Alkaline water electrolysis method and anode for alkaline water electrolysis

Abstract

Provided is an electrolysis technique by which it is possible to form a large amount of catalysts in a short time in a simple manner with constant current electrolysis so as to more efficiently form a catalyst layer, and which has a high practical value due to an exceedingly durable anode for alkaline water electrolysis that lowers susceptibility to deterioration in electrolysis performance during electrolytic operation even if power having large output fluctuations is used as the power source, and that more stably and efficiently maintains excellent catalytic activity over a long period of time.　Provided are an anode for alkaline water electrolysis and an alkaline water electrolysis method in which an electrolyte solution, in which hybrid nickel / iron / cobalt hydroxide (NixFeyCoz-hmh) of a complex of metal hydroxide and organic matter is dispersed, is supplied as a catalyst to at least an anode chamber of an electrolysis cell, electrolytic precipitation of NiFeCo-hmh is performed in the electrolysis cell during operation, and electrolytic precipitation and deposition of NixFeyCoz-hmh is performed on a surface of a conductive substrate obtained by forming a catalyst layer and constituting an oxygen generating anode, thereby recovering and improving electrolysis performance.

Description

[Technical Field]

[0001] The present invention relates to an alkaline water electrolysis method and an anode for alkaline water electrolysis. More specifically, the present invention relates to a technology that enables a large amount of catalyst to be formed in a short time by a simple means of supplying, as needed, an electrolyte solution containing a dispersed catalyst with a unique structure that exhibits good dispersibility to at least an anode chamber constituting an electrolytic cell, thereby realizing maintenance of the catalytic activity of an oxygen generating anode over a long period of time, thereby making it possible to perform alkaline water electrolysis more stably over a long period of time without deterioration of electrolysis performance even when electricity with large output fluctuations, such as renewable energy, is used as a power source. [Background technology]

[0002] Hydrogen is a secondary energy source that is suitable for storage and transportation and has a low environmental impact, so interest is growing in hydrogen energy systems that use hydrogen as an energy carrier. Currently, hydrogen is mainly produced by methods such as steam reforming of fossil fuels. However, in light of issues such as global warming and the depletion of fossil fuels, hydrogen production by water electrolysis using renewable energy sources such as solar and wind power is becoming increasingly important as a fundamental technology. Water electrolysis is low-cost and suitable for large-scale production, making it a promising technology for hydrogen production.

[0003] Currently, practical water electrolysis can be broadly divided into two types. One is alkaline water electrolysis, which uses a highly concentrated alkaline aqueous solution as the electrolyte. The other is solid polymer water electrolysis, which uses a solid polymer membrane (SPE) as the electrolyte. When using water electrolysis for large-scale hydrogen production, alkaline water electrolysis, which uses inexpensive materials such as iron-based metals such as nickel, is said to be more suitable than solid polymer water electrolysis, which requires electrodes that use large amounts of expensive precious metals.

[0004] High-concentration alkaline aqueous solutions become more conductive as the temperature rises, but they also become more corrosive. For this reason, the upper limit of the operating temperature for alkaline water electrolysis is limited to around 80-90°C. In recent years, the development of electrolytic cell components and various piping materials that can withstand high temperatures and high-concentration alkaline aqueous solutions, as well as the development of low-resistance diaphragms and electrodes with enlarged surface areas and catalysts, has led to the electrolytic cell voltage being reduced to a current density of 0.6 Acm. -2 The voltage has been improved to below 2V.

[0005] Nickel-based materials that are stable in highly concentrated alkaline aqueous solutions are used as anodes for alkaline water electrolysis, and it has been reported that nickel-based anodes have a lifespan of several decades or more when alkaline water electrolysis is performed using a stable power source (Non-Patent Documents 1 and 2). However, when renewable energy is used as the power source, harsh conditions such as frequent start-stops and load fluctuations are often encountered, and deterioration of the performance of nickel-based anodes is a problem (Non-Patent Document 3).

[0006] Both the nickel oxide production reaction and the reduction reaction of the produced nickel oxide proceed on the metal surface. Therefore, these reactions promote the detachment of the electrocatalyst formed on the metal surface. When the supply of power for electrolysis is discontinued, electrolysis stops, and the nickel-based anode is maintained at a potential lower than the oxygen evolution potential (1.23 V vs. RHE) and higher than the counter electrode, the cathode for hydrogen evolution (0.00 V vs. RHE). Various chemical species generate electromotive forces within the electrolytic cell, and as the cell reaction progresses, the anode potential is maintained low, promoting the reduction reaction of nickel oxide.

[0007] In the case of an electrolytic cell that combines multiple cells, such as an anode chamber and a cathode chamber, the current generated by the cell reaction leaks through the piping connecting the cells. One way to prevent this current leakage is to continue to flow a small current when the cell is shut down. However, continuing to flow a small current when the cell is shut down requires special power supply control and constantly generates oxygen and hydrogen, which requires excessive effort in terms of operation and management. Furthermore, while it is possible to intentionally prevent a reverse current state by draining the solution immediately after shutting down the cell, this is hardly an appropriate measure when operating with electricity that has large output fluctuations, such as renewable energy.

[0008] Conventionally, catalysts (anode catalysts) for oxygen generation used in alkaline water electrolysis include platinum group metals, platinum group metal oxides, valve metal oxides, iron group oxides, and lanthanide group metal oxides. Other known anode catalysts include nickel-based alloys such as Ni-Co and Ni-Fe; nickel with increased surface area; conductive oxides (ceramic materials) such as spinel-based Co3O4 and NiCo2O4, and perovskite-based LaCoO3 and LaNiO3; noble metal oxides; and oxides composed of lanthanide group metals and noble metals (Non-Patent Document 3).

[0009] In recent years, various configurations have been proposed as oxygen generating anodes for use in high-concentration alkaline water electrolysis. For example, an anode for alkaline water electrolysis in which a lithium-containing nickel oxide catalyst layer containing lithium and nickel at a predetermined molar ratio is formed on the surface of a nickel substrate (Patent Document 1), and an anode for alkaline water electrolysis in which a catalyst layer containing a nickel-cobalt oxide and an iridium oxide or a ruthenium oxide is formed on the surface of a nickel substrate (Patent Document 2) have been proposed.

