Catalyst material and use thereof

Abstract

To provide a catalyst material with superior catalytic performance.SOLUTION: A catalyst material contains Ni particles primarily composed of Ni elements, the Ni particles also containing oxygen elements. Based on elemental analysis using inert gas fusion-non-dispersive infrared absorption spectroscopy, the content ratio of the oxygen elements to the total amount of Ni particles in the catalyst material ranges from 2 mass% to 5 mass%. X-ray photoelectron spectroscopy analysis of the Ni particle surfaces reveals that, within the Ni2p orbital region, the ratio of the peak area corresponding to metallic Ni to the total peak area of metallic Ni, NiO, and Ni(OH)2 is 20% or more and 40% or less.SELECTED DRAWING: Figure 2

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] As described above in Patent Documents 1 and 2, conventional catalytic materials often use expensive metals such as rare metals and noble metals. On the other hand, metallic nickel is inexpensive and easily available, but it does not provide sufficient catalytic activity, and there is still room for improvement before it can be used as a catalytic material.

[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 is a catalyst material containing Ni particles mainly composed of Ni element, wherein the Ni particles contain O element, and the content of O element relative to the total amount of the Ni particles contained in the catalyst material based on elemental analysis by inert gas fusion-non-dispersive infrared absorption method is 2 mass% or more and 5 mass% or less, and is characterized in that in a photoelectron spectrum of the surface of the Ni particles measured by X-ray photoelectron spectroscopy, the ratio of the peak area of ​​the metal Ni to the total peak area of ​​metal Ni, NiO, and Ni(OH)2 in the region showing the Ni 2p orbital is 20% or more and 40% or less.

[0008] According to this configuration, first, by controlling the content of O element relative to the total amount of the Ni particles within the above range, sufficient catalytic activity can be obtained from the Ni particles. Furthermore, by controlling the ratio of the peak area of ​​the Ni metal to the total peak area of ​​the Ni metal, NiO, and Ni(OH)2 on the Ni particle surface within the above range, sufficient exposure of the Ni metal on the Ni particle surface can be achieved, resulting in good electronic conductivity. This achieves both catalytic activity and electronic conductivity, making it possible to realize Ni particles with excellent catalytic performance.

[0009] In a preferred embodiment of the catalytic material disclosed herein, the Ni particles further have an oxide coating on their surfaces, which provides favorable catalytic activity.

[0010] In a preferred embodiment of the catalyst material disclosed herein, the Ni particles have an average particle size of 150 nm or less, as determined by observation with a field emission scanning electron microscope. This configuration allows for high catalytic activity to be obtained.

[0011] In a preferred embodiment of the catalyst material disclosed herein, the volume resistivity of the Ni particles obtained by uniaxial pressing at a pressure of 64 MPa is 5000 Ω cm or less. With this configuration, the catalyst performance can be favorably maintained.

[0012] In a preferred embodiment of the catalytic material disclosed herein, the Ni particles further contain Fe, which can provide more favorable catalytic activity.

[0013] In a preferred embodiment of the catalytic material disclosed herein, the mass concentration of Fe relative to the total mass of Fe and Ni is 5 mass% or less, as determined by inductively coupled plasma atomic emission spectrometry. This configuration achieves a better balance between electronic conductivity and catalytic activity.

[0014] 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.

[0015] 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.

[0016] 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.

[0017] According to another aspect of the present disclosure, there is provided 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.

[0018] Another aspect of the technology disclosed herein provides a method for producing a catalytic material containing Ni particles mainly composed of Ni element. The method includes a Ni particle preparation step of preparing the Ni particles and an oxygen addition step of adding O element to the Ni particles. This method can provide a catalytic material containing Ni particles with excellent catalytic performance.

[0019] In a preferred embodiment of the production method disclosed herein, an organic compound attachment step of attaching an organic compound to the surface of the Ni particles is further included before the oxygen addition step, thereby making it possible to suitably control the amount of O element added to the Ni particles in the oxygen addition step.

[0020] In a preferred embodiment of the production method disclosed herein, an amine-based compound is used as the organic compound, which allows for more suitable control of the addition of O elements to the surface of the Ni particles.

[0021] In a preferred embodiment of the manufacturing method disclosed herein, Ni particles containing Fe are prepared in the Ni particle preparation step, which makes it possible to obtain a catalyst material with more suitable catalytic activity. [Brief explanation of the drawings]

[0022] [Figure 1] FIG. 1 is a cross-sectional view schematically showing a water electrolysis apparatus according to this embodiment. [Figure 2] FIG. 2 is a flow diagram showing a method for producing a catalyst material (Ni particles) according to this embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0023] 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.

[0024] 1. Catalyst materials First, the catalytic material of the present disclosure will be described. The Ni particles contained in the catalytic material according to this embodiment contain O element. The catalytic material having such a configuration will be specifically described below. In this specification, "Ni particles" refers to particles whose main element is Ni. That is, the term "Ni particles" in this specification is a concept that encompasses not only particles whose entire particle is composed of Ni (single Ni particles), but also Ni alloy particles, core-shell particles, etc.

[0025] First, the term "catalyst material" in this specification refers to a powder material (a group of particles) primarily composed of Ni particles. Here, "primarily composed of Ni particles" means that, among the inorganic particles contained in the powder material, the inorganic particles that are most abundant by weight are Ni particles containing O and primarily composed of Ni. More specifically, the term "catalyst 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 Ni particles having the above-described structure. In other words, the catalyst material disclosed herein may contain inorganic particles other than Ni particles having the above-described structure, as long as the effects of the technology disclosed herein are not significantly impaired. Examples of such minor components include Ni particles that do not contain O (e.g., metallic nickel particles) and inorganic particles whose main component is another metal element (e.g., Cu particles, Au particles, Ag particles, Pd particles, Pt particles, etc.).

[0026] Furthermore, "Ni particles mainly composed of Ni element" refers to particles in which, when the total number of metal elements constituting the particles is taken as 100 mol%, 50 mol% or more (preferably 60 mol% or more, more preferably 70 mol% or more, even more preferably 80 mol% or more, and particularly preferably 90 mol% or more) is Ni element. Metal elements other than Ni that may be contained in Ni particles include gold (Au), platinum (Pt), silver (Ag), palladium (pd), copper (Cu), aluminum (Al), zinc (Zn), lithium (Li), sodium (Na), potassium (K), magnesium (Mg), calcium (Ca), and barium (Ba). In addition to metal elements, Ni particles may also contain elements essential for production, such as carbon (C), nitrogen (N), sulfur (S), and phosphorus (P).

