Method for producing electrode, and raw material and slurry for electrode used therefor

Abstract

This electrode for a water electrolysis device comprises a base material and Raney nickel supported by the base material. This method for producing an electrode involves a step for obtaining Raney nickel. The step for obtaining Raney nickel involves an alkali treatment step for eluting aluminum from a NiAl alloy with an alkali substance. In a cross section of the NiAl alloy, the proportion of the area occupied by a region with an aluminum content of 45-70 mol% is 85% or more.

Description

Method for manufacturing electrodes, and raw materials and slurries for electrodes used therein.

[0001] This disclosure relates to a method for manufacturing electrodes, and to raw materials and slurries for electrodes used therein.

[0002] Water electrolysis is the process of electrolyzing water into hydrogen and oxygen, and is used, for example, as a technology for producing hydrogen. A water electrolysis apparatus includes, for example, an electrolytic cell containing an electrolyte such as alkaline water, and an anode and a cathode arranged in the electrolytic cell with a separator in between. In such a water electrolysis apparatus, alkaline water is electrolyzed by passing an electric current between the anode and the cathode, generating oxygen at the anode and hydrogen at the cathode.

[0003] Patent document 1 (Japanese Patent Publication No. 01-028837) discloses the use of Raney nickel as the anode of a water electrolysis apparatus. Raney nickel is obtained by dissolving aluminum from a NiAl alloy containing nickel and aluminum using an alkaline substance. Numerous pores are formed in Raney nickel due to the dissolution of aluminum.

[0004] Special Publication No. 01-028837

[0005] Repeated water electrolysis can make it difficult to achieve good water electrolysis performance in a water electrolysis device.

[0006] This disclosure aims to provide a method for manufacturing an electrode that can produce an electrode with excellent durability that exhibits good water electrolysis performance in a water electrolysis apparatus even after repeated water electrolysis, as well as raw materials and slurries for the electrode used therein.

[0007] The method for manufacturing an electrode is a method for manufacturing an electrode for a water electrolysis apparatus, wherein the electrode comprises a base material and Raney nickel supported on the base material, the manufacturing method includes a step of obtaining the Raney nickel, the step of obtaining the Raney nickel includes an alkali treatment step of dissolving aluminum from the NiAl alloy with an alkaline substance, and the area occupied by the region with an aluminum content of 45 to 70 mol% in the cross-section of the NiAl alloy is 85% or more.

[0008] The electrode raw material is a raw material for an electrode in a water electrolysis device, comprising a base material, a NiAl alloy and Ni metal supported on the base material, wherein the NiAl alloy is a raw material for Raney nickel and dissolves aluminum with an alkaline substance, and the total content of Al and Ni relative to all elements contained in the NiAl alloy is 50 mol% or more, the amount of Al contained in the NiAl alloy is greater than the amount of Ni, the Ni metal may contain Al, the Ni content of the Ni metal is more than 50 mass%, and the amount of Al contained in the Ni metal is less than the amount of Ni, and the area occupied by the region with an aluminum content of 45 to 70 mol% in the cross-section of the NiAl alloy is 85% or more.

[0009] The slurry is a slurry used in the manufacture of electrodes for a water electrolysis apparatus, wherein the slurry comprises NiAl alloy powder, Ni metal powder, and a solvent, the NiAl alloy is a raw material for Raney nickel and dissolves aluminum with an alkaline substance, the total content of Al and Ni relative to all elements contained in the NiAl alloy is 50 mol% or more, the amount of Al contained in the NiAl alloy is greater than the amount of Ni, the Ni metal may contain Al, the Ni content of the Ni metal is more than 50 mass%, and the amount of Al contained in the Ni metal is less than the amount of Ni, and the area occupied by the region with an aluminum content of 45 to 70 mol% in the cross-section of the NiAl alloy is 85% or more.

[0010] According to the electrode manufacturing method, and the raw materials and slurry used therein, it is possible to obtain an electrode with excellent durability that exhibits good water electrolysis performance in a water electrolysis apparatus even after repeated water electrolysis.

[0011] This is a flowchart showing an example of a method for manufacturing an electrode according to the embodiment.

[0012] Embodiments of this disclosure will be described below with reference to the drawings. In this specification, numerical ranges such as "m to n" include upper and lower limits unless otherwise specified, and represent numerical ranges of "m or more and n or less".

[0013] <Method for Manufacturing an Electrode> Figure 1 is a flowchart showing an example of a method for manufacturing an electrode according to this embodiment. The electrode manufactured by the electrode manufacturing method of this embodiment (hereinafter also referred to as "this manufacturing method") is used in a water electrolysis apparatus. The water electrolysis apparatus is preferably an alkaline water electrolysis apparatus.

[0014] This manufacturing method is a method for manufacturing electrodes for a water electrolysis apparatus, and the electrode comprises a substrate and Raney nickel supported on the substrate. This manufacturing method includes a step of obtaining Raney nickel, and the step of obtaining Raney nickel includes an alkali treatment step of dissolving aluminum (Al) from the NiAl alloy with an alkaline substance. In the cross-section of the NiAl alloy, the area occupied by the region with an aluminum content of 45 to 70 mol% (hereinafter also referred to as the "specific Al region") is 85% or more.

[0015] The percentage of the area occupied by the specific Al region refers to the value calculated from the cross-section of the NiAl alloy that appears when a molded body in which NiAl alloy is embedded in an embedding resin is cut. More specifically, the NiAl alloy region and the specific Al region are determined from elemental mapping data obtained by observing the cross-section of this NiAl alloy using energy-dispersive X-ray spectroscopy (EDX), and the percentage of the area occupied by the specific Al region relative to the area of ​​the NiAl alloy is calculated.

[0016] This manufacturing method may include a step of obtaining an electrode. The step of obtaining an electrode may be, for example, a step of obtaining an electrode by performing a step of obtaining Raney nickel while a NiAl alloy is supported on a substrate, or a step of obtaining an electrode by supporting the Raney nickel obtained from the NiAl alloy on a substrate.

[0017] This manufacturing method may also be a method for producing electrodes by, for example, [i] obtaining a NiAl alloy, [ii] preparing a slurry containing the NiAl alloy, [iii] applying the slurry to a substrate and firing it as necessary to support the NiAl alloy on the substrate, and [iv] obtaining Raney nickel supported on the substrate by alkali treatment of the NiAl alloy supported on the substrate.

[0018] NiAl alloys can be manufactured to have multiple phases with different compositions. Even when a NiAl alloy is manufactured to have a single phase, regions with partially different compositions may be formed. In a NiAl alloy, by setting the area ratio of a specific Al region to the above range, the amount of Al dissolved by the alkali treatment process and the porosity of Raney nickel can be adjusted so that they do not become too large or too small. As a result, the decrease in strength of Raney nickel can be suppressed, durability can be improved, and Raney nickel with a large porosity and a large specific surface area can be obtained. This makes it possible to manufacture electrodes with excellent durability that exhibit good water electrolysis performance in a water electrolysis device even after repeated water electrolysis. More specifically, it is possible to obtain a cathode with excellent durability that exhibits good catalytic activity for hydrogen generation and an anode with excellent durability that exhibits good catalytic activity for oxygen generation, even after repeated water electrolysis in a water electrolysis device.

[0019] The electrodes obtained by this manufacturing method can be used as either the cathode (hydrogen generation electrode) or the anode (oxygen generation electrode) of a water electrolysis apparatus. The electrode can be, for example, the cathode.

