Electrode catalyst ink, electrode catalyst layer, and membrane electrode assembly comprising solid electrolyte film

Abstract

This electrode catalyst ink contains an ionomer (A), an electrode catalyst (B) containing at least one of a non-noble metal and a non-noble metal oxide, and a solvent (C). The solvent (C) contains a ketone-based solvent and water, and the volume ratio (water / ketone-based solvent) of the water to the ketone-based solvent is in the range of 0.05 to less than 0.55.

Description

A membrane electrode assembly consisting of an electrode catalyst ink, an electrode catalyst layer, and a solid electrolyte membrane

[0001] The present disclosure relates to an electrode catalyst ink used to form an electrode catalyst layer of a water electrolysis cell of a water electrolysis device and an electrode catalyst layer of a membrane electrode assembly of a fuel cell, an electrode catalyst layer, and a membrane electrode assembly comprising a solid electrolyte membrane.

[0002] Conventionally, in order to produce an electrode catalyst layer of a membrane electrode assembly in a fuel cell system, etc., a manufacturing method has been known in which, for example, an electrode catalyst ink is applied to at least one surface of a solid electrolyte membrane or a gas diffusion layer and then dried. For example, Patent Document 1 (Japanese Patent No. 5813257) discloses an electrode catalyst ink composition for fuel cells in which the SP value and evaporation rate of an additive solvent are selected as a method for forming an electrode catalyst layer without causing cracks in the coating film.

[0003] In electrode catalyst inks, if catalyst materials such as catalysts and organic polymers aggregate, coating cracks in the catalyst layer occur, which can result in variations in electrode performance, increased manufacturing costs for the electrode catalyst, and reduced productivity of the electrode catalyst. Therefore, it is important to suppress aggregation of catalyst materials in electrode catalyst inks.

[0004] Conventionally, methods for applying an electrode catalyst layer of a membrane electrode assembly to at least one surface of a solid electrolyte membrane or a gas diffusion layer include spraying, die coating, slit coating, dipping, and inkjet coating. These methods result in an electrode catalyst layer containing an electrode catalyst on at least one of the anode and the cathode, but among these, the direct application method by die coating as disclosed in Patent Document 2 (Japanese Patent No. 4917741) is industrially preferred due to its advantages of being economical and easily achieving good adhesion between the electrolyte membrane and the catalyst layer.

[0005] Meanwhile, in recent years, efforts to achieve carbon neutrality have focused on the production of green hydrogen using water electrolysis equipment utilizing renewable energy sources such as solar and wind power. Innovations in highly efficient, long-life water electrolysis equipment are needed to produce hydrogen cheaply and reliably, and the development of new catalyst materials and solid electrolyte membranes is anticipated. Among water electrolysis methods, anion exchange membrane water electrolysis (AEMWE) using non-precious metal catalyst materials as an alternative to platinum and iridium is promising. For example, Non-Patent Document 1 (R. Wang et al. Int. J. Hydrog. Energy 47 (2022)) presents the results of a study on a catalyst-layered solid electrolyte membrane utilizing a non-precious metal catalyst material. According to this study, electrode catalysts containing at least one of non-precious metals and non-precious metal oxides have poorer water electrolysis performance than precious metal catalysts, and therefore require a catalyst layer thickness of 20-50 μm (dry thickness), approximately 10 times thicker than that of precious metal catalysts.

[0006] However, when an electrode catalyst ink is applied to at least one surface of a solid electrolyte membrane or a gas diffusion layer by a direct coating method such as die coating and then dried to a dry thickness of 20 to 40 μm, if the viscosity of the coating ink is low, it becomes difficult to adjust the film thickness of the electrode catalyst layer to a uniform thickness, resulting in problems such as variations in electrode performance, increased manufacturing costs for the electrode catalyst, and reduced productivity of the electrode catalyst.

[0007] For example, Patent Document 3 (Japanese Patent No. 5807654) discloses a method for achieving both aggregation of catalysts and catalyst materials such as organic polymers in an electrode catalyst ink and thickening of the electrode catalyst ink, in which a catalyst ink concentration step is provided and an alcohol with an SP value of 12.3 or less is added.

[0008] However, while this method is an effective means for thin film coating with a dry thickness of 2 to 3 μm, when an electrode catalyst containing at least one of a non-precious metal and an oxide of a non-precious metal is coated with a thick film with a dry thickness of 20 to 40 μm, there is a problem in that the dispersion stability of the electrode catalyst is insufficient, and it is not possible to sufficiently suppress the occurrence of cracks in the electrode catalyst layer due to aggregation of the electrode catalyst.

