Cathode catalyst layer, organic hydride production apparatus, and method for preparing cathode catalyst ink.

Abstract

This cathode catalyst layer 10 comprises: a cathode catalyst which hydrogenates an object to be hydrogenated; and a water repellent agent which has a higher affinity for the object to be hydrogenated and for an organic hydride than for water, and which is composed of aggregates of arbitrary primary particles. The volume fraction of the water repellent agent in the cathode catalyst layer is more than 10 vol% with respect to the volume of the total solid content of the cathode catalyst layer.

Description

[Technical Field]

[0001] The present invention relates to a cathode catalyst layer, an organic hydride production apparatus, and a method for preparing cathode catalyst ink. [Background technology]

[0002] In recent years, the use of renewable energy sources such as solar, wind, hydroelectric, and geothermal power generation has been anticipated as a way to reduce carbon dioxide emissions during energy production. For example, a system has been devised that uses electricity derived from renewable energy to electrolyze water and produce hydrogen. Furthermore, organic hydride systems are attracting attention as energy carriers for the large-scale transportation and storage of hydrogen derived from renewable energy.

[0003] Regarding the technology for producing organic hydrides, an organic hydride production apparatus is known that comprises an oxidation electrode that generates protons from water and a reduction electrode that hydrogenates organic compounds having unsaturated bonds (see, for example, Patent Document 1). In this organic hydride production apparatus, water is supplied to the oxidation electrode and the substance to be hydrogenated is supplied to the reduction electrode, and an electric current is passed between the oxidation electrode and the reduction electrode, thereby adding hydrogen to the substance to be hydrogenated and producing an organic hydride. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] International Publication No. 2012 / 091128 [Overview of the project] [Problems that the invention aims to solve]

[0005] As a result of diligent research into the above-mentioned organic hydride manufacturing technology, the inventors have come to recognize that there is room to improve the Faraday efficiency (current efficiency) of the organic hydride manufacturing apparatus in the conventional technology.

[0006] This invention has been made in view of these circumstances, and one of its objectives is to provide a technology to improve the Faraday efficiency of an organic hydride production apparatus. [Means for solving the problem]

[0007] One aspect of the present invention is a cathode catalyst layer that hydrogenates a hydride with protons to produce an organic hydride. This cathode catalyst layer comprises a cathode catalyst that hydrogenates the hydride and a water-repellent agent that has a higher affinity for the hydride and the organic hydride than for water and is composed of aggregates of arbitrary primary particles. The volume fraction of the water-repellent agent in the cathode catalyst layer is greater than 10 vol% of the total volume of solids in the cathode catalyst layer.

[0008] Another aspect of the present invention is an organic hydride production apparatus. This apparatus comprises an electrolyte membrane having a first surface and a second surface facing each other and for transferring protons; a cathode provided on the first surface side of the electrolyte membrane and having a cathode catalyst layer as described above; and an anode provided on the second surface side of the electrolyte membrane and oxidizing water to generate protons.

[0009] Another aspect of the present invention is a method for preparing a cathode catalyst ink used in a cathode catalyst layer that hydrogenates a hydride with a proton to produce an organic hydride. This method includes preparing a first solution by mixing a cathode catalyst and a solvent, preparing a second solution by adding to the first solution a dispersion of arbitrary primary particles in an amount such that the volume fraction of the water repellent in the cathode catalyst layer is greater than 10 vol% of the total volume of solids in the cathode catalyst layer, and agglomerating the primary particles in the second solution to form a water repellent composed of aggregates of primary particles, which has a higher affinity for the hydride and organic hydride than for water.

[0010] Any combination of the above components, as well as any conversion of the expressions of this disclosure between methods, apparatus, systems, etc., are also valid forms of this disclosure. [Effects of the Invention]

[0011] According to the present invention, the Faraday efficiency of an organic hydride production apparatus can be improved. [Brief explanation of the drawing]

[0012] [Figure 1] This is a cross-sectional view of an organic hydride production apparatus according to an embodiment. [Figure 2] Figure 2(a) is an SEM image of the surface of the cathode catalyst layer according to Example 1. Figure 2(b) is an SEM image of the cross-section of the cathode catalyst layer according to Example 1. [Figure 3] Figure 3 shows an SEM image of the surface of the cathode catalyst layer according to Comparative Example 1. [Figure 4] Figure 4(a) is an SEM image of the surface of the cathode catalyst layer according to Comparative Example 2. Figure 4(b) is an SEM image of the cross-section of the cathode catalyst layer according to Comparative Example 2. [Figure 5] Figure 5(a) is an SEM image of the surface of the cathode catalyst layer according to Comparative Example 3. Figure 5(b) is an SEM image of the cross-section of the cathode catalyst layer according to Comparative Example 3. [Figure 6] This figure shows the relationship between the toluene concentration in the cathode solution and the Faraday efficiency of the organic hydride production apparatus. [Figure 7] This figure shows the properties of the cathode catalyst layer and the performance of the organic hydride production apparatus in Test Examples 1 to 23. [Modes for carrying out the invention]

[0013] Hereinafter, the present invention will be described with reference to the drawings based on preferred embodiments. The embodiments are illustrative and do not limit the invention. Not all features and combinations thereof described in the embodiments are necessarily essential to the invention. The same or equivalent components, members, and processes shown in each drawing are denoted by the same reference numerals, and redundant descriptions will be omitted as appropriate. In addition, the scales and shapes of the respective parts shown in each figure are set for convenience in order to facilitate the explanation, and are not to be construed in a limited manner unless otherwise specified. Also, when terms such as "first", "second", etc. are used in this specification or claims, these terms do not represent any order or importance, but are for distinguishing one configuration from another. In addition, some members that are not important in explaining the embodiments are omitted in each drawing.

[0014] FIG. 1 is a cross-sectional view of an organic hydride production apparatus 1 according to an embodiment. In FIG. 1, the shapes of the respective parts are shown in a simplified manner. The organic hydride production apparatus 1 is an electrolytic cell (electrolytic bath) that hydrogenates a hydride by an electrochemical reduction reaction, and mainly includes an electrolyte membrane 2, a cathode 4, an anode 6, and a pair of end plates 8. The electrolyte membrane 2, the cathode 4, the anode 6, and the pair of end plates 8 are each approximately flat plate-shaped or thin film-shaped.

[0015] The electrolyte membrane 2 is disposed between the cathode 4 and the anode 6 and is a membrane that allows protons to move from the anode 6 side to the cathode 4 side. The electrolyte membrane 2 has a first surface 2a and a second surface 2b that face each other, the first surface 2a faces the cathode 4, and the second surface 2b faces the anode 6. The electrolyte membrane 2 is composed of, for example, a solid polymer electrolyte membrane having proton conductivity. The solid polymer electrolyte membrane is not particularly limited as long as it is a material through which protons can conduct, and examples include fluorine-based ion exchange membranes having a sulfonic acid group such as Nafion (registered trademark).

[0016] The electrolyte membrane 2 selectively conducts protons while suppressing the mixing and diffusion of substances between the cathode 4 and the anode 6. The thickness of the electrolyte membrane 2 is not particularly limited, but is, for example, 5 μm to 300 μm. By setting the thickness of the electrolyte membrane 2 to 5 μm or more, the desired strength of the electrolyte membrane 2 can be more reliably obtained. Also, by setting the thickness of the electrolyte membrane 2 to 300 μm or less, it is possible to suppress the excessive increase in ion transfer resistance. The electrolyte membrane 2 may contain any reinforcing material. By the electrolyte membrane 2 containing a reinforcing material, it is possible to suppress the swelling of the electrolyte and suppress the decrease in the strength of the electrolyte membrane 2.

