Cathode for water electrolysis and method for producing cathode for water electrolysis

Abstract

This cathode for water electrolysis includes a catalyst part and a reverse current absorber that is electrically connected to the catalyst part, wherein the reverse current absorber contains a hydrogen storage alloy, and the hydrogen storage alloy contains Al.

Description

Water electrolysis cathode and method for manufacturing water electrolysis cathode

[0001] The present disclosure relates to a cathode for water electrolysis and a method for manufacturing a cathode for water electrolysis.

[0002] Water electrolysis is the electrolysis of water into hydrogen and oxygen, and is used, for example, as a technology for producing hydrogen. A water electrolysis device for generating hydrogen includes, for example, an electrolytic cell containing an electrolyte solution such as alkaline water, and an anode and a cathode disposed in the electrolytic cell with a separator sandwiched therebetween. In the water electrolysis device, oxygen is generated at the anode and hydrogen is generated at the cathode by passing a current between the anode and the cathode.

[0003] On the other hand, it is known that a reverse current (a current in the opposite direction to the electrolysis current) occurs when the water electrolysis device is stopped, and that the reverse current deteriorates the electrodes, particularly the cathode. To prevent electrode deterioration, it is necessary to use electrodes that do not deteriorate due to oxidation even when a reverse current flows, and to prevent the potential from rising to a level at which the electrode catalyst deteriorates due to oxidation.

[0004] International Publication No. 2018 / 168863 (Patent Document 1) discloses that deterioration of the cathode is prevented by using a material having a lower oxidation-reduction potential than the catalytic element of the cathode as a reverse current absorber.

[0005] Japanese Patent Laid-Open No. 2001-234380 (Patent Document 2) discloses that an increase in the potential of an electrode is suppressed by applying a coating liquid containing a metal such as molybdenum and a metal such as nickel to a substrate, drying the coating liquid, and then heating the applied liquid to form a sintered electrode.

[0006] International Publication No. 2018 / 168863 Japanese Patent Application Laid-Open No. 2001-234380

[0007] Various techniques have been proposed to prevent electrode deterioration due to reverse current, as disclosed in Patent Documents 1 and 2. However, there is still room for improvement in these techniques.

[0008] An object of the present disclosure is to provide a cathode for water electrolysis that is suppressed from deterioration due to reverse current, and a method for manufacturing a cathode for water electrolysis.

[0009] A cathode for water electrolysis that solves the above-described problems includes a catalyst portion and a reverse current absorber electrically connected to the catalyst portion, the reverse current absorber including a hydrogen storage alloy, and the hydrogen storage alloy including Al.

[0010] The cathode for water electrolysis includes a reverse current absorber as a sacrificial electrode. The reverse current absorber includes 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 does not readily react with hydrogen but has excellent hydrogen release capacity. By including at least Al as metal B, it is expected that deterioration due to reverse current will be suppressed.

[0011] The method for manufacturing a cathode for water electrolysis includes a catalyst part-forming step of forming a catalyst part, and a reverse current absorber-forming step of forming a reverse current absorber including a hydrogen storage alloy containing Al, and the reverse current absorber-forming step includes a hydrogen storage alloy-applying step of mixing the hydrogen storage alloy and a solvent to obtain a slurry, and applying the slurry to a substrate.

[0012] According to the present disclosure, a cathode for water electrolysis in which deterioration due to reverse current is suppressed can be obtained.

[0013] FIG. 1 is a schematic diagram showing an example of a water electrolysis apparatus including a water electrolysis cathode according to the present disclosure. FIG. 2 is a schematic diagram showing another example of a water electrolysis apparatus including a water electrolysis cathode according to the present disclosure. FIG. 3 is a schematic diagram showing another example of a water electrolysis apparatus including a water electrolysis cathode according to the present disclosure. FIG. 4 is a schematic diagram showing another example of a water electrolysis apparatus including a water electrolysis cathode according to the present disclosure. FIG. 5 is a schematic diagram showing another example of a water electrolysis apparatus including a water electrolysis cathode according to the present disclosure. FIG. 6 is a schematic diagram showing the configuration of a water electrolysis apparatus according to Example 2. FIG. 7 is a schematic diagram showing another configuration of a water electrolysis apparatus according to Example 2. FIG. 8 is a bar graph showing experimental results according to Example 2. FIG. 9 is a graph showing the results of evaluation of the activity of water electrolysis electrodes in Reference Test 1. FIG. 10 is a graph showing the results of evaluation of the durability of water electrolysis electrodes in Reference Test 1.

[0014] Hereinafter, an embodiment of the present disclosure (hereinafter may be abbreviated as "the present embodiment") and an example of the present disclosure (hereinafter may be abbreviated as "the present example") will be described. However, the present embodiment and the example do not limit the technical scope of the present disclosure.

[0015] The water electrolysis cathode of this embodiment is used as an electrolysis cathode in a water electrolysis device. The water electrolysis cathode of this embodiment is suitably used in an alkaline water electrolysis device.

[0016] The average particle size of the Raney alloy refers to the particle size at 50% of the cumulative value in the particle size distribution determined by a laser diffraction / scattering method. The average particle size of the raw metal particles refers to the particle size measured by the Fischer method. The average particle size of the Raney nickel particles and the average particle size of the metal particles refer to the arithmetic mean of the minor axis diameters of 100 randomly selected Raney nickel particles and 100 randomly selected metal particles extracted from SEM images obtained by a scanning electron microscope (SEM).

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

[0018] In the cathode for water electrolysis according to this embodiment, it is sufficient that the catalytic portion and the reverse current absorber have the same potential. That is, there are no particular limitations on the configuration as long as the catalytic portion and the reverse current absorber are electrically connected. For example, as shown in FIG. 1 , the cathode may be a water electrolysis cathode 10 (hereinafter also referred to as a "first embodiment") in which the catalytic portion 1 and the reverse current absorber 2 are provided separately. For example, as shown in FIG. 2 , the cathode may be a water electrolysis cathode 10 (hereinafter also referred to as a "second embodiment") in which a catalyst-containing catalyst layer 4 is formed on one of the front and rear surfaces of a substrate 3 and a reverse current absorber 2 is formed on the other surface. For example, as shown in FIG. 3 , the cathode may be an electrolysis cathode 10 (hereinafter also referred to as a "third embodiment") in which a catalyst and a reverse current absorber are dispersed in a substrate. For example, the cathode 10 for water electrolysis may include a catalyst section 1 having a reverse current absorber 2 formed on one of the front and rear surfaces thereof as shown in Fig. 4 , or a water electrolysis cathode 10 including a catalyst section 1 having a reverse current absorber 2 formed on both the front and rear surfaces thereof as shown in Fig. 5 (hereinafter, the cathodes 10 for water electrolysis shown in Figs. 4 and 5 are also referred to as "fourth embodiment"). As will be described in the production method described later, the catalyst section 1 of this embodiment is obtained by applying a slurry containing catalyst raw materials to a substrate, and the reverse current absorber 2 of this embodiment is obtained by applying a slurry containing a hydrogen storage alloy containing Al to a substrate.

[0019] <<Substrate>> The substrate of this embodiment is a conductor capable of conducting electricity. The substrate is not particularly limited as long as it is conductive, and examples thereof include Ni-containing metals such as nickel metal and nickel alloys. The substrate may be formed entirely of nickel metal or nickel alloy, or only the surface may be formed of nickel metal or nickel alloy. When only the surface of the substrate is formed of nickel metal or nickel alloy, the surface of a metal material such as iron or stainless steel may be coated with nickel metal or nickel alloy. The substrate preferably contains nickel metal or nickel alloy as a main component. In terms of durability in the usage environment, the substrate is preferably made of nickel metal with a high Ni purity. Note that "containing nickel metal or nickel alloy as a main component" means that the Ni content of the nickel metal or nickel alloy in the substrate is greater than 50 mass%.