[0010] The present inventors have already proposed an oxygen generating anode with a novel configuration as a technology for solving the problems of the above-mentioned conventional technologies. Specifically, the inventors proposed an oxygen generating anode comprising a catalytic layer containing hybrid cobalt hydroxide nanosheets (Co-ns), which are a composite of a metal hydroxide and an organic substance, provided on the surface of a conductive substrate whose surface is made of nickel or a nickel-based alloy. Furthermore, the inventors proposed an alkaline water electrolysis method using this oxygen generating anode, in which an electrolyte containing dispersed hybrid cobalt hydroxide nanosheets (Co-ns), a component of the catalytic layer, is supplied to the anode chamber and cathode chamber constituting an electrolysis cell, and is used commonly for electrolysis in each chamber (Patent Document 3, Non-Patent Document 4).

[0011] Furthermore, because there was room for improvement in the performance of the electrodes formed by the above electrolysis method, we further investigated the nanosheet components and proposed the following technology. Specifically, we found that an oxygen-evolving anode provided with a catalyst layer containing a hybrid nickel-iron hydroxide nanosheet (NiFe-ns), a composite of a metal hydroxide and an organic substance, had superior electrode performance, and proposed an alkaline water electrolysis method in which an electrolyte with NiFe-ns dispersed therein is supplied to the anode and cathode chambers that make up the electrolysis cell and used commonly for electrolysis in each chamber (Patent Document 4). [Prior art documents] [Patent documents]

[0012] [Patent Document 1] Japanese Patent Application Laid-Open No. 2015-86420 [Patent Document 2] Japanese Patent Application Publication No. 2017-190476 [Patent Document 3] Re-tabled publication 2020 / 184607 [Patent Document 4] Patent Publication No. 2021-139027 [Non-patent literature]

[0013] [Non-Patent Document 1] PWTLu, S.Srinivasan, J.Electrochem.Soc.,125, 1416 (1978) [Non-patent document 2] CT Bowen, Int.J.Hydrogen Energy,9,59 (1984) [Non-patent document 3] S. Mitsushima et al., Electrocatalysis, 8, 422 (2017) [Non-patent document 4] Y. Kuroda, T. Nishimoto, S. Mitsushima, Electrochim. Acta, 323, Article 134812 (2019) Summary of the Invention [Problem to be solved by the invention]

[0014] However, according to the studies of the present inventors, the technology of Patent Document 4 described above has a new problem: the dispersibility of NiFe-ns in an alkaline aqueous solution is poor, making it difficult to form a sufficient catalytic layer in an electrolysis cell in a short time. This problem may hinder practical use and is an important issue that must be resolved. Here, the technology using Co-ns described in Patent Document 3 and the technology using NiFe-ns described in Patent Document 4, which is an extension of this technology, both achieve excellent electrocatalytic activity. However, according to the studies of the present inventors, even more effective alkaline water electrolysis anodes using NiFe-ns as a catalyst require further development. Specifically, conventional alkaline water electrolysis anodes, which are the target of these technologies, are prone to deterioration in electrolysis performance when powered by renewable energy or other sources with large output fluctuations, making it difficult to stably use them for long periods of time. These technical issues have yet to be fully addressed. That is, to fully solve the above technical problems, there is a need for high durability that enables the electrolysis performance to be more quickly restored and improved when the performance of the oxygen generating anode used deteriorates due to potential fluctuations caused by frequent start-stops or potential load fluctuations. In the specification of the present application, the alkaline water electrolysis anode that generates oxygen is also referred to as the "oxygen generating anode".

[0015] The present invention has been made in view of the above-mentioned conventional techniques, and an object of the present invention is to provide a useful electrode for electrolysis that is highly durable and that is resistant to deterioration in electrolytic performance and that maintains excellent catalytic activity more stably over a long period of time, even when powered by electricity with large output fluctuations, such as renewable energy. Furthermore, a final object of the present invention is to provide an operating method for alkaline water electrolysis that uses the above-mentioned excellent electrode for electrolysis and achieves more stable alkaline water electrolysis over a long period of time, and is resistant to deterioration in electrolytic performance, even when powered by electricity with large output fluctuations.

[0016] Therefore, an object of the present invention is to further develop the technology developed by the inventors mentioned above to make it more industrially applicable. Specifically, the object is to develop an oxygen generating anode with improved durability, which is less susceptible to degradation of electrolytic performance when powered by electricity with large output fluctuations, can efficiently recover degraded electrolytic performance (i.e., the catalytic layer self-repairs through electrolysis), and maintains excellent catalytic activity stably for a longer period of time, compared to conventional technologies using Co-ns or NiFe-ns catalysts. Another object is to develop a technology that enables the catalytic layer of an oxygen generating anode that provides such excellent effects to be formed efficiently over a long period of time using a more versatile material and a simple electrolysis method. [Means for solving the problem]

[0017] The above object can be achieved by the present invention described below. That is, the present invention provides the following alkaline water electrolysis method. Note that the abbreviation "hmh" used in the present invention is an abbreviation for "hybrid metal hydroxide." [1] Hybrid nickel-iron-cobalt hydroxide (Ni x Fe y Co z an electrolytic solution containing a dispersed catalyst comprising the compound (a) and the catalyst (b) (i.e., a catalyst containing the compound (a) and the catalyst (b)) is supplied to an anode chamber and a cathode chamber constituting an electrolytic cell, and is used in common for electrolysis in each chamber.

[0018] [2] Hybrid nickel-iron-cobalt hydroxide (Ni x Fe y Co z An electrolytic solution in which a catalyst containing Ni-hmh) is dispersed is supplied to at least the anode chamber constituting the electrolytic cell, and during operation, x Fe y Co z The electrolytic deposition of Ni-hmh is carried out in the electrolytic cell, and the Ni-hmh is deposited on the surface of a conductive substrate having a catalyst layer formed on the surface thereof, which constitutes an anode for oxygen generation. xFe y Co z An alkaline water electrolysis method characterized by recovering and improving electrolysis performance by electrolytic deposition of -hmh.