[0017] The cathode 4 (negative electrode) is provided on the first surface 2a side of the electrolyte membrane 2. The cathode 4 of the present embodiment has a cathode catalyst layer 10 and a cathode diffusion layer 12. The cathode catalyst layer 10 is disposed closer to the electrolyte membrane 2 side than the cathode diffusion layer 12. The cathode catalyst layer 10 of the present embodiment is in contact with the first surface 2a of the electrolyte membrane 2. The cathode catalyst layer 10 is a layer that hydrogenates the hydrogenated product with protons to generate an organic hydride.

[0018] The cathode catalyst layer 10 contains, for example, platinum (Pt), ruthenium (Ru), etc. as a cathode catalyst for hydrogenating the hydrogenated product. The average particle size of the cathode catalyst is, for example, 2 nm to 20 nm. The "average particle size" in the present embodiment means, for example, the average particle size D50 (particle size at 50% cumulative from the fine side) obtained by image analysis of the particles present in a scanning electron microscope (SEM) image at a magnification of 1000 times or a transmission electron microscope (TEM) image at a magnification of 1 million times. For example, for 100 particles present in one field of view in the SEM image or TEM image, the average particle size can be obtained by analyzing using the image analysis software "Image J". When the size of the particles is on the order of μm, it is preferable to calculate the average particle size using the SEM image, and when the size of the particles is on the order of nm, it is preferable to calculate the average particle size using the TEM image.

[0019] Preferably, the cathode catalyst layer 10 contains a porous catalyst support on which the cathode catalyst is supported. This suppresses aggregation of the cathode catalyst. The catalyst support is composed of an electronically conductive material such as porous carbon, porous metal, or porous metal oxide. When the catalyst support is particulate, the average particle size of the catalyst support is, for example, 1 μm to 10 μm.

[0020] Furthermore, the cathode catalyst is coated with an ionomer (a cation-exchange type ionomer). For example, the catalyst support on which the cathode catalyst is supported is coated with an ionomer. Examples of ionomers include perfluorosulfonic acid polymers such as Nafion® and Flemion®. It is preferable that the ionomer partially coats the cathode catalyst. This allows for the efficient supply of the three elements (hydrogenated substance, proton, and electron) necessary for the electrochemical reaction in the cathode catalyst layer 10 to the reaction field.

[0021] Furthermore, the cathode catalyst layer 10 of this embodiment contains a water-repellent agent. The water-repellent agent has a higher affinity for hydrides and organic hydrides than for water. As an example, the water-repellent agent has a lower affinity for water than the composite of the cathode catalyst, catalyst support, and ionomer. The water-repellent agent is also composed of aggregates of arbitrary primary particles. The aggregates and primary particles are preferably non-porous.

[0022] Examples of primary particles include polytetrafluoroethylene (PTFE), perfluoroalkoxyalkanes (PFA), and polyvinylidene fluoride (PVDF). The aggregate may consist of only one type of primary particle, or it may consist of a combination of two or more types of primary particles. Furthermore, the aggregate contained in the cathode catalyst layer 10 may consist of only one type, or it may be a combination of two or more types. In other words, the water repellent contains at least one substance selected from the group consisting of these candidate materials.

[0023] In this embodiment, when observing a cross-section of the cathode catalyst layer 10 (for example, by SEM observation), if a primary particle cluster that is three times or larger than the smallest primary particle cluster is present, that primary particle cluster is determined to be an aggregate. Also, if a primary particle cluster that is three times or larger than the primary particles used is present, that primary particle cluster is determined to be an aggregate. As an example, the size of an aggregate is the distance between two points on the contour of the particle cluster in the image where the distance between those two points is maximum.

[0024] Furthermore, whether or not primary particles are agglomerating in the cathode catalyst layer 10 can be determined by the agglomeration determination method shown below as an example. Specifically, first, an image of the cross-section of the cathode catalyst layer 10 (e.g., an SEM image) is analyzed to calculate the particle size distribution based on the number of primary particles. In this particle size distribution, primary particle clusters with a particle size three times or more the smallest particle size are defined as target clusters. If the particle size of the primary particles used is known, primary particle clusters with a particle size three times or more the particle size of the primary particles may also be defined as target clusters. Then, an area-based particle size distribution is calculated from the number and particle size of each cluster in the number-based particle size distribution. In the obtained area-based particle size distribution, if the area ratio of the target clusters to the total area of ​​the primary particle clusters is 20% or more, it can be determined that the primary particles are agglomerating.

[0025] The cathode catalyst and the water repellent are present in a mixed state in the cathode catalyst layer 10. Therefore, the water repellent is dispersed within the cathode catalyst layer 10. For example, the water repellent is particulate and dispersed substantially uniformly within the cathode catalyst layer 10. When the water repellent is particulate, the average particle size of the water repellent is, for example, 10 nm to 30 μm. The water repellent content in the cathode catalyst layer 10 is greater than 10 vol% in volume fraction relative to the total solid content volume of the cathode catalyst layer 10. Furthermore, this volume fraction is preferably 11 vol% or more, 12 vol% or more, 13 vol% or more, or 14 vol% or more, more preferably 15 vol% or more, and even more preferably 20 vol% or more. Furthermore, the volume fraction of the water repellent is preferably 80 vol% or less, more preferably 70 vol% or less, relative to the total solid content volume of the cathode catalyst layer 10.

[0026] By setting the volume fraction of the water repellent to over 10 vol%, the Faraday efficiency of the organic hydride manufacturing apparatus 1 can be improved. Furthermore, by setting the volume fraction of the water repellent to 15 vol% or more, the improvement in Faraday efficiency can be more reliably achieved. Furthermore, by setting the volume fraction of the water repellent to 20 vol% or more, an even greater improvement in Faraday efficiency can be obtained. Furthermore, by setting the volume fraction of the water repellent to 80 vol% or less, the conductivity required for the organic hydride manufacturing apparatus 1 can be more easily obtained. Furthermore, by setting the volume fraction of the water repellent to 70 vol% or less, the organic hydride manufacturing apparatus 1 can be given even better conductivity.

[0027] In this embodiment, "non-porous" means having a smaller porosity than a porous catalyst support. Alternatively, it means having lower permeability to fluids such as water, hydrides, and organic hydrides than a porous catalyst support. Alternatively, it means having fewer pores observed in scanning electron microscope (SEM) images (e.g., at 5000x magnification) than a porous catalyst support, or having no pores observed at all. Alternatively, it means not having pores through which fluids can enter or pass.

[0028] The cathode catalyst ink used to form the cathode catalyst layer 10 can be prepared, for example, by the following procedure. In the method for preparing the cathode catalyst ink according to this embodiment, the first preparation step, the second preparation step, and the aggregation step are carried out in this order.

[0029] First, in the first preparation step, the cathode catalyst, catalyst support, ionomer, and solvent are mixed to prepare the first solution. For example, the first solution can be obtained by putting each component into a grinding container and mixing them with a stirrer such as a jet mill or a rotary-orbit mixer. Examples of solvents include water and alcohol. Note that a catalyst support with the cathode catalyst already supported may also be used.

