Catalyst material and use thereof

Abstract

To provide a catalyst material with superior catalytic performance.SOLUTION: Provided is a catalyst material comprising alloy particles 1 that contain nickel oxide, iron oxide, and metallic nickel, in which the alloy particles 1 exhibit a gradient composition such that, from the surface 1s of the alloy particles toward a depth direction, the atomic concentration of Fe gradually decreases while the atomic concentration of Ni gradually increases. When measured by X-ray photoelectron spectroscopy up to a sputter depth of 5.5 nm in terms of SiO2 equivalence, the atomic concentration of Fe relative to the total of Fe and Ni at the surface is between 10 at% and 50 at%, and at a sputter depth of 5.5 nm, the atomic concentration of Fe relative to the total of Fe and Ni is between 3 at% and 17 at%, with the rate of decrease in Fe atomic concentration of the alloy particles from the surface to the sputter depth of 5.5 nm being between 0.5 at% / nm and 6 at% / nm. The catalyst material is used as an oxygen evolution electrode in water electrolysis.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The technology disclosed herein relates to catalytic materials and their uses. [Background technology]

[0002] From the perspective of energy and environmental issues, various technologies for converting renewable energy into electricity (such as solar cells and wind power generation) have been proposed. However, storing renewable energy in the form of electricity requires large-scale power storage facilities, which causes equipment costs to soar. In recent years, water electrolysis devices have been proposed that use electricity to decompose aqueous electrolytes (such as alkaline aqueous solutions) into oxygen and hydrogen. This allows renewable energy to be converted into useful gases, thereby reducing the equipment costs required for storing renewable energy.

[0003] In recent years, as demand for water electrolysis devices has increased, so has the demand for catalyst materials used in such devices. Regarding such technologies, for example, Patent Document 1 discloses a technology relating to a catalyst for oxygen generation reaction made of tungsten oxide. Furthermore, Patent Document 2 discloses a technology relating to a catalyst composition containing tin oxide particles at least partially coated with a noble metal oxide layer. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent Publication No. 2021-186750 [Patent Document 2] Special Publication No. 2020-500692 Summary of the Invention [Problem to be solved by the invention]

[0005] However, when using water electrolysis equipment in actual industries, high-performance catalyst materials are required that can generate sufficient amounts of useful gases even at low voltages. However, conventional catalyst materials do not have sufficiently high catalytic performance, and there is still room for improvement.

[0006] The technology disclosed herein has been made in view of the above circumstances, and its main purpose is to provide a catalyst material with excellent catalytic performance. [Means for solving the problem]

[0007] The catalyst material disclosed herein includes alloy particles containing nickel oxide, iron oxide, and metallic nickel, and has a gradient composition in which the atomic concentration of Fe gradually decreases and the atomic concentration of Ni gradually increases from the surface of the alloy particles in the depth direction. When the alloy particles are measured by X-ray photoelectron spectroscopy from the surface to a sputtering depth of 5.5 nm in SiO2 equivalent, the atomic concentration of Fe relative to the total of Fe and Ni at the surface is 10 at% to 50 at%. The atomic concentration of Fe relative to the total of Fe and Ni at the 5.5 nm sputtering depth is 3 at% to 17 at%. The rate of decrease in the atomic concentration of Fe in the alloy particles from the surface to a sputtering depth of 5.5 nm is 0.5 at% to 6 at% / nm.

[0008] The inventors have experimentally confirmed that the catalyst having the above-described configuration has significantly superior performance. Although it is not intended to limit the technology disclosed herein, it is speculated that this significant improvement in catalyst performance is due to the following mechanism.

[0009] First, the alloy particles constituting the catalytic material disclosed herein contain nickel oxide, iron oxide, and metallic nickel, and have a gradient composition in which the atomic concentration of Fe gradually decreases and the atomic concentration of Ni gradually increases from the surface to the depth of the alloy particle. This suggests that the surface of the alloy particle contains a large amount of iron oxide, which has excellent catalytic activity, while metallic nickel, which has excellent electronic conductivity, is present near the center of the alloy particle. The gradient composition is believed to be characterized by increasing catalytic activity toward the surface of the alloy particle. On the other hand, it is believed to be characterized by increasing electronic conductivity toward the depth of the alloy particle. Furthermore, by adjusting the atomic concentration of Fe relative to the sum of Fe and Ni at the surface and at a sputtering depth of 5.5 nm and the rate of decrease in the atomic concentration of Fe in the alloy particle from the surface to a sputtering depth of 5.5 nm within the above ranges, the balance between catalytic activity and electronic conductivity is believed to be favorably altered. This is expected to result in exceptionally excellent catalytic performance.

[0010] In a preferred embodiment of the catalyst material disclosed herein, the atomic concentration of Fe relative to the total of Fe and Ni at a sputtering depth of 3.3 nm is 6 at% to 20 at% and the rate of decrease in the atomic concentration of Fe in the alloy particles from the surface to a sputtering depth of 3.3 nm is 3 at% to 10 at% / nm, thereby achieving a balance between electronic conductivity and catalytic activity.

[0011] In a preferred embodiment of the catalytic material disclosed herein, the mass concentration of Fe relative to the total mass of Fe and Ni in the alloy particles is 0.5 mass% or more and 5 mass% or less, as determined by inductively coupled plasma atomic emission spectroscopy, thereby achieving a better balance between electronic conductivity and catalytic activity.

[0012] In a preferred embodiment of the catalyst material disclosed herein, the alloy particles have an average particle size of 20 nm to 200 nm as determined by field emission scanning electron microscope observation, which allows for high catalytic activity to be obtained.

[0013] In a preferred embodiment of the catalyst material disclosed herein, the CV value of the particle size of the alloy particles is 0.2 or less, as determined by field emission scanning electron microscope observation, which improves adhesion to electrodes and ion exchange membranes and allows for the formation of a smooth catalyst layer.

[0014] In a preferred embodiment of the catalyst material disclosed herein, the atomic concentration of Fe relative to the total of Fe and Ni on the surface is 45 at % or less, which allows for better electronic conductivity.

[0015] Another aspect of the technology disclosed herein provides an electrode including the above-described catalyst material, thereby realizing the provision of an electrode with excellent electrode performance.

[0016] In a preferred embodiment of the electrode disclosed herein, the electrode is used as an oxygen evolution electrode, thereby providing an electrode with excellent electrode performance.

[0017] Another aspect of the technology disclosed herein provides a membrane electrode assembly. The membrane electrode assembly disclosed herein includes an anion exchange membrane and a catalyst layer disposed on the anion exchange membrane, the catalyst layer including the catalyst material. This configuration improves adhesion between the anion exchange membrane and the catalyst layer, facilitating ion migration. The catalyst layer includes a catalyst material with excellent catalytic performance, thereby providing a membrane electrode assembly with excellent catalytic performance.