[0020] The shape of the substrate is not particularly limited and may be porous or non-porous. Examples of the shape of the porous substrate include punched metal, mesh, foam metal, and expanded metal. Examples of the shape of the non-porous substrate include a plate shape.

[0021] The thickness of the substrate is not particularly limited, and may be selected to be suitable for the water electrolysis device to be used.

[0022] The catalyst of the present embodiment contains a metal. Examples of the metal 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), tungsten (W), and rhenium (Rh). Examples of suitable metals include arsenic (Ar), osmium (Os), iridium (Ir), platinum (Pt), gold (Au), mercury (Hg), lead (Pb), bismuth (Bi), lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), eurobium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), and lutetium (Lu). The catalyst of this embodiment may contain oxides, hydroxides, nitrides, phosphides, sulfides, carbides, borides, and the like, of these metals. The catalyst of this embodiment may contain multiple metals.

[0023] The catalyst of this embodiment preferably contains the same metal as the substrate. This is expected to improve the affinity between the substrate and the catalyst and prevent the catalyst from falling off the substrate, resulting in increased durability against reverse current. From this perspective, the catalyst of this embodiment preferably contains Ni.

[0024] (Raney Nickel Particles) The catalyst of the present embodiment may contain Raney nickel particles. The Raney nickel particles contain Ni and Al. The Raney nickel particles are porous bodies with a large specific surface area in which many pores are formed, and have high activity.

[0025] The ratio of the total number of moles of Al to the total number of moles of Ni in the Raney nickel particles (hereinafter also referred to as "first Al / Ni ratio") is 1 or less, and preferably 0.6 or less. When the first Al / Ni ratio is 1 or less, improvement in activity is expected. The first Al / Ni ratio may 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 microscope-energy dispersive X-ray spectroscopy (SEM-EDX).

[0026] The Raney nickel particles may contain a first metal other than Ni and Al. By including the first metal in the Raney nickel particles, it is expected that the activity will be further improved. Examples of such first metals 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 of the Raney nickel particles (hereinafter also referred to as the "Raney alloy"). When the Raney nickel particles contain the first metal, the molar ratio of Ni to the first metal may be, for example, 1.99:0.01 to 1.15:1.85. The molar ratio of Ni to the first metal is preferably 1.99:0.05 to 1.5:0.5.

[0027] The Raney nickel particles may be an alloy composed of a single phase or an alloy composed of multiple phases. Examples of such phases include a phase consisting of only Ni, a phase consisting of Ni and Al, a phase consisting of Ni and the first metal, and a phase consisting of Ni, Al, and the first metal. The phases constituting the Raney nickel particles and their composition ratios can be confirmed, for example, by SEM-EDX.

[0028] The BET specific surface area of ​​the Raney nickel particles is, for example, 0.05 m ２ / g or more 100m２ / g or less. The BET specific surface area is the N ２ It means the surface area per unit mass of Raney nickel particles measured by adsorption.

[0029] The average particle size (D50) of the Raney nickel particles 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, improvement in activity and durability is expected. The average particle size of the Raney nickel particles may 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 producing Raney nickel particles] Raney nickel particles are generally obtained by treating a Raney alloy containing Ni and an alkali-soluble metal element with an alkaline substance and eluting the alkali-soluble metal element from the Raney alloy. The alkali-soluble metal element is preferably a metal element with a higher ionization tendency than Ni. Examples of alkali-soluble metal elements include amphoteric metals (Al, Zn, Sn, and Pb).

[0031] The Raney nickel particles can be obtained by treating a Raney alloy containing Ni and Al with an alkaline substance to dissolve Al from the Raney alloy. The Raney alloy may also contain a first metal.

[0032] A specific treatment method includes, for example, placing a Raney alloy (a substrate containing a Raney alloy) in an alkaline aqueous solution containing an alkaline substance, and then stirring the alkaline aqueous solution at a predetermined temperature for a predetermined time. Examples of the alkaline substance include alkali metal hydroxides and alkali metal salts. Examples of the alkali metal hydroxides include sodium hydroxide, potassium hydroxide, and lithium hydroxide. Examples of the alkali metal salts include sodium carbonate, potassium carbonate, and lithium carbonate. The alkaline substance is preferably an alkali metal hydroxide.

[0033] The treatment temperature is, for example, 100° C. or higher and 140° C. or lower. The treatment time is, for example, 1 hour or higher and 9 hours or lower. The amount of alkaline substance used in this step can be adjusted as appropriate.

[0034] The Raney alloy is preferably treated at high temperature using an alkaline aqueous solution of a high concentration of 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. Note that, in order to increase the treatment temperature, it is necessary to increase the concentration of the alkaline aqueous solution so that the boiling point of the alkaline aqueous solution is equal to or higher than the treatment temperature. For example, when the treatment temperature is 100°C or higher, the concentration of the alkaline aqueous solution is preferably 3 mol / L or more, and when the treatment temperature is 125°C or higher, the concentration of the alkaline aqueous solution is preferably 14 mol / L or more. Furthermore, this process is preferably carried out at atmospheric pressure. In this case, hydrogen generated during the treatment can be more easily removed compared to when pressurized.

[0035] By adopting these conditions, the reaction time between the alkaline aqueous solution and the Raney alloy can be shortened. The reaction time is, for example, 3 hours to 9 hours when the concentration of the alkaline aqueous solution is 3 mol / L or more and the treatment temperature is 100°C or more, and is, for example, 1 hour to 8 hours when the concentration of the alkaline aqueous solution is 14 mol / L or more and the treatment temperature is 125°C or more.

[0036] All of the Al contained in the Raney alloy may be dissolved, or a portion of the Al may be left undissolved.

[0037] Here, when the proportion of Al in a Raney alloy containing Ni and Al is high, the porosity of the Raney nickel particles obtained by eluting Al becomes high, i.e., the specific surface area becomes large. Therefore, from the viewpoint of obtaining Raney nickel particles that exhibit higher activity, it is preferable to use a Raney alloy with a high proportion of Al.

[0038] On the other hand, when the proportion of Al in a Raney alloy containing Ni and Al is small, the porosity of the Raney nickel particles obtained by dissolving Al is low, i.e., 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] From the viewpoint of obtaining Raney nickel particles that exhibit high activity while maintaining durability, 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. From this viewpoint, it is preferable to use a Raney alloy represented by the following formula (2):

[0040] Al ３ Ni （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 M element is preferably at least one element selected from Fe and Co. This is because, in addition to improving activity, a reduction in the amount used and a reduction in costs are expected. The M element more preferably contains at least Fe. From this viewpoint, it is more preferable to use a Raney alloy represented by the following formula (3):

[0042] Al ３ Ni （２－（ｙ＋ｚ）） Fe ｙ Co ｚ (3) In the above formula (3), y and z satisfy the relationships 0≦y≦0.1 and 0≦z≦0.1.

[0043] The Raney alloy is, for example, 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, improvement in activity and durability is expected. The average particle size of the Raney nickel particles may 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] The method for producing a Raney alloy is not particularly limited, and any known alloy production method can be applied, such as casting, quenching, mechanical alloying, and sputtering.

