Cathode for water electrolysis and method for manufacturing a cathode for water electrolysis

Abstract

A cathode for water electrolysis includes a catalyst section and a reverse current absorber electrically connected to the catalyst section, the reverse current absorber comprising a hydrogen storage alloy comprising Al.

Description

Technical Field

[0001] This disclosure relates to a cathode for water electrolysis and a method for manufacturing a cathode for water electrolysis. Background Technology

[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 for hydrogen production includes, for example, an electrolytic cell containing an electrolyte such as alkaline water, and an anode and a cathode sandwiched between separators within the electrolytic cell. In this water electrolysis apparatus, oxygen is produced at the anode and hydrogen is produced at the cathode by flowing current between the anode and cathode.

[0003] On the other hand, it is known that a reverse current (a current in the opposite direction to the electrolysis current) is generated when the water electrolysis device stops. Due to this reverse current, the electrodes, especially the cathode, will deteriorate. In addition, to prevent electrode deterioration, examples include using electrodes that do not oxidize and deteriorate even when the reverse current flows, and preventing the electrode catalyst from rising to a potential that would cause oxidation and deterioration.

[0004] International Publication No. 2018 / 168863 (Patent Document 1) discloses a method to prevent cathode deterioration by using a material having a lower redox potential than the catalyst element of the cathode as a reverse current absorber.

[0005] Japanese Patent Application Publication No. 2001-234380 (Patent Document 2) discloses an electrode whose potential rise is suppressed by using an electrode formed by applying a coating liquid containing metals such as molybdenum and nickel to a substrate, drying it, and then heating it to form a sintered body. Existing technical documents Patent documents

[0006] Patent Document 1: International Publication No. 2018 / 168863 Patent Document 2: Japanese Patent Application Publication No. 2001-234380 Summary of the Invention The problem the invention aims to solve

[0007] As disclosed in Patent Documents 1 and 2, various techniques have been proposed to prevent electrode degradation caused by reverse current. However, there is room for improvement in such techniques.

[0008] The purpose of this disclosure is to provide a cathode for water electrolysis that suppresses degradation caused by reverse current and a method for manufacturing a cathode for water electrolysis. Solution for solving the problem

[0009] A cathode for water electrolysis used to solve the above problems includes a catalyst section and a reverse current absorber electrically connected to the catalyst section. The reverse current absorber includes a hydrogen storage alloy, which includes Al.

[0010] The cathode for water electrolysis includes a reverse current absorber as a sacrificial electrode. The reverse current absorber contains a hydrogen storage alloy containing Al. The hydrogen storage alloy is an alloy of metal A, which readily reacts with hydrogen but has poor hydrogen release capacity, and metal B, which has poor hydrogen release capacity but is difficult to react with hydrogen. By including at least Al as metal B, it is expected to suppress degradation caused by the reverse current.

[0011] A method for manufacturing a cathode for water electrolysis includes: a catalyst section forming step, forming a catalyst section; and a reverse current absorber forming step, forming a reverse current absorber containing a hydrogen storage alloy comprising Al, wherein the reverse current absorber forming step includes a hydrogen storage alloy coating step, which involves coating a slurry obtained by mixing the hydrogen storage alloy with a solvent onto a substrate. Invention Effects

[0012] According to this disclosure, a cathode for water electrolysis that suppresses degradation caused by reverse current can be obtained. Attached Figure Description

[0013] Figure 1 This is a schematic diagram illustrating an example of a water electrolysis apparatus that includes a cathode for water electrolysis according to the present disclosure. Figure 2 This is a schematic diagram illustrating another example of a water electrolysis apparatus that includes a cathode for water electrolysis according to the present disclosure. Figure 3 This is a schematic diagram illustrating another example of a water electrolysis apparatus that includes a cathode for water electrolysis according to the present disclosure. Figure 4 This is a schematic diagram illustrating another example of a water electrolysis apparatus that includes a cathode for water electrolysis according to the present disclosure. Figure 5 This is a schematic diagram illustrating another example of a water electrolysis apparatus that includes a cathode for water electrolysis according to the present disclosure. Figure 6 This is a schematic diagram showing the configuration of the water electrolysis device in Example 2. Figure 7 This is a schematic diagram showing another configuration of the water electrolysis device in Embodiment 2. Figure 8 This is a bar chart showing the experimental results in Example 2. Figure 9 This is a coordinate graph showing the evaluation results of the activity of the electrode used for water electrolysis in Reference Experiment 1. Figure 10This is a coordinate graph showing the evaluation results of the durability of the electrodes used for water electrolysis in Reference Test 1. Detailed Implementation

[0014] The following describes embodiments of the present disclosure (hereinafter referred to as "the present embodiments") and examples of the present disclosure (hereinafter referred to as "the examples"). However, the present embodiments and examples do not limit the technical scope of the present disclosure.

[0015] The cathode for water electrolysis in this embodiment is used as the electrolysis cathode in a water electrolysis apparatus. The cathode for water electrolysis in this embodiment is suitable for use in an alkaline water electrolysis apparatus.

[0016] The average particle size of Raney alloys refers to the particle size at which the cumulative value in the particle size distribution, determined by laser diffraction scattering, reaches 50%. The average particle size of the raw material for metallic particles refers to the particle size determined by the Fisher method. The average particle size of Raney nickel particles and the average particle size of metallic particles refer to the arithmetic mean of the minor axis diameters of any 100 Raney nickel particles and metallic particles extracted from SEM images obtained using a scanning electron microscope (SEM).

[0017] <Cathode for water electrolysis> The cathode for water electrolysis in this embodiment includes a catalyst section and a reverse current absorber electrically connected to the catalyst section. The reverse current absorber includes a hydrogen storage alloy. The hydrogen storage alloy includes aluminum (Al). The catalyst section includes a substrate and a catalyst.

[0018] In this embodiment, the cathode for water electrolysis only needs to have the same potential as the catalyst section and the reverse current absorber. That is, as long as the catalyst section and the reverse current absorber are electrically connected, its configuration is not particularly limited. For example, such as... Figure 1 As shown, the cathode 10 for water electrolysis can be a separate assembly of the catalyst section 1 and the reverse current absorber 2 (hereinafter also referred to as "the first type"). For example, as Figure 2 As shown, alternatively, a catalyst layer 4 containing a catalyst can be formed on one side of the front and back surfaces of the substrate 3, and a reverse current absorber 2 can be formed on the other side for water electrolysis (hereinafter also referred to as "the second method"). For example, as Figure 3 As shown, an electrolytic cathode 10 (hereinafter also referred to as "the third type") may also be formed by dispersing a catalyst and a reverse current absorber in a substrate. For example, as Figure 4 As shown, the cathode 10 for water electrolysis can also be formed on one of the two sides of the catalyst section 1, such as the reverse current absorber 2. Figure 5 As shown, a water electrolysis cathode 10 (hereinafter referred to as a cathode) may also have a reverse current absorber 2 formed on both the front and back sides of the catalyst section 1. Figure 4 and5 The cathode 10 for water electrolysis described herein is also referred to as "the fourth method". Furthermore, as explained in the manufacturing method described later, the catalyst section 1 of this embodiment can be obtained by coating a slurry containing a catalyst raw material onto a substrate, and the reverse current absorber 2 of this embodiment can be obtained by coating a slurry containing a hydrogen storage alloy containing Al onto a substrate.

[0019] Substrate The substrate in this embodiment is a conductor capable of conducting electricity. As long as the substrate is conductive, there are no particular limitations, but examples include nickel metal, nickel alloys, and other metals containing Ni. The substrate can be formed entirely of nickel metal or nickel alloys, or only its surface can be formed of nickel metal or nickel alloys. In the case where only the surface of the substrate is formed of nickel metal or nickel alloys, nickel metal or nickel alloys can be coated onto the surface of a metal material such as iron or stainless steel. Preferably, the substrate contains nickel metal or nickel alloys as a main component. From the perspective of resistance to the operating environment, it is preferable that the substrate is composed of nickel metal with higher Ni purity. Furthermore, "containing nickel metal or nickel alloys as a main component" means that the Ni content in the nickel metal or nickel alloy in the substrate exceeds 50% by mass.

[0020] There are no particular restrictions on the shape of the substrate; it can be porous or non-porous. Examples of porous substrate shapes include perforated metal, mesh, foamed metal, and expanded metal. Examples of non-porous substrate shapes include sheet-like forms.

[0021] There are no particular restrictions on the thickness of the substrate, as long as it is set to be suitable for the water electrolysis device used.

