Composition for forming catalyst layer, method for producing catalyst layer using same, gas diffusion electrode and electrolysis cell using same

Abstract

A composition for forming a catalyst layer according to the present invention contains catalyst particles, a binder and a solvent; the catalyst particles have an average primary particle diameter of 1 to 500 nm; the solvent has a surface tension within the range of 23 to 33 mN / m; and the solid content concentration of this composition is 1 to 20% by mass. A gas diffusion electrode according to the present invention is provided with a conductive porous base material and a catalyst layer that is formed on the surface of the conductive porous base material; the conductive porous base material has a critical surface tension of less than 29 mN / m; the catalyst layer contains catalyst particles that have an average primary particle diameter of 1 to 500 nm, and a binder; the catalyst layer has a thickness of 10 µm or less; and the proportion of the uncoated part area of the catalyst layer as calculated by means of image analysis is 15% or less.

Description

[Technical field]

[0001] The present application relates to a catalyst layer-forming composition for forming a uniform catalyst layer on a porous substrate, a method for producing a catalyst layer using the same, and a gas diffusion electrode provided with a uniform catalyst layer and an electrolysis cell using the same. [Background technology]

[0002] Gas diffusion electrodes used in fuel cells, electrolysis cells, and the like, which reduce reactive gases such as oxygen and carbon dioxide at the positive electrode and oxidize reactive liquids such as methanol and water at the negative electrode, generally comprise a gas diffusion layer having a gas diffusion substrate and a microporous layer formed on the gas diffusion substrate, and a catalyst layer formed on the microporous layer of the gas diffusion layer (e.g., Patent Document 1, etc.).

[0003] The catalyst layer of the gas diffusion electrode is usually formed by applying a catalyst layer forming paint containing catalyst nanoparticles on the microporous layer of the gas diffusion layer and drying it. However, the microporous layer has many voids to maintain gas permeability. Therefore, when the catalyst layer forming paint is applied on the microporous layer, the catalyst layer forming paint penetrates into the voids of the microporous layer, making it difficult to apply the catalyst layer forming paint uniformly on the microporous layer.

[0004] On the other hand, gas diffusion electrodes are involved in electrochemical reactions in fuel cells, electrolysis cells, and the like, and the catalyst layer of the gas diffusion electrode is required to have a uniform surface. If the catalyst layer has an uneven surface, the electrochemical reaction will be uneven, promoting localized deterioration of the catalyst layer and making it difficult to stably use the fuel cell or electrolysis cell for a long period of time.

[0005] Here, by reducing the number of voids in the microporous layer, it is possible to prevent the paint for forming the catalyst layer from penetrating into the voids in the microporous layer, but at the same time, the gas permeability of the microporous layer decreases.

[0006] Furthermore, if the amount of catalyst layer-forming paint applied to the microporous layer is increased, the proportion of catalyst layer-forming paint that does not penetrate into the voids in the microporous layer and remains on the surface increases, thereby relatively improving the uniformity of the catalyst layer that is formed; however, this method results in a thick catalyst layer, making it impossible to form the catalyst layer as a thin film. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] JP 2011-076848 A Summary of the Invention [Problem to be solved by the invention]

[0008] The problem to be solved by the present application is to provide a catalyst layer-forming composition for forming a uniform catalyst layer on a porous substrate, a method for producing a catalyst layer using the same, and a gas diffusion electrode provided with a uniform catalyst layer and an electrolysis cell using the same. [Means for solving the problem]

[0009] The composition for forming a catalyst layer of the present application is a composition for forming a catalyst layer comprising catalyst particles, a binder, and a solvent, wherein the catalyst particles have an average primary particle size of 1 to 500 nm, the solvent has a surface tension in the range of 23 to 33 mN / m, and has a solid content concentration of 1 to 20 mass %.

[0010] The method for producing a catalyst layer of the present application includes a step of applying the catalyst layer-forming composition of the present application onto a conductive porous substrate and drying the composition, and is characterized in that the critical surface tension of the conductive porous substrate is less than 29 mN / m and is smaller than the surface tension of a solvent of the catalyst layer-forming composition.

[0011] The gas diffusion electrode of the present application is a gas diffusion electrode including a conductive porous substrate and a catalyst layer formed on a surface of the conductive porous substrate, characterized in that the critical surface tension of the conductive porous substrate is less than 29 mN / m, the catalyst layer includes catalyst particles having an average primary particle diameter of 1 to 500 nm and a binder, the thickness of the catalyst layer is 10 μm or less, and the proportion of an uncoated area of ​​the catalyst layer calculated by image analysis is 15% or less.

[0012] The electrolysis cell of the present application is an electrolysis cell including a positive electrode, a negative electrode, and an ion conductive membrane disposed between the positive electrode and the negative electrode, characterized in that the positive electrode is the gas diffusion electrode of the present application. Effect of the Invention

[0013] According to the present application, it is possible to provide a gas diffusion electrode having a uniform catalyst layer and an electrolysis cell using the same. [Brief description of the drawings]

[0014] [Figure 1] FIG. 1 is a schematic cross-sectional view showing an example of a gas diffusion electrode according to an embodiment. [Diagram 2] FIG. 2 is a schematic cross-sectional view illustrating an example of an electrolysis cell according to an embodiment. [Diagram 3] FIG. 3A is an SEM image of the catalyst layer surface of Example 1, and FIG. 3B is an extracted image of interparticle voids obtained by image analysis of the SEM image of the catalyst layer surface of Example 1. [Figure 4] FIG. 4A is an SEM image of the surface of the catalyst layer of Example 2, and FIG. 4B is an extracted image of interparticle voids obtained by image analysis of the SEM image of the surface of the catalyst layer of Example 2. [Diagram 5] FIG. 5 is a cross-sectional SEM image of the gas diffusion electrode of Example 2. [Figure 6] FIG. 6A is an SEM image of the surface of the catalyst layer of Reference Example 3, and FIG. 6B is an extracted image of interparticle voids obtained by image analysis of the SEM image of the surface of the catalyst layer of Reference Example 3. [Figure 7]FIG. 7A is an SEM image of the surface of the catalyst layer of Example 4, and FIG. 7B is an extracted image of interparticle voids obtained by image analysis of the SEM image of the surface of the catalyst layer of Example 4. [Figure 8] FIG. 8A is an SEM image of the surface of the catalyst layer of Reference Example 1, and FIG. 8B is an extracted image of interparticle voids obtained by image analysis of the SEM image of the surface of the catalyst layer of Reference Example 1. [Figure 9] FIG. 9 is a cross-sectional SEM image of the gas diffusion electrode of Reference Example 1. [Figure 10] FIG. 10A is an SEM image of the surface of the catalyst layer of Reference Example 2, and FIG. 10B is an extracted image of interparticle voids obtained by image analysis of the SEM image of the surface of the catalyst layer of Reference Example 2. [Figure 11] FIG. 11A is an SEM image of the surface of the catalyst layer of Comparative Example 1, and FIG. 11B is an extracted image of interparticle voids obtained by image analysis of the SEM image of the surface of the catalyst layer of Comparative Example 1. [Figure 12] FIG. 12 is a cross-sectional SEM image of the gas diffusion electrode of Comparative Example 1. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] (Catalyst layer forming composition) An embodiment of the composition for forming a catalyst layer of the present application will be described. The composition for forming a catalyst layer of the present embodiment includes catalyst particles, a binder, and a solvent, the catalyst particles having an average primary particle size of 1 to 500 nm, the solvent having a surface tension in the range of 23 to 33 mN / m, and a solid content concentration of 1 to 20 mass %.