[0018] Another aspect of the technology disclosed herein provides a water electrolysis device including the electrode or the membrane electrode assembly, which is capable of efficiently converting electric power from a power generation facility into useful gases because it includes a component having a catalytic material with excellent catalytic performance. [Brief explanation of the drawings]

[0019] [Figure 1] FIG. 1 is a cross-sectional view schematically showing alloy particles contained in the catalyst material according to this embodiment. [Figure 2] FIG. 2 is a cross-sectional view schematically showing the water electrolysis apparatus according to this embodiment. [Figure 3] FIG. 3 is a flow diagram showing the method for producing alloy particles according to this embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0020] Preferred embodiments of the technology disclosed herein are described below. Matters other than those specifically mentioned in this specification that are necessary for implementing the technology disclosed herein can be understood as design matters for a person skilled in the art based on the prior art in the relevant field. The technology disclosed herein can be implemented based on the content disclosed in this specification and the technical common sense in the relevant field. The following explanation is not intended to limit the technology disclosed herein to specific embodiments. In this specification and claims, when a specific numerical range is expressed as A to B (A and B are arbitrary numerical values), this means "greater than A and less than B." Therefore, "greater than A but less than B" is also included.

[0021] 1. Catalyst materials First, the catalytic material disclosed herein will be described. FIG. 1 is a cross-sectional view schematically showing an alloy particle 1 contained in the catalytic material according to this embodiment. For ease of explanation, hatching has been omitted in FIG. 1, with the dark areas representing regions containing Fe atoms and the white areas representing regions containing Ni atoms. The alloy particles disclosed herein contain nickel oxide, iron oxide, and metallic nickel. A catalytic material having such a configuration will be specifically described below. In this specification, the term "alloy" refers to a mixture of two or more metal elements at a microscopic level, and examples of alloy structures include solid solutions, intermetallic compounds, and those in which these coexist.

[0022] First, the term "catalytic material" in this specification refers to a powder material (a group of particles) primarily composed of alloy particles having the above-described structure. Here, "primarily composed of alloy particles" means that the inorganic particles contained in the powder material in the largest proportion by weight are alloy particles containing nickel oxide, iron oxide, and metallic nickel. More specifically, the term "catalytic material" in this specification refers to a powder material containing 50 wt % or more (preferably 60 wt % or more, more preferably 70 wt % or more, even more preferably 80 wt % or more, and particularly preferably 90 wt % or more) of alloy particles having the above-described structure. In other words, the catalytic material disclosed herein may contain inorganic particles other than the alloy particles having the above-described structure, as long as the balance between catalytic activity and electronic conductivity achieved by the technology disclosed herein is not significantly impaired. Examples of such minor components include nickel metal particles and inorganic particles primarily composed of other metal elements (e.g., Cu particles, Co particles, Au particles, Ag particles, Pd particles, Pt particles, etc.).

[0023] The alloy particle 1 according to this embodiment is characterized by a gradient composition in which the atomic concentration of Fe gradually decreases and the atomic concentration of Ni gradually increases from the surface 1s of the alloy particle 1 in the depth direction (center 1c). Nickel oxide and iron oxide are present on the surface 1s of the alloy particle 1. Nickel oxide and iron oxide have catalytic activity as water electrocatalysts, with iron oxide in particular exhibiting higher catalytic activity than nickel oxide. Nickel oxide and iron oxide, which have excellent catalytic activity, are abundant in the surface layer of the alloy particle 1, which is likely to come into contact with hydroxide ions. Meanwhile, the atomic concentration of Fe gradually decreases and the atomic concentration of Ni gradually increases from the alloy particle 1 in the depth direction (center 1c). The center 1c of the alloy particle 1 typically has a composition mainly composed of metallic nickel. Metallic nickel is a component with excellent electronic conductivity. Thus, the alloy particle 1 has the gradient composition described above, which favorably changes the balance between catalytic activity and electronic conductivity. Furthermore, it is believed that the gradient composition of the alloy particles 1 allows the iron oxide and nickel oxide to be more firmly arranged than in a configuration in which an oxide coating is formed on the particles. The term "nickel oxide" as used herein encompasses compounds containing Ni and O, such as NiO, Ni(OH)2, and NiOOH. Nickel oxide may also be in an amorphous state containing Ni and O. The term "iron oxide" as used herein encompasses compounds containing Fe and O, such as FeO, Fe3O4, Fe2O3, Fe(OH)2, Fe(OH)3, and FeOOH. Iron oxide may also be in an amorphous state containing Fe and O.

[0024] In this specification, the "surface of an alloy particle" refers to the escape depth region (the layer closest to the surface) of light excited by soft X-rays when the alloy particle is analyzed by X-ray photoelectron spectroscopy (XPS) described below without being subjected to sputtering treatment.

[0025] In this specification, "mainly composed of metallic nickel" means that, when the alloy particles are subjected to XPS analysis, the ratio of the peak area attributable to metallic nickel to the total area of ​​multiple Ni-containing component peaks contained in the 850 to 870 eV region representing the Ni2p3 orbital ((metallic Ni peak area) / (metallic Ni peak area + peak area of ​​other Ni-containing components) × 100) is 90% or more. The above-mentioned "peak area attributable to metallic nickel" can be confirmed in the 852.5 to 852.9 eV region.

[0026] The phrase "having a gradient composition in which the atomic concentration of Fe gradually decreases and the atomic concentration of Ni gradually increases from the surface to the depth direction of the alloy particles" as used herein can be confirmed by measuring the atomic concentrations of Fe and Ni using X-ray photoelectron spectroscopy (XPS). The alloy particles of the present disclosure are characterized in that the rate of decrease in the atomic concentration of Fe in the alloy particles from the surface to a sputtering depth of 5.5 nm in SiO2 equivalent is 0.5 at% / nm or more (more preferably 1 at% / nm or more, even more preferably 1.5 at% / nm or more, particularly preferably 2 at% / nm or more) to 6 at% / nm or less (more preferably 5.5 at% / nm or less, even more preferably 5 at% / nm or less, particularly preferably 4.5 at% / nm or less). The "atomic concentration of Fe in the alloy particles" refers to the atomic concentration of Fe relative to the total of Fe and Ni. The positive correlation between the rate of decrease in the Fe atomic concentration indicates that the alloy particles have a gradient composition in which the Fe atomic concentration gradually decreases and the Ni atomic concentration gradually increases in the depth direction. If the rate of decrease is too low (e.g., less than 0.5 at% / nm), the catalytic activity of the alloy particles may decrease. On the other hand, if the rate of decrease is too high (e.g., more than 6 at% / nm), the electronic conductivity of the alloy particles may decrease. Therefore, by ensuring that the rate of decrease in the Fe atomic concentration of the alloy particles from the surface to a sputtering depth of 5.5 nm satisfies the above range, alloy particles can be obtained that have a suitable gradient composition and that balance electronic conductivity and catalytic activity.

[0027] In this specification, the "atomic concentration (at%) of Fe relative to the total of Fe and Ni" can be specifically obtained as follows. Specifically, first, a photoelectron spectrum of the alloy particles is obtained using XPS. From the obtained photoelectron spectrum, the region of 850 to 870 eV representing the Ni2p3 orbital and the region of 48 to 60 eV representing the Fe3p orbital are separated. Note that these regions are derived from the Ni element and the Fe element, respectively. From these regions, the peak areas of the Ni element and the Fe element are obtained. Then, the "atomic concentration (at%) of Fe relative to the total of Fe and Ni" can be calculated from the obtained peak areas.

