchange capacity (IEC) of the ionomer is preferably 0.7 to 3 meq/g, more preferably 1 to 2.5 meq/g, and still more preferably 1.2 to 2 meq/g. When the catalyst carrier is porous carbon, the mass ratio I/C of the ionomer (I) to the catalyst carrier (C) is preferably 0.1 to 2, more preferably 0.2 to 1.5. and more preferably 0.3 to 1.1. When the mass ratio I/C is 0.1 or more, sufficient ionic conductivity can be obtained more reliably. On the other hand, by having a mass ratio I/C of 2 or less, the coating thickness of the ionomer on the reduction catalyst is suppressed from becoming excessive, and contact of the hydride to the catalyst active site is prevented from being inhibited. be able to.

Note that the ionomer preferably partially covers the reduction catalyst. By partially covering the cathode catalyst layer 21, the three elements necessary for the electrochemical reaction in the cathode catalyst layer 21, ie, the hydride, protons, and electrons, can be efficiently supplied to the reaction field.

The thickness of the cathode catalyst layer 21 is preferably 1 to 100 μm, more preferably 5 to 30 μm. When the thickness of the cathode catalyst layer 21 increases, not only the resistance to proton movement increases, but also the diffusivity of hydrides decreases. For this reason, it is desirable to adjust the thickness of the cathode catalyst layer 21 within the above-mentioned range.

The cathode catalyst layer 21 can be produced, for example, by the following method.
First, a catalyst component powder, a hydrophobic resin (fluorine component) which is a gas permeable material, water, a solvent such as naphtha, and an ionomer (for example, Nafion (registered trademark) dispersion DE521 (manufactured by DuPont)) are mixed. Mix. The amount of the 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 powder form, and its particle size is preferably 0.005 to 10 μm. A catalyst ink is prepared by appropriately adding a solvent to the obtained mixture.

Next, the obtained catalyst ink is applied onto the surface of the microporous layer 22, dried, and then hot pressed to fix the cathode catalyst layer 21 to the microporous layer 22. It is preferable to carry out hot pressing after the above-mentioned application and drying are performed in multiple steps. A homogeneous cathode catalyst layer 21 can be obtained by applying such catalyst ink, drying, and hot pressing.

Note that the cathode catalyst layer 21 may be formed on the electrolyte membrane 10. For example, a composite of the cathode catalyst layer 21 and the electrolyte membrane 10 can be produced by applying catalyst ink to one main surface of the electrolyte membrane 10 using a bar coater. Further, a composite of the cathode catalyst layer 21 and the electrolyte membrane 10 can be prepared by spraying the catalyst ink onto one main surface of the electrolyte membrane 10 and drying the solvent component in the catalyst ink. The catalyst ink is preferably applied so that the mass of the reduction catalyst 21a in the cathode catalyst layer 21 is 0.5 mg/cm ² per electrode area.

Microporous layer 22 is provided so as to be in contact with the main surface of cathode catalyst layer 21 on the side opposite to electrolyte membrane 10 . Furthermore, the diffusion layer 23 is provided so as to be in contact with the main surface of the microporous layer 22 on the side opposite to the cathode catalyst layer 21 .

The microporous layer 22 has a function of promoting diffusion of liquid hydride and organic hydride in the surface direction of the cathode catalyst layer 21 . The microporous layer 22 has a basic composition including conductive powder and a water repellent.

As the conductive powder, for example, conductive carbon such as Vulcan (registered trademark) can be used. As the water repellent, for example, a fluororesin such as tetrafluoroethylene resin (PTFE) can be used. The ratio of the conductive powder to the water repellent is appropriately determined within a range that provides desired conductivity and water repellency. As an example, when Vulcan (registered trademark) is used as the conductive powder and PTFE is used as the water repellent, the mass ratio (Vulcan:PTFE) is, for example, 4:1 to 1:1. Note that the microporous layer 22 can also be made of carbon cloth, carbon paper, etc., like the diffusion layer 23.

In the conventional cathode, the microporous layer 22 was made of the above-mentioned conductive powder and water repellent. In contrast, the cathode 20 of the present invention includes a hydrophilic porous oxide in addition to the conductive powder and the water repellent. In FIG. 1, the reference numeral 22a indicates a hydrophilic porous oxide.