[0030] Next, in the second preparation step, a dispersion of arbitrary primary particles is added to the first solution to prepare the second solution. The dispersion contains primary particles, a surfactant, and a solvent, and is a solution in which micelles of the surfactant containing the primary particles are colloidally dispersed in the solvent. The amount of dispersion added is such that the volume fraction of the water repellent in the final cathode catalyst layer 10 exceeds 10 vol% of the total solid volume of the cathode catalyst layer 10. The amount of dispersion added, in other words, the volume fraction of the water repellent in the cathode catalyst layer 10, can be calculated from the weight fraction and density of each component contained in the cathode catalyst layer 10. In one example of this calculation, the bulk density, which takes voids into account, is used as the density of the cathode catalyst. Also, the true density, which does not take voids into account, is used as the density of the primary particles and ionomer.

[0031] In the subsequent agglomeration step, primary particles in the second solution are agglomerated by a predetermined treatment to form a water-repellent agent composed of aggregates of primary particles. Examples of predetermined treatments include a long-duration weak mixing treatment and a short-duration strong mixing treatment. An example of a weak mixing treatment is applying ultrasonic vibration to the second solution. The duration of the weak mixing treatment, i.e., "long duration" in the case of a weak mixing treatment, is, for example, more than 40 minutes, preferably 60 minutes or more. Therefore, in the example of a weak mixing treatment, a treatment of 40 minutes or less is considered a short-duration weak mixing treatment. An example of a strong mixing treatment is stirring the second solution with a stirrer such as a jet mill or a rotary-orbit mixer. The duration of the strong mixing treatment, i.e., "short duration" in the case of a strong mixing treatment, is, for example, 300 seconds or less. The inventors have confirmed that aggregates are not formed in short-duration weak mixing treatments. The combination of mixing intensity and mixing time that can agglomerate primary particles can be set as appropriate by the implementer.

[0032] Through the above process, a cathode catalyst ink containing a cathode catalyst, a catalyst support, an ionomer, a solvent, and a water repellent is obtained. Then, a cathode catalyst layer 10 is formed using this cathode catalyst ink. For example, the cathode catalyst layer 10 is formed by coating the first surface 2a of the electrolyte membrane 2 with the cathode catalyst ink, or by transferring the cathode catalyst ink coated on a predetermined sheet to the electrolyte membrane 2.

[0033] The thickness of the cathode catalyst layer 10 is not particularly limited, but is for example 20 μm to 50 μm. By making the cathode catalyst layer 10 20 μm or thicker, the amount of catalyst required for the electrolytic reaction can be obtained more reliably. Furthermore, by making the thickness of the cathode catalyst layer 10 50 μm or less, it is possible to suppress an excessive decrease in the diffusibility of the hydride.

[0034] The cathode diffusion layer 12 is a layer that uniformly diffuses the liquid hydride supplied from the outside into the cathode catalyst layer 10. Furthermore, the organic hydride generated in the cathode catalyst layer 10 is discharged to the outside of the cathode catalyst layer 10 via the cathode diffusion layer 12. In this embodiment, the cathode diffusion layer 12 is in contact with the main surface of the cathode catalyst layer 10 on the side opposite to the electrolyte membrane 2.

[0035] The cathode diffusion layer 12 is composed of a conductive material such as carbon or metal. Alternatively, the cathode diffusion layer 12 may be a porous body such as a sintered fiber or particle body, or a foamed molded body. Specific examples of materials constituting the cathode diffusion layer 12 include woven carbon fabric (carbon cloth), nonwoven carbon fabric, and carbon paper. The thickness of the cathode diffusion layer 12 is not particularly limited, but is, for example, 200 μm to 700 μm. A thickness of 200 μm or more in the cathode diffusion layer 12 can more reliably enhance the diffusivity of the hydride. Furthermore, a thickness of 700 μm or less in the cathode diffusion layer 12 can suppress excessive electrical resistance.

[0036] The anode 6 is provided on the second surface 2b side of the electrolyte membrane 2. In this embodiment, the anode 6 is in contact with the second surface 2b of the electrolyte membrane 2. The anode 6 has a metal such as iridium (Ir), ruthenium (Ru), or platinum, or an oxide thereof, as an anode catalyst, and generates protons by oxidizing water. The anode catalyst may be dispersed and supported or coated on an electronically conductive substrate. The substrate is made of a material mainly composed of metals such as titanium (Ti) or stainless steel (SUS). Examples of substrate forms include woven or nonwoven sheets (fiber diameter: e.g., 10 μm to 30 μm), mesh (diameter: e.g., 500 μm to 1000 μm), porous sintered bodies, foamed molded bodies (foam), expanded metal, etc.

[0037] When the anode 6 has a structure in which the anode catalyst is dispersed and supported or coated on a substrate, the thickness of the anode 6, including the anode catalyst and substrate, is not particularly limited, but is for example 0.05 to 1 mm. By making the thickness of the anode 6 0.05 mm or more, the amount of catalyst required for the electrolytic reaction can be obtained more reliably. Furthermore, by making the thickness of the anode 6 1 mm or less, it is possible to suppress an excessive decrease in the diffusibility of the hydride.

[0038] When the anode catalyst is coated onto the substrate to form a layer, the thickness of the layer is not particularly limited, but is for example 0.1 μm to 50 μm. Alternatively, the anode 6 may be composed of a layer formed by directly coating the main surface of the electrolyte membrane 2 with the anode catalyst. In this case, the thickness of the layer constituting the anode 6 is not particularly limited, but is for example 0.1 μm to 50 μm. By setting the thickness of these layers to 0.1 μm or more, the amount of catalyst required for the electrolytic reaction can be obtained more reliably. Furthermore, by setting the thickness of these layers to 50 μm or less, it is possible to suppress an excessive decrease in the diffusibility of the hydride.

[0039] The pair of end plates 8 are made of a metal such as stainless steel or titanium. The thickness of each end plate 8 is not particularly limited, but is for example between 1 mm and 30 mm. By making the thickness of the end plates 8 1 mm or more, it is possible to avoid a significant impairment of machinability. Also, by making the thickness of the end plates 8 30 mm or less, it is possible to suppress an increase in cost.

[0040] One end plate 8a is installed on the opposite side of the cathode 4 from the electrolyte membrane 2. In this embodiment, the end plate 8a is in contact with the main surface of the cathode diffusion layer 12. The organic hydride production apparatus 1 has a frame-shaped spacer 14 positioned between the electrolyte membrane 2 and the end plate 8a. The end plate 8a, the electrolyte membrane 2, and the spacer 14 define a cathode chamber in which the cathode 4 is housed. The spacer 14 also serves as a sealant to prevent the cathode liquid from leaking out of the cathode chamber.

[0041] The cathode liquid is a mixture of the hydride and organic hydride supplied to the cathode chamber. The hydride is a compound that is hydrogenated into an organic hydride by an electrochemical reduction reaction in the organic hydride production apparatus 1; in other words, it is a dehydrogenated form of the organic hydride. The hydride is preferably a liquid at 20°C and 1 atm. For example, the cathode liquid does not contain organic hydrides before the start of operation of the organic hydride production apparatus 1, and after the start of operation, organic hydrides produced by electrolysis are mixed in, resulting in a mixture of the hydride and organic hydride.