[0028] Furthermore, the "decrease rate of the Fe atomic concentration of the alloy particle from the surface to a sputtering depth of 5.5 nm" in this specification can be obtained as follows. Specifically, XPS analysis is performed from the surface to a depth of 5.5 nm in SiO2 equivalent by sputtering, and the Fe atomic concentration (at%) at the surface and at a depth of 5.5 nm from the surface is determined by the method described above. From the obtained results, the value calculated by the following formula (1) can be used to determine the "decrease rate of the Fe atomic concentration of the alloy particle from the surface to a sputtering depth of 5.5 nm" (at% / nm). The decrease rate of the Fe atomic concentration of the alloy particle from the surface to a sputtering depth of 5.5 nm (at% / nm) = −((Fe atomic concentration at a depth of 5.5 nm (at%) − Fe atomic concentration at the surface (at%)) / 5.5 (nm) − 0 (nm)) (1)

[0029] The alloy particles 1 of the present disclosure are characterized in that the atomic concentration of Fe on the surface relative to the total of Fe and Ni is 10 at% or more (more preferably 12 at% or more, even more preferably 15 at% or more, particularly preferably 20 at% or more) and 50 at% or less (more preferably 48 at% or less, even more preferably 45 at% or less, particularly preferably 40 at% or less). If the atomic concentration of Fe is too low (e.g., less than 10 at%), the proportion of Fe atoms present on the alloy particle surface is reduced, and sufficient catalytic activity is not obtained. On the other hand, if the atomic concentration of Fe is too high (e.g., greater than 50 at%), the proportion of Ni atoms present on the alloy particle surface is reduced, and sufficient electronic conductivity is not obtained. Therefore, by ensuring that the atomic concentration of Fe satisfies the above range, alloy particles can be obtained that exhibit a balance between electronic conductivity and catalytic activity.

[0030] Furthermore, the alloy particles 1 of the present disclosure are characterized in that the atomic concentration of Fe relative to the total of Fe and Ni at a SiO2-equivalent sputtering depth of 5.5 nm is 3 at% or more (more preferably 3.2 at% or more, even more preferably 3.5 at% or more, particularly preferably 4 at% or more) and 17 at% or less (more preferably 16.5 at% or less, even more preferably 16 at% or less, particularly preferably 15 at% or less). If the atomic concentration of Fe is too low (e.g., less than 3 at%), sufficient catalytic activity cannot be obtained. On the other hand, if the atomic concentration of Fe is too high (e.g., greater than 20 at%), sufficient electronic conductivity cannot be obtained. Therefore, by ensuring that the atomic concentration of Fe satisfies the above range, alloy particles can be obtained that exhibit a good balance between electronic conductivity and catalytic activity.

[0031] When XPS measurements were performed from the surface of alloy particle 1 to a sputtering depth of 3.3 nm (SiO2 equivalent), the rate of decrease in the Fe atomic concentration of alloy particle 1 from the surface to a sputtering depth of 3.3 nm was preferably 3 at% / nm or more, more preferably 3.5 at% / nm or more, and even more preferably 4 at% / nm or more. This allows for more efficient electron transfer between alloy particles. Meanwhile, the upper limit of the rate of decrease in the Fe atomic concentration of alloy particle 1 from the surface to a sputtering depth of 3.3 nm is preferably 10 at% / nm or less, more preferably 9 at% / nm or less, and even more preferably 8 at% / nm or less.

[0032] When XPS measurements were performed from the surface of the alloy particle 1 to a sputtering depth of 3.3 nm in terms of SiO2, the atomic concentration of Fe relative to the total of Fe and Ni at the sputtering depth of 3.3 nm was preferably 6 at% or more, more preferably 6.5 at% or more, and even more preferably 7 at% or more. This allows for more favorable catalytic activity. On the other hand, from the viewpoint of obtaining sufficient electronic conductivity, the atomic concentration is preferably 20 at% or less, more preferably 19 at% or less, and even more preferably 18 at% or less.

[0033] In this specification, the "decrease rate of the Fe atomic concentration in the alloy particle from the surface to a sputtering depth of 3.3 nm" is determined by performing XPS analysis from the surface to a sputtering depth of 3.3 nm in SiO2 equivalent using the same method as above, and determining the Fe atomic concentration (at%) relative to the total of Fe and Ni at the surface and at a depth of 3.3 nm from the surface. From the results obtained, the following formula (2) can be used to determine the "decrease rate of the Fe atomic concentration in the alloy particle from the surface to a sputtering depth of 3.3 nm" (at% / nm). The decrease rate of the Fe atomic concentration of the alloy particle from the surface to a sputtering depth of 3.3 nm (at% / nm) = − ((Fe atomic concentration at a depth of 3.3 nm (at%) − Fe atomic concentration at the surface (at%)) / 3.3 (nm) − 0 (nm)) (2)

[0034] In ICP (inductively coupled plasma) optical emission spectroscopy, the mass concentration of Fe relative to the total of Fe and Ni in alloy particle 1 is preferably 0.5 mass% or more, more preferably 1 mass% or more, and even more preferably 2 mass% or more, from the viewpoint of obtaining good catalytic activity. On the other hand, in the viewpoint of obtaining sufficient electronic conductivity, the mass concentration of Fe relative to the total of Fe and Ni is preferably 5 mass% or less, more preferably 4.5 mass% or less, and even more preferably 4 mass% or less. In this specification, the "mass concentration of Fe relative to the total of Fe and Ni in ICP optical emission spectroscopy" can be specifically determined by measuring the entire alloy particle using an ICP optical emission spectroscopy analyzer, quantifying the contents of each element, Fe and Ni, and calculating the mass concentration.

[0035] The average particle size of the alloy particles 1 based on FE-SEM observation is preferably 200 nm or less, more preferably 150 nm or less, and even more preferably 100 nm or less. By using alloy particles 1 with a small average particle size, the surface activity of the alloy particles 1 is increased, thereby achieving high catalytic activity. On the other hand, the lower limit of the average particle size of the alloy particles 1 is not particularly limited, but from the viewpoints of productivity and handling, it is preferably 20 nm or more, more preferably 30 nm or more. In this specification, the "average particle size based on an FE-SEM image" refers to the cumulative 50% particle size (D ) based on the number in the particle size distribution of 1,000 alloy particles extracted from an image of the alloy particles taken using a field emission scanning electron microscope (FE-SEM). 50 ) is shown.

[0036] The CV value (coefficient of variation) of the alloy particles 1 is preferably 0.2 or less, more preferably 0.18 or less, and particularly preferably 0.16 or less. In this specification, the "CV value" refers to the ratio of the standard deviation σ to the average particle diameter of the alloy particles calculated above (standard deviation σ / average particle diameter). In other words, the smaller the CV value, the more uniform the particles. Therefore, alloy particles with a small CV value (in other words, uniform particles) can improve adhesion to electrodes and ion exchange membranes, and a smooth catalyst layer can be obtained.

[0037] The catalytic material according to this embodiment has been described above. As described above, the catalytic material according to this embodiment has a favorable balance between catalytic activity and electronic conductivity. Therefore, it can be suitably used as an oxygen evolution reaction (OER) catalyst for water electrolysis. However, without being limited thereto, the catalytic material according to this embodiment can be used as a material for magnetic storage media, magnetic sensors, magnetic devices, inductors, transformer components, and electromagnetic interference (EMI) shielding.

