Cathode, membrane electrode assembly and organic hydride production device

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

[Technical Field]

[0001] The present invention relates to a cathode for an organic hydride manufacturing apparatus, a membrane electrode assembly, and an organic hydride manufacturing apparatus. [Background technology]

[0002] 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.

[0003] One method for storing and transporting hydrogen is to use organic hydrides, that is, to hydrogenate hydrogen gas with aromatic hydrocarbons such as toluene to produce cyclic saturated hydrocarbons such as methylcyclohexane, store and transport these cyclic saturated hydrocarbons, and generate hydrogen at the consumption site by dehydrogenating the cyclic saturated hydrocarbons using a catalyst.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.

[0004] A technology has been developed for producing organic hydrides that uses water as a raw material, rather than hydrogen obtained by electrolysis of water, to hydrogenate aromatic hydrocarbons such as toluene through an electrochemical reaction with water to obtain cyclic saturated hydrocarbons such as methylcyclohexane. The hydrogenation device for organic compounds used in this technology includes an oxidation vessel containing water containing an electrolyte, a reduction vessel containing an organic compound having 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 having an unsaturated bond (see, for example, Patent Document 1).

[0005] 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). [Prior art documents] [Patent documents]

[0006] [Patent Document 1] International Publication No. 2012 / 091128 [Patent Document 2] Japanese Patent Application Publication No. 2018-31046 Summary of the Invention [Problem to be solved by the invention]

[0007] There is a continuing demand for improved power efficiency in organic hydride manufacturing equipment, and there is a demand for organic hydrides to be manufactured with higher power efficiency than ever before.

[0008] The present invention has been made to meet the above-mentioned demands, and an object of the present invention is to provide a cathode for an organic hydride production apparatus that can produce organic hydride with high power efficiency, a membrane electrode assembly including the cathode, and an organic hydride production apparatus. [Means for solving the problem]

[0009] 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. [Effects of the Invention]

[0010] According to the cathode of the present invention, organic hydride can be produced with good power efficiency in an organic hydride production apparatus. [Brief explanation of the drawings]

[0011] [Figure 1] 1 is a schematic diagram showing a main part of an organic hydride manufacturing apparatus according to the present invention. [Figure 2] 1A and 1B are diagrams illustrating the effects of the cathode of the present invention. [Figure 3] FIG. 1 is a schematic diagram showing an organic hydride production apparatus used in an experiment. [Figure 4] 1 is a graph showing the relationship between current density and cell voltage. [Figure 5] 1 is a graph showing the relationship between current density and cell voltage. [Figure 6] 1 is a graph showing the relationship between current density and the amount of produced water. [Figure 7] 1 is a graph showing the relationship between current density and current efficiency. DETAILED DESCRIPTION OF THE INVENTION

[0012] Hereinafter, embodiments of the cathode of an organic hydride manufacturing apparatus, the membrane electrode assembly, and the organic hydride manufacturing apparatus of the present invention will be described with reference to the drawings.

[0013] Fig. 1 shows a schematic diagram of the main components of an organic hydride production apparatus of the present invention. In Fig. 1, the electrolysis cell 1 includes 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 adjusting the power may be connected to the electrolyte membrane 10.

[0014] Water containing an electrolyte is passed through flow path 34 to anode 30 (the flow direction of the water is indicated by an arrow in the figure), and the water is electrochemically oxidized to generate protons. The generated protons move to cathode 20 through electrolyte membrane 10. A substance to be hydrogenated in electrolysis cell 1, specifically an organic compound having an unsaturated bond (toluene in FIG. 1), is passed through flow path 24 to cathode 20 (the flow direction of the substance to be hydrogenated is indicated by an arrow in the figure), and is electrochemically reduced and hydrogenated by the protons that have moved through electrolyte membrane 10.

[0015] [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.

[0016] The cathode catalyst layer 21 includes a reduction catalyst for hydrogenating a substance to be hydrogenated with protons transferred from the electrolyte membrane 10 to produce an organic hydride. In FIG. 1, the reduction catalyst is designated by the reference symbol 21a. The reduction catalyst may be particles selected from the group consisting of, for example, Pt, Ru, Pd, Ir, and alloys containing at least one of these metals. The reduction catalyst may be a commercially available product or one synthesized according to a known method. Alternatively, the reduction catalyst may be particles made of an alloy or intermetallic compound of at least one of the above-mentioned noble 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, 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 catalyst weight can be increased, 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.