[0009] Patent No. 5813257 Patent No. 4917741 Patent No. 5807654

[0010] R.Wang et al. Int.J.Hydrog. Energy 47 (2022) JPCC (Journal of Physical Chemistry C) 119 (2015) 18303 JACS (Journal of American Chemical Society) 134 (2012) 17253 JACS (Journal of American Chemical Society) 135 (2013) 16977 JACS (Journal of American Chemical Society) 135 (2013) 11580 IJHE (International Journal of Hydrogen Energy) 47 (2022) 4304

[0011] An electrode catalyst ink according to one embodiment of the present disclosure contains an ionomer (A), an electrode catalyst (B) containing at least one of a non-precious metal and an oxide of a non-precious metal, and a solvent (C), wherein the solvent (C) contains a ketone-based solvent and water, and the volume ratio of water to the ketone-based solvent [water / ketone-based solvent] is in the range of 0.05 or more and less than 0.55.

[0012] An electrode catalyst layer according to one embodiment of the present disclosure is an electrode catalyst layer including an ionomer (A) and an electrode catalyst (B) containing at least one of a non-precious metal and an oxide of a non-precious metal, wherein the ionomer (A) has a Hansen solubility parameter distance Ra1 with a solvent (C) of 7.5 MPa or less. １／２ More than 10.0 MPa １／２ The electrode catalyst (B) has a Hansen solubility parameter distance Ra2 of 7.0 MPa or less with respect to the solvent (C). １／２ Over 12.0 MPa １／２ is less than.

[0013] 1 is a conceptual diagram showing the Hansen solubility parameter distance Ra1 between an ionomer and a mixed solvent, and the Hansen solubility parameter distance Ra2 between an electrode catalyst and a mixed solvent in the Hansen space. Table 1 shows the Hansen solubility parameters of an example of an ionomer (A), an electrode catalyst (B), and a solvent (C). Table 2 shows the evaluation results of dispersibility and solubility in a solvent. Table 3 shows the volume ratio of the solvent (C) in Examples 1 to 7 and Comparative Examples 1 to 3. Table 4 shows the HSP distances Ra1 and Ra2 in Examples 1 to 7 and Comparative Examples 1 to 3. Table 5 shows the evaluation results in Examples 1 to 7 and Comparative Examples 1 to 3.

[0014] <Background to the present disclosure> When manufacturing an electrode catalyst ink by applying and drying a thick film using a direct application method such as the die coating method, it is important to control the coating viscosity of the electrode catalyst ink in addition to suppressing aggregation of the catalyst material and organic polymer in the electrode catalyst ink.

[0015] As a result of investigating means for solving the above problems, the inventors focused on the solvent contained in the electrode catalyst ink and discovered that it is important to design the solvent so that it has appropriate affinity for the catalyst and electrode catalyst materials such as organic polymers. They then discovered that it is possible to easily select a solvent that suppresses aggregation and provides viscosity, and have completed the present disclosure.

[0016] An object of the present disclosure is to provide an electrode catalyst ink with increased coating ink viscosity that enables the formation of a thick electrode catalyst layer.

[0017] An outline of this embodiment of the present disclosure will be described below.

[0018] The electrode catalyst ink according to this embodiment is used, for example, when producing an electrode catalyst layer for a membrane electrode assembly of a water electrolysis cell, a fuel cell, etc. by applying the electrode catalyst ink to at least one surface of a solid electrolyte membrane or a gas diffusion layer and drying the ink. In other words, the "electrode catalyst ink" is an ink for an electrode catalyst.

[0019] The electrode catalyst ink according to the first aspect contains an ionomer (A), an electrode catalyst (B) containing at least one of a non-precious metal and an oxide of a non-precious metal, and a solvent (C), wherein the solvent (C) contains a ketone-based solvent and water, and the volume ratio of water to the ketone-based solvent [water / ketone-based solvent] is in the range of 0.05 or more and less than 0.55.

[0020] According to the first aspect, an electrode catalyst ink can be provided that has excellent dispersion stability and viscosity increasing properties for the electrode catalyst (B) that contains at least one of a non-precious metal and an oxide of a non-precious metal.

[0021] The electrode catalyst ink according to the second aspect of the present disclosure is the electrode catalyst ink according to the first aspect, wherein the Hansen solubility parameter distance Ra1 between the ionomer (A) and the solvent (C) is 5.5 MPa. １／２ Over 13.5 MPa １／２ It may be less than.

[0022] According to the second aspect, an electrode catalyst layer having excellent dispersibility can be provided more reliably.

[0023] The electrode catalyst ink according to the third aspect of the present disclosure is the electrode catalyst ink according to the first or second aspect, wherein the Hansen solubility parameter distance Ra2 between the electrode catalyst (B) containing at least one of a non-precious metal and an oxide of a non-precious metal and the solvent (C) is 4.5 MPa or less. １／２ Over 12.5 MPa １／２ It may be less than.

[0024] According to the third aspect, it is possible to provide an electrode catalyst layer that more reliably has excellent dispersibility.

[0025] The electrode catalyst ink according to a fourth aspect of the present disclosure is any one of the first to third aspects, wherein the ketone solvent of the solvent (C) may be at least one selected from the group consisting of acetone, diacetone alcohol, cyclohexanone, and isophorone.

[0026] According to the fourth aspect, an electrode catalyst that more reliably has excellent viscosity increasing properties can be provided.