[0027] "Core-shell particles" are particles with a multilayer structure comprising a core particle and a shell covering the surface of the core particle. When core-shell particles are used as Ni particles, a shell containing Ni element is formed. On the other hand, examples of core particles include Cu particles, Au particles, Pt particles, Ag particles, and Pd particles. Forming a Ni shell on the surface of these core particles stabilizes particle size control during Ni particle production. Therefore, since a large amount of particles can be produced while maintaining a small particle diameter, such core-shell particles can be used as Ni particles from the perspective of improving productivity. Among the above core particles, Cu particles are preferred from the perspective of obtaining Ni particles at low material costs while suppressing a decrease in electronic conductivity. The shell need not completely cover the entire core particle as long as it covers at least a portion of the surface of the core particle. For example, core-shell particles (Ni particles) with sufficient conductivity can be obtained when the average coverage of the Ni shell based on SEM observation is 50% or more (more preferably 70% or more, even more preferably 80% or more, and particularly preferably 90% or more). The upper limit of the average coverage rate of the Ni shell may be 100% or less, 99% or less, or 95% or less.

[0028] The content of oxygen (O) in the Ni particles in this embodiment is 2 mass% or more (more preferably 2.5 mass% or more, even more preferably 2.7 mass% or more, and particularly preferably 3.0 mass% or more) relative to the total amount of Ni particles. The oxygen is typically thought to be derived from nickel oxide. Nickel oxide has excellent catalytic activity. Therefore, Ni particles containing a large amount of oxygen tend to have excellent catalytic activity. On the other hand, because nickel oxide has low electronic conductivity, if the O content becomes too high (for example, exceeds 5 mass%), the electrical conductivity of the Ni particles as a whole may decrease. Furthermore, metallic nickel has excellent electronic conductivity. Therefore, the upper limit of the oxygen (O) content in the Ni particles in this embodiment is 5 mass% or less (more preferably 4.5 mass% or less, even more preferably 4.0 mass% or less, and particularly preferably 3.5 mass% or less) relative to the total amount of Ni particles. This achieves a balance between electronic conductivity and catalytic activity. The oxygen element is preferably present as an oxide on the Ni surface. In other words, it is preferable that the surface of the Ni particles further comprises an oxide film. According to this configuration, as described above, a layer with excellent catalytic activity is disposed on the surface of the Ni particles. This more favorably achieves catalytic activity of the Ni particles. In this specification, the "oxygen element content" refers to the weight ratio, where the weight of all metal elements constituting the Ni particles is 100%, and is measured based on elemental analysis using inert gas fusion-non-dispersive infrared absorption spectroscopy. In this specification, the "nickel oxide" includes compounds containing Ni and O, such as NiO, Ni(OH)2, and NiOOH. In addition, the nickel oxide may be in an amorphous state containing Ni and O.

[0029] The surface properties of the Ni particles in this embodiment can be measured by X-ray photoelectron spectroscopy (XPS). The Ni particles of the present disclosure are characterized in that, in the photoelectron spectrum of the Ni particles measured by XPS, the ratio of the Ni peak area to the total peak area of ​​Ni, NiO, and Ni(OH)2 in the region showing the Ni 2p orbital is 20% or more (more preferably 22% or more, even more preferably 25% or more, particularly preferably 27% or more) and 40% or less (more preferably 38% or less, even more preferably 35% or less, particularly preferably 33% or less). This Ni peak area ratio indicates the proportion of Ni (metallic nickel) present on the surface of the Ni particles and indicates the presence of regions on the Ni particle surface where metallic Ni is exposed. If the Ni peak area ratio is too low (e.g., less than 20%), the proportion of metallic nickel present on the Ni particle surface will be small, and sufficient electronic conductivity will not be obtained. On the other hand, if the ratio of the Ni peak area is too high (for example, exceeding 40%), the proportion of nickel oxide present on the Ni particle surface will decrease, which may result in a decrease in catalytic activity. Therefore, by ensuring that the ratio of the Ni peak area satisfies the above range, Ni particles that achieve a balance between electronic conductivity and catalytic activity can be obtained.

[0030] In this specification, the "ratio of the Ni peak area to the total peak area of ​​Ni, NiO, and Ni(OH)2" can be specifically obtained as follows. Specifically, first, a photoelectron spectrum of Ni particles is obtained using XPS. From the obtained photoelectron spectrum, a region of 845 to 875 eV, which indicates the Ni 2p orbital, is separated. In this region, peaks derived from components that constitute the surface of the Ni particles are confirmed. From the separated region, the peak PA derived from Ni is Ni The peak areas of the peaks attributable to Ni (852.2 eV), NiO (854.3 eV), and Ni(OH)2 (855.6 eV) are measured. Next, the total peak area PA of Ni, NiO, and Ni(OH)2 is calculated from these peak areas. allThen, using this total peak area, the ratio of the peak area of ​​Ni to the total peak area of ​​Ni, NiO, and Ni(OH)2 (PA Ni / PA all In this specification, the "surface of the Ni particle" refers to the escape depth region (the layer closest to the surface) of light excited by soft X-rays when the Ni particle is analyzed by X-ray photoelectron spectroscopy (XPS) described below without being subjected to sputtering treatment.

[0031] The average particle size of Ni particles based on FE-SEM observation is preferably 150 nm or less, more preferably 100 nm or less, and even more preferably 80 nm or less. By using Ni particles with a small average particle size, the surface activity of the Ni particles is increased, thereby achieving high catalytic activity. On the other hand, the lower limit of the average particle size of Ni particles is not particularly limited, but from the viewpoints of productivity and handling, it is preferably 10 nm or more, more preferably 30 nm or more. In this specification, the "average particle size based on FE-SEM image" refers to the cumulative 50% particle size (D) based on the number in the particle size distribution of 1,000 Ni particles extracted from an image of Ni particles taken using a field emission scanning electron microscope (FE-SEM). 50 ) is shown.

[0032] The CV value (coefficient of variation) of the Ni particles is not particularly limited, but is preferably 0.2 or less, more preferably 0.18 or less, and particularly preferably 0.15 or less. In this specification, "CV value" refers to the ratio of the standard deviation σ to the average particle diameter of the Ni particles calculated above (standard deviation σ / average particle diameter). In other words, the smaller the CV value, the more uniform the particles. Therefore, Ni particles with a small CV value (in other words, uniform particles) can suppress a decrease in catalytic activity due to large coarse particles or secondary particles formed by aggregation of multiple fine particles. In addition, adhesion to electrodes and ion exchange membranes is improved, allowing for a smooth catalytic layer to be obtained.