[0038] 2.Water electrolysis device Another aspect of the technology disclosed herein provides a water electrolysis device. Hereinafter, a water electrolysis device will be described as an example of an application of the alloy particles disclosed herein. FIG. 2 is a cross-sectional view schematically showing a water electrolysis device according to this embodiment. The following describes an example of an application of the catalyst material, and is not intended to limit the application of the technology disclosed herein.

[0039] The water electrolysis device 100 shown in FIG. 2 includes an oxygen generating electrode (anode) 110, a hydrogen generating electrode (cathode) 120, and an anion exchange membrane 130. In this embodiment, the water electrolysis device 100 is an AEM (Anion Exchange Membrane) type water electrolysis device. The anion exchange membrane 130 is interposed between the oxygen generating electrode 110 and the hydrogen generating electrode 120. Components other than the oxygen generating electrode 110 and the anion exchange membrane 130 can be any components that can be used in this type of water electrolysis device without any particular restrictions, and therefore detailed description thereof will be omitted. The water electrolysis device 100 is an example of "a water electrolysis device including an anion exchange membrane and a catalyst layer disposed on the anion exchange membrane" in the technology disclosed herein.

[0040] Here, a water supply channel 162 is attached to the hydrogen generating electrode 120. An aqueous electrolyte is supplied to the hydrogen generating electrode 120 through this water supply channel 162. An alkaline aqueous solution such as an NaOH aqueous solution or a KOH aqueous solution is preferably used as the aqueous electrolyte. In addition, an oxygen recovery pipe 164 is attached to the oxygen generating electrode 110. This oxygen recovery pipe 164 passes through the first substrate 111 and is connected to the first catalyst layer 112. Meanwhile, a hydrogen recovery pipe 166 is attached to the hydrogen generating electrode 120. The hydrogen recovery pipe 166 passes through the second substrate 121 and is connected to the second catalyst layer 122.

[0041] Next, the oxygen evolving electrode 110 and the hydrogen evolving electrode 120 are electrically connected by a conductive line 140. Specifically, the conductive line 140 connects the first substrate 111 of the oxygen evolving electrode 110 and the second substrate 121 of the hydrogen evolving electrode 120. A power source 150 is also installed on this conductive line 140. The power source 150 may be, for example, a generator (such as a solar cell or wind power generator) that converts renewable energy into electricity.

[0042] Next, the operation of the water electrolysis device 100 will be described. First, in the water electrolysis device 100, an aqueous electrolyte is supplied from the water supply channel 162 to the hydrogen generating electrode 120. In addition, electrons (e -At this time, the aqueous electrolyte (H2O) is converted into hydrogen gas (H2) and hydroxide ions (OH - ) (see formula (3) below). The hydrogen gas produced at the hydrogen generating electrode 120 is then collected from the hydrogen recovery pipe 166. Meanwhile, the hydroxide ions produced at the hydrogen generating electrode 120 pass through the anion exchange membrane 130 and move to the oxygen generating electrode 110. As a result, oxygen gas (O2) and water (HO) are produced at the oxygen generating electrode 110, as shown in formula (4) below. The oxygen gas is then collected from the oxygen recovery pipe 164. The water is then discharged to the outside of the device through a drain pipe (not shown). As described above, this water electrolysis device 100 can convert the electricity generated by the power source 150 into oxygen gas and hydrogen gas. 4H2O+4e - →2H2+4OH - (3) 4OH - →O2+2H2O+4e - (4)

[0043] 3. Electrode Another aspect of the technology disclosed herein provides an electrode including the catalytic material according to this embodiment. Such an electrode can be suitably used as an oxygen evolving electrode. One embodiment of the electrode disclosed herein will be described below. Note that the oxygen evolving electrode 110 is an example of the "oxygen evolving electrode" and "electrode" in the technology disclosed herein.

[0044] The oxygen evolution electrode 110 is an electrode comprising a first substrate 111 and a first catalyst layer 112. The first catalyst layer 112 is disposed so as to face the anion exchange membrane 130. In this embodiment, the first catalyst layer 112 is disposed on the anion exchange membrane 130. In other words, the first catalyst layer 112 is supported on one surface of the anion exchange membrane 130. This configuration improves the adhesion between the anion exchange membrane 130 and the first catalyst layer 112, and the generation of hydroxide ions (OH - ) is easily moved.

[0045] Here, the first substrate 111 is a metal member having electrical conductivity (conductive substrate). Any conventionally known substrate that can be used for electrodes in water electrolysis devices can be used as the first substrate 111, without any particular restrictions. Examples of materials for the first substrate 111 include Ni, Ti, NiCr alloy, and SUS. Among these, a first substrate 111 made of Ni (Ni substrate) is particularly suitable. Note that the first substrate 111 in this embodiment is a plate-shaped member. However, the shape of the first substrate 111 does not limit the technology disclosed herein. The shape of the first substrate 111 can be changed as appropriate depending on the structure of the water electrolysis device to which it is applied.

[0046] The first substrate 111 is preferably a porous body having a plurality of pores. This allows fluids such as water and oxygen gas to easily pass through the first substrate 111. As a result, this contributes to improving the operating efficiency of the water electrolysis apparatus 100. For example, the average pore diameter in the first substrate 111 is preferably 0.05 mm or more, more preferably 0.1 mm or more, even more preferably 0.15 mm or more, and particularly preferably 0.2 mm or more. This ensures sufficient fluid permeability of the first substrate 111. On the other hand, the average pore diameter in the first substrate 111 is preferably 5.5 mm or less, more preferably 5.0 mm or less, even more preferably 4.5 mm or less, and particularly preferably 4.0 mm or less. This ensures sufficient strength of the first substrate 111.

[0047] Furthermore, the porosity of the first substrate 111 is preferably 70% or more, more preferably 75% or more, even more preferably 80% or more, and particularly preferably 85% or more. This allows the fluid permeability of the first substrate 111 to be more suitably improved. On the other hand, in consideration of the strength of the first substrate 111, the porosity of the first substrate 111 is preferably 98% or less, more preferably 97% or less, and particularly preferably 96% or less. Note that the "porosity of the conductive substrate" in this specification is measured according to the following procedure. First, the conductive substrate is placed in a 1 cm 3 The sample is cut into pieces, weighed, and the actual specific gravity is calculated. Next, the apparent specific gravity is calculated based on the specific gravity of the conductive substrate material (Ni, Ti, etc.). The result of the calculation of apparent specific gravity / actual specific gravity is then taken as the "porosity."

[0048] The thickness of the first substrate 111 is preferably 50 μm or more, more preferably 100 μm or more, and particularly preferably 150 μm or more. This ensures sufficient strength of the first substrate 111. On the other hand, the upper limit of the thickness of the first substrate 111 is preferably 500 μm or less, more preferably 450 μm or less, and particularly preferably 400 μm or less. This ensures sufficient fluid permeability in the first substrate 111.

[0049] The first catalyst layer 112 is a layer containing an oxidation catalyst that generates water and oxygen, as shown in the above formula (4). Here, by including the catalyst material (alloy particles) according to this embodiment as the oxidation catalyst, it is possible to provide an oxygen evolution electrode 110 that achieves a balance between catalytic activity and electronic conductivity.

[0050] The first catalyst layer 112 may contain additives other than the above-mentioned catalyst materials, as long as the additives do not significantly impair the effects of the technology disclosed herein. Examples of such additives include ion-conductive resins.