[0045] (Metal Particles) The affinity between the substrate and the catalyst is improved, and the catalyst is prevented from falling off from the substrate, which is expected to result in improved durability against reverse current. From this perspective, the catalyst of this embodiment may further contain, in addition to Raney nickel particles, metal particles containing Ni as a main component (hereinafter also simply referred to as "metal particles"). The metal particles are in contact with the Raney nickel particles. It is preferable that the metal particles are in contact with a plurality of Raney nickel particles. The metal particles function as a binder that binds the Raney nickel particles dispersed in the catalyst to each other and between the Raney nickel particles and the substrate. This function is explained as follows. Note that "containing Ni as a main component" means that the Ni content in the metal particles is greater than 50 mass%.

[0046] When the Raney alloy (Raney nickel particles) and metal particles contain a metal other than Ni (hereinafter also referred to as the "first additional element"), impurity diffusion occurs when thermal energy is applied to them, with the first additional element considered to be an impurity. That is, when thermal energy is applied by calcination or the like and the atoms of the first additional element undergo thermal vibration, the first additional element diffuses from the Raney alloy to the raw material for the metal particles (or from the Raney nickel particles to the metal particles) due to the concentration gradient of the first additional element between the Raney alloy and the raw material for the metal particles (or between the Raney nickel particles and the metal particles). Therefore, even between dissimilar substances such as metal particles and Raney nickel particles (or between the Raney alloy and the raw material for the metal particles), if they are in contact with each other, the Raney alloy and the raw material for the metal particles (or between the Raney nickel particles and the metal particles) are bound together by surface diffusion of the first additional element. This is expected to increase the surface area of ​​the catalyst and improve the activity of the water electrolysis cathode. Furthermore, the Raney alloy and the raw materials of the metal particles (or the Raney nickel particles and the metal particles) are firmly bound together, which inhibits them from falling off from the base material, and as a result, improvement in the durability of the cathode for water electrolysis is also expected.

[0047] The metal particles may contain Al. That is, in this embodiment, Al atoms diffuse from the Raney nickel particles, which have a higher Al content than the metal particles (or the raw material for the metal particles), to the metal particles (or from the Raney alloy to the raw material for the metal particles), driven by the Al concentration gradient. When the metal particles (or the raw material for the metal particles) contain Al, the function of the metal particles as a binder is improved, and as a result, a stronger electron conduction path is formed, which is expected to further improve the activity of the cathode for water electrolysis. Furthermore, since the Raney nickel particles and the metal particles (or the Raney alloy and the raw material for the metal particles) are more firmly bound together, 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, and preferably 0.35 or less. When the second Al / Ni ratio is 0.4 or less, improved activity is expected. The second Al / Ni ratio may be, for example, 0.005 or more, or 0.01 or more. The second Al / Ni ratio can be confirmed, for example, by SEM-EDX.

[0049] The first Al / Ni ratio is preferably greater than the second Al / Ni ratio. That is, the number of moles of Al contained in the Raney nickel particles is preferably greater than the number of moles of Al contained in the metal particles. As a result of improving the function of the metal particles as a binder, a stronger electron conduction path is formed, which is expected to further improve the activity of the water electrolysis cathode. In addition, since the Raney nickel particles and the metal particles are more firmly bound together, the durability of the water electrolysis cathode is also expected to improve.

[0050] The metal particles preferably contain Al on their surfaces, which is expected to further improve the function of the metal particles as a binder that binds the Raney nickel particles together and the Raney nickel particles to the substrate.

[0051] The average particle size of the metal particles is preferably 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 the Raney nickel particles can be in closer contact with each other, and the binder function of the metal particles is expected to be improved. The average particle size of the metal particles may be 5 times or more smaller than that of the Raney nickel particles, or 10 times or more smaller. The average particle size of the metal particles is 1 μm or more to 10 μm. The average particle size of the metal particles may be 1 μm or more to 5 μm or less, 1.5 μm or more to 3.5 μm or less, or 2 μm or more to 3 μm or less. The average particle size of the metal particles is preferably 2 μm or more to 3 μm or less. When the average particle size of the metal particles is 2 μm or more to 3 μm or less, improved durability is expected. Note that bonding of the metal particles to each other may result in the average particle size of the metal particles being larger than that of the Raney nickel particles.

[0052] (Method for producing a catalyst containing Raney nickel particles and metal particles) A ​​catalyst containing Raney nickel particles and metal particles is obtained by calcining a mixture containing a Raney alloy and a raw material for metal particles containing Ni as a main component (a base material containing a Raney alloy and a raw material for metal particles), and treating the mixture with an alkaline substance. Note that the treatment with the alkaline substance is the same as the method for producing Raney nickel particles described above, and therefore will not be described here.

[0053] 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.

[0054] The number of moles of Al in the raw material for the metal particles is preferably smaller than the number of moles of Al in the Raney alloy. When the number of moles of Al in the raw material for the metal particles is smaller than the number of moles of Al in the Raney alloy, Al diffuses from the Raney alloy to the raw material for the metal particles due to a concentration gradient during firing, and becomes metal particles. As a result, a stronger electron conduction path is formed, and improvement in catalyst activity and durability is expected.

[0055] The raw material of the metal particles may consist essentially of Ni. Since Ni is an alkali-resistant metal, it does not corrode even during use, and as a result, improved activity and durability of the electrolysis electrode are expected. Note that "consisting essentially of Ni" means that the Ni content in the metal particles is 95 mass% or more.

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

[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 be made of a hydrogen storage alloy. A hydrogen storage alloy is basically an alloy of metal A, which reacts easily with hydrogen but has poor hydrogen release ability, and metal B, which does not react easily with hydrogen but has excellent hydrogen release ability. 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, misch metals containing multiple rare earth elements (hereinafter sometimes abbreviated as Mm), and Pd. Furthermore, B may include Al, and elements other than Al include Fe, Co, Ni, Cr, Pt, Cu, Ag, Mn, Zn, and the like.

[0058] The hydrogen storage alloy of this embodiment may be any alloy containing Al, and the composition ratio and other elements that may be contained are not particularly limited. Examples include La(Mn)-Ni-Al-based alloys, La(Mn)-Mn-Al-based alloys, La(Mn)-Ni-Al-Mn-based alloys, La(Mn)-Ni-Al-Zr-based alloys, La(Mn)-Ni-Al-Co-based alloys, La(Mn)-Ni-Al-Mn-Co-based alloys, La(Mn)-Ni-Al-Te-based alloys, and La(Mn)-Ni-Al-Te-Co-based alloys. Specific examples include 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 etc.

[0059] The hydrogen storage alloy of this embodiment preferably contains La and Ni, and more preferably contains Mg in addition to La and Ni. More specifically, the hydrogen storage alloy containing La, Mg, Ni, and Al may be any alloy containing La, Mg, Ni, and Al, and the composition ratio and other elements that may be contained are not particularly limited. Examples of hydrogen storage alloys containing La, Mg, Ni, and Al include those 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] Specific examples of hydrogen storage alloys that satisfy the above formula (1) include LaNi 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 etc.

