JP7789358B2 - Cathode, membrane electrode assembly and organic hydride production device - Google Patents

Description

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

In order to curb global warming, efforts are being made to utilize renewable energy sources such as solar and wind power, which do not emit greenhouse gases. However, because the output of solar and wind energy fluctuates relatively widely, there is a need for technological advances that allow the energy to be stored and extracted when needed.
Furthermore, hydrogen energy is expected to be a next-generation energy source because it does not emit greenhouse gases, and research and development is being actively conducted into its production, storage, transportation, and use. If renewable energy is used for hydrogen production and storage, there will be a great synergistic effect.

One method of storing and transporting hydrogen is to use organic hydrides; that is, hydrogen gas is hydrogenated with aromatic hydrocarbons such as toluene to produce cyclic saturated hydrocarbons such as methylcyclohexane, which are then stored and transported in this form, and hydrogen is then generated from the cyclic saturated hydrocarbons at the point of consumption by a catalytic dehydrogenation reaction. By using organic hydrides, hydrogen can be transported at room temperature and pressure in the form of organic hydrides, specifically liquid cyclic saturated hydrocarbons such as methylcyclohexane, making it easy to handle and expected to enable mass transportation and supply.

Instead of using hydrogen obtained by electrolyzing water as a raw material for producing organic hydrides, a technology has been developed that uses water as a raw material to hydrogenate aromatic hydrocarbons such as toluene through an electrochemical reaction with water to obtain cyclic saturated hydrocarbons such as methylcyclohexane. The organic compound hydrogenation device used in this technology includes an oxidation vessel containing water containing an electrolyte, a reduction vessel containing an organic compound with an unsaturated bond, a proton-conductive electrolyte membrane separating the oxidation vessel and the reduction vessel, an oxidation electrode located in the oxidation vessel that generates protons from water, and a reduction electrode located in the reduction vessel that hydrogenates the organic compound with an unsaturated bond (see, for example, Patent Document 1).

In recent years, organic hydride production apparatuses have been proposed that are improvements on the above-mentioned hydrogenation apparatuses. These organic hydride production apparatuses use a membrane electrode assembly (MEA) that integrally combines a proton-conductive electrolyte membrane, a cathode (reducing electrode) that is provided on one side of the electrolyte membrane and hydrogenates a substance to be hydrogenated with protons to produce an organic hydride, and an anode (oxidizing electrode) that is provided on the other side of the electrolyte membrane and oxidizes water to produce protons.
Regarding the cathode of an organic hydride manufacturing apparatus, there is one that is provided with 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 Laid-Open No. 2018-31046

There is a continuing demand for improved power efficiency in organic hydride production equipment, and there is a need to produce organic hydrides more power-efficiently than ever before.

The present invention has been made to meet the above-mentioned demands, and aims to provide a cathode for an organic hydride production apparatus that can produce organic hydrides with high power efficiency, a membrane electrode assembly including the cathode, and an organic hydride production apparatus.

In order to achieve the above object, the cathode of the present invention is a cathode for an organic hydride manufacturing apparatus, and is characterized in that it comprises, from the electrolyte membrane side, a cathode catalyst layer, a microporous layer, and a diffusion layer, in that order, and the microporous layer contains a hydrophilic 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 manufacturing apparatus of the present invention is characterized by comprising the cathode or the membrane electrode assembly.

The cathode of the present invention enables organic hydride production in an organic hydride production apparatus with high power efficiency.

1 is a schematic diagram showing a main part of an organic hydride manufacturing apparatus according to the present invention. 1A and 1B are diagrams illustrating the effects of the cathode of the present invention. FIG. 1 is a schematic diagram showing an organic hydride production apparatus used in an experiment. 1 is a graph showing the relationship between current density and cell voltage. 1 is a graph showing the relationship between current density and cell voltage. 1 is a graph showing the relationship between current density and the amount of produced water. 1 is a graph showing the relationship between current density and current efficiency.

Embodiments of the cathode, membrane electrode assembly, and organic hydride production apparatus of the present invention will be described below with reference to the drawings.