[0042] The hydride and organic hydride used in this embodiment are not particularly limited as long as they are organic compounds that can be reversibly subjected to hydrogenation / dehydrogenation reactions to add / remove hydrogen. A wide range of acetone-isopropanol systems, benzoquinone-hydroquinone systems, aromatic hydrocarbon systems, etc., can be used. Among these, aromatic hydrocarbon systems are preferred from the viewpoint of transportability during energy transport.

[0043] Aromatic hydrocarbon compounds used as hydrogenates are compounds containing at least one aromatic ring, such as benzene, alkylbenzene, naphthalene, alkylnaphthalene, anthracene, and diphenylethane. Alkylbenzenes include compounds in which the 1st to 4th hydrogen atoms of the aromatic ring are substituted with a linear alkyl group having 1 to 6 carbon atoms or a branched alkyl group. Examples of such compounds include toluene, xylene, mesitylene, ethylbenzene, and diethylbenzene. Alkylnaphthalenes include compounds in which the 1st to 4th hydrogen atoms of the aromatic ring are substituted with a linear alkyl group having 1 to 6 carbon atoms or a branched alkyl group. Examples of such compounds include methylnaphthalene. These may be used individually or in combination.

[0044] The hydrogenated substance 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 hydrogenated substances. Organic hydrides are obtained by hydrogenating the above-mentioned hydrogenated substances, and examples include cyclohexane, methylcyclohexane, dimethylcyclohexane, and piperidine.

[0045] The end plate 8a has a supply channel 16 and a discharge channel 18 on its main surface facing the cathode diffusion layer 12. In this embodiment, the supply channel 16 and the discharge channel 18 are formed by grooves provided on the main surface of the end plate 8a. The supply channel 16 is in contact with one end of the cathode diffusion layer 12 in the in-plane direction, and the cathode liquid supplied to the cathode 4 flows through its interior. The discharge channel 18 is in contact with the other end of the cathode diffusion layer 12 in the in-plane direction, and the cathode liquid discharged from the cathode 4 flows through its interior. The in-plane direction of the cathode diffusion layer 12 is the direction in which the plane extends, perpendicular to the stacking direction of the electrolyte membrane 2 and the cathode 4.

[0046] In this embodiment, the supply channel 16 is in contact with the lower end of the cathode diffusion layer 12 in the vertical direction, and the discharge channel 18 is in contact with the upper end of the cathode diffusion layer 12. Each channel extends horizontally. A groove-shaped channel connecting the supply channel 16 and the discharge channel 18 may be provided on the surface of the end plate 8a. This can suppress uneven flow of the hydride within the cathode chamber and excessive pressure loss when the cathode liquid passes through the cathode chamber. The extension direction and shape of the supply channel 16, the discharge channel 18, and the channel connecting the two channels are not limited to those described above and can be set as appropriate by the implementer.

[0047] A cathode liquid storage tank (not shown) is connected to the supply channel 16. The cathode liquid storage tank contains cathode liquid. Between the supply channel 16 and the cathode liquid storage tank, a cathode liquid supply device (not shown) is provided, which consists of various pumps such as gear pumps and cylinder pumps, or gravity-fed devices. The cathode liquid contained in the cathode liquid storage tank is sent to the supply channel 16 by the cathode liquid supply device and supplied to the cathode catalyst layer 10 via the cathode diffusion layer 12. The discharge channel 18 is connected to the cathode liquid storage tank as an example. The cathode liquid, which contains organic hydrides generated in the cathode catalyst layer 10 and unreacted hydrogenated materials, is returned to the cathode liquid storage tank via the discharge channel 18.

[0048] The other end plate 8b is installed on the opposite side of the anode 6 from the electrolyte membrane 2. The organic hydride production apparatus 1 has a frame-shaped spacer 20 positioned between the electrolyte membrane 2 and the end plate 8b. The end plate 8b, the electrolyte membrane 2, and the spacer 20 define the anode chamber in which the anode 6 is housed. The spacer 20 also serves as a sealant to prevent the anode liquid from leaking out of the anode chamber. The anode liquid is a liquid containing water that is supplied to the anode chamber. Examples of anode liquids include aqueous sulfuric acid solution, aqueous nitric acid solution, aqueous hydrochloric acid solution, pure water, and deionized water.

[0049] The end plate 8b has a supply channel 22, a discharge channel 24, and a connecting channel 26 on its main surface facing the anode 6. In this embodiment, the supply channel 22, the discharge channel 24, and the connecting channel 26 are formed by grooves provided on the main surface of the end plate 8b. The supply channel 22 is in contact with one end of the anode 6 in the in-plane direction, and the anode liquid supplied to the anode 6 flows through it. The discharge channel 24 is in contact with the other end of the anode 6 in the in-plane direction, and the anode liquid discharged from the anode 6 flows through it. One end of the connecting channel 26 is connected to the supply channel 22, and the other end is connected to the discharge channel 24.

[0050] In this embodiment, the supply channel 22 is in contact with the lower end of the anode 6 in the vertical direction, and the discharge channel 24 is in contact with the upper end of the anode 6. The supply channel 22 and the discharge channel 24 extend horizontally, and the connecting channel 26 extends vertically. In addition, a plurality of connecting channels 26 are provided on the end plate 8b, and each connecting channel 26 is arranged at a predetermined interval in the horizontal direction. The extension direction and shape of the supply channel 22, the discharge channel 24, and the connecting channels 26 are not limited to those described above and can be set as appropriate by the implementer.

[0051] Furthermore, the anode chamber may contain an electronically conductive buffer material positioned between the anode 6 and the end plate 8b to press the anode 6 against the electrolyte membrane 2. The buffer material can reduce the contact resistance between the electrolyte membrane 2 and the anode 6. The buffer material may be pressed against the anode 6 by a biasing member such as a spring. Alternatively, the buffer material may be composed of a channel block with slits that constitute the supply channel 22, the discharge channel 24, and the connecting channel 26. In this case, the end plate 8b can be made of a flat plate without grooves that constitute each channel.

[0052] An anode liquid storage tank (not shown) is connected to the supply channel 22. The anode liquid storage tank contains anode liquid. Between the supply channel 22 and the anode liquid storage tank, an anode liquid supply device (not shown) is provided, which consists of various pumps such as gear pumps and cylinder pumps, or gravity-fed devices. The anode liquid contained in the anode liquid storage tank is sent to the supply channel 22 by the anode liquid supply device, and a portion is supplied directly to the anode 6, while another portion is supplied via the connecting channel 26. The discharge channel 24 is connected to the anode liquid storage tank as an example. The anode liquid supplied to the anode 6 is returned to the anode liquid storage tank via the discharge channel 24.

[0053] A control unit (not shown) may be connected to the organic hydride manufacturing apparatus 1. The control unit controls the cell voltage (electrolytic voltage) of the organic hydride manufacturing apparatus 1, or the current flowing through the organic hydride manufacturing apparatus 1. The control unit is implemented as a hardware component including a computer's CPU and memory, and as a software component using a computer program.

[0054] The control unit receives signals from a potential detection unit (not shown) provided in the organic hydride production apparatus 1, indicating the potential of each electrode or the cell voltage of the organic hydride production apparatus 1. The potential of each electrode and the cell voltage of the organic hydride production apparatus 1 can be detected by known methods. For example, a reference electrode is provided in the electrolyte membrane 2. The reference electrode is maintained at the reference electrode potential. For example, the reference electrode is a reversible hydrogen electrode (RHE). The potential detection unit detects the potential of each electrode relative to the reference electrode and transmits the detection result to the control unit. The potential detection unit is composed of, for example, a known voltmeter.