[0027] The electrode catalyst ink according to a fifth aspect of the present disclosure is the electrode catalyst ink according to any one of the first to fourth aspects, wherein the ionomer (A) may be a fluorine-containing polymer having a cationic functional group.

[0028] According to the fifth aspect, the catalytic activity of the electrode catalyst layer is likely to be maintained at a high level.

[0029] In the electrode catalyst ink according to a sixth aspect of the present disclosure, in any one of the first to fifth aspects, the electrode catalyst (B) containing at least one of a non-precious metal and an oxide of a non-precious metal may be Ni.

[0030] According to the sixth aspect, the electrode catalyst layer is more likely to have excellent catalytic activity with certainty.

[0031] The electrode catalyst ink according to a seventh aspect of the present disclosure is the electrode catalyst ink according to any one of the first to sixth aspects, wherein the volume ratio of water to the ketone-based solvent in the solvent (C) [water / ketone-based solvent] is in the range of 0.20 or more and less than 0.35.

[0032] According to the seventh aspect, an electrode catalyst layer having superior viscosity increasing properties can be provided.

[0033] An electrode catalyst layer according to an eighth aspect of the present disclosure is an electrode catalyst layer including an ionomer (A) and an electrode catalyst (B) containing at least one of a non-precious metal and an oxide of a non-precious metal, wherein the ionomer (A) has a Hansen solubility parameter distance Ra1 with a solvent (C) of 7.5 MPa or less. １／２ More than 10.0 MPa １／２ The electrode catalyst (B) has a Hansen solubility parameter distance Ra2 of 7.0 MPa or less with respect to the solvent (C). １／２ Over 12.0 MPa １／２ is less than.

[0034] According to the eighth aspect, the electrode catalyst layer is likely to have a low overvoltage.

[0035] An electrode catalyst layer according to a ninth aspect of the present disclosure may be the electrode catalyst layer of the eighth aspect, wherein the thickness of the electrode catalyst layer is 10 μm or more and less than 50 μm.

[0036] According to the ninth aspect, it is easy to reliably have excellent catalytic activity and durability.

[0037] A method for producing an electrode catalyst layer according to a tenth aspect of the present disclosure includes the steps of applying the electrode catalyst ink according to any one of the first to seventh aspects onto a substrate, and drying the solvent of the applied electrode catalyst ink to obtain an electrode catalyst layer containing an ionomer and an electrode catalyst.

[0038] According to the tenth aspect, it is easy to obtain economical efficiency and good adhesion between the electrolyte membrane and the catalyst layer.

[0039] A membrane electrode assembly according to an eleventh aspect of the present disclosure includes a substrate which is a solid electrolyte membrane or a gas diffusion layer, and the electrode catalyst layer according to the eighth or ninth aspect provided on the substrate in physical and electrical connection with the substrate.

[0040] According to the eleventh aspect, a membrane electrode assembly can be obtained in which the electrode catalyst layer has low overvoltage and durability.

[0041] Hereinafter, details of an electrode catalyst ink and a manufacturing method thereof, an electrode catalyst layer and a manufacturing method thereof, and a membrane electrode assembly according to embodiments of the present disclosure will be described. The present disclosure is not limited to the following embodiments.

[0042] (Embodiment 1) The electrode catalyst ink according to embodiment 1 contains an ionomer (A), an electrode catalyst (B) containing at least one of a non-precious metal and an oxide of a non-precious metal, and a solvent (C). The solvent (C) contains a ketone solvent and water, and the volume ratio of water to the ketone solvent [water / ketone solvent] is in the range of 0.05 or more and less than 0.55. With this configuration, an electrode catalyst ink having excellent dispersion stability and viscosity of the electrode catalyst (B) can be provided.

[0043] The components that make up this electrode catalyst ink will be described below.

[0044] [Ionomer (A)] As described above, the electrode catalyst ink contains an ionomer (A). The ionomer (A) is an organic polymer having ion conductivity. For example, the ionomer (A) may have proton conductivity or anion conductivity, but anion conductivity is preferred. If the ionomer (A) has anion conductivity, it can be applied to anion exchange membrane water electrolysis (AEMEW) utilizing the electrode catalyst (B). As a result, the electrode catalyst obtained by drying the electrocatalyst ink can have excellent catalytic activity in dilute alkaline solutions and pure water.

[0045] The ionomer (A) is not limited to a specific organic material. The ionomer (A) may be a fluorine-containing ion exchange resin or a fluorine-containing organic polymer. The inclusion of fluorine can improve the thermal stability and electrochemical stability of the ionomer (A). Furthermore, the inclusion of fluorine can more reliably improve the alkali resistance of the electrode catalyst.