[0033] The crystal structure of the Ni particles of this embodiment is preferably fcc (face-centered cubic) and / or hcp (hexagonal close-packed) from the viewpoint of stability, etc. The crystal structure of the Ni particles can be confirmed by peak analysis based on, for example, X-ray diffraction (XRD).

[0034] The shape of the Ni particles is not particularly limited and may be spherical or non-spherical. Examples of non-spherical Ni particles include plate-like, scale-like, flake-like, and irregularly shaped particles. When spherical Ni particles are used, the aspect ratio of the Ni particles is preferably 1.2 or less, more preferably 1.15 or less, and particularly preferably 1.1 or less. This facilitates an improvement in the packing density of the Ni particles during the formation of the catalyst layer. The lower limit of the aspect ratio of such spherical Ni particles is 1 or more. On the other hand, when non-spherical Ni particles are used, the aspect ratio of the Ni particles is preferably 1.3 or more, more preferably 1.5 or more, even more preferably 1.7 or more, and particularly preferably 2 or more. When Ni particles with such a high aspect ratio are used, the specific surface area of ​​the Ni particles increases during the formation of the catalyst layer, thereby increasing the reaction surface. This improves the reaction efficiency and results in better catalytic activity. On the other hand, in consideration of the ease of particle generation, the upper limit of the aspect ratio of non-spherical Ni particles is preferably 5 or less, more preferably 4 or less, and particularly preferably 3 or less. Furthermore, the catalyst material in this embodiment may be a mixed powder in which spherical particles and non-spherical particles are mixed.

[0035] The volume resistivity of the Ni particles obtained by uniaxial pressing at a pressure of 64 MPa is preferably 5000 Ω·cm or less, more preferably 4000 Ω·cm or less, even more preferably 2000 Ω·cm or less, and particularly preferably 1000 Ω·cm or less. If the volume resistivity is too high (e.g., greater than 5000 Ω·cm), the catalytic performance of the catalyst material may be impaired when it is used. In other words, the lower the volume resistivity, the better the catalytic performance can be maintained. Note that the "volume resistivity" in this specification can be obtained by compressing Ni particles with a uniaxial press under a load of 20 kN (equivalent to 64 MPa in pressure), maintaining the pressure for a certain period of time (e.g., 5 minutes) until the pressure stabilizes, and then measuring the resistance using a four-probe method.

[0036] In some preferred embodiments, the Ni particles may further contain Fe. When the Ni particles have such a structure, the Fe may typically exist as iron oxide. Iron oxide has particularly excellent properties for catalytic activity. Therefore, when the Ni particles further contain Fe, more favorable catalytic activity can be obtained. In this specification, "iron oxide" includes compounds containing Fe and O, such as FeO, Fe3O4, Fe2O3, Fe(OH)2, Fe(OH)3, and FeOOH. The nickel oxide may also be in an amorphous state containing Ni and O.

[0037] When the Ni particles further contain Fe, the Fe mass concentration of the Ni particles can be confirmed by ICP (inductively coupled plasma) optical emission spectroscopy. Here, if the Fe mass concentration relative to the total of Fe and Ni in the Ni particles is too high (e.g., greater than 5 mass%) in ICP optical emission spectroscopy, the proportion of metallic nickel will be reduced, potentially resulting in insufficient electronic conductivity. From this perspective, the Fe mass concentration relative to the total of Fe and Ni in the Ni particles in ICP optical emission spectroscopy is preferably 5 mass% or less, more preferably 4.5 mass% or less, and even more preferably 4 mass% or less. On the other hand, when the Ni particles further contain Fe, the lower limit of the Fe mass concentration is not particularly limited, but 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. In this specification, the "mass concentration of Fe relative to the total of Fe and Ni in ICP atomic emission spectroscopy" can be determined by measuring the entire Ni particle using an ICP atomic emission spectroscopy analyzer, quantifying the content of each element of Fe and Ni, and calculating it.

[0038] The catalytic material according to this embodiment has been described above. As described above, the catalytic material according to this embodiment has excellent catalytic performance. 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.

[0039] 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 Ni particles disclosed herein. FIG. 1 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 catalytic material, and is not intended to limit the application of the technology disclosed herein.

[0040] The water electrolysis device 100 shown in FIG. 1 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.

[0041] 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.

[0042] 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.

[0043] Next, the operation of the water electrolysis device 100 will be described. First, in the water electrolysis device 100, an aqueous electrolyte solution 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 (1) below). The hydrogen gas produced at the hydrogen generating electrode 120 is then recovered 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 (2) below. The oxygen gas is then recovered 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, with this water electrolysis device 100, it is possible to convert the electricity generated by the power source 150 into oxygen gas and hydrogen gas. 4H2O+4e - →2H2+4OH - (1) 4OH - →O2+2H2O+4e - (2)

[0044] 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.

[0045] 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 - ) becomes easier to move.

[0046] 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.

[0047] 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.

[0048] 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."

[0049] 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.

[0050] The first catalyst layer 112 is a layer containing an oxidation catalyst that generates water and oxygen, as shown in the above formula (2). Here, by including the catalyst material (Ni 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.

[0051] 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.

[0052] 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.

[0053] 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.

[0054] 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.

[0055] 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.

[0056] 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.

[0057] 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.

[0058] 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 (Ni particles) according to this embodiment is dispersed in an organic solvent to prepare an electrode printing paste. In addition to the Ni particles, the electrode printing paste may further contain, for example, the above-mentioned ion-conductive resin and dispersant.

[0059] 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.

[0060] 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.

[0061] 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. 1 ). 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.

[0062] 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.

[0063] 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.

[0064] 7. Manufacturing method of catalyst material (Ni particles) A method for producing a catalyst material (Ni particles) according to this embodiment will be described below. FIG. 2 is a flow diagram showing a method for producing a catalyst material (Ni particles) according to this embodiment. As shown in FIG. 2, the production method according to this embodiment includes a Ni particle preparation step S10 and an oxygen addition step S30. Furthermore, in the production method according to this embodiment, an organic compound attachment step S20 is carried out between the Ni particle preparation step S10 and the oxygen addition step S30. Each step will be described below.