[0022] "catalyst" The catalyst in this embodiment contains a metal. Examples of metals include aluminum (Al), titanium (Ti), vanadium (V), chromium (Cr), manganese (Mn), iron (Fe), cobalt (Co), nickel (Ni), copper (Cu), zinc (Zn), yttrium (Y), zirconium (Zr), niobium (Nb), molybdenum (Mo), ruthenium (Ru), rhodium (Rh), palladium (Pd), silver (Ag), cadmium (Cd), indium (In), tin (Sn), tantalum (Ta), and tungsten (…). The catalyst in this embodiment may also contain oxides, hydroxides, nitrides, phosphides, sulfides, carbides, borides, etc., of these metals. Furthermore, the catalyst in this embodiment may also contain oxides, hydroxides, nitrides, phosphides, sulfides, carbides, borides, etc., of these metals. The catalyst in this embodiment may also contain multiple metals.

[0023] Preferably, the catalyst in this embodiment comprises the same metal as the substrate. This increases the affinity between the substrate and the catalyst, suppresses catalyst detachment from the substrate, and consequently allows for improved durability against reverse current. From this perspective, the catalyst in this embodiment preferably comprises Ni.

[0024] (Raney nickel particles) The catalyst in this embodiment may also contain Raney nickel particles. Raney nickel particles contain Ni and Al. Raney nickel particles are porous bodies with a large specific surface area and numerous fine pores, exhibiting high activity.

[0025] The ratio of the total molar number of Al to the total molar number of Ni in the Raney nickel particles (hereinafter also referred to as the "first Al / Ni ratio") is 1 or less, preferably 0.6 or less. By making the first Al / Ni ratio 1 or less, an increase in activity is expected. The first Al / Ni ratio can be, for example, 0.005 or more, or 0.01 or more. The first Al / Ni ratio can be confirmed, for example, by scanning electron microscopy-energy dispersive X-ray spectrometry (SEM-EDX).

[0026] Raney nickel particles may also contain a first metal other than Ni and Al. By including a first metal in the Raney nickel particles, further enhanced activity is expected. Examples of such a first metal include magnesium (Mg), silicon (Si), Ti, Cr, Mn, Fe, Co, Cu, Ag, Pt, and Au. The proportion of the first metal contained in the Raney nickel particles is equal to the proportion of the first metal contained in the raw material for the Raney nickel particles (hereinafter also referred to as "Raney alloy"). When the Raney nickel particles contain a first metal, the molar ratio of Ni to the first metal can be, for example, 1.99:0.01 to 1.15:1.85. The preferred molar ratio of Ni to the first metal is 1.99:0.05 to 1.5:0.5.

[0027] Raney nickel particles can be alloys composed of a single phase or alloys composed of multiple phases. Examples of such phases include a phase composed solely of Ni, a phase composed of Ni and Al, a phase composed of Ni and a first metal, and a phase composed of Ni, Al, and a first metal. The phases constituting Raney nickel particles and their composition ratios can be identified, for example, by SEM-EDX.

[0028] The BET specific surface area of ​​Raney nickel particles is, for example, 0.05 m². 2 / g or more and 100m 2 / g or less. Furthermore, BET specific surface area refers to the surface area per unit mass of Raney nickel particles determined by N2 adsorption using the BET method.

[0029] The average particle size (D50) of Raney nickel particles is, for example, 5 μm or more and 100 μm or less. When the average particle size of Raney nickel particles is 5 μm or more and 100 μm or less, improved activity and durability can be expected. The average particle size of Raney nickel particles can also be 8 μm or more and 85 μm or less, 10 μm or more and 50 μm or less, 10 μm or more and 30 μm or less, or 15 μm or more and 30 μm or less.

[0030] [Method for manufacturing Raney nickel particles] Raney nickel particles are generally obtained by treating Raney alloys containing Ni and alkali-soluble metal elements with an alkaline substance, thereby dissolving the alkali-soluble metal element from the Raney alloy. Preferably, the alkali-soluble metal element is one with a higher ionization tendency compared to Ni. Examples of alkali-soluble metal elements include amphoteric metals (Al, Zn, Sn, and Pb).

[0031] Raney nickel particles are obtained by dissolving Al from a Raney alloy containing Ni and Al by treating it with an alkaline substance. The Raney alloy may also contain a first metal.

[0032] As a specific processing method, one example is to immerse the Raney alloy (a substrate containing the Raney alloy) in an alkaline aqueous solution containing an alkaline substance, maintain the temperature of the alkaline aqueous solution at a specified temperature, and stir for a specified time. Examples of alkaline substances 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. Alkali metal hydroxides are preferred as the alkaline substance.

[0033] The processing temperature is, for example, above 100°C and below 140°C. The processing time is, for example, above 1 hour and below 9 hours. The amount of alkaline substance used in this process can be adjusted appropriately.

[0034] Raney alloys are preferably treated at high temperatures using a high-concentration alkaline aqueous solution of an alkali metal hydroxide. The concentration of the alkaline aqueous solution is, for example, 3 mol / L or more, preferably 7 mol / L or more, and more preferably 14 mol / L or more. The concentration of the alkaline aqueous solution is 20 mol / L or less. The treatment temperature is, for example, 100°C or more, preferably 110°C or more, and more preferably 125°C or more. The treatment temperature is, for example, 148°C or less. Furthermore, to increase the treatment temperature, it is necessary to increase the concentration of the alkaline aqueous solution so that its boiling point is above the treatment temperature. For example, when the treatment temperature is 100°C or more, the concentration of the alkaline aqueous solution is preferably 3 mol / L or more; when the treatment temperature is 125°C or more, the concentration of the alkaline aqueous solution is preferably 14 mol / L or more. Additionally, this process is preferably carried out at atmospheric pressure. Under this condition, compared to pressurized conditions, hydrogen generated during treatment can be easily removed.

[0035] By setting these conditions, the reaction time between the alkaline aqueous solution and the Raney alloy can be shortened. For example, when the concentration of the alkaline aqueous solution is 3 mol / L or higher and the processing temperature is 100°C or higher, the reaction time is 3 hours or more and 9 hours or less; when the concentration of the alkaline aqueous solution is 14 mol / L or higher and the processing temperature is 125°C or higher, the reaction time is 1 hour or more and 8 hours or less.

[0036] In addition, it can be to dissolve all the Al contained in the Raney alloy, or to leave a portion of the Al undissolved.

[0037] In this case, when the proportion of Al in the Raney alloy containing Ni and Al is high, the porosity of the Raney nickel particles obtained by dissolving Al is higher, that is, the specific surface area is higher. Therefore, from the viewpoint of obtaining Raney nickel particles exhibiting higher activity, it is preferable to use a Raney alloy with a higher proportion of Al.

[0038] On the other hand, when the proportion of Al in a Raney alloy containing Ni and Al is low, the porosity of the Raney nickel particles obtained by dissolving Al is low, that is, the specific surface area is low. Therefore, from the viewpoint of obtaining Raney nickel particles with high durability (strength), it is preferable to use a Raney alloy with a low proportion of Al.

[0039] Thus, from the viewpoint of obtaining Raney nickel particles that maintain durability and exhibit high activity, it is preferable that the number of moles of Al contained in the Raney alloy is greater than the number of moles of Ni contained in the Raney alloy. Furthermore, from this viewpoint, it is preferable to use a Raney alloy represented by the following formula (2).

[0040] Al3Ni （2-x）） M x (2) In the above formula (2), M is at least one element selected from Mg, Si, Ti, Cr, Mn, Fe, Co, Cu, Ag, Pt and Au, and x satisfies the relationship 0≤x≤0.2.

[0041] The preferred element M is at least one element selected from Fe and Co. This is because, in addition to the expected increase in activity, it also allows for the expectation of reduced usage and lower costs. More preferably, the element M contains at least Fe. From this point of view, it is more preferable to use a Raney alloy represented by the following formula (3).

[0042] Al3Ni （2-（y+z）） Fe y Co z (3) In the above equation (3), y and z satisfy the relationship 0≤y≤0.1 and 0≤z≤0.1.

[0043] Raney alloy, for example, is in powder form. The average particle size of the Raney alloy is, for example, 5 μm or more and 100 μm or less. When the average particle size of the Raney nickel particles is 5 μm or more and 100 μm or less, improved activity and durability are expected. The average particle size of the Raney nickel particles can also be 8 μm or more and 85 μm or less, 10 μm or more and 50 μm or less, 10 μm or more and 30 μm or less, or 15 μm or more and 30 μm or less.

[0044] There are no particular restrictions on the manufacturing method of Raney alloys, and well-known alloy manufacturing methods can be used. Examples of manufacturing methods for Raney alloys include casting, quenching, mechanical alloying, and sputtering.