The effects of the microporous layer 22 containing a hydrophilic porous oxide will be explained using FIG. 2. Note that in FIG. 2, the same members as in FIG. 1 are denoted by the same reference numerals, and redundant explanation will be omitted below. Although FIG. 2 omits illustration of the flow path 24 on the cathode 20 side and the flow path 34 on the anode 30 side, it is assumed that non-hydride flows in the diffusion layer 23 and in the anode catalyst layer 31. It is assumed that water containing electrolytes is distributed.

According to the research of the present inventors, in the conventional cathode, water (produced water) moves from the anode 30 together with protons during operation of the organic hydride production apparatus, and this water that moves to the cathode side is transferred to the cathode catalyst layer. It was accumulated in 21. It was found that the accumulation of water in the cathode catalyst layer 21 inhibited the supply of the liquid hydrogenated product to the cathode catalyst layer 21, resulting in a decrease in power efficiency.

Therefore, as a result of intensive research to suppress the accumulation of accompanying water in the cathode catalyst layer 21, the present inventors found that the microporous layer 22 contains a hydrophilic porous oxide 22a. It was discovered that it is possible to prevent a decrease in power efficiency due to produced water and improve power efficiency.

The reason why the microporous layer 22 can improve power efficiency by including the hydrophilic porous oxide 22a is that the hydrophilic porous oxide makes a part of the microporous layer 22 hydrophilic, and water (associated water ), it is possible to prevent the supply of the hydride (for example, toluene) to the cathode catalyst layer 21 from being inhibited by the associated water as in the past, and improve the supply. As a result, it is presumed that the current efficiency improved.

Examples of the hydrophilic porous oxide 22a include diatomaceous earth, zeolite, mesoporous silica, and bentonite.
The particle size of the hydrophilic porous oxide 22a is preferably in the range of 0.5 to 10 μm. By having a particle size of 0.5 μm or more including secondary particles, a water discharge path can be reliably formed. By having a particle size of 10 μm or less, a water discharge path can be formed without adversely affecting the average flow rate pore size of the microporous layer 22. A more preferable particle size is 1.0 to 5.0 μm.

The hydrophilic porous oxide 22a is preferably contained in an amount of 5 to 15% by mass based on the entire microporous layer. If the amount is 5% by mass or more, a sufficient water discharge path amount can be formed. A sufficient improvement in current efficiency can be obtained with a content of 15% by mass or less. A more preferred content ratio is 5 to 10% by mass, and an even more preferred content ratio is 7 to 9% by mass.

The microporous layer 22 can be formed by applying a paste prepared by kneading the above-mentioned conductive powder, water repellent, and hydrophilic porous oxide onto the surface of the diffusion layer 23 and drying it.

The average flow pore diameter (dm) of the microporous layer 22 after hot pressing is preferably 100 nm to 20 μm, more preferably 500 nm to 5 μm. The average flow rate pore diameter of the microporous layer 22 can be measured using a mercury porosimeter or the like. By setting the average flow rate pore diameter 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 wall surface of the pore and the liquid hydride and organic hydride. In addition, by setting the average flow rate pore diameter to 20 μm or less, it is possible to more reliably suppress the decrease in fluidity due to a decrease in suction of the liquid to be hydrogenated and organic hydride due to capillary action. Further, by setting the average flow rate pore diameter to 100 nm to 20 μm, liquid hydrogenated substances and organic hydrides can be smoothly sucked and discharged by capillary action.

Further, the thickness of the microporous layer 22 is preferably 1 to 50 μm, more preferably 2 to 20 μm. Note that when the microporous layer 22 is formed so as to fall deeper into the interior than the surface of the diffusion layer 23, the average thickness of the microporous layer 22 itself, including the portion submerged in the diffusion layer 23, is It is defined as the thickness of the microporous layer 22. A metal component may coexist on the surface of the microporous layer 22. This improves the electronic conductivity of the microporous layer 22 and makes it possible to make the current uniform.

Note that the microporous layer 22 and the diffusion layer 23, which will be described in detail later, are normally used in a state where pressure is applied to each in the thickness direction. Therefore, it is not preferable that the conductivity in each thickness direction changes due to pressure applied in the thickness direction during use. For this reason, it is preferable that the microporous layer 22 and the diffusion layer 23 be pressed in advance. As a result, the carbon material in each layer is compressed, so that the conductivity in the thickness direction of each layer can be increased and stabilized. Furthermore, a cathode 20 having a stable filling rate of 20 to 50% can be realized.