[0017] The reduction catalyst is supported by a catalyst support made of an electron-conductive material. By supporting the reduction catalyst on the catalyst support, the surface area of ​​the cathode catalyst layer 21 can be increased 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. The electronic conductivity of the electronic conductive material is 1.0×10 -2 By making the conductivity S / cm or more, electron conductivity can be more reliably imparted to the cathode catalyst layer 21.

[0018] The catalyst support may be an electron-conductive material containing, as a main component, porous carbon (such as mesoporous carbon), porous metal, or porous metal oxide. Examples of porous carbon include carbon black such as Ketjen Black (registered trademark), acetylene black, furnace black, and Vulcan (registered trademark).

[0019] The porous carbon preferably has a BET specific surface area of ​​50 m2 or less as measured by nitrogen adsorption. 2 / g~1500m 2 / g, more preferably 500m 2 / g~1300m 2 / g, and more preferably 700m 2 / g~1000m 2 / g. The BET specific surface area of ​​the porous carbon is 50m 2 / g or more, the reduction catalyst can be more easily supported uniformly and the substance to be hydrogenated can be more reliably diffused. 2 / g or less, deterioration of the catalyst support can be suppressed during the reaction of the substance to be hydrogenated or during start-up or shutdown of the organic hydride manufacturing apparatus, and ultimately the catalyst support will have 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.

[0020] 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 porous metals, porous metal oxides, and porous metal carbonitrides preferably have a BET specific surface area of ​​1 m or less as measured by a nitrogen adsorption method. 2 / g or more, and more preferably 3m 2 / g or more, more preferably 10m2 / g or more. The BET specific surface area of ​​porous metals, porous metal oxides, porous metal carbonitrides, etc. is 1m 2 By setting the carrier content to 1 / g or more, it is easy to uniformly support the reduction catalyst.

[0021] The catalyst carrier carrying the reduction catalyst is usually coated with an ionomer. This can improve the ionic conductivity of the cathode 20. 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 even 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 even more preferably 0.3 to 1.1. A mass ratio I / C of 0.1 or more can more reliably obtain sufficient ionic conductivity. On the other hand, by making the mass ratio I / C 2 or less, it is possible to prevent the coating thickness of the ionomer on the reduction catalyst from becoming excessive, thereby avoiding the inhibition of contact of the substance to be hydrogenated with the catalytic active sites.

[0022] It is preferable that the ionomer partially coats the reduction catalyst, which allows the three elements necessary for the electrochemical reaction in the cathode catalyst layer 21, i.e., the substance to be hydrided, protons, and electrons, to be efficiently supplied to the reaction field.

[0023] The thickness of the cathode catalyst layer 21 is preferably 1 to 100 μm, and more preferably 5 to 30 μm. When 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 hydrogenated also decreases. For this reason, it is desirable to adjust the thickness of the cathode catalyst layer 21 within the above-mentioned range.

[0024] 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 such that the ratio of the mass of the ionomer to the mass of carbon in the catalyst component powder after drying 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 suitable solvent is added to the resulting mixture to prepare a catalyst ink.

[0025] Next, the obtained catalyst ink is applied to the surface of the microporous layer 22, dried, and then hot-pressed to fix the cathode catalyst layer 21 to the microporous layer 22. The hot-pressing is preferably carried out after the above-mentioned application and drying steps have been carried out multiple times. A homogeneous cathode catalyst layer 21 can be obtained by applying, drying, and hot-pressing the catalyst ink in this manner.

[0026] 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 then drying the solvent component in the catalyst ink. The catalyst ink is used in such a manner that the mass of the reduction catalyst 21a in the cathode catalyst layer 21 is 0.5 mg / cm per electrode area. 2 It is preferable to apply the solution so that the thickness becomes

[0027] The microporous layer 22 is provided so as to be in contact with the main surface of the cathode catalyst layer 21 opposite to the electrolyte membrane 10. The diffusion layer 23 is provided so as to be in contact with the main surface of the microporous layer 22 opposite to the cathode catalyst layer 21.

