TWI861241B - Porous substrate with catalyst supported thereon for water electrolysis, electrode for water electrolysis, gas diffusion layer, stack cell for water electrolysis, and cell module for water electrolysis - Google Patents

Abstract

An objective of the present invention is to provide a porous substrate with catalyst supported thereon having a new configuration (form), which is excellent in water electrolysis performance and durability thereof in a water electrolysis cell, an electrode for water electrolysis, and a stack cell for water electrolysis using the same.

As a solution, the present invention provides a porous substrate with catalyst supported thereon 3, an electrode for water electrolysis 2, a gas diffusion layer using the same, a single cell for water electrolysis 1, a stack cell for water electrolysis 9, and a cell module for water electrolysis 10. The porous substrate with catalyst supported thereon 3 is a porous substrate 3p on which a catalyst 3c is supported, which sandwiches a PEM and forms a cathode or an anode in contact with the PEM and also functions as a gas diffusion layer.

The catalyst 3c is supported on a side surface of the pores of the porous substrate 3p or a side surface of a fiber 3q forming the porous substrate 3p, and is present from the surface to the inside of the porous substrate 3p itself.

The ionomer 4 is in contact with the catalyst 3c and such filled that it has a concentration gradient in the thickness direction of the porous substrate 3p from the surface of the porous substrate 3p toward the inside.

Description

A porous substrate holding a catalyst for water electrolysis, an electrode for water electrolysis, a gas diffusion layer, a stacked unit for water electrolysis, and a unit module for water electrolysis

The present invention relates to a porous substrate holding a catalyst for water electrolysis and an electrode for water electrolysis. More specifically, it relates to a porous substrate holding a catalyst for water electrolysis, an electrode for water electrolysis, a gas diffusion layer, a stacked unit for water electrolysis, and a unit module for water electrolysis, which are used when a polymer electrolyte membrane (PEM) is used for water electrolysis and have characteristics in the catalyst holding form, the ionic polymer in contact with the catalyst, and its existence form (filling form).

The membrane electrode assembly (MEA) used in fuel cells or "water electrolysis units for hydrogen production devices" has: an electrode with a catalyst layer, and a polymer electrolyte membrane (PEM membrane) sandwiched by an anode and a cathode.

In addition, in the conventional membrane electrode assembly (MEA), as shown in one example in FIG. 1(b), FIG. 2(b) and FIG. 2(c), the catalyst exists in the membrane electrode assembly (MEA) as a catalyst layer. In addition, the gas diffusion layer contacts the catalyst layer to capture the generated gas.

The invention described in Patent Document 1 is related to a method for manufacturing a membrane electrode assembly (MEA) that is judged as good when the amount of sulfate ions contained in the electrode catalyst layer is below a specified value. Patent Document 1 discloses a membrane electrode assembly having an electrode catalyst layer formed on the surface of a polymer electrolyte membrane and a method for manufacturing the same.

The manufacturing steps in this manufacturing method are described as follows. An electrolyte membrane and an electrode catalyst layer are prepared, a catalyst layer forming film is prepared using the prepared electrolyte membrane and electrode catalyst layer, and then a gas diffusion layer is prepared, and a membrane electrode assembly (MEA) is manufactured using the prepared catalyst layer forming film and the prepared gas diffusion layer.

However, the membrane electrode assembly (MEA) of Patent Document 1 is not only used for fuel cells, but the electrode catalyst layer of the membrane electrode assembly (MEA) is produced by continuously applying an ink containing an ion polymer and a catalyst on the surface of a substrate or an electrolyte membrane and drying it (thereby reducing the amount of sulfuric acid ions).

Patent document 2 discloses a method for manufacturing a durable membrane electrode assembly in which a "diffusion medium stacked with a catalyst layer" is molded onto a membrane without being heated. In this patent document 2, a catalyst layer is stacked on a diffusion medium layer, and then an ion polymer layer is disposed on the surface of the catalyst layer to manufacture a membrane electrode assembly (MEA) for a fuel cell.

However, in addition to being used in fuel cells, the membrane electrode assembly (MEA) of Patent Document 2 has a catalyst formed on a diffusion medium in the form of a catalyst layer, and an ionic polymer is also disposed on the entire surface of the catalyst layer by spraying. In addition, the manufacturing method of the catalyst layer of the membrane electrode assembly (MEA) is to continuously transfer or coat the catalyst layer in the form of a slurry on the diffusion medium layer, and once the catalyst is coated on a transfer substrate, it is transferred to the membrane by heated molding.

In recent years, with the expansion of the demand for hydrogen, excellent water electrolysis technology is required. However, there are still some shortcomings in the previous technology, and the performance and durability of the water electrolysis unit are still required to be more excellent.

[Prior Art Literature]

[Patent Literature]

[Patent document 1] Japanese Patent No. 6128099

[Patent Document 2] Japanese Patent No. 4738350

The present invention was completed in view of the above situation. The subject is to provide a water electrolysis unit (including a single water electrolysis unit, a stacked water electrolysis unit, etc.) with excellent water electrolysis performance or durability, and a porous substrate with a catalyst and a novel structure (form) different from the conventional ones.

In other words, it is to provide an electrode for water electrolysis with excellent water electrolysis performance or durability and a porous matrix holding a catalyst used in the electrode for water electrolysis.

The inventors of the present invention have conducted careful research to solve the above problems, and found that the water electrolysis performance and durability are excellent when the concept of the so-called "catalyst layer" is broken away and the catalyst layer is not set on the (porous) substrate.

It was found that if the catalyst is held in the pores constituting the porous matrix or in the fibers forming the porous matrix, the water electrolysis performance or durability is excellent.

In addition, it was found that if the catalyst is held as described above and the resulting porous substrate holding the catalyst is used to sandwich the polymer electrolyte membrane (PEM), the catalyst is less likely to be detached due to gas lift, and performance degradation is less likely to occur.

Furthermore, it was discovered that by filling the ionic polymer in a specific state from the electrode surface contacting the polymer electrolyte membrane, that is, the surface of the porous substrate holding the catalyst to the inside, a porous substrate holding the catalyst for water electrolysis with a reduced unit voltage (electrolysis voltage) and excellent water electrolysis performance and durability can be obtained, thus completing the present invention.

That is, the present invention provides a porous substrate holding a catalyst, which has the following structure: it exists in a single unit for water electrolysis in the form of sandwiching a polymer electrolyte membrane (PEM), and contacts the polymer electrolyte membrane (PEM) to form a cathode or an anode, and also plays the role of a gas diffusion layer.

The catalyst is supported on the side of the hole of the porous matrix or the side of the fiber forming the porous matrix, and exists in a manner covering from the surface of the porous matrix itself to the inside, and

The ionic polymer contacts the catalyst and is filled in a state having a concentration gradient in the thickness direction of the porous matrix from the surface toward the inside of the porous matrix.

In addition, the present invention provides the above-mentioned porous substrate carrying a catalyst obtained by the following steps: a step of attaching a metal catalyst or a metal catalyst precursor to the side of the pores of the porous substrate before baking or to the side of the fibers forming the porous substrate before baking and then baking.

In addition, the present invention provides the porous substrate holding the catalyst, wherein the film thickness or particle size of the catalyst is smaller than the average diameter length of the "voids formed by the pores and/or the gaps between the fibers".

In other words, the porous matrix holding the catalyst is provided, wherein the film thickness when the catalyst is held by a film or the particle size when the catalyst is held by particles is smaller than the size of "the gaps of the 'pores' and/or the gaps between the fibers".

In addition, the present invention provides the above-mentioned porous substrate holding the catalyst, wherein the material of the above-mentioned porous substrate is titanium (Ti) or titanium (Ti) alloy or carbon (C).

In addition, the present invention provides an electrode for water electrolysis, which is the porous matrix holding the catalyst as mentioned above.

In addition, the present invention provides a gas diffusion layer, which is the porous substrate holding the catalyst as mentioned above.

In addition, the present invention provides a single unit for water electrolysis, which has a structure in which a polymer electrolyte membrane (PEM) is sandwiched by the porous substrate holding the catalyst.