[0055] The control unit controls the power output, the operation of the cathode liquid supply device and the anode liquid supply device, etc., during the operation of the organic hydride production apparatus 1 based on the detection results of the potential detection unit. The power source for the organic hydride production apparatus 1 is preferably renewable energy obtained from solar, wind, hydro, or geothermal power generation, but is not particularly limited thereto.

[0056] In the organic hydride production apparatus 1, the reaction that occurs when toluene (TL) is used as an example of the hydride is as follows: When toluene is used as the hydride, the resulting organic hydride is methylcyclohexane (MCH). <Electrode reaction at the anode> 3H2O → 3 / 2O2 + 6H + +6e - <Electrode reaction at the cathode> TL+6H + +6e - →MCH

[0057] In other words, the electrode reaction in the cathode catalyst layer 10 and the electrode reaction in the anode 6 proceed in parallel. Protons generated by the electrolysis of water in the anode 6 are supplied to the cathode catalyst layer 10 via the electrolyte membrane 2. Electrons generated by the electrolysis of water are also supplied to the cathode catalyst layer 10 via the end plate 8b, the external circuit, and the end plate 8a. The protons and electrons supplied to the cathode catalyst layer 10 are used for the hydrogenation of toluene in the cathode catalyst layer 10. This generates methylcyclohexane.

[0058] Therefore, according to the organic hydride production apparatus 1 of this embodiment, the electrolysis of water and the hydrogenation reaction of the hydrogenate can be carried out in a single step. For this reason, compared to conventional technology that produces organic hydrides in a two-step process consisting of a process to produce hydrogen by water electrolysis, etc., and a process to chemically hydrogenate toluene in a reactor such as a plant, the production efficiency of organic hydrides can be increased. Furthermore, since a reactor for chemical hydrogenation and a high-pressure vessel for storing hydrogen produced by water electrolysis, etc., are not required, equipment costs can be significantly reduced.

[0059] In cathode 4, along with the main reaction, the hydrogenation of toluene, the hydrogen evolution reaction described below may occur as a side reaction. Side reactions may occur when the supply of the material to be hydrogenated to the cathode catalyst layer 10 is insufficient, etc. The occurrence of side reactions leads to a decrease in the Faraday efficiency of the organic hydride production apparatus 1. <Potential side reactions at the cathode> 2H + +2e - →H2

[0060] When protons move from the anode 6 to the cathode 4 across the electrolyte membrane 2, they move accompanied by water molecules. Therefore, as the electrolytic reduction reaction progresses, water accumulates in the cathode catalyst layer 10. The water in the cathode catalyst layer 10 obstructs the flow of the hydride. As a result, when a large amount of water accumulates in the cathode catalyst layer 10, the supply of hydride to the reaction field in the cathode catalyst layer 10 decreases, making the aforementioned side reactions more likely to proceed.

[0061] In contrast, the cathode catalyst layer 10 of this embodiment contains a water-repellent agent. Therefore, water moving from the anode 6 side can be easily discharged to the outside of the cathode catalyst layer 10 by the water-repellent action of the water-repellent agent. Furthermore, the water-repellent agent is composed of aggregates of primary particles. Therefore, it is easy to increase the size of the water-repellent agent, and thus the water-repellent effect of the water-repellent agent can be more easily exerted. As a result, it is possible to suppress the progression of side reactions due to insufficient supply of hydride to the cathode catalyst layer 10.

[0062] Furthermore, preferably, the water repellent is non-porous. This makes it easier to discharge water from the cathode catalyst layer 10 compared to when a porous water repellent is used.

[0063] As described above, the cathode catalyst layer 10 according to this embodiment has a higher affinity for the hydride and organic hydrides than for water, and contains a water-repellent agent composed of aggregates of arbitrary primary particles. The volume fraction of the water-repellent agent in the cathode catalyst layer is greater than 10 vol% of the total volume of solids in the cathode catalyst layer 10. By containing more than 10 vol% of the water-repellent agent composed of aggregates in the cathode catalyst layer 10, water that has moved from the anode 6 side to the cathode catalyst layer 10 can be rapidly discharged from the system. Therefore, according to this embodiment, the Faraday efficiency of the organic hydride production apparatus 1 can be improved.

[0064] Furthermore, the cathode catalyst layer 10 in this embodiment contains a porous catalyst support on which the cathode catalyst is supported. This suppresses aggregation of the cathode catalyst. It also increases the surface area of ​​the cathode catalyst layer 10. Therefore, the production efficiency of organic hydrides can be further improved.

[0065] The embodiments of the present invention have been described in detail above. The embodiments described above are merely examples of how to implement the present invention. The content of the embodiments does not limit the technical scope of the present invention, and many design changes, such as changes, additions, and deletions of components, are possible as long as they do not depart from the spirit of the invention as defined in the claims. The new embodiments to which design changes have been made combine the effects of the respective embodiments and modifications. In the embodiments described above, the content in which such design changes are possible is emphasized with notations such as "in this embodiment" or "in this embodiment," but design changes are also permitted even if there are no such notations. Any combination of the above components is also valid as an embodiment of the present invention.

[0066] The embodiments may be specified by the items described below. [Item 1] A cathode catalyst layer (10) that hydrogenates a hydride with protons to produce an organic hydride, The invention comprises a cathode catalyst for hydrogenating the hydride, and a water-repellent agent having a higher affinity for the hydride and organic hydrides than for water, and composed of aggregates (30) of arbitrary primary particles. The volume fraction of the water repellent in the cathode catalyst layer (10) is greater than 10 vol% relative to the volume of the total solid content in the cathode catalyst layer (10). Cathode catalyst layer (10). [Item 2] The cathode catalyst layer (10) contains a porous catalyst support on which the cathode catalyst is supported. The cathode catalyst layer (10) described in item 1. [Item 3] An electrolyte membrane (2) having a first surface (2a) and a second surface (2b) facing each other, which moves protons, A cathode (4) is provided on the first surface (2a) side of the electrolyte membrane (2) and has a cathode catalyst layer (10) as described in item 1 or 2, The electrolyte membrane (2) is provided on the second surface (2b) side and comprises an anode (6) that oxidizes water to generate protons, Organic hydride production apparatus (1). [Item 4] A method for preparing a cathode catalyst ink used in a cathode catalyst layer (10) that hydrogenates a hydride with protons to produce an organic hydride, The cathode catalyst and solvent are mixed to prepare the first solution. A second solution is prepared by adding a dispersion of any primary particles to the first solution in an amount such that the volume fraction of the water repellent in the cathode catalyst layer (10) is greater than 10 vol% relative to the total volume of solids in the cathode catalyst layer (10). The method involves agglomerating primary particles in a second solution to form a water-repellent agent that has a higher affinity for hydrides and organic hydrides than for water, and is composed of aggregates (30) of primary particles. Method for preparing cathode catalyst ink. [Examples]

[0067] The following describes embodiments of the present invention, but these embodiments are merely illustrative examples for suitably illustrating the present invention and do not limit the present invention in any way.

[0068] The following Examples 1 and 2 and Comparative Examples 1 to 3 investigated the method of forming aggregates and the effect of the aggregates on the performance of the organic hydride production apparatus.