[0062] Such a hydrogen storage alloy is preferable because it is expected to improve the affinity between the substrate and the reverse current absorber (hydrogen storage alloy), suppressing the detachment of the hydrogen storage alloy from the substrate and thereby enhancing durability against reverse current. Furthermore, when the hydrogen storage alloy contains a metal element such as Al or La (hereinafter also referred to as the "second additional element") that is more diffusible than the metal element that constitutes the substrate, impurity diffusion occurs when thermal energy is applied to the hydrogen storage alloy, with the second additional element considered as an impurity. That is, when thermal energy is applied during firing or the like and the atoms of the second additional element undergo thermal vibration, the second additional element diffuses from the hydrogen storage alloy to the substrate due to the concentration gradient of the second additional element between the hydrogen storage alloy and the substrate. Therefore, even when the hydrogen storage alloy and the substrate are heterogeneous substances, if they are in contact with each other, the second additional element will bond the hydrogen storage alloy to the substrate through surface diffusion. Because the hydrogen storage alloy and the substrate are firmly bonded to each other, detachment from the substrate is suppressed, and this is expected to improve the durability of the water electrolysis cathode. That is, in the present embodiment, Al atoms diffuse from the hydrogen storage alloy containing a large amount of Al to the base material containing Ni as a main component, driven by the Al concentration gradient, resulting in stronger bonding, and therefore improvement in durability of the water electrolysis cathode is also expected.

[0063] The number of moles of La and Ni contained in the hydrogen storage alloy is preferably greater than the number of moles of Al, since Al diffuses more easily than La and Ni in the hydrogen storage alloy, and the second additive element diffuses more easily from the hydrogen storage alloy to the substrate.

[0064] The crystal structure of the hydrogen storage alloy of this embodiment is hexagonal CaCu ５ AB type crystal structure ５ Type, hexagonal MgZn ２ type or cubic MgCu ２ AB type crystal structure ２ type, AB type showing cubic CsCl type crystal structure, hexagonal Mg ２ A showing Ni-type crystal structure ２ B type, solid solution type showing body-centered cubic structure, and AB ５ Type and AB ２ A combination of AB type crystal structures ３ Type, A２ B ７ Type and A ５ B １９ The hydrogen storage alloy of this embodiment may have one of the above crystal structures, or may have two or more of the above crystal structures.

[0065] A.B. ５ As a hydrogen storage alloy, LaNi ５ , CaCu ５ , MmNi ５ AB ２ As a hydrogen storage alloy, MgZn ２ , ZrNi ２ , ZrCr ２ Examples of AB type hydrogen storage alloys include TiFe and TiCo. ２ As a type B hydrogen storage alloy, Mg ２ Ni, Mg ２ Examples of solid solution hydrogen storage alloys include Ti—V, V—Nb, and Ti—Cr. ３ As a hydrogen storage alloy, LaNi ３ Examples include: A ２ B ７ As a hydrogen storage alloy, La ２ Ni ７ Examples include: A ５ B １９ As a hydrogen storage alloy, La ５ Co １９ , Pr ５ Co １９ In each of the above crystal structures, a portion of the metal may be substituted with one or more other metals or elements.

[0066] The hydrogen storage alloy of this embodiment has a main phase of A ２ B ７ The hydrogen storage alloy of this embodiment preferably includes a hydrogen storage alloy having an A type crystal structure. ２ B ７ The hydrogen storage alloy may be of the type A. ２ B ７ The hydrogen storage alloy of type AB ２ The crystal structure of hydrogen storage alloys of the type (so-called AB ２type subunit) and AB ５ Crystal structure of hydrogen storage alloy (so-called AB ５ Since the main phase has a crystalline structure in which A-type subunits are stacked, the crystal is less likely to break and is thought to have excellent durability. In addition, since the crystal lattice system is large, hydrogen can easily penetrate, improving the hydrogen storage capacity, that is, the capacity is expected to improve. ２ B ７ "Having a crystal structure of the A type" means that the hydrogen storage alloy ２ B ７ This means that the proportion of the crystalline structure of this type is more than 50%.

[0067] The reverse current absorber of this embodiment may contain metal particles containing Ni as a main component. In this case, the metal particles are in contact with the hydrogen storage alloy. The metal particles function as a binder that binds the hydrogen storage alloys dispersed in the reverse current absorber together and between the hydrogen storage alloy and the substrate. By binding the hydrogen storage alloys together with the metal particles, the surface area of ​​the hydrogen storage alloy is increased, improving its activity as a reverse current absorber. Note that the metal particles have been described above, so details will be omitted.

[0068] The surface of the hydrogen storage alloy may be oxidized. It is believed that the oxidation of the surface of the hydrogen storage alloy suppresses unintended reactions between the hydrogen storage alloy and the electrolyte. In this case, the reverse current absorber may be made of a hydrogen storage alloy with an oxidized surface.

[0069] The surface of the hydrogen storage alloy may be oxidized by, for example, exposing the hydrogen storage alloy to air and oxidizing it with oxygen in the air, or by contacting the hydrogen storage alloy with an oxide such as hydrogen peroxide. In either method, however, it is preferable to cool the hydrogen storage alloy while oxidizing it in order to prevent excessive heat generation from the hydrogen storage alloy. Specifically, it is preferable to cool the hydrogen storage alloy by pouring water over it, or to place the hydrogen storage alloy in water or in an aqueous solution of an oxide such as hydrogen peroxide.

[0070] Before oxidizing the surface of the hydrogen storage alloy, the hydrogen storage alloy may be treated with an alkaline substance. In this embodiment, the alkaline substance treatment refers to treatment with an alkaline aqueous solution in which an alkali metal hydroxide is dissolved. The alkaline substance treatment is preferably performed by treating the hydrogen storage alloy with a first alkaline aqueous solution in which an alkali metal hydroxide is dissolved, and then by treating the hydrogen storage alloy with a second alkaline aqueous solution in which an alkali metal hydroxide is dissolved.

[0071] By treating the hydrogen storage alloy with the first alkaline aqueous solution, elements such as La, which are highly soluble in alkaline aqueous solutions, are eluted from the surface of the hydrogen storage alloy, and therefore elements such as Ni, which are less soluble in alkaline aqueous solutions, are concentrated on the surface of the hydrogen storage alloy after treatment with the first alkaline aqueous solution.

[0072] Examples of the alkali metal hydroxide contained in the first alkaline aqueous solution include lithium hydroxide, sodium hydroxide, and potassium hydroxide. The first alkaline aqueous solution is preferably a strong base, and the alkali metal hydroxide contained in the first alkaline aqueous solution is preferably sodium hydroxide. The concentration of the alkali metal hydroxide contained 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 with the first alkaline aqueous solution is preferably performed by immersing the hydrogen storage alloy in the first alkaline aqueous solution. The treatment is preferably performed by stirring and heating. The heating temperature may be, for example, 50°C or higher and 150°C or lower. The heating time may be appropriately set depending on the concentration and heating temperature of the first alkaline aqueous solution, and may be, for example, 0.1 hours or higher and 10 hours or lower.

[0074] The relationship between the amounts of the hydrogen storage alloy and the first alkaline aqueous solution may be, for example, a mass ratio of 1:0.5 to 1:100. If the amount of the first alkaline aqueous solution is small, Ni and the like may not be sufficiently concentrated on the surface of the hydrogen storage alloy. If the amount of the first alkaline aqueous solution is large, this is not preferable from the viewpoint of cost.

[0075] Next, the hydrogen storage alloy after treatment with the first alkaline aqueous solution may be further treated with a second alkaline aqueous solution in which an alkali metal hydroxide is dissolved.