[0019] Preferred embodiments of the alkaline water electrolysis method described above include the following. [3] The alkaline water electrolysis method according to [1] or [2], wherein the electrolytic solution is supplied intermittently. [4] The above Ni x Fe y Co z The alkaline water electrolysis method according to [1] to [3], wherein -hmh comprises at least one of a sheet-like substance having a layered molecular structure, a needle-shaped substance having a tunnel structure, and a particulate substance having an amorphous structure, all of which are substances with a size within the range of 1 to 200 nm. [5] The above Ni x Fe y Co z The alkaline water electrolysis method according to any one of [2] to [4], wherein the condition for electrolytically depositing -hmh on the surface of the conductive substrate is to maintain the conductive substrate in a potential range of 1.2 V to 1.8 V vs. RHE. [6] The Ni x Fe y Co z -hmh is dispersed in the electrolyte solution, and the concentration is 5 to 100 g / L. x Fe y Co z -hmh dispersion liquid, x Fe y Co z The alkaline water electrolysis method according to any one of [1] to [5], wherein the concentration of the -hmh dispersion added to the electrolytic solution is adjusted to be within the range of 0.1 to 8 mL / L. [7] The above Ni x Fe y Co z The alkaline water electrolysis method according to any one of [1] to [6], wherein -hmh has an atomic ratio of Ni / Fe / Co of 0.1-0.9 / 0.1-0.9 / 0.1-0.9.

[0020] In another embodiment, the present invention provides the following anode for alkaline water electrolysis, which is useful when applied to the alkaline water electrolysis method described above. [8] A conductive substrate whose surface is made of nickel or a nickel-based alloy, and a hybrid nickel-iron-cobalt hydroxide (Ni) formed on the surface of the conductive substrate, which is a composite of a metal hydroxide and an organic substance. x Fe y Co z and a catalyst layer comprising: [9] A conductive substrate having a surface made of nickel or a nickel-based alloy, and a conductive material having the composition formula Li formed on the surface of the conductive substrate. x Ni 2-x The intermediate layer is made of a lithium-containing nickel oxide represented by O2 (0.02≦x≦0.5), and the hybrid nickel·iron·cobalt hydroxide (Ni) is a composite of a metal hydroxide and an organic substance formed on the surface of the intermediate layer. x Fe y Co z and a catalyst layer comprising: [Effects of the Invention]

[0021] The present invention makes it possible to provide an alkaline water electrolysis anode (oxygen generating anode) that generates oxygen with improved durability, in which electrolysis performance is less likely to deteriorate during electrolysis operation and excellent catalytic activity is more stably and efficiently maintained over a long period of time, even when powered by electricity with large output fluctuations, such as renewable energy. Furthermore, the present invention makes it possible to more efficiently maintain the catalytic activity of the oxygen generating anode stably over a long period of time by the simple means of supplying a common electrolytic solution to the anode chamber and the cathode chamber, or by the simple means of supplying an electrolytic solution with a specific catalyst dispersed in it to the anode chamber as needed. The present invention makes it possible to provide an industrially useful alkaline water electrolysis method that is less likely to deteriorate in electrolytic performance of the oxygen generating anode and that enables more stable alkaline water electrolysis over a long period of time, particularly when powered by electricity with large output fluctuations. Furthermore, the material constituting the catalytic layer of the alkaline water electrolysis anode used in the present invention, which provides the above-mentioned excellent effects, is highly versatile and can be easily formed (deposited) in large quantities in a short time by constant current electrolysis, enabling more efficient formation of the catalytic layer, and in particular, stable and efficient self-repair of the catalytic layer. This makes the material highly applicable to industrial applications and extremely valuable in practical use. The above-mentioned excellent effects can be achieved by the hybrid nickel-iron-cobalt hydroxide (Ni), which is a metal hydroxide and an organic material newly proposed by the present inventors. x Fe y Co z -hmh)))))))))))))))))))))))))))))))))))))))))))))))))))) x Fe y Co zThis can be easily achieved by a new alkaline water electrolysis method in which electrolysis is performed using an electrolyte solution in which Fe-hmh is dispersed. Furthermore, it was confirmed that the above-mentioned favorable effects can be obtained compared to conventional techniques using an oxygen generating anode provided with a catalytic layer containing a hybrid (Fe-hmh) of an extremely common iron ion and an organic substance. Furthermore, it was confirmed that by configuring an oxygen generating anode with a catalytic layer containing not only Fe-hmh but also Fe-hmh and Co-ns coexisting, better performance is exhibited than either a catalytic layer containing Fe-hmh alone or a catalytic layer containing Co-ns alone. [Brief explanation of the drawings]

[0022] [Figure 1] FIG. 1 is a cross-sectional view schematically illustrating one embodiment of an oxygen generating anode used in the alkaline water electrolysis method of the present invention. [Figure 2A] FIG. 1 is a diagram showing a schematic molecular structure of a layered NixFeyCoz-Tris-NH2 having a tripodal ligand, which is an example of a catalyst component used in the present invention. [Figure 2B] FIG. 1 is a diagram showing a schematic diagram of a needle-shaped material with a tunnel structure, which is an example of a catalyst component used in the present invention, NixFeyCoz-Tris-NH2 having a tripod ligand. [Figure 3] FIG. 1 is a diagram schematically illustrating an example of a method for producing a catalyst according to the present invention and an example of the resulting reaction product. [Figure 4A] 1 is a graph showing current-potential changes (activity changes) in the potential cycle of Study Example 1 when the catalyst Ni11.5Fe70.5Co18-hmh constituting the present invention is used. [Figure 4B] 1 is a graph showing current-potential change (activity change) when Ni61.5Fe38.5-ns is used as a catalyst, for comparison in the potential cycle of Study Example 1. FIG. [Figure 4C] 4B. FIG. 4C is a graph showing the relationship between catalyst deposition time and catalyst deposition amount (accumulation amount) obtained using the peak areas of FIGS. 4A and 4B. FIG. [Figure 5]1 is a graph showing the change in electrolysis characteristics with respect to deposition time when Ni11.5Fe70.5Co18-hmh is used as a catalyst and when Ni61.5Fe38.5-ns is used as a catalyst in Study Example 1. [Figure 6] 1 is a graph showing changes in electrolysis characteristics when each catalyst component is used in an accelerated test carried out in Study Example 1. [Figure 7] 1 is a graph showing changes in electrolysis characteristics when each catalyst component was used in a test of continuous electrolysis at a constant current conducted in Study Example 2. [Figure 8] 10 is a graph showing changes in electrolysis characteristics when each catalyst component is used in an accelerated durability test conducted in Study Example 3. [Figure 9] FIG. 1 is a transmission electron microscope photograph showing the properties of Fe-hmh particles in a liquid, which is an example of a catalyst component that can provide the effects of the present invention. [Figure 10] FIG. 1 is a transmission electron microscope photograph showing a state in which Fe-hmh particles, which are an example of a catalyst component that can achieve the effects of the present invention, are dispersed in an electrolyte and precipitated on the surface of a Ni substrate by electrolysis. [Figure 11A] FIG. 1 is a field emission scanning electron microscope (FE-SEM) image showing the state in which Fe-hmh particles, which are an example of a catalyst component that can provide the effects of the present invention, are dispersed in an electrolyte solution together with Co-ns particles and precipitated on the surface of a Ni substrate by electrolysis. [Figure 11B] FIG. 11B is a field emission scanning electron microscope (FE-SEM) image showing the state of precipitation in a different field of view from that of FIG. 11A. [Figure 12] 10 is a graph showing the change in electrolytic characteristics when an electrolyte solution containing dispersed Fe-hmh particles and an electrolyte solution containing dispersed catalyst components containing coexisting Fe-hmh particles and Co-ns particles are used in Study Example 4. [Figure 13] 10 is a graph showing the change in the amount of Fe deposited relative to the amount of Co deposited after electrolysis and the electrolytic characteristics when electrolysis was performed using an electrolyte solution in which catalyst components in which Fe-hmh particles and Co-ns particles coexisted at different ratios were dispersed, as performed in Study Example 5. [Figure 14]10 is a graph showing the amounts of Co and Fe deposited after electrolysis in each of the electrolytes in which catalyst components, Fe-hmh particles and Co-ns particles, were dispersed in the presence of each other at different ratios, as performed in Study Example 5. DETAILED DESCRIPTION OF THE INVENTION