In addition, the present invention provides a stacked unit for water electrolysis, which is formed by stacking two or more of the above-mentioned single units for water electrolysis in a structure in which a polymer electrolyte membrane (PEM) is sandwiched by a porous substrate holding a catalyst as a single unit for water electrolysis.

In addition, the present invention provides a unit module for water electrolysis, which is formed by arranging the above-mentioned stacked units for water electrolysis in two or three dimensions.

According to the present invention, a method for solving the above-mentioned problems and issues can be provided. For example, due to the excellent water electrolysis performance such as the unit voltage maintaining a certain (low) value and being stable, and the catalyst being supported firmly and having good contact, a water electrolysis electrode with excellent durability can be provided. In addition, a single unit for water electrolysis or a stacked unit for water electrolysis using the water electrolysis electrode can be provided.

Specifically, the catalyst is supported on the porous matrix in a specific form or shape, so that the catalyst and the porous matrix can be integrated. Specifically, the catalyst is supported on the "surface of the pores or fibers constituting the porous carbon matrix" by catalyst particles or catalyst films, thereby having better water electrolysis performance and durability than the form of depositing the catalyst layer on the upper surface (or lower surface) of the (porous) matrix.

Specifically, for example, in the conventional method of stacking the catalyst on the substrate in a layered form, the catalyst layer may potentially peel off from the substrate due to air lift. However, according to the present invention, a porous substrate or an electrode for water electrolysis that holds a catalyst and prevents the catalyst from peeling off from a porous substrate or the catalyst from peeling off from a material constituting the porous substrate can be provided.

In addition, a single unit for water electrolysis or a stacked unit for water electrolysis using the porous substrate (electrode for water electrolysis) holding a catalyst can be provided.

Furthermore, by allowing the ionic polymer to exist (or fill) in a porous matrix holding a catalyst in a manner having a concentration gradient in the thickness direction, a stable low value of unit voltage (applied voltage) can be achieved, and an electrode for water electrolysis that is less likely to cause catalyst peeling or catalyst separation caused by air lift can be provided.

This "catalyst (film or particle) detachment" can be effectively prevented and suppressed by the synergistic effect of the aforementioned "support of the catalyst in a specific form by the porous matrix" and the aforementioned "presence of the ionic polymer layer in a specific form".

The porous substrate of the present invention that holds a catalyst is used as an electrode for water electrolysis, and a water electrolysis unit having a water electrolysis cathode, a polymer electrolyte membrane (PEM), and a water electrolysis anode in sequence can perform water electrolysis at a low electrolysis voltage without causing the catalyst membrane or catalyst particles to peel off or separate, so the durability is extremely high.

In addition, even if the unit voltage (applied voltage) is low, the single unit will operate, so the stacked unit for water electrolysis formed by stacking two or more "single units for water electrolysis using the porous matrix holding the catalyst" will operate even if the applied voltage is low. That is, when two or more single units for water electrolysis are stacked, the effect of "low voltage operation" can be achieved, and more hydrogen (and oxygen) can be obtained with less electricity.

1: Single unit for water electrolysis

2: Electrode for water electrolysis

3: Porous substrate holding the catalyst

3c: Metal catalyst, metal oxide catalyst, catalyst

3p: porous matrix

3q: Fibers and fibers forming a porous matrix

4: Ionic polymer

5: Polymer electrolyte membrane (PEM)

6: Power supply

7: Resin tank

8: Bipolar board

9: Stacking unit for water electrolysis

10: Unit module for water electrolysis

Figure 1 is a schematic unfolded three-dimensional diagram of a water electrolysis unit having a single unit for water electrolysis. (a) is a schematic unfolded three-dimensional diagram of a porous substrate (electrode for water electrolysis, gas diffusion layer) carrying a catalyst using the present invention, and (b) is a schematic unfolded three-dimensional diagram of a conventional water electrolysis unit.

FIG2 is a schematic cross-sectional view of a single unit for water electrolysis showing the existence form of the catalyst. (a) is a schematic cross-sectional view showing the "support form of the catalyst in the porous matrix" in the porous matrix holding the catalyst of the present invention, and (b) and (c) are schematic cross-sectional views showing the existence form of the conventional catalyst.

FIG3 is a schematic enlarged cross-sectional view of the porous substrate carrying the catalyst of the present invention.

FIG4 is an enlarged cross-sectional view showing that the ionic polymer and the contact catalyst are filled in a porous matrix carrying a catalyst in a state with a concentration gradient from the surface to the inside of the porous matrix. (a) is a schematic enlarged cross-sectional view corresponding to FIG3, and (b) is a SEM photograph showing the cross section of the actual porous matrix carrying a catalyst.

Figure 5 is a schematic enlarged cross-sectional view of a single unit for water electrolysis of the present invention, which is formed by sandwiching a polymer electrolyte membrane (PEM) with a porous substrate (which can be an electrode for water electrolysis or a gas diffusion layer) holding a catalyst.

Figure 6 is a schematic enlarged cross-sectional view showing an example of a state in which an ion polymer is filled in a state with a concentration gradient in the thickness direction from the surface of a water electrolysis electrode (a porous substrate holding a catalyst) toward the inside. (a) is a state in which an ion polymer is filled in a state with a concentration gradient from the surface on the side in contact with the polymer electrolyte membrane (PEM) and the power supply body (i.e., from both sides) toward the inside, and (b) is a state in which an ion polymer is filled in a state with a concentration gradient from the surface on the side in contact with the polymer electrolyte membrane (PEM) toward the inside.

FIG. 7 is a schematic unfolded three-dimensional diagram of the stacked unit for water electrolysis of the present invention formed by laminating two single units for water electrolysis of the present invention.

Figure 8 is a schematic diagram of the stacking unit for water electrolysis of the present invention. (a) is a three-dimensional diagram of the stacking unit connected with wiring and piping, (b) is a schematic cross-sectional diagram showing the "hydrogen outlet" on the cathode side and the "water inlet" and "water outlet and oxygen outlet" on the anode side, and (c) is a three-dimensional diagram of the stacking unit with wiring and piping omitted.

FIG9 is a schematic three-dimensional diagram of a unit module for water electrolysis in which the stacked units for water electrolysis of the present invention are arranged three-dimensionally.

The following is an explanation of the present invention, but the present invention is not limited to the following specific forms and can be arbitrarily modified within the scope of the technical concept.

<Porous substrate holding a catalyst>

The porous substrate holding a catalyst of the present invention is a porous substrate holding a catalyst having the following structure: it exists in a single unit for water electrolysis in the form of sandwiching a polymer electrolyte membrane (PEM (Polymer Electrolyte Membrane)), and contacts the polymer electrolyte membrane (PEM) to form a cathode or an anode, and also has a structure that functions as a gas diffusion layer,

The catalyst is supported on the side of the hole of the porous matrix or the side of the fiber forming the porous matrix, and exists in a manner covering from the surface of the porous matrix itself to the inside, and

The ionic polymer contacts the catalyst and is filled in a state having a concentration gradient in the thickness direction of the porous matrix from the surface toward the inside of the porous matrix.

The porous substrate with a catalyst of the present invention is used in a "single unit for water electrolysis" or a "stacked unit for water electrolysis formed by stacking two or more single units for water electrolysis" (hereinafter, both are sometimes collectively referred to as "units for water electrolysis").

As shown in Figures 1(a), 2(a), and 5, the porous substrate 3 holding the catalyst in the water electrolysis unit 1 of the present invention exists in the form of sandwiching the polymer electrolyte membrane (PEM) 5, and contacts the polymer electrolyte membrane (PEM) 5 to form the water electrolysis electrode 2 (cathode or anode).

In the present invention, the cathode or anode of the single unit 1 for water electrolysis must be composed of the porous substrate 3 holding the catalyst of the present invention, and preferably, both the cathode and the anode are composed of the porous substrate 3 holding the catalyst of the present invention.

