WO2023095858A1

WO2023095858A1 - Oxygen evolution reaction catalyst and method for producing same

Info

Publication number: WO2023095858A1
Application number: PCT/JP2022/043486
Authority: WO
Inventors: 泰之池田; 健二寺田; 宏明鈴木
Original assignee: 株式会社フルヤ金属
Priority date: 2021-11-25
Filing date: 2022-11-25
Publication date: 2023-06-01

Abstract

[Problem] To provide a catalyst for electrolysis, the catalyst being suppressed in the amount of iridium used therefor, while enabling a high oxygen evolution reaction. [Solution] An oxygen evolution reaction catalyst which contains an oxide that contains yttrium and iridium, while having a BET specific surface area of 50 m2/g or more.

Description

Oxygen evolution reaction catalyst and method for producing the same

The present invention relates to an oxygen evolution reaction catalyst, and more specifically, the present invention relates to an oxygen evolution reaction catalyst used for electrolysis of water. Furthermore, the present invention relates to a method for producing an oxide contained in the oxygen evolution reaction catalyst.

Hydrogen has a high energy conversion efficiency and does not generate carbon dioxide when burned. Therefore, it is attracting attention as an energy source due to the global trend toward decarbonization. Hydrogen is produced by reforming hydrocarbons, producing from methanol produced from biomass, using by-products produced in processes such as iron manufacturing, and obtaining from renewable energy. It has been known. Among them, a method of electrolyzing water with electricity generated by renewable energy such as solar power generation and wind power generation is attracting attention as a preferable method for producing hydrogen because carbon dioxide is not generated.
In addition, surplus electricity can be used effectively by electrolyzing water and storing energy as hydrogen. Surplus electricity can be converted to hydrogen and stored in gaseous or liquid form for immediate use as fuel. Additionally, hydrogen can be converted to other compounds such as chemicals such as ammonia or methanol for industrial use.
Therefore, production of hydrogen by electrolysis of water is attracting attention also from the point of view of effective use of energy.

As a method for water electrolysis (hereinafter also referred to as water electrolysis), an alkaline water electrolysis system and a solid molecular membrane (hereinafter also referred to as "PEM") water electrolysis system are being considered. Compared to alkaline water electrolysis systems, the PEM type water electrolysis system allows a smaller electrolyzer because the current flowing through the same area is higher than that of the alkaline water electrolysis system. There is an advantage that the generated hydrogen is of high purity.

The PEM type water electrolysis cell has a catalyst coated membrane (catalyst coated membrane, hereinafter also abbreviated as CCM) in which a cation exchange polymer electrolyte membrane such as Nafion (registered trademark) is sandwiched between an anode catalyst layer and a cathode catalyst layer. Furthermore, a membrane electrode assembly (hereinafter also abbreviated as MEA) sandwiched between gas diffusion layers is used as one structural unit, and a plurality of such assemblies are connected in series via separators. When water is supplied to the anode catalyst layer, the reaction of the following formula (1) occurs in the anode catalyst layer, and the reaction of the following formula (2) occurs in the cathode catalyst layer, oxygen (O ₂ ) on the anode side, hydrogen (H ₂ ) occurs.
H ₂ O→ 1/2O ₂ (g) + 2H ⁺ + 2e ⁻ (1)
2H ⁺ + 2e ⁻ → H ₂ (g) (2)
The rate-determining step of the overall reaction is the oxidation of water and the oxygen evolution reaction on the anode side, and the oxygen evolution reaction (hereinafter also referred to as "OER") mass activity of the anode catalyst is an important factor that determines the efficiency of the system. .

The oxygen generation reaction at the anode of the PEM type water electrolysis system has a slow reaction rate, and a high voltage needs to be applied to generate more oxygen. For this reason, anodes in PEM-type water electrolysis systems have utilized catalysts containing iridium or iridium oxides that are electrically conductive and have high durability in highly oxidizing or high voltage environments.
On the other hand, annual production of iridium is low and scarcity is high, so catalysts with lower iridium content have been required to exhibit high oxygen evolution reaction and high durability in highly oxidizing or high voltage environments.

Patent Document 1 discloses an electrode catalyst composition in which iridium and ruthenium oxides are supported on tin oxide.

In Patent Document 2, a core and a shell covering the surface of the core are provided, the core contains ruthenium oxide or metallic ruthenium at least on the surface, and the shell is made of titania or a composite oxide of titanium and ruthenium. A core-shell type oxygen evolution reaction catalyst has been proposed.

Patent Literature 3 proposes a catalyst film containing an electrocatalyst containing platinum or platinum alloyed with one or more other metals and an oxygen evolution reaction catalyst, wherein the oxygen evolution reaction catalyst has a high oxygen evolution reaction rate. It has been reported to have mass activity.

Non-Patent Document 1 reports an oxide of yttrium and iridium having a BET specific surface area of 21 m ² /g or more, a particle size of about 200 nm, and a pyrochlore type crystal structure.

Non-Patent Document 2 reports an oxide of yttrium and iridium having a BET specific surface area of 7.3 m ² /g or more, a particle size of about 200 nm, and a pyrochlore type crystal structure.

Japanese Patent Publication No. 2020-500692 Japanese Patent No. 6763009 Japanese Patent No. 5978224

In the future, it is expected that a large amount of iridium will be used if the practical application of hydrogen production technology by electrolysis of water is accelerated. On the other hand, the annual production of iridium is about 9 tons, and since it is highly scarce, there is a demand for the development of an oxygen evolution reaction catalyst for water electrolysis that exhibits a high oxygen evolution reaction while suppressing the amount of iridium used. .

The present inventors have completed the present invention as a result of diligent studies aimed at solving the above problems. That is, the present invention has the following aspects.

[1]
An oxygen evolution reaction catalyst containing an oxide containing yttrium and iridium and having a BET specific surface area of 50 m ² /g or more.
[2] The oxygen evolution reaction catalyst according to [1] above, wherein the oxide has an average particle size of 100 nm or less.
[3] An oxygen evolution catalyst layer containing the oxygen evolution catalyst according to [1] or [2] and a proton transport agent.
[4] An electrolytic cell comprising the oxygen evolution reaction catalyst layer of [3] and an ion-exchange polymer electrolyte membrane.
[5] The electrolytic cell according to [4] above, wherein the ion-exchange polymer electrolyte membrane is a cation-exchange polymer electrolyte.