Furthermore, improving the degree of bonding between the cathode catalyst layer 21 and the microporous layer 22 also contributes to improving the conductivity of the cathode 20. Moreover, the improvement in the degree of bonding improves the ability to supply raw materials and the ability to remove produced substances. When forming the cathode catalyst layer 21 on the surface of the microporous layer 22, performing hot pressing contributes to improving the degree of bonding. Further, after the cathode catalyst layer 21 is formed on the surface of the microporous layer 22, the cathode catalyst layer 21 and the microporous layer 22 can be press-worked, and this can be expected to improve the degree of bonding. As the press processing device, known devices such as a hot press and a hot roller can be used. Further, as pressing conditions, temperature: room temperature to 360°C, pressure: 0.1 to 5 MPa are preferable.

The diffusion layer 23 has a function of uniformly diffusing the liquid hydrogenated substance supplied from the flow path 24 into the cathode catalyst layer 21 . It is preferable that the material constituting the diffusion layer 23 has a high affinity for the substance to be hydrogenated. Examples of the material constituting the diffusion layer 23 include a porous conductive base material, a fiber sintered body, and the like. These are preferred because they have porosity suitable for supplying and removing gas and liquid and can maintain sufficient electrical conductivity. The diffusion layer 23 preferably has a thickness of 10 to 5000 μm, a porosity of 30 to 95%, and a typical pore size of 1 to 1000 μm. Further, the electron conductivity of the material constituting the diffusion layer 23 is preferably 10 ⁻² S/cm or more.

More specific examples of the material constituting the diffusion layer 23 include carbon woven cloth (carbon cloth), carbon nonwoven cloth, carbon paper, and the like. Carbon cloth is a bundle of several hundred carbon fibers with a diameter of several micrometers, and this bundle is made into a woven fabric. Further, carbon paper is obtained by using carbon raw material fibers as a thin film precursor using a paper manufacturing method and sintering this.

[anode]
As shown in FIG. 1, the anode 30 is provided on the opposite side of the electrolyte membrane 10 from the cathode 20 and in contact with the main surface of the electrolyte membrane 10. The anode 30 includes an anode catalyst layer 31 and a flow path 34 connected to the anode catalyst layer 31.

Anode catalyst layer 31 is in contact with the other main surface of electrolyte membrane 10 . The anode catalyst layer 31 is a layer containing a catalyst for oxidizing water in the anode solution to generate protons. As the catalyst contained in the anode catalyst layer 31, for example, particles selected from the group consisting of Ru, Rh, Pd, Ir, Pt, and an alloy containing at least one of these metals can be used.

The catalyst may be dispersed and supported on or coated on a metal substrate having electron conductivity. Such metal base materials include metals such as Ti, Cr, Mn, Fe, Co, Ni, Cu, Zn, Nb, Mo, Ta, and W, or alloys containing these as main components. Examples include metal fibers (fiber diameter: for example, 10 to 30 μm), mesh (mesh diameter: for example, 500 to 1000 μm), sintered bodies of porous metal bodies, foams, expanded metals, and the like. The base material used for the anode catalyst layer 31 is a plate with a thickness of 0.1 to 2 mm from the viewpoint of having sufficient electrical conductivity to flow the current necessary for electrolysis and sufficient mechanical strength. Preferably, the material is Further, the base material is preferably porous and has excellent corrosion resistance against the anolyte in order to avoid an increase in resistance due to air bubbles and promote the supply of the anolyte. As such a base material, expanded mesh made of titanium is commonly used. In the expanded mesh, the distance between the centers in the short direction is preferably 0.1 to 4 mm, the distance between the centers in the long direction is preferably 0.1 to 4 mm, and the aperture ratio is preferably about 30 to 70%. .

[Membrane electrode assembly]
The membrane electrode assembly 40 includes the electrolyte membrane 10 described above, the cathode 20, and the anode 30. As described above, the cathode 20 includes the hydrophilic porous oxide 22a in the microporous layer 22, thereby improving current efficiency.