[0065] (1)Ni particle preparation step S10 In the Ni particle preparation step S10, Ni particles are prepared. For example, Ni particles can be generated by a thermal decomposition method in which a Ni salt is added to an organic solvent to generate a Ni complex, followed by heat treatment to precipitate the Ni particles. Note that the Ni particle preparation step S10 in the technology disclosed herein does not necessarily require the Ni particles to be generated by hand; commercially available Ni particles may be purchased. In other words, the detailed procedure of the Ni particle preparation step S10 does not limit the technology disclosed herein, and conventionally known means can be used without particular restriction.

[0066] Here, the Ni particles prepared in the Ni particle preparation step S10 will be described.

[0067] Nickel particles (Ni particles) are the main component of the manufactured catalytic material. By adding O element to these Ni particles, a catalytic material with excellent catalytic performance can be produced inexpensively. The detailed structure of the Ni particles has already been explained, so a duplicate explanation will be omitted.

[0068] When generating Ni particles by thermal decomposition in the Ni particle preparation step S10, a nickel salt is used as the Ni source. Examples of nickel salts include nickel formate, nickel nitrate, nickel sulfate, nickel carbonate, nickel carboxylate, nickel hydroxide, and nickel chloride. Adding these nickel salts to an organic solvent generates a nickel complex. Heating this nickel complex produces a particle slurry in which Ni particles are dispersed in an organic solvent. When generating core-shell particles with a Ni shell by thermal decomposition, a salt of a metal element that will form the core particles can be added to the organic solvent along with the nickel salt. If the standard potential of the added metal element is higher than that of Ni, the metal element will precipitate preferentially. This allows for the formation of a Ni shell on the surface of the core particles after the core particles containing the desired metal element are generated. Examples of salts of metal elements that can generate such core particles include iron salts, copper formate, copper acetate, copper chloride, copper sulfate, copper nitrate, silver acetate, silver nitrate, silver chloride, silver oxalate, palladium chloride, chloroplatinic acid, and chloroauric acid. The salts of the metal elements can be, for example, commercially available ones, without any particular limitations. Furthermore, when Ni particles further containing Fe element are produced by a thermal decomposition method, an iron salt can be added to an organic solvent together with the nickel salt. Since the standard potential of Ni is higher than that of Fe, Ni is preferentially precipitated. This allows for the production of Ni particles further containing Fe element (specifically, Fe element is typically disposed on the surface layer of the Ni particles). Examples of such iron salts include iron chloride, iron sulfate, iron acetate, iron bromide, iron nitrate, iron carbonate, and iron sulfide. Iron salts may be anhydrous or hydrated. Among these, iron chloride is preferably used because its decomposition temperature is relatively close to that of nickel carboxylate.

[0069] The organic solvent is not particularly limited as long as it is one that is conventionally used for producing Ni particles, but when producing Ni particles by a thermal decomposition method, it is preferable to use an organic solvent that forms a nickel complex when dissolving a nickel salt. Examples of such organic solvents include amine compounds such as n-octylamine, 2-ethylhexylamine, n-decylamine, n-dodecylamine, n-tetradecylamine, n-hexadecylamine, stearylamine, and oleylamine.

[0070] When Ni particles are generated by a pyrolysis method, the Ni particles can be separated from the particle slurry after particle generation. This allows the Ni particles of this embodiment to be prepared. Note that the separation method can be any conventional separation method used to separate powder from a slurry, without any particular restrictions. Examples of such separation methods include static separation, centrifugation, and filtration. The Ni particles separated from the particle slurry can be washed with a predetermined cleaning medium. This washing method preferably involves dispersing the separated Ni particles in a liquid cleaning medium and then separating the Ni particles from the cleaning medium again. Note that this separation is not essential. Depending on the type of organic solvent used in the particle slurry and the subsequent implementation, the particle slurry after the Ni particle preparation step S10 can also be directly subjected to the organic compound attachment step S20 or the oxygen addition step S30.

[0071] (2) Organic Compound Adhesion Step S20 In some preferred embodiments, the organic compound attachment step S20 can be performed before the oxygen addition step S30. In the organic compound attachment step S20, an organic compound is attached (typically adsorbed) to the surface of Ni particles. More specifically, in the organic compound attachment step S20, Ni particles are dispersed in the organic compound and then heated to attach the organic compound to the Ni particles. The organic compound attached to the particle surface prevents the surface of the Ni particles from being excessively oxidized (in other words, from adding too much O element). This allows for optimal control of the amount of O element added to the Ni particles in the oxygen addition step S30. Note that the organic compound attachment step S20 is not an essential step in the manufacturing method disclosed herein. The oxygen addition step S30 may be performed on Ni particles prepared in the Ni particle preparation step S10. In this case, O element can still be added to the Ni particles.

[0072] The organic compound used in the organic compound attachment step S20 may be, for example, a carboxylic acid or an amine-based compound. Examples of the carboxylic acid include n-octanoic acid, 2-ethylhexanoic acid, n-decanoic acid, n-dodecanoic acid, n-tetradecanoic acid, n-hexadecanoic acid, stearic acid, and oleic acid. Among these, amine-based compounds are preferred as the organic compound, as they can more effectively control the addition of O elements to the surfaces of the Ni particles.

[0073] The type of amine compound is not particularly limited, and examples thereof include primary amines such as pentylamine, hexylamine, heptylamine, octylamine, nonylamine, decylamine, undecylamine, dodecylamine (laurylamine), tridecylamine, tetradecylamine, pentadecylamine, hexadecylamine, stearylamine, oleylamine, nonadecylamine, and eicosylamine; secondary amines such as dibutylamine, dipentylamine, dihexylamine, diheptylamine, dioctylamine, dinonylamine, and didecylamine; and tertiary amines such as triethylamine, tripropylamine, tributylamine, tripentylamine, trihexylamine, triheptylamine, trioctylamine, trinonylamine, and tridecylamine; and the like. One type may be used alone, or two or more types may be used in appropriate combination. Among these, from the viewpoint of more suitably controlling the adsorption force to the Ni particle surface and the addition of O element to the Ni particle surface, it is preferable to use a primary amine or a secondary amine, and it is more preferable to use a primary amine. Among primary amines, from the viewpoint of more suitably controlling the addition of O element, oleylamine (C 18 H 37 It is preferable to use octylamine (CH3(CH2)7NH2) or octylamine (CH3(CH2)7NH2), and it is more preferable to use octylamine.