Moreover, this invention has the following aspects.
[6] (1) Dispersing yttrium nanoparticles and iridium nanoparticles or yttrium hydroxide particles and iridium hydroxide particles in a dispersion medium to obtain a dispersion, or (2) dissolving an yttrium compound and an iridium compound in a solvent A step A of obtaining a solution by allowing
A step B in which the temperature of water is 100 ° C. or higher and a pressure in excess of 0.1 MPa, and a step C of mixing the dispersion or the solution obtained in the step A and the high-temperature and high-pressure water obtained in the step B. The method for producing the oxide according to [1] above, comprising:
[7] The method for producing an oxide according to [6] above, including the step of adding an oxidizing agent in the step B.
[8] The method for producing an oxide according to [7] above, wherein the oxidizing agent is an oxidizing agent that releases oxygen atoms.
[9] The step B includes (1) adding an oxidizing agent that releases oxygen atoms to water and then bringing the water to the above temperature and pressure, and (2) after bringing the water to the above temperature and pressure. , adding an oxidizing agent that releases oxygen atoms, or (3) adding an oxidizing agent that releases oxygen atoms to water, bringing the water to the above temperature and pressure, and further adding an oxidizing agent that releases oxygen atoms. The method for producing the oxide according to [8] above, comprising any one of the steps of adding

According to the present invention, there is provided a catalyst for water decomposition, particularly water electrolysis, which has a high oxygen generating capacity even when the amount of iridium used is small.

1 is an example of an apparatus for producing yttrium and iridium oxides according to this embodiment. 1 is an X-ray diffraction pattern in Example 1. FIG. 4 is an X-ray diffraction pattern in Comparative Example 1. FIG. 4 is an X-ray diffraction pattern of iridium oxide of Comparative Example 2. FIG. 1 is a TEM image of Example 1. FIG.

Hereinafter, the present invention will be described in detail by showing embodiments, but the present invention is not construed as being limited to these descriptions. Various modifications may be made to the embodiments as long as the effects of the present invention are achieved.

The oxygen evolution reaction catalyst of the present invention (hereinafter also referred to as the present catalyst) is an oxide containing yttrium and iridium and having a BET specific surface area of 50 m ² /g or more (hereinafter also referred to as the "present oxide"). include.

The present oxide may contain yttrium oxide or iridium oxide, may contain a mixture of yttrium oxide and iridium oxide _, and may include a composite oxide of yttrium and iridium represented by the general formula _YxIryOz _. may contain. The present oxide may also contain a mixture of these. This oxide preferably contains a composite oxide of yttrium and iridium from the viewpoint of oxygen evolution reaction activity. In the above general formula, the subscripts x, y and z usually satisfy the following.
0.1≤x≤3
0.1≤y≤3
1≤z≤10
When the present oxide contains a composite oxide of yttrium and iridium, the above x, y, and z more preferably contain a composite oxide that satisfies the following ranges.
0.2≤x≤2
0.2≤y≤2
2≤z≤8
When the present oxide contains the composite oxide, it is more preferable that the composite oxide is the main component. The complex oxide as the main component means that the diffraction peak attributed to yttrium oxide and iridium oxide is below the detection limit when X-ray diffraction of the powder of the oxide is measured.

The present oxide may contain other metals besides yttrium and iridium. Other metals include platinum, ruthenium, rhodium, palladium, nickel, aluminum, strontium, bismuth, titanium, tin, zinc, iron, copper, silver, gold, lanthanum, antimony. These metals may be oxides of each metal, or may be halides or hydroxides other than oxides. Also, yttrium, iridium, or a composite oxide of both of them may be used.

The elemental ratio of yttrium and iridium in the present oxide is preferably 40 to 60 atm% for yttrium and 60 to 40 atm% for iridium, where the total elemental amount of yttrium and iridium is 100 atm%, from the viewpoint of oxygen generation reaction activity. is more preferably 50 atm % and 50 atm % iridium.

The BET specific surface area of the present oxide is more preferably 100 m ² /g or more, still more preferably 150 m ² /g or more, from the viewpoint of the oxygen evolution reaction.
The BET specific surface area is determined by the BET method by low-temperature physical adsorption of an inert gas, and is a specific surface area determined from the obtained adsorption isotherm.

The average particle size of the present oxide is preferably 100 nm or less. More preferably, the average particle size is 50 nm or less. Average particle size can be measured by transmission electron microscopy (TEM) or scanning transmission electron microscopy (STEM). By decreasing the average particle size, it can be expected that the active sites of the catalyst will increase and the OER mass activity will improve.
The average particle size was measured according to the method described in JIS H 7804:2005. That is, 200 or more primary particles are selected from the metal particles shown in the image taken by the TEM, and the longest length of these particles is visually measured as the particle diameter. The average particle size was obtained by dividing the total particle size of each particle by the number of particles whose particle sizes were measured. The field of view to be photographed was a location containing 200 or more primary particles.
The number of primary particles to be measured is not particularly limited as long as it is 200 or more.

The shape of the present oxide may be spherical, ellipsoidal, columnar, or irregular, but a spherical or nearly spherical shape is preferable from the viewpoint of handling.
The average particle size of the present oxide is the value obtained by measuring the major axis when observed by TEM or STEM.

The present catalyst may be the present oxide itself or may contain other components. For example, the oxide may be supported on a carrier to form the catalyst.
As the carrier, a corrosion-resistant carbon powder such as graphitized carbon black or acetylene black or a conductive oxide powder carrier such as Ti ₄ O ₇ is preferably used.

When the present oxide is supported on the carrier to form the present catalyst, the content of the present oxide in the present catalyst is preferably 20% by mass or more, preferably 30% by mass, with the total mass of the present oxide and the support being 100% by mass. % or more is more preferable.
The present catalyst may contain other components such as a stabilizer, if necessary, in addition to the carrier.