[Electrolytic cell]
The electrolytic cell 1 includes the membrane electrode assembly 40 described above and a pair of end plates sandwiching the membrane electrode assembly 40 therebetween. In FIG. 1, the illustration of the end plate is omitted. One of the pair of end plates is located outside the flow path 24 of the cathode 20 when viewed from the membrane electrode assembly 40, and the other of the pair of end plates is located outside of the flow path 34 of the anode 30 at the membrane electrode junction. It is arranged on the outside when viewed from the body 40. The end plate on the cathode 20 side can have a shape that constitutes a part of the channel 24 of the cathode 20. Further, the end plate on the anode 30 side can have a shape that constitutes a part of the flow path 34 of the anode 30.

[Organic hydride production equipment]
The organic hydride manufacturing apparatus includes the electrolytic cell 1 described above. In addition, a catholyte tank for storing the hydride to be supplied to the cathode 20, a pump and circulation path for supplying the liquid from the catholyte tank to the cathode 20 and recovering organic hydride and unreacted hydride to the catholyte tank, and circulation. A separation tank provided in the middle of the route to separate the organic hydride and unreacted hydride, an anolyte tank that stores water containing electrolyte to be supplied to the anode 30, and a tank that supplies the liquid to the anode 30 and removes the unreacted liquid. A pump and circulation path for recovering the anolyte into the anolyte tank, a DC power source for applying voltage to the electrolytic cell 1, and the like can be provided as necessary.

The organic hydride used in the organic hydride production apparatus and supplied to the cathode 20 is not particularly limited as long as it is an organic compound that can add/desorb hydrogen by reversibly causing a hydrogenation reaction/dehydrogenation reaction. -Isopropanol type, benzoquinone-hydroquinone type, aromatic hydrocarbon type, etc. can be widely used. Among these, from the viewpoint of transportability during energy transport, toxicity, safety, storage stability, etc., the amount of hydrogen that can be transported per volume or mass, the ease of hydrogenation and dehydrogenation reactions, and the Gibbs free energy. From the viewpoint of energy conversion efficiency such as not significantly changing, aromatic hydrocarbons such as toluene-methylcyclohexane are preferred.

The aromatic hydrocarbon compound used as a dehydrogenated organic hydride is a compound containing at least one aromatic ring, and examples thereof include benzene, alkylbenzene, naphthalene, alkylnaphthalene, anthracene, diphenylethane, and the like. Alkylbenzenes include compounds in which 1 to 4 hydrogen atoms in the aromatic ring are substituted with straight chain alkyl groups or branched alkyl groups having 1 to 6 carbon atoms, such as toluene, xylene, mesitylene, ethylbenzene, diethylbenzene, etc. Can be mentioned. Alkylnaphthalene includes compounds in which 1 to 4 hydrogen atoms in an aromatic ring are substituted with a straight chain alkyl group or a branched alkyl group having 1 to 6 carbon atoms, such as methylnaphthalene. These may be used alone or in combination. The aromatic hydrocarbon compound is preferably at least one of toluene and benzene. Note that nitrogen-containing heteroaromatic compounds such as pyridine, pyrimidine, pyrazine, quinoline, isoquinoline, N-alkylpyrrole, N-alkylindole, and N-alkyldibenzopyrrole can also be used as the dehydrogenated product.

The water containing electrolyte used in the organic hydride production apparatus and supplied to the anode 30 is ion-exchanged water, pure water, or an aqueous solution obtained by adding an acid such as sulfuric acid, phosphoric acid, nitric acid, or hydrochloric acid to these water. The ionic conductivity is preferably 0.01 S/cm or more when measured at 20°C. By setting the ionic conductivity to 0.01 S/cm or more, an industrially sufficient electrochemical reaction can be caused.

[Method for producing organic hydride]
Organic hydride can be manufactured using an organic hydride manufacturing apparatus. Since the microporous layer 22 in the cathode 20 of the electrolytic cell 1 of the organic hydride production apparatus contains the hydrophilic porous oxide 22a, organic hydride can be produced with high current efficiency.