[0051] The ion-conductive resin may be an anion-exchange resin having an anion-exchange group (such as a quaternary ammonium group or a pyridinium group). Examples of anion-exchange resins that can be used include Sustainion ionomer manufactured by Dioxide Materials and Piperion ionomer manufactured by Versogen. The proportion of the ion-conductive resin in the first catalyst layer 112 is, for example, 90 parts by mass or more, and preferably 95 parts by mass or more, per 100 parts by mass of the catalyst material. Meanwhile, the proportion of the ion-conductive resin in the first catalyst layer 112 is, for example, 110 parts by mass or less, and preferably 105 parts by mass or less.

[0052] The thickness of first catalytic layer 112 is not particularly limited, but from the viewpoint of obtaining sufficient catalytic activity, it is preferably 10 μm or more, and more preferably 20 μm or more. The upper limit of the thickness of first catalytic layer 112 is not particularly limited, but can be, for example, 100 μm or less.

[0053] The hydrogen generating electrode 120 is an electrode including a second substrate 121 and a second catalyst layer 122. The second catalyst layer 122 is disposed so as to face the anion exchange membrane 130. Here, the second catalyst layer 122 may be disposed on the anion exchange membrane 130 (on the other side). Alternatively, the second catalyst layer 122 may be disposed on the second substrate 121. The detailed configuration of the hydrogen generating electrode 120 can be changed as appropriate based on conventionally known technical common sense and does not characterize the technology disclosed herein. Therefore, a description thereof will be omitted here.

[0054] 4.Membrane electrode assembly As described above, the first catalyst layer 112 of this embodiment takes the form of a so-called membrane electrode assembly, which is disposed (supported) on (one surface of) the anion exchange membrane 130. As another aspect of the technology disclosed herein, a membrane electrode assembly is provided. The membrane electrode assembly disclosed herein includes an anion exchange membrane and a catalyst layer disposed on the anion exchange membrane. Note that "the anion exchange membrane 130 and the first catalyst layer 112 disposed on the anion exchange membrane 130" is an example of "a membrane electrode assembly including an anion exchange membrane and a catalyst layer disposed on the anion exchange membrane" in the technology disclosed herein.

[0055] The anion exchange membrane 130 is an electrolyte membrane having ion conductivity. ... - Any conventionally known electrolyte membrane that can be used for a water electrolysis device and through which the anion exchange membrane 130 can move can be used without particular limitation. As the anion exchange membrane 130, for example, an anion exchange resin having an anion exchange group such as a quaternary ammonium group or a pyridinium group can be used.

[0056] The thickness of the anion exchange membrane 130 is not particularly limited, but is preferably 10 μm or more, more preferably 20 μm or more, and particularly preferably 30 μm or more. On the other hand, the upper limit of the thickness of the anion exchange membrane 130 is preferably 100 μm or less, more preferably 90 μm or less, and particularly preferably 80 μm or less.

[0057] 5. Method for forming first catalyst layer 112 The first catalyst layer 112 can be formed, for example, by the following method. First, the catalyst material (alloy particles 1) according to this embodiment is dispersed in an organic solvent to prepare an electrode printing paste. In addition to the alloy particles 1, the electrode printing paste may further contain, for example, the above-mentioned ion-conductive resin and dispersant.

[0058] Examples of organic solvents that can be used to prepare the electrode printing paste include lower alcohols such as methanol, ethanol, propanol, and isopropanol, ethylene glycol, diethylene glycol derivatives, toluene, xylene, butyl carbitol, isobornyl acetate, terpineol, and dihydroterpineol.

[0059] After preparing the electrode printing paste as described above, the first catalyst layer 112 according to this embodiment can be disposed (supported) on the anion exchange membrane 130 by applying the paste to one surface of the anion exchange membrane 130 and drying it. Note that the application method can be a conventionally known method such as screen printing. The electrode printing paste can be dried at a temperature of about 50 to 80°C, for example. The electrode printing paste can be dried for a time of about 30 to 60 minutes, for example.

[0060] 6. Other Embodiments The foregoing describes one embodiment of the water electrolysis device disclosed herein. However, the water electrolysis device disclosed herein is not limited to the above embodiment. In the above embodiment, the first catalyst layer 112 is disposed (supported) on the anion exchange membrane 130 by the catalyst-coated membrane (CCM) method, which forms a catalyst layer on an electrolyte membrane (see FIG. 2). However, the present invention is not limited to this. In some preferred embodiments, the first catalyst layer containing the catalyst material according to the present embodiment may be disposed (supported) on a first substrate by the catalyst-coated substrate (CCS) method, which forms a catalyst layer on a substrate. In other words, in some preferred embodiments, the electrode may be disposed (supported) on a first substrate, which contains the catalyst material according to the present embodiment. Even in this embodiment, power generated by a power source can be converted into oxygen gas and hydrogen gas by a mechanism similar to the above process. Note that an "electrode in which a first catalyst layer containing the catalyst material according to the present embodiment is disposed on a first substrate" is an example of an "oxygen evolving electrode" and an "electrode" in the technology disclosed herein.

[0061] The method for disposing the first catalyst layer 112 on the first substrate 111 (CCS method) can be achieved by preparing a paste similar to the electrode printing paste described above, applying the paste to the first substrate 111 under the same conditions as above, and drying the paste, so a redundant description will be omitted here. The catalyst material according to the present disclosure has good adhesion to both the electrolyte membrane and the substrate. Therefore, a catalyst layer with excellent catalytic performance can be obtained by either the CCM method or the CCS method.

[0062] Furthermore, in the above description, an oxygen evolution electrode (electrode) in which the first catalytic layer 112 is disposed (supported) on the first substrate 111 has been described as another embodiment. However, the electrode may include layered members other than the oxygen evolution electrode 110 and the first catalytic layer 112. For example, in another embodiment of the technology disclosed herein, an adhesive layer may be formed on the first catalytic layer 112. This adhesive layer is a layer containing, as its main components, an ion-conductive resin, a catalytic material, a conductive material, or the like. An electrode having this adhesive layer has improved adhesion to the ion exchange membrane (e.g., an anion exchange membrane) of a water electrolysis device, which can further contribute to improving cell performance.

[0063] 7. Manufacturing method of alloy particles A preferred example of the method for producing alloy particles according to this embodiment will be described below. However, it is not intended that the method for producing alloy particles be limited to the following production method. FIG. 3 is a flow diagram showing the method for producing alloy particles according to this embodiment. As shown in FIG. 3, the production method according to this embodiment includes a preparation step S10, a particle generation step S20, and a separation step S30. Each step will be described below.

[0064] (1) Preparation process S10 In the preparation step S10, a precursor solution is prepared in which an organic solvent, a nickel salt, and an iron salt are dispersed. This precursor solution is typically prepared by dispersing or dissolving the material in a predetermined solvent under an inert atmosphere at room temperature (e.g., 25±5°C). The order in which these materials are added is not particularly limited; all materials may be mixed at the same time, or the materials may be added in several batches (e.g., dispersing or dissolving one material in a solvent, and then dispersing or dissolving the other materials).