Figure 1 shows a schematic diagram of the main components of the organic hydride production apparatus of the present invention. In Figure 1, the electrolytic cell 1 comprises a proton-conductive electrolyte membrane 10, a cathode 20 provided on one side of the electrolyte membrane 10 in contact with the electrolyte membrane 10, and an anode 30 provided on the other side of the electrolyte membrane 10 in contact with the electrolyte membrane 10. The positive electrode of a DC power supply (not shown) is electrically connected to a terminal (not shown) of the anode 30, and the negative electrode of the DC power supply is electrically connected to a terminal (not shown) of the cathode 20, so that a predetermined voltage is applied between the anode 30 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 via the flow path 34 (the arrow in the figure indicates the direction of water flow), and the water is electrochemically oxidized to generate protons. The generated protons migrate to the cathode 20 via the electrolyte membrane 10. The substance to be hydrogenated in the electrolytic cell 1, specifically an organic compound with unsaturated bonds (toluene in Figure 1), is passed through the flow path 24 to the cathode 20 (the arrow in the figure indicates the direction of flow of the substance to be hydrogenated), and is electrochemically reduced and hydrogenated by the protons that have migrated through the electrolyte membrane 10.

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

The cathode catalyst layer 21 contains a reduction catalyst that uses protons transferred from the electrolyte membrane 10 to hydrogenate the target substance and produce an organic hydride. In FIG. 1, the reduction catalyst is designated by the reference symbol 21a. The reduction catalyst can be particles selected from the group consisting of Pt, Ru, Pd, Ir, and alloys containing at least one of these metals. The reduction catalyst can be a commercially available product or one synthesized according to a known method. The reduction catalyst can also be particles made of an alloy or intermetallic compound of at least one of the aforementioned precious metals Pt, Ru, Pd, and Ir with at least one selected from Cr, Mn, Fe, Co, Ni, Cu, Zn, Mo, Ru, Sn, W, Re, Pb, and Bi. The average particle size of the reduction catalyst is preferably 1 nm to 1 μm, and more preferably 1 nm to 5 nm. Setting the average particle size of the reduction catalyst to 1 μm or less increases the surface area per catalyst weight, thereby improving the reaction. Furthermore, by setting the average particle size of the reduction catalyst to 1 nm or more, it is possible to prevent a decrease in durability due to aggregation of catalyst particles.

The reduction catalyst is supported by a catalyst support made of an electron-conductive material. Supporting the reduction catalyst on the catalyst support increases the surface area of the cathode catalyst layer 21 and suppresses aggregation of the reduction catalyst. The electron conductivity of the catalyst support material is preferably 1.0×10 ⁻² S/cm or more. By making the electron conductivity of the electron-conductive material 1.0×10 ⁻² S/cm or more, electron conductivity can be more reliably imparted to the cathode catalyst layer 21.

The catalyst support can be, for example, an electron-conductive material containing porous carbon (such as mesoporous carbon), porous metal, or porous metal oxide as its main component. Examples of porous carbon include carbon blacks such as Ketjen Black (registered trademark), acetylene black, furnace black, and Vulcan (registered trademark).

The porous carbon preferably has a BET specific surface area of 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 1000 m ² /g, as measured by the nitrogen adsorption method. When the BET specific surface area of the porous carbon is 50 m ² /g or more, it becomes easier to uniformly support the reduction catalyst and more reliably diffuse the substance to be hydrogenated. Furthermore, when the BET specific surface area of the porous carbon is 1500 m ² /g or less, it becomes possible to suppress deterioration of the catalyst support during the reaction of the substance to be hydrogenated or during start-up or shutdown of the organic hydride production apparatus, and ultimately the catalyst support has sufficient durability. The average particle size of the carbon fine particles, such as carbon black, used as the catalyst support is preferably 0.01 μm to 1 μm.