<Preparation of microporous layer>
As a raw material for microporous layer,
・2g and 1.78g of Ketjen Black (manufactured by Lion Corporation, EC-300J)
・0.222g, 0.444g of diatomaceous earth (manufactured by MP Biomedicals Co., Ltd., 157607)
・18 g of polyoxyethylene (10) octylphenyl ether (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., 169-211-5),
Each was prepared.
Two types of diatomaceous earth, 0.222g and 0.444g, were prepared. This is to see the difference in properties due to the difference in the mixing ratio of diatomaceous earth in the microporous layer. The amount of Ketjenblack was adjusted so that the mixing ratio of diatomaceous earth was 8% by mass and 16% by mass.

These raw materials and zirconia beads (φ5 mm×40, φ10 mm×8) were placed in a 100 mL ball mill pot made of polytetrafluoroethylene, and subjected to ball milling at 333 rpm for 20 minutes and then at 227 rpm for 10 minutes.
Take out the pot once,
・0.92g of PTFE dispersion liquid (Mitsui DuPont Fluorochemical, 31-JR)
was added, and ball milled again at 333 rpm for 20 minutes and 227 rpm for 10 minutes to obtain a paste.

Carbon paper (manufactured by Toray Industries, Ltd., TGP-H-090H) was prepared as a diffusion layer of the cathode. This carbon paper was cut into a size of 10.5 x 10.5 ^cm2 , masked with a 0.1 mm thick aluminum foil with a hole of 10 x 10 ^cm2 , and the above paste was applied using a bar coater. Thereafter, it was dried at 60° C. for 60 minutes using a dryer.

The carbon paper coated with the microporous layer in this manner was placed in a Petri dish, and immersed in 60 to 70 mL of methanol for 20 minutes to remove polyoxyethylene (10) octylphenyl ether. This was repeated six times. Thereafter, it was dried at 50° C. for 30 minutes using a dryer. Furthermore, the microporous layer of the example containing diatomaceous earth was produced by drying at 300° C. for 5 minutes using a muffle furnace.
The proportions of diatomaceous earth in the two types of microporous layers with different amounts of diatomaceous earth were 8% by mass (Example 1) and 16% by mass (Example 2), respectively.

As a comparative example, a microporous layer was fabricated using the same raw materials and steps as the microporous layer fabrication process described above, except that diatomaceous earth was not prepared as a raw material.
Conventional examples include commercially available carbon paper with a microporous layer (carbon paper (manufactured by Toray Industries, TGP-H-090H)), microporous layer (manufactured by Chemix, water repellency 20% (carbon: polytetrafluoroethylene = 80%: 20) %)) was prepared.

<Preparation of MEA>
The microporous layers of Example 1, Example 2, Comparative Example, and Conventional Example described above, the cathode catalyst layer described below, and the electrolyte layer were stacked and brought into close contact to produce an MEA.

(Preparation of cathode catalyst layer)
2 mL of a 0.004 g/mL H ₂ PtCl _{6.6H 2} O aqueous solution and 1-propanol were dropped onto carbon paper and dried for 1 hour.
0.04 g of NaBH ₄ was placed in a Petri dish, dissolved in pure water, and pure water was added to the level of about 80% of the Petri dish. Carbon paper was immersed in this and left for 2 hours. It was replaced with pure water and left for about 12 hours.
The carbon paper was taken out from the petri dish and dried in a dryer at 50° C. for about 5 minutes. Thereafter, the amount of platinum supported on the carbon paper was measured using XRF.

As a raw material for the cathode catalyst layer,
・0.6g of fuel cell catalyst (Tanaka Kikinzoku Co., Ltd., TEC61E54),
・0.72g of pure water,
・4.568g of Nafion dispersion liquid 5 mass%,
・4.8g of 1-propanol,
Each was prepared.

These raw materials and zirconia beads (φ3 mm×15) were placed in a 100 mL ball mill pot made of polytetrafluoroethylene and ball milled at 200 rpm for 30 minutes to obtain a catalyst ink.

The above carbon paper was masked with a 0.45 mm thick aluminum foil with a hole of 10 x 10 cm ² , and the above catalyst ink was applied using a bar coater to prepare a cathode catalyst layer.

Nafion 117 as an electrolyte membrane was cut into a size of 15 x 15 cm ² and one side was polished with No. 2000 emery paper.
The unpolished surface of Nafion 117 was stacked so as to be in contact with the catalyst ink coated surface of the carbon paper, and two 0.1 mm thick polytetrafluoroethylene sheets were sandwiched on each side. Hot pressing was performed to bond the electrolyte membrane and the carbon paper on which the cathode catalyst layer was formed.