[0046] For example, the ionomer (A) can suppress aggregation of the electrode catalyst (B) by its steric hindrance effect when present on or near at least a portion of the surface of the electrode catalyst (B). The equivalent weight (EW) of the ionomer (A) is not limited to a specific value. The equivalent weight refers to the weight of the ionomer (A) per mole of cationic functional group. The equivalent weight of the ionomer (A) may be 1,100 g / mol or less, or may be 900 g / mol or less. This can more reliably suppress aggregation of the electrode catalyst (B). As a result, the electrode catalyst (B) and the ionomer (A) in the electrode catalyst ink are more likely to have excellent dispersibility. The lower limit of the equivalent weight of the ionomer (A) is not limited to a specific value and may be 500 g / mol. The smaller the equivalent weight, the more easily hydrogen-bonded interactions with water, one of the solvents (C), are formed, enabling an increase in coating viscosity.

[0047] The ionomer (A) is, for example, a proton-conductive ionomer, which is a perfluorocarbon polymer containing sulfonic acid groups, such as Nafion (registered trademark). Nafion is a perfluorocarbon polymer having the following chemical formula:

[0048]

[0049] Anion-conducting ionomers are made by adding ion exchange groups consisting of ammonium or imidazolium cations to a hydrocarbon-based main chain skeleton, such as polystyrene, polyethersulfone, polyphenylene, or a copolymer, to impart anion conductivity. In particular, the inclusion of polyarylene ether chains or perfluoroalkyl chains in the hydrophobic portion of the main chain skeleton provides a good balance between anion conductivity and membrane properties. Examples include PAP-BP, PAP-TP (PiperION Anion Exchange Resin manufactured by PiperION), FAA-3 manufactured by Fumatech, and Sustainion manufactured by Dioxide Materials. PAP-BP has the following chemical formula:

[0050]

[0051] Furthermore, if necessary, an organic polymer that does not have ion conductivity may be added to the ionomer (A). Even in this case, aggregation of the electrode catalyst (B) can be suppressed due to steric hindrance caused by the ionomer (A). This makes it easier for the electrode catalyst (B) and the ionomer (A) to have excellent dispersibility in the electrode catalyst ink. An example of an organic polymer that does not have ion conductivity is polytetrafluoroethylene (PTFE).

[0052] [Electrode Catalyst (B)] As described above, the electrode catalyst ink contains an electrode catalyst (B). The electrode catalyst (B) is a material that is active in a reaction for producing gases such as hydrogen and oxygen, for example, at the anode or cathode of a water electrolysis cell. Conventionally, IrOx, a noble metal catalyst, has been used as the electrode catalyst on the anode side, for example. However, because IrOx is resource-limited and expensive, development of alternative non-noble metal electrode catalysts is currently underway.

[0053] The electrode catalyst (B) is, for example, NiO ２ , Fe ２ O ３ , Ni-Fe alloy, Ni-Al alloy, NiCo ２ O ４ , NiFe ２ O ４ , NiFeCoOx, MnFe ２ Ox, CoFeOx, CuFe ２ Ox, CuCoO ３ , CeMnFeO, NiAlMo, CaFe ２ O ４ , CaFeO ３ , SrFeO ３ , LaFeO ３ , YFeO ３ , BaFe ２ O ４ , Ni / CeO ２ -La ２ O ３ / C, etc. In particular, those containing two or more transition metals are preferred. For example, they contain at least two selected from the group consisting of V, Cr, Mn, Fe, Co, Ni, Ti, Cu, and Zn. In particular, it is preferable to include a transition metal with an atomic number smaller than that of Ni on the catalyst surface, as this lowers the Fermi level and promotes the electrochemical reaction. For example, Non-Patent Documents 2 to 6 disclose Ni-Fe alloys, NiCoOx, NiFeOx, NiFeCoOx, MnFeOx, CoFeOx, CuCoOx, etc.

[0054] The average primary particle size of the electrode catalyst (B) may be 100 nm or less, preferably 10 to 80 nm. The lower limit of the average particle size is not limited to a particular value. The electrode catalyst (B) typically has a particle shape. The particle shape is not limited to a particular shape. Examples of the shape may be spherical, ellipsoidal, fibrous, or scale-like.

[0055] [Solvent (C)] The solvent (C) is a solvent that disperses the ionomer (A) and the electrode catalyst (B) in the electrode catalyst ink, and also a solvent that increases the coating viscosity of the electrode catalyst ink.

[0056] The solvent (C) is a mixed solvent containing water and a ketone solvent. The ketone solvent is, for example, at least one selected from the group consisting of acetone, MEK, MIBK, MIPK, DEK, DIBK, cyclohexanone, diacetone alcohol, and isophorone. The ketone solvent is preferably acetone, cyclohexanone, diacetone alcohol, or isophorone, and more preferably acetone or diacetone alcohol. As the ketone solvent, at least one ketone solvent selected from these may be used alone, or a combination of multiple types may be used.