However, the types or forms of the actual catalyst 3c, porous matrix 3p, etc. in the cathode and anode, and even their manufacturing methods, etc., may be different in the cathode and anode according to their respective polarities.

The porous substrate 3 holding the catalyst of the present invention has a structure that has the function of the electrode 2 for water electrolysis and also has the function of a gas diffusion layer. Therefore, the porous substrate 3 holding the catalyst of the present invention is also a gas diffusion layer.

As shown in Figures 3, 4 (a), (b) and the cross-sectional view of Figure 5, the porous substrate 3 holding the catalyst of the present invention holds the catalyst on a porous support that can diffuse the gas. That is, the gas generated near the catalyst of the porous substrate 3 holding the catalyst is moved (diffused) and captured to the outside because the porous substrate holding the catalyst itself also functions as a gas diffusion layer.

《Porous matrix》

In the present invention, "porous" means a structure (property) that can hold the catalyst to the inside, and is not limited to the form of openings formed only on the plane (upper surface), but also includes the state of roughening by chemical or physical etching, sputtering, etc.; porous state; state with space; aggregates of fiber-like things; knitted, woven, non-woven fabrics, etc. The above-mentioned "holes" or "gaps formed by aggregates of fiber-like things" can also form irregular gaps in the thickness direction. In addition, "porous" can also be referred to as a state or property with air permeability.

Figure 3 is a schematic cross-sectional view before the ion polymer 4 is added, the left figure is before the catalyst is added, and the right figure is after the catalyst is added. However, the porous matrix 3p of the present invention can be any as long as it has space not only on the outside but also to the inside to hold the catalyst. It can be a material with so-called through holes (but the existence of independent holes is not excluded), or a woven fiber or a non-woven fabric. For example, the fiber aggregate of non-woven fabrics also has holes in the gaps between the fibers, so it is broadly referred to as a "porous matrix" in the present invention.

As shown in Figures 3 to 5, the present invention is characterized in that the catalyst (catalytic particles or catalyst film) exists in a manner that covers from the surface of the porous substrate 3p itself to the inside, and the ionic polymer 4 exists in a manner that covers from the surface of the porous substrate 3p itself to the inside, so the porous substrate 3p of the present invention must have a gap that allows the catalyst or ionic polymer 4 to enter (can be given to) its inside.

The material of the porous substrate 3p of the present invention is not particularly limited as long as it has electrical conductivity. It is preferably a material having electronic conductivity, being non-corrosive (oxidation, etc.), being non-susceptible to various chemical reactions or electrochemical reactions, and having high strength. Specifically, it is preferably a titanium group metal, an alloy of a titanium group metal, a compound of a titanium group metal, or carbon (C).

The so-called "titanium group metals" here means titanium, zirconium or einsteinium. That is, the matrix of the titanium group can be listed as: titanium matrix, zirconium matrix, einsteinium matrix, titanium alloy matrix, zirconium alloy matrix or einsteinium alloy matrix.

In addition, examples of “titanium group metal compounds” include titanium nitride (titanium nitride (TiN)), titanium carbide (titanium carbide (TiC)), titanium diboride (titanium diboride (TiB ₂ )), and the like.

From the perspective of low cell voltage and better prevention of catalyst particles from escaping from the electrode substrate, the titanium group metal or alloy is preferably titanium or titanium alloy, and titanium is particularly preferred.

In addition, carbon (C) preferably has a graphite structure (graphene structure).

The porous matrix 3p of the present invention is preferably an aggregate of titanium fibers or titanium alloy fibers, or an aggregate of carbon fibers.

"Tactile Media"

In the present invention, the catalyst exists in a manner that covers from the surface of the porous substrate 3p itself to the inside as described above. Specifically, the catalyst is supported on the side of the hole of the porous substrate 3p or the side of the fiber 3q forming the porous substrate 3p, and exists in a manner that covers from the surface of the porous substrate 3p itself to the inside (Figures 3 to 5).

FIG5 is a schematic cross-sectional view of the porous substrate 3 carrying the catalyst of the present invention. Fibers 3q such as carbon fibers and titanium fibers constitute the porous substrate 3p. Catalyst particles are carried not only on the surface of the fibers 3q on the surface of the porous substrate 3p itself but also on the surface of the fibers 3q inside the porous substrate 3p itself.

The above-mentioned "surface of the porous substrate itself" is a term relative to the "interior of the porous substrate itself". Therefore, the above-mentioned "surface of the porous substrate itself" does not mean the side of the hole possessed by the porous substrate 3p or the surface of the material (fiber, etc.) constituting the porous substrate 3p.

In the present invention, the catalyst is preferably not merely deposited on the surface of the porous substrate 3p itself as a catalyst layer, but is supported on the side of the holes of the porous substrate 3p or the side of the fibers 3q forming the porous substrate 3p, and exists in a manner covering from the surface of the porous substrate 3p itself to the inside (Figures 3 to 5).

In the case where the catalyst is in the form of a catalyst layer, in other words, the catalyst exists (formed or accumulated) only on the surface of the polymer electrolyte membrane (PEM) 5 as shown in FIG2(b), or exists (formed or accumulated) only on the surface of the porous substrate 3p itself as shown in FIG2(c), the contact area between the catalyst and the porous substrate 3p becomes smaller. In addition, the contact area between the catalyst and the polymer electrolyte membrane (PEM) 5 becomes smaller, so the excellent effect of the present invention cannot be obtained.

The porous substrate 3 holding the catalyst of the present invention preferably has the following structure, that is, a structure obtained by attaching a metal catalyst or a metal catalyst precursor to the side of the pores of the porous substrate 3p before baking or forming the side of the fiber 3q of the porous substrate 3p before baking and performing a baking step.

In the above preferred form of the present invention, the form and composition of the catalyst formed in the porous matrix 3p or the form of the catalyst particles supported, etc., cannot be achieved or is impractical, whether it is directly specified or specified by parameters. Therefore, the above preferred structure (form) can only be specified by the manufacturing method.

Specifically, the catalyst of the present invention is preferably formed and obtained by applying a coating liquid in which "metal catalyst or metal catalyst precursor" is dissolved or finely dispersed on a porous substrate 3p, and then baking it.

That is, the catalyst of the present invention is preferably obtained by applying and drying the coating liquid so that the "metal catalyst or metal catalyst precursor" is attached to the side of the hole of the porous substrate 3p or the side of the fiber 3q, and then baking.

Here, the coating method is not particularly limited, and can be listed as: spray coating via a sprayer, immersion coating, brush coating, bristle brush coating, coating via screen printing, etc. After coating, it can be dried according to common methods as needed to remove the coating solvent.

"Baking" after attachment generally refers to general heat treatment. The baking temperature depends on the type of catalyst (precursor) and is not particularly limited. It is preferably 160°C to 800°C, more preferably 230°C to 750°C, and particularly preferably 300°C to 700°C.

The baking time (heat treatment time) is not particularly limited as long as the catalytic effect can be achieved. It is preferably more than 10 minutes and less than 8 hours, more preferably more than 30 minutes and less than 5 hours, and particularly preferably more than 1 hour and less than 3 hours.

When the baking time is above the lower limit, the same effect as when the baking temperature is above the lower limit can be obtained. When the baking time is below the upper limit, the same effect as when the baking temperature is below the upper limit can be obtained, and the catalyst can be better supported.

As shown in FIG2(b), when the catalyst exists on the polymer electrolyte membrane (PEM) 5 and is intended to be held by baking, the polymer electrolyte membrane (PEM) 5 has poor heat resistance and will melt or deteriorate at the above baking temperature. Therefore, in the case of the type shown in FIG2(b), the catalyst cannot be generated by baking.

According to the present invention, since the metal catalyst or metal catalyst precursor can be attached to the porous substrate 3p (generally having a strong tendency to be heat-resistant) and baked to obtain the catalyst (held thereon), the adhesion to the porous substrate 3p is improved compared to the case where only coating, drying and baking are performed, and the catalyst of excellent shape and composition can be used, and the range of catalysts that can be used is wider.