Examples of porous metals include Pt black, Pd black, and fractally precipitated Pt metal. Examples of porous metal oxides include oxides of Ti, Zr, Nb, Mo, Hf, Ta, and W. Furthermore, porous metal compounds such as nitrides, carbides, oxynitrides, carbonitrides, and partially oxidized carbonitrides of metals such as Ti, Zr, Nb, Mo, Hf, Ta, and W (hereinafter referred to as porous metal carbonitrides, etc.) can also be used. The BET specific surface area of porous metals, porous metal oxides, and porous metal carbonitrides, measured by a nitrogen adsorption method, is preferably 1 m ² /g or more, more preferably 3 m ² /g or more, and even more preferably 10 m ² /g or more. By making the BET specific surface area of the porous metal, porous metal oxide, porous metal carbonitride, etc. 1 m ² /g or more, it becomes easier to uniformly support the reduction catalyst.

The catalyst support carrying the reduction catalyst is typically coated with an ionomer, thereby improving the ionic conductivity of the cathode 20. Examples of ionomers 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 even more preferably 1.2 to 2 meq/g. When the catalyst support is porous carbon, the mass ratio I/C of the ionomer (I) to the catalyst support (C) is preferably 0.1 to 2, more preferably 0.2 to 1.5, and even more preferably 0.3 to 1.1. A mass ratio I/C of 0.1 or greater ensures sufficient ionic conductivity. On the other hand, by keeping the mass ratio I/C at 2 or less, it is possible to prevent the ionomer coating thickness on the reduction catalyst from becoming excessive, thereby avoiding the inhibition of contact of the substance to be hydrogenated with the catalytic active sites.

It is preferable that the ionomer partially coat the reduction catalyst. This partial coating allows the three elements required for the electrochemical reaction in the cathode catalyst layer 21 - the substance to be hydrided, protons, and electrons - to be efficiently supplied to the reaction site.

The thickness of the cathode catalyst layer 21 is preferably 1 to 100 μm, and more preferably 5 to 30 μm. As the thickness of the cathode catalyst layer 21 increases, not only does the resistance to proton transfer increase, but the diffusibility of the substance to be hydrided also 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) that 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. The amount of ionomer added is preferably an amount that will result in a ratio of the mass of the ionomer to the mass of carbon in the catalyst component powder after drying of 1:10 to 10:1. The hydrophobic resin is in powder form, and its particle size is preferably 0.005 to 10 μm. A suitable solvent is added to the resulting mixture to prepare a catalyst ink.

The resulting catalyst ink is then applied to the surface of the microporous layer 22, dried, and then hot-pressed to adhere the cathode catalyst layer 21 to the microporous layer 22. Hot-pressing is preferably performed after the above-described application and drying steps have been performed multiple times. A homogeneous cathode catalyst layer 21 can be obtained by applying, drying, and hot-pressing the catalyst ink in this manner.

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. Alternatively, a composite of the cathode catalyst layer 21 and the electrolyte membrane 10 can be produced by spraying the catalyst ink onto one main surface of the electrolyte membrane 10 by spray coating and drying the solvent component in the catalyst ink. The catalyst ink is preferably applied so that the mass of the reduction catalyst 21a in the cathode catalyst layer 21 is 0.5 mg/ ^cm2 per electrode area.

The microporous layer 22 is provided so as to contact the main surface of the cathode catalyst layer 21 opposite the electrolyte membrane 10. The diffusion layer 23 is also provided so as to contact the main surface of the microporous layer 22 opposite the cathode catalyst layer 21.

The microporous layer 22 functions to promote the diffusion of the liquid substance to be hydrided and the organic hydride in the planar direction of the cathode catalyst layer 21. The microporous layer 22 has a basic composition containing conductive powder and a water repellent agent.

The conductive powder can be made of conductive carbon such as Vulcan (registered trademark). The water repellent can be made of fluororesin such as polytetrafluoroethylene (PTFE). The ratio of conductive powder to water repellent can be determined as appropriate within a range that achieves the 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. The microporous layer 22 can also be made of carbon cloth, carbon paper, or the like, similar to the diffusion layer 23.