[0020] The following details the substrate and Raney nickel contained in the electrodes, the NiAl alloy used in this manufacturing method, and each step of this manufacturing method.

[0021] (Substrate) The substrate of the electrode manufactured by this manufacturing method is a support for Raney nickel, and is, for example, a conductor. The substrate preferably contains nickel (Ni) or a Ni alloy. The substrate may be entirely made of Ni or a Ni alloy, or it may have a core layer and a surface layer, the surface layer may be made of Ni or a Ni alloy, and the core layer may be made of a material other than Ni and a Ni alloy. For example, the substrate may have a core layer of iron or stainless steel with a surface layer coated with Ni or a Ni alloy. The substrate is preferably Ni or a Ni alloy, and more preferably Ni.

[0022] The substrate may be a porous substrate or a non-porous substrate. Examples of porous substrates include perforated metal, mesh, foamed metal, and expanded metal. Examples of non-porous substrates include metal foil and metal plate. Preferably, the substrate is a porous substrate capable of supporting Raney nickel within its pores.

[0023] (Raney Nickel) Raney nickel can be used as a catalyst in the electrodes of water electrolysis devices. Raney nickel is obtained by alkali treatment, in which aluminum is leached from a NiAl alloy using an alkaline substance. Raney nickel may be a porous body obtained by alkali treatment of a NiAl alloy, as described later, or it may be a porous body with an oxidized surface obtained by oxidation treatment, in which the surface of the porous body is oxidized.

[0024] (NiAl Alloy) The NiAl alloy used in the alkali treatment step of this manufacturing method is an alloy containing Ni and Al, and may also contain elements other than Ni and Al, namely Me. The element Me is preferably a metal. Examples of element Me, excluding unavoidable impurities, include one or more selected from the group consisting of magnesium (Mg), silicon (Si), titanium (Ti), chromium (Cr), manganese (Mn), iron (Fe), cobalt (Co), copper (Cu), zirconium (Zr), niobium (Nb), molybdenum (Mo), silver (Ag), tin (Sn), platinum (Pt), iridium (Ir), and gold (Au).

[0025] Preferably, the NiAl alloy is an alloy in which the total content of Al and Ni relative to the total elements contained in the NiAl alloy is 50 mol% or more, and the amount of Al (in moles) contained in the NiAl alloy is greater than the amount of Ni (in moles). The molar ratio of Al to the total amount of Ni and Me in the NiAl alloy may be, for example, Al:(Ni+Me) = 3.00:0.80 to 3.00:2.70, Al:(Ni+Me) = 3.00:1.00 to 30:2.50, or Al:(Ni+Me) = 3.00:1.20 to 3.00:2.30. The molar ratio of Ni to Me in a NiAl alloy may be Ni:Me = 1.99:0.01 to 1.15:1.85, Ni:Me = 1.90:0.10 to 1.20:1.80, Ni:Me = 1.80:0.20 to 1.30:1.70, or Ni:Me = 1.50:0.50 to 1.40:1.60. The amount of substance (number of moles) of Me is the total amount of substance (total number of moles) of all elements Me contained in the NiAl alloy.

[0026] The NiAl alloy may be composed of a single phase or of multiple phases with different compositions, as long as the proportion of the area occupied by a specific Al region is within the range described above. The multiple phases may include, for example, at least a main phase and further include a secondary phase. The main phase is as described in NiAl alloy (I) below.

[0027] The component composition of NiAl alloy, excluding unavoidable impurities, is preferably represented by the following compositional formula (I). ３．００ Ni （２．００－ｘ） M ｘ (x is a value satisfying 0.00 < x < 1.00, and M is one or more elements selected from the group consisting of Mg, Si, Ti, Cr, Mn, Fe, Co, Cu, Zr, Nb, Mo, Ag, Sn, Pt, Ir, and Au.) (I)

[0028] The NiAl alloy represented by compositional formula (I) (hereinafter also referred to as "NiAl alloy (I)") means that the molar ratio of Al, Ni, and M in the entire alloy, excluding unavoidable impurities, is Al:Ni:M = 3.00:(2.00-x):x. If NiAl alloy (I) contains two or more types of M, the amount of M (molar amount) refers to the total amount of the two or more elements.

[0029] In empirical formula (I), x may be in the range 0.00 < x < 1.00, but may also be 0.01 ≤ x ≤ 0.99, 0.02 ≤ x ≤ 0.90, 0.03 ≤ x ≤ 0.70, 0.05 ≤ x ≤ 0.60, or 0.07 ≤ x ≤ 0.50.

[0030] NiAl alloy (I) is Al as long as the proportion of the area occupied by a specific Al region is within the above range. ３．００ Ni （２．００－ｘ） M ｘ The alloy may consist of a single phase, or it may consist of multiple phases with different compositions. The multiple phases may include, for example, at least a main phase and further include a secondary phase. In this specification, the main phase of NiAl alloy (I) means a phase that satisfies at least one of the following volume and area conditions.

[0031] Volume Condition: The main phase of NiAl alloy (I) is defined as one phase whose volume ratio exceeds 50% of the total NiAl alloy (I), or two phases whose combined volume ratio (the volume ratio of the phase with the largest volume ratio and the volume ratio of the next largest phase) exceeds 50% of the total NiAl alloy (I). The volume ratio when there is one main phase, and the combined volume ratio when there are two main phases, may be 60% or more, 70% or more, 80% or more, or 90% or more. The volume of each phase constituting NiAl alloy (I) can be calculated, for example, by performing Rietveld analysis on X-ray diffraction (XRD) measurement data of NiAl alloy (I).

[0032] Area Condition: The main phase of NiAl alloy (I) is defined as one phase whose area ratio to the entire cross-section of NiAl alloy (I) exceeds 50%, or two phases whose combined area ratio (the area ratio of the phase with the largest area ratio in any cross-section of NiAl alloy (I) plus the area ratio of the next largest phase) exceeds 50%. The arbitrary cross-section of NiAl alloy (I) may be the cross-section of NiAl alloy (I) observed in the cross-section of the molded body used to calculate the area ratio occupied by a specific Al region. The area ratio when there is one main phase, and the total area ratio when there are two main phases, may be 60% or more, 70% or more, 80% or more, or 90% or more. The area of ​​each phase in the cross-section of NiAl alloy (I) can be calculated, for example, by image analysis of elemental mapping data of the cross-section of NiAl alloy (I) obtained by scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDX).

[0033] The element M contained in NiAl alloy (I) may be one or more of the elements described above. Element M may be, for example, one or more selected from the group consisting of Fe, Co, and Cu, or it may be Fe. When element M is one or more selected from the group consisting of Fe, Co, and Cu, x may be 0.00 < x < 1.00, 0.01 ≤ x ≤ 0.99, 0.02 ≤ x ≤ 0.90, 0.03 ≤ x ≤ 0.70, 0.05 ≤ x ≤ 0.60, or 0.07 ≤ x ≤ 0.50.

[0034] NiAl alloy (I) may contain unavoidable impurities. Unavoidable impurities are impurities originating from the raw materials of NiAl alloy (I) or impurities that are inevitably introduced during the manufacturing process. Examples of unavoidable impurities include elements other than those contained in composition formula (I), such as one or more selected from the group consisting of zinc (Zn) and lead (Pb). The amount of unavoidable impurities contained in NiAl alloy (I) does not need to affect the catalytic properties of Raney nickel obtained from NiAl alloy (I).