In the present invention, the volume of the pores constituting the porous matrix 3p may change due to calcination, making the pores larger or the thickness of the fibers 3q constituting the porous matrix 3p thinner. On the contrary, when this phenomenon occurs, the catalyst is easily held on "the side of the pores of the porous matrix or the side of the fibers 3q forming the porous matrix". In the case of the catalyst being particles, the size can become more generous, making it easier for the catalyst to exist (hold) slowly (uniformly) in a manner that covers the surface of the porous matrix 3p itself to the inside.

Furthermore, the ionic polymer 4 described later is sometimes easily filled in a state having a concentration gradient in the thickness direction of the porous substrate 3p from the surface toward the inside.

The porous substrate 3 of the present invention that holds a catalyst is preferably obtained by attaching a metal catalyst or a metal catalyst precursor to a porous substrate 3p and baking it. The metal in the metal catalyst or the metal catalyst precursor is not particularly limited as long as the catalyst particles or catalyst film formed by baking it can play a catalytic role. Among them, from the point of view of high catalytic effect, it is preferably a metal selected from the group consisting of platinum (Pt), ruthenium (Ru), iridium (Ir), palladium (Pd), tantalum (Ta) and nickel (Ni). The above metals can be one or two or more. In addition, it can also be used in combination with metals other than the above.

In other words, the catalyst of the present invention is preferably one or more metals or metal-containing compounds selected from the group consisting of platinum (Pt), ruthenium (Ru), iridium (Ir), palladium (Pd), tantalum (Ta) and nickel (Ni).

The metal compounds in the metal catalyst/metal catalyst precursor which is a raw material of the catalyst are not limited to those shown below. Specifically, for example, platinum compounds such as chloroplatinum (IV) acid n-hydrate, ammonium chloroplatinum (IV) acid, dinitrodiammineplatinum (II), platinum (II) dichloride, platinum (IV) tetrachloride, tetraammineplatinum (II) dichloride n-hydrate, tetraammineplatinum (II) hydroxide, hexahydroxyplatinum (IV) acid, etc.; ruthenium compounds such as ruthenium (III) chloride hydrate, ruthenium (III) nitrate, ruthenium (IV) oxide hydrate, etc. ; iridium compounds such as chloromyrium (IV) acid n-hydrate, iridium (III) chloride n-hydrate, iridium (III) chloride anhydrous, iridium (IV) nitrate, ammonium chloromyrium (IV) acid, hexaammine iridium (III) hydroxide; palladium compounds such as palladium (II) chloride, palladium (II) nitrate, dinitrodiammine palladium (II), palladium (II) acetate, tetraammine palladium (II) dichloride; nickel compounds such as nickel (II) chloride anhydrous, nickel (II) chloride hexahydrate, nickel (II) nitrate hexahydrate; tantalum pentachloride, tantalum alkoxide, etc.

The metal catalyst precursor is not particularly limited, and specifically, for example, alcohol coordinated to the above metal compound can be cited. It is particularly preferred to dissolve the above metal compound in an alcohol solvent to prepare the metal catalyst precursor, and then apply the coating liquid containing the metal catalyst precursor to the porous substrate 3p and dry it, and then bake it to convert it into a catalyst and support it to prepare a porous substrate 3 that supports the catalyst.

In the case where the metal catalyst or metal catalyst precursor is attached to the porous substrate 3p by coating, the "solvent (dispersion medium) of the coating liquid used for the coating" and/or the above-mentioned "alcohol coordinated with the metal compound" can preferably be listed as: methanol, ethanol, propanol, isopropanol, butanol, pentanol, hexanol, cyclohexanol, etc.

When the coating is applied to the porous carbon substrate by coating, the coating method of the coating liquid is not limited, but the preferred methods include: brushing method, spraying method, spray coating method, immersion method, etc.

In addition, as shown in Figures 3 and 4, the catalyst can be supported on the side of the hole or the side of the fiber 3q in the form of a film, or as shown in Figure 5, it can be supported on the side of the hole or the side of the fiber 3q in the form of particles.

Usually, iridium (Ir), tantalum (Ta), etc. are supported in the form of films on the holes or the sides of the fibers 3q, and platinum (Pt), etc. are supported in the form of particles on the holes or the sides of the fibers 3q.

The average particle size of the catalyst particles varies depending on the type of catalyst and is not particularly limited. The number average particle size is preferably 300 μm or less, more preferably 200 μm or less, and particularly preferably 100 μm or less. The number average particle size of the present invention can be obtained by observing the cross section of the porous material holding the catalyst after baking using a scanning electron microscope (SEM), randomly selecting 20 catalyst particles and obtaining the average value of the diameter, and then defining it by the average value of the diameter obtained in this way.

When the average particle size of the catalyst particles is too large, the catalyst effect is reduced, sometimes causing the unit voltage to increase or detaching from the electrode substrate.

Furthermore, in addition to this, in the case of the present invention, as described later, it is particularly difficult for the catalyst particles to enter the interior of the porous matrix 3p, and sometimes it is difficult to be held inside the porous matrix 3p.

On the other hand, when the average particle size is too small, it may penetrate into the microscopic depth from the side of the hole of the porous matrix 3p or the side of the fiber 3q. However, if the catalyst surface area can be increased by making multiple tiny particles adjacent and bonded, it does not necessarily need to be within the above particle size range.

The so-called "cell voltage" refers to the electrolytic voltage applied between the cathode and anode of the water electrolysis unit in order to perform water electrolysis.

When the catalyst is supported in the form of a membrane on the side of the hole of the porous substrate 3p or the side of the fiber 3q, the average film thickness of the film varies depending on the type of catalyst and is not particularly limited, but is preferably 50μm or less, more preferably 40μm or less, and particularly preferably 30μm or less. The average film thickness can be obtained by observing the cross section of the porous substrate supporting the catalyst after baking using a scanning electron microscope (SEM), and then defined by the obtained value.

《Ionic polymer》

The porous substrate 3 of the present invention that holds the catalyst preferably has an ionic polymer 4 on the side adjacent to the polymer electrolyte membrane (PEM) 5.

Here, "ionic polymer" is also called cation exchange polymer, polymer with strong acid group in the side chain, proton conductive polymer, ion conductive polymer, etc. The so-called "ionic polymer" means a polymer having the above chemical structure or physical properties.

For example, the upper surface of the porous substrate 3p of the aggregate of carbon fiber, titanium fiber, etc. is not originally flat (Figure 2 (a), Figure 3 to Figure 5), so the contact with the polymer electrolyte membrane (PEM) 5 is sometimes insufficient, and therefore, the contact between the catalyst and the polymer electrolyte membrane (PEM) is sometimes insufficient.

In addition, in the present invention, since the catalyst also exists inside the porous matrix 3p, and a large amount of the catalyst also exists inside the porous matrix 3p, if there is no ionic polymer 4, the contact between the catalyst and the polymer electrolyte membrane (PEM) will become even more insufficient.

According to the present invention, in the state shown in FIG. 2(a) and FIG. 3 to FIG. 6, due to the presence of the ion polymer 4, the gaps existing inside the porous substrate 3p itself and between the porous substrate 3p and the polymer electrolyte membrane (PEM) are filled, so that the contact between them is good, and the contact between the ion polymer 4 and the catalyst and the contact between the polymer electrolyte membrane (PEM) 5 and the catalyst are good.

In the porous matrix carrying a catalyst of the present invention, the ionic polymer 4 contacts the carried catalyst and is filled in a state having a concentration gradient in the thickness direction of the porous matrix 3p from the surface toward the inside (refer to FIG. 2(a), FIG. 4 to FIG. 6).

The direction where the ionic polymer concentration is high is the side of the porous substrate that holds the catalyst and contacts the polymer electrolyte membrane (PEM) 5 (Fig. 6(b)). In addition, the concentration is preferably high on the opposite side, that is, the side that contacts the power supply 6, and is filled in a state with a concentration gradient in the thickness direction of the porous substrate 3p from the surface toward the inside (Fig. 6(a)).