[0045] (Metal particles) The increased affinity between the substrate and the catalyst, and the suppression of catalyst detachment from the substrate, result in improved durability against reverse current. From this perspective, the catalyst of this embodiment may contain not only Raney nickel particles but also metal particles (hereinafter simply referred to as "metal particles") with Ni as a main component. The metal particles are in contact with the Raney nickel particles. Preferably, the metal particles are in contact with multiple Raney nickel particles. The metal particles function as a binder, adhering the Raney nickel particles dispersed in the catalyst to each other or to the substrate. This function will be explained below. Furthermore, "containing Ni as a main component" means that the Ni content in the metal particles exceeds 50% by mass.

[0046] In cases where the Raney alloy (Raney nickel particles) and metal particles contain metals other than Ni (hereinafter also referred to as "the first additive element"), when heat is applied to them, impurity diffusion occurs, where the first additive element is considered an impurity. That is, if heat is applied through processes such as sintering, causing thermal vibrations in the atoms of the first additive element, the first additive element diffuses from the Raney alloy to the metal particle feedstock (or from Raney nickel particles to metal particles) due to the concentration gradient of the first additive element between the Raney alloy and the metal particle feedstock (or between Raney nickel particles and metal particles). Therefore, even between different substances such as metal particles and Raney nickel particles (or between Raney alloy and metal particle feedstock), if they are in contact, the first additive element will undergo surface diffusion, resulting in adhesion between the Raney alloy and the metal particle feedstock (or between Raney nickel particles and metal particles). This increases the surface area of ​​the catalyst, and an increase in the activity of the cathode for water electrolysis can be expected. Furthermore, since the Raney alloy is firmly bonded to the raw materials of the metal particles (or Raney nickel particles and metal particles), detachment from the substrate is suppressed, and as a result, the durability of the cathode for water electrolysis can also be expected to be improved.

[0047] The metal particles may also contain Al. That is, in this embodiment, the Al concentration gradient is used as the driving force, and Al atoms diffuse from Raney nickel particles (or from Raney alloy to metal particle raw materials) where the amount of Al is greater than that of the metal particles (or the raw materials of metal particles). Furthermore, by including Al in the metal particles (or the raw materials of metal particles), the function of the metal particles as a binder is enhanced, resulting in the formation of a stronger electron conduction path, and thus, the activity of the cathode for water electrolysis is expected to be further improved. In addition, since the Raney nickel particles are more firmly bonded to the metal particles (or the Raney alloy to the raw materials of metal particles), the durability of the cathode for water electrolysis is also expected to be improved.

[0048] In this embodiment, the ratio of the total number of moles of Al to the total number of moles of Ni in the metal particles (hereinafter also referred to as the "second Al / Ni ratio") is 0.4 or less, preferably 0.35 or less. By making the second Al / Ni ratio 0.4 or less, an increase in activity is expected. The second Al / Ni ratio can, for example, be 0.005 or more, or 0.01 or more. The second Al / Ni ratio can be confirmed, for example, by SEM-EDX.

[0049] Preferably, the first Al / Ni ratio is larger than the second Al / Ni ratio. That is, it is preferable that the Raney nickel particles contain more moles of Al than the metal particles. The improved function of the metal particles as a binder results in the formation of a stronger electron conduction path, leading to potentially higher activity of the cathode for water electrolysis. Furthermore, the stronger bond between the Raney nickel particles and the metal particles also suggests improved durability of the cathode for water electrolysis.

[0050] Preferably, the metal particles contain Al on their surface. By containing Al on the surface of the metal particles, it is expected that the function of the metal particles as an adhesive for bonding Raney nickel particles to each other or to a substrate will be further enhanced.

[0051] Preferably, the average particle size of the metal particles is smaller than that of the Raney nickel particles. When the average particle size of the metal particles is smaller than that of the Raney nickel particles, the metal particles can penetrate into the gaps between the Raney nickel particles. As a result, the metal particles and Raney nickel particles can be in closer contact, and the function of the metal particles as a binder is expected to be further improved. The average particle size of the metal particles can be more than 5 times smaller than that of the Raney nickel particles, or more than 10 times smaller. The average particle size of the metal particles is 1 μm or more and 10 μm. The average particle size of the metal particles can also be 1 μm or more and 5 μm or less, 1.5 μm or more and 3.5 μm or less, or 2 μm or more and 3 μm or less. Preferably, the average particle size of the metal particles is 2 μm or more and 3 μm or less. When the average particle size of the metal particles is 2 μm or more and 3 μm or less, improved durability is expected. Furthermore, through the bonding of the metal particles with each other, sometimes the average particle size of the metal particles is larger than that of the Raney nickel particles.

[0052] (Method for manufacturing a catalyst containing Raney nickel particles and metal particles) The catalyst containing Raney nickel particles and metal particles is obtained by calcining a mixture of raw materials containing Raney alloy and metal particles containing Ni as the main component (a substrate containing Raney alloy and metal particles) and treating it with an alkaline substance. Furthermore, the treatment with the alkaline substance is the same as the method for manufacturing Raney nickel particles described above, and therefore is omitted.

[0053] The firing temperature can be, for example, above 600℃ and below 900℃. The firing time can be, for example, above 1 hour and below 24 hours.

[0054] The preferred raw material for metal particles contains fewer moles of Al than that in the Raney alloy. When the raw material for metal particles contains fewer moles of Al than that in the Raney alloy, during calcination, Al diffuses from the Raney alloy to the raw material for metal particles due to the concentration gradient, becoming metal particles. As a result, a more robust electronic conduction pathway is formed, leading to a greater expectation of improved catalyst activity and durability.

[0055] The raw material for the metal particles can also be substantially composed of Ni. Ni is an alkali-resistant metal, therefore it does not corrode even during use. As a result, improvements in the activity and durability of the electrodes used for water electrolysis can be expected. Furthermore, "substantially composed of Ni" means that the Ni content in the metal particles is 95% by mass or more.

[0056] The raw material for the metal particles is, for example, in powder form. Preferably, the average particle size of the raw material is smaller than that of the Raney alloy. When the average particle size of the raw material is smaller than that of the Raney alloy, the function of the metal particles as a binder is expected to be further improved. The average particle size of the raw material can be more than 5 times smaller than that of the Raney nickel particles, or more than 10 times smaller. The average particle size of the raw material can also be 1 μm or more and 10 μm, 1 μm or more and 5 μm or less, 1.5 μm or more and 3.5 μm or less, or 2 μm or more and 3 μm or less. Preferably, the average particle size is 2 μm or more and 3 μm or less. When the average particle size is 2 μm or more and 3 μm or less, improved durability is expected.

[0057] Reverse current absorber The reverse current absorber of this embodiment includes a hydrogen storage alloy. The hydrogen storage alloy includes Al. The reverse current absorber may also be composed of a hydrogen storage alloy. The hydrogen storage alloy is basically an alloy of metal A, which readily reacts with hydrogen but has poor hydrogen release capacity, and metal B, which is difficult to react with hydrogen but has excellent hydrogen release capacity. Examples of A include Group 2 elements such as Mg; Group 3 elements such as scandium (Sc) and lanthanides; Group 4 elements such as Ti and Zr; Group 5 elements such as V and Ta; mixed rare earth metals containing multiple rare earth elements (hereinafter sometimes simply referred to as Mm), Pd, etc. In addition, as long as B contains Al, it is sufficient. Examples of elements other than Al include Fe, Co, Ni, Cr, Pt, Cu, Ag, Mn, Zn, etc.

[0058] The hydrogen storage alloy in this embodiment can be any alloy containing Al, and its composition ratio and other elements that can be included are not particularly limited. Examples include La(Mn)-Ni-Al, La(Mn)-Mn-Al, La(Mn)-Ni-Al-Mn, La(Mn)-Ni-Al-Zr, La(Mn)-Ni-Al-Co, La(Mn)-Ni-Al-Mn-Co, La(Mn)-Ni-Al-Te, and La(Mn)-Ni-Al-Te-Co. Specifically, LaNi... 4.3 Al 0.7 MmNi 4.5 Al 0.5 MmNi 4.5 Al 0.25 Co 0.25 MmNi 4.5 Al 0.25 Mn 0.25 MmNi 3.55 Mn 0.4 Al 0.3 Co 0.75 La 0.77 Mg 0.23 Ni 3.3 Al 0.1 wait.