[0016] In the catalyst layer-forming composition of this embodiment, the surface tension of the solvent (dispersion medium) constituting the composition is in the range of 23 to 33 mN / m. Therefore, if the critical surface tension of the substrate to which the composition is applied is smaller than the surface tension of the solvent, the wettability of the substrate to the composition is reduced. Even when the catalyst layer-forming paint is applied directly to a conductive porous substrate having a large number of pores used in gas diffusion electrodes of fuel cells, electrolysis cells, etc., the paint for forming a catalyst layer is prevented from penetrating into the pores of the conductive porous substrate, and a catalyst layer consisting of a uniform thin film can be formed on the conductive porous substrate.

[0017] That is, the critical surface tension of the conductive porous substrate to which the catalyst layer forming composition of the present embodiment is applied is usually less than 29 mN / m, so that the catalyst layer forming composition containing a solvent having a surface tension in the range of 23 to 33 mN / m can be appropriately selected as a conductive porous substrate having a critical surface tension smaller than the surface tension of the solvent and being difficult to wet with the composition. Therefore, even if the catalyst layer forming coating material is directly applied to a conductive porous substrate having a large number of voids, the catalyst layer forming coating material is prevented from penetrating into the voids of the conductive porous substrate, and a catalyst layer consisting of a uniform thin film is easily formed on the conductive porous substrate.

[0018] On the other hand, if the surface tension of the solvent of the composition for forming a catalyst layer is attempted to be made smaller than 23 mN / m, not only would the solvents that can be used be limited, but also the conductive porous substrates that can be used would be limited, so the surface tension of the solvent is adjusted to be 23 mN / m or more.

[0019] Furthermore, if the surface tension of the solvent of the catalyst layer-forming composition exceeds 33 mN / m, it becomes difficult to apply the composition uniformly to the conductive porous substrate, and therefore the surface tension of the solvent is adjusted to 33 mN / m or less.

[0020] Even if the surface tension of the solvent of the composition for forming a catalyst layer is in the range of 23 to 33 mN / m, if the difference between the surface tension of the solvent and the critical surface tension of the conductive porous substrate becomes too large, the wettability of the substrate to the composition will be too low, making it difficult to uniformly apply the paint for forming a catalyst layer to the surface of the conductive porous substrate. Therefore, the difference between the surface tension of the solvent and the critical surface tension of the conductive porous substrate: (surface tension of the solvent) - (critical surface tension of the conductive porous substrate) is desirably 6 mN / m or less, and more desirably 4 mN / m or less.

[0021] The surface tension of a solvent can be measured by the pendant drop method, plate method, ring method, etc., if a literature value is available. If no literature value is available, the surface tension of the liquid can be measured by the pendant drop method, plate method, ring method, etc. The pendant drop method is a method in which a liquid is dropped from the end of a vertically placed thin tube and the surface tension of the liquid is calculated by analyzing the shape of the largest hanging drop that does not fall. The plate method is a method in which a platinum plate is immersed in the liquid and the force with which the plate is pulled by the liquid is measured to calculate the surface tension of the liquid. The ring method is a method in which a ring is immersed in the liquid and then gradually pulled up, and the force with which the liquid pulls the ring is measured at the moment when the film formed between the ring and the liquid surface breaks, to calculate the surface tension of the liquid.

[0022] In addition, since the composition for forming a catalyst layer contains catalyst particles with an average primary particle diameter of 1 to 500 nm, the surface area of ​​the catalyst particles can be increased, and a catalyst layer with a large active surface can be formed. The primary particle diameter of the catalyst particles can be measured from images measured with a scanning electron microscope (SEM) or the like, and the average value for 200 particles can be taken as the average particle diameter, for example.

[0023] The solid content of the catalyst layer forming composition must be 1 to 20% by mass. If the solid content exceeds 20% by mass, precise adjustment of the coating gap in the coating process of the catalyst layer forming composition is required, making it difficult to form a thin-film catalyst layer by a continuous coating method. On the other hand, if the solid content is below 1% by mass, the amount of solvent in the catalyst layer forming composition increases, and as described above, even if the surface tension of the solvent is set in the range of 23 to 33 mN / m, the catalyst layer forming composition (paint) tends to penetrate into the voids of the conductive porous substrate, making it difficult to form a uniform thin-film catalyst layer on the conductive porous substrate.

[0024] The catalyst particles can be composed of a metal or metal oxide containing at least one element selected from the group consisting of copper (Cu), tin (Sn), manganese (Mn), iron (Fe), nickel (Ni), titanium (Ti), cobalt (Co), zinc (Zn), indium (In), molybdenum (Mo), tungsten (W), yttrium (Y), zirconium (Zr), palladium (Pd), gold (Au), silver (Ag), ruthenium (Ru), rhodium (Rh), platinum (Pt), cerium (Ce), iridium (Ir), and bismuth (Bi).

[0025] The binder may be at least one selected from the group consisting of polyperfluorocarbon sulfonic acid, polystyrene, polyether ketone, polyether ether ketone, polysulfone, polyether sulfone, polyvinylidene fluoride, polytetrafluoroethylene, polyacrylic acid, and polyimide. The binder may be selected according to compatibility with the substrate on which the catalyst layer forming composition is applied, catalyst particles, solvent, and the like used together.

[0026] The solvent may be at least one selected from the group consisting of isopropanol, 2-isopropoxyethanol, methoxypropanol, butylpropylene diglycol, isobutyl diglycol, dimethyl diglycol, propylene glycol, methylpropylene triglycol, butyl diglycol, methyl glycol, propylpropylene diglycol, isopropyl diglycol, benzyl glycol, benzyl diglycol, phenyl glycol, and ethylene glycol.

[0027] (Method of manufacturing catalyst layer) An embodiment of the method for producing a catalyst layer of the present application will be described. The method for producing a catalyst layer of the present application includes a step of applying the above-mentioned composition for forming a catalyst layer of the present application onto a conductive porous substrate and drying the composition, and the critical surface tension of the conductive porous substrate is less than 29 mN / m and is smaller than the surface tension of the solvent of the composition for forming a catalyst layer.

