JP2020094282A - Electrode for water electrolysis and production method thereof - Google Patents

Abstract

To provide an electrode for water electrolysis that has excellent electrolytic performance and durability and a water electrolytic cell using the same, in which the exfoliation and/or detachment of a catalyst from a base substance, or more specifically, the exfoliation of a catalyst film from the base substance and/or the detachment of a catalyst (particles) from a material comprising the base substance are prevented.SOLUTION: An electrode for water electrolysis 2 is arranged adjacent to a solid polymer electrolyte membrane (PEM) 5 in a water electrolytic cell 1. The electrode for water electrolysis 2 has "a catalyst-carried porous electrode base 3, in which a metal catalyst 3c or a metal oxide catalyst 3c is carried", and which is made by depositing a metal catalyst or a metal catalyst precursor onto a porous base 3a and by firing it. Preferably, the electrode for water electrolysis 2 further has an ionomer (layer) 4 on the side, adjacent to the solid polymer electrolyte membrane 5, of the catalyst-carried porous electrode base 3, including the production method thereof. In addition, preferably, the water electrolytic cell 1 has the electrode for water electrolysis 2 and the solid polymer electrolyte membrane, and a water electrolytic stack cell 9 has the water electrolytic cells 1 combined.SELECTED DRAWING: Figure 2

Description

The present invention relates to an electrode for water electrolysis, and more specifically, an electrode for water electrolysis used in water electrolysis using a solid polymer electrolyte membrane (PEM), a method for producing the same, and an electrode for water electrolysis. A water electrolysis cell having the same.

A membrane electrode assembly (MEA) used in a fuel cell or a "water electrolysis cell for a hydrogen generator" has a structure in which each electrode catalyst is formed on both sides of a solid polymer electrolyte membrane (PEM) ( See FIG. 5B).

The invention described in Patent Document 1 relates to a method for producing a membrane electrode assembly (MEA) that is regarded as a good product when the amount of sulfate ions contained in the electrode catalyst layer is equal to or less than a specified value. A membrane-electrode assembly in which an electrode catalyst layer is formed on the surface of a membrane and a method for producing the same are disclosed.
The manufacturing process in this manufacturing method is described as follows. Prepare an electrolyte membrane, prepare an electrode catalyst layer, prepare a catalyst layer forming film using the prepared electrolyte membrane and electrode catalyst layer, prepare a gas diffusion layer, prepare a catalyst layer forming film and prepare gas diffusion The layers are used to make a membrane electrode assembly (MEA).

However, in addition to the membrane electrode assembly (MEA) of Patent Document 1 for fuel cells, the electrode catalyst layer of the membrane electrode assembly (MEA) is produced by applying a catalyst ink and drying. (And thereby reduce the amount of sulfate ion).

Patent Document 2 discloses a method for producing a durable membrane electrode assembly in which a "catalyst-coated diffusion medium" is not bonded to a membrane, and a catalyst layer is deposited on the diffusion medium layer, and then the catalyst layer is deposited. An ionomer layer is sprayed on the top of the membrane to produce a membrane electrode assembly (MEA) for a fuel cell.

However, in addition to the membrane electrode assembly (MEA) of Patent Document 2 for a fuel cell, regarding the method for producing a catalyst layer included in the membrane electrode assembly (MEA), a catalyst is provided on a diffusion medium layer. It was rolled or applied as a slurry. The catalyst was once coated on a transfer substrate and then transferred to a film by a hot press.

In recent years, as the demand for hydrogen has expanded, excellent electrolysis technology for water has been required, but the conventional technology is not sufficient, and an excellent technology for the performance and durability of the water electrolysis cell is required. Was wanted.

Japanese Patent No. 6128099 Japanese Patent No. 4738350

The present invention has been made in view of the above, and its problem is a water electrolysis electrode having excellent electrolysis performance and durability of water, and a water electrolysis cell or a water electrolysis stack cell using the water electrolysis electrode. To provide.
Specifically, for example, in the conventional method of depositing a catalyst layer on a substrate, there is a possibility that the catalyst layer is potentially peeled off from the substrate due to gas lift. An electrode for water electrolysis in which desorption is prevented, in particular, a catalyst film from the substrate is prevented from peeling and the catalyst (particles) from the material constituting the substrate is prevented, and the electrode for water electrolysis is used. It is to provide a water electrolysis cell.

The present inventor, as a result of extensive studies to solve the above problems, does not necessarily require depositing a catalyst layer on a substrate, but rather a material constituting a porous substrate (on the substrate itself), By supporting the catalyst such as catalyst particles or catalyst membrane and forming the solid polymer electrolyte membrane layer on the electrode, it becomes difficult for the catalyst membrane to be peeled off or the catalyst (particles) to be detached due to the gas lift, resulting in performance deterioration. The present invention has been completed by finding that it does not occur. Since the present invention does not use a "membrane electrode assembly (MEA) having a catalyst layer", a so-called conventional "catalyst layer" is not essential.

Furthermore, by coating the surface of the electrode surface in contact with the solid polymer electrolyte membrane (PEM) with the ionomer dispersion liquid and/or by allowing the ionomer to penetrate into the porous voids in the electrode, the cell voltage ( The present invention has been completed by finding that the electrolysis voltage) is reduced.

That is, the present invention provides an electrode for water electrolysis adjacent to a solid polymer electrolyte membrane (PEM) in a water electrolysis cell,
An electrode for water electrolysis, which has a "catalyst-supporting porous electrode base material on which a metal catalyst or a metal oxide catalyst is supported", which is obtained by adhering a metal catalyst or a metal catalyst precursor to a porous substrate and firing it. Is provided.

The present invention also provides the above-mentioned electrode for water electrolysis, which further has an ionomer layer on the side of the catalyst-supporting porous electrode base material adjacent to the solid polymer electrolyte membrane.

Further, the present invention, the ionomer layer is also penetrated into the porous voids of the catalyst-supporting porous electrode substrate, and, of the void volume of the catalyst-supporting porous electrode substrate, the ionomer layer It is intended to provide the above-mentioned electrode for water electrolysis in which the ratio of filling voids is 10 vol% or more and 90 vol% or less.

The present invention also provides the above-mentioned electrode for water electrolysis, wherein the firing is performed at 200°C or higher and lower than 600°C in the presence of an oxygen-containing gas.

Further, the present invention provides the above-mentioned electrode for water electrolysis, wherein the porous substrate is a porous titanium group substrate, a porous titanium group alloy substrate or a porous titanium group compound substrate, or a porous carbon substrate. Is.

Further, the present invention is a method for producing the above-mentioned electrode for water electrolysis,
Production of a catalyst-supporting porous electrode substrate included in the electrode for water electrolysis is characterized in that a metal catalyst or a metal catalyst precursor is attached to a porous substrate, and then the catalyst is supported on the porous electrode substrate by firing. The present invention provides a method for producing an electrode for water electrolysis.

Further, the present invention is characterized by comprising at least a water electrolysis cathode that is the above-mentioned water electrolysis electrode, a solid polymer electrolyte membrane (PEM), and a water electrolysis anode in this order. The present invention provides a water electrolysis cell.

According to the present invention, the above problems and the above problems are solved, for example, water electrolysis having excellent performance such as low cell voltage and excellent durability by strengthening the catalyst (layer). It is possible to provide an electrode for water and a water electrolysis cell using the electrode.

Specifically, the catalyst and the catalyst can be prepared by supporting the catalyst on a porous substrate such as a porous titanium group substrate, a porous titanium group alloy substrate or a porous titanium group compound substrate, or a porous carbon substrate by a specific method. The catalyst can be integrated with the substrate, and by supporting the catalyst on "a material such as titanium fiber or carbon fiber forming the porous substrate", the catalyst such as catalyst particles or catalyst film can be formed from the material. Detachment is prevented and durability is improved.

Furthermore, by coating the surface of the electrode with an ionomer dispersion (providing an ionomer layer), the cell voltage is reduced, and the catalyst film peeling or catalyst (particle) desorption due to gas lift is less likely to occur in water. An electrode for electrolysis can be provided. Such "peeling of the catalyst membrane and desorption of the catalyst (particles)" is particularly referred to as "supporting the catalyst on the porous substrate by a specific method" and "presence of the ionomer (layer)". And synergistically act to effectively prevent and suppress.
The present invention does not use a “membrane electrode assembly (MEA) having a catalyst layer” (see FIGS. 5 and 7 ), that is, a so-called conventional “catalyst layer” is not (essentially) necessary. The conventional peeling of the “catalyst layer” itself cannot occur in the first place.