In conventional cathodes, the microporous layer 22 is made of the conductive powder and water-repellent agent described above. In contrast, the cathode 20 of the present invention contains a hydrophilic porous oxide in addition to the conductive powder and water-repellent agent. In Figure 1, the hydrophilic porous oxide is designated by the reference symbol 22a.

The effect of the microporous layer 22 containing a hydrophilic porous oxide will be explained using Figure 2. Note that the same components in Figure 2 as those in Figure 1 are designated by the same reference numerals, and redundant explanations will be omitted below. Also, Figure 2 does not show the flow path 24 on the cathode 20 side and the flow path 34 on the anode 30 side, but it is assumed that non-hydride flows through the diffusion layer 23, and that water containing an electrolyte flows through the anode catalyst layer 31.

According to the inventors' research, with conventional cathodes, water (produced water) migrates from the anode 30 along with protons during operation of an organic hydride production apparatus, and this water that migrates to the cathode side accumulates in the cathode catalyst layer 21. It was discovered that the accumulation of water in the cathode catalyst layer 21 prevents the liquid substance to be hydrogenated from being supplied to the cathode catalyst layer 21, resulting in a decrease in power efficiency.

The inventors therefore conducted extensive research to prevent the accumulation of produced water in the cathode catalyst layer 21 and discovered that by including a hydrophilic porous oxide 22a in the microporous layer 22, 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 contains a hydrophilic porous oxide 22a and is able to improve power efficiency is thought to be that the hydrophilic porous oxide hydrophilizes part of the microporous layer 22, forming a path for water (produced water). This prevents the produced water from impeding the supply of the substance to be hydrogenated (e.g., toluene) to the cathode catalyst layer 21, as was the case in the past, and improves the supply, resulting in improved current efficiency.

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. A particle size of 0.5 μm or more, including secondary particles, ensures the formation of a water drainage path. A particle size of 10 μm or less ensures the formation of a water drainage path without adversely affecting the mean flow pore size of the microporous layer 22. A more preferred particle size is 1.0 to 5.0 μm.

The hydrophilic porous oxide 22a is preferably contained in the range of 5 to 15 mass% of the entire microporous layer. A content of 5 mass% or more can create a sufficient number of water discharge paths. A content of 15 mass% or less can provide a sufficient improvement in current efficiency. A more preferred content is 5 to 10 mass%, and an even more preferred content is 7 to 9 mass%.

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

The mean flow pore diameter (dm) of the microporous layer 22 after hot pressing is preferably 100 nm to 20 μm, and more preferably 500 nm to 5 μm. The mean flow pore diameter of the microporous layer 22 can be measured using a mercury porosimeter or the like. By setting the mean flow pore diameter to 100 nm or more, it is possible to more reliably prevent an increase in diffusion resistance due to an excessively large contact area between the pore wall surface and the liquid material to be hydrided and organic hydride. Furthermore, by setting the mean flow pore diameter to 20 μm or less, it is possible to more reliably prevent a decrease in fluidity due to a decrease in the suction of the liquid material to be hydrided and organic hydride by capillary action. Furthermore, by setting the mean flow pore diameter to 100 nm to 20 μm, it is possible to smoothly suction and discharge the liquid material to be hydrided and organic hydride by capillary action.

The thickness of the microporous layer 22 is preferably 1 to 50 μm, and more preferably 2 to 20 μm. If the microporous layer 22 is formed so that it sinks deeper than the surface of the diffusion layer 23, the thickness of the microporous layer 22 is defined as the average film thickness of the microporous layer 22 itself, including the portion submerged in the diffusion layer 23. A metal component may also be present on the surface of the microporous layer 22. This improves the electronic conductivity of the microporous layer 22 and makes it possible to achieve uniform current flow.

The microporous layer 22 and the diffusion layer 23, which will be described in detail later, are typically used with pressure applied in the thickness direction. Therefore, it is undesirable for the electrical conductivity of each layer in the thickness direction to change due to pressure applied in the thickness direction during use. For this reason, it is preferable to press the microporous layer 22 and the diffusion layer 23 in advance. This compresses the carbon material in each layer, thereby increasing and stabilizing the electrical conductivity of each layer in the thickness direction. It is also possible to achieve a cathode 20 with a stable filling rate of 20 to 50%.