[0074] Furthermore, it is preferable that the organic compound be added at a certain ratio or more relative to the weight of the Ni particles to be treated. For example, the amount of organic compound added relative to the weight (100%) of the Ni particles is preferably 100% or more (more preferably 120% or more, even more preferably 140% or more, and particularly preferably 150% or more). This allows a sufficient amount of organic compound to adhere to the surfaces of the Ni particles. On the other hand, from the viewpoint of productivity, it is preferable that the amount of organic compound added relative to the weight of the Ni particles is 200% or less (more preferably 190% or less, even more preferably 180% or less, and particularly preferably 170% or less).

[0075] Furthermore, the heating temperature in the organic compound attachment step S20 is preferably 50°C or higher, more preferably 80°C or higher, and particularly preferably 100°C or higher. Heat treatment at a temperature above the melting point of the organic compound facilitates attachment of the organic compound to the surface of the Ni particles. Meanwhile, the heating temperature in this step is preferably 200°C or lower, more preferably 180°C or lower, and particularly preferably 150°C or lower. This prevents decomposition and vaporization of the organic compound. Furthermore, the heating time is preferably 30 minutes or longer, more preferably 60 minutes or longer, and particularly preferably 90 minutes or longer. This ensures sufficient time for the organic compound to attach. Meanwhile, the heating time is preferably 210 minutes or shorter, more preferably 180 minutes or shorter, and particularly preferably 150 minutes or shorter. This prevents a decrease in manufacturing efficiency due to a prolonged organic compound attachment step S20.

[0076] Furthermore, the heat treatment in the organic compound adhesion step S20 is preferably carried out in an inert atmosphere (e.g., N2 gas, etc.), which allows for suitable control of the amount of O element added to the Ni particles in the subsequent oxygen addition step S30.

[0077] By carrying out the organic compound attachment step S20, an organic compound can be attached to the surface of the manufactured Ni particles. Such an organic compound functions as a protective agent that protects the surface of the Ni particles. More specifically, it has the effect of suppressing further addition of O elements (typically, the progress of oxidation) to the surface of the manufactured Ni particles. This makes it possible to control the content of O elements on the surface of the Ni particles within a suitable range. Such organic compounds can be analyzed, for example, by GC-MS (gas chromatography-mass spectrometry). The detailed composition of the organic compound has already been explained, so a repeated explanation will be omitted.

[0078] (3) Oxygen addition step S30 In the oxygen addition step S30, O (oxygen) elements are added to the Ni particles. This allows the catalyst material according to this embodiment to be obtained. The method for adding O elements in the oxygen addition step S30 is not particularly limited, and various methods can be used. Several examples of the oxygen addition step S30 will be described below, but the present invention is not limited to these examples.

[0079] For example, the oxygen addition step S30 can employ a method in which a Ni particle slurry in which Ni particles are dispersed in a solvent is heated while bubbling oxygen gas. More specifically, the Ni particle slurry is heated at a predetermined temperature for a predetermined time while bubbling oxygen gas, and then the Ni particles are recovered from the Ni slurry. This allows O elements to be added to the Ni particles.

[0080] When heating the Ni particle slurry while bubbling oxygen gas, the heating temperature is preferably 100°C or higher, more preferably 150°C or higher. This allows the O element to be suitably added to the Ni particles. On the other hand, from the viewpoint of preventing excessive addition of the O element to the Ni particles (excessive oxidation), the heating temperature in this step is preferably 300°C or lower, more preferably 250°C or lower. Furthermore, the heating time is not particularly limited as it can be changed appropriately depending on the amount of oxygen gas supplied, etc., but can be, for example, 5 minutes or higher, preferably 10 minutes or higher. On the other hand, the upper limit of the heating time is not particularly limited, but can be, for example, 60 minutes or lower, preferably 30 minutes or lower.

[0081] The organic solvent used for the Ni slurry is not particularly limited, and examples of suitable solvents include low-polarity solvents such as ethylene glycol, alcohols, amine compounds, N,N-dimethylformamide, dimethyl sulfoxide, and acetone. The Ni slurry preferably contains Ni particles in a predetermined range relative to the organic solvent. Specifically, dispersing a certain amount of Ni particles in the organic solvent allows the oxygenation step S30 to be carried out efficiently. From this perspective, the Ni particle content, relative to the weight (g) of the organic solvent as 100%, is preferably 0.5% or more, more preferably 1% or more, and particularly preferably 5% or more. On the other hand, if the Ni particle content is too high, the Ni particles may not be adequately dispersed in the organic solvent, potentially resulting in an uneven reaction in the oxygenation step S30. From this perspective, the upper limit of the Ni particle content is preferably 30% or less, more preferably 25% or less, and particularly preferably 20% or less.

[0082] When Ni particles are prepared in the Ni particle preparation step S10 by a thermal decomposition method, the Ni particles are dispersed in an organic solvent, and therefore the Ni slurry may be directly subjected to the oxygen addition step S30. Similarly, when the organic compound attachment step S20 is performed, the Ni particles are dispersed in an organic solvent, and therefore the Ni slurry may be directly subjected to the oxygen addition step S30.

[0083] The oxygen gas supply rate during bubbling was 100 cm per 1 L of Ni slurry. 3 / min or more is preferable, and 200cm 3 / min or more is preferable, and 300cm 3 / min or more is particularly preferable. This allows the amount of oxygen added to the Ni particles to be appropriately controlled. On the other hand, the upper limit of the supply amount of oxygen gas is not particularly limited, and is preferably 5000 cm3 / L of Ni slurry. 3 / min or less is also acceptable, and 3000cm 3 / min or less is also acceptable, and 1000cm 3 / min or less is also acceptable.

[0084] Alternatively, the oxygen addition step S30 may employ a method of mixing Ni particles with an oxidizing agent solution. Specifically, the Ni particles and the oxidizing agent solution are mixed for a predetermined time, and then the Ni particles are collected from the mixture. This method also allows O to be added to the Ni particles.

[0085] When Ni particles are mixed with an oxidant solution, the oxidant solution may be, for example, an aqueous solution of nitric acid, an aqueous solution of hypochlorous acid, or an aqueous solution of hydrogen peroxide. The concentration of the oxidant solution is not particularly limited and can be changed appropriately depending on the oxidant solution used, but is preferably 0.1% or more, and more preferably 0.5% or more.