[0057] By adjusting the volume ratio of water to the ketone solvent (water / ketone solvent) in the solvent (C) to 0.05 or more and less than 0.55, the ionomer (A) can form a strong hydrogen-bonding network due to water, thereby achieving specific viscosity enhancement. At the same time, the affinity between the electrode catalyst (B) and the solvent (C) is maintained at a good level. The present inventors have found that, as a result of adjusting the volume ratio of water to the ketone solvent (water / ketone solvent) to 0.05 or more and less than 0.55, the dispersion stability of the electrode catalyst (B) is significantly improved. More preferably, the volume ratio of water to the ketone solvent (water / ketone solvent) is 0.20 or more and less than 0.35.

[0058] The contents of water and ketone solvent in solvent (C) are not limited to specific values. It is desirable that the solvents in solvent (C) are mutually compatible and do not undergo phase separation. Therefore, for example, in addition to water and ketone solvent, a suitable solvent may be added as needed. Polar solvents are preferred, and alcohols and glycols are preferred.

[0059] [About Hansen Solubility Parameter (HSP)] The Hansen Solubility Parameter (hereinafter also referred to as "HSP") is a parameter that represents the solubility characteristics between substances. HSP refers to a vector parameter obtained by dividing the Hildebrand solubility parameter into three cohesive energy components: London dispersion force, dipole-dipole force, and hydrogen bonding force. In this disclosure, the component of HSP corresponding to the London dispersion force is referred to as the dispersion term δd, the component corresponding to the dipole-dipole force is referred to as the polar term δp, and the component corresponding to the hydrogen bonding force is referred to as the hydrogen bonding term δh. The units of each parameter are MPa. １／２ is.

[0060] Fig. 1 is a conceptual diagram showing the Hansen solubility parameter distance Ra1 between an ionomer and a mixed solvent, and the Hansen solubility parameter distance Ra2 between an electrode catalyst and a mixed solvent in the Hansen space. Fig. 2 is Table 1 showing the Hansen solubility parameters of an example of an ionomer (A), an electrode catalyst (B), and a solvent (C).

[0061] Because HSP is a vector quantity, for example, few pure substances have the same HSP value. HSP databases have been constructed for commonly used substances. By referencing these databases, it is possible to obtain the HSP value of a specific substance. On the other hand, for substances for which HSP values ​​are not registered in the database, the HSP value can be calculated from the substance's chemical structure using computer software such as Hansen Solubility Parameters in Practice (HSPiP). In addition, the HSP value of a mixture containing multiple substances can be calculated as the sum of the HSP values ​​of each substance multiplied by the volume ratio of each substance to the total mixture. For example, the HSP value of a mixed solvent Sm consisting of solvents Sa and Sb can be expressed by the following equation (1) when the volume ratio of the solvents in the mixed solvent is x:y, where x is the volume of solvent Sa:y is the volume of solvent Sb:

[0062]

[0063] Therefore, using the HSP values ​​of the ionomer (A) and the electrode catalyst (B), which suppress the aggregation of catalyst materials such as the ionomer (A) and the electrode catalyst (B), and the HSP value of the solvent (C) contained in the electrode catalyst ink, the HSP distance Ra1 between the ionomer (A) and the solvent (C) in the HSP space, and the HSP distance Ra2 between the electrode catalyst (B) and the solvent (C) were calculated using the following formula: Ra1 = 4 × (δda - δdc) 2 + (δpa-δpc) 2 + (δha-δhc) 2 Ra2=4×(δdb−δdc) 2 +(δpb-δpc) 2 + (δhb-δhc) 2 The dispersion term, polar term, and hydrogen bond term of the HSP of the ionomer (A) are δda, δpa, and δha, respectively; the dispersion term, polar term, and hydrogen bond term of the HSP of the electrode catalyst (B) are δdb, δpb, and δhb, respectively; and the dispersion term, polar term, and hydrogen bond term of the HSP of the solvent (C) are δdc, δpc, and δhc, respectively.

[0064] As a result, in the illumination catalyst ink, when the solvent (C) contains water and a ketone solvent, the Hansen solubility parameter distance Ra1 between the ionomer (A) and the solvent (C) is 4.6 MPa. １／２ Over 9.9 MPa １／２ The Hansen solubility parameter distance Ra2 between the electrode catalyst (B) and the solvent (C) is preferably 3.5 MPa or less. １／２ Over 12.8 MPa １／２ It has been found that the following is preferable:

[0065] This makes it difficult for the ionomer (A) to aggregate, and the electrode catalyst (B) and the ionomer (A) are likely to be adsorbed to each other, resulting in the ionomer (A) being present on the surface of the electrode catalyst (B). In addition, in the electrode catalyst ink, the affinity between the electrode catalyst (B) and the solvent (C) is maintained well, and the electrode catalyst (B) is likely to be well dispersed in the electrode catalyst ink. Furthermore, in the electrode catalyst ink, the ionomer (A) is unlikely to separate from the surface of the electrode catalyst (B). As a result, the electrode catalyst (B) and the ionomer (A) are likely to have excellent dispersibility more reliably in the electrode catalyst ink, thereby ensuring excellent anion conductivity.