[0035] Raney nickel obtained using NiAl alloy (I) is thought to exhibit catalytic activity by generating complex (acid) hydroxides during the operation of a water electrolysis apparatus. Complex (acid) hydroxides refer to a compound of at least two (acid) hydroxides from among Ni(O)OH, M(O)OH, and Al(O)OH. Because NiAl alloy (I) contains element M, electrodes obtained by this manufacturing method tend to generate highly active complex (acid) hydroxides during the operation of a water electrolysis apparatus and tend to exhibit high catalytic activity. If the content of element M in NiAl alloy (I) becomes too high, when used as an electrode in a water electrolysis apparatus, element M tends to dissolve as ions into the electrolyte. Ions of element M dissolved in the electrolyte can cause increased resistance due to separator clogging, and can also cause internal short circuits by depositing as metal or compounds on the electrode surface. Electrodes containing Raney nickel obtained from NiAl alloy (I) tend to suppress increased resistance and internal short circuits in water electrolysis apparatuses.

[0036] The NiAl alloy used in this manufacturing method has the specified Al region described above. The Al content in the specified Al region may be 45 to 70 mol%, but may also be 47 to 68 mol%, 50 to 65 mol%, or 52 to 63 mol%.

[0037] The proportion of the area occupied by a specific Al region in the cross-section of a NiAl alloy may be 85% or more, but may also be 87% or more, 90% or more, 92% or more, 93% or more, 94% or more, or 95% or more. The proportion of the area occupied by a specific Al region may be 85% or more and 100% or less, 87% or more and less than 100%, 90% to 99%, 92% to 98%, 93% to 98%, 94% to 97%, or 95% to 97%.

[0038] The ratio of the area occupied by the above-mentioned specific Al region can be combined with any of the ranges of the Al content in the above-mentioned specific Al region. For example, when the Al content in the specific Al region is 45 to 70 mol%, it may be 85 to 100%, may be 87% or more and less than 100%, may be 90 to 99%, may be 92 to 98%, may be 93 to 98%, may be 94 to 97%, or may be 95 to 97%. Similarly, when the Al content in the specific Al region is 46 to 68 mol%, it may be 85 to 100%, may be 87% or more and less than 100%, may be 90 to 99%, may be 92 to 98%, may be 93 to 98%, may be 94 to 97%, or may be 95 to 97%.

[0039] The ratio of the area occupied by the specific Al region can be calculated by the following procedure, and more specifically, it can be calculated by the method described in the examples. First, a molded body in which the NiAl alloy is embedded in an embedding resin is produced. The embedding resin can be the resin described in the examples described later. Next, the cross-section of this molded body is observed by EDX attached to a scanning electron microscope (SEM) to obtain elemental mapping data. In the elemental mapping data, the specific Al region among the regions of the cross-section of the NiAl alloy, the region other than the specific Al region among the regions of the cross-section of the NiAl alloy, and the region of the embedding resin are multi-valued using image analysis software (ImageJ), and the area occupied by the NiAl alloy region and the area occupied by the specific Al region in the elemental mapping data are calculated, and the ratio of the area occupied by the specific Al region to the area occupied by the NiAl alloy region is calculated.

[0040] In the step of obtaining Raney nickel, Al in the NiAl alloy is eluted by an alkali treatment step. In the NiAl alloy, in a region where the Al content is higher than that in a specific Al region, the amount of Al that can be eluted by the alkali treatment step increases. Therefore, the porosity of Raney nickel increases, the strength decreases, and the durability is likely to decrease. In addition, when an electrode is formed, it may be difficult to form an electron conduction path, and it may be difficult to obtain good water electrolysis performance of the water electrolysis device. In the NiAl alloy, in a region where the Al content is lower than that in a specific Al region, Al may be difficult to elute by the alkali treatment step. Therefore, the porosity of Raney nickel decreases and the specific surface area decreases, which may cause a decrease in water electrolysis performance.

[0041] In the NiAl alloy used in this manufacturing method, since the ratio of the area occupied by the specific Al region is within the above range, it can be said that regions with an excessive Al content and regions with an insufficient Al content are reduced. The Raney nickel obtained from this NiAl alloy has appropriate porosity and specific surface area, so it can have good durability. In addition, when an electrode is formed, an electron conduction path is likely to be formed, so it can also be expected that the water electrolysis performance of the water electrolysis device will be improved.

[0042] The manufacturing method of the NiAl alloy is not particularly limited, and it can be manufactured by known alloy manufacturing methods such as a casting method, a rapid solidification method, a mechanical alloying method, and a sputtering method. A NiAl alloy in which the ratio of the area of the specific Al region is within the above range can be obtained, for example, by adjusting the composition of the NiAl alloy and / or the cooling rate when casting the NiAl alloy. In order to obtain a NiAl alloy in which the ratio of the area of the specific Al region is within the above range, heat treatment may be performed after casting the NiAl alloy. The composition of the NiAl alloy may be adjusted, for example, by adjusting the molar ratio of Al to the total amount of Ni and Me in the NiAl alloy and the molar ratio of Ni to Me in the NiAl alloy to the above ranges.

[0043] (Process for obtaining Raney nickel) The process for obtaining Raney nickel includes the alkali treatment process described above (Figure 1). This alkali treatment process causes Al, a component soluble in alkali substances, to leach from the NiAl alloy. Therefore, this manufacturing method makes it possible to produce electrodes containing Raney nickel, which has a porous structure with a large specific surface area formed by numerous pores.

[0044] The process for obtaining Raney nickel may further include an oxidation step in which the surface of the porous body obtained by the alkali treatment step is oxidized (Figure 1). The process for obtaining Raney nickel may or may not include the oxidation step, as long as it includes the alkali treatment step.

[0045] (Alkali treatment process) The alkali treatment process is carried out by bringing the NiAl alloy into contact with an alkaline substance. When the NiAl alloy comes into contact with the alkaline substance, the NiAl alloy and the alkaline substance react, and the Al in the NiAl alloy dissolves to obtain a porous material. This porous material may be used as Raney nickel contained in the electrode. The alkali treatment process may dissolve all of the Al contained in the NiAl alloy, but if a porous material is formed, some of the NiAl alloy may remain without dissolving.

[0046] Examples of alkaline substances include solutions of alkali metal compounds, preferably aqueous solutions of alkali metal compounds. Examples of alkali metal compounds include alkali metal hydroxides and alkali metal salts. Examples of alkali metal hydroxides include sodium hydroxide, potassium hydroxide, and lithium hydroxide. Examples of alkali metal salts include sodium carbonate, potassium carbonate, and lithium carbonate. The alkaline substance is preferably an alkali metal hydroxide.

[0047] The method for eluting Al from a NiAl alloy is not particularly limited as long as the NiAl alloy and the alkaline substance are brought into contact so that the NiAl alloy reacts with the alkaline substance. If the alkaline substance is a solution, the NiAl alloy and the alkaline substance may be brought into contact by spraying the alkaline substance onto the NiAl alloy or by immersing the NiAl alloy in the alkaline substance. If the NiAl alloy is in powder form, the NiAl alloy and the alkaline substance may be brought into contact by adding it to a solution of the alkaline substance and stirring.

[0048] The shape and form of the NiAl alloy in contact with the alkaline substance are not particularly limited. The NiAl alloy may be, for example, a powdered NiAl alloy, or a NiAl alloy supported on a first substrate (base material) that serves as the base material for the electrode. The first substrate may support a powdered NiAl alloy. The first substrate only needs to support at least a NiAl alloy, and may also support components other than the NiAl alloy (hereinafter, the components such as the NiAl alloy supported on the first substrate will be collectively referred to as "supported components").