Since this catalyst has a high ability to generate oxygen, it can be used as a catalyst layer such as an oxygen generation reaction catalyst layer in a water electrolysis system. As described above, in the water electrolysis system, when water supplied from the outside is supplied to the anode catalyst layer, which is the oxygen evolution reaction catalyst layer, the reaction of the following formula (1) occurs in the anode catalyst layer, and water is converted into oxygen and hydrogen. converted to ions (protons). The hydrogen ions travel through the proton transport agent and move to the cathode catalyst layer, which is the hydrogen generation reaction catalyst layer, and the reaction of the following formula (2) occurs in the cathode catalyst layer, producing oxygen (O 2 ) on the anode side and oxygen (O ₂ ) on the cathode side. Hydrogen ( _H2 ) is generated.
H ₂ O → 1/2O ₂ + 2H ⁺ + 2e ⁻ (1)
2H ⁺ + 2e ⁻ → H ₂ (2)
In the PEM type water electrolysis system, due to the above reaction, the protons generated by the decomposition of water in the MEA are transported from the anode catalyst layer to the cathode catalyst layer through the ion-exchange polymer electrolyte membrane. Move to the cathode catalyst layer.

Therefore, the present catalyst can be used as an oxygen evolution reaction catalyst layer, that is, an anode catalyst layer of the water electrolysis system by using it together with a proton transport agent.
The proton transport agent has a role of conducting protons, and may have a function of transporting protons to the vicinity of the catalyst in the catalyst layer for the electrolysis reaction and a function as a binder that fixes the catalyst to the substrate. By using a proton transport agent to attach catalyst particles to each other, it is possible to change the proton transport path and the packing structure of the catalyst, so the proton transport agent is an important factor in improving the catalyst performance. becomes.
Examples of proton transport agents include perfluorosulfonic acid proton transport agents, sulfonated polyethylene ether ketone proton transport agents, and sulfonated polybenzimidazole proton transport agents. Among them, Nafion (registered trademark, manufactured by DuPont), Flemion (registered trademark, manufactured by AGC), Aciplex (registered trademark, manufactured by Asahi Kasei), Fumion (registered trademark, manufactured by Fumatech) and Aquivio, which are perfluorosulfonic acid-based proton transport agents. (registered trademark, manufactured by Solvay) and the like are preferable.

The present catalyst can be used as an electrolytic cell of the above-mentioned water-splitting system by using it with an ion-exchange polymer electrolyte membrane. As the ion-exchange polymer membrane, a cation-exchange polymer electrolyte membrane is usually used.
The cation-exchange polymer electrolyte membrane preferably has physical strength, low gas permeability, and a membranous shape. The cation-exchange polymer electrolyte is usually sandwiched between a cathode catalyst layer and an anode catalyst layer, and thus has a film-like shape.
A catalyst coated membrane (CCM) used in the water electrolysis system is formed by forming a multi-layered structure by providing a cation exchange polymer electrolyte membrane and the oxygen evolution reaction catalyst layer and the hydrogen evolution reaction catalyst layer on both sides thereof. can be done.
Materials constituting the cation exchange polymer electrolyte membrane include the same materials as those constituting the proton transport agent.

The oxygen evolution reaction catalyst layer and the electrolysis cell are obtained by coating the present catalyst on the proton transport agent or the cation exchange polymer electrolyte membrane, for example. The ink used for coating may be prepared by stirring and mixing the proton transport agent and the present catalyst in a solvent. The ratio of the catalyst to the proton transport agent is not particularly limited, but the composition is preferably 1:0.2 to 1:0.05, more preferably 1:0.15 to 1:0.07. Although the solvent is not particularly limited, water or a mixture of water and a lower aliphatic alcohol such as ethanol, propanol or butanol is preferably used.
When the present catalyst is applied to the cation exchange polymer membrane, the amount of the present catalyst applied is preferably 0.001 mg/cm ² to 4 mg/cm ² per unit area of the cation exchange polymer electrolyte membrane, and 0.1 mg. /cm ² to 2 mg/cm ² is more preferred.

The electrolysis cell has a cathode layer, which is a hydrogen generation reaction catalyst layer, on the surface of the cation exchange polymer electrolyte membrane opposite to the main catalyst. Platinum is usually used as the hydrogen generation reaction catalyst in the cathode layer.
An MEA is formed by sandwiching the catalyst layer of the electrolysis cell with diffusion layers. When a plurality of these units are connected in series via separators and water is supplied to the anode catalyst layer, which is the oxygen evolution reaction catalyst layer, the reaction of the above formula (1) occurs in the anode catalyst layer. At , the reaction of the formula (2) occurs, and oxygen is generated on the anode side and hydrogen is generated on the cathode side.

The catalyst can also be used in fuel cell anodes.
In the fuel cell, hydrogen molecules supplied from the outside release two electrons at the anode and become hydrogen ions (protons). Electrons released from the hydrogen flow as current through an external circuit to the opposite cathode, where electrical power is generated.

At the cathode, oxygen molecules taken in from the air receive electrons returned from the external circuit and become oxygen ions. Oxygen ions combine with hydrogen ions that have migrated through the proton transport agent to form water.

The chemical reaction on the anode side can be expressed by the following formula (3), the chemical reaction on the cathode side by the following formula (4), and the overall reaction by the following formula (5).
2H ₂ → 4H ⁺ + 4e ⁻ (3)
4H ⁺ + O ₂ +4e ⁻ → 2H ₂ O (4)
2H ₂ + O ₂ → 2H ₂ O (5)
When the hydrogen supply to the anode side becomes insufficient when starting or stopping the fuel cell, a fuel starvation state occurs, and a reverse potential occurs in which current is forced to flow from other cells connected in series to the cell in the fuel starvation state. . As a result, the reaction of the following formula (6) occurs. Since a platinum-supported carbon-based electrode catalyst is usually used for the anode catalyst layer of a fuel cell, the carbon of the anode catalyst is oxidized and corroded according to the following formula (6), resulting in severe deterioration of the fuel cell.
C + 2H ₂ O → CO ₂ + 4H ⁺ + 4e ⁻ (6)
2H ₂ O → O ₂ + 4H ⁺ + 4e ⁻ (7)
By using an electrocatalyst that electrolyzes water on the anode side of the fuel cell by the reaction of formula (7) under such reverse potential conditions, oxidative corrosion of the carbon support by water can be suppressed.
Therefore, when the present catalyst with high oxygen evolution reaction ability and an anode catalyst containing platinum-supported carbon are used as the anode of a fuel cell, the reaction of formula (7) proceeds, preventing catalyst deterioration due to hydrogen deficiency in the anode of the fuel cell. can be done.