[0023] The present invention will be described in detail below, taking preferred embodiments into consideration. The aforementioned Non-Patent Document 4 reported for the first time that an electrolyte containing a self-repairing catalyst Co-ns for the anode improved anode performance while having almost no effect on the cathode electrode. However, as mentioned above, although the present inventors have proposed new self-repairing catalysts for the anode, they have found that there is still room for improvement in anode performance, and that there are important issues to be resolved, particularly for practical application. Specifically, the previously proposed NiFe-ns catalyst has poor dispersibility in alkaline aqueous solutions, making it difficult to form a sufficient catalyst layer in an electrolytic cell in a short time when used in an electrolyte. Therefore, the development of a useful technology for recovering (repairing) electrolytic performance more efficiently and stably has been desired. As a result of extensive research aimed at solving the above problems, the present inventors have discovered the following: first, a hybrid nickel-iron-cobalt hydroxide (NiFe-ns) x Fe y Co z The present inventors have found that a composite (composite of a self-repairing electrode catalyst) can function more effectively as the highly durable self-repairing electrode catalyst targeted by the present invention, and that the use of this composite can solve the above-mentioned problems in the prior art to a higher degree, thereby completing the present invention.

[0024] Specifically, the inventors have developed hybrid nickel-iron-cobalt hydroxide (Ni), which is a composite of metal hydroxide and organic material. x Fe y Co z -hmh) is dispersed in an electrolyte and used as a self-repairing electrode catalyst. x Fe y Co zIt was found that -hmh acts as a catalyst and anticorrosion coating, and can significantly improve the durability of Ni-based anodes against potential fluctuations compared to the previously proposed anodes using Co-ns as a catalyst. x Fe y Co z When -hmh is used as a catalyst, a larger amount of catalyst can be formed (deposited) on the anode surface in a shorter time during electrolysis than when NiFe-ns is used as the catalyst previously proposed. x Fe y Co z We found that -hmh is a useful material that can restore electrolytic performance more efficiently and stably.

[0025] Furthermore, during the course of the above-mentioned investigations, the inventors discovered that even in the case of an anode using Fe-hmh as a catalyst, in which the only metal ion is the commonly used metal iron, the durability of a Ni-based anode against potential fluctuations can be improved compared to anodes using the previously proposed Co-ns as a catalyst. Furthermore, as a result of extensive research aimed at improving the practicality of using the above-mentioned Fe-hmh as a catalyst, the inventors discovered that a greater effect can be achieved by using the following configuration. Specifically, they discovered that even in the case of an anode configured to use a precipitate of Fe-hmh and Co-ns prepared separately and coexisting with each other as a catalyst, the durability of a Ni-based anode against potential fluctuations can be improved compared to anodes using Fe-hmh alone as a catalyst.

[0026] [anode] FIG. 1 is a cross-sectional view schematically illustrating one embodiment of an alkaline water electrolysis anode for generating oxygen, which is used in the alkaline water electrolysis method of the present invention. The oxygen generating anode 10 of the embodiment shown in FIG. 1 comprises a conductive substrate 2, an intermediate layer 4 formed on the surface of the conductive substrate 2, and a catalytic layer 6 formed on the surface of the intermediate layer 4. Details of the oxygen generating anode used in the alkaline water electrolysis method of the present invention will now be described with reference to the drawings. In the following description, the alkaline water electrolysis anode is configured to include the intermediate layer 4 shown in FIG. 1 . However, in the alkaline water electrolysis anode of the present invention, the intermediate layer 4 is formed between the conductive substrate 2 and the catalytic layer 6 as needed and is not an essential component.

[0027] <Conductive substrate> The conductive substrate 2 is a conductor for conducting electricity for electrolysis and functions as a carrier for depositing the intermediate layer 4 and catalyst layer 6. At least the surface of the conductive substrate 2 (the surface on which the intermediate layer 4 is formed) is made of nickel or a nickel-based alloy. That is, the entire conductive substrate 2 may be made of nickel or a nickel-based alloy, or only the surface may be made of nickel or a nickel-based alloy. Specifically, the conductive substrate 2 may be made of a metal material such as iron, stainless steel, aluminum, or titanium, with a coating of nickel or a nickel-based alloy applied by plating or the like.

[0028] The thickness of the conductive substrate 2 is preferably about 0.05 to 5 mm. The conductive substrate is preferably shaped to have openings for removing bubbles of oxygen, hydrogen, etc. that are generated. For example, an expanded mesh or a porous expanded mesh can be used as the conductive substrate 2. When the conductive substrate has openings, the opening ratio of the conductive substrate is preferably 10 to 95%.

[0029] The oxygen generating anode used in the water electrolysis method of the present invention can be obtained, for example, by forming an intermediate layer 4 and a catalyst layer 6 on the surface of the above-mentioned conductive substrate 2 as follows. (Pretreatment process) Before carrying out the steps of forming the intermediate layer 4 and the catalyst layer 6, it is preferable to perform a chemical etching treatment on the conductive substrate 2 in advance to remove contaminant particles such as metals and organic substances from the surface. The amount of wear of the conductive substrate due to the chemical etching treatment is 30 g / m 2 More than 400g / m 2 It is preferable that the surface of the conductive substrate be roughened in advance to increase the adhesion to the intermediate layer. Methods for roughening the surface include blasting, which sprays powder, etching, which uses an acid that is soluble in the substrate, and plasma spraying.