[0049] The average particle size of the powdered NiAl alloy is, for example, 1 to 150 μm, but may also be 5 to 100 μm or 5 to 50 μm. The average particle size of the NiAl alloy refers to the particle size at 50% of the cumulative value in the particle size distribution determined by laser diffraction and scattering.

[0050] The first substrate supporting the NiAl alloy is, for example, a conductor. The first substrate may also be a material that constitutes part of the electrodes of a water electrolysis device. Examples of materials that form the first substrate include the materials described above for use in the substrate. The first substrate may be a porous substrate or a non-porous substrate, and examples of their shapes and structures include the shapes and structures described above for the substrate. Preferably, the first substrate is a porous substrate that can support the supporting component to be supported on the first substrate within its pores.

[0051] The method for supporting the supporting component on the first substrate is not particularly limited. For example, the NiAl alloy may be supported on the first substrate by thermal spraying. Plasma spraying is one example of a thermal spraying method. Alternatively, the process for obtaining Raney nickel may further include a step of applying a first slurry containing a NiAl alloy and a first solvent to the first substrate, and the supporting component such as a NiAl alloy may be supported on the first substrate by this application step. Examples of the first solvent include water, N-methyl-2-pyrrolidone (NMP), and N-ethyl-2-pyrrolidone (NEP).

[0052] The first slurry may be applied using a known coating device such as a die coater, roll coater, knife coater, blade coater, bar coater, spray coater, or screen printing device, or it may be applied by immersing the first substrate in the first slurry. The first slurry may be applied to the entire surface of the first substrate, or to a part of the surface of the first substrate. If the first substrate is in the form of a plate, the first slurry may be applied to one or both sides of the first substrate. If the first substrate is a porous substrate, the first slurry may be impregnated into the pores of the first substrate by pressing the first substrate to which the first slurry has been applied. If the first substrate is a porous substrate, any first slurry that has not impregnated into the pores and remains on the surface of the first substrate may be scraped off using a spatula or the like.

[0053] The process for obtaining Raney nickel may further include a step of drying and calcining the first slurry applied to the first substrate. In this case, the alkali treatment step is preferably carried out after the calcination step. For example, the first substrate supporting the supported component may be obtained by applying the first slurry to the first substrate and drying it, or by calcining after application and drying. The drying of the first slurry applied to the first substrate can be carried out using known drying equipment such as a hot air drying oven, an infrared drying oven, and a hot plate. The drying temperature may be, for example, 40 to 120°C, or 50 to 100°C. The drying time may be, for example, 1 to 300 minutes, or 30 to 200 minutes. After drying the first slurry, the first substrate to which the first slurry has been applied may be pressed.

[0054] The first slurry, applied to the first substrate and dried, may be fired. This firing helps to suppress unevenness in the thickness of the first substrate supporting the supported component, and if the first substrate is a porous substrate, it facilitates uniform penetration of the supported component into the first substrate. If the supported component contains Ni metal, as described later, firing facilitates bonding between NiAl alloys and / or between NiAl alloys and the first substrate.

[0055] If the first substrate has a supported component, the alkali treatment step only requires eluting Al from the NiAl alloy contained in the supported component on the first substrate. As described above, if the step of obtaining Raney nickel includes a step of thermal spraying a NiAl alloy onto the first substrate, or if the step of obtaining Raney nickel includes a step of applying a first slurry to the first substrate, the NiAl alloy treated in the alkali treatment step may be supported on the first substrate. The supported component supported on the first substrate may be a calcined product obtained by calcining the first slurry as described above. In the alkali treatment step, for example, Al can be eluted from the NiAl alloy by immersing the entire first substrate supporting the supported component in an alkaline solution. This makes it possible to obtain a first substrate with a porous body supported on it.

[0056] The NiAl alloy contained in the first slurry is preferably in powder form. The average particle size of the powdered NiAl alloy can be within the range described above.

[0057] The first slurry may further contain Ni metal. The Ni metal is a metal that may contain Al, where the Ni content of the Ni metal is more than 50% by mass, and the amount of Al contained in the Ni metal is less than the amount of Ni contained in the Ni metal. The Ni content in the Ni metal may be 60% by mass or more, 80% by mass or more, 90% by mass or more, 95% by mass or more, or 98% by mass or more. The Ni metal may contain Al within the above-mentioned range of amounts, but may not contain Al. The metal content contained in the Ni metal can be determined, for example, by scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDX).

[0058] Ni metal can function as a binder that binds NiAl alloys together, and / or NiAl alloys together with the first substrate, by firing the first substrate to which the first slurry has been applied. As a result, Raney nickels together, and / or Raney nickels together with the first substrate, can be bonded well.

[0059] The Ni metal may contain metals other than Ni, for example, one or more selected from the group consisting of Al, Cu, Mg, Si, Ti, Cr, Mn, Co, Zn, Sn, Pb, Fe, Ag, Pt, and Au. When the Ni metal contains metals other than Ni, the Ni metal is an alloy other than the NiAl alloy described above, and more specifically, an alloy in which the amount of Al contained in the Ni metal is less than the amount of Ni contained in the Ni metal. The Ni metal may be Raney nickel, for example, Raney nickel obtained in the process for obtaining Raney nickel described herein.

[0060] It is preferable that the ratio of the amount of substance (moles) of Ni to the total amount of substance (moles) of all elements contained in the Ni metal [mol%] is greater than the ratio of the amount of substance (moles) of Ni to the total amount of substance (moles) of all elements contained in the NiAl alloy [mol%]. Furthermore, it is preferable that the ratio of the total amount of substance (total moles) of metals other than Ni to the total amount of substance (moles) of all elements contained in the Ni metal [mol%] is less than the ratio of the total amount of substance (total moles) of the element Me to the total amount of substance (moles) of all elements contained in the NiAl alloy [mol%]. When the first slurry is fired as described above, Al and the element Me diffuse from the NiAl alloy to the Ni metal at the contact area between the NiAl alloy and the Ni metal due to the thermal energy from firing and the elemental concentration gradient. This makes it easier for the NiAl alloy and the Ni metal to bond. When NiAl alloy and Ni metal bond together, strong electron conduction paths are more easily formed, making it easier to obtain electrodes with excellent water electrolysis performance in water electrolysis devices.

[0061] Ni metal is preferably in powder form. The average particle size of the Ni metal is, for example, 1 to 10 μm, but may also be 1 to 8 μm or 2 to 5 μm. The average particle size of the Ni metal refers to the value measured by the Fischer method.

[0062] When the NiAl alloy and Ni metal contained in the first slurry are in powder form, it is preferable that the average particle size of the NiAl alloy is larger than the average particle size of the Ni metal. This makes it easier for the Ni metal to penetrate the gaps in the NiAl alloy, allowing the Ni metal to function more effectively as a binder.

[0063] The Ni metal content in the first slurry may be 15 to 95% by mass, 20 to 90% by mass, or 25 to 85% by mass, relative to the total amount of NiAl alloy and Ni metal. The solvent content in the first slurry may be 15 to 70% by mass, 20 to 60% by mass, 25 to 55% by mass, or 27 to 50% by mass, relative to the total amount of the first slurry.

[0064] The first slurry may further contain components other than the NiAl alloy, the first solvent, and the Ni metal. For example, the first slurry may contain a thickening agent to adjust the viscosity of the first slurry. Examples of thickening agents include carboxymethylcellulose (CMC), polytetrafluoroethylene (PTFE), and polyvinylidene fluoride (PVdF).