Using the electrode for water electrolysis of the present invention, a water electrolysis cell comprising a cathode for water electrolysis, a solid polymer electrolyte membrane, and an anode for water electrolysis in this order has a low cell voltage during water electrolysis, and a catalyst film or a catalyst. It has extremely high durability because there is no peeling or detachment of particles.

It is a schematic sectional drawing of the water electrolysis cell which has the electrode for water electrolysis of this invention. A schematic perspective view of a catalyst-supporting porous electrode substrate in the electrode for water electrolysis of the present invention, and "the porous substrate is a titanium group fiber, titanium group alloy fiber or titanium group compound fiber, or an aggregate of carbon fibers It is a schematic enlarged view of the fiber carrying the catalyst (particles) at a certain time. It is a graph which shows the "current density (A/cm< ² >) dependence of cell voltage (V)" of the water electrolysis cell obtained in Examples 1-6 and the comparative example 1. 5 is a graph showing “current density (A/cm ² ) dependence of cell voltage (V)” of the water electrolysis cells obtained in Examples 13 and 14 and Comparative Example 1. It is a schematic development perspective view of a water electrolysis cell. (A) Water electrolysis cell having an electrode for water electrolysis of the present invention (b) Water electrolysis cell having a conventional electrode for water electrolysis (water electrolysis cell using a conventional membrane electrode assembly (MEA)) It is a schematic development perspective view of the water electrolysis cell (water electrolysis stack cell) which has two pairs of electrodes for water electrolysis of the present invention. It is a schematic sectional drawing of the water electrolysis cell of this invention which shows the state which sandwiched the solid polymer electrolyte membrane (PEM) with the electrode for water electrolysis of this invention.

Hereinafter, the present invention will be described, but the present invention is not limited to the following specific forms and can be arbitrarily modified within the scope of the technical idea.

[Electrode for water electrolysis]
The electrode 2 for water electrolysis of the present invention is the electrode 2 for water electrolysis adjacent to the solid polymer electrolyte membrane (PEM) 5 in the water electrolysis cell 1,
It is characterized in that it has a "catalyst-supporting porous electrode substrate 3 carrying a metal catalyst 3c or a metal oxide catalyst 3c" which is obtained by depositing a metal catalyst or a metal catalyst precursor on a porous substrate 3a and firing it. ..
FIG. 1, FIG. 5A and FIG. 7 show a schematic sectional view or a schematic exploded perspective view of a preferred example of a water electrolysis cell 1 using the electrode 2 for water electrolysis of the present invention. That is, the electrode 2 for water electrolysis of the present invention has the catalyst-supporting porous electrode base material 3 on which the “metal catalyst 3c or the metal oxide catalyst 3c” is supported. It is obtained by adhering a metal catalyst or a metal catalyst precursor to the porous substrate 3a and firing it.

The water electrolysis electrode 2 of the present invention can be used as both a water electrolysis cathode and a water electrolysis anode.
Hereinafter, the "metal catalyst or metal oxide catalyst" in the above "" may be simply abbreviated as "catalyst", and the above "catalyst-supporting porous electrode substrate" and "porous electrode substrate" are simply referred to as "electrodes". It may be abbreviated as "base material". Further, the "electrode for water electrolysis" may be simply abbreviated as "electrode".
Further, the “catalyst particles” and the “catalyst film” may be collectively referred to as “catalyst”.
In addition, "a porous titanium group substrate, a porous titanium group alloy substrate or a porous titanium group compound substrate" may be collectively referred to simply as "a porous titanium group-based substrate". "Group alloy fiber or titanium group compound fiber" may be collectively referred to as "titanium fiber".

<Catalyst-supporting porous electrode substrate>
In the electrode substrate 3 of the present invention, specifically, a “metal catalyst or metal catalyst precursor” is dissolved or finely dispersed in a porous substrate 3a such as a porous titanium group-based substrate or a porous carbon substrate. It is obtained by applying a coating liquid and then firing it to form a catalyst film or catalyst 3c such as catalyst particles on the surface of the constituent material of the porous substrate 3a (on the electrode base material). It is preferable that it is (see FIG. 7). That is, in other words, it is preferable that the “adhesion” is caused by coating and drying the coating liquid. Here, “baking” performed after the adhesion means a general heat treatment.

In the present invention, in what form the catalyst 3c is formed on the electrode base material; "in the form of the titanium fiber 3b or the carbon fiber 3b constituting the porous substrate 3a", the catalyst particle, etc. It is impossible or impractical to specify directly whether or not the catalyst 3c of 3 is supported; That is, it is not possible to directly specify "the electrode base material obtained by adhering the metal catalyst or the metal catalyst precursor to the porous substrate 3a and firing it" by its form (shape) or by directly specifying the parameters or the like. Since it is impossible or almost impractical, the electrode substrate in the present invention can only be specified by its manufacturing method.

<< Porous Titanium Group Substrate >>
The electrode of the present invention has a catalyst-supporting porous electrode substrate 3 in which a catalyst 3c is supported on a porous substrate 3a such as a porous titanium group-based substrate or a porous carbon substrate. "Metal)" refers to titanium, zirconium or hafnium. Further, the "titanium group-based" means the titanium group metal simple substance, an alloy thereof, or a compound thereof.
That is, the porous titanium group substrate in the present invention is preferably a porous titanium group substrate, a porous titanium group alloy substrate or a porous titanium group compound substrate.
Examples of the “titanium group compound” include titanium nitride (titanium nitride (TiN)), titanium carbide (titanium carbide (TiC)), titanium boride (titanium diboride (TiB ₂ )) and the like.

Among them, the porous titanium group-based substrate is more preferably a porous titanium substrate, a porous zirconium substrate or a porous hafnium substrate, or a porous titanium alloy substrate, a porous zirconium alloy substrate or a porous hafnium alloy substrate.
When used as the porous substrate 3a of the electrode 2 for water electrolysis, the cell voltage is low, and the catalyst (particles) 3c is prevented from being desorbed from the electrode substrate. Titanium or a titanium alloy is more preferable, and titanium is particularly preferable.
For the same reason, it is particularly preferable that the porous titanium group substrate is a porous titanium substrate and the porous titanium group alloy substrate is a porous titanium alloy substrate, and the porous substrate 3a of the present invention is porous. Most preferably, it is a titanium substrate.

Here, "porous" is not limited to a form in which holes are simply formed in a plane, and is an aggregate of "titanium group fiber, titanium group alloy fiber or titanium group compound fiber" (titanium fiber). Thus, it refers to all forms such as paper, woven fabric, non-woven fabric, etc. that are in a roughened state, a porous state, a spatial state, etc. in order to increase the surface area. The electrode base material 3 electrolyzes water to generate hydrogen as a gas, and it is necessary to take out the gas. Therefore, the porous substrate 3a is permeable to the power supply body 6 and/or the resin tank body 7 side. Need to have.

The porous titanium-group-based substrate is preferably an aggregate of titanium-group fibers, titanium-group alloy fibers or titanium-group compound fibers. Above all, in order to exert the effects of the present invention suitably, It is particularly preferable that the titanium group base 3a is an aggregate of titanium fibers.
As a particularly preferable form, an example in which the porous substrate 3a is an aggregate of titanium fibers 3b is shown in FIG.

<< Porous carbon substrate >>
The electrode of the present invention has a catalyst-supporting porous electrode substrate 3 in which a catalyst 3c is supported on a porous substrate 3a such as a porous titanium group substrate or a porous carbon substrate. The porous carbon substrate 3a is It is necessary to have electrical conductivity because it is necessary to apply electricity to decompose water electrochemically. The porous carbon substrate 3a is made of a conductive carbonaceous material, and is not particularly limited as long as it is porous, but it is desirable that it is electrochemically stable. The carbonaceous material preferably has a graphite structure (graphene structure).

Regarding the shape of the carbonaceous material, if the carbonaceous materials are in contact with each other and electrically connected to the power supply body 6, the carbonaceous materials are not necessarily fixed to each other, but they are treated as actual electrodes. It is desirable to have the above mechanical strength.

Here, “porous” is not limited to a form in which holes are simply formed on a plane, but is an aggregate of carbonaceous materials, and is intended to have a large surface area such as paper, woven fabric, and nonwoven fabric. , All the forms such as a roughened state, a porous state, and a spatial state. However, since the electrode base material 3 electrolyzes water to generate hydrogen as a gas, and it is necessary to take out the gas, the porous substrate 3a is transferred to the power supply body 6 and/or the resin tank body 7 side. Must be breathable.
FIG. 2 illustrates an example in which the porous carbon substrate 3a is an aggregate of carbon fibers 3b.
Further, by using the porous carbon substrate 3a whose surface is roughened by etching or sputtering using a chemical, it is possible to further reduce the energy required for electrolysis of water.