[0065] The organic solvent is not particularly limited as long as it can disperse the alloy particles. Examples of such organic solvents include low-polarity solvents such as ethylene glycol, alcohols, amine compounds, N,N-dimethylformamide, dimethyl sulfoxide, and acetone. Among them, amine compounds such as n-octylamine, 2-ethylhexylamine, n-decylamine, n-dodecylamine, n-tetradecylamine, n-hexadecylamine, stearylamine, and oleylamine are particularly suitable.

[0066] Examples of the nickel salt include nickel carboxylate, nickel chloride, nickel carbonate, nickel nitrate, and nickel hydroxide. Among these, nickel carboxylate, which has a relatively low decomposition temperature during reduction, is preferred. Examples of such nickel carboxylate include nickel formate and nickel acetate. Nickel carboxylate may be an anhydride or a hydrate. Examples of such hydrates include nickel formate dihydrate and nickel acetate tetrahydrate. Commercially available nickel salts can be used without particular limitation.

[0067] Examples of the iron salt include iron chloride, iron sulfate, iron acetate, iron bromide, iron nitrate, iron carbonate, and iron sulfide. The iron salt may be an anhydride or a hydrate. Among these, iron chloride is preferably used because its decomposition temperature is relatively close to that of nickel carboxylate. As the iron salt, for example, commercially available products can be used without any particular limitations.

[0068] From the viewpoint of production efficiency, the total weight of the nickel salt and the iron salt relative to the weight of the organic solvent is preferably 50% or more, more preferably 60% or more, and particularly preferably 70% or more. On the other hand, if the total weight of the nickel salt and the iron salt is too high, the nickel salt and the iron salt may not be properly dispersed in the organic solvent. Therefore, the upper limit of the total weight of the nickel salt and the iron salt relative to the weight of the organic solvent is preferably 95% or less, more preferably 90% or less.

[0069] The molar concentration of the iron salt relative to the total of the nickel salt and the iron salt is preferably 0.5 mol% or more, more preferably 1 mol% or more. This allows the mass range of Fe relative to the total of Fe and Ni in the alloy particles to be adjusted to a desired range. The ratio of the iron salt relative to the total of the nickel salt and the iron salt is preferably 10 mol% or less, more preferably 9 mol% or less.

[0070] (2) Particle generation process S20 In the particle generation step S20, the precursor solution prepared in the preparation step S10 is heated in an inert atmosphere at a first temperature T1 for a predetermined time. The precursor solution is then heated to a second temperature T2 and further heated for a predetermined time. After heating, the alloy particle slurry is allowed to cool naturally. Then, the inert atmosphere is released (the inflow of inert gas is stopped), and the alloy particle slurry is exposed to the air. This results in a slurry in which the alloy particles according to this embodiment are dispersed in an organic solvent.

[0071] Although the detailed mechanism by which the alloy particles according to this embodiment are formed is unclear, the following formation process is believed to be involved. First, when a precursor solution containing the nickel salt and iron salt described above is heated to a first temperature T1, Ni, which has a high standard potential, is preferentially precipitated. Then, by maintaining the first temperature T1 for a predetermined time, particles primarily composed of Ni metal are generated and grow. Next, by raising the precursor solution to a second temperature T2, the iron salt in the precursor solution begins to thermally decompose, and Fe begins to fuse to the surface of the particles. Further heating leaves much of the iron salt in the precursor solution, as the nickel salt in the precursor solution has decomposed first. Therefore, as particle growth progresses, the atomic concentration of Ni formed on the particle surface gradually decreases, while the atomic concentration of Fe gradually increases. After natural cooling, the slurry is exposed to the atmosphere, whereby the particle surfaces are rapidly oxidized, forming nickel oxide and iron oxide on the particle surfaces. This is believed to be how the alloy particles with a gradient composition according to this embodiment are formed.

[0072] The first temperature T1 may be, for example, about 120°C to 150°C, and preferably about 130°C to 140°C, as long as it is higher than the thermal decomposition temperature of the nickel salt and lower than the thermal decomposition temperature of the iron salt.

[0073] The retention time at the first temperature T1 is not particularly limited, as it may vary depending on, for example, the first temperature T1 and the composition of the precursor solution (e.g., the type of raw material compound, the type of solvent, the amount of water added, etc.). The retention time at the first temperature T1 should be set so as not to exceed the saturated concentration of nuclei in the solution. When using a nuclei solution as described in the following embodiment, the retention time can be approximately 120 minutes or less, for example, 60 to 90 minutes.

[0074] The second temperature T2 may be any temperature higher than the first temperature T1, as long as it is a temperature at which the iron salt can be thermally decomposed. The second temperature T2 may be, for example, about 210°C to 250°C, and preferably about 220°C to 240°C. The second temperature T2 may be continuously heated after the heating at the first temperature T1, or the solution may be cooled to room temperature (e.g., 25±10°C) and then heated to the second temperature T2.

[0075] The holding time at the second temperature T2 is not particularly limited, as it may vary depending on, for example, the second temperature T2 and the composition of the precursor solution (for example, the type of raw material compound, the type of solvent, the amount of water added, etc.) The holding time at the second temperature T2 can be set to approximately 30 minutes or more, for example, 60 to 90 minutes, from the viewpoint of the reduction yield.

[0076] (3) Separation process S30 In this step, the alloy particles are separated from the particle slurry. This allows the alloy particles according to this embodiment to be obtained. In this step, any conventionally known separation means used to separate powder from a slurry can be used without any particular restrictions. Examples of such separation means include magnetic separation, static separation, centrifugation, and filtration. This separation step S30 is not an essential step in producing the alloy particles according to this embodiment. For example, depending on the type of organic solvent used in the particle slurry, the particle slurry after the particle generation step S20 can be used as an electrode paste as is.

[0077] (4) Other processes The alloy particles separated from the particle slurry can be washed with a predetermined washing medium, which may involve dispersing the separated alloy particles in a liquid washing medium and then separating the alloy particles from the washing medium again.

[0078] An embodiment of the technology disclosed herein has been described above. However, the above-described embodiment is not intended to limit the technology disclosed herein. In other words, the technology disclosed herein may include various modifications of the above-described embodiment.

[0079] [Test example] Test examples relating to the technology disclosed herein will be described below, but the technology disclosed herein is not limited to the following test examples.

[0080] 1. Sample Preparation In this test example, three types of alloy particle samples (Examples 1 to 3) with different compositions were prepared. The procedure for producing the alloy particle samples according to each example will be described below.

[0081] (Example 1) A precursor solution was obtained by mixing 6.53 g of nickel acetate tetrahydrate, 0.11 g of iron chloride tetrahydrate, and 159.6 g of oleylamine (organic solvent) in a three-neck flask at room temperature. A nitrogen gas flow (2 L / min) was introduced into the reaction vessel containing the precursor solution, creating an inert atmosphere inside the reaction vessel. Under a nitrogen atmosphere, the temperature inside the reaction vessel was raised to 135°C and heated for 1 hour. The temperature inside the reaction vessel was then raised to 230°C and heated for another hour or more. The heating was then stopped, and the mixture was allowed to cool naturally to room temperature. The nitrogen gas flow was then stopped, and the reaction vessel was returned to an air atmosphere. This resulted in a particle slurry in which alloy particles were dispersed in oleylamine.