[0028] The method for producing a catalyst layer of this embodiment includes a step of applying the above-mentioned catalyst layer-forming composition of the present application, i.e., a catalyst layer-forming composition containing a solvent (a single solvent or a mixed solvent of two or more solvents) having a surface tension in the range of 23 to 33 mN / m, onto a conductive porous substrate having a critical surface tension of less than 29 mN / m, which is smaller than the surface tension of the solvent, and drying the composition.As described above, even if the catalyst layer-forming paint is directly applied to a conductive porous substrate having a large number of pores used in gas diffusion electrodes of fuel cells, electrolysis cells, etc., the paint for forming a catalyst layer is prevented from penetrating into the pores of the conductive porous substrate, and a catalyst layer consisting of a uniform thin film can be formed on the conductive porous substrate.

[0029] That is, the critical surface tension is the surface tension of a liquid that can completely wet a solid surface (contact angle is 0°), and when a catalyst layer forming composition containing a solvent having a surface tension greater than the critical surface tension of the conductive porous substrate is applied to the conductive porous substrate, the catalyst layer forming composition is less likely to wet the conductive porous substrate. Therefore, even if the catalyst layer forming paint is directly applied to a conductive porous substrate having a large number of voids, the catalyst layer forming paint is prevented from penetrating into the voids of the conductive porous substrate, and a catalyst layer consisting of a uniform thin film can be formed on the conductive porous substrate.

[0030] The critical surface tension is measured by a method conforming to JIS K 6768, and can be obtained by measuring the contact angle (θ) between the film made of the conductive porous substrate and the liquid using several types of known liquids with different surface tensions, plotting cosθ against the surface tension, and finding the point where cosθ = 1. Examples of known liquids with different surface tensions include water (73.0 mN / m), formamide (58.0 mN / m), ethylene glycol monoethyl ether (30.0 mN / m), methanol (22.6 mN / m), and the like, as well as a mixed solution of the liquids described in JIS K 6768.

[0031] In addition, in the method for producing a catalyst layer of this embodiment, the catalyst layer forming composition can be applied to the conductive porous substrate by, for example, a bar coating method or a spin coating method. When a conventional catalyst layer forming composition is applied to a conductive porous substrate by a bar coating method or a spin coating method, the catalyst layer forming paint penetrates into the voids of the conductive porous substrate, making it difficult to form a catalyst layer made of a uniform thin film on the conductive porous substrate. Furthermore, when the catalyst layer forming paint penetrates into the voids of the conductive porous substrate, the application itself may be difficult. However, in the method for producing a catalyst layer of this embodiment, since the catalyst layer forming composition of the present application is used, even if the catalyst layer forming composition is directly applied to the conductive porous substrate by a bar coating method or a spin coating method, the catalyst layer forming paint is prevented from penetrating into the voids of the conductive porous substrate, and a catalyst layer made of a uniform thin film can be formed on the conductive porous substrate.

[0032] In particular, when the above-mentioned catalyst layer-forming composition is applied onto the conductive porous substrate by a bar coating method, there is little aggregation of catalyst particles even in microscopic areas, and a thin film composed of catalyst nanoparticles can be uniformly formed on the conductive porous substrate.

[0033] On the other hand, when the catalyst layer forming composition is applied to the conductive porous substrate by spray coating, the coating surface is more likely to be non-uniform due to the droplets of the spray coating liquid than by bar coating or spin coating. That is, depending on the device, the amount of the spray coating liquid applied (spray amount) is small, so that it is difficult to suppress the aggregation of catalyst particles in microscopic regions, especially when forming a thin film, and it may be difficult to ensure uniformity. Therefore, it is preferable to use bar coating or spin coating, especially when forming a thin catalyst layer.

[0034] The conductive porous substrate preferably has a contact angle with the catalyst layer-forming composition of 15 to 130°. Even if the contact angle is within this range, even if the catalyst layer-forming composition is directly applied to a conductive porous substrate having a large number of voids, the catalyst layer-forming paint is reliably prevented from penetrating into the voids of the conductive porous substrate, and a catalyst layer consisting of a uniform thin film can be formed on the conductive porous substrate.

[0035] If the contact angle is less than 15°, the paint for forming the catalyst layer will easily penetrate into the pores of the conductive porous substrate, the fluidity of the paint will decrease over a short period of time, and it will be difficult to form a uniform coating film. On the other hand, if the contact angle is more than 130°, the wettability of the paint with respect to the conductive porous substrate will be too low, and the paint may be repelled, resulting in uncoated areas.

[0036] The conductive porous substrate may be a porous film containing conductive particles having an average particle size of 10 to 100 nm and a binder. The conductive porous substrate will be described in detail in the description of the gas diffusion electrode of the present application below.

[0037] The drying temperature of the catalyst layer forming composition in the catalyst layer manufacturing method of this embodiment is preferably 25 to 180 ° C. If the drying temperature is lower than 25 ° C., the organic solvent may remain in the formed catalyst layer in excess of the allowable amount. When the catalyst layer in which the organic solvent remains in excess of the allowable amount is used as an electrode for a fuel cell or an electrolytic cell, an unnecessary side reaction occurs, and the reaction product adheres to the catalyst particles, which causes the catalyst particles to be inactivated or the resistance to increase. On the other hand, if the drying temperature exceeds 180 ° C., the binder used in the catalyst layer forming composition may be denatured. Therefore, it is more preferable to dry the catalyst layer at a low temperature of 150 ° C. or less under vacuum conditions that minimize the inflow and outflow of oxygen.

[0038] (Gas diffusion electrode) An embodiment of the gas diffusion electrode of the present application will be described. The gas diffusion electrode of this embodiment includes a conductive porous substrate and a catalyst layer formed on the surface of the conductive porous substrate, the critical surface tension of the conductive porous substrate is less than 29 mN / m, the catalyst layer includes catalyst particles having an average primary particle diameter of 1 to 500 nm and a binder, the thickness of the catalyst layer is 10 μm or less, and the ratio of the uncoated area of ​​the catalyst layer calculated by image analysis is 15% or less.

[0039] The gas diffusion electrode of the present embodiment is involved in electrochemical reactions in fuel cells, electrolysis cells, and the like, and the catalytic layer of the gas diffusion electrode is required to have a uniform surface. If the catalytic layer has an uneven surface, the electrochemical reaction becomes uneven, promoting local deterioration of the catalytic layer, and making it difficult to stably use the fuel cell or electrolysis cell for a long period of time.