[0030] <Middle class> The intermediate layer 4 is a layer formed on the surface of the conductive substrate 2. The intermediate layer prevents corrosion of the conductive substrate and stably fixes the catalyst layer 6 to the conductive substrate. The intermediate layer also plays a role in quickly supplying current to the catalyst layer. The intermediate layer is, for example, a layer having a composition formula of Li x Ni 2-x It is preferable that the intermediate layer 4 be formed of a lithium-containing nickel oxide represented by the formula O2 (0.02≦x≦0.5). If x in the above composition formula is less than 0.02, the electrical conductivity will be insufficient. On the other hand, if x exceeds 0.5, the physical strength and chemical stability will decrease. The intermediate layer 4 formed of the lithium-containing nickel oxide represented by the above composition formula has sufficient electrical conductivity for electrolysis and exhibits excellent physical strength and chemical stability even when used for a long period of time.

[0031] The thickness of the intermediate layer is preferably 0.01 μm or more and 100 μm or less, and more preferably 0.1 μm or more and 10 μm or less. If the thickness of the intermediate layer is less than 0.01 μm, the above-mentioned functions are not exhibited. On the other hand, if the thickness of the intermediate layer exceeds 100 μm, the voltage loss due to the resistance in the intermediate layer increases, and the above-mentioned functions are not exhibited and there may be some disadvantages in terms of manufacturing costs, etc.

[0032] (Coating process for forming intermediate layer) In the coating step, an aqueous precursor solution containing lithium ions and nickel ions is coated onto the surface of the conductive substrate 2. The intermediate layer is formed by a so-called pyrolysis method. When forming the intermediate layer by pyrolysis, first, an aqueous precursor solution for the intermediate layer is prepared. Known precursors containing a lithium component, such as lithium nitrate, lithium carbonate, lithium chloride, lithium hydroxide, and lithium carboxylate, can be used. Examples of lithium carboxylates include lithium formate and lithium acetate. Known precursors containing a nickel component, such as nickel nitrate, nickel carbonate, nickel chloride, and nickel carboxylate, can be used. Examples of nickel carboxylates include nickel formate and nickel acetate. Using at least one of a lithium carboxylate and a nickel carboxylate as the precursor is particularly preferred, as it allows for the formation of a dense intermediate layer even when fired at a low temperature, as described below.

[0033] The heat treatment temperature when forming an intermediate layer by thermal decomposition can be set appropriately. Considering the decomposition temperature of the precursor and production costs, the heat treatment temperature is preferably 450°C or higher and 600°C or lower, and more preferably 450°C or higher and 550°C or lower. For example, the decomposition temperature of lithium nitrate is approximately 430°C, and the decomposition temperature of nickel acetate is approximately 373°C. By setting the heat treatment temperature to 450°C or higher, each component can be decomposed more reliably. If the heat treatment temperature exceeds 600°C, oxidation of the conductive substrate is likely to proceed, which may increase electrode resistance and lead to increased voltage loss. The heat treatment time can be set appropriately, taking into account the reaction rate, productivity, oxidation resistance of the catalyst layer surface, etc.

[0034] The thickness of the intermediate layer formed can be controlled by appropriately setting the number of times the aqueous solution is applied in the above-mentioned application step. The application and drying of the aqueous solution may be repeated for each layer, and the entire structure may be heat-treated after the top layer is formed. Alternatively, the application and heat treatment (pretreatment) of the aqueous solution may be repeated for each layer, and the entire structure may be heat-treated after the top layer is formed. The temperatures for the pretreatment and the overall heat treatment may be the same or different. It is preferable that the time for the pretreatment is shorter than the time for the overall heat treatment.

[0035] <Catalyst layer> The oxygen generating anode used in the alkaline water electrolysis method of the present invention has a catalytic layer 6 made of a specific catalytic component formed on the outermost surface of the conductive substrate 2, thereby achieving the remarkable effects of the present invention when applied to alkaline water electrolysis. The catalytic layer, which is important for achieving the remarkable effects of the present invention, is described below.

[0036] (catalyst component) The catalytic component used in the present invention, which characterizes the present invention, is a hybrid nickel-iron-cobalt (Ni x Fe y Co z Ni-hmh) can be easily produced, for example, as follows: x Fe y Co z -hmh can be synthesized, for example, by mixing an aqueous solution of the tripodal ligand tris(hydroxymethyl)aminomethane (Tris-NH2) with an aqueous solution of NiCl2, FeCl2, and CoCl2, and reacting them at 90°C for 24 hours. The reaction product synthesized above is separated as a gel by filtration and washing with pure water, and this is subjected to ultrasonic treatment in pure water to produce the Ni-based electrolytic solution used in the alkaline water electrolysis method of the present invention. x Fe y Co z The Ni-hmh dispersion is easily obtained. x Fe y Co zThe concentration of -hmh is preferably about 5 to 100 g / L. In the test examples of the present invention described later, a dispersion liquid with a concentration of 5 g / L was used. x Fe y Co z The dispersion in which the -hmh catalyst is dispersed is called "NiFeCo-hmh dispersion." x Fe y Co z The "NiFeCo-hmh dispersion" obtained by the above-mentioned manufacturing method was used as the electrolyte in which -hmh was dispersed. When using the electrolyte, the catalyst was added at an appropriate concentration. In the explanation of the present invention, Tris-NH2 shown in Figure 2A was used as a representative example of a tripodal ligand, but the tripodal ligand is not particularly limited and may be any ligand having a molecular structure similar to Tris-NH2.

[0037] Ni x Fe y Co z -hmh has a composite structure in which a metal hydroxide and a tripodal ligand are covalently fixed, and according to the inventors' investigations, it is available in layered, tunnel, and amorphous structures. x Fe y Co z -hmh is, for example, a layered Ni complex having a tripodal ligand, as illustrated in FIG. 2A. x Fe y Co z The Ni-Fe-NH2-based brucite nanoparticles have a -Tris-NH2 molecular structure, and consist of a brucite layer to which Tris molecules are covalently immobilized. The Tris-NH2 modification enhances the exfoliation and dispersion capabilities in the layered nickel-iron-cobalt hydroxide electrolyte. x Fe y Co z TEM images confirmed that the molecular structure of -hmh is a nanosheet-like substance with a layered molecular structure, similar to the previously proposed "NiFe-ns," with a thickness of about 1.3 nm and a lateral size of about 10 to 100 nm. In addition, XRD revealed that Ni x Fe y Coz It was confirmed that -hmh has a layered structure with expanded basal spacing.