[0069] [Example 1] (Preparation of cathode catalyst ink) A first solution was prepared by mixing a PtRu / C catalyst (TEC61E54E, manufactured by Tanaka Kikinzoku Kogyo Co., Ltd.), pure water, a 20 wt% Nafion® solution (manufactured by DuPont), and 1-propanol (manufactured by Wako) in a grinding container using a jet mill. A second solution was obtained by mixing a PTFE dispersion (manufactured by Mitsui Chemours Fluoroproducts Co., Ltd.) with this first solution. The particle size of the PTFE particles contained in the PTFE dispersion was 20 nm. The second solution was then mixed in an ultrasonic cleaner (output: 125 W, frequency: 42 kHz) for 240 minutes. This mixing process corresponds to a long-duration weak mixing process. A cathode catalyst ink was obtained through the above process. The Nafion / carbon ratio of the cathode catalyst ink was set to 0.3. The amount of PTFE dispersion added to the cathode catalyst ink was set so that the volume fraction of the water repellent (PTFE aggregates) was 70 vol% relative to the total volume of solids in the final cathode catalyst layer.

[0070] (Fabrication of membrane electrode assemblies) A cathode catalyst layer was formed by coating Nafion® N117 (manufactured by DuPont) as the electrolyte membrane with cathode catalyst ink. Subsequently, a membrane electrode assembly was fabricated by layering carbon paper (39BA, manufactured by SGL Carbon, 10cm x 10cm) as the cathode diffusion layer with the electrolyte membrane on which the cathode catalyst layer was formed. In the membrane electrode assembly, the amount of catalyst metal was 0.60 mg / cm³. 2 That's what I decided.

[0071] (Construction of an organic hydride production device) As the anode, a web-shaped DSE (Dimensionally Stable Electrode) electrode (manufactured by Denora Permelec) was prepared, consisting of a 1 mm thick Ti substrate coated with IrTa oxide. The geometric area of ​​the anode was 12.25 cm². 2 The membrane electrode assembly and the anode were then stacked. A channel block with a vertically extending slit was pressed against the anode with a spring. These were sandwiched between a pair of end plates and fastened with bolts and nuts. This resulted in an organic hydride manufacturing apparatus.

[0072] [Example 2] A cathode catalyst ink was prepared in the same manner as in Example 1, except that the second solution was mixed for 30 seconds using a stirrer (Awatori Rentaro AR-100, manufactured by Shinki Co., Ltd.), and an organic hydride production apparatus was obtained. The mixing treatment of the second solution in Example 2 corresponds to a short-time strong mixing treatment.

[0073] [Comparative Example 1] A cathode catalyst ink was prepared in the same manner as in Example 1, except that PTFE was not mixed into the cathode catalyst ink, and an organic hydride production apparatus was obtained.

[0074] [Comparative Example 2] A cathode catalyst ink was prepared in the same manner as in Example 1, except that the amount of PTFE dispersion added was set to a volume fraction of 50 vol%, and the second solution was mixed in an ultrasonic cleaning device (output: 125 W, frequency: 42 kHz) for 30 minutes, thereby obtaining an organic hydride production apparatus. The mixing treatment of the second solution in Comparative Example 2 corresponds to a short-time weak mixing treatment.

[0075] [Comparative Example 3] A cathode catalyst ink was obtained by mixing a PtRu / C catalyst (TEC61E54E, manufactured by Tanaka Kikinzoku Kogyo Co., Ltd.), pure water, a 20 wt% Nafion® solution (manufactured by DuPont), 1-propanol (manufactured by Wako), and PTFE particles (manufactured by Solvay) in a ball mill container. The particle size of the PTFE particles was 4 μm. The Nafion / carbon ratio of the cathode catalyst ink was set to 0.3. The amount of PTFE particles added to the cathode catalyst ink was such that the volume fraction of the water repellent was 50 vol% relative to the total solid content volume of the cathode catalyst layer obtained in the end.

[0076] The surface and cross-section of the cathode catalyst layer were observed using SEM for each of Example 1 and Comparative Examples 2 and 3. In addition, the surface of the cathode catalyst layer for Comparative Example 1 was observed using SEM. Figure 2(a) is an SEM image of the surface of the cathode catalyst layer 10 according to Example 1. Figure 2(b) is an SEM image of the cross-section of the cathode catalyst layer 10 according to Example 1. Figure 3 is an SEM image of the surface of the cathode catalyst layer according to Comparative Example 1. Figure 4(a) is an SEM image of the surface of the cathode catalyst layer according to Comparative Example 2. Figure 4(b) is an SEM image of the cross-section of the cathode catalyst layer according to Comparative Example 2. Figure 5(a) is an SEM image of the surface of the cathode catalyst layer according to Comparative Example 3. Figure 5(b) is an SEM image of the cross-section of the cathode catalyst layer according to Comparative Example 3. The magnification of the SEM images in Figures 2(a), 3, 4(a), and 5(a) is 100x, while the magnification of the SEM images in Figures 2(b), 4(b), and 5(b) is 1000x.

[0077] As shown in Figure 2(a), it was confirmed that numerous protrusions 28, approximately 10 μm to 30 μm in size, were scattered on the surface of the cathode catalyst layer 10 of Example 1. Furthermore, as shown in Figure 2(b), it was confirmed that these protrusions 28 contained aggregates 30 of PTFE, approximately 1 μm to 20 μm in size. From this, it can be understood that by adding a dispersion of primary particles to a pre-prepared mixture of cathode catalyst and other materials (first solution), and subjecting this solution (second solution) to a long-term weak mixing treatment, aggregates of primary particles, i.e., the water-repellent agent in the above-described embodiment, can be formed.

[0078] As shown in Figure 3, a small number of protrusions 32 were also observed on the surface of the cathode catalyst layer in Comparative Example 1, but these protrusions 32 did not contain aggregates 30. The protrusions 32 were formed due to uneven coating of the cathode catalyst ink, etc., and are mainly composed of catalyst supports. The protrusions 32 composed of catalyst supports were also included in the cathode catalyst layer 10 of Example 1, and the white raised areas visible in the SEM image in Figure 2(b) correspond to the protrusions 32.

[0079] As shown in FIGS. 4(a) and 5(a), convex portions 32 were also observed on the surfaces of the cathode catalyst layers of Comparative Example 2 and Comparative Example 3. However, as shown in FIGS. 4(b) and 5(b), these convex portions 32 did not contain aggregates 30. From this, it can be understood that even if a dispersion liquid of primary particles is added to a previously prepared mixed liquid such as a cathode catalyst, aggregates are not formed by a weak mixing treatment for a short time. Also, it can be understood that aggregates are not formed even when the cathode catalyst etc. and the primary particles are mixed simultaneously.

[0080] Although not shown, the cathode catalyst layer of Example 2 contained aggregates {{30}}. From this, it can be understood that aggregates of primary particles can be formed by adding a dispersion liquid of primary particles to a mixed liquid such as a cathode catalyst and subjecting this solution to a strong mixing treatment for a short time.