[0059] The hydrogen storage alloy of this embodiment preferably contains La and Ni, and more preferably contains not only La and Ni but also Mg. More specifically, the hydrogen storage alloy containing La, Mg, Ni and Al is any alloy containing La, Mg, Ni and Al, and there are no particular restrictions on its composition ratio or other elements that may be contained. For example, a hydrogen storage alloy containing La, Mg, Ni and Al can be represented by the following formula (1).

[0060] (La) 1-a M a ) 1-b Mg b Ni c Al d T e (1) In the above formula (1), M is at least one element selected from Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, calcium (Ca), strontium (Sr), Sc, Y, Ti, Zr, and Hf; T is at least one element selected from Mn, Co, Ti, V, Nb, W, Ta, Cr, Mo, Fe, Al, gallium (Ga), Zn, Sn, In, Cu, Si, lithium (Li), phosphorus (P), sulfur (S), and boron (B); and a, b, c, d, and e satisfy the relationships 0 ≤ a ≤ 0.1, 0 < b < 0.3, 2.5 ≤ c ≤ 4.7, 0 < d ≤ 0.1, and 0 ≤ e ≤ 0.01, respectively. Furthermore, it is preferable that c satisfies the relationship 2.5 ≤ c ≤ 3.7.

[0061] As a hydrogen storage alloy that satisfies the above equation (1), specifically, LaNi can be cited as an example. 4.3 Al 0.7 LaNi 4.5 Al 0.25 Co 0.25 LaNi 4.5 Al 0.25 Mn 0.25 LaNi 3.55 Mn 0.4 Al 0.3 Co 0.75 La 0.77 Mg 0.23 Ni 3.3 Al 0.1 wait.

[0062] The reason for favoring such a hydrogen storage alloy is that the increased affinity between the substrate and the reverse current absorber (hydrogen storage alloy) suppresses the detachment of the hydrogen storage alloy from the substrate, resulting in improved durability against reverse current. Furthermore, when the hydrogen storage alloy contains metal elements such as Al and La (hereinafter referred to as "secondary additive elements") that are more easily diffused than the main metal element of the substrate, applying heat will cause impurity diffusion, where the secondary additive elements are considered impurities. That is, if heat is applied through processes such as firing, the atoms of the secondary additive elements undergo thermal vibration, and due to the concentration gradient of the secondary additive elements between the hydrogen storage alloy and the substrate, the secondary additive elements diffuse from the hydrogen storage alloy to the substrate. Therefore, even between different materials such as the hydrogen storage alloy and the substrate, if they are in contact, the secondary additive elements will undergo surface diffusion, thereby bonding the hydrogen storage alloy to the substrate. Because the hydrogen storage alloy is firmly bonded to the substrate, detachment from the substrate is suppressed, resulting in improved durability of the cathode for water electrolysis. That is, in this embodiment, the concentration gradient of Al is used as the driving force, and Al atoms diffuse from the hydrogen storage alloy with a large amount of Al to the substrate with Ni as the main component, resulting in a stronger bond, and thus an improvement in the durability of the cathode for water electrolysis can be expected.

[0063] Preferably, the hydrogen storage alloy contains more molar amounts of La and Ni than of Al. In this case, Al diffuses more readily within the hydrogen storage alloy than La and Ni, and the second added element diffuses more readily from the hydrogen storage alloy to the substrate.

[0064] Examples of crystal structures for hydrogen storage alloys in this embodiment include: AB5 type exhibiting a hexagonal CaCu5 crystal structure; AB2 type exhibiting a hexagonal MgZn2 or cubic MgCu2 crystal structure; AB type exhibiting a cubic CsCl crystal structure; A2B type exhibiting a hexagonal Mg2Ni crystal structure; solid solution type exhibiting a body-centered cubic crystal structure; and AB3, A2B7, and A5B types, which are combinations of AB5 and AB2 crystal structures. 19 The hydrogen storage alloy of this embodiment may have one of the above crystal structures, or it may have two or more crystal structures.

[0065] Examples of AB5-type hydrogen storage alloys include LaNi5, CaCu5, and MmNi5. Examples of AB2-type hydrogen storage alloys include MgZn2, ZrNi2, and ZrCr2. Examples of AB-type hydrogen storage alloys include TiFe and TiCo. Examples of A2B-type hydrogen storage alloys include Mg2Ni and Mg2Cu. Examples of solid solution-type hydrogen storage alloys include Ti-V, V-Nb, and Ti-Cr. Examples of AB3-type hydrogen storage alloys include LaNi3. Examples of A2B7-type hydrogen storage alloys include La2Ni7. As for A5B... 19 Type-3 hydrogen storage alloys, such as La5Co, can be cited as an example. 19 Pr5Co 19 In the crystal structures described above, some of the metals can be replaced by one or more other metals or elements.

[0066] As the hydrogen storage alloy of this embodiment, a hydrogen storage alloy comprising a main phase having an A2B7 type crystal structure is preferred. The hydrogen storage alloy of this embodiment may also be composed of an A2B7 type hydrogen storage alloy. The A2B7 type hydrogen storage alloy has a crystal structure formed by stacking the crystal structures of AB2 type hydrogen storage alloys (so-called AB2 type subunits) and AB5 type hydrogen storage alloys (so-called AB5 type subunits), therefore, the crystal is not easily broken and has excellent durability. Furthermore, since the lattice system is larger, hydrogen can easily penetrate, increasing the hydrogen storage capacity, i.e., an increase in capacity can be expected. In addition, "the main phase having an A2B7 type crystal structure" means that the proportion of the A2B7 type crystal structure in the hydrogen storage alloy exceeds 50%.

[0067] The reverse current absorber of this embodiment may also contain metal particles comprising Ni as a main component. In this case, the metal particles are in contact with the hydrogen storage alloy. The metal particles function as an adhesive to bond the hydrogen storage alloy dispersed in the reverse current absorber to each other or to the substrate. By bonding the hydrogen storage alloy to each other with the metal particles, the surface area of ​​the hydrogen storage alloy is increased, thereby improving its activity as a reverse current absorber. Furthermore, the metal particles are as described above, so detailed descriptions are omitted.

[0068] Hydrogen storage alloys can also have their surfaces oxidized. It is conceivable that by oxidizing the surface of the hydrogen storage alloy, unintended reactions between the alloy and the electrolyte can be suppressed. Furthermore, in this case, the reverse current absorber can also be made of a hydrogen storage alloy with its surface oxidized.

[0069] Methods for oxidizing the surface of a hydrogen storage alloy can include, for example, exposing the alloy to air and oxidizing it with oxygen in the air, or oxidizing it by contacting it with oxides such as hydrogen peroxide. However, in either method, it is preferable to cool the hydrogen storage alloy while doing so to suppress excessive heating. Specifically, it is preferable to cool the hydrogen storage alloy by pouring water onto it, or to place the alloy in water or in an aqueous solution of oxides such as hydrogen peroxide.

[0070] Alternatively, the hydrogen storage alloy can be treated with an alkaline substance before its surface is oxidized. In this embodiment, the treatment with an alkaline substance refers to treatment with an alkaline aqueous solution containing dissolved alkali metal hydroxide. Preferably, the treatment with an alkaline substance is performed after the first alkaline aqueous solution treatment with dissolved alkali metal hydroxide, followed by the second alkaline aqueous solution treatment with dissolved alkali metal hydroxide.

[0071] By treating the hydrogen storage alloy with a first alkaline aqueous solution, substances such as La, which have high solubility relative to the alkaline aqueous solution, dissolve from the surface of the hydrogen storage alloy. Therefore, substances such as Ni, which have low solubility relative to the alkaline aqueous solution, are concentrated on the surface of the hydrogen storage alloy after treatment with the first alkaline aqueous solution.

[0072] Examples of alkali metal hydroxides included in the first alkaline aqueous solution include lithium hydroxide, sodium hydroxide, and potassium hydroxide. Preferably, the first alkaline aqueous solution is a strong base, and sodium hydroxide is the preferred alkali metal hydroxide included in the first alkaline aqueous solution. The concentration of the alkali metal hydroxide included in the first alkaline aqueous solution is, for example, 10% by mass or more and 60% by mass or less.

[0073] The treatment of the hydrogen storage alloy using the first alkaline aqueous solution preferably involves immersing the hydrogen storage alloy in the first alkaline aqueous solution. Furthermore, this treatment preferably includes stirring and heating. The heating temperature can be, for example, 50°C or higher and 150°C or lower. The heating time can be appropriately set according to the concentration of the first alkaline aqueous solution and the heating temperature, for example, 0.1 hours or higher and 10 hours or lower.