From the perspective of the necessity of contact, it is important in the present invention to surround the catalyst film or catalyst particles with the ionic polymer 4. Furthermore, the ionic polymer 4 is filled in a state with a concentration gradient in the thickness direction of the porous substrate 3p.

As shown in FIG6(b), near the deep part of the porous substrate 3p (which holds the catalyst) (i.e., the side opposite to the side in contact with the polymer electrolyte membrane (PEM) 5), the ionomer 4 may not exist or be relatively small. Furthermore, from the perspective of permeability, it is preferred to have a part where the ionomer 4 does not exist or is relatively small.

In addition, as shown in FIG6(a), near the deep part of the porous substrate 3p (which holds the catalyst) (i.e., the part away from the contact surface with the PEM 5 and the power supply body 6), the ion polymer 4 may not exist or be relatively small. Furthermore, from the perspective of permeability, it is better to have a part where the ion polymer 4 does not exist or is relatively small.

As mentioned above, baking is performed to prepare the catalyst. However, when the fibers 3q constituting the porous substrate 3p become thinner, it becomes more difficult to contact. For example, as shown in FIG5 , when the ion polymer 4 contacts the catalyst 3c and exists in a state with a concentration gradient from the surface to the inside of the porous substrate 3p, the porous substrate (catalyst 3c) holding the catalyst and the polymer electrolyte membrane (PEM) 5 become extremely well in contact.

That is, the ionomer 4 has the function of conducting "hydrogen ions (protons) to the cathode side", and by existing on the side of the porous substrate 3 holding the catalyst adjacent to the polymer electrolyte membrane (PEM) 5, it can greatly reduce the resistance when protons are conducted from the polymer electrolyte membrane (PEM) 5 to the catalyst surface.

Therefore, by filling the ion polymer 4 toward the inside of the porous matrix 3 holding the catalyst, the protons generated in the "catalyst on the power supply and/or resin tank side that cannot directly contact the polymer electrolyte membrane (PEM)" can be conducted to the cathode side, thereby improving the utilization efficiency of the catalyst.

As a result, when the ionomer 4 is filled in the above-mentioned form of the present invention and operated under the condition of a constant current value, the water electrolysis unit operates even if the unit voltage (electrolysis voltage) is low, and the detachment of catalyst particles caused by the generated gas is suppressed.

The amount of the ionic polymer 4 varies with the thickness or porosity of the porous substrate 3 holding the catalyst, and the conditions of use of the water electrolysis unit, such as the amount of hydrogen generated per unit time, and is not particularly limited. However, gas is generated with water electrolysis and needs to be captured to the outside, so it is better not to cover the entire surface of the catalyst with a thicker ionic polymer 4, but to expose the catalyst surface partially at the microscopic level. It is better not to fill all the gaps of the porous substrate 3 holding the catalyst with the ionic polymer 4, but to fill it in a state with a concentration gradient in the thickness direction of the porous substrate 3 holding the catalyst, and discharge the generated gas.

Since the generated gas needs to be captured from the power supply 6 and/or the resin tank 7, in order to capture the gas more efficiently, it is better to make the amount of ionomer 4 have a slope between the "polymer electrolyte membrane (PEM)" and the "power supply 6 and/or the resin tank 7".

Therefore, although not particularly limited, the ratio of the volume of the voids in the porous substrate 3 holding the catalyst to be filled by the ionomer 4 (hereinafter sometimes referred to as the "filling rate") is preferably 10 volume % or more and 90 volume % or less, more preferably 20 volume % or more and 80 volume % or less, and particularly preferably 30 volume % or more and 70 volume % or less.

That is, the present invention is also: the ionic polymer 4 is injected into the voids of the porous substrate 3 holding the catalyst, and the ratio of the voids filled by the ionic polymer 4 in the porous substrate 3 holding the catalyst is 10 volume % or more and 90 volume % or less.

The above-mentioned effect of the ionomer 4 can be preferably achieved for any electrode, whether it is a cathode for water electrolysis or an anode for water electrolysis (refer to FIG. 5).

The filling of the ion polymer 4 can be formed, for example, by applying the ion polymer dispersion or ion polymer solution to the porous substrate 3p holding the catalyst.

The present invention also provides: after the catalyst is supported on the porous substrate 3p, the solution of the ionic polymer 4 is applied and dried, and the ionic polymer 4 is filled in a manner having a concentration gradient from the surface toward the inside of the porous substrate 3p to obtain the porous substrate 3 supporting the catalyst.

The coating can be applied from the side in contact with the polymer electrolyte membrane (PEM) 5 to obtain a porous substrate 3 with a concentration gradient as shown in FIG6(b), or further, the coating can be applied from the side in contact with the power supply 6 to obtain a porous substrate 3 with a concentration gradient on both sides as shown in FIG6(a).

In the preferred embodiment of the present invention, it is impossible or almost impractical to specify directly or by parameters what kind of mass and form the ion polymer 4 is filled in the porous matrix 3p, or what kind of form it contacts the catalyst, etc. Therefore, the above preferred embodiment (structure) can only be specified by the manufacturing method.

The coating methods include: brush coating, spray coating, spray coating, etc.

After applying the ionic polymer dispersion (ionic polymer solution), the solvent (dispersion medium) is volatilized at about 60°C, preferably at 120°C to 250°C, particularly preferably at 140°C to 200°C, and preferably at 1 minute to 1 hour, particularly preferably at 3 minutes to 30 minutes.

《Chemical Structure of Ionic Polymers》

The above-mentioned ionic polymer 4 is not particularly limited as long as it has ionic conductivity, especially proton conductivity, and can be used in the single unit 1 for water electrolysis. That is, the so-called "ionic polymer" of the present invention refers to a proton conductive polymer.

The ionic polymer 4 is not particularly limited and may be a fluorine-based ionic polymer 4 having fluorine atoms in the molecule, or a non-fluorine-based ionic polymer 4 having no fluorine atoms in the molecule.

Although not particularly limited, the preferred polymer is a fluorine-based ion polymer, and the most preferred polymer is an ion-conducting polymer (proton-conducting polymer) having a polyfluoroethylene skeleton as the main chain and a sulfonic acid group as the side chain at the end and having a perfluorovinyl ether skeleton.

Although not particularly limited, examples of particularly preferred ionic polymers 4 used in the present invention are shown below.

In formula (1), m is a natural number.

In formula (2), p is a natural number.

In formula (3), n is a natural number.

The ionic polymer represented by formula (1) is a polymer composed of a polytetrafluoroethylene (PTFE) skeleton as the main chain and a perfluoroether pendant side chain with a sulfonic acid group at the end. Since the side chain is relatively long, it is also called a long-side-chain (LSC) ionic polymer.

The equivalent weight (EW) of the ionic polymer represented by formula (1) (the mass of the polymer required to provide 1 mol of protons) is not limited, but is preferably 900 g/mol to 1200 g/mol. The preferred range of m in formula (1) is the range that can be calculated from the equivalent weight.

The long side chain (LSC) ionomer represented by formula (1) is not limited, and commercially available products can be preferably used, and examples thereof include Nafion (registered trademark) manufactured by Du Pont.

The preferred long side chain (LSC) ion polymer represented by formula (1) is Nafion (registered trademark) (EW = 1100 g/mol, m = 6.6 in formula (1)).

The ionic polymer represented by formula (2) or formula (3) is a polymer composed of a polytetrafluoroethylene (PTFE) skeleton as the main chain and a perfluoro pendant side chain with a sulfonic acid group at the end. Since the side chain is relatively short, it is also called a short-side-chain (SSC) ionic polymer.

The equivalent weight (EW) of the ionic polymer represented by formula (2) or formula (3) is not limited, and is preferably 700 g/mol to 950 g/mol. The preferred range of p in formula (2) and the preferred range of n in formula (3) are ranges that can be calculated from the equivalent weight.

The short side chain (SSC) ionomer represented by formula (2) or formula (3) is not limited, and commercially available products can be preferably used, for example, 3M ionomer manufactured by 3M Corporation can be cited.