[0038] The reaction product, Ni, can be easily obtained by heating the mixture of raw materials and causing a reaction. x Fe y Co z We further investigated the NiFeCo-hmh nanoparticles. As a result, we found that the dispersed materials in the "NiFeCo-hmh dispersion" contained needle-like crystals characteristic of a tunnel structure, in addition to the nanosheet-like material shown in Figure 2A. This indicates the existence of "needle-shaped materials with a tunnel structure." Figure 9 shows a transmission electron microscope image of Fe-hmh as an example of such a structure. As mentioned above, Fe-hmh, whether used alone or in combination with Co-ns, can improve the durability of Ni-based anodes against potential fluctuations compared to the previously proposed anode using Co-ns alone. The tunnel-structured materials were needle-like crystals with widths of approximately 5 nm and lengths of mostly less than 100 nm. While some were longer, most were less than 200 nm. We also observed irregularly shaped particles consistent with an amorphous structure. Although the primary particles of this fine particle material are not clearly observed, they are expected to be about 1 to 5 nm in size, and in actual existence, primary particles of this size aggregate to form secondary particles of the order of microns. x Fe y Co z -hmh can be said to be a substance with a size in the range of 1 to 200 nm.

[0039] Furthermore, as a result of the investigations by the present inventors, it was found that the amount of the above-mentioned substances present in the reaction product is affected by the atomic ratio of Ni / Fe / Co. For example, when the Fe content is 70 mol% or less, the substance tends to become a nanosheet-like substance with a layered structure. On the other hand, when the Fe content is more than 70 mol%, the substance tends to become a particulate substance with an amorphous structure. Furthermore, as will be described later, when the catalyst contains Ni, x Fe y Co zThe electrolytic performance of the anode for oxygen evolution of the present invention using -hmh is x Fe y Compared to conventional technology using -ns as a catalyst, the effect of differences in the atomic ratio of Ni / Fe / Co in the composition was less, and a tendency for stable electrolysis performance was observed.

[0040] The reaction product was dispersed in water and ultrasonicated to test its water dispersibility. x Fe y When the -ns catalyst was dispersed in an electrolyte, it did not disperse well in water in the dry fine powder state. Therefore, the dispersion used in the electrolyte was prepared from the hydrogel obtained by filtration. On the other hand, the Ni x Fe y Co z In the case of NiFeCo-hmh, a dispersion could be prepared from the dry powder. x Fe y As in the case of using the -ns catalyst, it can also be prepared from the hydrogel obtained by filtration. The inventors believe that this difference in dispersibility is the cause of the difference in the amount of catalyst layer formed (deposited) on the surface of the oxygen generating anode by constant electrolysis, as will be described later. In other words, it is thought that when a catalyst showing good dispersibility is used, the amount of material that can contribute to the formation (deposition) of the catalyst layer (effectively usable) in the electrolyte in which the catalyst is dispersed increases, and this is the reason why Ni x Fe y Co z In the present invention, in which -hmh is used as a catalyst, the Ni x Fe y It is inferred that compared to when Ni-ns was used as a catalyst, a large amount of catalyst layer was formed (deposited) over a long period of time. x Fe y Co zIt is believed that the use of an electrolyte solution containing a dispersed -hmh catalyst has made it possible to realize the objective of the present invention of providing a superior oxygen generating anode that is less susceptible to deterioration in electrolysis performance and enables more stable alkaline water electrolysis over a long period of time, as well as an alkaline water electrolysis method using the same.

[0041] Ni that can be suitably used for the above-mentioned purpose of the present invention x Fe y Co z Examples of -hmh include those having a Ni / Fe / Co atomic ratio of (0.1 to 0.9) / (0.1 to 0.9) / (0.1 to 0.9). The Ni / Fe / Co atomic ratio is more preferably (0.1 to 0.7) / (0.3 to 0.8) / (0.05 to 0.2) (see FIG. 7). As described above, when used in the alkaline water electrolysis method of the present invention, Ni x Fe y Co z The size of the -hmh substance is preferably in the range of 1 to 200 nm in length (major axis). According to the study by the present inventors, if it is larger than this, the efficiency of electrolytic deposition decreases, and the overvoltage improvement and repair effect tend to be difficult to achieve, which is not preferable. Ni, which can be used as a catalyst suitable for the purpose of the present invention, x Fe y Co z Examples of -hmh include at least one of a sheet-like substance having a layered molecular structure, a needle-shaped substance having a tunnel structure, and a particulate substance having an amorphous structure.

[0042] Ni that can obtain the effects of the present invention and can be suitably used for the purpose of the present invention x Fe y Co zExamples of Fe-hmh include those made of extremely versatile materials with a Ni / Fe / Co atomic ratio of (0.0) / (1.0) / (0.0) that do not contain metal ions other than Fe. As mentioned above, Fe-hmh has the geometric characteristic of being a "tunnel-structured needle-shaped substance." Other examples include those made of materials containing Fe and Co metal ions with a Ni / Fe / Co atomic ratio of (0.0) / (0.1-0.9) / (0.1-0.9). According to the inventors' research, it has been found that the use of Fe-hmh and Co-ns in combination as a catalyst results in the deposition of Co components, which is characterized by the deposition of more highly active Fe-hmh than when Fe-hmh is used alone as a catalyst. This point will be discussed later.

[0043] According to the investigations of the present inventors, the catalytic component that characterizes the present invention, which is used to form the catalytic layer of the anode for alkaline water electrolysis and is contained in the electrolyte, is a hybrid nickel-iron-cobalt (Ni x Fe y Co z By using the composites (cobalt hydroxide nanosheets -hmh), better effects can be obtained compared to the technology using hybrid cobalt hydroxide nanosheets (Co-ns) previously proposed by the present inventors. Specifically, the above composites were used to form the catalytic layer of the anode, and the resulting anode was used to supply electrolytes containing the above different composites as catalysts to the anode chamber, and an accelerated degradation test of electrolysis performance was carried out to examine the dependency of the oxygen evolution overpotential on potential fluctuation cycles. As a result, compared to when Co-ns was used as the catalytic component, Ni x Fe y Co z When -hmh was used, a significant decrease in the initial overvoltage was clearly observed, confirming that the catalyst had excellent durability. Details will be described later. Furthermore, the Ni used as the catalyst component in the present invention x Fe y Co z-hmh can be synthesized by a simple method from general-purpose materials, and as mentioned above, has excellent dispersibility, so it also has extremely important industrial advantages, such as being easy to use as a dispersion liquid containing a dispersed catalyst, which is required in the present invention, or as an electrolyte liquid prepared using said dispersion liquid.