[0076] The hydrogen storage alloy before treatment with the first alkaline aqueous solution may be separated by, for example, filtration or centrifugation, or may be separated after treatment with the first alkaline aqueous solution. Alternatively, the hydrogen storage alloy may be treated with the first alkaline aqueous solution together with a substrate, Raney nickel particles (Raney alloy), or metal particles (raw material for the metal particles). Treatment of the hydrogen storage alloy with the second alkaline aqueous solution may involve, for example, immersing the hydrogen storage alloy in the second alkaline aqueous solution or pouring the second alkaline aqueous solution onto the hydrogen storage alloy. Treatment of the hydrogen storage alloy with the second alkaline aqueous solution may involve pouring the second alkaline aqueous solution onto the hydrogen storage alloy following or during the separation. The hydrogen storage alloy may be treated with the second alkaline aqueous solution together with a substrate, Raney nickel particles (Raney alloy), or metal particles (raw material for the metal particles).

[0077] Examples of the alkali metal hydroxide contained in the second alkaline aqueous solution include lithium hydroxide, sodium hydroxide, potassium hydroxide, etc. The alkali metal hydroxide contained in the second alkaline aqueous solution is preferably sodium hydroxide.

[0078] The concentration of the alkali metal hydroxide in the first alkaline aqueous solution is C １ , the concentration C of the alkali metal hydroxide in the second alkaline aqueous solution ２ , then C １ >C ２ Since the viscosity of an alkaline aqueous solution with a low concentration is low, it is preferable that the relationship １ >C ２ It is believed that the treatment with the second alkaline aqueous solution proceeds smoothly under the condition that satisfies the relationship below. The concentration of the alkali metal hydroxide in the second alkaline aqueous solution may be, for example, 0.01% by mass or more and 10% by mass or less.

[0079] From the viewpoint of production costs, etc., it is preferable to treat the hydrogen storage alloy with the second alkaline aqueous solution under lower temperature conditions than the treatment of the hydrogen storage alloy with the first alkaline aqueous solution. The treatment temperature of the hydrogen storage alloy with the second alkaline aqueous solution may be, for example, 0 to 100° C. The treatment temperature of the hydrogen storage alloy with the second alkaline aqueous solution may be determined by the temperature of the environment in which the hydrogen storage alloy exists, or by the temperature of the second alkaline aqueous solution.

[0080] The relationship between the amounts of the hydrogen storage alloy and the second alkaline aqueous solution may be, for example, a mass ratio of 1:0.5 to 1:100. If the amount of the second alkaline aqueous solution is small, the removal of hydroxides of La and the like may be insufficient. If the amount of the second alkaline aqueous solution is large, this is not preferable from the viewpoint of cost.

[0081] Furthermore, following the treatment with the second alkaline aqueous solution, the hydrogen storage alloy may be washed with water. By washing with water, the second alkaline aqueous solution adhering to the surface of the hydrogen storage alloy can be removed. The mass ratio of the amount of hydrogen storage alloy to the amount of water during washing with water may be 1:1 to 1:50. Note that washing the hydrogen storage alloy with water in the atmosphere may be a method for oxidizing the surface of the hydrogen storage alloy.

[0082] The hydrogen storage alloy is, for example, in powder form. The average particle size of the hydrogen storage alloy is preferably 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. The average particle size of the hydrogen storage alloy is preferably 8 μm or more and 110 μm or less.

[0083] <Method for manufacturing cathode for water electrolysis> The method for manufacturing a cathode for water electrolysis according to this embodiment includes at least (a) a catalyst portion-forming step of forming a catalyst portion, and (b) a reverse current absorber-forming step of forming a reverse current absorber. Examples of manufacturing methods for each embodiment are listed below. However, the method for manufacturing a cathode for water electrolysis according to this embodiment is not limited to these.

[0084] <<First embodiment>> (a) Catalyst portion forming step) The catalyst portion forming step is not particularly limited. For example, the catalyst may be formed by thermally spraying a catalyst raw material onto a first substrate. An example of the thermal spraying method is plasma thermal spraying. The thermal spraying conditions are not particularly limited. The thermal spraying conditions can be changed as appropriate depending on the catalyst raw material, the substrate, etc. The catalyst raw material and the substrate are as described above.

[0085] For example, the catalyst may be formed by mixing raw materials for the catalyst and a solvent to obtain a first slurry, which is then applied to a first substrate (hereinafter also referred to as a coating method). Examples of the solvent include water, N-methyl-2-pyrrolidone (NMP), and N-ethyl-2-pyrrolidone (NEP). The first slurry may further contain a thickener. Examples of the thickener 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 device. The application of the first slurry may be carried out 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 by immersing the first substrate in the first slurry. The first slurry may be applied to the entire surface of the first substrate, or may be applied to a portion of the surface of the first substrate. When the first substrate is plate-shaped, the first slurry may be applied to one or both sides of the first substrate. When the first substrate is a porous substrate, the first slurry may be impregnated into the pores of the first substrate by, for example, pressing the first substrate to which the first slurry has been applied. When the first substrate is a porous substrate, the 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.

[0087] The catalyst portion forming step may further include a catalyst portion drying step of drying the first slurry applied to the first substrate. For example, the first slurry is dried using a hot air drying oven, an infrared dryer, a hot plate, or the like. The drying temperature and drying time can be adjusted as appropriate.

[0088] The catalyst portion forming step may further include a catalyst portion calcining step in which the first substrate (catalyst portion) containing the applied first slurry is calcined (heat-treated). The catalyst portion calcining step is preferably performed after the catalyst portion drying step. In this case, the alkali treatment step is preferably performed after the catalyst portion calcining step. The calcination temperature may be, for example, 600°C or higher and 900°C or lower. The calcination time may be, for example, 1 hour or higher and 24 hours or lower.

[0089] The first substrate (catalyst portion) after plasma spraying, or the first substrate (catalyst portion) containing the first slurry after coating, may be pressed. The thickness of the first substrate (catalyst portion) is adjusted by pressing. Furthermore, when the catalyst portion contains Raney nickel particles and metal particles, the contact area between the Raney nickel particles and the metal particles (raw materials for the Raney alloy and metal particles) is increased by pressing. The pressure can be adjusted appropriately depending on the desired thickness of the first substrate (catalyst portion). The pressing of the first substrate may be performed at any timing.

[0090] The catalyst portion may be a catalyst layer containing a catalyst formed on the surface of the first substrate, or may be a catalyst dispersed in the first substrate. 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 may be formed on both the front and back surfaces of the first substrate.

[0091] When forming a catalyst portion in the form of a catalyst dispersed in a 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 thought to be due to the following reasons. That is, the lower the basis weight, the higher the porosity of the substrate. The higher the porosity of the substrate, the greater the amount of slurry supported (amount of catalyst portion supported), and therefore higher activity is expected. Furthermore, the higher the viscosity (concentration) of the slurry, the greater the concentration of the catalyst portion in the slurry, which facilitates contact between Raney nickel particles and metal particles, and therefore improved durability is expected. Furthermore, by using a substrate with a low basis weight, the interior of the water electrolysis cathode can maintain a high porosity even when a high-viscosity slurry is penetrated, and therefore high activity is expected. Note that a "low basis weight" refers to, for example, a thickness of 100 g / m ２ More than 600g / m ２ Preferably 200 g / m or less ２ More than 400g / m ２ The term "high viscosity" refers to, for example, a state in which the proportion of the solvent in the first slurry is 10% by mass or more and 50% by mass or less, and preferably 20% by mass or more and 45% by mass or less.

[0092] (b) Reverse Current Absorber Forming Step The reverse current absorber forming step includes a hydrogen storage alloy coating step of coating a second substrate with a second slurry obtained by mixing a hydrogen storage alloy containing Al and a solvent.