Above all, in order to preferably exert the effects of the present invention, the porous carbon substrate 3a is preferably an aggregate of carbon fibers 3b, and among the aggregates of carbon fibers 3b, carbon paper and carbon cloth. , Carbon felt and the like are more preferable. Further, among them, carbon paper is particularly preferable, and carbon paper used for a gas diffusion layer for a fuel cell is most preferable for the above reason.
Particularly, by roughening the surface of the “aggregate of carbon fibers 3b” such as carbon paper, carbon cloth, and carbon felt by etching using chemicals or sputtering, the energy required for electrolysis can be further reduced. Can be achieved.

<<Metal Catalyst or Metal Catalyst Precursor>>
The electrode substrate 3 in the present invention is such that it can be obtained by adhering a metal catalyst or a metal catalyst precursor to the porous substrate 3a and calcining the metal, and the metal in the metal catalyst or the metal catalyst precursor is There is no particular limitation as long as the catalyst 3c obtained by baking the above acts as a catalyst, but platinum (Pt), ruthenium (Ru), iridium (Ir), palladium (Pd), tantalum (Ta), and nickel A metal selected from the group consisting of (Ni) is preferable from the viewpoint of high catalytic effect. The above metals may be used alone or in combination of two or more. It is also possible to use together with metals other than the above.

Specific examples of the metal compound in the metal catalyst/metal catalyst precursor which is a raw material of the catalyst (metal catalyst or metal oxide catalyst) 3c include, for example, platinum (IV) chloride n-hydrate and platinum chloride (IV ) Ammonium acid, dinitrodiammine platinum (II), platinum (II) chloride, platinum (IV) chloride, tetraammine platinum (II) dichloride n hydrate, tetraammine platinum (II) hydroxide, hexahydroxyplatinum (IV) Platinum-containing compound such as acid; Ruthenium (III) chloride hydrate, Ruthenium (III) nitrate, Ruthenium oxide (IV) hydrate and other ruthenium-containing compounds; Iridium chloride (IV) acid n-hydrate, Iridium(III) chloride n-hydrate, iridium(III) chloride anhydrate, iridium(IV) nitrate, iridium(IV) chloride ammonium, hexaammineiridium(III) hydroxide, and other iridium-containing compounds; palladium chloride (II), palladium (II) nitrate, dinitrodiammine palladium (II), palladium (II) acetate, tetraammine palladium (II) dichloride and other palladium-containing compounds; tantalum chloride, tantalum alkoxides and other tantalum-containing compounds; nickel chloride ( II) nickel-containing compounds such as anhydrous products, nickel chloride (II) hexahydrate, nickel nitrate (II) hexahydrate; and the like.

Examples of the metal catalyst precursor include those in which alcohol is coordinated to the above metal compound. “Catalyst particles or catalyst film” is prepared by dissolving the above metal compound in an alcohol solvent or the like to prepare a metal catalyst precursor, applying a coating liquid containing the metal catalyst precursor to the porous substrate 3a, and then firing the solution. It is particularly preferable to prepare the electrode base material 3 (catalyst-supporting porous electrode base material 3) by converting it into 3c and supporting it.

When the deposition of the metal catalyst or the metal catalyst precursor to the porous substrate 3a is performed by coating, as the "solvent (dispersion medium) of the coating liquid used for the coating", or the above "coordinate with the metal compound" Preferred examples of the "alcohol" include methanol, ethanol, propyl alcohol, isopropyl alcohol, butanol, pentanol, hexanol, cyclohexanol and the like.

When applying to the porous substrate 3a by coating, the coating method of the coating liquid is not limited, but a brush coating method, a spraying method, a spray coating method, a dipping method, and the like are preferable.
The drying after coating is not particularly limited as long as it is a temperature at which the solvent evaporates, but is preferably 20° C. or higher and 100° C. or lower, and particularly preferably 40° C. or higher and 90° C. or lower.
The drying time is not particularly limited as long as the solvent evaporates, but is preferably 5 minutes or more and 120 minutes or less, more preferably 10 minutes or more and 90 minutes or less, and particularly preferably 20 minutes or more and 50 minutes or less. ..

The catalyst 3c is a metal catalyst or a metal oxide catalyst, and examples thereof include those obtained by firing the "metal catalyst or metal catalyst precursor". The metal of the metal catalyst or metal catalyst precursor is a metal selected from the group consisting of platinum (Pt), ruthenium (Ru), iridium (Ir), palladium (Pd), tantalum (Ta), and nickel (Ni). Is preferred.
Specifically, for example, platinum (Pt), platinum oxide, ruthenium (Ru), ruthenium oxide, iridium (Ir), iridium oxide, palladium (Pd), palladium oxide, tantalum (Ta), tantalum oxide, nickel (Ni). ), nickel oxide and the like are preferable. In addition to the above, the catalyst 3c may be used in combination with another metal or an oxide of another metal, or may be mixed with another catalyst.

When the catalyst 3c is catalyst particles, the number average particle diameter of the catalyst particles is preferably 300 μm or less, more preferably 200 μm or less, and particularly preferably 100 μm or less.

If the average particle size of the catalyst particles is too large, the catalytic effect may decrease, the cell voltage may increase, or may be detached from the electrode base material.On the other hand, if it is too small, the electrode base material may dig into the deep part. There are cases where it will end up.
However, as long as the surface area of the catalyst can be increased by suppressing the infiltration into the deep part by adjoining and binding a plurality of fine particles, the shape is not necessarily limited to the above particle size range, and any shape, for example, a lump or It may be in the form of granules, or microscopically, it may be carried in a state of partially covering the electrode base material.
The "cell voltage" means an electrolysis voltage applied between the cathode and the anode of the water electrolysis cell 1 for electrolysis of water.

When the catalyst 3c is in the form of a catalyst film and is carried on the side surface of the pores of the porous substrate 3a or the side surface of the fiber 3b, the average film thickness of the film is not particularly limited depending on the type of catalyst. However, 50 μm or less is preferable, 40 μm or less is more preferable, and 30 μm or less is particularly preferable. The average film thickness can be obtained by observing a cross section of the catalyst-supporting porous electrode substrate 3 obtained after firing with a scanning electron microscope (SEM), and is defined as obtained in this way.

2 and 7, a preferred embodiment of the present invention, that is, the porous substrate 3a is an aggregate of titanium fibers 3b or carbon fibers 3b, and the "metal catalyst or metal oxide catalyst" 3c is the titanium fibers 3b or The state where the catalyst-supporting porous electrode substrate 3 is supported by the carbon fibers 3b is shown.

2 and 7, a particularly preferred embodiment of the present invention, that is, the porous titanium group-based substrate is an aggregate of titanium group fibers (titanium fibers), and the "metal catalyst or metal oxide catalyst" 3c is the titanium. A state in which the catalyst-supporting porous electrode base material 3 is supported by a group fiber is shown.

<<Baking>>
The calcination is not particularly limited as long as it can generate the catalyst 3c by heating, but it is preferable to perform it in the presence of an oxygen-containing gas from the viewpoint of obtaining a high catalytic effect. Further, when the porous substrate 3a is a porous carbon substrate, it is preferable from the viewpoint of activating the porous carbon substrate.
The firing temperature (heat treatment temperature) is preferably 200°C or higher and lower than 600°C, and particularly preferably 280°C or higher and 590°C or lower.

By firing in the above firing temperature range, the porous substrate 3a is not excessively deteriorated, and the mechanical strength of the electrode base material 3 can be maintained.
Specifically, when the porous substrate 3a is a porous carbon substrate, if the upper limit of the firing temperature is not higher than the above, the carbon fibers 3b (such as carbon fibers of carbon paper) forming the porous carbon substrate are excessive. It does not become too thin, the residual mass ratio described below does not become too small, and the mechanical strength can be maintained without deterioration of the porous carbon substrate itself.

On the other hand, when the porous substrate 3a is a porous carbon substrate and the lower limit of the firing temperature is the above or higher, the metal catalyst precursor is preferably the catalyst 3c, and a metal oxide having a high catalytic effect is produced. The "mass reduction of the porous carbon substrate" and the "thinning of the material such as the carbon fibers 3b constituting the porous carbon substrate" as described below occur suitably (moderately), and the carbon fibers of the catalyst (particles) 3c As a result, the catalyst (particles) 3c can be favorably supported on the "raw material such as the carbon fibers 3b constituting the porous carbon substrate", and the catalyst (particles) 3c is reduced. Detachment from the material is prevented.