[0065] The treatment temperature for the alkali treatment step is preferably 90 to 150°C, but may also be 95 to 145°C or 100 to 140°C. If the alkaline substance is a solution, the alkali treatment step may be carried out while the temperature of the solution is adjusted and maintained within the above range. For example, the alkali treatment step may be carried out after adding the NiAl alloy to the alkaline substance in solution and then heating it to the above treatment temperature.

[0066] The processing time for the alkali treatment step is, for example, 60 to 360 minutes, but may also be 100 to 300 minutes or 120 to 240 minutes.

[0067] The amount of alkali substance used in the alkali treatment process should be set according to the amount of Al contained in the NiAl alloy. The amount of alkali substance may be less than the stoichiometric amount of Al contained in the NiAl alloy, may be the same amount, or may be in excess. The mass ratio of the NiAl alloy to the alkali substance in the solution (NiAl alloy: alkali substance in the solution) in the alkali treatment process may be, for example, 1:10 to 1:500, but may also be 1:20 to 1:450, or 1:30 to 1:400.

[0068] When the alkaline substance is a solution of an alkali metal compound, the concentration of the solution may be, for example, 1 to 20 mol / L, 2 to 18 mol / L, or 3 to 15 mol / L.

[0069] The above-mentioned conditions in the alkali treatment process can be combined in any way. For example, if the treatment temperature in the alkali treatment process is 100°C or higher, the concentration of the alkali metal compound solution may be 3 mol / L or higher, and if the treatment temperature in the alkali treatment process is 140°C or higher, the concentration of the alkali metal compound solution may be 14 mol / L or higher. In the alkali treatment process, it is preferable to raise the treatment temperature as the concentration of the alkali metal compound solution increases.

[0070] The alkali treatment process is preferably carried out under atmospheric pressure (10¹³ hPa). This allows for easier removal of hydrogen generated during the alkali treatment process compared to carrying out the process under pressure, thus preventing the need for complex hydrogen removal equipment.

[0071] The porous material obtained through the alkaline treatment process may be washed if necessary. Washing can be done with water. If powdered NiAl alloy is immersed in an alkaline solution, the porous material may be recovered by solid-liquid separation such as filtration.

[0072] (Oxidation Process) The oxidation process is a process of oxidizing the surface of the porous material obtained by the alkali treatment process, in which Al is dissolved from the NiAl alloy with an alkaline substance. The surface of the porous material obtained by the alkali treatment process is highly reactive with oxygen and may spontaneously ignite in air, making it difficult to handle during storage, etc. By carrying out the oxidation process to oxidize the surface of the porous material, the reactivity of the porous material with oxygen can be reduced, thereby improving the ease of handling during storage, etc. If part or all of the surface of the porous material is not oxidized, the porous material may be stored in a solvent or the like to suppress contact with air.

[0073] The oxidation process is carried out by bringing the porous material into contact with an acidic substance. When the acidic substance comes into contact with the surface of the porous material, the surface of the porous material is oxidized. The porous material with an oxidized surface may be used as Raney nickel. The oxidation process only needs to oxidize at least a portion of the surface of the porous material, but it is preferable to oxidize the entire surface of the porous material.

[0074] Examples of acidic substances include acidic solutions. Examples of acidic solutions include aqueous solutions of hydrogen peroxide, sodium peroxide, sodium percarbonate, and sodium perborate, with aqueous hydrogen peroxide being preferred.

[0075] The shape and form of the porous body that comes into contact with the acidic substance are not particularly limited. The porous body may be, for example, a powdered porous body, or a porous body supported on a first substrate. The porous body supported on the first substrate may be obtained by treating the first substrate supporting the supporting component in an alkali treatment step. The porous body supported on the first substrate may be supported on the first substrate in a state mixed with components other than the porous body or their raw materials.

[0076] The method for bringing a porous material into contact with an acidic substance is not particularly limited as long as the surface of the porous material is oxidized. If the acidic substance is an acidic solution, the porous material may be brought into contact with the acidic substance by spraying the acidic solution onto the porous material; or by immersing a powdered porous material or a porous material supported on a first substrate in an acidic solution. If the porous material is in powder form, the porous material may be brought into contact with the acidic substance by adding it to an acidic solution and stirring.

[0077] The processing temperature for the oxidation process is, for example, 10 to 80°C, but may also be 15 to 70°C or 15 to 60°C. The processing time for the oxidation process is, for example, 5 to 720 minutes, but may also be 60 to 700 minutes or 120 to 650 minutes. When an acidic solution is used as the acidic substance, the concentration of the acidic solution is, for example, 0.1 to 10 mol / L, but may also be 0.3 to 8 mol / L. The mass ratio of the porous material to the acidic solution (porous material: acidic solution) in the oxidation process is, for example, 1:5 to 1:100, but may also be 1:7 to 1:80 or 1:9 to 1:50.

[0078] The Raney nickel obtained through the oxidation process may be washed if necessary. Washing can be done with water. If the powdered porous material is immersed in an acidic solution, the Raney nickel may be recovered by solid-liquid separation such as filtration.

[0079] (Step to obtain electrodes) The step to obtain electrodes may be to carry out the step to obtain Raney nickel while supporting a NiAl alloy on a first substrate, or it may be a step to obtain electrodes by supporting the Raney nickel obtained from the NiAl alloy on a substrate (hereinafter also referred to as the "second substrate").

[0080] Methods for supporting a NiAl alloy on a first substrate, and for performing an alkali treatment step and an oxidation step while the NiAl alloy is supported on the first substrate, include the methods described above. This makes it possible to obtain an electrode on which Raney nickel is supported on the first substrate. From the viewpoint of making it difficult for the Raney nickel to fall off the first substrate, the method of supporting the NiAl alloy on the first substrate is preferably one using the first slurry described above, and preferably includes a step of applying the first slurry to the first substrate.

[0081] When obtaining an electrode by supporting Raney nickel on a second substrate, it is preferable to perform an alkali treatment step and, if necessary, an oxidation step on the NiAl alloy that is not supported on a substrate such as the first substrate to obtain Raney nickel.

[0082] The second substrate is, for example, a conductor and can be formed from a carbon material, a metal material, or a polymer electrolyte. The second substrate may be a porous substrate or a non-porous substrate. The second substrate may be one of those described for the first substrate.

[0083] One method for supporting Raney nickel on a second substrate is to coat the second substrate with a second slurry containing Raney nickel and a second solvent. Examples of the second solvent include water; alcohols such as methanol, ethanol, and propanol; and mixed solvents of water and alcohol.

[0084] The second slurry may contain components other than Raney nickel and the second solvent. Examples of such components include conductive porous carbon, ionomers, and conductive oxides. Examples of porous carbon include carbon black such as Ketjenblack and acetylene black, activated carbon, graphite, and carbon nanotubes. Examples of ionomers include fluorine-based resins such as perfluorocarbon sulfonic acid polymers. Examples of conductive oxides include niobium-substituted titanium dioxide.

[0085] The second slurry can be applied by the method described for the application of the first slurry. The second slurry may be applied to the entire surface of the second substrate, or to a portion of the surface of the second substrate. If the second substrate is in the form of a plate, the second slurry may be applied to one or both sides of the second substrate. If the second substrate is a porous substrate, the second slurry may be impregnated into the pores of the second substrate by pressing the second substrate to which the second slurry has been applied. If the second substrate is a porous substrate, any second slurry that has not impregnated into the pores and remains on the surface of the second substrate may be scraped off using a spatula or the like.