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

[0094] In the hydrogen storage alloy coating process, the second slurry can be coated on the surface of the second substrate using any coating device. Coating of the second slurry can be carried out 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 by immersing the second substrate in the second slurry. The second slurry can be coated on the entire surface of the second substrate, or on a portion of the surface of the second substrate. When the second substrate is plate-shaped, the second slurry can be coated on one or both sides of the second substrate. When the second substrate is a porous substrate, the second slurry can be impregnated into the pores of the second substrate by, for example, pressing the second substrate coated with the second slurry. When the second substrate is a porous substrate, the first slurry that has not impregnated into the pores and remains on the surface of the second substrate can be scraped off using a spatula or the like.

[0095] The reverse current absorber forming step may further include a reverse current absorber drying step of drying the second substrate (reverse current absorber) containing the second slurry after the hydrogen storage alloy coating step. The drying method is as described above. The drying temperature and drying time may be adjusted as appropriate.

[0096] The reverse current absorber forming step may further include a reverse current absorber firing step of firing (heat treating) the second base material (reverse current absorber) containing the second slurry. The reverse current absorber firing step is preferably performed after the reverse current absorber drying step. 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 step may further include a pressing step of pressing the second substrate (reverse current absorber) containing the second slurry. The thickness of the second substrate (reverse current absorber) containing the second slurry is adjusted by pressing. The pressure may be appropriately adjusted depending on the desired thickness of the second substrate (reverse current absorber) containing the second slurry. Note that the second substrate may be pressed before the application of the second slurry, or the second substrate (reverse current absorber) containing the second slurry may be pressed before the reverse current absorber baking step.

[0098] The second slurry may contain metal particles. The reverse current absorber may be one in which a reverse current absorber layer containing a hydrogen storage alloy is formed on the surface of a second substrate, or one in which a hydrogen storage alloy is dispersed in the second substrate. When a reverse current absorber layer is formed, it is sufficient that the reverse current absorber layer is formed on at least one of the front and back surfaces of the second substrate, and it may be formed on both the front and back surfaces of the second substrate. When forming a reverse current absorber in which a hydrogen storage alloy is dispersed in the second substrate, it is preferable to use a second substrate with a low basis weight and a second slurry with a high viscosity.

[0099] <<Second embodiment>> In the second embodiment, a cathode for water electrolysis is produced by the same method as in the first embodiment, except that a catalytic layer (catalytic portion) is formed on one of the front and back surfaces of a substrate, and a reverse current absorber is formed on the other surface. In the second embodiment, it is not necessary to use separate substrates as in the first embodiment. There is no particular limitation on the order in which the catalytic layer and the reverse current absorber are formed.

[0100] <<Third embodiment>> In the third embodiment, a cathode for water electrolysis is produced by the same method as in the first embodiment, except that a mixed slurry containing a catalyst material and an Al-containing hydrogen storage alloy is applied to a substrate. In the third embodiment, the first and second slurries do not need to be prepared separately as in the first embodiment. That is, in the third embodiment, the catalyst portion and the reverse current absorber are formed simultaneously. Therefore, in the third embodiment, the above-described (a) catalyst portion-forming step and (b) reverse current absorber-forming step may be collectively referred to as a "water electrolysis cathode-forming step." When the water electrolysis cathode of the third embodiment is produced, the catalyst portion is formed by a coating method, because the slurry is applied to the substrate.

[0101] <<Fourth embodiment>> In the fourth embodiment, a water electrolysis cathode is produced by the same method as in the first embodiment, except that after forming a catalytic part in a form in which a catalyst is dispersed in a substrate, a reverse current absorber is formed on at least one of the front and rear surfaces of the catalytic part. The reverse current absorber may be formed on only one of the front and rear surfaces of the catalytic part, or on both the front and rear surfaces of the catalytic part. When producing the water electrolysis cathode of the fourth embodiment, the catalytic part is formed by a coating method because the slurry is applied to the substrate.

[0102] The above-described method for producing Raney nickel particles, the method for producing a catalyst containing Raney nickel particles and metal particles, and the method for oxidizing the surface of a hydrogen storage alloy may be included as one step in a method for producing a cathode for water electrolysis. For example, when Raney nickel particles are used as the catalyst, a slurry obtained by mixing a Raney alloy and a solvent may be applied to a substrate and dried. After drying, the substrate and the layer obtained by drying the slurry may be treated with an alkaline substance to elute Al from the Raney alloy, thereby forming a catalytic portion. For example, when Raney nickel particles and metal particles are used as the catalyst, a slurry obtained by mixing a Raney alloy, raw materials for the metal particles, and a solvent may be applied to a substrate and dried. After drying, the substrate and the layer obtained by drying the slurry may be sintered. After sintering, the substrate and the layer obtained by sintering the slurry may be treated with an alkaline substance to elute Al from the Raney alloy, thereby forming a catalytic portion.

[0103] <Raw Materials> The materials used in this example are as follows.

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

[0105] <Hydrogen storage alloy> 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 to 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 to 25 μm) B3: LaNi ５ (Average particle size: 20μm)

[0106] <<Raney alloy>> C1: Composition formula Al ３ Ni ２ C1: Nickel-aluminum alloy (manufactured by Japan Metals and Chemical Industries, Ltd., average particle size: 23 μm) C2: Composition formula Al ３ Ni １．９５ Fe ０．０５ C1: Nickel-aluminum-iron alloy (manufactured by Japan Metals and Chemical Industries, Ltd., average particle size: 16 μm) C2: Composition formula Al ３ Ni １．９５ Fe ０．０５ C4: Nickel-aluminum-iron alloy (manufactured by Japan Metals and Chemical Industries, Ltd., average particle size: 23 μm) ３ Ni １．９５ Fe ０．０５ C5: Nickel-aluminum-iron alloy (manufactured by Japan Metals and Chemical Industries, Ltd., average particle size: 38 μm) ３ Ni １．９５ Fe ０．０５ Nickel-aluminum-iron alloy (manufactured by Japan Metals and Chemical Industries, Ltd., average particle size: 85 μm)

[0107] <<Metal Particle Raw Materials>> D1: Nickel particles (manufactured by Kojundo Chemical Laboratory Co., Ltd., Ni (NIE10PB)) (average particle size: 2-3 μm) D2: Nickel particles (manufactured by Kojundo Chemical Laboratory Co., Ltd., NIE11PB) (average particle size: 3-5 μm)

[0108] Other: Thickener: CMC (Cellogen EP, manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) Solvent: Water

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

[0110] The above slurry was applied to both sides of the substrate A1 using a die coater. After application, the slurry remaining on the surface of the substrate A1 was smoothed off with a spatula.

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

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

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

[0114] (E2) Reverse current absorber E2 was produced in the same manner as reverse current absorber E1, except that hydrogen storage alloy B2 was used.

[0115] (E3) Reverse current absorber E3 was produced in the same manner as reverse current absorber E1, except that hydrogen storage alloy B3 was used.

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

[0117] (No. 2) Raney alloy C1 and water were mixed to prepare a slurry. The slurry was applied to both sides of substrate A1 using a die coater. After application, the remaining slurry on the surface of substrate A1 was smoothed off with a spatula. Substrate A1 containing the slurry was dried at 80°C for 60 minutes. The dried substrate A1 was fired at 700°C for 2 hours. The fired substrate A1 was immersed in a 14 mol / L aqueous sodium hydroxide solution at 125°C for 3 hours. Substrate A1 was then washed with water and oxidized using hydrogen peroxide to produce water electrolysis electrode No. 2.