[0044] (Method for forming catalyst layer) The method for forming the catalyst layer 6 will be described. A 1.0 M KOH aqueous solution was used as the electrolyte. To clean the surface of the conductive substrate 2, it is preferable to perform potential manipulation in the electrolyte. For example, potential cyclic manipulation (-0.5 to 0.5 V vs. RHE, 200 mV / s, 200 cycles) is performed. Thereafter, a 1.0 M KOH aqueous solution containing the NiFeCo-hmh dispersion obtained as described above at an additive concentration of 1 mL / L was prepared and used as the electrolyte. Then, Ni x Fe y Co z To deposit -hmh on the Ni substrate surface, 800mA / cm 2 The electrolysis was carried out eight times for 30 minutes at constant current. x Fe y Co z The dispersibility of -hmh is reduced by oxidation of the hydroxide layer and oxidative decomposition of the surface organic groups, and Ni is deposited on the electrode surface. x Fe y Co z -hmh was deposited.

[0045] In the above, the concentration of the "NiFeCo-hmh dispersion" added to the electrolyte is preferably in the range of 0.1 to 10 mL / L, more preferably 0.1 to 8 mL / L. According to the study by the present inventors, if the concentration is higher than this, the NiFeCo-hmh dispersion in the electrolyte may be easily dissolved. x Fe y Co zThis is undesirable because the dispersion of -hmh becomes insufficient, making it difficult to obtain uniform deposition during electrolysis. Furthermore, if the concentration is lower than this, a sufficient amount cannot be obtained within a practical time period during electrolysis. Furthermore, as electrolysis conditions for deposition, it is preferable to maintain the conductive substrate in a potential range of 1.2 V to 1.8 V vs. RHE. The deposition reaction does not proceed below 1.2 V, but if it exceeds 1.8 V, oxygen generation simultaneously proceeds, inhibiting deposition, which is undesirable.

[0046] A transmission electron microscope photograph is shown below of an example of the deposit formed when a catalyst was deposited on a Ni substrate using an electrolyte solution containing dispersed Fe-hmh and electrolysis under the above conditions for 4 hours. As shown in Figure 10, in this case, the Ni substrate surface was found to be covered with a network of fibrous material in which Fe-hmh was bundled.

[0047] Figures 11A and 11B show field-emission scanning electron microscopy (FE-SEM) images of the precipitates formed on a Ni substrate by electrolysis using a combination of Fe-hmh and Co-ns particles dispersed in an electrolyte. The electrode surface was uniformly covered with a catalyst layer, and Figure 11B and its enlarged image (not shown) reveal that the microstructure is composed of nanosheet (Co-ns) aggregates. Furthermore, as shown in Figure 11A, a different view confirmed that the Fe-hmh particles were elongated and incorporated into the aggregates. Analysis revealed that the co-deposition significantly increased the amount of Fe-hmh deposited (estimated to be approximately 60 times the amount obtained when Fe-hmh was used alone), indicating that the use of Co-ns particles in the catalyst layer resulted in a significant increase in the amount of Fe-hmh deposited. Although the mechanism is not yet clear, dispersing both Fe-hmh particles and Co-ns particles in the electrolyte significantly increases the amount of Fe-hmh precipitated due to the precipitation of the Co-ns component, which is thought to be the reason for the improved catalytic activity.

[0048] The alkaline water electrolysis method of the present invention requires the use of an electrode having the above-described specific catalyst layer as the oxygen generating anode. The cathode (negative electrode) and diaphragm are not particularly limited, and any suitable materials used in conventional alkaline water electrolysis may be used. These are described below.

[0049] [Cathode] As the cathode, it is preferable to select and use a substrate made of a material that can withstand alkaline water electrolysis and a catalyst with a small cathode overvoltage. As the cathode substrate, a nickel substrate or a nickel substrate coated with an active cathode can be used. The shape of the cathode substrate can be a plate, an expanded mesh, a porous expanded mesh, or the like.

[0050] Cathode materials include porous nickel with a large surface area and Ni-Mo-based materials. Other examples include Raney nickel-based materials such as Ni-Al, Ni-Zn, and Ni-Co-Zn; sulfide-based materials such as Ni-S; and hydrogen storage alloy-based materials such as TiNi. Preferred catalysts have properties such as low hydrogen overvoltage, high short-circuit stability, and high poisoning resistance. Other preferred catalysts include metals such as platinum, palladium, ruthenium, and iridium, as well as oxides of these metals.

[0051] [diaphragm] Any of the conventionally known electrolytic diaphragms can be used, such as asbestos, nonwoven fabrics, ion exchange membranes, porous polymer membranes, and composite membranes of inorganic materials and organic polymers. Specifically, an ion-permeable diaphragm can be used, which comprises a mixture of a hydrophilic inorganic material, such as a calcium phosphate compound or calcium fluoride, and an organic binder, such as polysulfone, polypropylene, or polyvinylidene fluoride, and an organic fiber cloth embedded therein. Alternatively, an ion-permeable diaphragm can be used, which comprises a film-forming mixture of a granular inorganic hydrophilic material, such as an oxide or hydroxide of antimony or zirconium, and an organic binder, such as a fluorocarbon polymer, polysulfone, polypropylene, polyvinyl chloride, or polyvinyl butyral, and an expanded organic fiber cloth embedded therein.

[0052] In the alkaline water electrolysis method of the present invention, an alkaline water electrolysis cell including the oxygen generating anode characterizing the present invention as a constituent element can be used to electrolyze a high-concentration alkaline aqueous solution. The alkaline aqueous solution used as the electrolyte is preferably an aqueous solution of an alkali metal hydroxide such as potassium hydroxide (KOH) or sodium hydroxide (NaOH). The concentration of the alkaline aqueous solution is preferably 1.5% by mass or more and 40% by mass or less. Furthermore, a concentration of 15% by mass or more and 40% by mass or less is preferable because it provides high electrical conductivity and reduces power consumption. Furthermore, in consideration of cost, corrosiveness, viscosity, operability, etc., the concentration of the alkaline aqueous solution is preferably 20% by mass or more and 30% by mass or less.