[0074] The ratio of the amount of hydrogen storage alloy to the first alkaline aqueous solution can be, for example, by mass ratio of 1:0.5 to 1:100. If the amount of the first alkaline aqueous solution is small, there is a possibility that Ni and other materials may not be sufficiently concentrated on the surface of the hydrogen storage alloy. From a cost perspective, using a large amount of the first alkaline aqueous solution is not preferable.

[0075] Next, the hydrogen storage alloy treated with the first alkaline aqueous solution can be further treated with a second alkaline aqueous solution containing dissolved alkali metal hydroxide.

[0076] The hydrogen storage alloy before treatment with the first alkaline aqueous solution can be separated, for example, by filtration or centrifugation, or it can be separated after treatment with the first alkaline aqueous solution. Alternatively, the hydrogen storage alloy can be treated with the first alkaline aqueous solution together with the substrate, Raney nickel particles (Raney alloy), and metal particles (raw material for the metal particles). Treatment of the hydrogen storage alloy with the second alkaline aqueous solution can be performed by immersing the hydrogen storage alloy in the second alkaline aqueous solution, or by pouring the second alkaline aqueous solution onto the hydrogen storage alloy. Treatment of the hydrogen storage alloy with the second alkaline aqueous solution can also be performed after the above separation or simultaneously with the separation. The hydrogen storage alloy can also be treated with the second alkaline aqueous solution together with the substrate, Raney nickel particles (Raney alloy), and metal particles (raw material for the metal particles).

[0077] Examples of alkali metal hydroxides included in the second alkaline aqueous solution include lithium hydroxide, sodium hydroxide, and potassium hydroxide. Sodium hydroxide is preferred as the alkali metal hydroxide included in the second alkaline aqueous solution.

[0078] Furthermore, when the concentration of the alkali metal hydroxide in the first alkaline aqueous solution is set as C1 and the concentration of the alkali metal hydroxide in the second alkaline aqueous solution is set as C2, it is preferable that the relationship C1 > C2 is satisfied. Since the viscosity of the alkaline aqueous solution with a lower concentration is lower, it is conceivable that the treatment using the second alkaline aqueous solution will proceed smoothly under the condition that the relationship C1 > C2 is satisfied. The concentration of the alkali metal hydroxide in the second alkaline aqueous solution can, for example, be 0.01% by mass or more and 10% by mass or less.

[0079] From the perspective of manufacturing costs, it is preferable to perform the treatment of the hydrogen storage alloy using the second alkaline aqueous solution at a lower temperature than the treatment using the first alkaline aqueous solution. The treatment temperature using the second alkaline aqueous solution can be, for example, 0–100°C. The treatment temperature using the second alkaline aqueous solution can be determined by the temperature of the environment in which the hydrogen storage alloy is located, or by the temperature of the second alkaline aqueous solution.

[0080] The ratio of the hydrogen storage alloy to the second alkaline aqueous solution can be, for example, by mass ratio of 1:0.5 to 1:100. If the amount of the second alkaline aqueous solution is small, there is a possibility of insufficient removal of hydroxides such as La. From a cost perspective, a large amount of the second alkaline aqueous solution is not preferable.

[0081] Alternatively, after treatment with the second alkaline aqueous solution, the hydrogen storage alloy can be cleaned with water. Cleaning with water removes the second alkaline aqueous solution adhering to the surface of the hydrogen storage alloy. The mass ratio of hydrogen storage alloy to water during water cleaning can be 1:1 to 1:50. Furthermore, a method can be used to oxidize the surface of the hydrogen storage alloy by cleaning it with water under atmospheric conditions.

[0082] The hydrogen storage alloy is, for example, in powder form. Preferably, the average particle size of the hydrogen storage alloy is larger than the average particle size of the metal particles. The average particle size of the hydrogen storage alloy is, for example, 5 μm or more and 150 μm or less. Preferably, the average particle size of the hydrogen storage alloy is 8 μm or more and 110 μm or less.

[0083] <Manufacturing Method of Cathode for Water Electrolysis> The method for manufacturing a cathode for water electrolysis according to this embodiment includes at least (a) a catalyst section forming step and (b) a reverse current absorber forming step. Hereinafter, manufacturing methods from various embodiments are illustrated. However, the method for manufacturing a cathode for water electrolysis according to this embodiment is not limited thereto.

[0084] Method 1 (a) Catalyst formation process) There are no particular limitations on the catalyst formation process. For example, it can be formed by spraying the catalyst raw material onto the first substrate. As a spraying method, plasma spraying can be cited as an example. There are no particular limitations on the spraying conditions. The spraying conditions can be appropriately changed depending on the catalyst raw material, substrate, etc. Furthermore, the catalyst raw material and substrate are as described above.

[0085] For example, it can also be formed by coating a first slurry obtained by mixing a catalyst feedstock and a solvent onto a first substrate (hereinafter also referred to as the coating method). Examples of solvents include water, N-methyl-2-pyrrolidone (NMP), and N-ethyl-2-pyrrolidone (NEP). The first slurry may also contain a thickener. Examples of thickeners include carboxymethyl cellulose (CMC), polytetrafluoroethylene (PTFE), and polyvinylidene fluoride (PVDF).

[0086] The first slurry can be applied to the surface of the first substrate using any coating apparatus. The application of the first slurry can be performed using known coating apparatuses such as die coaters, roller coaters, knife coaters, doctor blade coaters, bar coaters, spray coaters, and screen printing equipment, or by immersing the first substrate in the first slurry. The first slurry can be applied to the entire surface of the first substrate or to a portion of its surface. If the first substrate is plate-shaped, the first slurry can be applied to one or both sides. If the first substrate is porous, the first slurry can be pressed to allow it to penetrate into the pores of the substrate. If the first substrate is porous, any remaining first slurry that has not penetrated into the pores can be scraped off using a doctor blade or similar tool.

[0087] The catalyst forming process may further include a catalyst drying process for drying the first slurry coated on the first substrate. For example, the first slurry may be dried using a hot air drying oven, an infrared dryer, a hot plate, etc. The drying temperature and drying time can be adjusted appropriately.

[0088] The catalyst forming process may further include a catalyst firing process, which involves firing (heat treating) the first substrate (catalyst portion) containing the coated first slurry. Preferably, the catalyst firing process is performed after the catalyst drying process. In this case, it is preferable to perform an alkali treatment process after the catalyst firing process. The firing temperature can be, for example, 600°C or higher and 900°C or lower. The firing time can be, for example, 1 hour or more and 24 hours or less.

[0089] The first substrate (catalyst section) after plasma spraying, or the first substrate (catalyst section) containing the coated first slurry, can also be pressed. Pressing adjusts the thickness of the first substrate (catalyst section). Furthermore, when the catalyst section contains Raney nickel particles and metal particles, pressing increases the contact area between the Raney nickel particles and the metal particles (the raw material of Raney alloy and metal particles). The pressure can be appropriately adjusted according to the desired thickness of the first substrate (catalyst section). Moreover, pressing of the first substrate can be performed at any time.

[0090] The catalyst section can be a catalyst section in which a catalyst layer containing a catalyst is formed on the surface of the first substrate, or a catalyst section in which a catalyst is dispersed in the first substrate. Furthermore, when a catalyst layer is formed, the catalyst layer may be formed on at least one of the front and back surfaces of the first substrate, or it may be formed on both the front and back surfaces of the first substrate.

[0091] In the case where the catalyst portion is formed by dispersing the catalyst in the first substrate, it is preferable to use a first substrate with a low basis weight and a first slurry with a high viscosity (high concentration). By using such a first substrate and first slurry, the first slurry can easily penetrate into the first substrate. This is conceivable because the lower the basis weight, the higher the porosity of the substrate. Higher substrate porosity leads to a higher slurry loading (catalyst portion loading), thus allowing for higher activity. Furthermore, a higher viscosity (higher concentration) slurry results in a higher concentration of catalyst portion within the slurry, facilitating contact between Raney nickel particles and metal particles, thus allowing for improved durability. Moreover, by using a low basis weight substrate, even when impregnated with a high-viscosity slurry, a high porosity can be maintained inside the cathode for water electrolysis, thus allowing for high activity. "Low basis weight" refers to, for example, 100 g / m³. 2 Above and 600g / m 2 The preferred value is 200g / m³. 2 Above and 400g / m 2 The term "high viscosity" refers to, for example, a solvent content in the first slurry of 10% by mass or more and 50% by mass or less, preferably 20% by mass or more and 45% by mass or less.

[0092] (b) Reverse current absorber forming process) The reverse current absorber forming process includes a hydrogen storage alloy coating process, which involves coating a second slurry obtained by mixing an Al-containing hydrogen storage alloy with a solvent onto a second substrate.