[0086] After applying the second slurry to the second substrate, the second slurry may be dried. The drying of the second slurry can be carried out, for example, using the apparatus, temperature, and time described for drying the first slurry. After drying the second slurry, the second substrate coated with the second slurry may be pressed.

[0087] <Electrode Raw Materials> The electrode raw materials of this embodiment are used for electrodes in a water electrolysis apparatus. The electrode raw materials include a first substrate (base material), and a NiAl alloy and Ni metal supported on the first substrate. The NiAl alloy is a raw material for Raney nickel, which dissolves aluminum with an alkaline substance, and the total content of Al and Ni relative to all elements contained in the NiAl alloy is 50 mol% or more, and the amount of Al contained in the NiAl alloy is greater than the amount of Ni. The Ni metal is a metal which may contain Al, and the Ni content of the Ni metal is more than 50 mass%, and the amount of Al contained in the Ni metal is less than the amount of Ni. In the cross-section of the above NiAl alloy, the area occupied by the region with an aluminum content of 45 to 70 mol% (specific Al region) is 85% or more.

[0088] Since the electrode raw materials can be used to manufacture electrodes for water electrolysis devices, it is possible to obtain a highly durable cathode that exhibits good catalytic activity for hydrogen generation and a highly durable anode that exhibits good catalytic activity for oxygen generation, even when water electrolysis is repeated in a water electrolysis device.

[0089] Examples of the first substrate, NiAl alloy, and Ni metal are those described above. The NiAl alloy can be manufactured by the manufacturing method described above. The proportion of the area occupied by the specific Al region is calculated by the method described above. Examples of alkali substances and methods for dissolving Al from the NiAl alloy using alkali substances are those described above. Examples of methods for obtaining Raney nickel from the NiAl alloy are those described above.

[0090] As a method for supporting the NiAl alloy and Ni metal on the first substrate, the above-described method is used, but it is preferable to apply a slurry containing the NiAl alloy and Ni metal to the first substrate. The slurry may be the first slurry described above.

[0091] The NiAl alloy and Ni metal supported by the first substrate may be in powder form. The average particle size of the powdered NiAl alloy and Ni metal may be within the range described above. The first substrate may also contain other components besides the NiAl alloy and Ni metal. Examples of other components include the thickeners described above.

[0092] <Slurry> The slurry of this embodiment is a slurry used in the manufacture of electrodes for a water electrolysis apparatus (hereinafter also referred to as "this slurry"). This slurry contains NiAl alloy powder, Ni metal powder, and a solvent. The NiAl alloy is a raw material for Raney nickel, which dissolves aluminum with an alkaline substance, and the total content of Al and Ni relative to all elements contained in the NiAl alloy is 50 mol% or more, and the amount of Al contained in the NiAl alloy is greater than the amount of Ni. The Ni metal is a metal which may contain Al, and the Ni content of the Ni metal is more than 50 mass%, and the amount of Al contained in the Ni metal is less than the amount of Ni. In the cross-section of the above NiAl alloy, the area occupied by the region with an aluminum content of 45 to 70 mol% (specific Al region) is 85% or more.

[0093] This slurry can be used to manufacture electrodes for a water electrolysis apparatus, and even when water electrolysis is repeated in the water electrolysis apparatus, it is possible to obtain a highly durable cathode that exhibits good catalytic activity for hydrogen generation and a highly durable anode that exhibits good catalytic activity for oxygen generation. This slurry may also be the first slurry described above.

[0094] Examples of NiAl alloys include those listed above. The average particle size range of the NiAl alloy powder is within the range listed above. NiAl alloys can be manufactured using the manufacturing method described above. The percentage of the area occupied by the specific Al region is calculated using the method described above. The process for obtaining Raney nickel may be the process described above, and may include the alkali treatment process described above, and may also include the oxidation process described above if necessary. Examples of alkali substances and methods for dissolving Al from NiAl alloys using alkali substances include those listed above.

[0095] Examples of Ni metals include those listed above. The average particle size range of the Ni metal powder is within the range described above. Examples of solvents include those described in the first solvent section above.

[0096] This slurry may contain other components besides NiAl alloy powder, Ni metal powder, and solvent. Examples of other components include the thickening agents mentioned above.

[0097] The present disclosure will be described in more detail below with reference to examples and comparative examples. [Example 1] (Preparation of NiAl alloy) Aluminum, nickel, and iron were weighed to obtain the compositional formula shown in Table 1, and these were mixed to obtain a mixture. This mixture was heated and melted at 1600°C using a high-frequency induction melting furnace, and then cooled while adjusting the cooling rate to obtain an alloy ingot of NiAl alloy represented by the compositional formula shown in Table 1. By crushing the obtained alloy ingot, a powder of NiAl alloy with the above composition was obtained. The average particle size of the obtained powder was in the range of 20 to 40 μm as a result of measurement by laser diffraction and scattering method.

[0098] (Preparation of materials to be used) NiAl alloy powder: NiAl alloy powder prepared as described above Ni metal powder: Ni nickel "NIE10PB" (average particle size: 2-3 μm) (manufactured by Kojun Chemical Laboratory Co., Ltd.) Thickener: CMC "Selogen EP" (manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) First solvent: Water First base material: Ni metal porous material "Cellmet (registered trademark) #8" (50 mm long, 50 mm wide, 1.2 mm thick) (manufactured by Sumitomo Electric Industries, Ltd.)

[0099] (Preparation of the first slurry) The first slurry was prepared by mixing NiAl alloy powder, Ni metal powder, a thickener, and the first solvent. The amounts of NiAl alloy powder and Ni metal powder were adjusted so that the amount of Ni metal powder in the first slurry was 48% by mass relative to the total amount of NiAl alloy powder and Ni metal powder.

[0100] (Electrode Preparation) The first slurry was applied to both sides of the first substrate, and the first slurry that remained on the surface without being impregnated into the pores of the first substrate was scraped off with a spatula. The first slurry applied to the first substrate was dried at 80°C for 60 minutes, and then fired at 700°C for 2 hours to obtain the first substrate on which the fired body is supported. The fired body and the first substrate were immersed in a 14 mol / L sodium hydroxide aqueous solution at 140°C for 3 hours (alkali treatment step), washed with water, and obtained the first substrate on which the porous body is supported. The first substrate on which the porous body is supported was immersed in a hydrogen peroxide aqueous solution to oxidize the surface of the porous body (oxidation step), washed with water, and obtained an electrode, which was used as the working electrode.

[0101] [Comparative Example 1] (Preparation of materials to be used) Following the same procedure as described in Example 1, a NiAl alloy powder represented by the composition formula shown in Table 1 was obtained. The average particle size of the obtained powder was in the range of 40 to 60 μm, as measured by laser diffraction and scattering. As the first substrate, a Ni porous metal body (50 mm long x 50 mm wide x 4 mm thick, manufactured by NanoMaterials development experts) was prepared.

[0102] (Electrode Fabrication) NiAl alloy powder was plasma sprayed onto a first substrate to support the NiAl alloy powder on the first substrate. The first substrate supporting the NiAl alloy powder was immersed in a 14 mol / L sodium hydroxide aqueous solution at 130°C for 3 hours (alkali treatment step), washed with water, and a first substrate supporting a porous material was obtained. The first substrate supporting the porous material was immersed in a hydrogen peroxide aqueous solution to oxidize the surface of the porous material (oxidation step), washed with water, and an electrode was obtained, which was used as the working electrode.