[0040] In contrast, the gas diffusion electrode of the present embodiment has a catalyst layer thickness of 10 μm or less, and the ratio of the uncoated area of ​​the catalyst layer calculated by image analysis is 15% or less, so that a catalyst layer made of a uniform thin film can be provided on a conductive porous substrate, which makes the electrochemical reaction uniform, suppresses local deterioration of the catalyst layer, and enables stable long-term use of fuel cells and electrolysis cells.

[0041] The ratio of the uncoated area of ​​the catalyst layer can be calculated by image analysis using image analysis software "ImageJ". A specific method for measuring the ratio of the uncoated area of ​​the catalyst layer will be described in the examples below.

[0042] Next, an embodiment of the gas diffusion electrode of the present application will be described with reference to the drawings. Fig. 1 is a schematic cross-sectional view showing an example of the gas diffusion electrode of this embodiment. In Fig. 1, the gas diffusion electrode 10 includes a gas diffusion layer 11 in which a gas diffusion substrate 11a and a conductive porous substrate 11b formed on the gas diffusion substrate 11a are laminated, and a catalyst layer 12 formed on the conductive porous substrate 11b of the gas diffusion layer 11.

[0043] <Gas diffusion layer> The gas diffusion layer 11 is composed of a gas diffusion substrate 11 a and a conductive porous substrate 11 b, and has high gas permeability in order to supply a reaction gas to the catalyst layer 12.

[0044] [Conductive porous base material] The conductive porous substrate may be a porous membrane (nanoparticle-dispersed porous membrane) containing conductive particles (nanoparticles) having an average particle size of 10 to 100 nm and a binder. The conductive porous substrate corresponds to the microporous layer described in Patent Document 1, and is formed on one side of the gas diffusion substrate to provide the gas diffusion layer with a shielding property against the reaction solution. The conductive porous substrate also functions as a substrate for supporting the catalyst layer.

[0045] The conductive porous substrate can be made of a fibrous material or a nonwoven fabric as long as gas permeability is ensured, but it is preferable to use the nanoparticle-dispersed porous membrane. By using the nanoparticle-dispersed porous membrane containing the nanoparticles, fine pores are easily generated inside the substrate due to the shape of the nanoparticles and the distance between the particles, and the critical surface tension of the conductive porous substrate is easily set to less than 29 mN / m.

[0046] When an aqueous solution containing an electrolyte is used as the reaction liquid, it is desirable for the conductive porous substrate to have a critical surface tension of less than 23 mN / m in order to ensure sufficient water repellency against the reaction liquid.

[0047] The conductive porous substrate preferably has an average pore size of 0.1 to 1 μm in order to improve gas permeability. The conductive porous substrate also preferably has a porosity of 30 to 70 volume %, more preferably 50 to 70 volume %, in order to improve gas permeability. The average pore size and the porosity can be measured by a mercury intrusion method using a mercury porosimeter.

[0048] The thickness of the conductive porous substrate is not particularly limited, but if it is too thin, the shielding effect against the reaction solution decreases, so it is usually set to about 1 to 100 μm.

[0049] The conductive particles constituting the conductive porous substrate are used to impart conductivity to the conductive porous substrate. As the conductive particles, in consideration of electronic conductivity, electrochemical stability, etc., carbon black such as channel black, furnace black, ketjen black, acetylene black, lamp black, etc.; graphite; activated carbon; carbon nanohorn; carbon nanotube; etc., as well as conductive metal oxides such as ITO and ATO, etc., can be used, but carbon particles are the most preferred. Conductive metal oxides such as ITO and ATO are soluble in alkaline aqueous solutions and acidic aqueous solutions, so they can be used only when the reaction solution used is neutral.

[0050] The conductive particles have an average particle size of 10 to 100 nm. The average particle size of the conductive particles can be measured using a particle size distribution measuring device "LA-920" manufactured by Horiba, Ltd.

[0051] The binder constituting the conductive porous substrate may be polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polystyrene, polyether ketone, polyether ether ketone, polysulfone, polyether sulfone, polyacrylic acid, polyimide, or the like. In order to impart water repellency to the conductive porous substrate, a fluororesin such as PVDF or PTFE is preferred.

[0052] [Gas diffusion substrate] The gas diffusion substrate is used to impart gas permeability, which is the original function of the gas diffusion layer, and is also used as a substrate for holding the conductive porous substrate. For this reason, the gas diffusion substrate may be a substrate that has excellent mechanical durability, excellent gas permeability, and good compatibility with the conductive porous substrate, and is not necessarily conductive. However, when a catalyst layer is laminated on the gas diffusion layer to be used as a gas diffusion electrode, current collection can be obtained from the gas diffusion substrate, so it is preferable that the gas diffusion substrate also has conductivity. For this reason, the gas diffusion substrate is preferably formed from a porous conductive material. Specifically, carbon nonwoven fabric, carbon paper, etc. can be used as the gas diffusion substrate.

[0053] The thickness of the gas diffusion substrate is not particularly limited, but is usually set to, for example, about 100 to 300 μm.

[0054] The method for producing the gas diffusion layer is not particularly limited, but a composition containing the conductive particles and the binder (e.g., a paint consisting of a paste, slurry, etc.) can be applied onto a gas diffusion substrate and dried to form a gas diffusion layer in which a conductive porous substrate corresponding to the microporous layer described above is disposed on one side of the gas diffusion substrate.

[0055] The composition used in the production of the gas diffusion layer preferably contains a solvent to disperse the conductive particles and the binder. The solvent is not particularly limited as long as it can disperse each component sufficiently, and examples of the solvent that can be used include N-methyl-2-pyrrolidone (NMP), methanol, ethanol, water, etc.

[0056] The method for applying the composition is not particularly limited, and for example, a bar coater, a knife coater, a blade coater, a dip coater, a spin coater, a roll coater, a die coater, or the like can be used.

[0057] The amount of the composition to be applied on the gas diffusion substrate is not particularly limited, but is, for example, 0.8 to 3.0 mg / cm in terms of solid content. 2 This can be done as follows.

[0058] The drying temperature and drying time after coating the composition are not particularly limited, and for example, vacuum drying may be performed at a temperature of about 90 to 200° C. for about 1 to 10 hours.

[0059] <Catalyst layer> The catalyst layer 12 contains catalyst particles having an average primary particle size of 1 to 500 nm and a binder. The catalyst particles and binder constituting the catalyst layer 12 may be the same as those described in the embodiment of the composition for forming a catalyst layer of the present application.

[0060] The thickness of the catalyst layer is 10 μm or less. If the thickness of the catalyst layer is too small, there is a risk that the catalyst function may not be exerted, and therefore, the thickness of the catalyst layer is preferably 0.1 μm or more.

[0061] Furthermore, the proportion of the uncoated area of ​​the catalyst layer calculated by image analysis is 15% or less. Ideally, the proportion of the uncoated area should be 0%. However, taking into account factors such as analytical errors, it is difficult to achieve 0% in practice, and the lower limit is usually around 1%.