[0028] The microporous layer 22 has a function of promoting the diffusion of the liquid substance to be hydrided and the organic hydride in the surface direction of the cathode catalyst layer 21. The microporous layer 22 has a basic composition containing a conductive powder and a water repellent agent.

[0029] The conductive powder may be, for example, conductive carbon such as Vulcan (registered trademark). The water repellent may be, for example, fluororesin such as polytetrafluoroethylene (PTFE). The ratio of the conductive powder to the water repellent is determined appropriately 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 may also be made of carbon cloth, carbon paper, or the like, similar to the diffusion layer 23.

[0030] 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.

[0031] 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 denoted 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 a non-hydride flows through the diffusion layer 23, and that water containing an electrolyte flows through the anode catalyst layer 31.

[0032] According to research by the present inventors, in a conventional cathode, when an organic hydride manufacturing apparatus is in operation, water (produced water) moves from the anode 30 together with protons, and this water that moves to the cathode side accumulates in the cathode catalyst layer 21. It was found 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.

[0033] Therefore, the inventors 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.

[0034] The reason why the microporous layer 22 can improve power efficiency by including the hydrophilic hydrophilic porous oxide 22a is that the hydrophilic porous oxide hydrophilizes part of the microporous layer 22, forming a discharge path for water (produced water). As a result, the produced water is prevented from impeding the supply of the substance to be hydrogenated (e.g., toluene) to the cathode catalyst layer 21, as in the conventional case, and the supply can be improved, resulting in an improvement in current efficiency.

[0035] 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. When the particle size, including secondary particles, is 0.5 μm or more, a water discharge path can be reliably formed. When the particle size is 10 μm or less, a water discharge path can be formed 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.

[0036] 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 form 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 %.

[0037] The microporous layer 22 can be formed by applying a paste obtained 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.

[0038] 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.

[0039] The thickness of the microporous layer 22 is preferably 1 to 50 μm, and more preferably 2 to 20 μm. When the microporous layer 22 is formed so as to sink 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 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.

[0040] 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 in the thickness direction during use. Therefore, it is preferable to pre-press the microporous layer 22 and the diffusion layer 23. This compresses the carbon material in each layer, thereby increasing and stabilizing the electrical conductivity of each layer in the thickness direction. Furthermore, a cathode 20 with a stable filling rate of 20 to 50% can be achieved.

[0041] Improving the bonding strength between the cathode catalyst layer 21 and the microporous layer 22 also contributes to improving the conductivity of the cathode 20. This improved bonding strength also improves the ability to supply raw materials and remove generated materials. Hot pressing when forming the cathode catalyst layer 21 on the surface of the microporous layer 22 also contributes to improving the bonding strength. 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 be pressed together, which is expected to improve the bonding strength. Known pressing devices such as hot presses and hot rollers can be used as the pressing device. The pressing conditions are preferably a temperature of room temperature to 360°C and a pressure of 0.1 to 5 MPa.

[0042] 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 bodies. These are preferred because they have porosity suitable for supplying and removing gases and liquids 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. In addition, the electronic conductivity of the material constituting the diffusion layer 23 is preferably 10 -2 S / cm or more.

[0043] More specific examples of materials constituting 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 several μm and then woven into fabric. Carbon paper is made by sintering a thin film precursor made from raw carbon fiber using a papermaking method.

[0044] [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.

[0045] 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 generate 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.

[0046] The catalyst may be dispersed and supported on or coated on an electronically conductive metal substrate. Examples of such metal substrates include metal fibers (fiber diameter: e.g., 10 to 30 μm), meshes (mesh diameter: e.g., 500 to 1000 μm), sintered porous metals, foamed molded bodies, and expanded metals, all of which are made of metals such as Ti, Cr, Mn, Fe, Co, Ni, Cu, Zn, Nb, Mo, Ta, and W, or alloys containing these metals as their main components. The substrate used for the anode catalyst layer 31 is preferably a plate-shaped material with a thickness of 0.1 to 2 mm, from the viewpoints of sufficient electrical conductivity and mechanical strength to pass the current required for electrolysis. Furthermore, the substrate is preferably porous and has excellent corrosion resistance against the anode electrolyte, in order to avoid increased resistance due to bubbles and promote the supply of the anode electrolyte. Titanium expanded mesh is commonly used as such a substrate. The expanded mesh preferably has a center-to-center distance in the short direction of 0.1 to 4 mm, a center-to-center distance in the long direction of 0.1 to 4 mm, and an opening rate of about 30 to 70%.