Further, the fact that the catalyst (particles) 3c is appropriately reduced on the material such as the carbon fibers 3b and is suitably supported on the porous carbon substrate can be further improved by combining with the formation of the ionomer layer 4 described later. , Synergistically suppressing the desorption of the catalyst (particles) 3c from the material.
In addition, the “material forming the porous carbon substrate” such as the carbon fibers 3b undergoes changes (deterioration, etc.) such as thinning due to the above firing, and the ionomer layer 4 follows the changes (deterioration, etc.). Will give you. In other words, by forming the ionomer layer 4 to be described later, even if the material is thin, the catalyst (particles) 3c is less likely to come off, and the durability of the electrode base material 3 can be improved.

The firing time (heat treatment time) is not particularly limited as long as the above effect is exhibited, but is preferably 10 minutes or more and 8 hours or less, more preferably 30 minutes or more and 5 hours or less, and particularly preferably 1 hour or more and 3 hours or less. ..
When the firing time is the lower limit or more, the same effect as when the firing temperature is the lower limit or more is obtained, and when the firing time is the upper limit or less, the same effect as when the firing temperature is the upper limit or less. Is obtained.

When the porous substrate 3a in the present invention is a porous carbon substrate, a value obtained by dividing the residual amount (g) of the mass of the porous carbon substrate after firing by the mass (g) of the porous carbon substrate before firing. Is defined as "mass residual rate". If the firing conditions (heat treatment conditions) are strong (for example, the firing temperature is high, the firing time is long, etc.), the mass residual rate becomes small.
The mass residual rate was determined by the method described in the examples. That is, the mass ratio of carbon and platinum was measured before and after firing using an analyzer (SEM-EDX) using a scanning electron microscope and energy dispersive X-ray spectroscopy, and the mass of platinum was unchanged before and after firing. It was calculated by taking advantage of the fact.

When the porous substrate 3a in the present invention is a porous carbon substrate, the mass residual rate of the porous carbon substrate due to firing is such that the catalyst (particles) 3c is preferably produced, and the catalyst (particles) 3c are carbon fibers 3b. It is preferable to reduce the amount of the carbon fiber 3b to a range such that the ionomer layer 4 can cover the thinness of the carbon fiber 3b.
Specifically, the above-mentioned effect is obtained by performing the firing so that the mass of the porous carbon substrate after firing is 55% by mass or more and 99% by mass or less of the mass of the porous carbon substrate before firing. It is preferable in order to obtain it suitably.
The mass residual ratio of the porous carbon substrate by firing is more preferably 70% by mass or more and 97% by mass or less, and particularly preferably 90% by mass or more and 95% by mass or less.

<<<ionomer>>>
The electrode 2 for water electrolysis of the present invention further has an ionomer layer 4 and an ionomer 4 on at least the side of the catalyst-supporting porous electrode substrate 3 adjacent to the solid polymer electrolyte membrane (PEM) 5. Is preferred (see FIG. 7). The ionomer layer 4 and the ionomer 4 may be provided on both sides of the electrode base material 3.
Here, the "ionomer" is also referred to as a cation exchange polymer, a polymer having a strong acid group in the side chain, a proton conductive polymer, an ion conductive polymer, etc., and the "ionomer (layer)" is the above-mentioned chemistry. A polymer (layer) having a structure and physical properties.

Since the electrode base material 3 is not flat as it is represented by the surface of the aggregate of the titanium fibers 3b or the carbon fibers 3b (because it has a mesh shape), contact with the solid polymer electrolyte membrane (PEM) 5 May not be sufficient, and therefore the contact between the catalyst 3c and the solid polymer electrolyte membrane (PEM) 5 may not be sufficient, but when the ionomer (layer) 4 is present, the “electrode substrate 3 itself” or The voids existing “between the electrode base material 3 and the solid polymer electrolyte membrane (PEM) 5” are filled, and the contact becomes good.
Further, as described above, by firing the porous carbon substrate, the material forming the porous carbon substrate such as the carbon fiber 3b becomes thin, and the electrode base material 3 becomes the solid polymer electrolyte when the water electrolysis cell 1 is manufactured. Where the membrane (PEM) 5 becomes more difficult to be buried, when the ionomer (layer) 4 is present, the contact between the electrode base material 3 carrying the catalyst (particles) 3c and the solid polymer electrolyte membrane (PEM) 5 is good. Becomes

That is, the ionomer layer 4 has a function of conducting water and “hydrogen ions (protons) particularly to the cathode side”, and at least the solid of the catalyst-supporting porous electrode substrate 3 described above. By being present on the side adjacent to the polymer electrolyte membrane (PEM) 5, the resistance when conducting protons from the solid polymer electrolyte membrane (PEM) 5 to the surface can be significantly reduced.
Therefore, if the ionomer layer 4 is in contact with the surfaces of the solid polymer electrolyte membrane (PEM) 5 and the catalyst layer 3c, it needs to be "a flat plate layer having no holes and a uniform thickness depending on the location". There is no. For example, even if a layer is present on the surface of the fiber 3b constituting the electrode base material 3 itself, it is referred to as an "ionomer layer".
Rather, as shown in FIG. 7, for example, the ionomer 4 penetrates into the voids of the porous electrode substrate 3 and into the more microscopic pores (these may also be referred to as “porous voids”). By being filled, protons can be conducted also to the “catalyst 3c on the side of the power feeding body 6 that cannot be in direct contact with the solid polymer electrolyte membrane” to facilitate the water electrolysis reaction.

As a result, by providing the ionomer layer 4 on the side of the solid polymer electrolyte membrane (PEM) 5 of the electrode base material 3, the utilization efficiency of the carried catalyst 3c may be improved, and the water electrolysis cell 1 may be used as a low cell. It is operated at a voltage (electrolytic voltage). Further, desorption of the catalyst particles 3c and the catalyst film 3c due to the generated gas can be suppressed.

The amount of the ionomer layer 4 formed varies depending on the thickness and porosity of the catalyst-supporting porous electrode substrate 3 and the usage conditions of the water electrolysis cell 1, for example, the amount of hydrogen generated per unit time, and therefore is not always limited. However, since the gas is generated by water electrolysis and it is necessary to take out the gas to the outside of the cell, microscopically, the polymer chains forming the ionomer 4 completely cover the surface of the catalyst (particle) 3c. It is desirable that the surface of the catalyst (particles) 3c is exposed microscopically and partially without being covered thickly, and macroscopically, all the voids of the catalyst-supporting porous electrode base material 3 are covered by the ionomer 4. It is desirable to have a void that allows the generated gas to escape without being filled (see FIG. 7).

Further, since the generated gas is taken out from the power supply body 6 and/or the resin tank body 7 side, the side of the electrode base material 3 in contact with the solid polymer electrolyte membrane (PEM) 5 is arranged so that the gas can be taken out more efficiently. It is also preferable that the abundance (local filling rate) of the ionomer 4 be distributed between the side in contact with the power supply body 6.
Therefore, although not necessarily limited, the ratio of the volume of the voids filled by the ionomer (layer) 4 to the void volume of the catalyst-supporting porous electrode substrate 3 itself (hereinafter referred to as “filling ratio”). In some cases) is preferably 10% by volume or more and 90% by volume or less, more preferably 20% by volume or more and 80% by volume or less, and particularly preferably 30% by volume or more and 70% by volume or less.
The above numerical values are average values in the thickness direction of the electrode base material 3 when the abundance (filling rate) of the ionomer 4 differs in the thickness direction of the electrode base material 3.

That is, according to the present invention, the ionomer layer 4 penetrates into the porous voids of the catalyst-supporting porous electrode substrate 3 and, in the void volume of the catalyst-supporting porous electrode substrate 3, It is also the above-mentioned electrode 2 for water electrolysis in which the ratio of the voids filled with the ionomer layer 4 is 10% by volume or more and 90% by volume or less.

The above effect of the ionomer (layer) 4 is suitably exerted on any electrode regardless of whether the electrode 2 for water electrolysis is used as a cathode for water electrolysis or an anode for water electrolysis ( (See FIG. 1).

The formation of the ionomer layer 4 and the filling of the ionomer 4 can be performed, for example, by applying the ionomer dispersion liquid to the electrode base material 3 carrying the catalyst 3c. Examples of the method for applying the ionomer dispersion liquid include a brush coating method, a spraying method, and a spray coating method.
After coating the ionomer dispersion liquid, it is preferable to volatilize the solvent of the ionomer dispersion liquid at about 60° C., and then perform heat treatment at 120° C. or higher and 200° C. or lower, preferably 1 minute or longer and 1 hour or shorter.

<<<Chemical structure of ionomer>>>>
The ionomer 4 is not particularly limited as long as it has ion conductivity, particularly proton conductivity, and can be used in the water electrolysis cell 1. That is, the “ionomer” of the present invention refers to a proton conductive polymer.
The ionomer 4 is not particularly limited, and may be a fluorine-based ionomer having a fluorine atom in the molecule or a non-fluorine-based ionomer having no fluorine atom in the molecule.