[0081] (Faraday efficiency measurement) For Examples 1 and 2 and Comparative Examples 1 and 2, the Faraday efficiency of the organic hydride production apparatus was measured. Specifically, the anode chamber of the organic hydride production apparatus of each example and the sulfuric acid bottle were connected by a circulation path, and 1M sulfuric acid as the anode liquid was circulated at a flow rate of 20 mL / min. The cathode chamber and the toluene bottle were connected by a circulation path, and toluene as the cathode liquid was circulated at a flow rate of 20 mL / min. While maintaining the temperature of the organic hydride production apparatus at 60°C, a voltage was applied between the anode and the cathode, and a constant current was passed at a current density of 0.7 A / cm 2 of the current density. The cathode liquid was periodically collected from the toluene bottle, and the concentrations of toluene and methylcyclohexane in the cathode liquid were quantified using a gas chromatograph mass spectrometer (GC-MS) (product name: JMS-T100 GCV, manufactured by JEOL Ltd.). From the obtained concentrations of toluene and methylcyclohexane, the amount of charge (A) used in the target main reaction was calculated. And the ratio (A / B×100%), that is, the Faraday efficiency, was calculated with the current (B) passed during the reaction.

[0082] Figure 6 shows the relationship between the toluene concentration of the cathode solution and the Faraday efficiency of the organic hydride production apparatus. As shown in Figure 6, when the toluene concentration was approximately 40% or less, the organic hydride production apparatus of Examples 1 and 2, which contained a water-repellent agent composed of aggregates in the cathode catalyst layer, exhibited higher Faraday efficiency than the organic hydride production apparatus of Comparative Examples 1 and 2, which did not contain a water-repellent agent composed of aggregates in the cathode catalyst layer. This confirms that mixing a water-repellent agent composed of aggregates into the cathode catalyst layer can suppress the decrease in Faraday efficiency when the toluene concentration decreases, thereby improving the Faraday efficiency of the organic hydride production apparatus.

[0083] Furthermore, a comparison between Example 1 and Comparative Example 1 confirmed that the performance of the organic hydride manufacturing apparatus, specifically the Faraday efficiency, can be improved by more than 20%. In this case, it is possible to reduce the size of the organic hydride manufacturing apparatus by more than 15% while maintaining the organic hydride production capacity.

[0084] The following test examples 1 to 23 further investigated the effect of aggregated water-repellent agents on the performance of organic hydride production equipment.

[0085] [Test Examples 1-11] Cathode catalyst inks were prepared in the same manner as in Comparative Example 3, with different amounts of PTFE particles added in each test example, to obtain an organic hydride production apparatus. In Test Examples 1-8, PTFE particles with a particle size of 4 μm were used, while in Test Examples 9-11, PTFE particles with a particle size of 10 μm were used. The 10 μm PTFE particles were adopted as particles with a size close to that of aggregates. In Test Example 1, the amount of PTFE particles added was 10 vol% when converted to the volume fraction of PTFE relative to the total volume of solids in the final cathode catalyst layer. In Test Examples 2-8, the amounts of PTFE particles added were 20, 30, 40, 50, 60, 70, and 80 vol%, respectively, when converted to the above volume fraction. In Test Examples 9-11, the amounts of PTFE particles added were 10, 20, and 30 vol%, respectively, when converted to the above volume fraction.

[0086] [Trial trial [Examples 12, 13] Cathode catalyst inks were prepared in the same manner as in Comparative Example 2, with different amounts of PTFE dispersion added in each test example, to obtain an organic hydride production apparatus. The amounts of PTFE dispersion added in Test Examples 12 and 13 were 30 and 50 vol%, respectively, based on the above volume fraction.

[0087] [Test Examples 14-23] Cathode catalyst inks were prepared in the same manner as in Example 1, with different amounts of PTFE dispersion added in each test, to obtain an organic hydride production apparatus. The amounts of PTFE particles added in Test Examples 14-23 were 5, 10, 15, 20, 30, 40, 50, 60, 70, and 80 vol%, respectively, when converted to the above volume fraction.

[0088] (Evaluation of aggregation) For each test example, the presence or absence of PTFE aggregation was evaluated in the cathode catalyst layer using the aggregation determination method described above. In this evaluation, ○ was used when aggregation was confirmed, and × was used when aggregation was not confirmed.

[0089] (Evaluation of strength) The strength (self-supporting or shape retention) of each cathode catalyst layer was evaluated. In this evaluation, a ○ was given if the cathode catalyst layer maintained its shape after the constant current electrolysis test described later, a △ was given if it collapsed during the constant current electrolysis test and the test could not be continued, and a × was given if the cathode catalyst layer collapsed under its own weight and the constant current electrolysis test could not be performed. ○ is an acceptable evaluation, and △ and × are unacceptable evaluations. Cathode catalyst layers with a strength evaluation of ○ have strength equivalent to or greater than that of a conventional catalyst layer (corresponding to Comparative Example 1) that does not involve the addition of PTFE dispersion as performed in Examples 1 and 2 and Comparative Example 2, or the addition of PTFE particles as performed in Comparative Example 3; in other words, it does not involve the addition of PTFE aimed at improving Faraday efficiency through the water-repellent effect of a water-repellent agent.

[0090] (Evaluation of conductivity) The conductivity of each test example of organic hydride production apparatus was evaluated. In this evaluation, if the resistance value of the organic hydride production apparatus measured by a known method in the constant current electrolysis test described later was less than or equal to the resistance value of the conventional organic hydride production apparatus equipped with the catalyst layer described above (hereinafter referred to as the conventional apparatus as appropriate), it was evaluated as ◎; if it was more than 1 times and 2 times or less the conventional resistance value, it was evaluated as ○; and if it was more than 2 times the conventional resistance value, it was evaluated as ×. ○ and ◎ are acceptable evaluations, and × is an unacceptable evaluation.

[0091] (Evaluation of the overall Faraday efficiency improvement effect) The following constant-current electrolysis tests were conducted using the organic hydride production apparatus for each test example. Specifically, 2 moles of toluene were first supplied to each organic hydride production apparatus as the cathode solution, and constant-current electrolysis was started. Then, a current sufficient to electrochemically convert 2 moles of toluene into methylcyclohexane was applied. The conditions were the same as those for the Faraday efficiency measurement described above. Subsequently, the composition of the final cathode solution was analyzed using a gas chromatograph-mass spectrometer (GC-MS) (product name: JMS-T100 GCV, manufactured by JEOL), and the final toluene concentration in the cathode solution was calculated. This constituted one test, and the test was repeated 10 times.

[0092] The calculated toluene concentration was subtracted from 100 to determine the overall Faraday efficiency (%). The difference between the overall Faraday efficiency obtained in the first test and the overall Faraday efficiency of the conventional device described above was defined as the improvement in overall Faraday efficiency at the time of the first evaluation. The difference between the overall Faraday efficiency obtained in the 10th test and the overall Faraday efficiency of the conventional device was defined as the improvement in overall Faraday efficiency at the time of the 10 evaluations. A value of over 2% in each overall Faraday efficiency improvement effect was evaluated as ◎, a difference between 0% and 2% or less was evaluated as ○, and a value of 0% or less was evaluated as ×. ○ and ◎ are acceptable evaluations, while × is an unacceptable evaluation. Note that Faraday efficiency is substantially equal to the yield of organic hydride. In the technical field to which Organic Hydride Production Equipment 1 belongs, even a slight improvement in overall Faraday efficiency leads to increased profits, and a 1% improvement is expected to result in significant profits. Furthermore, an improvement of over 2% in overall Faraday efficiency leads to extremely large profits in this technical field.