[0103] [Calculation of the percentage of area occupied by specific Al regions] The NiAl alloys obtained in Example 1 and Comparative Example 1 were mixed with a two-component epoxy resin (ZeroMar S, manufactured by IMT Co., Ltd.) used as the embedding resin, and the mixture was allowed to stand for at least 8 hours to cure the epoxy resin. The cured epoxy resin with the NiAl alloy embedded in it was polished with a polishing machine (Refine Polisher HV, manufactured by Refine Tech Co., Ltd.) to produce a molded body. The molded body was a rectangular parallelepiped with dimensions of 5 mm in length, 8 mm in width, and 2 mm in height.

[0104] A cross-section was obtained by cutting the molded body in directions parallel to the lateral and height directions using a cross-section preparation device (Cooled Cross-Section Polisher®, manufactured by JEOL Ltd.). This cross-section was analyzed using an EDX (Ultim MAX, manufactured by OXFORD INSTRUMENTS) attached to a SEM (Gemini SEM500, manufactured by Carl Zeiss), and elemental mapping data of the observation field was obtained using the following procedure. First, an SEM image (secondary electron image) of the cross-section of the molded body was obtained. The measurement conditions for acquiring the SEM image were an acceleration voltage of 15 kV and an observation magnification of 500x. The observation field was set to a rectangular shape of approximately 230 μm in the lateral direction and 160 μm in the height direction so that 10 or more NiAl alloy particles were included in the SEM image. The distribution of elements in this observation field was analyzed using the EDX attached to the SEM, and elemental mapping data was obtained.

[0105] In all elemental mapping data, there were no regions within the NiAl alloy cross-section where the Al content was less than 45 mol%. Therefore, the regions within the NiAl alloy cross-section where the Al content was between 45 and 70 mol% (specific Al regions), regions where the Al content was greater than 70 mol%, and the embedding resin regions were trinarized using image analysis software (ImageJ 1.53). The area occupied by the NiAl alloy region and the area occupied by the specific Al region in the elemental mapping data were calculated, and the percentage of the area occupied by the specific Al region was calculated according to the following formula: Percentage of area occupied by the specific Al region [%] = (Area occupied by the specific Al region / Area occupied by the NiAl alloy region) × 100

[0106] [Evaluation of catalytic activity for hydrogen generation] The working electrode obtained in Example 1 or Comparative Example 1, and a nickel mesh as the counter electrode, were immersed in a 7 mol / L potassium hydroxide solution as the electrolyte. A mercury-mercury oxide electrode was used as the reference electrode and connected to the electrolyte via a liquid junction. The potential of the working electrode was swept at 1 mV / s relative to the reference electrode, and the current value was read when the potential of the working electrode was -0.15 V. The current value was greater in Example 1 than in Comparative Example 1, indicating that Example 1 had superior catalytic activity for hydrogen generation compared to Comparative Example 1.

[0107] The working electrode potential was held at -0.1V for 1 minute, followed by a cycle of holding the working electrode potential at 0.4V for 1 minute. This cycle was repeated 1000 times. Afterward, the working electrode potential was swept at 1 mV / s relative to the reference electrode, and the current value was read when the working electrode potential was -0.15V. The results are shown in Table 1. A larger current value in Table 1 indicates better catalytic activity for hydrogen generation and superior durability, even after repeated water electrolysis.

[0108]

[0109] [Examples 2-7] (Preparation of NiAl alloy) Aluminum, nickel, copper (if present), and iron were weighed to obtain the compositional formula shown in Table 2, and these were mixed to obtain a mixture. This mixture was heated and melted at 1600°C using a high-frequency melting furnace, and then cooled while adjusting the cooling rate to obtain an alloy ingot of NiAl alloy represented by the compositional formula shown in Table 2. By crushing the obtained alloy ingot, a powder of NiAl alloy with the above composition was obtained. The average particle size of the obtained powder was in the range of 20 to 40 μm as measured by laser diffraction and scattering method.

[0110] (Preparation of materials to be used) NiAl alloy powder: NiAl alloy powder prepared as described above Ni metal powder: Ni nickel "NIE10PB" (average particle size: 2-3 μm) (manufactured by Kojun Chemical Laboratory Co., Ltd.) Thickener: CMC "Selogen EP" (manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) First solvent: Water First base material: Ni metal porous material "Cellmet (registered trademark) #8" (50 mm long, 50 mm wide, 1.2 mm thick) (manufactured by Sumitomo Electric Industries, Ltd.)

[0111] (Preparation of the first slurry) The first slurry was prepared by mixing NiAl alloy powder, Ni metal powder, a thickener, and the first solvent. The amounts of NiAl alloy powder and Ni metal powder were adjusted so that the content of Ni metal powder in the first slurry was 78% by mass relative to the total amount of NiAl alloy powder and Ni metal powder.

[0112] (Electrode Preparation) The first slurry was applied to both sides of the first substrate, and the first slurry that remained on the surface without being impregnated into the pores of the first substrate was scraped off with a spatula. The first slurry applied to the first substrate was dried at 80°C for 60 minutes, and then fired at 700°C for 2 hours to obtain the first substrate on which the fired body is supported. The fired body and the first substrate were immersed in a 14 mol / L sodium hydroxide aqueous solution at 130°C for 4 hours (alkali treatment step), washed with water, and obtained the first substrate on which the porous body is supported. The first substrate on which the porous body is supported was immersed in a hydrogen peroxide aqueous solution to oxidize the surface of the porous body (oxidation step), washed with water to obtain an electrode, which was used as the working electrode.

[0113] [Calculation of the Ratio of the Area Occupied by the Specific Al Region] The ratio of the area occupied by the specific Al region was calculated for each of the NiAl alloys (2) to (7) according to the above-described procedure for calculating the ratio of the area occupied by the specific Al region except that the NiAl alloys obtained in Examples 2 to 7 were used instead of the NiAl alloys obtained in Example 1 and Comparative Example 1.

[0114] [Evaluation of Catalytic Activity for Oxygen Generation] The working electrodes obtained in Examples 2 to 7 and a nickel mesh as a counter electrode were immersed in a 7 mol / L potassium hydroxide solution as an electrolyte. A mercury-mercuric oxide electrode was used as a reference electrode and connected to the electrolyte through a liquid junction. After holding the potential of the working electrode at 1.5 V (vs. reversible hydrogen electrode) for 1 minute, a cycle of holding the potential of the working electrode at 0.0 V (vs. reversible hydrogen electrode) for 1 minute was repeated 1500 times. Then, the potential of the working electrode (vs. reversible hydrogen electrode) was scanned at 1 mV / s with respect to the reference electrode, and the current value when it reached 1.49 V (vs. reversible hydrogen electrode) was read. The results are shown in Table 2. It can be said that the higher the current value shown in Table 2, the better the catalytic activity for oxygen generation in water electrolysis.