〈Relationship between "film thickness or particle size of catalyst" and "voids in porous matrix"〉

In the porous substrate 3 of the present invention that holds the catalyst, the film thickness or particle size of the catalyst held in the porous substrate 3p is preferably smaller than the average diameter length of the "space formed by the gaps between the pores and/or fibers". In larger cases, the catalyst is sometimes difficult to be held preferably in the material constituting the porous substrate 3p.

In addition, although the above-mentioned voids are the voids of the porous substrate 3p after holding the catalyst by baking, the voids of the porous substrate 3p before holding the catalyst by baking are preferably larger than the size (film thickness or particle size) of the catalyst obtained by holding. In the case of a smaller size, the "metal catalyst or metal catalyst precursor" dissolved or finely dispersed in the catalyst coating liquid sometimes has difficulty entering the porous interior, and as a result, the catalyst sometimes cannot exist in a way that covers the surface of the porous substrate 3p itself to the inside.

In addition, in the porous matrix carrying a catalyst of the present invention, the porosity of the porous matrix 3 carrying a catalyst excluding the ionic polymer 4 expressed by the following definition formula (1) is preferably greater than 3 volume % and less than 80 volume %.

Porosity (volume %) = 100 × [volume of voids in the porous matrix holding the catalyst] / [volume of the porous matrix holding the catalyst] (1)

Since the so-called "porous substrate holding a catalyst" means a substrate that already holds a catalyst, when the catalyst is held by baking, the "voids" in the above "porosity" refer to the voids in the porous substrate 3p after baking.

Since the volume of the catalyst particles (catalyst film) is very small compared to the volume of the above-mentioned voids, the "voids in the porous matrix" are almost equal to the "voids in the porous matrix holding the catalyst".

The numerator of the above definition formula (1) can be used to measure the weight and volume of the porous matrix 3 holding the catalyst, and the true specific gravity of the material (Ti, C, etc.) can be used for calculation. Since the denominator is also easy to measure, the above porosity can be obtained in this way and defined based on the obtained value.

The porosity is preferably measured before imparting (filling) the ionic polymer 4.

The porosity is preferably 5 volume % or more and 70 volume % or less, and particularly preferably 10 volume % or more and 60 volume % or less.

When the porosity is too small, it is difficult to hold the catalyst, and sometimes it cannot be held inside the porous matrix 3p. In addition, it is difficult for the ion polymer solution/dispersion to flow into the interior of the porous matrix 3p, and sometimes the ion polymer 4 cannot be filled into the interior of the porous matrix 3p, or cannot be filled in a state with a concentration gradient in the thickness direction of the porous matrix 3p. In addition, the diffusion of the gas deteriorates, and the function as a gas diffusion layer sometimes deteriorates.

On the other hand, when the porosity is too large, the strength of the porous matrix 3 holding the catalyst may decrease, or the conductivity may decrease.

In the porous substrate 3 of the present invention that holds a catalyst, the sum of the "microscopic area of the catalyst that exists from the surface of the porous substrate itself to the inside" that contacts the above-mentioned ionic polymer is preferably more than twice the "macroscopic area of the surface of the porous substrate 3 that holds the catalyst that contacts the above-mentioned polymer electrolyte membrane (PEM) 5". The above ratio is referred to as the "contact area ratio".

The above microscopic area is obtained by observing the cross section of the porous matrix 3 holding the catalyst after being filled with the ionic polymer using a scanning electron microscope (SEM), and the surface area of the catalyst can be calculated from the cross section of the catalyst therein. The surface (area) of the catalyst inside the porous matrix 3 holding the catalyst that is not filled with the ionic polymer 4 is excluded from the microscopic area.

For example, when the porous substrate 3 holding the catalyst is rectangular, the above-mentioned macroscopic area can be obtained by multiplying its longitudinal length and transverse length.

The above "contact area ratio" is obtained by dividing the above microscopic area by the above macroscopic area, so it can be defined by the value obtained in this way.

The contact area ratio is preferably 3 times or more, more preferably 4 times or more and less than 300 times, and particularly preferably 5 times or more and less than 100 times.

When the contact area ratio is too small, the aforementioned "(filling) effects of the ionic polymer 4" may not be obtained. When it is too large, it may be difficult to manufacture the porous substrate 3 that holds the catalyst.

〈Electrode for water electrolysis〉

As mentioned above, the present invention is also an electrode 2 for water electrolysis, which is characterized by the porous substrate 3 of the present invention that holds a catalyst.

In addition, as mentioned above, the present invention is also a gas diffusion layer, which is characterized by the porous substrate 3 of the present invention that carries the catalyst.

That is, as mentioned above, from the form and function of the porous substrate 3 holding a catalyst of the present invention, the porous substrate 3 holding a catalyst of the present invention can also be used as the function of the electrode 2 for water electrolysis. In addition, the porous substrate 3 holding a catalyst of the present invention can also be used as the function of the gas diffusion layer.

〈Single unit for water electrolysis〉

The present invention is also a single unit 1 for water electrolysis, which is characterized by having a structure in which a polymer electrolyte membrane (PEM) 5 is sandwiched by the porous substrate 3 holding a catalyst as described above.

As shown in one example in FIG. 1(a), the single cell 1 for water electrolysis of the present invention has a structure in which a polymer electrolyte membrane (PEM) 5 is sandwiched by a porous substrate 3 holding a catalyst of the present invention, and more specifically, it is sandwiched by a gasket, a power supply body 6, a resin tank body 7, etc. In addition, the single cell 1 for water electrolysis of the present invention is formed by sandwiching a porous substrate 3 (electrode for water electrolysis) holding a catalyst as shown in FIG. 5 by the above-mentioned structure.

The structures of the power supply body 6, the resin tank body 7, etc. are not particularly limited, and generally known ones can be used.

FIG. 7 shows a water electrolysis stacking unit 9 that connects two single water electrolysis units of the present invention, and the right and left sides thereof are single water electrolysis units 1, respectively.

The invention of the single unit 1 for water electrolysis of the present invention does not exclude the use (combination use) of other layers or other components/structures, etc., in addition to those described above or illustrated.

〈Stacking unit for water electrolysis〉

The present invention is also a stacked unit 9 for water electrolysis, which is formed by stacking two or more of the above-mentioned single units 1 for water electrolysis, when a single unit 1 for water electrolysis is formed by sandwiching a polymer electrolyte membrane (PEM) 5 between a porous substrate 3 holding a catalyst.

FIG7 shows the outline of the stacked unit 9 for water electrolysis of the present invention. As shown in FIG7 , the stacked unit 9 for water electrolysis of the present invention is formed by clamping the bipolar plate 8 by the single unit 1 for water electrolysis of the present invention.

The stacked unit 9 for water electrolysis of the present invention is formed by stacking 2 or more single units for water electrolysis of the present invention, preferably 3 or more and 10 or less, and particularly preferably 4 or more and 6 or less.

When the number of layers is too small, the water electrolysis efficiency (hydrogen generation efficiency) may deteriorate. On the other hand, when the number of layers is too large, the voltage required for water electrolysis may increase.

As mentioned above, the single cell 1 for water electrolysis using the porous substrate 3 holding a catalyst of the present invention is characterized in that the cell voltage is small, so even if a plurality of single cells 1 for water electrolysis are connected in series, the electrolysis voltage between the cathode and the anode of the stacked cell 9 for water electrolysis can be reduced.

The invention of the stacked unit 9 for water electrolysis of the present invention does not exclude the use (combination use) of other layers or other components/structures, etc., in addition to those described above or illustrated.

Figures 8 (a) and (b) are conceptual diagrams showing that the stacked unit 9 for water electrolysis of the present invention is further provided with cathode wiring, anode wiring, water inlet, water outlet, hydrogen discharge piping (hydrogen outlet), oxygen discharge piping (oxygen outlet), etc. The water outlet and oxygen discharge piping (oxygen outlet) can be the same (shared).