Furthermore, the present catalyst can be used as a co-catalyst for photocatalysts.
Materials such as gallium phosphide, gallium arsenide, cadmium sulfide, strontium titanate, titanium oxide, zinc oxide, iron oxide, tungsten oxide, and tin oxide are known as photocatalysts.
The photocatalyst-based water splitting reaction begins when the photocatalyst absorbs light with energy greater than the bandgap and generates excited electrons in the conduction band and holes in the valence band. Then, the excited electrons and holes reduce and oxidize water to produce hydrogen and oxygen, thereby proceeding a photocatalytic reaction.
On the other hand, there are very few metal oxide photocatalyst materials that can respond to visible light, and there is a problem that hydrogen cannot be produced efficiently. Improvements are being considered. By using this catalyst as an oxygen evolution reaction catalyst, hydrogen can be produced efficiently. In this case, metal fine particles such as platinum, rhodium, iridium, ruthenium, nickel and gold can be used as the hydrogen generation reaction catalyst.

This catalyst can be used as an electrode by using it with a metal plate. The electrode obtained can be suitably used as a cathode in the soda industry.
When the present catalyst is used with a metal plate to form an electrode, the present catalyst can be applied to the metal plate to form the electrode. The content of ^the present oxide in the present catalyst is preferably 1 mg/cm ² to 3 mg/cm 2 , more preferably 2 mg/cm ² to 3 mg/cm ² per unit area of the metal plate.

The soda industry electrolyzes salt water to produce caustic soda, chlorine and hydrogen. In addition to disinfection and sterilization and bleaching of paper and pulp, chlorine is used as a raw material for synthetic resins such as vinyl chloride resin, epoxy resin, silicon resin, and fluorine resin, chlorinated solvents, refrigerants, agricultural chemicals, pharmaceuticals, and other chemical products. Used.
Caustic soda is also used as a raw material for making products such as paper and pulp bleaching, chemical fibers, detergents and soaps, raw materials for industrial chemicals, and seasonings, which are indispensable in daily life.

Industrially established electrolysis methods include the mercury method, diaphragm method, and ion-exchange membrane method, but the electrode containing the present catalyst and metal plate is preferably used for the ion-exchange membrane method, which is environmentally friendly and cost-effective. .
In the ion-exchange membrane method, a cathode chamber and an anode chamber of an electrolytic cell are separated by a cation-exchange polymer electrolyte, and a metal electrode such as titanium is used for the cathode and a metal electrode such as nickel is used for the anode.

In particular, for the cathode, DSA (registered trademark: Dimensionally Stable Anode) coated with a mixed oxide layer containing a platinum group metal oxide based on titanium is used. DSA (registered trademark) has many excellent properties such as high electrochemical catalytic activity for oxygen and chlorine evolution, high electrical conductivity, good processing properties, corrosion resistance, energy saving, and light weight, so it is widely used. It is Regarding the platinum group metal oxide coated on the surface of the DSA (registered trademark), iridium is widely used from the viewpoint of durability and the like. The amount of iridium used can be suppressed and caustic soda, chlorine, and hydrogen can be efficiently produced by using the platinum group metal oxide obtained as the catalyst of the present invention.

The method for producing the present oxide will be described below.
The method for producing the present oxide (hereinafter also referred to as the present production method) includes (1) dispersing yttrium nanoparticles and iridium nanoparticles, or yttrium hydroxide particles and iridium hydroxide particles in a dispersion medium to obtain a dispersion liquid (hereinafter also referred to as "this dispersion"), or (2) a step A of dissolving an yttrium compound and an iridium compound in a solvent to obtain a solution (hereinafter also referred to as "this solution"); A step B in which the water temperature is 100 ° C. or higher and the pressure is higher than 0.1 MPa, and a step C in which the dispersion or the solution obtained in the step A and the high-temperature and high-pressure water obtained in the step B are mixed. and

Here, an example of an oxide manufacturing apparatus will be described with reference to FIG. The present oxide production apparatus 100 includes a first supply source 1 that supplies the present dispersion or the present solution, a second supply source 2 that supplies water, and heats the water supplied from the second supply source 2. It has a heating unit 3 for Water supplied from the second supply source 2 is heated to a temperature of 100° C. or higher by the heating unit 3 . Moreover, the pressure exceeds 0.1 MPa by the pressure adjustment mechanism 10, which will be described later. Further, the production apparatus 100 is a reaction unit in which the main dispersion or the main solution and water (hereinafter also referred to as "main high-temperature water") having a temperature of 100 ° C. or higher and a pressure of over 0.1 MPa in the step B are combined. 4. The water supplied from the second supply source 2 may contain an oxidant, which will be described later, if necessary.
The first supply source 1 and the reaction section 4 are connected by a liquid feeding route 5 , and the main dispersion or the main dissolving liquid is fed from the first supply section 1 to the reaction section 4 through the liquid feeding route 5 . The second supply source 2 and the reaction section 4 are connected by a liquid feeding route 6 , and a liquid containing water is fed from the second supply section 2 to the reaction section 4 by the liquid feeding route 6 . The oxidizing agent may be added to the water at any point along the liquid feeding route 6 as required.