[0066] The type of solvent contained in the electrode catalyst ink can be determined qualitatively and quantitatively by, for example, gas chromatography, mass spectrometry, and nuclear magnetic resonance spectroscopy. When the solvent contained in the electrode catalyst ink is a mixed solvent containing multiple types of solvents, the content ratio of each solvent contained in the mixed solvent can also be determined by the above-mentioned methods.

[0067] The solids concentration in the electrode catalyst ink is preferably in the range of 3 to 50 mass %, more preferably in the range of 5 to 40 mass %, and particularly preferably in the range of 10 to 30 mass %, from the viewpoint of forming a uniform and thick catalyst layer on at least one surface of the solid electrolyte membrane or the gas diffusion layer.

[0068] [Additives] The electrode catalyst ink may contain, but is not essential for, a dispersant for dispersing catalyst particles. Examples of dispersants include anionic surfactants, cationic surfactants, amphoteric surfactants, and nonionic surfactants. Among these, nonionic surfactants are preferred. The electrode catalyst ink may also contain additives such as plasticizers, stabilizers, adhesion aids, water retention agents, and colorants, as long as they do not impair the effects of the present disclosure.

[0069] The method for preparing the electrode catalyst ink is not particularly limited, and any method known in the art can be used. Examples include a method in which electrode catalyst particles are kneaded and stirred in a solvent, an ionomer is added and stirred again, and then dispersed in a dispersing device; or a method in which electrode catalyst particles are kneaded in a solvent, an ionomer is added and stirred, more solvent is added and stirred again, and then dispersed in a dispersing device. Examples of the dispersing device include a homogenizer, a ball mill, a bead mill, a jet mill, a planetary mixer, a dissolver, an ultrasonic dispersing device, and a kneading degassing device.

[0070] The electrode catalyst ink according to the first embodiment can increase the viscosity of the coating ink while suppressing aggregation of the catalyst and catalyst materials such as organic polymers in the electrode catalyst ink. This allows the electrode catalyst ink to be applied directly to at least one surface of a solid electrolyte membrane or a gas diffusion layer to form a thick electrode catalyst layer for a membrane electrode assembly.

[0071] (Embodiment 2) [Electrode catalyst layer] The electrode catalyst layer according to embodiment 2 is formed using the electrode catalyst ink according to embodiment 1, and is a solid material containing an ionomer (A) and an electrode catalyst (B). Specifically, this electrode catalyst layer has a Hansen solubility parameter distance Ra1 with respect to a solvent (C) of 5.5 MPa. １／２ Over 13.5 MPa １／２ The Hansen solubility parameter distance Ra2 between the ionomer (A) and the solvent (C) is less than 4.5 MPa. １／２ Over 12.5 MPa １／２In this case, the electrode catalyst layer is formed using the electrode catalyst ink, but the solvent (C) has been lost by drying, and the electrode catalyst layer is substantially free of the solvent (C) in the electrode catalyst ink.

[0072] In addition, in the electrode catalyst layer, the mass ratio of the content of the electrode catalyst (B) to the content of the ionomer (A) [mass of (B) / mass of (A)] is preferably in the range of 2.0 to 20.0, particularly preferably in the range of 3.0 to 10.0.

[0073] This controls the dispersibility of the ionomer (A) and the electrode catalyst (B) in the electrode catalyst layer, and forms a microstructure of the catalyst layer that is appropriate from the viewpoints of electrolysis performance, gas diffusibility, and durability, thereby enabling the electrode to have a low overvoltage.

[0074] Furthermore, the thickness of the electrode catalyst layer is preferably 10 to 50 μm, particularly preferably 20 to 40 μm, from the viewpoints of electrolytic performance, gas diffusibility and durability.

[0075] [Method for manufacturing electrode catalyst layer] The electrode catalyst layer can be formed, for example, by the following steps: (1) The electrode catalyst ink according to embodiment 1 is applied onto a substrate. The substrate may be, for example, a solid electrolyte membrane. (2) The solvent of the applied electrode catalyst ink is dried to obtain an electrode catalyst layer containing an ionomer and an electrode catalyst.

[0076] (Embodiment 3) [Membrane Electrode Assembly and Manufacturing Method Thereof] A membrane electrode assembly according to Embodiment 3 includes a substrate which is a solid electrolyte membrane or a gas diffusion layer, and the above-described electrode catalyst layer provided on the substrate in physical and electrical connection with the substrate. The electrode catalyst layer is the electrode catalyst layer according to Embodiment 2. This membrane electrode assembly is used in, for example, a proton exchange membrane water electrolysis apparatus, an anion exchange membrane water electrolysis apparatus, or an alkaline diaphragm water electrolysis apparatus. Furthermore, this membrane electrode assembly can be used as at least one of the anode and the cathode in the above-described water electrolysis apparatus.

[0077] The electrode catalyst layer is formed by applying the electrode catalyst ink to a substrate and drying it. The substrate is not particularly limited, but examples include a solid electrolyte membrane or a gas diffusion layer made of porous carbon paper. As the substrate, a solid electrolyte membrane is industrially preferred because of its advantages of being economical and easily achieving adhesion to the catalyst layer.