[0093] Regarding the Al-containing hydrogen storage alloy, substrate, and solvent, as described above. The amount of Al-containing hydrogen storage alloy is not particularly limited and can be appropriately set. The second slurry may also contain a thickener. Regarding the thickener, as described above. Furthermore, the first substrate and the second substrate may be the same substrate or different substrates. Preferably, the first substrate and the second substrate are the same substrate.

[0094] In the hydrogen storage alloy coating process, the second slurry can be applied to the surface of the second substrate using any coating apparatus. The application of the second slurry can be performed using known coating apparatus such as a die coater, roller coater, knife coater, doctor blade coater, bar coater, spray coater, or screen printing apparatus, or by immersing the second substrate in the second slurry. The second slurry can be applied to the entire surface of the second substrate or to a portion of its surface. If the second substrate is plate-shaped, the second slurry can be applied to one or both sides. If the second substrate is porous, the second slurry can be pressed to allow it to penetrate into the pores of the substrate. If the second substrate is porous, the first slurry that has not penetrated into the pores and remains on the surface of the second substrate can be scraped off using a doctor blade or similar tool.

[0095] The reverse current absorber forming process may further include a reverse current absorber drying process, which involves drying the second substrate (reverse current absorber) containing the second slurry after the hydrogen storage alloy coating process. Regarding the drying method, as described above, the drying temperature and drying time can be adjusted appropriately.

[0096] The reverse current absorber forming process may further include a reverse current absorber firing process, which involves firing (heat-treating) the second substrate (reverse current absorber) containing the second slurry. Preferably, the reverse current absorber firing process is performed after the reverse current absorber drying process. The firing temperature may be, for example, 600°C or higher and 900°C or lower. The firing time may be, for example, 1 hour or higher and 24 hours or lower.

[0097] The reverse current absorber forming process may further include a pressing process for pressing the second substrate (reverse current absorber) containing the second slurry. Through pressing, the thickness of the second substrate (reverse current absorber) containing the second slurry is adjusted. The pressure can be appropriately adjusted according to the thickness of the second substrate (reverse current absorber) containing the desired second slurry. Furthermore, the second substrate can be pressed before the coating of the second slurry, or the second substrate (reverse current absorber) containing the second slurry can be pressed before the reverse current absorber firing process.

[0098] The second slurry may also contain metal particles. The reverse current absorber may be a reverse current absorber with a reverse current absorber layer containing a hydrogen storage alloy formed on the surface of the second substrate, or a reverse current absorber with a hydrogen storage alloy dispersed in the second substrate. Furthermore, when forming a reverse current absorber layer, the reverse current absorber layer may be formed on at least one of the front and back surfaces of the second substrate, or it may be formed on both sides of the second substrate. When forming a reverse current absorber with a hydrogen storage alloy dispersed in the second substrate, a second substrate with a low weight per unit area and a high viscosity second slurry are preferred.

[0099] Method 2 In the second method, the cathode for water electrolysis is manufactured using the same method as in the first method, except that a catalyst layer (catalyst portion) is formed on one side of the substrate and a reverse current absorber is formed on the other side. In the second method, the substrate can be used separately as in the first method. There are no particular restrictions on the formation order of the catalyst layer and the reverse current absorber.

[0100] The Third Way In the third method, the cathode for water electrolysis is manufactured using the same method as in the first method, except that a mixed slurry containing a catalyst and an Al-containing hydrogen storage alloy is coated onto the substrate. In the third method, the first and second slurries are not manufactured separately as in the first method. That is, in the third method, the catalyst section and the reverse current absorber are formed simultaneously. Therefore, in the third method, the aforementioned (a) catalyst section formation process and (b) reverse current absorber formation process can be combined and referred to as the "cathode formation process for water electrolysis." Furthermore, in manufacturing the cathode for water electrolysis in the third method, the catalyst section is formed by a coating method in order to coat the slurry onto the substrate.

[0101] The Fourth Way In the fourth embodiment, except that after forming a catalyst section in which the catalyst is dispersed in the substrate, a reverse current absorber is formed on at least one of the front and back surfaces of the catalyst section, the cathode for water electrolysis is manufactured using the same method as in the first embodiment. The reverse current absorber can be formed on only one of the front and back surfaces of the catalyst section, or it can be formed on both the front and back surfaces of the catalyst section. Furthermore, in manufacturing the cathode for water electrolysis according to the fourth embodiment, the catalyst section is formed by a coating method in order to coat the slurry onto the substrate.

[0102] Furthermore, the aforementioned methods for manufacturing Raney nickel particles, manufacturing catalysts containing Raney nickel particles and metal particles, and surface oxidation of hydrogen storage alloys can be incorporated into a single step of the method for manufacturing a cathode for water electrolysis. For example, when using Raney nickel particles as a catalyst, a slurry obtained by mixing a Raney alloy and a solvent is applied to a substrate and dried. After drying, the substrate and the dried slurry layer are treated with an alkaline substance to dissolve Al from the Raney alloy, thereby forming a catalyst section. Alternatively, when using both Raney nickel particles and metal particles as catalysts, a slurry obtained by mixing a Raney alloy, metal particles, and a solvent is applied to a substrate and dried. After drying, the substrate and the dried slurry layer are sintered. After sintering, the substrate and the sintered slurry layer are treated with an alkaline substance to dissolve Al from the Raney alloy, thereby forming a catalyst section. Example

[0103] <Raw Materials> The materials used in this embodiment are shown below.

[0104] Substrate A1: Porous metal body made of Ni (manufactured by Sumitomo Electric Industries, Ltd., CELMET (registered trademark), product number #8) (size: 50mm x 50mm, thickness: 1.2mm) A2: Porous metal body made of Ni (manufactured by NanoMaterials development experts) (size: 50mm × 50mm, thickness: 4mm)

[0105] Hydrogen Storage Alloys B1: (La) 0.9 Sm 0.07 Y 0.03 ) 0.77 Mg 0.23 Ni 3.305 Al 0.09 Cr 0.005 (Average particle size: 20–25 μm) B2: (La) 0.975 Ce 0.02 Y 0.005 ) 0.75 Mg 0.25 Ni 3.305 Al 0.09 Cr 0.005 (Average particle size: 20–25 μm) B3: LaNi5 (average particle size: 20 μm)

[0106] Raney Alloy C1: Nickel-aluminum alloy with Al3Ni2 composition (manufactured by Japan Heavy Chemical Industry Co., Ltd., average particle size: 23μm) C2: Al3Ni 1.95 Fe 0.05 Nickel-aluminum-iron alloy (manufactured by Japan Heavy Chemical Industry Co., Ltd., average particle size: 16μm) C3: Al3Ni 1.95 Fe 0.05 Nickel-aluminum-iron alloy (manufactured by Japan Heavy Chemical Industry Co., Ltd., average particle size: 23μm) C4: Al3Ni 1.95 Fe 0.05 Nickel-aluminum-iron alloy (manufactured by Japan Heavy Chemical Industry Co., Ltd., average particle size: 38μm) C5: Composition Al3Ni 1.95 Fe 0.05 Nickel-aluminum-iron alloy (manufactured by Japan Heavy Chemical Industry Co., Ltd., average particle size: 85μm)

[0107] Raw Materials for Metal Particles D1: Nickel particles (manufactured by High Purity Chemical Research Institute, Inc., Ni nickel (NIE10PB)) (average particle size: 2-3 μm) D2: Nickel particles (manufactured by High Purity Chemical Research Institute, Co., Ltd., NIE11PB) (average particle size: 3-5 μm)

[0108] "other" Thickener: CMC (manufactured by Daiichi Kogyo Pharmaceutical Co., Ltd., CELLOGEN EP) Solvent: Water

[0109] <Reverse Current Absorber> (E1) A slurry was prepared by mixing hydrogen storage alloy B1, CMC and water.

[0110] The above-mentioned slurry is applied to both sides of the substrate A1 using a die-coating machine. After application, any remaining slurry on the surface of the substrate A1 is scraped off with a scraper.

[0111] The substrate A1 containing the slurry is dried at 80°C for 60 minutes.

[0112] The dried substrate A1 was fired at 700°C for 2 hours.

[0113] The calcined substrate A1 was immersed in a 14 mol / L sodium hydroxide aqueous solution at 125°C for 3 hours. Then, substrate A1 was washed with water and oxidized using hydrogen peroxide solution to produce the reverse current absorber E1. The resulting reverse current absorber is a reverse current absorber in which a hydrogen storage alloy is dispersed in the substrate.

[0114] (E2) Except for the use of hydrogen storage alloy B2, the reverse current absorber E2 was made using the same method as the reverse current absorber E1.