Increasing 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. This improved degree of bonding also improves the ability to supply raw materials and remove product materials. Hot pressing when forming the cathode catalyst layer 21 on the surface of the microporous layer 22 also contributes to improving the degree of bonding. After forming the cathode catalyst layer 21 on the surface of the microporous layer 22, the cathode catalyst layer 21 and the microporous layer 22 can also be pressed together, which is expected to improve the degree of bonding. Known pressing devices such as hot presses and hot rollers can be used as pressing devices. Pressing conditions are preferably a temperature of room temperature to 360°C and a pressure of 0.1 to 5 MPa.

The diffusion layer 23 functions to uniformly diffuse the liquid substance to be hydrogenated supplied from the flow path 24 into the cathode catalyst layer 21. The material constituting the diffusion layer 23 preferably has a high affinity for the substance to be hydrogenated. Examples of materials constituting the diffusion layer 23 include porous conductive substrates and sintered fiber compacts. These are preferred because they have porosity suitable for the supply and removal of 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. Furthermore, the electronic conductivity of the material constituting the diffusion layer 23 is preferably 10 ⁻² S/cm or higher.

Specific examples of materials that can be used to form the diffusion layer 23 include woven carbon fabric (carbon cloth), nonwoven carbon fabric, and carbon paper. Carbon cloth is made by bundling hundreds of thin carbon fibers with diameters of a few micrometers together and then woven into a fabric. Carbon paper is made by sintering raw carbon fiber fibers, which are then turned into a thin film precursor using a papermaking method.

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

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

The catalyst may be dispersed or coated on an electronically conductive metal substrate. Examples of such metal substrates include metal fibers (fiber diameter: e.g., 10-30 μm), mesh (mesh diameter: e.g., 500-1000 μm), sintered porous metals, foamed molded bodies, and expanded metals, all composed of metals such as Ti, Cr, Mn, Fe, Co, Ni, Cu, Zn, Nb, Mo, Ta, and W, or alloys primarily composed of these metals. The substrate used for the anode catalyst layer 31 is preferably a plate-shaped material with a thickness of 0.1-2 mm, as it has sufficient electrical conductivity and mechanical strength to pass the current required for electrolysis. Furthermore, the substrate is preferably porous and highly corrosion-resistant to the anode fluid, in order to avoid increased resistance due to air bubbles and promote the supply of the anode fluid. Titanium expanded mesh is commonly used as such a substrate. The center-to-center distance in the short direction of the expanded mesh is preferably 0.1 to 4 mm, the center-to-center distance in the long direction is preferably 0.1 to 4 mm, and the opening rate is preferably approximately 30 to 70%.

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

[Electrolytic cell]
The electrolysis cell 1 includes the above-described membrane electrode assembly 40 and a pair of end plates sandwiching the membrane electrode assembly 40. The end plates are not shown in FIG. 1 . One of the pair of end plates is located further outward from the flow path 24 of the cathode 20 as viewed from the membrane electrode assembly 40, and the other of the pair of end plates is located further outward from the flow path 34 of the anode 30 as viewed from the membrane electrode assembly 40. The end plate on the cathode 20 side can be shaped to form a part of the flow path 24 of the cathode 20. The end plate on the anode 30 side can be shaped to form a part of the flow path 34 of the anode 30.

[Organic hydride manufacturing equipment]
The organic hydride manufacturing apparatus includes the electrolytic cell 1. In addition, the apparatus may be equipped with, as necessary, a cathode fluid tank for storing the material to be hydrogenated to be supplied to the cathode 20, a pump and circulation path for supplying a liquid from the cathode fluid tank to the cathode 20 and recovering the organic hydride and the unreacted material to be hydrogenated in the cathode fluid tank, a separation tank provided in the circulation path for separating the organic hydride from the unreacted material to be hydrogenated, an anolyte tank for storing water containing an electrolyte to be supplied to the anode 30, a pump and circulation path for supplying a liquid to the anode 30 and recovering the unreacted liquid in the anolyte tank, a DC power supply for applying a voltage to the electrolytic cell 1, and the like.