〈Unit module for water electrolysis〉

The present invention is also a water electrolysis unit module 10, which is characterized by arranging the above-mentioned water electrolysis stacking units 9 in two-dimensional or three-dimensional configuration.

FIG9 is a schematic three-dimensional diagram showing a water electrolysis unit module 10 formed by three-dimensionally arranging the water electrolysis stacking units 9 of the present invention.

By forming a water electrolysis unit module 10, a large amount of water can be efficiently electrolyzed to obtain a large amount of hydrogen or oxygen.

In addition, as shown in FIG9 , a setting plate can be installed, and only a part of the water electrolysis stacking unit 9 can be extracted for replacement or maintenance or the power supply can be stopped (set power outage period), which can improve the operation efficiency.

The invention of the water electrolysis unit module 10 of the present invention does not exclude the use (combination use) of other components added thereto in addition to those described above or illustrated.

[Implementation example]

The following are examples and comparative examples to more specifically illustrate the present invention, but the present invention is not limited to these examples without departing from its main purpose.

Unless otherwise specified, the values related to ratio or % are mass ratio or mass %.

Example 1

〈Manufacturing of porous substrates with catalysts and electrodes for water electrolysis〉

Using a sprayer, an alcohol-based coating liquid containing chloroiridium (IV) acid hexahydrate as a metal catalyst (metal precursor) was applied to a porous substrate 3p in which titanium fibers with a fiber diameter of 50 μm were aggregated like a flat plate as a catalyst in a manner that would not produce unevenness.

At this time, it has been confirmed that the coating liquid has penetrated from the surface of the porous substrate 3p itself into the interior.

Next, in order to volatilize the solvent in the coating liquid, the porous substrate is heated at 70°C for 30 minutes for drying. In order to improve the adhesion between the metal catalyst 3c and the material surface (the side of the fiber) of the porous substrate, it is heated at 600°C for 2 hours, which is higher than the temperature during the above drying, for heat treatment.

The "porous matrix holding the catalyst before ionic polymer filling" observed by scanning electron microscope (SEM) is shown in Figures 2 to 4. The iridium catalyst is held on the side of the titanium fiber forming the porous matrix 3p, and exists in the form of a jacket covering the surface of the porous matrix 3p itself and the titanium fiber inside. The film thickness of the catalyst is 0.3μm to 10μm.

Using a sprayer, a dispersion of an ionic polymer (Nafion (registered trademark) manufactured by Du Pont) is applied to the porous substrate 3p holding the metal catalyst 3c from the side in contact with the PEM.

At this time, it has been confirmed that the dispersion liquid has penetrated from the surface of the porous substrate 3 holding the catalyst into the interior.

Then, in order to volatilize the dispersion medium of the ionic polymer dispersion, the porous substrate 3 holding the catalyst is heated at 100°C for 30 minutes to dry.

The "porous matrix with catalyst after ionic polymer filling" obtained by observation with a scanning electron microscope (SEM) is shown in Figures 4 and 5. It can be confirmed that the ionic polymer 4 contacts the iridium belonging to the catalyst and is filled in a state with a concentration gradient in the thickness direction from the surface to the inside of the porous matrix 3p (especially refer to Figures 4(b) and 6(b)).

The obtained "porous matrix holding a catalyst after being filled with ionic polymer" has a porosity of 40 volume %, a contact area ratio of 10 times, and an average diameter length of "the gaps formed by the gaps between the fibers constituting the porous matrix" of 25μm to 50μm.

Example 2

In Example 1, except that a porous substrate 3p composed of carbon fibers is used instead of a porous substrate 3p composed of titanium fibers, the porous substrate 3 (electrode 2 for water electrolysis) holding a catalyst is obtained in the same manner as in Example 1.

During the process, it was confirmed that the catalyst coating liquid penetrated from the surface of the porous substrate 3p itself into the interior.

In addition, it was confirmed that the ionic polymer dispersion liquid penetrated from the surface of the porous substrate 3 holding the catalyst into the interior.

By observing the obtained porous substrate 3 holding the catalyst using a scanning electron microscope (SEM), it can be seen that the iridium catalyst is held on the side of the carbon fiber forming the porous substrate 3p, and exists in a manner covering from the surface of the porous substrate 3p itself to the inside.

In addition, it can be confirmed that the ionic polymer 4 contacts the catalyst and is filled in a state with a concentration gradient in the thickness direction from the surface toward the inside of the porous substrate 3p (especially refer to Figure 4(b) and Figure 6(b)).

Example 3

In Example 1, except for using a platinum catalyst instead of an iridium catalyst, the other steps are the same as in Example 1 to obtain a porous substrate 3 (electrode 2 for water electrolysis) holding a catalyst.

During the process, it was confirmed that the catalyst coating liquid penetrated from the surface of the porous substrate 3p itself into the interior.

In addition, it was confirmed that the ionic polymer dispersion liquid penetrated from the surface of the porous substrate 3 holding the catalyst into the interior.

By observing the obtained porous substrate 3 holding the catalyst using a scanning electron microscope (SEM), it can be seen that the platinum catalyst is held on the side of the titanium fiber forming the porous substrate 3p, and exists in a manner covering from the surface of the porous substrate 3p itself to the inside.

In addition, it can be confirmed that the ionic polymer 4 contacts the catalyst and is filled in a state with a concentration gradient in the thickness direction from the surface toward the inside of the porous substrate 3p (especially Figure 5 and Figure 6(b)).

Comparison Example 1

In Example 1, except for using a substrate composed of titanium fiber with a porosity of 1 volume % as the (porous) substrate, the other steps are the same as in Example 1 to obtain the water electrolysis electrode 2 (catalyst layer forming substrate).

The matrix used as the (porous) matrix is composed of titanium fibers with a porosity of 1 volume %. Since the pores (voids) are smaller than the metal catalyst particles, it is difficult for the catalyst coating liquid to penetrate from the surface of the porous matrix 3p itself into the interior.

By observing the obtained water electrolysis electrode 2 with a scanning electron microscope (SEM), it can be seen that the catalyst does not exist inside the porous substrate 3p itself, but forms a catalyst layer on the (porous) substrate. That is, it becomes a layer structure of "porous substrate\metal catalyst layer\ion polymer layer".

Comparison Example 2

In Example 1, except that the ionic polymer 4 is not filled, that is, the dispersion of the ionic polymer 4 is not coated, the other steps are the same as in Example 1 to obtain a porous substrate 3 holding a catalyst.

By observing the porous matrix 3 holding the catalyst using a scanning electron microscope (SEM), it can be seen that although the catalyst exists inside the porous matrix 3p itself, the catalyst is isolated because it is not filled with the ionic polymer 4.

Comparison Example 3

The conventional membrane electrode assembly (MEA) is used as the electrode for water electrolysis.

The membrane electrode assembly (MEA) used has carbon particles and "platinum particles as catalyst" coated on one side of the PEM, and "antimony oxide particles as catalyst" coated on the other side, and then dried to fix.

Evaluation Example 1

〈Assembly of a single unit for water electrolysis〉

The single unit 1 for water electrolysis is assembled in the structure shown in Figure 1(a).

Specifically, a polymer electrolyte membrane (PEM) is arranged in the center, and the "porous substrate 3 (electrode for water electrolysis 2) having a metal catalyst 3c and an ionic polymer 4" obtained in the above-mentioned embodiment or the electrode for water electrolysis obtained in the comparative example is arranged on both outer sides.

Furthermore, after configuring the power supply body 6 on the two sides and further configuring the resin tank body 7 on the two outer sides, the two ends are locked by bolts to clamp the various components and assemble the single unit 1 for water electrolysis.

〈Initial performance evaluation based on water electrolysis test〉

Pure water at a temperature of 20°C is circulated in the single unit 1 for water electrolysis obtained in the above-mentioned embodiment and comparative example by a pump, and the pure water for electrolysis is supplied to the anode side of the water electrolysis unit, and a DC power supply is used to record the value of the unit voltage during water electrolysis at a given current density.

The initial cell voltage (V) at a current density of 100A/ ^dm2 is shown in Table 1 below.