Although not limited thereto, a fluorine-based ionomer is preferable among them, and it is an ion conductive polymer (proton conductive polymer) having a polyfluoroethylene skeleton as a main chain and a fluoroethylene ether skeleton having a sulfonic acid group at a terminal as a side chain. More preferably. The fluoroethylene ether skeleton is particularly preferably a perfluoroethylene ether skeleton.
Although not particularly limited, examples of preferable ionomer 4 used in the present invention are shown below.

[In Formula (1), m is a natural number]

[In Expression (2), p is a natural number]

[In the formula (3), n is a natural number]

The ionomer represented by the formula (1) is a polymer having a polytetrafluoroethylene (PTFE) skeleton as a main chain and a perfluoroether pendant side chain having a sulfonic acid group at the terminal. Since the side chain is relatively long, it is called a long-side-chain (LSC) ionomer.
The equivalent mass (EW: equivalent weight) of the ionomer represented by the formula (1) (mass of polymer required to supply 1 mol of protons) is, but not limited to, 900 g/mol to 1200 g/mol. Is particularly preferable. A preferable range of m in the formula (1) is a range that can be calculated from the equivalent mass.

The long side chain (LSC) ionomer represented by the formula (1) is preferably, but not limited to, a commercially available product such as Nafion (Nafion (registered trademark)) manufactured by DuPont.
As the long side chain (LSC) ionomer represented by the formula (1), Nafion (Nafion (registered trademark)) (EW=1100 g/mol, the average value of m in the formula (1) is 6.6) and the like are preferable. ..

The ionomer represented by the formula (2) or the formula (3) is a polymer having a polytetrafluoroethylene (PTFE) skeleton as a main chain and a perfluoro pendant side chain having a sulfonic acid group at the terminal. Since the side chain is relatively short, it is referred to as a short-side-chain (SSC) ionomer.
The equivalent mass (EW) of the ionomer represented by formula (2) or formula (3) is not particularly limited, but 700 g/mol to 950 g/mol is particularly preferable. The preferable range of p in the formula (2) and the preferable range of n in the formula (3) are ranges that can be calculated from the equivalent mass.

The short side chain (SSC) ionomer represented by the formula (2) or the formula (3) is not limited, but a commercially available product is also used, and examples thereof include 3M ionomer manufactured by 3M Corporation.

<Use as cathode for water electrolysis and/or anode for water electrolysis>
The above-mentioned electrode 2 for water electrolysis of the present invention can be used as either a cathode for water electrolysis or an anode for water electrolysis.
The water electrolysis electrode 2 of the present invention has an effect of increasing the current density (A/cm ² ) at a low voltage regardless of whether it is used as a water electrolysis cathode or a water electrolysis anode (constant current). When electrolyzed at a density, it has the effect of lowering the cell voltage).
Further, by providing the ionomer layer 4 and the ionomer 4, the cell voltage drop effect is produced regardless of whether it is the cathode or the anode. That is, the effect of the ionomer layer does not matter whether it is a cathode or an anode.

However, when the porous substrate 3a is a porous carbon substrate, the water electrolysis electrode 2 of the present invention is preferably used as a water electrolysis cathode from the viewpoint of ensuring safety against oxygen generated at the anode.
In the present invention, the catalyst (particularly platinum (Pt), platinum oxide, palladium (Pd), palladium oxide, etc.) supported on the porous carbon substrate by a special method is particularly superior when it is the cathode, The electrode 2 for water electrolysis of the present invention is preferably used at least as a cathode when the porous substrate 3a is a porous carbon substrate.

[Method for producing water electrolysis electrode]
The present invention is a method for producing the above-mentioned electrode 2 for water electrolysis, in which the catalyst-supporting porous electrode substrate 3 included in the electrode 2 for water electrolysis is produced by using a metal catalyst or a metal catalyst precursor on the porous substrate 3a. Is also adhered and then calcined to support the catalyst 3c on the porous electrode substrate 3, which is also a "method for producing an electrode for water electrolysis".
The steps of the production method are as described above, and the preferred embodiments of the production method are also as described above.

In the above "method for producing electrode for water electrolysis", there is a step of further forming an ionomer layer 4 on the side of the catalyst-supporting porous electrode base material 3 adjacent to the solid polymer electrolyte membrane (PEM) 5. Is preferred. The method of forming the ionomer layer 4, the mode (shape), the effect, and the like are as described above.

[Water electrolysis cell]
The present invention also provides a water electrolysis cell 1 including at least the above-mentioned electrode 2 for water electrolysis and a solid polymer electrolyte membrane (PEM) 5.
The present invention is characterized by comprising at least a water electrolysis cathode, which is the above-mentioned water electrolysis electrode 2, a solid polymer electrolyte membrane (PEM) 5, and a water electrolysis anode in this order. It is particularly preferable to use the water electrolysis cell 1 (see, for example, FIG. 1 and FIG. 5A).
The water electrolysis cell 1 of the present invention does not exclude the presence of layers other than those shown in FIGS. 1 and 5(a).
For example, as shown in FIG. 1 and FIG. 5A, it is preferable that a power supply body 6 and a resin tank body 7 are provided outside the water electrolysis electrode 2. The power supply body 6 and the resin tank body 7 are not particularly limited, and known materials can be used.

Furthermore, it is a water electrolysis cell 1 comprising at least the above-mentioned electrode 2 for water electrolysis and a solid polymer electrolyte membrane (PEM) 5, and preferably at least "the above-mentioned electrode 2 for water electrolysis, solid. The water electrolysis cell 1 comprises a polymer electrolyte membrane (PEM) 5 and the above-mentioned electrode 2 for water electrolysis in this order, but as shown in FIG. It is also preferable that the water electrolysis stack cell 9 is formed by stacking the inside of the above "".
Here, the “bipolar plate” has a structure in which circulating water, generated hydrogen, and the like are distributed (supplied) by dividing into two or more units in the above “”.

That is, the present invention has “a water electrolysis cathode which is the above-mentioned water electrolysis electrode 2, a solid polymer electrolyte membrane (PEM) 5, and a water electrolysis anode which is the above-mentioned water electrolysis electrode 2 in this order. This is also the water electrolysis stack cell 9 in which a plurality of "units formed by" are stacked in series.

Although FIG. 6 has two inside “”, the number of water electrolysis stack cells 9 is preferably 2 or more and 12 or less, more preferably 3 or more and 10 or less, and 4 or more 8 The number of pieces or less is particularly preferable. When the number is in the above range, the amount of hydrogen produced per unit time (acquisition efficiency) increases, while the voltage applied to one water electrolysis stack cell 9 does not become too high when electrolysis is performed at a constant current.

Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples, but the present invention is not limited to these Examples as long as the gist thereof is not exceeded.
Hereinafter, values relating to ratios and% are mass ratios and mass% unless otherwise specified.

Example 1
[Water electrolysis electrode in which catalyst is supported on porous carbon substrate]
A "catalyst-supporting porous electrode base material supporting a metal catalyst or a metal oxide" was prepared by depositing a metal catalyst or a metal catalyst precursor on a porous carbon substrate and then calcining it.

<Substrate>
・Base 1
<< Porous Carbon Substrate for Cathode and/or Anode >>
As the porous carbon substrate, carbon paper (aggregate of carbon fibers) whose material is carbon fiber, having a fiber diameter of 10 μm and a porosity of 78% by volume, having a size of 25 mm×25 mm and a thickness of 0.28 mm A porous carbon substrate was prepared.

・Base 2
<<Substrate for anode>>
The material is titanium paper, the fiber diameter is 50 μm, the porosity is 60% by volume, and the substrate having a size of 25 mm×25 mm and a thickness of 0.5 mm is etched using an etching solution of hydrochloric acid 12 mol/L. After that, the substrate was prepared by washing with pure water and drying.

<Coating liquid of metal catalyst or metal catalyst precursor>
・Coating liquid 1
Platinum (IV) chloride hexahydrate was used as the metal raw material for the catalyst, and isopropanol containing 1% by mass of hydrochloric acid was used as the organic solvent. The coating liquid 1 was prepared by stirring for 1 hour under.

・Coating liquid 2
Platinum (IV) chloride hexahydrate was used as the metal raw material for the catalyst, and isopropanol containing 1% by mass of hydrochloric acid was used as the organic solvent. The coating liquid 2 was prepared by stirring for 1 hour under.

・Coating liquid 3
A coating liquid 3 was prepared in the same manner as the coating liquid 2 except that palladium (II) chloride was used as the metal raw material for the catalyst.