[0062] The content of the binder in the catalyst layer may be 2 to 100 parts by mass with respect to 100 parts by mass of the catalyst material.

[0063] The method for producing the catalyst layer is not particularly limited, but since the critical surface tension of the conductive porous substrate is less than 29 mN / m, it is preferable to produce the catalyst layer by the method for producing the catalyst layer of the present application using the composition for forming the catalyst layer of the present application. By doing so, as described above, the catalyst layer forming paint can be applied onto the conductive porous substrate having a large number of voids without penetrating into the voids, so that a catalyst layer made of a uniform thin film can be formed on the conductive porous substrate. More specifically, the thickness of the catalyst layer is 10 μm or less, and the ratio of the uncoated area of ​​the catalyst layer calculated by image analysis can be 15% or less.

[0064] (Electrolysis Cell) An embodiment of the electrolysis cell of the present application will be described. The electrolysis cell of this embodiment includes a positive electrode, a negative electrode, and an ion conductive membrane disposed between the positive electrode and the negative electrode, and uses the gas diffusion electrode of the present application as the positive electrode.

[0065] The electrolytic cell of the present embodiment uses the above-described gas diffusion electrode of the present application as the positive electrode, and thus has a catalyst layer made of a uniform thin film on the conductive porous substrate. This makes the electrochemical reaction uniform, suppresses local deterioration of the catalyst layer, and enables stable long-term use of the electrolytic cell.

[0066] Each of the components of the electrolytic cell of this embodiment will be described below, but since the gas diffusion electrode of the present invention is used for the positive electrode, the description thereof will be omitted.

[0067] <Negative electrode> The negative electrode functions as an oxidation electrode that oxidizes water to generate oxygen, and includes a gas diffusion layer and a negative electrode catalyst layer, but the negative electrode may be composed of only the negative electrode catalyst layer. The gas diffusion layer can be composed of a porous electron conductive material, and for example, carbon nonwoven fabric, carbon paper, etc. can be used.

[0068] The negative electrode catalyst layer can be formed from a catalyst material, a conductive material, and a binder. Examples of the catalyst material used for the negative electrode catalyst layer include fine metal particles such as platinum (Pt) and palladium (Pd).

[0069] The conductive material is not particularly limited, but in consideration of electronic conductivity, electrochemical stability, etc., carbon material powders with a large specific surface area, such as carbon black, activated carbon, carbon nanohorns, and carbon nanotubes, are preferred.

[0070] The particle diameter of the metal particles used in the negative electrode catalyst material is preferably 1 to 50 nm in order to enhance catalytic activity. The negative electrode catalyst material is preferably supported on the surface of the conductive material powder. This is because the electronic conductivity of the negative electrode catalyst material is improved. The content of the negative electrode catalyst material in the conductive material supporting the negative electrode catalyst material is not particularly limited, but can be, for example, 10 to 500 parts by mass relative to 100 parts by mass of the conductive material.

[0071] The binder may be the same as that used in the catalyst layer of the positive electrode (the gas diffusion electrode of the present application described above). The content of the binder in the negative electrode catalyst layer may be 2 to 100 parts by mass with respect to 100 parts by mass of the negative electrode catalyst material.

[0072] The negative electrode catalyst layer can be formed, for example, by preparing a catalyst paint containing a support in which a catalyst material is supported on a conductive material, a binder, and a solvent, applying this catalyst paint to the negative electrode gas diffusion layer, and then removing the solvent.

[0073] <Ion-conductive membrane> A cation exchange membrane can be used as the ion conductive membrane. The cation exchange membrane preferably contains a proton conductive organic material such as polyperfluorocarbon sulfonic acid, polystyrene, polyether ketone, polyether ether ketone, polysulfone, or polyether sulfone. This is because the stability of these organic materials can be improved by forming a crosslinked structure or by partially fluorinating them. In particular, the proton conductive organic material is preferably polyperfluorocarbon sulfonic acid, which exhibits good proton conductivity in a wet state.

[0074] An anion exchange membrane can also be used as the ion conductive membrane. An anion exchange membrane is a membrane that converts, for example, an anion (OH - The anion exchange membrane can be formed of hydrotalcite or the like having selective permeability to the anion-exchange membrane. In addition, as the anion exchange membrane, a membrane having a polymer matrix and particles of a metal compound dispersed in the matrix can also be used.

[0075] Next, an embodiment of the electrolytic cell of the present application will be described with reference to the drawings. Fig. 2 is a schematic cross-sectional view showing an example of a carbon dioxide electrolytic cell of this embodiment. In Fig. 2, the electrolytic cell 30 includes a membrane electrode assembly 31, which is composed of a positive electrode 21, a negative electrode 22, and an ion conductive membrane 23. However, since Fig. 2 is a schematic cross-sectional view for facilitating understanding of the drawing, the thickness ratio of each member constituting the electrolytic cell may differ from the actual ratio.

[0076] The positive electrode 21 includes a gas diffusion layer 21a and a catalyst layer 21b. Since the gas diffusion electrode of the present application described above is used for the positive electrode 21, the gas diffusion layer 21a is composed of a conductive porous substrate and a gas diffusion substrate, but the distinction between them is omitted in Fig. 2. The negative electrode 22 includes a gas diffusion layer 22a and a catalyst layer 22b, but the negative electrode 22 may be composed of only the catalyst layer 22b.

[0077] The electrolysis cell 30 includes current collectors 24, 25 on the outside of the gas diffusion layer 21a of the positive electrode 21 and the gas diffusion layer 22a of the negative electrode 22, respectively. The current collector 24 on the positive electrode 21 side is provided with a hole 24a for taking in a reactive gas (gas containing carbon dioxide), and is further connected to a lead body 24b. In addition, a reactive gas flow path 26 is provided on the outside of the current collector 24.

[0078] A hole 25a for taking in the electrolyte is provided in the current collector 25 on the negative electrode 22 side, and a lead body 25b is further connected to the hole 25a. An electrolyte container 27 is provided on the outside of the current collector 25 and is filled with electrolyte .

[0079] The electrolyte solution is an aqueous solution containing an electrolyte, and the electrolyte is, for example, hydroxide ions (OH - ), hydrogen ion (H + ), potassium ion (K + ), sodium ion (Na + ), chloride ion (Cl - ), bromide ion (Br - ), iodide ion (I -), nitrate ion (NO 3 - ), sulfate ion (SO 4 2- ), phosphate ion (PO 4 2- ), bicarbonate ion (HCO 3 - ), carbonate ion (CO 3 2- ) etc.

[0080] The current collecting plates 24, 25 may be made of, for example, a precious metal such as platinum or gold, a corrosion-resistant metal such as stainless steel, or a carbon material, etc. Furthermore, the surfaces of these materials may be plated or painted to improve corrosion resistance.