[0078] Any commonly known solid electrolyte membrane that exhibits ionic conductivity of protons or anionic hydroxide ions can be used, but proton exchange resins and anion exchange resins are preferably used because they provide good performance. Both proton exchange resins and anion exchange resins are often classified into two types: those made of hydrocarbon-based polymers and those made of fluoropolymers. When durability is important, proton exchange resins and anion exchange resins made of fluoropolymers are used, but in recent years, proton exchange resins and anion exchange resins made of hydrocarbon-based polymers have also been used from an environmental perspective. Among these, solid electrolyte membranes made of anion exchange resins are preferred from the viewpoint of interfacial adhesion with the electrode catalyst ink.

[0079] When the substrate is a solid electrolyte membrane, a catalyst-coated solid electrolyte membrane (CCM) can be produced by applying an electrode catalyst layer-forming paste using the above-mentioned electrode catalyst ink to the solid electrolyte membrane by screen printing, die coater application, etc., to form an electrode catalyst layer. A membrane-electrode assembly can then be produced by joining a gas diffusion layer thereto.

[0080] Furthermore, by using the membrane electrode assembly, a water electrolysis device or a fuel cell can be obtained.

[0081] The present disclosure will be described in more detail below with reference to examples. Note that the following examples are examples of the present disclosure, and the present disclosure is not limited to the following examples.

[0082] (Example) [Raw Materials for Electrode Catalyst Ink] As an example, an electrode catalyst ink was prepared using the raw materials shown below. Ionomer (A): Anion conductive ionomer: PAP-BP (manufactured by PiperION) Proton conductive ionomer: C ７HF １３ O ５ S.C. ２ F ４ (Manufactured by Sigma-Aldrich) Electrode catalyst (B) NiFeOx catalyst: Solvent (C) Water: Pure water Ketone-based solvents: Acetone, cyclohexanone, diacetone alcohol, isophorone Alcohol-based solvents: Methanol, ethanol [Calculation of Hansen solubility parameter] The Hansen solubility parameters of the above raw materials are shown in Table 1. Values ​​from a publicly known database were used for the data. Note that for the anion-conducting ionomer: PAP-BP (manufactured by PiperION) and the NiFeOx catalyst, the solubility parameters were calculated by the Hansen sphere method using the solvents shown in Table 2 of Figure 3.

[0083] The solubility of the ionomers and the dispersibility of the electrode catalysts in Table 2 of Figure 3 were evaluated as follows. Dispersions prepared by adding 20 ml of each solvent to 0.02 g of each catalyst material were subjected to ultrasonic treatment using an ultrasonic homogenizer, and then the dispersions were left at room temperature. Regarding the electrode catalysts, dispersions that did not settle even after being left for 15 minutes or more were evaluated as "A." Dispersions that settled in 5 minutes or more but less than 15 minutes were evaluated as "B." Dispersions that settled in less than 5 minutes were evaluated as "C." The average particle size in each solvent, water, acetone, and ethanol, was measured using a particle size distribution analyzer. The results showed that the better the dispersibility of the solution, the smaller the particle size.

[0084] Regarding the ionomer, when visually observed, the ionomer was evaluated as "good" if it was completely dissolved and transparent, and when visually observed, the ionomer was evaluated as "poor" if it was not completely dissolved.

[0085] [Preparation of electrode catalyst ink] Ionomer (A) and a NiFeOx catalyst as electrode catalyst (B) were mixed at a mass ratio of 5:1 to a total mass of 120 mg. A total mass of 350 mg of a mixed solvent was added to the resulting mixture in the volume ratio shown in Table 3 of Figure 4 to prepare an electrode catalyst ink precursor. The electrode catalyst ink precursor was subjected to micro-processing using a wet atomization device to prepare the electrode catalyst inks of the examples and comparative examples.

[0086] In Examples 1 to 7 and Comparative Examples 1 to 3, PAP-BP (manufactured by PiperION) was used as the ionomer (A). ７ HF １３ O ５ S.C. ２ F ４ (Nafion) was used.

[0087] [Calculation of HSP distances Ra1 and Ra2] In the electrode catalyst inks according to the examples and comparative examples, the HSP distance Ra1 [MPa １／２ ], the HSP distance Ra2 between the solvent (C) and the electrode catalyst (B) [MPa １／２ The HSP distances Ra1 and Ra2 are shown in Table 4 of FIG.