Furthermore, the reaction section 4 is connected to a recovery section 8 for recovering the produced reaction product by a liquid feeding route 7 , and a cooling section 9 is arranged around the liquid feeding route 7 between the reaction section 4 and the recovery section 8 . As a result, the reactant produced in the reaction section 4 is cooled by the cooling section 9 and sent to the collection section 8 when passing through the liquid sending route 7 .
Furthermore, the manufacturing apparatus 100 has a pressure adjusting mechanism 10 for the purpose of setting the reaction section to a high pressure condition. The pressure adjusting mechanism 10 may be connected to the recovery section 8 as shown in FIG.
A plunger, a cylinder, and a regulator can be considered as the pressure adjusting mechanism, but from the viewpoint of clogging or wear, the cylinder is preferable.

The liquid feeding routes 5 to 7 are formed by, for example, piping.
According to the manufacturing apparatus 100, oxides of yttrium and iridium can be stably produced.

In the reaction section 4, the present dispersion or the present solution is mixed with the present high-temperature water to oxidize the yttrium and iridium in the present dispersion or the present solution to produce an oxide containing yttrium and iridium. . Yttrium and iridium may be oxidized using only the high-temperature water, but by adding an oxidizing agent to the high-temperature water, yttrium and iridium can be oxidized more efficiently. Water is obtained by the heating section 3 and the pressure regulation mechanism 10 . The pressure adjustment mechanism 10 is located downstream of the manufacturing apparatus 100 and is connected to the reaction section 4, the liquid feeding route 5, the liquid feeding route 6, and the liquid feeding route 7, so that the pressure of the entire manufacturing apparatus 100 has a function to adjust The pressure adjustment mechanism 10 adjusts the pressure of the reaction section and all of the above-described liquid feeding routes to obtain high-temperature water at the above-described temperature and pressure.
The oxidizing agent is preferably an oxidizing agent that releases oxygen, and is preferably an oxidizing agent that releases oxygen such as oxygen, hydrogen peroxide, and ozone. When oxygen gas is used as the oxidizing agent, it is preferable to heat the water to a saturated oxygen concentration at a high temperature and a high pressure.

A liquid feeding route 5 connecting the first supply source 1 and the reaction section 4 has liquid feeding means. As the means for sending the main dispersion liquid or the main dissolving liquid, there can be exemplified a liquid sending means that disposes the first supply source 1 at a position higher than the reaction section 4 and utilizes the height difference. In this case, the present dispersion or the present solution can be transported from the first supply source 1 to the reaction section 4 by connecting with a pipe. At this time, a flow rate adjusting means such as a needle valve or a stop valve may be arranged in the liquid feeding route 5 to adjust the flow rate.

A liquid feeding route 6 connecting the second supply source 2 and the reaction section 4 has liquid feeding means. As the means for sending the high-temperature water, a means for disposing the second supply source 1 at a position higher than the reaction section 4 and using the height difference can be exemplified. In this case, the water-containing liquid and the high-temperature water can be transported from the second supply source 2 to the reaction section 4 by connecting with a pipe. At this time, similarly to the liquid feeding route 5, the liquid feeding route 6 may be provided with means for adjusting the flow rate, such as a needle valve and a stop valve.

The oxide manufacturing apparatus according to the above embodiment may have flow

rate adjusting mechanisms

11 and 12 for unidirectionally transferring the liquid flowing through either or both of the liquid feeding route 5 and the liquid feeding route 6 . The yttrium and iridium oxide manufacturing apparatus 100 shown in FIG. In addition to the route 7, the recovery section 8, the cooling section 9, and the pressure adjustment mechanism 10, the flow

rate adjustment mechanisms

11 and 12 are provided in the liquid feed route 5 and the liquid feed route 6, respectively. In this aspect, the flow rate and flow rate of the present dispersion or the present solution in the liquid sending route 5 and the flow rate and flow rate of the liquid containing water in the liquid sending route 6 can be stably controlled. oxides can be produced exponentially.

Mechanisms

11, 12 can be, for example, plungers, cylinders or regulators.

The dispersion medium used in this dispersion is a medium for dispersing yttrium nanoparticles and iridium nanoparticles, or yttrium hydroxide particles and iridium hydroxide particles. Examples include water and organic solvents.
The solvent used for this dispersion is a solvent that dissolves the yttrium compound and the iridium compound, and is liquid at room temperature. Examples include water and organic solvents. In the present embodiment, normal temperature is 15°C to 30°C, preferably 20°C to 25°C.

When the step A is the dispersion of yttrium nanoparticles and iridium nanoparticles of (1), the average particle size of the yttrium nanoparticles or iridium nanoparticles is usually 100 nm or less, preferably 3 nm or less. It is more preferably 5 nm or less. If the average particle size of the yttrium nanoparticles and iridium nanoparticles is too large, the particle size of the oxide containing yttrium and iridium may become too large when reacting yttrium and iridium with oxygen. may result in insufficient oxidation at
For the yttrium nanoparticles and iridium nanoparticles, for example, yttrium nanoparticles and iridium nanoparticles adjusted to a desired average particle size by sizing or the like may be used.
The method for measuring the average particle size is the same as described above.

Further, when the step A is the dispersion liquid of the yttrium hydroxide particles and the iridium hydroxide particles of (1), the average particle diameter of the yttrium hydroxide particles and the iridium hydroxide particles is usually 100 nm or less, It is preferably 3 nm or less, more preferably 2.5 nm or less. The average particle size of yttrium hydroxide particles and iridium hydroxide particles is too large. It may become too large, and there is a possibility that the oxidation in the oxidation reaction described below will be insufficient.
For the yttrium hydroxide particles and iridium hydroxide particles, for example, yttrium hydroxide particles and iridium hydroxide particles having a desired average particle size by sizing or the like may be used.
The method for measuring the average particle size is the same as described above.

The present dispersion can be obtained by adding the yttrium nanoparticles and iridium nanoparticles or the yttrium hydroxide particles and iridium hydroxide particles to the dispersion medium. Examples of dispersion media include water and ethanol.

In step A (2), the yttrium compound includes yttrium-containing salts such as yttrium nitrate, yttrium acetate, yttrium sulfate, and yttrium chloride, and metal complexes such as yttrium acetylacetonate and yttrium carbonyl. . Among these compounds, yttrium nitrate compounds, yttrium sulfate compounds, and yttrium acetate compounds are preferred.