〈Durability evaluation of single unit for water electrolysis based on water electrolysis test〉

Similar to the above initial performance evaluation, pure water was circulated and supplied to the single unit 1 for water electrolysis, and a DC power supply was used to set the current value so that the current density became 100 A/dm ² , and electrolysis was continuously performed and the unit voltage was recorded.

The cell voltage [V] after 500 hours is shown in Table 2 below.

Evaluation Example 2

〈Assembly of stacked units for water electrolysis〉

The single water electrolysis unit 1 is stacked in the structure shown in FIG. 7 to assemble the water electrolysis stacking unit 9.

Specifically, a single unit 1 for water electrolysis is composed of a porous substrate (anode) holding a catalyst/polymer electrolyte membrane (PEM)/porous substrate (cathode) holding a catalyst, and five of the single units are stacked (stacked) with a bipolar plate 8 interposed therebetween to form a stacked unit 9 for water electrolysis. In FIG. 7 , two single units are stacked, and in Evaluation Example 2, five are stacked.

〈Initial performance evaluation of stacked units for water electrolysis〉

Pure water at a temperature of 20°C is circulated by a pump through the stacked water electrolysis unit 9 in which five "single units for water electrolysis obtained in the above-mentioned embodiments and comparative examples" are stacked as described above, and pure water for electrolysis is supplied to the anode side of the water electrolysis unit (refer to Figure 8), and a DC power supply is used to record the value of the stacked unit voltage during water electrolysis at a given current density.

The initial stacked cell voltage at a current density of 100A/ ^dm2 is shown in Table 3 below.

〈Durability evaluation of stacked units for water electrolysis〉

Using the stacked unit 9 for water electrolysis obtained by stacking the porous substrate 3 (electrode 2 for water electrolysis) with a catalyst obtained in Example 1 as in Evaluation Example 2, water electrolysis was continuously performed under the condition of a constant current value, and the change in the voltage of the stacked unit was recorded.

Although the stacked cell voltage after 500 hours has slightly increased compared to the initial stacked cell voltage, it is at the level corresponding to Table 2 for a single cell, so there is no special problem.

Initial performance evaluation of a single unit for water electrolysis (initial unit voltage)

[Table 1]

Durability evaluation of a single unit for water electrolysis (unit voltage after 500 hours)

[Table 2]

Initial performance evaluation of stack unit 9 for water electrolysis (initial stack unit voltage)

[Table 3]

From Tables 1 to 3, it can be seen that the cell voltage (necessary applied voltage) of the water electrolysis electrode 2, the single cell 1 and the stacked cell 9 for water electrolysis using the porous substrate 3 with a catalyst of the present invention is a stable low value at the beginning of water electrolysis.

In addition, this value can be maintained after the endurance test.

On the other hand, the comparative example water electrolysis electrode 2, the single unit 1 for water electrolysis, and the stacked unit 9 for water electrolysis have high unit voltages (necessary applied voltages) at the beginning of water electrolysis, and also high values after the endurance test.

Even when the porous substrate 3 holding the catalyst obtained in Examples 2 and 3 is used, the cell voltage is stable and low, as in Example 1. That is, the initial cell voltage, the cell voltage after 500 hours, the initial stacked cell voltage, and the stacked cell voltage after 500 hours are almost the same as the results in Tables 1 to 3 of Example 1, and the voltage is lower.

[Industrial applicability]

The porous substrate 3 of the present invention that holds the catalyst has excellent properties as an electrode or gas diffusion layer for water electrolysis. The unit voltage of the water electrolysis single unit or the water electrolysis stacking unit 9 using the single unit is low, and the catalyst is prevented from escaping from the electrode substrate. The manufacturing performance and durability are excellent, so it is widely used in all fields that require hydrogen or oxygen.

2: Electrode for water electrolysis

3: Porous substrate holding the catalyst

3c: Metal catalyst or metal oxide catalyst

3q: Fibers forming a porous matrix

Claims (15)

A porous substrate holding a catalyst has the following structure: a polymer electrolyte membrane (PEM) is sandwiched in a single unit for water electrolysis. The present invention relates to a structure in which a porous matrix exists in the form of a porous membrane and contacts the polymer electrolyte membrane (PEM) to form a cathode or an anode, and also plays the role of a gas diffusion layer. The catalyst is supported on the side of the hole of the porous matrix or the side of the fiber forming the porous matrix, and exists in a manner covering from the surface of the porous matrix itself to the inside. The ionic polymer contacts the catalyst and is filled in a state having a concentration gradient from the surface of the porous matrix toward the inside in the thickness direction of the porous matrix. The catalyst is selected from platinum (Pt), ruthenium (Ru), iridium (Ir), palladium (Pd ), tantalum (Ta) and nickel (Ni), the material of the porous matrix is a titanium group metal, an alloy of a titanium group metal or a compound of a titanium group metal, or carbon (C), the ionomer is a fluorine-based ionomer having fluorine atoms in the molecule, and the porosity of the porous matrix holding the catalyst after excluding the ionomer as represented by the following definition formula (1) is 3 volume % or more and 80 volume % or less, and the porosity (volume %) = 100 × [volume of voids in the porous matrix holding the catalyst] / [volume of the porous matrix holding the catalyst] (1). The porous substrate holding a catalyst as described in claim 1 is obtained by the following steps: a step of attaching a metal catalyst or a metal catalyst precursor to the side of the pores of the porous substrate before baking or to the side of the fibers of the porous substrate before baking and then baking. A porous substrate holding a catalyst as described in claim 1, wherein the film thickness or particle size of the catalyst is smaller than the average diameter length of "the gaps formed by the pores and/or the gaps between the fibers". The porous substrate holding a catalyst as described in claim 1, wherein the catalyst is not merely deposited on the surface of the porous substrate itself as a catalyst layer, but is held on the side of the holes of the porous substrate or the side of the fibers forming the porous substrate, and exists in a manner covering from the surface of the porous substrate itself to the inside. The porous substrate holding a catalyst as described in claim 1, wherein the ionic polymer is filled in the voids of the porous substrate holding a catalyst, and the ratio of the volume of the voids filled by the ionic polymer to the total volume of the voids of the porous substrate holding a catalyst is not less than 10 volume % and not more than 90 volume %. The porous substrate holding the catalyst as described in claim 1, wherein the total microscopic area of "the above-mentioned catalyst existing in a manner covering from the surface of the above-mentioned porous substrate itself to the inside" in contact with the above-mentioned ionic polymer is more than twice the macroscopic area of the surface of the porous substrate holding the catalyst in contact with the above-mentioned polymer electrolyte membrane (PEM). The porous substrate holding the catalyst as described in claim 1, wherein the ionic polymer is obtained by applying a solution or dispersion of the ionic polymer and drying it after the catalyst is held on the porous substrate, so as to fill the porous substrate with a concentration gradient from the surface toward the inside. The porous substrate holding a catalyst as described in claim 1, wherein the material of the porous substrate is titanium (Ti) or titanium (Ti) alloy or carbon (C). The porous matrix holding the catalyst as described in claim 1, wherein the porous matrix is titanium fiber or titanium alloy fiber or an aggregate of carbon fibers. The porous matrix holding a catalyst as described in claim 1, wherein the above-mentioned ionic polymer is a proton conductive polymer. An electrode for water electrolysis, which is a porous substrate holding a catalyst as described in any one of claims 1 to 10. A gas diffusion layer, which is a porous substrate carrying a catalyst as described in any one of claims 1 to 10. A single unit for water electrolysis, which has a structure in which a polymer electrolyte membrane (PEM) is sandwiched by a porous substrate holding a catalyst as described in any one of claims 1 to 10. A stacked unit for water electrolysis, which is formed by stacking two or more single units for water electrolysis as described in claim 13, when a structure obtained by sandwiching a polymer electrolyte membrane (PEM) between a porous substrate holding a catalyst is used as a single unit for water electrolysis. A unit module for water electrolysis, which is formed by arranging the stacked units for water electrolysis as described in claim 14 in two or three dimensions.