[0093] The results of each evaluation are shown in Figure 7. Figure 7 shows the properties of the cathode catalyst layer and the performance of the organic hydride production apparatus in Test Examples 1 to 23. In Test Examples 12 and 13, the PTFE did not aggregate and was uniformly dispersed, so the particle size was conveniently set to 4 or less. In Test Examples 14 to 23, the size of the aggregates was conveniently indicated as the particle size.

[0094] As shown in Figure 7, in Test Examples 1 to 11, where the cathode catalyst ink was prepared using the same procedure as in Comparative Example 3, the PTFE particles did not aggregate. Similarly, in Test Examples 12 and 13, where the cathode catalyst ink was prepared using the same procedure as in Comparative Example 2, the PTFE particles did not aggregate. However, in Test Examples 6 to 8, which contained 4 μm PTFE particles and had a PTFE volume fraction of 60 vol% or more, and in Test Example 11, which contained 10 μm PTFE particles and had a PTFE volume fraction of 30 vol%, the cathode catalyst layer collapsed, making it impossible to perform the constant current electrolysis test.

[0095] For Test Examples 1-5 and 9, although constant current electrolysis tests could be conducted, no improvement in overall Faraday efficiency was observed in either the initial evaluation or the 10th evaluation. Furthermore, in Test Example 5, the strength of the cathode catalyst layer and the conductivity of the organic hydride production apparatus were lower compared to Test Examples 1-4. For Test Example 10, although a constant current electrolysis test could be conducted and an improvement in overall Faraday efficiency was observed in the initial evaluation, no improvement in overall Faraday efficiency was observed in the 10th evaluation. Furthermore, in Test Example 10, the strength of the cathode catalyst layer and the conductivity of the organic hydride production apparatus were lower compared to Test Example 9.

[0096] In Test Examples 14-23, where the cathode catalyst ink was prepared using the same procedure as in Example 1, the PTFE particles contained in the dispersion aggregated. In other words, the water-repellent agent described in the above embodiment was formed. Furthermore, in Test Examples 14-23, the cathode catalyst layer had sufficient strength, and the organic hydride production apparatus had sufficient conductivity. In Test Examples 14 and 15, where the volume fraction of PTFE was 10 vol% or less, no improvement in overall Faraday efficiency was obtained in either the initial evaluation or the 10th evaluation. However, in Test Examples 16-23, where the volume fraction of PTFE was greater than 10 vol%, an improvement in overall Faraday efficiency was obtained in either the initial evaluation or the 10th evaluation. From this, it was confirmed that the Faraday efficiency of the organic hydride production apparatus can be improved by setting the volume fraction of the water-repellent agent in the cathode catalyst layer to more than 10 vol%.

[0097] Furthermore, it was confirmed that a better overall improvement in Faraday efficiency can be obtained by setting the volume fraction of PTFE to 20 vol% or higher. It was also confirmed that better conductivity can be obtained by setting the volume fraction of PTFE to 70 vol% or lower.

[0098] Test Examples 10 and 17 both used the same volume fraction of 20 vol%. Furthermore, the PTFE particles used in Test Example 10 were closer in size to aggregates than the PTFE particles used in Test Examples 1-8. However, no improvement in overall Faraday efficiency was observed in Test Example 10 after 10 evaluations. On the other hand, an improvement in overall Faraday efficiency was observed in Test Example 17 after 10 evaluations.

[0099] Test Examples 11 and 18 both used the same volume fraction of 30 vol%. Furthermore, the PTFE particles used in Test Example 11 were closer in size to aggregates than the PTFE particles used in Test Examples 1-8. However, in Test Example 11, the strength of the cathode catalyst layer was insufficient, making it impossible to perform the constant current electrolysis test. On the other hand, in Test Example 18, the cathode catalyst layer had sufficient strength, and a good overall Faraday efficiency improvement effect was obtained in both the initial evaluation and the 10th evaluation.

[0100] The inventors investigated the reasons for the performance differences observed between Test Example 10 and Test Example 17, and between Test Example 11 and Test Example 18. They found that differences in the state of PTFE can lead to performance differences. Specifically, when PTFE aggregates during the formation of the cathode catalyst layer, the aggregated PTFE can solidify while freely changing shape in accordance with the flow of the surrounding cathode catalyst and catalyst support. In other words, aggregates can take on various shapes. On the other hand, the PTFE particles themselves do not deform substantially. Therefore, aggregates can exist in the cathode catalyst layer in a state of closer contact with the surrounding cathode catalyst and catalyst support compared to individual particles of the same size. For this reason, it is thought that the strength of the cathode catalyst layer is higher in Test Examples 17 and 18, which contain PTFE aggregates, compared to Test Examples 10 and 11, which contain PTFE particles. As a result, it is thought that a better overall Faraday efficiency improvement effect was obtained in Test Examples 17 and 18 during the 10 evaluations.

[0101] It is believed that the aggregation of aggregates closely adhering to the surrounding cathode catalyst and catalyst support can be more easily formed by using a dispersion of primary particles. In other words, in a dispersion of primary particles, the primary particles are dispersed colloidally, encapsulated within surfactant micelles. In this case, the primary particles are thought to be in a liquid state or above the glass transition temperature within the micelles. Therefore, the primary particles or their aggregates can deform freely when the surfactant micelles break and the primary particles are released. This increases the degree of freedom in the shape of the aggregates, making it possible to adhere the aggregates closely to the surrounding cathode catalyst and catalyst support. [Industrial applicability]

[0102] This invention relates to an apparatus for producing organic hydrides. [Explanation of symbols]

[0103] 1 Organic hydride production apparatus, 2 Electrolyte membrane, 2a First surface, 2b Second surface, 4 Cathode, 6 Anode, 10 Cathode catalyst layer, 30 Aggregates.

Claims

1. A cathode catalyst layer that hydrogenates a hydride with protons to produce an organic hydride, The system comprises a cathode catalyst for hydrogenating the substance to be hydrogenated, and a water-repellent agent composed of aggregates of any type of primary particles that have a higher affinity for the substance to be hydrogenated and the organic hydride than for water. The volume fraction of the water-repellent agent in the cathode catalyst layer is 15 vol% or more and 70 vol% or less relative to the volume of the total solid content in the cathode catalyst layer. Cathode catalyst layer.

2. The cathode catalyst layer contains a porous catalyst support on which the cathode catalyst is supported. The cathode catalyst layer according to claim 1.

3. An electrolyte membrane having a first surface and a second surface facing each other, which moves protons, A cathode provided on the first surface side of the electrolyte membrane and having the cathode catalyst layer according to claim 1 or 2, The electrolyte membrane comprises an anode provided on the second surface side, which oxidizes water to generate protons, Organic hydride manufacturing equipment.

4. A method for preparing a cathode catalyst ink used in a cathode catalyst layer that hydrogenates a hydride with protons to produce an organic hydride, The cathode catalyst and solvent are mixed to prepare the first solution. A dispersion of any type of primary particles having a higher affinity for the hydrogenated substance and the organic hydride than for water, wherein the amount of the dispersion such that the volume fraction of the water repellent in the cathode catalyst layer is 15 vol% or more and 70 vol% or less relative to the total volume of solids in the cathode catalyst layer, is added to the first solution to prepare the second solution. This includes agglomerating the primary particles in the second solution to form a water-repellent agent which has a higher affinity for the hydrogenated substance and the organic hydride than for water and is composed of aggregates of the primary particles. Method for preparing cathode catalyst ink.

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