Examples of iridium compounds include iridium-containing salts such as iridium nitrate compounds, iridium sulfate compounds, iridium acetate compounds, and iridium chlorides, and metal complexes such as iridium acetylacetonate and iridium carbonyl. Among these compounds, iridium nitrate compounds, iridium sulfate compounds, and iridium acetate compounds are preferred. The present solution can be obtained by adding the yttrium compound and the iridium compound to the solvent. Examples of the solvent include water in the case of the yttrium-containing salt or the iridium-containing salt, and ethanol, ethyl acetate, or the like in the case of the yttrium-containing metal complex or the iridium-containing metal complex. When the salt and the complex are mixed, the solvent is water, ethanol, ethyl acetate and the like. In step A (2), it is preferable to dissolve the yttrium compound or iridium compound in the solvent at room temperature, for example, 15°C to 30°C.

In step B, the high-temperature water is obtained by setting the temperature of water to 100° C. or higher and the pressure to exceed 0.1 MPa.
The temperature of the high temperature water is preferably 150°C or higher, more preferably 374°C or higher, for example about 400°C. The pressure of the high temperature water is preferably 0.5 MPa or higher, more preferably 22.1 MPa or higher, for example about 30 MPa. Pure water is preferable as the water for obtaining the high-temperature water. An oxidizing agent such as oxygen, hydrogen peroxide, or ozone may be added in advance to the water.
From the viewpoint of keeping the BET specific surface area within the range of the present oxide, the temperature of the present high-temperature water is preferably 100 ° C. or higher and the pressure is 0.5 MPa or higher, more preferably 374 ° C. or higher and the pressure is 22.1 MPa or higher. More preferably, it is in a critical state.

In order to efficiently carry out the oxidation reaction in step C, which will be described later, step B preferably further includes a step of adding an oxidizing agent, and more preferably includes a step of adding an oxidizing agent that releases oxygen atoms. The step of adding an oxidizing agent that releases oxygen atoms includes (1) adding an oxidizing agent that releases oxygen atoms to the water, and then converting the water to high-temperature water that satisfies the temperature and pressure; A step of adding an oxidizing agent that releases oxygen atoms after making this hot water satisfying the temperature and pressure, or (3) adding an oxidizing agent that releases oxygen atoms to the water and then satisfying the temperature and pressure. It is further preferable to include any of the steps of obtaining the high-temperature water and adding an oxidizing agent that releases oxygen atoms.

In step C, the present dispersion or solution obtained in step A and the present high-temperature water obtained in step B are mixed. In step C, the iridium and yttrium contained in the present dispersion or the present solution are oxidized to form oxides.
As for the conditions for mixing, when using the present oxide manufacturing apparatus 100, the present dispersion obtained in step A or the present solution obtained in step B is sent through the liquid sending route 5 and the present obtained in step B By merging the liquid feeding routes 6 through which the high-temperature water is fed, it is possible to obtain a dispersion liquid in which oxides containing yttrium and iridium are dispersed in the high-temperature water. In FIG. 1, they are mixed in the reaction section 4 .

The dispersion liquid obtained in step C is cooled in the cooling unit 9 shown in FIG. The present oxide containing yttrium and iridium can be obtained by dehydration with .

In addition to the above method, for example, the present dispersion or solution obtained in step A and the present high-temperature water obtained in step B are placed in the same container and mixed by stirring or the like to perform an oxidation reaction. Thus, a dispersion liquid in which the present oxide containing yttrium and iridium is dispersed in the present high-temperature water can be obtained.
In this case, water may be brought to the above temperature and pressure in another container, and the resulting high-temperature water may be added to the container containing the dispersion or the solution, or the container containing the high-temperature water may be added to the high-temperature water. The dispersion or the solution may be added, or the dispersion or the solution and the hot water may be placed in one container at the same time.
Said addition may be continuous or intermittent.

In order to make the BET specific surface area of the present oxide 50 m ² /g by the above method, for example, the present high-temperature water is used, and the present dispersion or the present solution obtained in step A and the present high-temperature water are mixed in step C Therefore, it is preferable to mix in as short a time as possible and to cool in as short a time as possible after step C.
In particular, if the high-temperature water is in a supercritical state, the yttrium ions and iridium ions in the dispersion or solution are directly oxidized, resulting in a smaller particle size of the resulting oxides and further cooling in a short period of time. Thus, it is considered that the BET specific surface area of the resulting oxide containing yttrium and iridium can be within the desired range.

A production method using a liquid feeding route as shown in FIG. 1 is preferable because the present oxide can be produced continuously and the average particle diameter of the resulting oxide can be reduced.
In the case of the production method using the liquid feeding route as shown in FIG. By controlling, the average particle diameter of the present oxide to be obtained can be controlled within the preferred range.
For example, the mixing time in step C varies depending on the size of the manufacturing apparatus used, the material of the apparatus, etc., but is, for example, 0.1 to 60 seconds. The cooling time after the step C also varies depending on the size of the manufacturing apparatus used, the material of the apparatus, etc., but is, for example, 1 second to 60 seconds.

When the present oxide contains a metal other than yttrium and iridium, metal particles or a metal compound containing the desired metal may be added separately in step A or step C.
Further, when the present oxide is supported on the carrier, the present oxide may be isolated and then supported on the carrier by a conventional method. If necessary, the present oxide may be mixed with other components such as a stabilizer to form the present catalyst.
Furthermore, the obtained present catalyst can be applied to the proton transport agent or the cation exchange polymer electrolyte membrane to form an oxygen reaction generating catalyst layer and an electrolytic cell.
Application methods include metal mask printing, electrostatic coating, dip coating, spray coating, roll coating, doctor blade, gravure coating, and screen printing.

The method for producing the present catalyst and the present oxide has been described above. However, the present invention is not limited to the configurations of the above embodiments.
For example, in the configuration of the above embodiment, the present catalyst may be added with any other configuration, or may be replaced with any configuration that exhibits the same function. In addition, the method for producing the oxide of the present invention may additionally include other arbitrary steps in the configuration of the above-described embodiments, or may be replaced with arbitrary steps that produce similar effects.