[0118] (No. 3) A slurry containing hydrogen storage alloy B1, CMC, and water was applied by a die coater to the surface of the water electrolysis electrode No. 1 on which the catalyst portion was formed, and the resulting coating was dried at 80°C for 60 minutes to obtain water electrolysis electrode No. 3. The hydrogen storage alloy B1 was previously immersed in a 14 mol / L aqueous sodium hydroxide solution at 110°C for 3 hours, washed with water, and oxidized with aqueous hydrogen peroxide.

[0119] Example 1 A reverse current absorber made of a hydrogen storage alloy installed in a water electrolysis system gradually absorbs hydrogen generated during continuous operation, until the hydrogen storage alloy is completely filled with hydrogen, and when the system is stopped, it releases some of the hydrogen that was filled during operation as it absorbs the reverse current.

[0120] Therefore, it is believed that the reverse current absorber made of a hydrogen storage alloy installed in the water electrolysis device alternates between being fully filled with hydrogen at a high temperature of 50° C. or higher and releasing a small amount of hydrogen, which is the general operating temperature of the water electrolysis device.

[0121] To evaluate the performance of the resulting reverse current absorber, a durability test was conducted at 50°C, in which the reverse current absorber was repeatedly charged with hydrogen (100%) and charged to 90%. The hydrogen desorption capacity of the reverse current absorber was measured before and after the durability test. Specifically, a 7 mol / L aqueous potassium hydroxide solution was used as the electrolyte, and the reverse current absorbers E1 to E3 and the counter electrode, nickel hydroxide, were immersed in the electrolyte. Subsequently, a charging current was applied at a 1 / 3 C rate for a time period until the hydrogen filling state reached 100%, thereby filling the reverse current absorber with hydrogen. After charging, a discharging current was applied at a 1 / 3 C rate for a time period until the hydrogen filling state reached 90%, thereby releasing hydrogen from the reverse current absorber. Hydrogen charging and desorption were repeated 100 times, and the hydrogen desorption capacities for the first and 100th cycles were measured. To measure the hydrogen desorption capacity, a current was first applied at a 1 / 3 C rate until the hydrogen filling amount reached 100%. Thereafter, the battery was discharged at a rate of 1 / 3 C until the potential of the nickel hydroxide, which was the counter electrode to the reverse current absorber, reached 1.0 V, and the hydrogen release capacity was calculated from the discharge time. The results are shown in Table 1.

[0122]

[0123] As shown in Table 1, the hydrogen desorption capacity of reverse current absorbers E1 and E2 did not change significantly even at the 100th cycle. On the other hand, the hydrogen desorption capacity of reverse current absorber E3 decreased significantly at the 100th cycle. Therefore, it is considered that the reverse current absorbers E1 and E2 are less susceptible to degradation due to reverse current than the reverse current absorber E3. Furthermore, unlike the reverse current absorber E3, the reverse current absorbers E1 and E2 contain Al, which strengthens the conductive path and may have prevented the reverse current absorber from collapsing.

[0124] Example 2 To evaluate performance under reverse current, a durability test was conducted, and the electrolysis voltage was measured before and after the durability test. The electrolysis voltage is the minimum voltage required for steady and continuous deposition of electrolysis products during electrolysis. Generally, the larger the current, the greater the amount of hydrogen generated, and the smaller the voltage, the smaller the energy loss. Therefore, it is preferable to perform electrolysis at a large current and a low voltage. In this example, the fact that the electrolysis voltage after the durability test was lower than the electrolysis voltage before the durability test means that the activation of the electrodes has progressed due to the application of current.

[0125] Specifically, as shown in Figures 6 and 7, a bipolar electrolytic cell was constructed by connecting any one of electrodes No. 1 to 3 in series. A nickel plate was used as the current collector 5 of the electrolytic cell. A 7 mol / L potassium hydroxide aqueous solution was supplied to the electrolytic cell by a pump while the water temperature was raised to 80°C, and a current of 440 mA / cm was applied. ２ Electrolysis and termination were repeated 500 times, and the electrolysis voltages were measured for the first and 500th cycles. The results are shown in Table 2 and Fig. 8. In Figs. 6 and 7, the water electrolysis electrode installed to the right of the current collector 5 is the anode, and the water electrolysis electrode installed to the left is the cathode.

[0126]

[0127] In the device shown in Figure 6, the electrolysis voltage after the durability test was higher than the electrolysis voltage before the durability test in all of cells a to c. This is thought to be because the water electrolysis cathode was oxidized, resulting in a decrease in performance. On the other hand, in the device shown in Figure 7, the electrolysis voltage after the durability test was not higher than the electrolysis voltage before the durability test in all of cells d to f. This is thought to be because the device is provided with a reverse current absorber, which caused the hydrogen storage alloy contained in the reverse current absorber to react, preventing oxidation of the cathode and maintaining performance. The decrease in voltage after the durability test is thought to be due to a decrease in resistance caused by activation by current flow.

[0128] <Reference Test 1> A potential fluctuation durability test was carried out to evaluate the influence of the average particle size of the Raney alloy (Raney nickel particles) on the cathode for water electrolysis. First, the following water electrolysis electrodes were prepared.

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

[0130] The above slurry was applied to both sides of the substrate A1 using a die coater. After application, the slurry remaining on the surface of the substrate A1 was smoothed off with a spatula.

[0131] The substrate A1 containing the slurry was 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 aqueous sodium hydroxide solution at 125° C. for 3 hours, then washed with water and oxidized with hydrogen peroxide to produce water electrolysis electrode No. 11.

[0134] (No. 12) An electrode for water electrolysis No. 12 was prepared in the same manner as No. 11, except that Raney alloy C3 was used.

[0135] (No. 13) An electrode for water electrolysis No. 13 was prepared in the same manner as No. 11, except that Raney alloy C4 was used.

[0136] (No. 14) An electrode for water electrolysis No. 14 was prepared in the same manner as No. 11, except that Raney alloy C5 was used.

[0137] <Potential Fluctuation Durability Test> The potential fluctuation durability test was conducted as follows. A 7 M potassium hydroxide aqueous solution was used as the electrolyte, and a nickel mesh serving as the counter electrode and each of the water electrolysis electrodes No. 11 to 14 were immersed in the electrolyte. A mercury-mercury oxide electrode was used as the reference electrode, and it was connected to the electrolyte via a liquid junction. Before and after the potential fluctuation durability test, the potential of the working electrode relative to the reference electrode was swept at 1 mV / s, and the hydrogen generation current versus electrode potential was measured. The current value when the cathode potential was −0.15 V (vs. reversible hydrogen electrode) was read and used as an index of hydrogen generation activity. The potential fluctuation durability test consisted of holding the electrode at −0.1 V (vs. reversible hydrogen electrode) for 1 minute, followed by holding it at 0.4 V (vs. reversible hydrogen electrode) for 1 minute, and this cycle was repeated 1,000 times.

[0138] (Current Density) The current density was measured before the potential fluctuation durability test. The results are shown in Table 3 and FIG. 9. When the current density was 200 mA / cm ２ In the above cases, the electrode was deemed to have good activity for water electrolysis.