[0086] When mixing Ni particles with an oxidant solution, the mixing time is not particularly limited because it can be changed appropriately depending on the oxidant solution used, etc., but it can be, for example, 5 minutes or more, preferably 10 minutes or more. On the other hand, the upper limit of the mixing time is not particularly limited, but from the viewpoint of production efficiency, it can be, for example, 60 minutes or less, preferably 30 minutes or less.

[0087] When mixing Ni particles with an oxidant solution, it is preferable to perform the process while irradiating with ultrasonic waves. According to this embodiment, aggregation of Ni particles in the solution can be suppressed, and the aggregated Ni particles can be prevented from becoming linked particles when growing an oxide film. Furthermore, when mixing Ni particles with an oxidant solution, it is preferable to perform the process while stirring. According to this embodiment, the oxidant solution and Ni particles are in good contact with each other, so that O element can be added to the Ni particles in a good manner. For such stirring, any conventionally known device can be used without any restrictions.

[0088] The oxygen-adding step S30 may be performed in any manner other than as described above. For example, the oxygen-adding step S30 may involve mixing Ni particles with an alkaline solution and heating the mixture. Alternatively, dried Ni particles may be heated in the atmosphere. Even in such a method, O elements can be added to the Ni particles.

[0089] In the oxygen addition step S30, it is preferable to add O element to the Ni particles so that the content of O element relative to the total amount of Ni particles is 2 mass% or more (more preferably 2.5 mass% or more, even more preferably 2.7 mass% or more, particularly preferably 3.0 mass% or more) and 5 mass% or less (more preferably 4.5 mass% or less, even more preferably 4.0 mass% or less, particularly preferably 3.5 mass% or less). The amount of O element added can be controlled by adjusting various conditions depending on the method performed in the oxygen addition step S30.

[0090] 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.

[0091] [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.

[0092] 1. Sample Preparation In this test example, 12 types of samples (Examples 1 to 12) were prepared using different manufacturing methods. The manufacturing procedures for each sample are described below.

[0093] (Example 1) <Preparation of precursor solution> A precursor solution was obtained by mixing 6.64 g of nickel acetate tetrahydrate and 159.6 g of oleylamine in a reaction vessel (three-neck flask).

[0094] (Synthesis of Ni particles) Nitrogen gas (2 L / min) was flowed into the reaction vessel containing the precursor solution to create an inert atmosphere. Under a nitrogen atmosphere, the temperature in the reaction vessel was raised to 135°C and heated for 1 hour to promote the dehydration process. The temperature in the reaction vessel was then raised to 230°C and heated for another hour or more to allow Ni particles to grow. Heating was then stopped and the vessel was allowed to cool naturally to room temperature. The temperature in the reaction vessel was then raised to 200°C under a nitrogen atmosphere and heated for 30 minutes. This resulted in a particle slurry in which Ni particles were dispersed in oleylamine. A magnet was placed near the bottom of the reaction vessel containing the particle slurry, and the Ni particles were attracted by the magnetic force, causing them to settle. The supernatant liquid in the particle slurry was then removed. A concentrated slurry was thus obtained.

[0095] <Cleaning> 5 g of the concentrated slurry was mixed with 5 g of ethanol as a cleaning solvent and stirred while irradiating with ultrasound in an ultrasonic cleaner to disperse the Ni particles. A magnet was then placed near the bottom of the reaction vessel, magnetically attracting the particles in the slurry, causing the Ni particles to settle, and the supernatant was removed. The Ni particles were washed by repeating the above process three times.

[0096] <Drying> The washed Ni particles were dried in a dryer at 120° C. for 1 hour, and then crushed in an agate mortar to obtain Ni particles for evaluation according to Example 1.

[0097] (Example 2) In Example 2, the synthesis of Ni particles was carried out in the same manner as in Example 1 up to the step of natural cooling. After natural cooling, the temperature in the reaction vessel was raised to 200°C in a nitrogen atmosphere and heated for 30 minutes. Then, while the temperature in the reaction vessel was maintained at 200°C, oxygen gas was introduced at a rate of 500 cm. 3 Heating was continued for another 30 minutes while bubbling at 1 / min. Except for this, the procedure was the same as in Example 1. In this way, Ni particles for evaluation according to Example 2 were obtained.

[0098] (Example 3) In Example 3, acetone was used instead of ethanol as the washing solvent for the Ni particles when washing them. After washing the Ni particles, a mixed solution of 0.10 g of 60% aqueous nitric acid solution and 15 g of acetone was added to the particles, and the mixture was stirred for 5 minutes while irradiating with ultrasound. The particles were then washed three times with acetone. After washing, the particles were dried in a vacuum oven at 60°C for 1 hour. The rest of the procedure was the same as in Example 1. In this way, Ni particles for evaluation according to Example 3 were obtained.

[0099] (Example 4) In Example 4, the procedure was the same as in Example 3, except that after washing the particles, the mixed solution added to the particles was changed to a mixed solution of 0.40 g of a 60% aqueous nitric acid solution and 15 g of acetone, thereby obtaining Ni particles for evaluation according to Example 4.

[0100] (Example 5) In Example 5, commercially available nickel powder (manufactured by Sigma-Aldrich) was used as the particles according to Example 5 and was subjected to the following evaluation.

[0101] (Example 6) In Example 6, commercially available nickel oxide powder (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) was used as the particles according to Example 6 and was subjected to the following evaluation.

[0102] (Example 7) In Example 7, the procedure was the same as in Example 3, except that a precursor solution was obtained using 159.6 g of octylamine instead of oleylamine. In this way, Ni particles for evaluation according to Example 7 were obtained.

[0103] (Example 8) In Example 8, the procedure was the same as in Example 4, except that a precursor solution was obtained using 159.6 g of octylamine instead of oleylamine. In this way, Ni particles for evaluation according to Example 8 were obtained.

[0104] (Example 9) In Example 9, the commercially available nickel oxide powder prepared in Example 6 was treated in the same manner as in Example 3. That is, after washing the commercially available nickel oxide powder, a mixed solution of 0.10 g of 60% aqueous nitric acid solution and 15 g of acetone was added to the particles, and the mixture was stirred for 5 minutes while irradiating with ultrasonic waves. The particles were then washed three times with acetone. After washing, the particles were dried in a vacuum oven at 60°C for 1 hour. In this way, Ni particles for evaluation according to Example 9 were obtained.