[0047] [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 a hydrophilic porous oxide 22a in the microporous layer 22, which improves current efficiency.

[0048] [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 disposed outward of 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 disposed outward of 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.

[0049] [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.

[0050] 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, and a wide range of organic hydrides can be used, such as acetone-isopropanol, benzoquinone-hydroquinone, aromatic hydrocarbons, etc. Among these, aromatic hydrocarbons, typified by toluene-methylcyclohexane, are preferred from the viewpoints 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 not-significantly large Gibbs free energy change.

[0051] 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 1 to 4 hydrogen atoms of the aromatic ring are substituted with a linear or branched alkyl group having 1 to 6 carbon atoms, such as toluene, xylene, mesitylene, ethylbenzene, and diethylbenzene. Alkylnaphthalenes include compounds in which 1 to 4 hydrogen atoms of the aromatic ring are substituted with a linear or 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. Nitrogen-containing heterocyclic aromatic compounds such as pyridine, pyrimidine, pyrazine, quinoline, isoquinoline, N-alkylpyrrole, N-alkylindole, and N-alkyldibenzopyrrole may also be used as the dehydrogenated product.

[0052] The water containing the electrolyte used in the organic hydride manufacturing apparatus 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 thereto. The ionic conductivity is preferably 0.01 S / cm or more when measured at 20°C. By ensuring that the ionic conductivity is 0.01 S / cm or more, an electrochemical reaction sufficient for industrial applications can be generated.

[0053] [Method for producing organic hydrides] 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, organic hydride can be produced with good current efficiency. [Example]

[0054] <Fabrication of microporous layer> As a raw material for the microporous layer, 2g and 1.78g of Ketjenblack (Lion Corporation, EC-300J) Diatomaceous earth (MP Biomedicals, Inc., 157607) 0.222g, 0.444g 18g 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, 0.222g and 0.444g. This was to observe the difference in properties due to the difference in the blending ratio of diatomaceous earth in the microporous layer. The amount of Ketjen black was adjusted so that the blending ratio of diatomaceous earth was 8% by mass and 16% by mass.

[0055] These raw materials and zirconia beads (φ5 mm×40, φ10 mm×8) were placed in a 100 mL polytetrafluoroethylene ball mill pot 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 (manufactured by Mitsui DuPont Fluorochemicals, 31-JR) was added. The mixture was ball-milled again at 333 rpm for 20 min and then at 227 rpm for 10 min to obtain a paste.

[0056] Carbon paper (manufactured by Toray, TGP-H-090H) to be the diffusion layer of the cathode was prepared. This carbon paper was cut into 10.5×10.5 cm 2 and masked with 0.1 mm thick aluminum foil with holes of 10×10 cm 2 The above paste was applied using a bar coater. Then, it was dried at 60 °C for 60 min using a dryer.

[0057] The carbon paper with the micro-porous layer applied and formed in this way was placed in a petri dish and immersed in 60 - 70 mL of methanol for 20 min to remove polyoxyethylene (10) octyl phenyl ether. This was repeated 6 times. Then, it was dried at 50 °C for 30 min using a dryer. Further, it was dried at 300 °C for 5 min using a muffler furnace to prepare the micro-porous layer of the example containing diatomaceous earth. The ratios of diatomaceous earth in the two types of micro-porous layers with different amounts of diatomaceous earth were 8 mass% (Example 1) and 16 mass% (Example 2), respectively.

[0058] As a comparative example, a micro-porous layer was prepared using the same raw materials and processes as the above micro-porous layer manufacturing process without preparing diatomaceous earth as a raw material. As a conventional example, commercially available carbon paper with a micro-porous layer (carbon paper (manufactured by Toray, TGP-H-090H)), micro-porous layer (manufactured by Chemix, water repellency 20% (carbon: polytetrafluoroethylene = 80%: 20%)) was prepared.