[0088] The dispersion term δda, polar term δpa, and hydrogen bond term δha of the HSP of the ionomer (A) were used, the dispersion term δdb, polar term δpb, and hydrogen bond term δhb of the HSP of the NiO catalyst were used, and the dispersion term δdc, polar term δpc, and hydrogen bond term δhc of the HSP of the solvent (C) were used. ２ =4×(δda−δdc) ２ + (δpa-δpc) ２ + (δha-δhc) ２ Formula (2) Ra2 ２ =4×(δdb−δdc) ２ +(δpb-δpc) ２ + (δhb-δhc) ２ [Evaluation of Dispersibility of Electrode Catalyst Ink] The dispersibility evaluation results for the electrode catalyst inks according to the Examples and Comparative Examples are shown in Table 5 in Figure 6. Dispersions of the electrode catalyst inks of the Examples and Comparative Examples, obtained by micro-treating the electrode catalyst ink precursor using a wet atomization device, that did not settle even when left for 15 minutes or more were rated "A". Dispersions that settled within 5 minutes or more but less than 15 minutes were rated "B". Dispersions that settled within less than 5 minutes were rated "C".

[0089] [Evaluation of Viscosity of Electrode Catalyst Ink] Viscosity evaluation results for the electrode catalyst inks according to the Examples and Comparative Examples are shown in Table 5 of Figure 6. The electrode catalyst ink electrode catalysts of the Examples and Comparative Examples, which were obtained by subjecting the electrode catalyst ink precursor to micro-processing using a wet atomization device, were evaluated using a rheometer / viscometer to a viscosity of 30 cp or more and 200 cp or less at a shear rate of 100 (l / s). If the viscosity was 200 cp or more, it was evaluated as "B." If the viscosity was less than 30 cp, it was evaluated as "C."

[0090] (Evaluation of Appearance of Solidified Electrode Catalyst Ink) The electrode catalyst inks according to Examples 1, 2, and 6 and Comparative Examples 1 and 3 were applied to a Nafion membrane with an applicator to a dry thickness of 20 μm, and then dried at room temperature to obtain solidified products. Visual appearance evaluation of the solids was carried out. The results are shown in Table 5 in FIG. 6.

[0091] The electrode catalyst ink according to the present disclosure can provide an electrode catalyst ink that has excellent dispersion stability and viscosity increasing properties for electrode catalysts and electrode catalyst materials such as organic polymers.

[0092] The electrode catalyst ink according to the present disclosure has an increased coating ink viscosity, making it possible to form a thick electrode catalyst layer using an electrode catalyst containing at least one of a non-precious metal and a non-precious metal oxide, and is therefore used to form electrode catalyst layers for water electrolysis cells in water electrolysis devices and for membrane electrode assemblies in fuel cells.

Claims

1. An electrode catalyst ink comprising: an ionomer (A); an electrode catalyst (B) containing at least one of a non-precious metal and an oxide of a non-precious metal; and a solvent (C), wherein the solvent (C) contains a ketone-based solvent and water, and the volume ratio of the water to the ketone-based solvent [water / ketone-based solvent] is in the range of 0.05 or more and less than 0.

55.

2. The Hansen solubility parameter distance Ra1 between the ionomer (A) and the solvent (C) is 5.5 MPa. １／２ More than 13.5MPa １／２ 2. The electrocatalyst ink of claim 1 , wherein 3. The Hansen solubility parameter distance Ra2 between the electrode catalyst (B) and the solvent (C) is 4.5 MPa. １／２ More than 12.5MPa １／２ 2. The electrocatalyst ink of claim 1 , wherein 4. The electrode catalyst ink according to claim 1, wherein the ketone solvent of the solvent (C) is at least one selected from the group consisting of acetone, diacetone alcohol, cyclohexanone, and isophorone.

5. The electrode catalyst ink according to any one of claims 1 to 4, wherein the ionomer (A) is a fluorine-containing polymer having a cationic functional group.

6. The electrode catalyst ink according to any one of claims 1 to 5, wherein the electrode catalyst (B) is Ni.

7. The electrode catalyst ink according to any one of claims 1 to 6, wherein the volume ratio of water to the ketone-based solvent in the solvent (C) [water / ketone-based solvent] is in the range of 0.20 or more and less than 0.

35.

8. An electrode catalyst layer comprising an ionomer (A) and an electrode catalyst (B) containing at least one of a non-precious metal and an oxide of a non-precious metal, wherein the ionomer (A) has a Hansen solubility parameter distance Ra1 with a solvent (C) of 7.5 MPa or less. １／２ More than 10.0 MPa １／２ The electrode catalyst (B) has a Hansen solubility parameter distance Ra2 with the solvent (C) of 7.0 MPa or less. １／２ More than 12.0 MPa １／２ an electrode catalyst layer, 9. The electrode catalyst layer according to claim 8, wherein the thickness of the electrode catalyst layer is 10 μm or more and less than 50 μm.

10. A method for producing an electrode catalyst layer, comprising: a step of applying the electrode catalyst ink according to any one of claims 1 to 7 onto a substrate; and a step of drying the solvent from the applied electrode catalyst ink to obtain an electrode catalyst layer comprising the ionomer and the electrode catalyst.

11. A membrane electrode assembly comprising: a substrate which is a solid electrolyte membrane or a gas diffusion layer; and an electrode catalyst layer according to claim 8 or 9 provided on said substrate and physically and electrically connected to said substrate.

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