[0081] The membrane electrode assembly 31 is sandwiched between current collector plates 24 and 25 and sealed with a sealant 29 to form an electrolysis cell 30 .

[0082] In FIG. 2, when a current is supplied between the negative electrode 22 and the positive electrode 21, the negative electrode 22 2 O→4H + +O 2 +4e - of water (H 2 O) occurs, and protons H + and e - This proton H + moves to the positive electrode 21 through the ion conductive membrane 23. Meanwhile, at the positive electrode 21, protons H + and e - This results in the following carbon dioxide (CO 2 ) is reduced to carbon monoxide (CO) and methane (CH 4 ), ethylene (C 2 H 4 ) and other carbon compounds are produced.

[0083] 2CO 2 +4H + +4e - →2CO+2H 2 O CO+6H + +6e -→CH 4 +H 2 O 2CO+8H + +8e - →C 2 H 4 +2H 2 O EXAMPLES

[0084] The present application will be described below with reference to examples, but the present application is not limited to the following examples.

[0085] Example 1 <Preparation of conductive porous substrate forming paint> Carbon black (CB, average particle size: 50 nm) was prepared as conductive particles, polytetrafluoroethylene (PTFE) dispersion (solid content concentration: 60%) was prepared as binder resin, ion-exchanged water was prepared as solvent, and polyoxyethylene (10) octylphenyl ether (OPE) was prepared as surfactant. Next, the above components were mixed in a mass ratio of CB: PTFE dispersion: ion-exchanged water: OPE = 1: 0.3: 12: 0.1 to prepare a conductive porous substrate forming paint.

[0086] <Preparation of gas diffusion layer> A carbon nonwoven fabric with a thickness of 205 μm and a porosity of 83% was prepared as the gas diffusion substrate of the gas diffusion layer. Next, the prepared conductive porous substrate forming paint was applied to one side of the carbon nonwoven fabric, dried, and baked for 1 hour in a nitrogen atmosphere at 360°C to prepare a gas diffusion layer in which the conductive porous substrate was laminated on the carbon nonwoven fabric. After baking, the conductive porous substrate had a thickness of 15 μm, an average pore size of 0.25 μm, a porosity of 44.5 vol% and a critical surface tension of 22.6 mN / m.

[0087] <Preparation of catalyst layer forming paint> Copper particles (Cu, average particle size: 25 nm) were prepared as catalyst particles, 5 mass% Nafion dispersion solution was prepared as binder resin, and methoxypropanol (PGM, surface tension: 23.5 mN / m) was prepared as solvent. Next, the above components were mixed in a mass ratio of Cu: 5 mass% Nafion dispersion solution: PGM = 3: 5: 55 to prepare a catalyst layer forming paint. The solid content concentration of the prepared catalyst layer forming paint was 5 mass%, and the contact angle of the catalyst layer forming paint with respect to the conductive porous substrate was 42.1°.

[0088] <Preparation of gas diffusion electrode> The catalyst layer forming paint thus prepared was applied to the surface of the conductive porous substrate of the gas diffusion layer in an amount of 0.2 mg / cm. 2 The mixture was applied using a bar coater to prepare a gas diffusion electrode of Example 1.

[0089] <Calculation of the ratio of uncoated area of ​​catalyst layer by image analysis> First, a scanning electron microscope (SEM) image of the surface of the catalyst layer of the gas diffusion electrode was taken. The SEM image is shown in Figure 3A.

[0090] Next, the captured SEM images were analyzed using the image analysis software “ImageJ” in the following procedure.

[0091] (1) Divide the particle-present part and the particle-absent part by binarization, and perform binary conversion in which the particle-present part is set to 0 and the particle-absent part is set to 255. (2) Using the Analyze Particles function, measure the area of ​​each non-existent region within the field of view. There are no upper or lower limits for the area, and all sizes from 0 to infinity are measured. At this time, turn on the "include holes" setting to not count small gaps within one region (in this case, rare particles scattered here and there in an area that can be determined to be an uncoated area). (3) The results of the image analysis are shown in Figure 3B as an extracted image of interparticle voids.

[0092] Thereafter, all the counted uncoated areas were tabulated using a tabulation software such as Excel, and an area distribution diagram of the uncoated areas was obtained. From this area distribution diagram, the percentage of the uncoated area of ​​the catalyst layer was calculated, which was 4.63%.

[0093] The thickness of the catalyst layer measured from the cross-sectional SEM image of the prepared gas diffusion electrode was 0.4 to 1.1 μm. Moreover, from the cross-sectional SEM image, in the gas diffusion electrode of this example, the catalyst layer was formed smoothly, no coating unevenness of the catalyst layer occurred, and furthermore, soaking of the catalyst layer-forming paint into the conductive porous substrate was not observed.

[0094] Example 2 A catalyst layer-forming paint was prepared in the same manner as in Example 1, except that the solid content concentration of the catalyst layer-forming paint was changed to 18 mass %, and the amount of the catalyst layer-forming paint applied to the surface of the conductive porous substrate was 1.7 mg / cm. 2 A gas diffusion electrode of Example 2 was produced in the same manner as in Example 1, except for changing the above.

[0095] Fig. 4A shows an SEM image of the surface of the catalyst layer of the prepared gas diffusion electrode, and Fig. 4B shows an extracted diagram of interparticle voids as a result of measurement by image analysis carried out in the same manner as in Example 1. Furthermore, the proportion of the uncoated area of ​​the catalyst layer was determined in the same manner as in Example 1 and was found to be 0.11%.

[0096] A cross-sectional SEM image of the produced gas diffusion electrode is shown in Fig. 5. The thickness of the catalyst layer measured from Fig. 5 was 8.0 to 8.5 µm. Also, from Fig. 5, in the gas diffusion electrode of this example, the catalyst layer was formed smoothly, no coating unevenness of the catalyst layer occurred, and furthermore, soaking of the catalyst layer-forming paint into the conductive porous substrate was not observed.

[0097] ( reference Example 3) The solvent for the catalyst layer forming paint is P Polypropylene glycol (PG, surface tension: 35.4A catalyst layer-forming paint was prepared in the same manner as in Example 1, except that the pressure change was changed to 1.0 mN / m and the solid content concentration was changed to 10 mass %. The contact angle of the prepared catalyst layer-forming paint with respect to the conductive porous substrate was 125.8°.

[0098] The same procedure as in Example 1 was carried out except that this catalyst layer forming paint was used. reference The gas diffusion electrode of Example 3 was prepared.

[0099] Fig. 6A shows an SEM image of the surface of the catalyst layer of the prepared gas diffusion electrode, and Fig. 6B shows an extracted diagram of interparticle voids as a result of measurement by image analysis carried out in the same manner as in Example 1. Furthermore, the ratio of the uncoated area of ​​the catalyst layer was determined in the same manner as in Example 1, and was found to be 12.85%.