[0082] The reaction vessel containing the particle slurry was placed on a magnetic table, and the particles in the slurry were attracted by the magnetic force and allowed to settle. The supernatant was removed from the particle slurry in this state. In this manner, particles were obtained from the particle slurry. The particles were then washed three times using hexane. After that, the particles were removed from the reaction vessel and dried in a vacuum oven at 60°C for 1 hour. After drying, the particles were crushed using a mortar and pestle to prepare them for characterization. In this manner, alloy particles according to Example 1 were obtained.

[0083] (Example 2 to Example 3) In Examples 2 and 3, the same procedures as in Example 1 were carried out except that the masses of nickel acetate tetrahydrate and iron chloride tetrahydrate were as shown in Table 1. In this manner, alloy particles according to Examples 2 and 3 were obtained.

[0084] [Table 1]

[0085] 2. Evaluation (1) Measurement of average particle size and CV value An FE-SEM image of the alloy particles of each example was obtained using an FE-SEM (manufactured by Hitachi High-Tech Corporation, model: SU8230). 1000 particles in which the entire outer periphery of the particle could be confirmed were randomly selected from the obtained FE-SEM images, and the Heywood diameter was measured to obtain the particle size distribution. Based on the obtained particle size distribution, the average particle diameter (D 50 The particle size and coefficient of variation (CV value) were measured. The measurement results are shown in Table 2.

[0086] (2)ICP analysis 0.1 g of alloy particles according to each example was dissolved in 8 ml of aqua regia, and the volume was adjusted to 250 ml. The alloy particle solution after the adjustment was then diluted 50 times, and the Fe and Ni contents of the alloy particles according to Examples 1 and 2 were quantified using an ICP apparatus (Agilent, 5800 ICP-OES). The mass concentration (mass%) of Fe relative to the total mass of Fe and Ni was calculated from the obtained masses of Fe and Ni. The results are shown in the "Fe mass concentration" section of Table 2.

[0087] (3)XPS analysis Here, in order to evaluate the compositions of the alloy particles according to Examples 1 and 2, analysis was carried out by XPS.

[0088] (3-1) Preparation of samples for XPS analysis First, samples for XPS analysis according to Examples 1 and 2 were prepared. Specifically, approximately 10 mg of alloy particles of each example was placed in an aluminum pan (Rigaku Corporation, aluminum sample container) (φ5 mm, height 2.5 mm), and the container containing the alloy particles was pressed using a press with a stroke of 1.0 MPa. Thereafter, the alloy particles formed into a pellet and supported by the aluminum pan were removed. In this way, samples for XPS analysis according to Examples 1 and 2 were prepared.

[0089] (3-2) XPS measurement The samples for XPS analysis according to Examples 1 and 2 obtained above were measured using a photoelectron spectrometer (PHI X-tool, manufactured by ULVAC-PHI, Inc.) under the following measurement conditions. First, XPS measurement was performed without sputtering, with the sputtering depth set to 0 nm. Next, surface measurement and depth direction measurement were performed from the surface (0 nm) by sputtering to a depth of 5.5 nm (SiO2 equivalent). After the XPS measurement, the XPS data was analyzed using data analysis software (Multipack Ver. 9.9, manufactured by ULVAC-PHI, Inc.). The Shirley method was used for background processing. Excitation X-ray source: Monochromated Al-Kα Accelerating voltage: 15 kV Output: 24.6W Detection angle: 45° Measured elements: C1s, O1s, Fe3p, Ni2p3 Pass energy: 26.0 eV during depth analysis Step: 0.05 eV / step during depth direction analysis X-ray irradiation diameter: φ approx. 100μm (111.9μm) Sputtered ion species: Ar monomer ions Sputtering rate: 2.20 nm / min (SiO2 equivalent) Sputtering interval: 30 seconds Energy correction value: None

[0090] After analyzing the XPS data, quantitative analysis was performed on the Fe and Ni elements at the surface and at depths of 3.3 nm and 5.5 nm. For each example, the Fe atomic concentration (at%) relative to the total of Fe and Ni was determined from the results obtained, and the Fe atomic concentration for each example was calculated. This is shown in the "Fe atomic concentration" column in Table 2.

[0091] Furthermore, the rate of decrease (at% / nm) of the Fe atomic concentration from the surface to a sputtering depth of 3.3 nm was calculated using the following formula (I): Similarly, the rate of decrease (at% / nm) of the Fe atomic concentration from the surface to a sputtering depth of 5.5 nm was calculated using the following formula (II): The results are shown in the "Surface to 3.3 nm" and "Surface to 5.5 nm" sections of the "Fe decrease slope" column in Table 1. The decrease in the atomic concentration of Fe in the alloy particle from the surface to a sputtering depth of 3.3 nm (at% / nm) = −((atomic concentration of Fe at a depth of 3.3 nm (at%) − atomic concentration of Fe at the surface (at%)) / 3.3 (nm) − 0 (nm)) (I) The decrease rate of the Fe atomic concentration of the alloy particle from the surface to a sputtering depth of 5.5 nm (at% / nm) = −((Fe atomic concentration at a depth of 5.5 nm (at%) − Fe atomic concentration at the surface (at%)) / 5.5 (nm) − 0 (nm)) (II)

[0092] (4) Catalytic performance evaluation Here, in order to evaluate the catalytic performance of each example, the overvoltage in the oxygen evolution reaction (OER) was measured.

[0093] (4-1) Preparation of electrodes for evaluation First, an electrode for evaluation was prepared as a sample for catalytic performance evaluation. Specifically, 1.11 g of ethanol (99.5%), 90 mg of alloy particles according to each example, and 90 mg of Sustainion XB-7 (registered trademark) (Dioxide Materials, 5 wt% dispersion) as an organic solvent were mixed, and the mixture was subjected to ultrasonic dispersion treatment for 60 minutes to prepare a catalyst ink. The prepared catalyst ink was placed on a 0.5 × 0.5 cm 2 The catalyst was dropped onto nickel foam and dried at 80°C for one hour. The catalyst loading was measured by measuring the weight of the nickel foam before and after dropping. Note that the catalyst loading on the nickel foam was 4 to 6 mg / cm. 2 The amount of catalyst ink dropped was adjusted so that the drop amount was within the range of 1. In this way, an electrode (working electrode) for evaluating catalytic activity was prepared, in which a thin film of alloy particles according to each example was formed on nickel foam.

[0094] (4-2) Construction of evaluation cell Here, a three-electrode electrochemical cell (hereinafter referred to as "evaluation cell") was constructed in which a working electrode, a counter electrode, and a reference electrode were immersed in an aqueous electrolyte. Specifically, the evaluation electrode prepared above was used as the working electrode. The counter electrode had an area of ​​18 cm. 2 A platinum (Pt) substrate was used. A mercury-mercury oxide (Hg / HgO) reference electrode was used. 1 mol / L KOH was used as the aqueous electrolyte.