[0115] (E3) Except for the use of hydrogen storage alloy B3, the reverse current absorber E3 was made using the same method as the reverse current absorber E1.

[0116] <Electrodes for water electrolysis> (No.1) Plasma spraying of Raney alloy C1, which is used as a raw material for spraying, was performed on substrate A2 to obtain water electrolysis electrode No. 1.

[0117] (No.2) A slurry was prepared by mixing Raney alloy C1 with water. This slurry was then applied to both sides of substrate A1 using a die-coating machine. After coating, any remaining slurry on the surface of substrate A1 was scraped off with a scraper. Substrate A1 containing the slurry was dried at 80°C for 60 minutes. The dried substrate A1 was then fired at 700°C for 2 hours. The fired substrate A1 was then immersed in a 14 mol / L sodium hydroxide aqueous solution at 125°C for 3 hours. Finally, substrate A1 was washed with water and oxidized using hydrogen peroxide water to produce the water electrolysis electrode No. 2.

[0118] (No.3) A slurry consisting of hydrogen storage alloy B1, CMC, and water was applied to the surface of the water electrolysis electrode No. 1 containing the catalyst using a die-coating machine. This slurry was then dried at 80°C for 60 minutes to obtain the water electrolysis electrode No. 3. Furthermore, hydrogen storage alloy B1 was prepared by pre-immersing it in a 14 mol / L sodium hydroxide aqueous solution at 110°C for 3 hours, followed by washing with water and oxidation with hydrogen peroxide solution.

[0119] <Example 1> The reverse current absorber, made of hydrogen storage alloy, installed in the water electrolysis device gradually stores the hydrogen generated during continuous operation until it is completely filled with hydrogen. When the operation stops, a portion of the hydrogen that was filled during operation is released as the reverse current is absorbed.

[0120] Therefore, it can be imagined that the reverse current absorber, made of hydrogen storage alloy, installed in the water electrolysis device, is repeatedly filled with hydrogen at temperatures above 50°C and releases a small amount of hydrogen. Furthermore, the aforementioned temperatures are typical operating temperatures for water electrolysis devices.

[0121] Therefore, to evaluate the performance of the obtained reverse current absorber, repeated durability tests were conducted at 50°C in a state of being fully filled with hydrogen (100%) and in a state of being filled with 90% hydrogen. The hydrogen release capacity of the reverse current absorber was measured before and after the durability tests. Specifically, a 7 mol / L potassium hydroxide aqueous solution was used as the electrolyte, and the reverse current absorbers E1–E3 and nickel hydroxide (as the counter electrode) were immersed in the electrolyte. Then, a charging current was applied at a rate of 1 / 3C for the time it took for the hydrogen filling state to reach 100%, thereby filling the reverse current absorber with hydrogen. After filling, a discharging current was applied at a rate of 1 / 3C for the time it took for the hydrogen filling state to reach 90%, thereby releasing hydrogen from the reverse current absorber. The hydrogen filling and release were repeated 100 times, and the hydrogen release capacity was measured for the first and 100th cycles. In the determination of the hydrogen release capacity, firstly, an electric current was applied at a rate of 1 / 3C until the hydrogen filling level reached 100%. Then, the discharge was carried out at a rate of 1 / 3C until the potential of nickel hydroxide, which serves as the counter electrode relative to the reverse current absorber, reached 1.0V, and the hydrogen release capacity was calculated from the discharge time. The results are shown in Table 1.

[0122] [Table 1]

[0123] As shown in Table 1, the hydrogen release capacity of reverse current absorbers E1 and E2 did not change significantly even after 100 cycles. On the other hand, the hydrogen release capacity of reverse current absorber E3 decreased significantly after 100 cycles. Therefore, it can be assumed that reverse current absorbers E1 and E2 suppressed the degradation caused by reverse current compared to reverse current absorber E3. In addition, unlike reverse current absorber E3, reverse current absorbers E1 and E2 contain Al, so it can be assumed that the conductive path is robust and the reverse current absorber will not collapse and will be maintained.

[0124] <Example 2> To evaluate the performance resulting from reverse current, a durability test was conducted, and the electrolysis voltage was measured before and after the test. Electrolysis voltage is the minimum voltage required to stabilize and continuously deposit the electrolytic products during electrolysis. Generally, a higher current results in greater hydrogen production, while a lower voltage results in less energy loss; therefore, it is preferable to perform electrolysis with a high current and low voltage. In this embodiment, the decrease in electrolysis voltage after the durability test compared to before the test indicates that electrode activation was promoted by applying current.

[0125] Specifically, such as Figure 6 and 7 As described, any one of the electrodes No. 1 to 3 was connected in series to form a bipolar electrolytic cell. A nickel plate was used as the current collector 5 in the electrolytic cell. While supplying the electrolytic cell with a 7 mol / L potassium hydroxide aqueous solution via a pump, the water temperature was raised to 80°C at a rate of 440 mA / cm². 2 The electrolysis was repeated 500 times, and the electrolysis voltage was measured at the first and 500th cycles. (See Table 2 and...) Figure 8 The results are shown in [the document]. Furthermore, in [the document]... Figure 6 and Figure 7 In the middle, the water electrolysis electrode located on the right side of the current collector 5 is the anode, and the water electrolysis electrode located on the left side is the cathode.

[0126] [Table 2]

[0127] exist Figure 6 In the apparatus shown, for any of the monomers a to c, the electrolysis voltage after the durability test was higher than the electrolysis voltage before the durability test. This can be attributed to the degradation in performance of the cathode oxidation used in water electrolysis. On the other hand, in Figure 7 In the device shown, for any of the monomers d to f, the electrolysis voltage after the durability test did not increase compared to the electrolysis voltage before the durability test. This can be attributed to the fact that, due to the presence of a reverse current absorber, the hydrogen storage alloy contained within the absorber reacted, thus preventing cathode oxidation and maintaining performance. The voltage drop after the durability test can be attributed to the decrease in resistance due to activation caused by the current flow.

[0128] <Reference Experiment 1> To evaluate the effect of the average particle size of Raney alloy (Raney nickel particles) on the cathode used in water electrolysis, a potential variation durability test was conducted. First, the following electrodes for water electrolysis were fabricated.

[0129] (No. 11) A slurry was prepared by mixing Raney alloy C2, raw material D1 of metal particles, CMC, and water. The mass ratio of Raney alloy C2 to raw material D1 of metal particles was 52:48. The proportion of solvent in the slurry was more than 24% by mass and less than 40% by mass.

[0130] The above-mentioned slurry is applied to both sides of the substrate A1 using a die-coating machine. After application, any remaining slurry on the surface of the substrate A1 is scraped off with a scraper.

[0131] The substrate A1 containing the slurry is dried at 80°C for 60 minutes.

[0132] The dried substrate A1 was fired at 700°C for 2 hours.

[0133] The fired substrate A1 was immersed in a 14 mol / L sodium hydroxide aqueous solution at 125°C for 3 hours. Then, the substrate A1 was washed with water and oxidized with hydrogen peroxide water to produce the water electrolysis electrode No. 11.

[0134] (No. 12) Except for the use of Raney alloy C3, the water electrolysis electrode for No. 12 was made using the same method as No. 11.

[0135] (No. 13) Except for the use of Raney alloy C4, the water electrolysis electrode for No. 13 was made using the same method as No. 11.

[0136] (No. 14) Except for the use of Raney alloy C5, the water electrolysis electrode of No. 14 was made using the same method as No. 11.

[0137] <Potential Variation Durability Test> The following potential variation durability test was conducted. A 7M potassium hydroxide aqueous solution was used as the electrolyte, and the nickel mesh (counter electrode) and water electrolysis electrodes No. 11-14 were immersed in the electrolyte. A mercury-mercury oxide electrode was used as the reference electrode, connected to the electrolyte via a liquid junction. Before and after the potential variation durability test, the potential of the active electrode was scanned at 1 mV / s, and the oxygen generation current relative to the electrode potential was measured. The current value at a cathode potential of -0.15V (vs. reversible hydrogen electrode) was used as an indicator of hydrogen generation activity. As part of the potential variation durability test, 1000 cycles were repeatedly performed, maintaining a voltage of -0.1V (vs. reversible hydrogen electrode) for 1 minute followed by a voltage of 0.4V (vs. reversible hydrogen electrode) for 1 minute.

[0138] (Current density) The current density was measured before the potential variation durability test. See Table 3 and... Figure 9 The results are shown below. At a current density of 200 mA / cm². 2 Under the above conditions, the electrode is considered to exhibit good activity for water electrolysis.