[0139] (Catalyst Residual Rate) The catalyst residual rate after the potential fluctuation durability test was determined by multiplying the basis weight of the water electrolysis electrode before the potential fluctuation durability test by X (mg / cm ２ ), and the basis weight of the water electrolysis electrode after the potential fluctuation durability test was Y (mg / cm ２ ) was calculated based on the following formula (i). The results are shown in Table 3 and Figure 10. When the catalyst portion remaining rate is less than 100%, it means that the catalyst portion has fallen off, i.e., durability is poor. When the catalyst portion remaining rate is 100%, it means that no reduction in the catalyst portion is observed before and after the potential fluctuation durability test, and durability is excellent. Note that if a portion of the catalyst portion is oxidized during the potential fluctuation durability test, the catalyst portion remaining rate may be 100% or more, but the catalyst portion is maintained without falling off, and this does not affect durability. Catalyst portion remaining rate = Y / X x 100 (i)

[0140]

[0141] As shown in Table 3 and FIG. 9, in Nos. 11 to 14, the current density before the potential fluctuation durability test was 200 mA / cm ２In addition, in Nos. 12 and 13, the current density before the potential fluctuation durability test was 800 mA / cm ２ That was all.

[0142] 10 , the catalytic portion residual rate exceeded 100% in Samples Nos. 12 to 14. From the above, it is considered that a cathode for water electrolysis exhibiting good activity and durability can be obtained by adjusting the average particle size of the Raney alloy (Raney nickel particles) to an appropriate range.

[0143] <Reference Test 2> A potential fluctuation durability test was conducted to evaluate the influence of the average particle size of the raw material (metal particles) of the metal particles on the cathode for water electrolysis. First, the following water electrolysis electrodes were prepared. The test method was the same as that of Reference Test 1.

[0144] (No. 15) An electrode for water electrolysis No. 15 was prepared in the same manner as No. 11, except that Raney alloy C3 was used and the dried substrate A1 was pressed to a thickness of 0.6 mm.

[0145] (No. 16) An electrode for water electrolysis No. 16 was prepared in the same manner as No. 15, except that raw material D2 for metal particles was used.

[0146] (Current Density) The current density was measured before and after the potential fluctuation durability test. The results are shown in Table 4. When the current density was 200 mA / cm ２ In the above cases, the electrode was deemed to have good activity for water electrolysis.

[0147] (Catalyst Residual Rate) After the potential fluctuation durability test, the catalyst residual rate was calculated based on the above formula (i). The results are shown in Table 4.

[0148]

[0149] As shown in Table 4, in No. 15, the current density before and after the potential fluctuation durability test was 200 mA / cm ２ On the other hand, in No. 16, the current density before the potential fluctuation durability test was 200 mA / cm ２ However, the current density after the potential fluctuation durability test was significantly reduced.

[0150] Furthermore, as shown in Table 4, the catalytic portion remaining rate exceeded 100% in Sample No. 15. On the other hand, almost no catalytic portion remained in Sample No. 16. From the above, it is considered that a water electrolysis cathode exhibiting good activity and durability can be obtained by adjusting the average particle size of the raw material of the metal particles (metal particles) to an appropriate range.

[0151] [Aspects] Next, the technical ideas that can be understood from the above-described embodiments will be additionally described below.

[0152] (Aspect 1) A cathode for water electrolysis, comprising: a catalyst section; and a reverse current absorber electrically connected to the catalyst section, wherein the reverse current absorber contains a hydrogen storage alloy, and the hydrogen storage alloy contains Al.

[0153] (Aspect 2) The cathode for water electrolysis according to aspect 1, wherein the hydrogen storage alloy further contains La and Ni.

[0154] (Aspect 3) The cathode for water electrolysis according to Aspect 2, wherein the hydrogen storage alloy further contains Mg.

[0155] (Aspect 4) The hydrogen storage alloy has a main phase of A ２ B ７ A cathode for water electrolysis according to any one of Aspects 1 to 3, having a crystal structure of the type ZnO.

[0156] (Aspect 5) The hydrogen storage alloy is represented by the following formula (1): (La １－ａ M ａ ) １－ｂ Mg ｂ Ni ｃ Al ｄ T ｅ(1) wherein, in 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 respectively satisfy the relationships of 0≦a≦0.1, 0<b<0.3, 2.5≦c≦4.7, 0<d≦0.1, and 0≦e≦0.01.

[0157] (Aspect 6) The cathode for water electrolysis according to any one of Aspects 1 to 5, wherein the catalytic portion contains Raney nickel particles.

[0158] (Aspect 7) The cathode for water electrolysis according to Aspect 6, wherein the catalytic portion further includes metal particles containing Ni as a main component, and the metal particles are in contact with the Raney nickel particles.

[0159] (Aspect 8) The cathode for water electrolysis according to aspect 7, wherein the hydrogen storage alloy is in contact with the metal particles.

[0160] (Aspect 9) The cathode for water electrolysis according to Aspect 7 or 8, wherein the metal particles further contain Al, and a 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 a ratio of the total number of moles of Al to the total number of moles of Ni in the metal particles.

[0161] (Aspect 10) A method for producing a cathode for water electrolysis, comprising: a catalyst portion-forming step of forming a catalyst portion; and a reverse current absorber-forming step of forming a reverse current absorber including a hydrogen storage alloy containing Al, wherein the reverse current absorber-forming step comprises a hydrogen storage alloy-applying step of mixing the hydrogen storage alloy and a solvent to obtain a slurry and applying the slurry to a substrate.

[0162] The present embodiment and examples are illustrative in all respects. The present embodiment and examples are not limiting. The technical scope of the present disclosure encompasses all modifications within the meaning and scope equivalent to the claims. For example, it is intended from the beginning that any configuration may be extracted from the present embodiment and examples and that they may be combined in any desired manner.

[0163] REFERENCE SIGNS LIST 1 Catalyst portion, 2 Reverse current absorber, 3 Substrate, 4 Catalyst layer, 5 Current collector plate, 10 Water electrolysis cathode

Claims

1. It includes a catalyst part and a reverse current absorber electrically connected to the catalyst part, the reverse current absorber includes a hydrogen storage alloy, and the hydrogen storage alloy includes Al, which is a cathode for water electrolysis.

2. The hydrogen storage alloy further includes La and Ni, and the cathode for water electrolysis according to claim 1.

3. The hydrogen storage alloy further includes Mg, and the cathode for water electrolysis according to claim 2.

4. The hydrogen storage alloy has a main phase of A ２ B ７ type crystal structure, and the cathode for water electrolysis according to any one of claims 1 to 3.

5. The hydrogen storage alloy is represented by 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, and 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. a, b, c, d, and e satisfy the relationships of 0 ≦ a ≦ 0.1, 0 < b < 0.3, 2.5 ≦ c ≦ 4.7, 0 < d ≦ 0.1, and 0 ≦ e ≦ 0.01, respectively. The cathode for water electrolysis according to any one of claims 1 to 4.

6. The catalyst part includes Raney nickel particles, and the cathode for water electrolysis according to any one of claims 1 to 5.

7. The catalyst part further includes metal particles mainly containing Ni, and the metal particles are in contact with the Raney nickel particles, and the cathode for water electrolysis according to claim 6.

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

9. The metal particles further include Al, and the ratio of the total number of moles of Al to the total number of moles of Ni in the Raney nickel particles is larger than the ratio of the total number of moles of Al to the total number of moles of Ni in the metal particles, and the cathode for water electrolysis according to claim 7 or 8.

10. It includes a catalyst part forming step of forming a catalyst part and a reverse current absorber forming step of forming a reverse current absorber including a hydrogen storage alloy containing Al, and the reverse current absorber forming step includes a hydrogen storage alloy coating step of coating a slurry obtained by mixing the hydrogen storage alloy and a solvent on a substrate, which is a manufacturing method of a cathode for water electrolysis.

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