[0095] (4-3)LSV analysis Next, the electrochemical cell configured as described above was subjected to linear sweep voltammetry (LSV) analysis to measure the overpotential in the OER activity. Specifically, in this test, the electrolytic cell was first purged with nitrogen gas for 30 minutes to create an inert atmosphere. Then, the aqueous electrolyte was decomposed while changing the potential of the working electrode from 0.68 V to 0.08 V at a sweep rate of 10 mV / s, and a polarization curve was measured. The current density was normalized to the geometric area, and the measured potential was calculated as the reversible hydrogen electrode potential (E RHE ) and the current density was 10 mA / cm 2 When E reaches RHE The value was taken as the potential required for the electrolysis of water (in other words, the potential at which the decomposition of the aqueous electrolyte solution begins). The theoretical potential of the decomposition reaction calculated based on thermodynamics (equilibrium electrode potential E e ) was set to 1.23 V, and the overvoltage η (mV) was calculated based on the following formula (IV). Note that a smaller overvoltage value indicates higher catalytic performance. The results are shown in Table 2. E RHE =0.917V+E Hg / HgO (III) η=E RHE -1.23V (IV)

[0096] [Table 2]

[0097] As shown in Table 2 above, Examples 1 and 2 have a gradient composition in which the atomic concentration of Fe gradually decreases and the atomic concentration of Ni gradually increases from the surface to the depth of the gold particles. It is presumed that iron oxide, which has excellent catalytic activity, increases toward the surface of the particles in Examples 1 and 2, and metallic Ni, which has excellent electronic conductivity, increases toward the depth. Furthermore, Examples 1 and 2 had lower overvoltage values ​​than Example 3, which did not have a gradient composition. This is presumed to be because Examples 1 and 2 have the gradient composition described above, and the rate of decrease in the atomic concentration of Fe on the particle surface and at a sputtering depth of 5.5 nm, and from the surface to a sputtering depth of 5.5 nm, is within a predetermined range, allowing electron transfer and catalytic reactions to occur smoothly throughout the particle, resulting in a significant improvement in catalytic performance.

[0098] The technology disclosed herein has been described in detail above, but these are merely examples and do not limit the scope of the claims. The technology described in the claims includes various modifications and variations of the specific examples exemplified above. In other words, the technology disclosed herein encompasses the aspects described in the following sections.

[0099] <Section 1> A catalytic material comprising alloy particles containing nickel oxide, iron oxide, and metallic nickel, The alloy particles have a gradient composition in which the atomic concentration of Fe gradually decreases and the atomic concentration of Ni gradually increases in a depth direction from the surface thereof, When the above alloy particles were measured by X-ray photoelectron spectroscopy from the surface to a sputtering depth of 5.5 nm in SiO2 equivalent in the depth direction, the atomic concentration of Fe relative to the total of Fe and Ni on the surface is 10 at % or more and 50 at % or less, the atomic concentration of Fe relative to the total of Fe and Ni at the sputtering depth of 5.5 nm is 3 at % or more and 17 at % or less, The rate of decrease in the Fe atomic concentration of the alloy particles from the surface to a sputtering depth of 5.5 nm is 0.5 at% / nm or more and 6 at% / nm or less. Catalyst materials.

[0100] <Section 2> At a sputtering depth of 3.3 nm, the atomic concentration of Fe relative to the total of Fe and Ni is 6 at% or more and 20 at% or less, Item 2. The catalyst material according to item 1, wherein the rate of decrease in the Fe atomic concentration of the alloy particles from the surface to a sputtering depth of 3.3 nm is 3 at% / nm or more and 10 at% / nm or less.

[0101] <Section 3> Item 3. The catalyst material according to item 1 or 2, wherein the mass concentration of Fe relative to the total mass of Fe and Ni in the alloy particles is 0.5 mass% or more and 5 mass% or less, as determined by inductively coupled plasma atomic emission spectrometry.

[0102] <Section 4> 4. The catalyst material according to any one of items 1 to 3, wherein the alloy particles have an average particle size of 20 nm or more and 200 nm or less, as determined by observation with a field emission scanning electron microscope.

[0103] <Section 5> 5. The catalyst material according to any one of items 1 to 4, wherein the CV value of the particle size of the alloy particles is 0.2 or less, as determined by observation with a field emission scanning electron microscope.

[0104] <Section 6> Item 6. The catalyst material according to any one of items 1 to 5, wherein the atomic concentration of Fe relative to the total of Fe and Ni on the surface is 45 at % or less.

[0105] <Section 7> Item 7. An electrode comprising the catalyst material according to any one of items 1 to 6.

[0106] <Section 8> Item 8. The electrode according to item 7, which is used as an oxygen evolution electrode.

[0107] <Section 9> an anion exchange membrane; and a catalyst layer disposed on the anion exchange membrane; A membrane electrode assembly, wherein the catalyst layer comprises the catalyst material according to any one of items 1 to 6.

[0108] <Section 10> Item 7. A water electrolysis device comprising the electrode according to item 7 or 8 or the membrane electrode assembly according to item 9. [Explanation of symbols]

[0109] 1 Alloy particles 1c center 1s surface 100 Water electrolysis equipment 110 Oxygen evolution electrode (anode) 111 First base material 112 1st catalyst layer 120 Hydrogen evolution electrode (cathode) 121 Second base material 122 2nd catalyst layer 130 Anion Exchange Membrane 140 Conductive Line 150 Power supply 162 Water supply channel 164 Oxygen recovery pipe 166 Hydrogen recovery pipe

Claims

1. A catalytic material comprising alloy particles containing nickel oxide, iron oxide, and metallic nickel, The alloy particles have a gradient composition in which the atomic concentration of Fe gradually decreases and the atomic concentration of Ni gradually increases in a depth direction from the surface thereof, SiO in the depth direction from the surface of the alloy particle ２ When the measurement was performed by X-ray photoelectron spectroscopy up to a sputtering depth of 5.5 nm in terms of conversion, the atomic concentration of Fe relative to the total of Fe and Ni on the surface is 10 at % or more and 50 at % or less, the atomic concentration of Fe relative to the total of Fe and Ni at the sputtering depth of 5.5 nm is 3 at % or more and 17 at % or less; The rate of decrease in the Fe atomic concentration of the alloy particles from the surface to a sputtering depth of 5.5 nm is 0.5 at% / nm or more and 6 at% / nm or less. Catalyst materials.

2. At a sputtering depth of 3.3 nm, the atomic concentration of Fe relative to the total of Fe and Ni is 6 at% or more and 20 at% or less, 2. The catalyst material according to claim 1, wherein the rate of decrease in the atomic concentration of Fe in the alloy particles from the surface to a sputtering depth of 3.3 nm is 3 at % / nm or more and 10 at % / nm or less.

3. 2. The catalyst material according to claim 1, wherein the mass concentration of Fe relative to the total of Fe and Ni in the alloy particles is 0.5 mass% or more and 5 mass% or less, as determined by inductively coupled plasma atomic emission spectroscopy.

4. 2. The catalyst material according to claim 1, wherein the alloy particles have an average particle size of 20 nm or more and 200 nm or less, as determined by observation with a field emission scanning electron microscope.

5. 2. The catalyst material according to claim 1, wherein the CV value of the particle size of the alloy particles is 0.2 or less, as determined by field emission scanning electron microscope observation.

6. 2. The catalytic material according to claim 1, wherein the atomic concentration of Fe relative to the total of Fe and Ni on the surface is 45 at % or less.

7. An electrode comprising the catalytic material of claim 1.

8. The electrode according to claim 7 , which is used as an oxygen evolution electrode.

9. An anion exchange membrane and a catalyst layer disposed on the anion exchange membrane, The catalyst layer comprises the catalyst material of claim 1 .

10. A water electrolysis device comprising the electrode according to claim 8 or the membrane electrode assembly according to claim 9.

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