Examples of the present invention will be described below, but the present invention is not limited to these.

(Example 1) Production of oxide (YI-1) containing yttrium and iridium Iridium nitrate solution (manufactured by Furuya Metals Co., Ltd.) was added to 2.8 L of water with an iridium weight of 1.92 g and yttrium nitrate hydrate (Fuji Film Co., Ltd.). (manufactured by Kojunyaku Co., Ltd.) was added, and a homogeneous metal compound mixed solution containing an iridium compound and an yttrium compound was obtained by stirring and ultrasonic treatment. Next, 10 mL of 30% aqueous hydrogen peroxide solution was added to 10 L of water at room temperature (25° C.), then the water temperature was adjusted to 430° C. and the water pressure was adjusted to 29 MPa to obtain high-temperature, high-pressure water. Next, the metal compound mixed solution obtained above is flowed to the reaction section through the liquid feeding route at a rate of 30 ml / min, and the high temperature and high pressure water obtained above is flowed through the liquid feeding route at a rate of 200 ml / min to the reaction section. Mixing was carried out by pouring the mixture into a solution to obtain an oxide dispersion containing iridium and yttrium. After that, the mixed oxide dispersion containing iridium and yttrium was adjusted to 1 atm in the cooling section, cooled to 20° C., and collected in the collecting section. Then, after filtering with a membrane filter, the filtered cake was dried with an electric dryer at 80° C. for 4 hours to obtain an oxide containing yttrium and iridium.

(Comparative Example 1) Preparation of oxide (YI-2) containing yttrium and iridium In a 1 L beaker made of Teflon (registered trademark, hereinafter the same), iridium (IV) chloride acid (H ₂ IrCl ₆ · nH ₂ O) in terms of iridium weight and yttrium chloride hexahydrate (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) were added, 170 mL of pure water was added, and the mixture was stirred at 200 rpm for 1 hour while raising the liquid temperature to 80°C. A mixed solution of iridium chloride and yttrium chloride was prepared. Next, 25 g of sodium hydroxide was weighed out, dissolved in 250 mL of pure water to prepare a 10% sodium hydroxide solution, and added dropwise to the iridium chloride-yttrium chloride mixed solution at a rate of 3 mL/min until the pH reached 11. . After the dropwise addition was completed, the mixture was further stirred for 5 hours while maintaining the liquid temperature at 80°C.

The resulting slurry was allowed to cool to room temperature and then allowed to stand, and the supernatant liquid was decanted. 300 mL of pure water was added to the Teflon beaker containing the remaining slurry, and the mixture was stirred for 1 hour while the temperature was raised to 80° C. again. Such decantation washing was carried out until the conductivity of the supernatant did not change. Filtration was then carried out to obtain a filter cake. This filter cake was dried in an electric dryer at 60° C. for 20 hours and then fired in the atmosphere at 1000° C. for 10 hours in an electric furnace to obtain an oxide containing yttrium and iridium.

(Comparative Example 2) Preparation of Iridium Oxide (IO-1) Into a 5 L Teflon beaker, 50 g of iridium chloride tetravalent preparation (H ₂ IrCl ₆ ·nH ₂ O manufactured by Furuya Metals Co., Ltd.) was added. 6 L was added, and the mixture was stirred at 200 rpm for 1 hour while raising the liquid temperature to 80° C. to prepare an iridium chloride solution.
Next, 70 g of sodium hydroxide was weighed and dissolved in 700 mL of pure water to prepare a 10% sodium hydroxide solution, and the 10% sodium hydroxide solution was added dropwise to the iridium chloride solution at a rate of 12 mL/min. After the dropwise addition was completed, the mixture was further stirred for 10 hours while maintaining the liquid temperature at 80°C.

The resulting slurry was allowed to cool to room temperature and then allowed to stand, and the supernatant liquid was decanted. 1,300 mL of pure water was added to the Teflon beaker containing the remaining slurry, and the mixture was stirred for 1 hour while the temperature was again raised to 80° C., allowed to cool to room temperature, allowed to stand, and the supernatant liquid was again decanted. Such decantation washing was continued until the conductivity of the supernatant did not change. After filtration, the filter cake was dried in an electric dryer at 60° C. for 20 hours and then calcined in the atmosphere at 400° C. for 10 hours in an electric furnace to obtain iridium oxide. 70 g of φ0.65 mm zirconia balls, 16 g of pure water, and 7 g of the iridium oxide were weighed into a 45 cc zirconia container, placed in a planetary ball mill P-6 manufactured by Fritsche, and pulverized at 500 rpm for 7.5 minutes. The pulverized iridium oxide slurry was separated from the φ0.65 mm zirconia balls, and the iridium oxide slurry was filtered. The filter cake was dried in an electric dryer at 60° C. for 20 hours, and the iridium oxide was pulverized in an agate mortar to obtain iridium oxide.

Powder X-ray diffraction was performed on the oxides containing yttrium and iridium obtained in Example 1 (YI-1), Comparative Example 1 (YI-2) and Comparative Example 2 (IO-1).
Powder X-ray diffraction is measured using an X-ray diffraction (XRD) device (manufactured by Rigaku, Ultima
IV). As specific measurement conditions, CuKα rays were used, and the diffraction angle was first adjusted so that the diffraction angle 2θ of Si (2,2,0) in the RSRP-Si standard powder sample was 48.28. A glass substrate was filled with the obtained oxide, and 2θ=10 to 90° was first swept at a sampling interval of 0.02° 2θ and a scanning speed of 10° 2θ/min to perform XRD measurement. Results are shown in FIGS. 2, 3 and 4. FIG.

As a result of powder X-ray diffraction, the catalyst of Example 1 (YI-1) has a broad peak in the vicinity of 30 ° to 35 ° in 2θ, and no other specific peaks are seen. It is considered to be an amorphous structure with no structure. On the other hand, the catalyst of Comparative Example 1 (YI-2) has 29.5°, 34.3°, 49.2° and 58.4° at 2θ, which are characteristic peaks of the pyrochlore type Y ₂ Ir ₂ O ₇ . was detected, the catalyst of Comparative Example 1 (YI-2) was considered to be pyrochlore-type Y ₂ Ir ₂ O ₇ .