・Coating liquid 4
A coating liquid 4 was prepared in the same manner as the coating liquid 2 except that ruthenium (II) chloride hydrate was used as the metal raw material for the catalyst.

・Coating liquid 5
A coating liquid 5 was prepared in the same manner as the coating liquid 2 except that iridium chloride (IV) acid hexahydrate was used as the metal raw material for the catalyst.

・Coating liquid 6
A coating liquid 6 was prepared in the same manner as the coating liquid 2 except that nickel (II) chloride anhydride was used as the metal raw material for the catalyst.

・Coating liquid 7
Iridium (IV) chloride hexahydrate was used as the metal raw material for the catalyst, isopropanol containing 1% by mass of hydrochloric acid was used as the organic solvent, and the mixture was mixed at a molar ratio of 1:3 to obtain a nitrogen atmosphere. The coating liquid 7 was prepared by stirring under 1 hour.

<Ionomer dispersion>
Ionomer A dispersion liquid [Ionomer A dispersion liquid in which 25% of the following ionomer A was dispersed in a liquid composition of [water]:[1-propanol]:[2-propanol]=20:40:40 was prepared. ..
“Ionomer A” is a long side chain (LSC) ionomer represented by the above formula (1) in which the equivalent mass of the ionomer is 950 g/mol.

Ionomer B Dispersion Liquid An ionomer B dispersion liquid in which 20% of the following ionomer B was dispersed was prepared.
"Ionomer B" is a short side chain (SSC) ionomer represented by the above formula (3) in which the equivalent mass of the ionomer is 720 g/mol.

<Calculation method of mass residual rate>
-Using a scanning electron microscope and an analyzer (SEM-EDX) that uses energy dispersive X-ray spectroscopy, "the surface after deposition of the metal catalyst precursor and the like before drying and before firing" and "the electrode after firing" The "surface of the substrate" was analyzed and the mass ratio of carbon and platinum was measured. From the measured mass ratio and the mass of the porous carbon substrate and the mass of the electrode substrate after firing, the mass change of the carbon substrate before and after firing was obtained, and the "mass residual ratio (%)" of the porous carbon substrate by firing was obtained. Was calculated.

<Production of electrode>
・Electrode 1
The coating liquid 1 was applied to the surface of the porous carbon substrate (substrate 1, carbon paper substrate) prepared above by a brush coating method, and baked in air at 400° C. for 1 hour. After firing, the mixture was allowed to stand at room temperature for 3 hours to prepare a water electrolysis electrode (electrode base material).
The “mass residual ratio (%)”, which is the carbon mass of the substrate after baking, was 94% by mass with respect to the carbon mass of the substrate before baking.

・Electrode 2
The coating liquid 1 was applied to the surface of the porous carbon substrate (substrate 1, carbon paper substrate) prepared above by a brush coating method, and baked in air at 400° C. for 1 hour. After firing, the mixture was allowed to stand at room temperature for 3 hours, then the above “ionomer A dispersion” was applied on one side of the electrode so that the concentration was 50 mg/cm ^2, and heat treatment was performed at 140° C. for 10 minutes to form an ionomer layer and water. An electrode for electrolysis (electrode base material) was produced.
The “mass residual ratio (%)”, which is the carbon mass of the substrate after baking, was 94% by mass with respect to the carbon mass of the substrate before baking.

・Electrode 3
The coating liquid 1 was applied to the surface of the porous carbon substrate (substrate 1, carbon paper substrate) prepared above by a brush coating method, and baked in air at 400° C. for 1 hour. After firing, the mixture was allowed to stand at room temperature for 3 hours, then the above “ionomer B dispersion” was applied at 40 mg/cm ² and heat-treated at 160° C. for 10 minutes to form an ionomer layer, which was then used as an electrode for water electrolysis (electrode). A base material) was prepared.
The “mass residual ratio (%)”, which is the carbon mass of the substrate after baking, was 94% with respect to the carbon mass of the substrate before baking.

・Electrode 4
The porous carbon substrate (substrate 1, carbon paper substrate) produced above is subjected to a roughening treatment by etching with a chemical, and then the coating liquid 1 is applied to the surface of the roughened substrate. It was applied by a brush coating method and baked in air at 400° C. for 1 hour. After leaving the baked substrate at room temperature for 3 hours, "Ionomer B dispersion liquid" is applied at 40 mg/cm ² and heat-treated at 160°C for 10 minutes to prepare an electrode for water electrolysis (electrode substrate). did.
The “mass residual ratio (%)”, which is the carbon mass of the substrate after baking, was 93% by mass with respect to the carbon mass of the substrate before baking.

・Electrode 5
The coating liquid 2 was applied to the surface of the porous carbon substrate (substrate 1, carbon paper substrate) produced above by a brush coating method, and baked in air at 400° C. for 1 hour. Coating and baking of the coating liquid 2 were performed three times in total. The other conditions were the same as those for the electrode 3.
The “mass residual ratio (%)”, which is the carbon mass of the substrate after baking, was 56% by mass with respect to the carbon mass of the substrate before baking.

・Electrode 15
The coating liquid 3 was applied to the surface of the porous carbon substrate (substrate 1, carbon paper substrate) prepared above by a brush coating method. The other conditions were the same as those for the electrode 3.

・Electrode 16
The coating liquid 4 was applied to the surface of the porous carbon substrate (substrate 1, carbon paper substrate) prepared above by a brush coating method. The other conditions were the same as those for the electrode 3.

・Electrode 17
The coating liquid 5 was applied to the surface of the porous carbon substrate (substrate 1, carbon paper substrate) prepared above by a brush coating method. The other conditions were the same as those for the electrode 3.

・Electrode 18
The coating liquid 6 was applied to the surface of the porous carbon substrate (substrate 1, carbon paper substrate) prepared above by a brush coating method. The other conditions were the same as those for the electrode 3.

・Electrode 19
The coating liquid 1 was applied to the surface of the porous carbon substrate (substrate 1, carbon paper substrate) prepared above by a brush coating method and dried at 70° C. for 1 hour without firing. The other conditions were the same as those of the electrode 2.
The “mass residual ratio (%)” was 101% by mass because firing was not performed.

・Electrode A
The coating liquid 7 was applied to the surface of the titanium paper substrate (substrate 2) by a brush coating method, and baked in air at 400° C. for 1 hour. The baked substrate was left standing at room temperature for 3 hours to prepare an electrode.

・Electrode B
The coating liquid 7 was applied to the surface of the titanium paper substrate (substrate 2) by a brush coating method, and baked in air at 400° C. for 1 hour. After the calcined substrate was left standing at room temperature for 3 hours, the ionomer A dispersion liquid was applied at 50 mg/cm ² and heat-treated at 140° C. for 10 minutes to prepare an electrode.

・Electrode C
The coating liquid 7 was applied to the surface of the titanium paper substrate (substrate 2) by a brush coating method, and baked in air at 400° C. for 1 hour. After the baked substrate was allowed to stand at room temperature for 3 hours, the ionomer B dispersion liquid was applied at 40 mg/cm ² and heat-treated at 160° C. for 10 minutes to prepare an electrode.

<Solid polymer electrolyte membrane>
A solid polymer electrolyte membrane A having a size of 35 mm×35 mm and a thickness of 120 μm, which is composed of a long side chain (LSC) ionomer represented by the above formula (1) having an equivalent mass of 1100 g/mol (other than Example 6). Alternatively, a solid polymer electrolyte membrane B having a size of 35 mm×35 mm and a thickness of 120 μm, which is composed of a short side chain (SSC) ionomer represented by the formula (3) and has an equivalent mass of 870 g/mol (Examples). 6 only) was used.

<Water electrolysis cell>
A small water electrolysis cell for evaluation was assembled with the following configuration.

Anode for water electrolysis Cathode for water electrolysis Solid polymer electrolyte membrane Example 1 Electrode A Electrode 1 Solid polymer electrolyte membrane A
Example 2 Electrode B Electrode 2 Solid polymer electrolyte membrane A
Example 3 Electrode C Electrode 3 Solid polymer electrolyte membrane A
Example 4 Electrode C Electrode 4 Solid polymer electrolyte membrane A
Example 5 Electrode C Electrode 5 Solid polymer electrolyte membrane A
Example 6 Electrode C Electrode 3 Solid polymer electrolyte membrane B
Example 13 Electrode 1 Electrode 1 Solid polymer electrolyte membrane A
Example 14 Electrode 3 Electrode 3 Solid polymer electrolyte membrane A
Example 15 Electrode C Electrode 15 Solid polymer electrolyte membrane A
Example 16 Electrode C Electrode 16 Solid polymer electrolyte membrane A
Example 17 Electrode C Electrode 17 Solid polymer electrolyte membrane A
Example 18 Electrode C Electrode 18 Solid polymer electrolyte membrane A
Comparative Example 1 Electrode B Electrode 19 Solid Polymer Electrolyte Membrane A

<Water electrolysis cell evaluation method>
Pure water having a temperature of 20° C. is circulated by a pump in the small water electrolysis cell for evaluation described above, pure water for electrolysis is supplied to the anode side of the water electrolysis cell 1, and a predetermined current density is obtained using a DC power supply. The value of the cell voltage during water electrolysis was recorded. The evaluation results of Examples 1 to 14 and Comparative Example 1 are extracted and shown in FIGS. 3 and 4, respectively.
For Examples 3 to 15 to 18 in Table 1, the cell voltage values at a current density of 100 A/dm ² are shown in Table 1.