[0115]

[0116] [Supplementary Note] It is understood by those skilled in the art that the above-exemplified embodiments are specific examples of the following embodiments. (Aspect 1) A method for manufacturing an electrode of a water electrolysis device, The electrode includes a base material and Raney nickel supported on the base material, The manufacturing method includes a step of obtaining the Raney nickel, The step of obtaining the Raney nickel includes an alkali treatment step of eluting aluminum from a NiAl alloy with an alkali substance, In the cross-section of the NiAl alloy, the ratio of the area occupied by a region where the aluminum content is 45 to 70 mol% is 85% or more. A method for manufacturing an electrode. (Aspect 2) The component composition excluding inevitable impurities of the NiAl alloy has the composition formula Al ３．００ Ni （２．００－ｘ） M ｘA method for manufacturing an electrode according to Embodiment 1, wherein x is a value satisfying 0.00 < x < 1.00, and M is one or more elements selected from the group consisting of Mg, Si, Ti, Cr, Mn, Fe, Co, Cu, Zr, Nb, Mo, Ag, Sn, Pt, Ir, and Au. (Embodiment 3) A method for manufacturing an electrode according to Embodiment 1 or 2, wherein the step of obtaining the Raney nickel further includes an oxidation step of oxidizing the surface of the porous body obtained by the alkali treatment step. (Embodiment 4) A method for manufacturing an electrode according to any one of Embodiments 1 to 3, wherein the step of obtaining the Raney nickel further includes a step of applying a slurry containing the NiAl alloy powder and a solvent to the substrate, and the NiAl alloy treated in the alkali treatment step is supported on the substrate. (Aspect 5) The method for manufacturing an electrode according to aspect 4, wherein the slurry further comprises Ni metal powder, the NiAl alloy has a total content of Al and Ni of 50 mol% or more relative to all elements contained in the NiAl alloy, the amount of Al contained in the NiAl alloy is greater than the amount of Ni, the Ni metal may contain Al, the Ni content of the Ni metal is more than 50 mass%, and the amount of Al contained in the Ni metal is less than the amount of Ni. (Aspect 6) The method for manufacturing an electrode according to aspect 4 or 5, wherein the step of obtaining the Raney nickel includes a step of drying and firing the slurry coated in the coating step, and the alkali treatment step is performed after the firing step.(Aspect 7) A raw material for an electrode in a water electrolysis apparatus, comprising a base material, a NiAl alloy and Ni metal supported on the base material, wherein the NiAl alloy is a raw material for Raney nickel and dissolves aluminum with an alkaline substance, and the total content of Al and Ni relative to all elements contained in the NiAl alloy is 50 mol% or more, and the amount of Al contained in the NiAl alloy is greater than the amount of Ni, and the Ni metal is a metal that may contain Al, the Ni content of the Ni metal is more than 50 mass%, and the amount of Al contained in the Ni metal is less than the amount of Ni, and the proportion of the area occupied by the region with an aluminum content of 45 to 70 mol% in the cross-section of the NiAl alloy is 85% or more. (Aspect 8) The component composition of the NiAl alloy, excluding unavoidable impurities, is compositional formula Al. ３．００ Ni （２．００－ｘ） M ｘ The raw material for the electrode according to embodiment 7, represented as follows: (x is a value satisfying 0.00 < x < 1.00, and M is one or more elements selected from the group consisting of Mg, Si, Ti, Cr, Mn, Fe, Co, Cu, Zr, Nb, Mo, Ag, Sn, Pt, Ir, and Au.) (Aspect 9) A slurry used in the manufacture of electrodes for a water electrolysis apparatus, wherein the slurry comprises NiAl alloy powder, Ni metal powder, and a solvent, the NiAl alloy is a raw material for Raney nickel and dissolves aluminum with an alkaline substance, the total content of Al and Ni relative to all elements contained in the NiAl alloy is 50 mol% or more, the amount of Al contained in the NiAl alloy is greater than the amount of Ni, the Ni metal may contain Al, the Ni content of the Ni metal is more than 50 mass%, and the amount of Al contained in the Ni metal is less than the amount of Ni, and the area occupied by the region with an aluminum content of 45 to 70 mol% in the cross-section of the NiAl alloy is 85% or more.

[0117] The embodiments and examples disclosed herein should be considered in all respects to be illustrative and not restrictive. The scope of this disclosure is indicated by the claims rather than the foregoing description, and all modifications are intended to be in the sense and scope equivalent to the claims.

Claims

1. A method for manufacturing an electrode for a water electrolysis apparatus, wherein the electrode comprises a base material and Raney nickel supported on the base material, the manufacturing method includes a step of obtaining the Raney nickel, the step of obtaining the Raney nickel includes an alkali treatment step of dissolving aluminum from a NiAl alloy with an alkaline substance, and the area occupied by a region with an aluminum content of 45 to 70 mol% in the cross-section of the NiAl alloy is 85% or more.

2. The component composition of the NiAl alloy, excluding unavoidable impurities, is: Composition formula Al ３．００ Ni （２．００－ｘ） M ｘ A method for manufacturing an electrode according to claim 1, wherein x is a value satisfying 0.00 < x < 1.00, and M is one or more elements selected from the group consisting of Mg, Si, Ti, Cr, Mn, Fe, Co, Cu, Zr, Nb, Mo, Ag, Sn, Pt, Ir, and Au.

3. The method for manufacturing an electrode according to claim 1 or 2, wherein the step of obtaining the Raney nickel further includes an oxidation step of oxidizing the surface of the porous body obtained by the alkali treatment step.

4. The method for manufacturing an electrode according to any one of claims 1 to 3, wherein the step of obtaining the Raney nickel further includes a step of applying a slurry containing the NiAl alloy powder and a solvent to the substrate, and the NiAl alloy treated in the alkali treatment step is supported on the substrate.

5. The method for manufacturing an electrode according to claim 4, wherein the slurry further comprises Ni metal powder, the NiAl alloy has a total content of Al and Ni of 50 mol% or more relative to the total elements contained in the NiAl alloy, the amount of Al contained in the NiAl alloy is greater than the amount of Ni, and the Ni metal may contain Al, the Ni content of the Ni metal is greater than 50 mass%, and the amount of Al contained in the Ni metal is less than the amount of Ni.

6. The method for manufacturing an electrode according to claim 4 or 5, wherein the step of obtaining the Raney nickel includes a step of drying and firing the slurry applied in the coating step, and the alkali treatment step is performed after the firing step.

7. A raw material for an electrode in a water electrolysis apparatus, comprising a base material, a NiAl alloy and Ni metal supported on the base material, wherein the NiAl alloy is a raw material for Raney nickel and dissolves aluminum with an alkaline substance, and the total content of Al and Ni relative to all elements contained in the NiAl alloy is 50 mol% or more, and the amount of Al contained in the NiAl alloy is greater than the amount of Ni, and the Ni metal may contain Al, and the Ni content of the Ni metal is more than 50 mass%, and the amount of Al contained in the Ni metal is less than the amount of Ni, and the area occupied by the region with an aluminum content of 45 to 70 mol% in the cross-section of the NiAl alloy is 85% or more.

8. The component composition of the NiAl alloy, excluding unavoidable impurities, is: Composition formula Al ３．００ Ni （２．００－ｘ） M ｘ The raw material for the electrode according to claim 7, represented as follows: (where x is a value satisfying 0.00 < x < 1.00, and M is one or more elements selected from the group consisting of Mg, Si, Ti, Cr, Mn, Fe, Co, Cu, Zr, Nb, Mo, Ag, Sn, Pt, Ir, and Au).

9. A slurry used in the manufacture of electrodes for a water electrolysis apparatus, wherein the slurry comprises NiAl alloy powder, Ni metal powder, and a solvent, the NiAl alloy is a raw material for Raney nickel and dissolves aluminum with an alkaline substance, the total content of Al and Ni relative to all elements contained in the NiAl alloy is 50 mol% or more, the amount of Al contained in the NiAl alloy is greater than the amount of Ni, the Ni metal may contain Al, the Ni content of the Ni metal is more than 50 mass%, and the amount of Al contained in the Ni metal is less than the amount of Ni, and the area occupied by the region with an aluminum content of 45 to 70 mol% in the cross-section of the NiAl alloy is 85% or more.

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