The specific surface areas of the catalysts of Example 1 (YI-1), Comparative Example 1 (YI-2) and Comparative Example 2 (IO-1) were measured using a specific surface area/pore size distribution measuring device, BELSORP-miniII, and nitrogen It was carried out by the adsorption method. In addition, the obtained adsorption isotherm data was analyzed by the BET method of the analysis software BEL Master built into the specific surface area/pore size distribution measuring device to determine the specific surface area. Table 1 shows the results.

From Table 1, it was confirmed that the BET specific surface area of Example 1 was 50 m ² /g or more.

The STEM observation of Example 1 (YI-1) was performed. In the measurement, a model JEM-ARM200CF manufactured by JEOL Ltd. was used, and an STEM photograph image was shown in FIG. 5 at an acceleration voltage of 200 kV. As is clear from FIG. 5, it was confirmed that the particle size of the oxide containing yttrium and iridium obtained in Example 1 was 100 nm or less.

Oxygen Evolution Reaction (OER) Mass Activity Evaluation Using the oxides containing yttrium and iridium obtained in Example 1 (YI-1) and Comparative Examples 1 and 2 (YI-2 and IO-1) as oxygen evolution reaction catalysts, 14.7 mg of each was weighed in a mixed solution of 15 mL of ultrapure water, 10 mL of 2-propanol (hereinafter referred to as IPA), and 0.1 mL of 5 wt % Nafion dispersing solution, and dispersed by ultrasonic waves. The resulting dispersion was added onto a rotating disk gold electrode using a micropipette to prepare a 30 μg/cm ² catalyst-coated electrode. A rectangular wave durability test was performed on the electrode thus produced using an electrochemical measurement system (HZ-7000, manufactured by Hokuto Denko Co., Ltd.). As the electrolytic solution, a 60 wt % perchloric acid solution (reagent for precision analysis, manufactured by Kanto Kagaku Co., Ltd.) was prepared to 0.1 M, degassed with Ar gas, and used as an electrolytic solution. A three-electrode method was employed as the measurement method, and a hydrogen standard electrode in which hydrogen gas was passed over platinum black was used as a reference electrode, and the measurement was carried out in a constant temperature bath at 25°C.

Oxygen evolution reaction (hereinafter also referred to as OER: Oxyge Evolution Reaction) mass activity evaluation sweeps the voltage range of 1.0 V to 1.8 V at a rate of 10 mV / sec, current density at 1.5 V (mA /cm ² ) by the amount of catalyst applied to the electrode (30 μg/cm ² ). The results are shown in Table 2. In Example 1 (YI-1) and Comparative Example 1 (YI-2), both oxides containing yttrium and iridium, the OER mass activity at 1.5 V was determined by the total yttrium and iridium applied to the electrode. It was found that Example 1 (YI-1) was 1.8 times higher than that of Example 1 (YI-1). When the OER mass activity converted from the amount of iridium applied to the electrode was calculated, it was confirmed that Example 1 (YI-1) was about 3.9 times higher.
In addition, when comparing Example 1 (YI-1) and Comparative Example 2 (IO-1), comparing the OER mass activity at 1.5 V with the total amount of metal applied to the electrode, Example 1 (YI- 1) was found to be about 2.5 times higher. Further, when the OER mass activity converted from the amount of iridium applied to the electrode was calculated, it was confirmed that Example 1 (YI-1) was about 3.9 times higher.

As is clear from the above results, the catalysts containing the present oxides are iridium-only catalysts and pyrochlore-type composite oxides of yttrium and iridium in terms of OER mass activity, but have a BET specific surface area of less than 50 m ² /g. showed higher performance compared to
Therefore, by using the present oxide, the amount of iridium used can be reduced, and an electrolysis catalyst having a high oxygen evolution mass activity can be provided.

1: First supply source 2: Second supply source 3: Heating unit 4: Reaction unit 5: Liquid feeding route 6: Liquid feeding route 7: Liquid feeding route 8: Recovery unit 9: Cooling unit 10: Pressure adjustment mechanism 11; Flow rate adjusting means 12: Flow rate adjusting means 100: manufacturing apparatus

Claims

An oxygen evolution reaction catalyst containing an oxide containing yttrium and iridium and having a BET specific surface area of 50 m 2 /g or more.
2. The oxygen evolution reaction catalyst according to claim 1, wherein the oxide has an average particle size of 100 nm or less.
An oxygen evolution reaction catalyst layer containing the oxygen evolution reaction catalyst according to claim 1 or 2 and a proton transport agent.
An electrolytic cell comprising the oxygen evolution reaction catalyst layer according to claim 3 and an ion-exchange polymer electrolyte membrane.
The electrolytic cell according to claim 4, wherein the ion-exchange polymer electrolyte membrane is a cation-exchange polymer electrolyte membrane.
(1) Yttrium nanoparticles and iridium nanoparticles or yttrium hydroxide particles and iridium hydroxide particles are dispersed in a dispersion medium to obtain a dispersion, or (2) an yttrium compound and an iridium compound are dissolved in a solvent and dissolved. A step of obtaining a liquid;
A step B in which the water temperature is 100 ° C. or higher and the pressure is higher than 0.1 MPa, and a step C in which the dispersion or the solution obtained in the step A and the high-temperature and high-pressure water obtained in the step B are mixed. The method for producing an oxide according to claim 1, comprising:
The method for producing an oxide according to claim 6, wherein the step B includes a step of adding an oxidizing agent.
The method for producing an oxide according to claim 7, wherein the oxidizing agent is an oxidizing agent that releases oxygen atoms.
The step B includes (1) adding an oxidizing agent that releases oxygen atoms to water, and then bringing the water to the above temperature and pressure; (2) bringing the water to the above temperature and pressure, and then or (3) adding an oxidizing agent that releases oxygen atoms to water, bringing the water to the above temperature and pressure, and further adding an oxidizing agent that releases oxygen atoms. 9. The method for producing an oxide according to claim 8, comprising the step of any one of .