[0105] (Example 10) In Example 10, the procedure was the same as in Example 9, except that after the particles were washed, the mixed solution added to the particles was changed to a mixed solution of 0.40 g of a 60% aqueous nitric acid solution and 15 g of acetone. In this way, Ni particles for evaluation according to Example 10 were obtained.

[0106] (Example 11) 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 in a three-neck flask. A nitrogen gas flow (2 L / min) was introduced into the reaction vessel containing the precursor solution to create 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 to promote the dehydration process. The temperature inside the reaction vessel was then raised to 230°C and heated for an additional hour or more to promote particle growth. The heating was then stopped and the mixture was allowed to cool naturally to room temperature. Subsequent treatment was the same as in Example 1. As a result, Ni particles for evaluation according to Example 11, with Fe elements attached to the Ni particle surface, were obtained.

[0107] (Example 12) Example 12 was the same as Example 11, except that the weight of nickel acetate tetrahydrate was changed to 6.41 g and the weight of iron chloride tetrahydrate was changed to 0.21 g. As a result, particles according to Example 12 in which Fe elements were attached to the surfaces of the Ni particles were obtained.

[0108] 2. Evaluation (1) Measurement of average particle size and CV value The Ni particles of each example were photographed using an FE-SEM (SU8230, manufactured by Hitachi High-Technologies Corporation). 1,000 particles whose entire peripheries 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 1.

[0109] (2) Measurement of O element content For each Ni particle, the O element content (mass%) was measured using an oxygen / nitrogen analyzer (Horiba, Ltd., Model: EMGA-930) based on inert gas fusion non-dispersive infrared absorption (NDIR). The sample weight was 0.01 g. The results are shown in the "O element content" section of Table 1.

[0110] (3)XPS analysis Here, XPS analysis was performed to evaluate the surface composition of the Ni particles according to each example. First, an indium wire was pressed onto aluminum foil, and the nickel powder of each example was sprinkled on the indium and pressed again to create a sample for XPS analysis. Then, a photoelectron spectrum was obtained from the analysis sample in a narrow scan from 845 to 870 eV using a photoelectron spectrometer (manufactured by ULVAC-PHI, Model: XPS PHI5000 VersaProbe). The measurement conditions are as follows: X-ray source: Monochromatic Al-Kα Tube voltage: 15kV Output: 200W Neutralization gun: Not used Pass energy: 11.75 eV Step: 0.1 eV Capture time: 200ms Accumulation count: 30 times

[0111] From the photoelectron spectrum obtained above, the region of 845 to 875 eV, which indicates the Ni 2p orbital, was separated. From this separated region, the peak PA originating from Ni was observed. NiThe peak areas of the peaks attributable to Ni (852.2 eV), NiO (854.3 eV), and Ni(OH)2 (855.6 eV) were measured. Next, the total peak area PA of Ni, NiO, and Ni(OH)2 was calculated from these peak areas. all Then, using this total peak area, the ratio of the peak area of ​​Ni to the total peak area of ​​Ni, NiO, and Ni(OH)2 (PA Ni / PA all × 100) was calculated. The results are shown in the "Metal Ni Peak Area Ratio" section of Table 1.

[0112] (4)GC-MS analysis Here, to analyze the organic matter attached to the surface of the Ni particles according to each example, analysis was performed using GC-MS (gas chromatography mass spectrometry). Specifically, the Ni particles according to each example were heated at 300°C to gasify the organic matter attached to the surface, and the gasified organic matter was analyzed using a GC-MS device (Shimadzu Corporation, GCMS-QP-2010Ultra). The results are shown in Table 1.

[0113] (5)ICP analysis Here, ICP analysis was performed to evaluate the Fe mass concentration of the Ni particles according to Examples 11 and 12. Specifically, 0.1 g of the Ni particles according to Examples 11 and 12 was dissolved in an acidic solution to prepare a sample for ICP analysis. The mass concentration (mass%) of Fe in the Ni particles of each example was measured using an ICP measurement device (Agilent, 5800 ICP-OES). The results are shown in the "Fe mass concentration" section of Table 1.

[0114] (6) Conductivity evaluation Here, the volume resistivity was measured to evaluate the conductivity of the Ni particles according to each example. Specifically, the Ni particles according to each example were filled into a sample section, and a load of 20 kN (equivalent to 64 MPa in pressure) was applied using a uniaxial press to compress the Ni particles. After applying pressure, the pressure was maintained for 5 minutes until it stabilized, and then the volume resistivity (Ω·cm) was measured. This measurement was performed using a powder resistivity measurement system (MCP-PD51, manufactured by Mitsubishi Chemical Analytech Co., Ltd.) with a four-point probe method. The resistivity meter used was a low resistivity meter Loresta GX (MCP-T700, manufactured by Mitsubishi Chemical Analytech Co., Ltd.). The results are shown in Table 1. The particles according to Example 6 had a volume resistivity below the measurement limit (1.0 × 10 7 Since the resistance exceeded the value of Ω·cm and was therefore unmeasurable, it is shown in Table 1 as "excessive."

[0115] (7) Electrode performance evaluation Here, in order to evaluate the electrode performance of the Ni particles according to each example, the overpotential in the oxygen evolution reaction (OER) was measured.

[0116] (7-1) Preparation of electrodes for evaluation First, an electrode for evaluation was prepared as a sample for catalytic activity evaluation. Specifically, 1.11 g of ethanol (99.5%), 90 mg of Ni 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 it was within the range of

[0045] In this way, an electrode (working electrode) for evaluating catalytic activity was produced, in which a thin film of Ni particles according to each example was formed on the nickel foam.

[0117] (7-2) 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 The substrate was made of platinum (Pt). The reference electrode was a mercury-mercury oxide (Hg / HgO) reference electrode. 1 mol / L KOH was used as the aqueous electrolyte.