<Evaluation result>
As can be seen from FIGS. 3 and 4 in which all the platinum catalysts (particles) were evaluated in a unified manner, Comparative Example 1 in which the non-calcined electrode 19 was used as the cathode for water electrolysis was too high in cell voltage and was unsatisfactory. Although the results were acceptable, all of the other Examples 1 to 14 were acceptable levels without the cell voltage becoming too high.

Among them, Examples 3 to 6 using the cathode for water electrolysis having the ionomer layer of the ionomer B, which were evaluated by unifying the firing temperatures, were excellent in that the cell voltage was extremely low. That is, Examples 3 and 6 in which the electrode 3 is used for the water electrolysis cathode, Example 4 in which the electrode 4 is used in the water electrolysis cathode, and Example 5 in which the electrode 5 is used for the water electrolysis cathode are The cell voltage was extremely low and excellent (see FIG. 3).
Example 1 using the electrode 1 having no ionomer layer and Example 2 using the electrode 2 having the ionomer layer of the ionomer A are at the passing level, but the cell voltage is slightly higher than those of Examples 3 to 6. became.

Further, in all the examples in which the catalyst (particle)-supporting porous electrode substrate obtained by adhering the metal catalyst (precursor) to the porous carbon substrate and firing it was used as the cathode for water electrolysis, the catalyst film by gas lift was used. Peeling off and desorption of catalyst (particles) did not occur easily, performance deterioration did not occur, and it was excellent in durability.
On the other hand, in Comparative Example 1 in which the non-calcined electrode 19 was used as the cathode for water electrolysis, the catalyst film was easily peeled off and the catalyst (particles) was easily detached, and the durability was poor (not shown).

In Example 13 and Example 14 of FIG. 4, not only the cathode but also the anode was prepared from the carbon-based material in which the platinum-based catalyst (particles) was supported on the surface of the porous carbon substrate (base 1, carbon paper substrate). The "electrode base material" was used, but both the cathode and anode electrodes 1 of Example 13 and the cathode and anode electrodes 3 of Example 14 were fired in air at 400°C for 1 hour. Therefore, the cell voltage was extremely low and excellent.
On the other hand, in Comparative Example 1 in which the electrode 19 which was not fired was used as the cathode, the cell voltage was too high and was rejected.

In FIG. 4, in particular, Example 14 using the electrode 3 having the ionomer layer of the ionomer B in both electrodes was superior to Example 13 using the electrode 1 having no ionomer layer in both electrodes, and was excellent in cell voltage. It was

Table 1 shows that all of the same porous carbon substrates (substrate 1, carbon paper) were coated with a coating liquid containing each metal catalyst precursor, and baked at 400° C. for 1 hour in air to obtain ionomer B. As shown in Table 1, platinum (Pt), ruthenium (Ru), iridium (Ir), palladium (Pd), nickel (Ni) metal (oxidation) is used, although an electrode having an ionomer layer is used. The cell voltage at a current density of 100 A/dm ² was low for all the catalysts).
The tendency of good "low cell voltage" was Pt=Pd≥Ru≥Ir≥Ni (lower and better toward the left).

Example 2
[Electrode for water electrolysis in which catalyst is supported on porous titanium group-based substrate]
A porous titanium substrate is adopted as the porous titanium-group-based substrate, a metal catalyst or a metal catalyst precursor is attached to the porous titanium substrate, and then firing is performed, whereby "a metal catalyst or a metal oxide is supported. A catalyst-supporting porous electrode base material" was prepared.

<Substrate>
<< Porous Titanium Substrate for Cathode and/or Anode >>
The material is titanium paper, the fiber diameter is 50 μm, the porosity is 60% by volume, and the substrate having a size of 25 mm×25 mm and a thickness of 0.5 mm is etched using an etching solution of hydrochloric acid 12 mol/L. Then, it was washed with pure water and dried to prepare a porous titanium substrate.

<Coating liquid of metal catalyst or metal catalyst precursor>
・Coating liquid 21
Platinum (IV) chloride hexahydrate was used as the metal raw material for the catalyst, and isopropanol containing 1% by mass of hydrochloric acid was used as the organic solvent. The coating liquid 21 was prepared by stirring under 1 hour.

・Coating liquid 22
A coating liquid 22 was prepared in the same manner as the coating liquid 21 except that palladium (II) chloride was used as the metal raw material for the catalyst.

・Coating liquid 23
A coating liquid 23 was prepared in the same manner as the coating liquid 21, except that iridium chloro(IV) chloride hexahydrate was used as the metal raw material for the catalyst.

・Coating liquid 24
A coating liquid 24 was prepared in the same manner as the coating liquid 21, except that nickel (II) chloride anhydride was used as the metal raw material for the catalyst.

<Ionomer dispersion>
Ionomer A dispersion liquid [Ionomer A dispersion liquid in which 25% of the following ionomer A was dispersed in a liquid composition of [water]:[1-propanol]:[2-propanol]=20:40:40 was prepared. ..
“Ionomer A” is a long side chain (LSC) ionomer represented by the above formula (1) in which the equivalent mass of the ionomer is 950 g/mol.

Ionomer B Dispersion Liquid An ionomer B dispersion liquid in which 20% of the following ionomer B was dispersed was prepared.
"Ionomer B" is a short side chain (SSC) ionomer represented by the above formula (3) in which the equivalent mass of the ionomer is 720 g/mol.

<Production of electrode>
・Electrode 21
The coating solution 21 was applied to the surface of the porous titanium substrate (titanium paper substrate) prepared above by a brush coating method, and baked in air at 400° C. for 1 hour to obtain an electrode substrate.

・Electrode 22
The coating liquid 21 was applied to the surface of the porous titanium substrate (titanium paper substrate) prepared above by a brush coating method, and baked in air at 400° C. for 1 hour. After firing, the mixture was allowed to stand at room temperature for 3 hours, then the above “ionomer A dispersion liquid” was applied to one surface of the electrode so that the concentration was 40 mg/cm ^2, and heat treatment was performed at 140° C. for 10 minutes to form an ionomer layer. A base material was prepared (see FIG. 7).

・Electrode 23
The coating liquid 21 was applied to the surface of the porous titanium substrate (titanium paper substrate) prepared above by a brush coating method, and baked in air at 400° C. for 1 hour. After firing, the mixture was allowed to stand at room temperature for 3 hours, and then the above “ionomer B dispersion liquid” was applied to one surface of the electrode so as to have a concentration of 40 mg/cm ² and heat-treated at 160° C. for 10 minutes to form an ionomer layer. A base material was prepared (see FIG. 7).

・Electrode 24
The coating liquid 22 was applied to the surface of the porous titanium group substrate (titanium paper substrate) prepared above by a brush coating method, and baked in air at 400° C. for 1 hour. After firing, the mixture was allowed to stand at room temperature for 3 hours, then the above "ionomer B dispersion liquid" was applied at 40 mg/cm ² and heat-treated at 160°C for 10 minutes to form an ionomer layer to prepare an electrode substrate. ..

・Electrode 25
The coating liquid 23 was applied to the porous titanium substrate (titanium paper substrate) prepared above by a brush coating method, and the coating was baked in air at 400° C. for 1 hour. The baked substrate was allowed to stand at room temperature for 3 hours, then the “ionomer B dispersion liquid” was applied at 40 mg/cm ² and heat-treated at 160° C. for 10 minutes to prepare an electrode substrate.

・Electrode 26
The coating liquid 24 was applied to the porous titanium substrate (titanium paper substrate) produced above by a brush coating method, and the coating was baked in air at 400° C. for 1 hour. The baked substrate was allowed to stand at room temperature for 3 hours, then the “ionomer B dispersion liquid” was applied at 40 mg/cm ² and heat-treated at 160° C. for 10 minutes to prepare an electrode substrate.

-Electrode 27 (electrode for Comparative Example 21)
The coating solution 21 was applied to the surface of the porous titanium substrate (titanium paper substrate) prepared above by a brush coating method, and dried at 70° C. for 1 hour without firing to obtain an electrode substrate.