<Electrochemical measurement>
An electrolytic cell was assembled using the obtained MEA, and its electrochemical properties were investigated.
[Electrolysis cell conditions]
Anode end plate: Ti, parallel flow path Cathode end plate: Ti, no flow path Anode electrolyte: 1M H ₂ SO ₄
Cathode electrolyte: 10% toluene (ratio to methylcyclohexane)
Anode electrode: DSE for anode oxygen generation
Membrane cathode assembly (MEA): Electrolyte membrane Nafion 117 + cathode 0.5 to 0.7 mg/cm ² PtRu/C (TEC61E54 manufactured by TKK), N/C = 0.8
Electrode area: ^100cm2

[Experiment conditions]
Cell temperature: 60℃
Flow rate: 10mL/min for both anode and cathode

[Preprocessing]
1M H ₂ SO ₄ was supplied to the anode side and 10% toluene was supplied to the cathode side at 10 mL/min, and the mixture was circulated for 1 h. Thereafter, constant current electrolysis was performed at 0.4 A/cm ² for 1 h.

[Measurement of associated water volume]
After circulating at 10 mL/min for 20 minutes, constant current electrolysis was performed at 0.4 A/cm ² for 20 minutes. At this time, the associated water accumulated in the reservoir on the cathode side was taken out with a Pasteur pipette and its weight was measured. These operations were repeated at 0.3 A/cm ² , 0.2 A/cm ² and 0.1 A/cm ² .

[AC impedance measurement]
At each voltage of 0.6V, 1.0V, 1.3V, 1.5V, 1.6V, 1.7V, 1.8V, 1.85V, constant voltage measurement for 3 minutes, AC amplitude 10mV, measurement frequency 105 ~ AC impedance measurements were performed for 1 min at 10 ⁻¹ Hz.

[Current efficiency measurement]
Constant voltage electrolysis was performed at an appropriate voltage between 0 V and 1.5 to 1.85 V, and the current value after 3 minutes was recorded. The solution was passed through the current efficiency measurement line. The time until the line was filled and the current value at that time were recorded, and the amount of liquid accumulated in the line was measured.
The current efficiency was calculated using Faraday's law from the volume ratio of H ₂ generated by the side reaction.

4 and 5 show graphs in which the horizontal axis represents the current density and the vertical axis represents the cell voltage. 4 and 5, there was almost no difference in cell voltage between Example 1, which contained 8% by mass of diatomaceous earth in the microporous layer, and the comparative example and the conventional example.
FIG. 6 shows a graph in which the horizontal axis represents the current density and the vertical axis represents the amount of associated water. From FIG. 6, there was almost no difference in Example 1 containing 8% by mass of diatomaceous earth in the microporous layer compared to the comparative example and the conventional example.

FIG. 7 shows a graph in which the horizontal axis represents current density and the vertical axis represents current efficiency. From FIG. 7, Examples 1 and 2 in which diatomaceous earth was included in the microporous layer had significantly improved current efficiency compared to comparative examples and commercially available conventional examples that did not contain diatomaceous earth. Among them, Example 1 containing 8% by mass of diatomaceous earth had excellent current efficiency even when compared with Example containing 16% by mass.

1 Organic hydride production apparatus 10 Electrolyte membrane 20 Cathode 21 Cathode catalyst layer 21a Reduction catalyst 22 Microporous layer 22a Hydrophilic porous oxide 23 Diffusion layer 24 Channel 30 Anode 31 Anode catalyst layer 40 Membrane electrode assembly

Claims (4)

A cathode for an organic hydride production device,
A cathode catalyst layer, a microporous layer, and a diffusion layer are provided in that order from the electrolyte membrane side.
A cathode, wherein the microporous layer includes a hydrophilic porous oxide. The cathode according to claim 1, wherein the hydrophilic porous oxide comprises diatomaceous earth. an electrolyte membrane having proton conductivity;
The cathode according to claim 1 or 2, provided on one side of the electrolyte membrane;
A membrane electrode assembly characterized by comprising: An organic hydride production apparatus comprising the cathode according to claim 1 or 2 or the membrane electrode assembly according to claim 3.