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 undergoing hydrogenation/dehydrogenation reactions. A wide range of organic hydrides can be used, including acetone-isopropanol, benzoquinone-hydroquinone, and aromatic hydrocarbons. Of these, aromatic hydrocarbons, such as toluene-methylcyclohexane, are preferred from the standpoints of transportability during energy transport, toxicity, safety, storage stability, etc., as well as energy conversion efficiency, such as the amount of hydrogen that can be transported per volume or mass, ease of hydrogenation and dehydrogenation reactions, and a modest Gibbs free energy change.

The aromatic hydrocarbon compound used as the dehydrogenated product of the organic hydride is a compound containing at least one aromatic ring, such as benzene, alkylbenzene, naphthalene, alkylnaphthalene, anthracene, and diphenylethane. Alkylbenzenes include compounds in which one to four hydrogen atoms on the aromatic ring are substituted with a linear or branched alkyl group having one to six carbon atoms, such as toluene, xylene, mesitylene, ethylbenzene, and diethylbenzene. Alkylnaphthalenes include compounds in which one to four hydrogen atoms on the aromatic ring are substituted with a linear or branched alkyl group having one to six 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. Nitrogen-containing heterocyclic aromatic compounds such as pyridine, pyrimidine, pyrazine, quinoline, isoquinoline, N-alkylpyrrole, N-alkylindole, and N-alkyldibenzopyrrole can also be used as the dehydrogenated product.

The electrolyte-containing water used in organic hydride production equipment and supplied to the anode 30 may be ion-exchanged water, pure water, or an aqueous solution of these with an acid such as sulfuric acid, phosphoric acid, nitric acid, or hydrochloric acid added. The ionic conductivity is preferably 0.01 S/cm or higher when measured at 20°C. By ensuring an ionic conductivity of 0.01 S/cm or higher, an electrochemical reaction sufficient for industrial use can be generated.

[Method for producing organic hydride]
An organic hydride can be produced using the organic hydride production apparatus. Since the microporous layer 22 in the cathode 20 of the electrolysis cell 1 of the organic hydride production apparatus contains the hydrophilic porous oxide 22a, the organic hydride can be produced with good current efficiency.

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

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 ball milled at 333 rpm for 20 minutes and then at 227 rpm for 10 minutes.
Once the pot is removed,
0.92 g of PTFE dispersion (Mitsui DuPont Fluorochemicals, 31-JR)
The mixture was then ball milled again at 333 rpm for 20 minutes and at 227 rpm for 10 minutes to obtain a paste.

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

The carbon paper coated with the microporous layer was placed in a petri dish and immersed in 60-70 mL of methanol for 20 minutes to remove the polyoxyethylene (10) octylphenyl ether. This process was repeated six times. The carbon paper was then dried at 50°C for 30 minutes using a dryer. The microporous layer containing diatomaceous earth was then prepared using a muffle furnace for 5 minutes at 300°C.
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 produced using the same raw materials and steps as those for producing the microporous layer described above, except that diatomaceous earth was not prepared as a raw material.
As a conventional example, commercially available carbon paper with a microporous layer (carbon paper (Toray, TGP-H-090H)) and a microporous layer (Chemics, water repellency rate 20% (carbon: polytetrafluoroethylene = 80%: 20%)) were prepared.

<Preparation of MEA>
The microporous layers of the above-mentioned Example 1, Example 2, Comparative Example, and Conventional Example, the cathode catalyst layer described below, and the electrolyte layer were stacked and tightly attached to each other to prepare MEAs.

(Preparation of cathode catalyst layer)
2 mL of 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 _NaBH4 was placed in a petri dish, dissolved in pure water, and pure water was added to the dish up to about 80% of its height. Carbon paper was immersed in this and left for 2 hours. The water was then replaced with pure water and left for about 12 hours.
The carbon paper was removed from the dish and dried for about 5 minutes in a dryer at 50° C. Thereafter, the amount of platinum supported on the carbon paper was measured using XRF.