-Electrode 28 (electrode for Comparative Example 22)
The coating liquid 21 was applied to the surface of the porous titanium substrate (titanium paper substrate) prepared above by a brush coating method, and dried at 70° C. for 1 hour without firing. After the dried substrate was allowed to stand at room temperature for 3 hours, "Ionomer B dispersion liquid" was applied at 40 mg/cm ² and heat-treated at 160°C for 10 minutes to prepare an electrode substrate.

-Electrode 29 (electrode for Comparative Example 23)
The coating liquid 21 was applied to the surface of the porous titanium substrate (titanium paper substrate) prepared above by a brush coating method, and baked in air at 150° C. for 1 hour. After firing, the mixture was allowed to stand at room temperature for 3 hours, then the above “ionomer B dispersion liquid” was applied to one surface of the electrode so that the concentration was 40 mg/cm ^2, and heat treatment was performed at 160° C. for 10 minutes to form an ionomer layer. It was used as a base material.

-Electrode 30 (electrode for Comparative Example 24)
Platinum on both sides of a solid polymer electrolyte membrane A having a size of 25 mm×25 mm and a thickness of 120 μm, which is composed of a long side chain (LSC) ionomer represented by the above formula (1) having an equivalent mass of 1100 g/mol, An electrode catalyst layer was formed by applying and drying the carbon dispersion liquid to obtain a membrane electrode assembly (MEA) (see FIG. 5B).

<Solid polymer electrolyte membrane>
A solid polymer electrolyte membrane (PEM) having a size of 35 mm×35 mm and a thickness of 120 μm, which is composed of a long side chain (LSC) ionomer represented by the above formula (1) and has an equivalent mass of 1100 g/mol, was used.

<Water electrolysis cell>
A small water electrolysis cell for evaluation was assembled with the configuration shown in Table 2 below (FIG. 5A).

<Method for evaluating initial characteristics of water electrolysis cell>
Pure water having a temperature of 20° C. is circulated by a pump in the small water electrolysis cell 1 for evaluation described above, pure water for electrolysis is supplied to the anode side of the water electrolysis cell 1, and a predetermined current is supplied using a DC power supply. The value of the cell voltage during water electrolysis at the density was recorded.
Table 3 shows the cell voltage values of Examples 21 to 27 and Comparative Examples 21 to 24 at the current densities of 50 A/dm ² and 100 A/dm ² as evaluation results.

<Water electrolysis cell durability evaluation method>
Pure water having a temperature of 20° C. is circulated by a pump in the small-sized water electrolysis cell for evaluation described above, pure water for electrolysis is supplied to the anode side of the water electrolysis cell 1, and a DC power source is used to generate 50 A/dm. Electrolysis was continued at a current density of ² and the change in cell voltage over time was recorded.
Table 4 shows the initial (0 hour) and 250 hour elapsed cell voltage values of Examples 21 to 27 and Comparative Examples 21 to 24 as evaluation results.

<Results of initial characteristic evaluation>
In Comparative Example 21 and Comparative Example 22 not fired, Comparative Example 23 fired at a low temperature of 200° C., and Comparative Example 24 using the membrane electrode assembly (MEA) formed by applying and drying a catalyst, This resulted in higher voltage.
In Example 21, the cell voltage was lowered by firing at 400° C., and in Example 22 to 27 in which the ionomer layer was provided on the surface in contact with the solid electrolyte membrane (PEM), further decrease in cell voltage was confirmed. did it.

<Durability evaluation result>
Examples 21 to 27 using the "catalyst-supporting porous electrode base material obtained by adhering a metal catalyst (precursor) to a porous titanium base material and firing" as a cathode for water electrolysis are the catalyst films by gas lift. Peeling and desorption of catalyst (particles) became difficult to occur, performance deterioration did not occur, and durability was excellent.

On the other hand, Comparative Examples 21 and 22 that were not fired, Comparative Example 23 that was fired at a low temperature of 200° C., and “Membrane electrode assembly (MEA) formed by applying and drying an electrode catalyst” were used. In Comparative Example 24, peeling of the catalyst film and desorption of the catalyst (particles) were likely to occur, and the durability was poor.

The water electrolysis cell using the electrode for water electrolysis of the present invention, when electrolyzing at a constant current, the cell voltage is stable low, the catalyst is prevented from desorption from the electrode substrate, Since it has excellent properties and durability, it is widely used in all fields that require hydrogen and oxygen.

1 Water Electrolysis Cell 2 Electrode for Water Electrolysis 3 Catalyst-Supporting Porous Electrode Base Material 3a Porous Titanium Group Substrate or Porous Substrate 3b Titanium Fiber or Carbon Fiber 3c Metal Catalyst (Particle) or Metal Oxide Catalyst (Particle)
4 Ionomer layer or ionomer 5 Solid polymer electrolyte membrane (PEM)
6 Feeder 7 Resin tank 8 Bipolar plate 9 Water electrolysis stack cell

Claims (15)

An electrode for water electrolysis adjacent to a solid polymer electrolyte membrane (PEM) in a water electrolysis cell,
An electrode for water electrolysis, which has a "catalyst-supporting porous electrode base material on which a metal catalyst or a metal oxide catalyst is supported", which is obtained by adhering a metal catalyst or a metal catalyst precursor to a porous substrate and firing it. .. The electrode for water electrolysis according to claim 1, further comprising an ionomer layer on the side of the catalyst-supporting porous electrode substrate adjacent to the solid polymer electrolyte membrane. The electrode for water electrolysis according to claim 2, wherein the ionomer layer is a layer of an ion conductive polymer having a polyfluoroethylene skeleton as a main chain and a fluoroethylene ether skeleton having a sulfonic acid group at a terminal as a side chain. .. The ionomer layer is also penetrated into the porous voids of the catalyst-supporting porous electrode substrate, and in the void volume of the catalyst-supporting porous electrode substrate, the proportion of voids filled by the ionomer layer Is 10 vol% or more and 90 vol% or less, The electrode for water electrolysis according to claim 2 or 3. The electrode for water electrolysis according to any one of claims 1 to 4, wherein the firing is performed at 200°C or higher and lower than 600°C in the presence of an oxygen-containing gas. 6. The porous substrate according to claim 1, wherein the porous substrate is a porous titanium group substrate, a porous titanium group alloy substrate, a porous titanium group compound substrate, or a porous carbon substrate. Electrode for water electrolysis. The electrode for water electrolysis according to claim 6, wherein the porous titanium group substrate is a porous titanium substrate, and the porous titanium group alloy substrate is a porous titanium alloy substrate. The electrode for water electrolysis according to any one of claims 1 to 6, wherein the porous substrate is an aggregate of titanium group fibers, titanium group alloy fibers or titanium group compound fibers, or carbon fibers. The porous substrate is a porous carbon substrate, and the firing is performed such that the mass of the porous carbon substrate after firing is 55% by mass or more and 99% by mass or less of the mass of the porous carbon substrate before firing. The electrode for water electrolysis according to any one of claims 1 to 6, which is performed. The metal of the metal catalyst or metal catalyst precursor is a metal selected from the group consisting of platinum (Pt), ruthenium (Ru), iridium (Ir), palladium (Pd), tantalum (Ta), and nickel (Ni). The water electrolysis electrode according to any one of claims 1 to 9. A method for manufacturing an electrode for water electrolysis according to any one of claims 1 to 10,
Production of a catalyst-supporting porous electrode substrate included in the electrode for water electrolysis is characterized in that a metal catalyst or a metal catalyst precursor is attached to a porous substrate, and then the catalyst is supported on the porous electrode substrate by firing. And a method for producing an electrode for water electrolysis. The method for producing an electrode for water electrolysis according to claim 11, further comprising a step of forming an ionomer layer on a side of the catalyst-supporting porous electrode substrate adjacent to the solid polymer electrolyte membrane (PEM). A water electrolysis cell comprising at least the electrode for water electrolysis according to any one of claims 1 to 10 and a solid polymer electrolyte membrane (PEM). At least a cathode for water electrolysis, which is the electrode for water electrolysis according to any one of claims 1 to 10, a solid polymer electrolyte membrane (PEM), and any one of claims 1 to 10. 14. The water electrolysis cell according to claim 13, comprising a water electrolysis anode which is the electrode for water electrolysis according to claim 1 in this order. A cathode for water electrolysis, which is the electrode for water electrolysis according to any one of claims 1 to 10, a solid polymer electrolyte membrane (PEM), and any one of claims 1 to 10. A water electrolysis stack cell, wherein a plurality of units each having a water electrolysis anode, which is the water electrolysis electrode according to the item, are stacked in series.