[0059] <Fabrication of MEA> The micro-porous layers of the above Example 1, Example 2, comparative example, and conventional example were stacked and adhered closely with the cathode catalyst layer and electrolyte layer described below to fabricate a MEA.

[0060] (Fabrication of cathode catalyst layer) 2 mL of 0.004 g / mL H2PtCl6·6H2O aqueous solution and 1-propanol were dropped onto carbon paper and dried for 1 h. 0.04g 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 approximately 5 minutes in a dryer at 50°C, after which the amount of platinum supported on the carbon paper was measured using XRF.

[0061] As the raw material for the cathode catalyst layer, 0.6g of fuel cell catalyst (Tanaka Kikinzoku, TEC61E54) 0.72g of purified water ·4.568g of Nafion dispersion 5 mass%, 4.8g of 1-propanol, Each one was prepared.

[0062] 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.

[0063] 10 x 10 cm on the above carbon paper 2 The cathode catalyst layer was prepared by masking with 0.45 mm thick aluminum foil having holes therein and applying the above catalyst ink with a bar coater.

[0064] The electrolyte membrane was Nafion117, 15 x 15 cm 2 The pieces were cut into pieces 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 two sheets were then 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.

[0065] <Electrochemical measurements> The obtained MEA was used to assemble an electrolysis cell, and its electrochemical properties were investigated. [Electrolytic cell conditions] Anode end plate: Ti, parallel flow path Cathode end plate: Ti, no flow path Anodic electrolyte: 1M H2SO4 Cathode electrolyte: 10% toluene (to methylcyclohexane) Anode electrode: DSE for anodic oxygen evolution Membrane cathode assembly (MEA): electrolyte membrane Nafion 117 + cathode 0.5-0.7 mg / cm 2 PtRu / C (TEC61E54 manufactured by TKK), N / C=0.8 Electrode area: 100cm 2

[0066] [Experimental conditions] Cell temperature: 60℃ Flow rate: 10 mL / min for both anode and cathode

[0067] [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. The mixture was circulated for 1 hour. After that, the flow rate was 0.4 A / cm 2 Constant current electrolysis was carried out at 40°C for 1 hour.

[0068] [Measurement of produced water volume] After circulating at 10 mL / min for 20 min, the flow rate was 0.4 A / cm 2 Constant current electrolysis was carried out for 20 min at 0.3 A / cm. At this time, the produced water accumulated in the reservoir on the cathode side was taken with a Pasteur pipette and its weight was measured. These operations were carried out at 0.3 A / cm. 2 , 0.2A / cm 2 , 0.1A / cm 2 repeated.

[0069] [AC impedance measurement] At each voltage of 0.6V, 1.0V, 1.3V, 1.5V, 1.6V, 1.7V, 1.8V, and 1.85V, constant voltage measurement was performed for 3 minutes, and the AC amplitude was 10mV and the measurement frequency was 105-10 -1 AC impedance measurements were performed at 100 Hz for 1 minute.

[0070] [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 coming out of the cathode outlet was passed 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 in the side reaction.

[0071] 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 contains 8% by mass of diatomaceous earth in the microporous layer, and the Comparative Example and Conventional Example. Figure 6 shows a graph with the horizontal axis representing current density and the vertical axis representing the amount of produced water. Figure 6 shows that Example 1, which contains 8% by mass of diatomaceous earth in the microporous layer, showed almost no difference from the Comparative Example and Conventional Example.

[0072] 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 compared to the example containing 16% by mass of diatomaceous earth. [Explanation of symbols]

[0073] 1. Organic hydride production equipment 10 Electrolyte membrane 20 cathode 21 Cathode catalyst layer 21a Reduction catalyst 22 Microporous layer 22a Hydrophilic porous oxide 23 Diffusion Layer 24 flow paths 30 anodes 31 Anode catalyst layer 40 Membrane electrode assembly

Claims

1. 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.

2. 10. The cathode of claim 1, wherein the hydrophilic porous oxide comprises diatomaceous earth.

3. 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:

4. An organic hydride manufacturing apparatus comprising the cathode according to claim 1 or 2 or the membrane electrode assembly according to claim 3.

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