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

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

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

Nafion 117 as an electrolyte membrane was cut into ^{a size} of 15 x 15 cm2, and one side was polished with 2000 grit emery paper.
The unpolished surface of the Nafion 117 was placed in contact with the catalyst ink-coated surface of the carbon paper, and two 0.1 mm thick polytetrafluoroethylene sheets were sandwiched between each side. The resulting mixture was hot pressed at 120°C, 15 MPa, and 5 minutes to bond the electrolyte membrane and the carbon paper on which the cathode catalyst layer was formed.

<Electrochemical measurements>
An electrolytic cell was assembled using the obtained MEA, and the electrochemical properties were investigated.
[Electrolytic cell conditions]
Anode end plate: made of Ti, parallel flow channels Cathode end plate: _made of Ti, no flow channels Anode electrolyte: 1M _H2SO4
Cathode electrolyte: 10% toluene (to methylcyclohexane)
Anode electrode: DSE for anodic 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

[Experimental conditions]
Cell temperature: 60°C
Flow rate: 10 mL/min for both anode and cathode

[Preprocessing]
1M _H2SO4 was supplied to the anode side at 10 mL/min, _and 10% toluene was supplied to the cathode side at 10 mL/min, and circulated for 1 hour. Thereafter, constant current electrolysis was carried out at 0.4 A/ ^cm2 for 1 hour.

[Measurement of produced water volume]
After circulating at 10 mL/min for 20 min, constant current electrolysis was carried out at 0.4 A/ ^cm² for 20 min. The produced water accumulated in the cathode reservoir was collected with a Pasteur pipette and its weight was measured. These operations were repeated at 0.3 A/ ^cm² , 0.2 A/ ^cm² , and 0.1 A/ ^cm² .

[AC impedance measurement]
At each voltage of 0.6V, 1.0V, 1.3V, 1.5V, 1.6V, 1.7V, 1.8V and 1.85V, a 3-minute constant voltage measurement and a 1-minute AC impedance measurement at an AC amplitude of 10 mV and a measurement frequency of 105 to 10 ⁻¹ Hz were performed.

[Current efficiency measurement]
Constant-voltage electrolysis was carried out at an appropriate voltage between 0 V and 1.5 to 1.85 V, the current value after 3 minutes was recorded, and the solution coming out of the cathode outlet was allowed to flow through the current efficiency measurement line, as shown in Figure 3, which shows the organic hydride production apparatus used in the experiment. The time until this line was filled and the current value at that time were recorded, and the amount of solution accumulated in the line was measured.
The current efficiency was calculated using Faraday's law from the volume ratio of _H2 produced by the side reaction.

4 and 5 are graphs with the horizontal axis representing current density and the vertical axis representing cell voltage. As can be seen from Figures 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 Conventional Example.
Figure 6 shows a graph with the current density on the horizontal axis and the amount of produced water on the vertical axis. As can be seen from Figure 6, Example 1, which contains 8% by mass of diatomaceous earth in the microporous layer, shows almost no difference from the Comparative Example and Conventional Example.

Figure 7 shows a graph with current density on the horizontal axis and current efficiency on the vertical axis. Figure 7 shows that Examples 1 and 2, which contain diatomaceous earth in the microporous layer, have significantly improved current efficiency compared to the comparative example and commercially available conventional examples that do not contain diatomaceous earth. In particular, Example 1, which contains 8% by mass of diatomaceous earth, had superior current efficiency even compared to the example containing 16% by mass of diatomaceous earth.

REFERENCE SIGNS LIST 1 Organic hydride manufacturing apparatus 10 Electrolyte membrane 20 Cathode 21 Cathode catalyst layer 21a Reduction catalyst 22 Microporous layer 22a Hydrophilic porous oxide 23 Diffusion layer 24 Flow path 30 Anode 31 Anode catalyst layer 40 Membrane electrode assembly

Claims (4)

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