[0100] The thickness of the catalyst layer measured from the cross-sectional SEM image of the prepared gas diffusion electrode was 0.7 to 2.0 μm. In addition, from the cross-sectional SEM image, in the gas diffusion electrode of this example, the catalyst layer was formed smoothly, no coating unevenness of the catalyst layer occurred, and furthermore, soaking of the catalyst layer forming paint into the conductive porous substrate was not observed.

[0101] Example 4 Except for changing the solvent of the catalyst layer-forming paint to methyl glycol (MG, surface tension: 26.6 mN / m) and changing the solid content concentration to 8 mass%, a catalyst layer-forming paint was prepared in the same manner as in Example 1. The contact angle of the prepared catalyst layer-forming paint with respect to the conductive porous substrate was 52.0°.

[0102] A gas diffusion electrode of Example 4 was produced in the same manner as in Example 1, except that this catalyst layer-forming paint was used.

[0103] Fig. 7A shows an SEM image of the surface of the catalyst layer of the prepared gas diffusion electrode, and Fig. 7B shows an extracted diagram of interparticle voids as a result of measurement by image analysis carried out in the same manner as in Example 1. Furthermore, the ratio of the uncoated area of ​​the catalyst layer was determined in the same manner as in Example 1, and was found to be 4.57%.

[0104] The thickness of the catalyst layer measured from the cross-sectional SEM image of the prepared gas diffusion electrode was 0.4 to 1.2 μm. Moreover, from the cross-sectional SEM image, in the gas diffusion electrode of this example, the catalyst layer was formed smoothly, no coating unevenness of the catalyst layer occurred, and furthermore, soaking of the catalyst layer-forming paint into the conductive porous substrate was not observed.

[0105] (Reference example 1) A catalyst layer-forming paint was prepared in the same manner as in Example 1, and this catalyst layer-forming paint was applied to the surface of the conductive porous substrate of the gas diffusion layer prepared in the same manner as in Example 1 in an amount of 1.5 mg / cm. 2 A gas diffusion electrode of Reference Example 1 was produced in the same manner as in Example 1, except that the coating was performed using a spray coater.

[0106] Fig. 8A shows an SEM image of the surface of the catalyst layer of the prepared gas diffusion electrode, and Fig. 8B shows an extracted diagram of interparticle voids as a result of measurement by image analysis carried out in the same manner as in Example 1. Furthermore, the ratio of the uncoated area of ​​the catalyst layer was determined in the same manner as in Example 1, and was found to be 17.02%.

[0107] A cross-sectional SEM image of the prepared gas diffusion electrode is shown in Fig. 9. The thickness of the catalyst layer measured from Fig. 9 was 5 to 11 µm. Also, from Fig. 9, in the gas diffusion layer of this reference example, the catalyst layer-forming paint was not seen to soak into the conductive porous substrate, but the catalyst layer was not formed in the area indicated by the arrow in the figure, and coating unevenness of the catalyst layer occurred.

[0108] (Reference example 2) A catalyst layer-forming paint was prepared in the same manner as in Example 1, and this catalyst layer-forming paint was applied to the surface of the conductive porous substrate of the gas diffusion layer prepared in the same manner as in Example 1 in an amount of 0.2 mg / cm. 2 A gas diffusion electrode of Reference Example 2 was produced in the same manner as in Example 1, except that the coating was performed using a spray coater.

[0109] Fig. 10A shows an SEM image of the surface of the catalyst layer of the prepared gas diffusion electrode, and Fig. 10B shows an extracted diagram of interparticle voids measured by image analysis carried out in the same manner as in Example 1. The proportion of the uncoated area of ​​the catalyst layer was determined in the same manner as in Example 1 and was found to be 41.7%.

[0110] The thickness of the catalyst layer measured from the cross-sectional SEM image of the prepared gas diffusion electrode was 0.4 to 1 μm. In addition, the cross-sectional SEM image showed that the catalyst layer-forming paint was not soaked into the conductive porous substrate in the gas diffusion electrode of this reference example, but the coating unevenness of the catalyst layer was greater than that in the gas diffusion electrode of reference example 1.

[0111] Comparative Example 1 A catalyst layer-forming paint was prepared in the same manner as in Example 1, except that the solvent of the catalyst layer-forming paint was changed to isopropyl alcohol (IPA, surface tension: 20.8 mN / m) and the solid content concentration was changed to 10 mass %. The contact angle of the prepared catalyst layer-forming paint with respect to the conductive porous substrate was 8.1°.

[0112] This catalyst layer-forming paint was applied to the surface of the conductive porous substrate of the gas diffusion layer prepared in the same manner as in Example 1 in an amount of 1 mg / cm. 2 When the coating was performed using a bar coater, within a few to several tens of seconds after coating had begun, only the solvent of the catalyst layer-forming paint had penetrated into the conductive porous substrate, and coating could not be continued due to the paint clumping and the appearance of streaks of uncoated areas.

[0113] Fig. 11A shows an SEM image of the surface of the catalytic layer of the gas diffusion electrode formed immediately after the start of coating, and Fig. 11B shows an extracted diagram of interparticle voids measured by image analysis carried out in the same manner as in Example 1. The proportion of the uncoated area of ​​the catalytic layer was determined in the same manner as in Example 1 and was found to be 1.53%.

[0114] A cross-sectional SEM image of the prepared gas diffusion electrode is shown in FIG. 12. The thickness of the catalyst layer measured from FIG. 12 was 3 to 5 μm. Also, from FIG. 12, in the gas diffusion layer of this comparative example, unevenness was generated at the interface between the catalyst layer and the conductive porous substrate, and soaking of the catalyst layer forming paint into the conductive porous substrate was confirmed. Furthermore, it can be seen that the catalyst layer was not formed in the area indicated by the arrow in the figure, and coating unevenness of the catalyst layer occurred.

[0115] Comparative Example 2 <Preparation of conductive porous substrate forming paint> A conductive porous substrate-forming coating material was prepared in the same manner as in Example 1, except that carbon black having an average particle size of 40 nm was used as the conductive particles.

[0116] <Preparation of gas diffusion layer> A carbon nonwoven fabric with a thickness of 160 μm and a porosity of 70.1% was prepared as the gas diffusion substrate of the gas diffusion layer. Next, the prepared conductive porous substrate forming paint was applied to one side of the carbon nonwoven fabric and dried, and a gas diffusion layer was prepared in which the conductive porous substrate was laminated on the carbon nonwoven fabric without performing a baking treatment. After drying, the conductive porous substrate had a thickness of 75 μm, an average pore size of 0.39 μm, a porosity of 62.7%, and a critical surface tension of 24.2 mN / m.