[0118] (7-3)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 (II). The smaller the overvoltage value, the higher the catalytic performance. The results are shown in Table 1. In addition, if the overvoltage was 0.40 V or less, it was marked as "Good", and if it was more than 0.40 V, it was marked as "Poor", and these are shown in the "Evaluation" section of Table 1. E RHE =0.917V+E Hg / HgO (I) η=E RHE -1.23V (II)

[0119] [Table 1]

[0120] As shown in Table 1, Examples 1-3, 7-8, and 11-12, in which the oxygen content was controlled to between 2 and 5 mass% and the peak area ratio of metallic Ni on the Ni particle surface was controlled to between 20 and 40%, all achieved low volume resistivities and good overvoltage results. Example 5, which used commercially available metallic Ni particles, had a volume resistivity of 230 Ω·cm, but a high overvoltage of 0.56 V, resulting in poor catalytic activity. This is because metallic Ni has high electronic conductivity, resulting in low resistivity, but the absence of sufficient oxygen leads to low catalytic activity. This is thought to be why sufficient catalytic performance was not achieved. On the other hand, Example 6, which used commercially available nickel oxide powder, also had a high overvoltage of 0.56 V, resulting in poor catalytic activity. This is thought to be because the low electrical conductivity of nickel oxide resulted in a very high volume resistivity, which in turn impaired catalytic performance and increased overvoltage. From the above, it was found that good catalytic performance can be obtained by using Ni particles in which the content of O element and the ratio of the peak area of ​​metallic Ni on the Ni particle surface are controlled within a suitable range.

[0121] Next, good overpotential results were also obtained for Examples 11 and 12, which contained elemental Fe. This is presumably because in Examples 11 and 12, the Fe present on the surface of the Ni particles was present on the Ni particles as iron oxide with good catalytic activity due to the O addition process.

[0122] Comparing Examples 3 and 7 and Examples 4 and 8, respectively, we found that, despite the same oxidation conditions except for whether the attached organic compound was octylamine or oleylamine, Examples 7 and 8, in which octylamine was attached to the Ni particle surface, achieved better results in terms of volume resistivity and overvoltage than Examples 3 and 4. In particular, Example 4 had a high O element content of 8.64 mass%, with a peak area ratio of metallic Ni of 13.56%, resulting in poor volume resistivity and overvoltage. While the detailed mechanism underlying these results is unclear, the present inventors speculate as follows: First, octylamine is more polar than oleylamine and therefore has a stronger adsorption force to the Ni particle surface. Furthermore, octylamine has a linear alkyl group structure, whereas oleylamine has a bent structure due to a double bond. Given this structure, octylamine is thought to adsorb more densely to the Ni particle surface, thereby favorably controlling the addition of O elements.

[0123] 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 alterations of the specific examples exemplified above. In other words, the technology disclosed herein encompasses the aspects described in the following paragraphs.

[0124] <Section 1> A catalytic material containing Ni particles mainly composed of Ni elements, The Ni particles contain an O element, the content of O element relative to the total amount of Ni particles contained in the catalyst material is 2 mass% or more and 5 mass% or less, based on elemental analysis by inert gas fusion-non-dispersive infrared absorption method, A catalytic material in which, in a photoelectron spectrum of the surface of the Ni particles measured by X-ray photoelectron spectroscopy, the ratio of the peak area of ​​the metallic Ni to the total peak area of ​​metallic Ni, NiO, and Ni(OH)2 in the region showing the Ni2p orbital is 20% or more and 40% or less.

[0125] <Section 2> Item 1. The catalytic material according to item 1, further comprising an oxide coating on the surface of the Ni particles.

[0126] <Section 3> Item 3. The catalyst material according to item 1 or 2, wherein the average particle size of the Ni particles is 150 nm or less, as determined by observation with a field emission scanning electron microscope.

[0127] <Section 4> 4. The catalyst material according to any one of items 1 to 3, wherein the Ni particles have a volume resistivity of 5000 Ω·cm or less when uniaxially pressed at a pressure of 64 MPa.

[0128] <Section 5> Item 5. The catalyst material according to any one of items 1 to 4, wherein the Ni particles further contain Fe elements.

[0129] <Section 6> Item 7. The catalyst material according to item 6, wherein the mass concentration of Fe relative to the total of Fe and Ni is 5 mass% or less, as determined by inductively coupled plasma optical emission spectroscopy.

[0130] <Section 7> Item 7. An electrode comprising the catalyst material according to any one of items 1 to 6.

[0131] <Section 8> Item 8. The electrode according to item 7, which is used as an oxygen evolution electrode.

[0132] <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.

[0133] <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.

[0134] <Section 11> A method for producing a catalyst material containing Ni particles mainly composed of Ni elements, comprising: a Ni particle preparation step of preparing the Ni particles; and an oxygen addition step of adding O element to the Ni particles. Method for producing catalytic materials.

[0135] <Section 12> Item 12. The manufacturing method according to Item 11, further comprising an organic compound attachment step of attaching an organic compound to the surface of the Ni particles before the oxygen addition step.

[0136] <Section 13> Item 13. The method according to item 12, wherein the organic compound is an amine compound.

[0137] <Section 14> Item 14. The manufacturing method according to any one of items 11 to 13, wherein in the Ni particle preparation step, Ni particles containing Fe element are prepared. [Explanation of symbols]

[0138] 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 containing Ni particles mainly composed of Ni elements, The Ni particles contain an O element, a content of O element relative to the total amount of Ni particles contained in the catalyst material, based on elemental analysis by inert gas fusion-non-dispersive infrared absorption method, being 2 mass% or more and 5 mass% or less; In the photoelectron spectrum of the Ni particle surface measured by X-ray photoelectron spectroscopy, metallic Ni, NiO, and Ni(OH) in the region showing Ni 2p orbitals ２ A catalyst material, wherein the ratio of the peak area of ​​the metal Ni to the total peak area of

2. The catalytic material of claim 1 , further comprising an oxide coating on the surface of the Ni particles.

3. 2. The catalyst material according to claim 1, wherein the average particle size of the Ni particles is 150 nm or less, as determined by observation with a field emission scanning electron microscope.

4. 2. The catalyst material according to claim 1, wherein the Ni particles have a volume resistivity of 5000 Ω·cm or less when uniaxially pressed at a pressure of 64 MPa.

5. The catalytic material of claim 1 , wherein the Ni particles further contain Fe elements.

6. 6. The catalyst material according to claim 5, wherein the mass concentration of Fe relative to the total of Fe and Ni, as determined by inductively coupled plasma atomic emission spectroscopy, is 5 mass% 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.

11. A method for producing a catalyst material containing Ni particles mainly composed of Ni elements, comprising: a Ni particle preparation step of preparing the Ni particles; and an oxygen addition step of adding O element to the Ni particles. Method for producing catalytic materials.

12. The manufacturing method according to claim 11, further comprising an organic compound attachment step of attaching an organic compound to the surface of the Ni particles before the oxygen addition step.

13. The method according to claim 12, wherein the organic compound is an amine compound.

14. The manufacturing method according to any one of claims 11 to 13, wherein in the Ni particle preparation step, Ni particles containing Fe element are prepared.

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