[0139] (Catalyst residue rate) Let X (mg / cm³) be the weight per unit area of ​​the water electrolysis electrode before the potential variation durability test. 2 The weight per unit area of ​​the water electrolysis electrode after the potential variation durability test is set as Y (mg / cm²). 2The catalyst residue rate after the potential variation durability test was calculated based on the following formula (i). See Table 3 and... Figure 10 The results are shown in the figure. When the catalyst residue is less than 100%, it means the catalyst has detached, indicating poor durability. When the catalyst residue is 100%, no reduction in catalyst residue is observed before and after the potential variation durability test, indicating excellent durability. Furthermore, even if a portion of the catalyst is oxidized during the potential variation durability test, the catalyst residue may exceed 100%, but the catalyst remains intact and does not detach, thus not affecting durability. Catalyst residue rate = Y / X × 100 (i)

[0140] [Table 3]

[0141] As shown in Table 3 and Figure 9 As shown, in Nos. 11 to 14, the current density before the potential variation durability test was 200 mA / cm². 2 That's all. Additionally, in Nos. 12 and 13, the current density before the end of the potential variation durability test was 800 mA / cm². 2 above.

[0142] Additionally, as shown in Table 3 and Figure 10 As shown, in Nos. 12 to 14, the catalyst residue exceeded 100%. Based on the above, it can be seen that by setting the average particle size of the Raney alloy (Raney nickel particles) to an appropriate range, a cathode for water electrolysis exhibiting good activity and durability can be obtained.

[0143] <Reference Experiment 2> To evaluate the effect of the average particle size of the raw material (metal particles) on the cathode used in water electrolysis, a potential variation durability test was conducted. First, the following electrodes for water electrolysis were fabricated. Furthermore, the test method was the same as in Reference Test 1.

[0144] (No. 15) Apart from using Raney alloy C3 and pressing the dried substrate A1 to a thickness of 0.6 mm, the water electrolysis electrode for No. 15 was manufactured using the same method as No. 11.

[0145] (No. 16) Except for the use of raw material D2 made of metal particles, the electrode for water electrolysis of No. 16 was made using the same method as No. 15.

[0146] (Current density) The current density was measured before and after the potential variation durability test. The results are shown in Table 4. The current density was 200 mA / cm². 2 Under the above conditions, the electrode is considered to exhibit good activity for water electrolysis.

[0147] (Catalyst residue rate) The catalyst residue rate after the potential variation durability test was calculated based on the above equation (i). The results are shown in Table 4.

[0148] [Table 4]

[0149] As shown in Table 4, in No. 15, the current density before and after the potential variation durability test was 200 mA / cm². 2 That's all. On the other hand, in No. 16, the current density before the potential variation durability test was 200 mA / cm². 2 However, the current density decreased significantly after the potential variation durability test was completed.

[0150] Furthermore, as shown in Table 4, in No. 15, the catalyst residue exceeded 100%. On the other hand, in No. 16, there was almost no catalyst residue. Based on the above, it can be seen that by setting the average particle size of the raw material (metal particles) to an appropriate range, a cathode for water electrolysis exhibiting good activity and durability can be obtained.

[0151] [plan] Next, the technical ideas that can be grasped from the above implementation methods will be summarized below.

[0152] (Option 1) A cathode for water electrolysis, It includes a catalyst section and a reverse current absorber electrically connected to the catalyst section. The reverse current absorber comprises a hydrogen storage alloy. The hydrogen storage alloy contains Al.

[0153] (Option 2) According to the cathode for water electrolysis described in Scheme 1, wherein, The hydrogen storage alloy also contains La and Ni.

[0154] (Option 3) According to the cathode for water electrolysis described in Scheme 2, wherein, The hydrogen storage alloy also contains Mg.

[0155] (Option 4) The cathode for water electrolysis according to any one of schemes 1 to 3, wherein, The main phase of the hydrogen storage alloy has an A2B7 type crystal structure.

[0156] (Option 5) The cathode for water electrolysis according to any one of schemes 1 to 4, wherein, The hydrogen storage alloy is composed of the following formula (1): (La) 1-a M a ) 1-b Mg b Ni c Al d T e (1) In the above formula (1), M is at least one element selected from Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Ca, Sr, Sc, Y, Ti, Zr and Hf, T is at least one element selected from Mn, Co, Ti, V, Nb, W, Ta, Cr, Mo, Fe, Al, Ga, Zn, Sn, In, Cu, Si, Li, P, S and B, and a, b, c, d and e satisfy the relationships 0≤a≤0.1, 0<b<0.3, 2.5≤c≤4.7, 0<d≤0.1 and 0≤e≤0.01 respectively.

[0157] (Option 6) The cathode for water electrolysis according to any one of schemes 1 to 5, wherein, The catalyst section contains Raney nickel particles.

[0158] (Option 7) According to the cathode for water electrolysis described in Scheme 6, wherein, The catalyst section also contains metal particles with Ni as the main component. The metal particles are in contact with the Raney nickel particles.

[0159] (Option 8) According to the cathode for water electrolysis described in Scheme 7, wherein, The hydrogen storage alloy is in contact with the metal particles.

[0160] (Option 9) According to the cathode for water electrolysis described in scheme 7 or 8, wherein, The metal particles also contain Al. The ratio of the total number of moles of Al to the total number of moles of Ni in the Raney nickel particles is greater than the ratio of the total number of moles of Al to the total number of moles of Ni in the metal particles.

[0161] (Option 10) A method for manufacturing a cathode for water electrolysis. Includes: a catalyst forming process to form a catalyst section; and a reverse current absorber forming process to form a reverse current absorber containing a hydrogen storage alloy comprising Al. The reverse current absorber forming process includes a hydrogen storage alloy coating process, which involves coating a slurry obtained by mixing the hydrogen storage alloy with a solvent onto a substrate.

[0162] This embodiment and this example are illustrative in all respects. This embodiment and this example are not limiting. The scope of this disclosure includes all modifications within the meaning and scope equivalent to the claims. For example, it was originally intended that arbitrary configurations be extracted from this embodiment and this example and combined arbitrarily. Explanation of reference numerals in the attached figures

[0163] 1 Catalyst section; 2 Reverse current absorber; 3 Substrate; 4 Catalyst layer; 5 Current collector; 10 Cathode for water electrolysis.

Claims

1. A cathode for water electrolysis, characterized in that, It includes a catalyst section and a reverse current absorber electrically connected to the catalyst section. The reverse current absorber comprises a hydrogen storage alloy. The hydrogen storage alloy contains Al.

2. The cathode for water electrolysis according to claim 1, wherein, The hydrogen storage alloy also contains La and Ni.

3. The cathode for water electrolysis according to claim 2, wherein, The hydrogen storage alloy also contains Mg.

4. The cathode for water electrolysis according to any one of claims 1 to 3, wherein, The main phase of the hydrogen storage alloy has an A2B7 type crystal structure.

5. The cathode for water electrolysis according to any one of claims 1 to 4, wherein, The hydrogen storage alloy is derived from the following formula (1): (La 1-a M a ) 1-b Mg b Ni c Al d T e (1) In the above formula (1), M is at least one element selected from Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Ca, Sr, Sc, Y, Ti, Zr and Hf, T is at least one element selected from Mn, Co, Ti, V, Nb, W, Ta, Cr, Mo, Fe, Al, Ga, Zn, Sn, In, Cu, Si, Li, P, S and B, and a, b, c, d and e satisfy the relationships 0≤a≤0.1, 0<b<0.3, 2.5≤c≤4.7, 0<d≤0.1 and 0≤e≤0.01 respectively.

6. The cathode for water electrolysis according to any one of claims 1 to 5, wherein, The catalyst section contains Raney nickel particles.

7. The cathode for water electrolysis according to claim 6, wherein, The catalyst section also contains metal particles with Ni as the main component. The metal particles are in contact with the Raney nickel particles.

8. The cathode for water electrolysis according to claim 7, wherein, The hydrogen storage alloy is in contact with the metal particles.

9. The cathode for water electrolysis according to claim 7 or 8, wherein, The metal particles also contain Al. The ratio of the total number of moles of Al to the total number of moles of Ni in the Raney nickel particles is greater than the ratio of the total number of moles of Al to the total number of moles of Ni in the metal particles.

10. A method for manufacturing a cathode for water electrolysis, characterized in that, Includes: a catalyst forming process to form a catalyst section; and a reverse current absorber forming process to form a reverse current absorber containing a hydrogen storage alloy comprising Al. The reverse current absorber forming process includes a hydrogen storage alloy coating process, which involves coating a slurry obtained by mixing the hydrogen storage alloy with a solvent onto a substrate.

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