[0117] <Preparation of gas diffusion electrode> A catalyst layer-forming paint prepared in the same manner as in Example 1, which has a contact angle of 10.3° with respect to the conductive porous substrate, was applied to the surface of the conductive porous substrate of the prepared gas diffusion layer in an amount of 0.2 mg / cm. 2 When the coating was applied using a bar coater, the coating material penetrated into the conductive porous substrate as soon as coating began, and the coating could not be spread using the bar coater.

[0118] The above results are summarized in Table 1.

[0119] [Table 1]

[0120] From Table 1, Example 1 in which the catalyst layer forming paint was applied by the bar coating method 、2、 It can be seen that in the gas diffusion electrode of 4, a catalyst layer consisting of a uniform thin film can be formed on the conductive porous substrate.

[0121] On the other hand, in Reference Example 1, in which the same paint as in Example 1 was spray-coated at an increased amount, and in Reference Example 2, in which the same paint as in Example 1 was spray-coated at the same amount as in Example 1, 、2、 As with the gas diffusion electrode of Example 4, the catalyst layer forming paint was prevented from penetrating into the pores of the conductive porous substrate. However, the ratio of the uncoated area exceeded 15% in both cases, and the catalyst layer forming paint was prevented from penetrating into the pores of the conductive porous substrate. 、2、 As a result, the uniformity of the catalyst layer was lower than that of the gas diffusion electrode of Example 4. In addition, in both Comparative Example 1 and Comparative Example 2, in which the surface tension of the paint solvent was set to a value smaller than the critical surface tension of the substrate, the catalyst layer-forming paint penetrated into the voids of the conductive porous substrate, and therefore, coating could not be continued or coating could not be performed at all.

[0122] The present application can be implemented in other forms than those described above. The embodiments disclosed in the present application are merely examples and are not limited thereto. The scope of the present application shall be interpreted in accordance with the appended claims rather than the above description of the specification, and all modifications within the scope of the claims are intended to be included in the scope of the claims. [Industrial Applicability]

[0123] As described above, the gas diffusion electrode of the present application has a uniform catalytic layer. Therefore, in an electrolysis cell using the gas diffusion electrode, the electrochemical reaction becomes uniform, local deterioration of the catalytic layer can be suppressed, and the electrolysis cell can be used stably for a long period of time. [Explanation of symbols]

[0124] 10 Gas diffusion electrode 11 Gas diffusion layer 11a Gas diffusion substrate 11b Conductive porous substrate 12 Catalyst layer 21 Positive electrode 21a Gas diffusion layer 21b Catalyst layer 22 Negative electrode 22a Gas diffusion layer 22b Catalyst layer 23 Ion-conducting membrane 24, 25 Current collector plate 24a, 25a hole 24b, 25b lead body 26 Reaction gas flow path 27 Electrolyte container 28 Electrolyte 29 Sealing materials 30 Electrolysis Cell 31 Membrane electrode assembly

Claims

1. A catalyst layer forming composition comprising catalyst particles, a binder, and a solvent, The catalyst particles have an average primary particle size of 1 to 500 nm, The solvent has a surface tension in the range of 23 to 33 mN / m; A composition for forming a catalyst layer, characterized in that the solid content concentration is 1 to 20 mass %.

2. 2. The catalyst layer forming composition according to claim 1, wherein the catalyst particles are composed of a metal or metal oxide containing at least one element selected from the group consisting of Cu, Sn, Mn, Fe, Ni, Ti, Co, Zn, In, Mo, W, Y, Zr, Pd, Au, Ag, Ru, Rh, Pt, Ce, Ir, and Bi.

3. 2. The catalyst layer forming composition according to claim 1, wherein the binder is at least one selected from the group consisting of polyperfluorocarbon sulfonic acid, polystyrene, polyether ketone, polyether ether ketone, polysulfone, polyether sulfone, polyvinylidene fluoride, polytetrafluoroethylene, polyacrylic acid, and polyimide.

4. 2. The catalyst layer forming composition according to claim 1, comprising as the solvent at least one selected from the group consisting of isopropanol, 2-isopropoxyethanol, methoxypropanol, butylpropylene diglycol, isobutyl diglycol, dimethyl diglycol, propylene glycol, methylpropylene triglycol, butyl diglycol, methyl glycol, propylpropylene diglycol, isopropyl diglycol, benzyl glycol, benzyl diglycol, phenyl glycol, and ethylene glycol.

5. The method includes a step of applying the catalyst layer forming composition according to any one of claims 1 to 4 onto a conductive porous substrate and drying the composition, A method for producing a catalyst layer, characterized in that the critical surface tension of the conductive porous substrate is less than 29 mN / m, and the critical surface tension is a value smaller than the surface tension of a solvent of the composition for forming a catalyst layer.

6. The method for producing a catalyst layer according to claim 5, wherein the coating is carried out by a bar coating method or a spin coating method.

7. 6. The method for producing a catalyst layer according to claim 5, wherein the conductive porous substrate has a contact angle with the composition for forming a catalyst layer of 15 to 130°.

8. 6. The method for producing a catalyst layer according to claim 5, wherein the conductive porous substrate is a porous film containing conductive particles having an average particle size of 10 to 100 nm and a binder.

9. The method for producing a catalyst layer according to claim 8, wherein the conductive particles are carbon particles.

10. The method for producing a catalyst layer according to claim 5, wherein the drying temperature of the composition for forming a catalyst layer is 25 to 180°C.

11. A gas diffusion electrode comprising a conductive porous substrate and a catalyst layer formed on a surface of the conductive porous substrate, The critical surface tension of the conductive porous substrate is less than 29 mN / m; The catalyst layer includes catalyst particles having an average primary particle size of 1 to 500 nm and a binder, The thickness of the catalyst layer is 10 μm or less, A gas diffusion electrode, characterized in that the ratio of an uncoated area of ​​the catalyst layer calculated by image analysis is 15% or less.

12. 12. The gas diffusion electrode according to claim 11, wherein the catalyst layer has a thickness of 0.1 μm or more.

13. 12. The gas diffusion electrode according to claim 11, wherein the conductive porous substrate is a porous film containing conductive particles having an average particle size of 10 to 100 nm and a binder.

14. 14. The gas diffusion electrode of claim 13, wherein the conductive particles are carbon particles.

15. 12. The gas diffusion electrode according to claim 11, wherein the conductive porous substrate has an average pore size of 0.1 to 1 μm.

16. 12. The gas diffusion electrode according to claim 11, wherein the conductive porous substrate has a porosity of 30 to 70 volume %.

17. An electrolysis cell comprising a positive electrode, a negative electrode, and an ion-conducting membrane disposed between the positive electrode and the negative electrode, 17. An electrolytic cell, wherein the positive electrode is the gas diffusion electrode according to claim 11.

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