[0053] [How to drive] The catalytic layer 6 constituting the alkaline water electrolysis anode can be formed by electrolysis as described below before being incorporated into an electrolytic cell. In the alkaline water electrolysis method of the present invention, for example, Ni, a component forming the catalytic layer 6 that characterizes the present invention, is added to a common electrolyte supplied to the anode chamber and the cathode chamber constituting the electrolytic cell. x Fe y Co z By suspending -hm and initiating electrolysis in this state, as described above, a large amount of catalyst components can be deposited on the anode surface and accumulated in a short time to form a catalyst layer. Therefore, the alkaline water electrolysis technology of the present invention makes it possible to restore the performance of an electrolytic cell whose performance has deteriorated during operation without the need to disassemble the electrolytic cell, and to stably maintain the performance of the catalyst layer over a long period of time. Therefore, the alkaline water electrolysis technology of the present invention is practical and has significant industrial benefits. [Example]

[0054] Next, the present invention will be described in more detail with reference to examples, experimental examples, and comparative examples. First, the present invention will be described with reference to the Ni catalyst component, which is a characteristic of the present invention. x Fe y Co zThe deposition state and effect of -hmh on the surface of the electrode when it is dispersed in an electrolyte and electrolyzed were investigated. x Fe y A similar test was also carried out when -ns was used.

[0055] (Study example 1) Electrolysis was performed using a three-electrode cell made of PFA, a fluororesin. The working electrode was a Ni wire etched with boiling hydrochloric acid for 6 minutes, the reference electrode was a reversible hydrogen electrode (RHE), the counter electrode was a Ni coil, and the electrolyte was 250 mL of 1.0 M KOH aqueous solution. The operation was carried out at 30±1°C. First, as a pretreatment, cyclic voltammetry (0.5 to 1.5 V vs. RHE, 200 mV / s, 200 cycles) was performed without adding the NiFeCo-hmh dispersion to the electrolyte. The electrolyte used in this study was prepared as follows. Specifically, a NiFeCo-hmh dispersion with a concentration of 5 g / L obtained by the same method as described above was mixed with the electrolyte used in the pretreatment, and the dispersion was adjusted to an additive concentration of 8 mL / L to obtain an electrolyte containing a dispersed catalyst. The pretreated three-electrode cell was then used with this electrolyte, and a current of 800 mA / cm was applied. 2 Electrolysis was carried out at a constant current for 30 minutes. By electrolysis in this manner, the Ni catalyst component was dissolved on the electrode surface. x Fe y Co z -hmh is oxidized, and Ni x Fe y Co z The dispersibility of -hmh is reduced by oxidation of the hydroxide layer and oxidative decomposition of the surface organic groups, and Ni is deposited on the electrode surface. x Fe y Co z -hmh was deposited to obtain an anode with a specific catalyst layer.

[0056] Figure 4A shows Ni 11.5 Fe 70.5 Co 18The change in cyclic voltammetry during the catalyst layer formation process in -hmh was shown. After 30 minutes of electrolysis, oxidation peaks were observed at 1.33 V and 1.40 V vs. RHE. These were the oxidation peaks of Co, 2+ / Co 3+ , Ni 2+ / Ni 3+ These peaks were attributed to the reaction of 240 minutes and 600 minutes, and were thought to be derived from the deposited catalyst. As the electrolysis time increased to 240 minutes and 600 minutes, a shift to the higher potential side and an increase in peak area were confirmed. These observations suggest that the amount of catalyst deposited on the electrode increased with increasing electrolysis time.

[0057] For comparison, conventional Ni 61.5 Fe 38.5 Constant current electrolysis was carried out in the same manner as above, except that an electrolyte solution containing a dispersed -ns catalyst was used, to obtain an anode with a catalyst layer. 61.5 Fe 38.5 The change in cyclic voltammetry during the catalyst layer formation process at -ns is shown. An oxidation peak was observed at 1.40 V vs. RHE after 30 minutes and 240 minutes of electrolysis, but unlike the case of Figure 4A, the peak height did not increase any further. This suggests that the amount of catalyst deposited on the electrode when the NiFe-ns catalyst was used was smaller than when the NiFeCo-hmh catalyst constituting the present invention was used. In other words, the NiFe-ns catalyst used as a catalyst in the present invention 11.5 Fe 70.5 Co 18 As shown in Figure 4A, the peak area of ​​-hmh was significantly increased compared to Figure 4B, which uses a catalyst that does not contain Co in its composition. 11.5 Fe 70.5 Co 18 Since the dispersibility of -hmh was improved compared to the NiFe-ns catalyst, it is thought that the inclusion of Co in the composition improved the dispersibility of the catalyst, which made it easier to form (deposit) the catalyst layer on the electrode. Figure 4C shows a graph of the relationship between catalyst deposition time and catalyst deposition amount obtained using the peak areas of Figures 4A and 4B. As shown in Figure 4C, the NiFe-ns catalyst of the prior art x Fey It was confirmed that a larger catalyst layer could be deposited by using NiFeCo-hmh of the present invention as a catalyst compared to using -ns as a catalyst.

[0058] Figure 5 shows the Ni 11.5 Fe 70.5 Co 18 -hmh and Ni 61.5 Fe 38.5 Current density of 100 mA / cm versus catalyst deposition time in tests performed using -ns 2 As shown in Figure 5, the change in overpotential at Ni 11.5 Fe 70.5 Co 18 When -hmh is used as a catalyst, Ni 61.5 Fe 38.5 Overvoltages smaller than -ns were obtained.

[0059] Next, an accelerated potential test was performed under the following conditions using electrolytes in which various catalysts were dispersed. The accelerated potential test consisted of 2000 cycles of cyclic voltammetry at 0.5-1.7 V vs. RHE and 500 mV / s, and electrode performance measurements included two cycles of cyclic voltammetry at 0.5-1.8 V vs. RHE and 5 mV / s, and two cycles of cyclic voltammetry at 0.5-1.5 V vs. RHE and 50 mV / s. The catalysts dispersed in the electrolyte were Co-ns, Fe-hmh, and Ni. 11.5 Fe 70.5 Co 18 -hmh, Ni 61.5 Fe 38.5 For comparison, a test was conducted using an electrolyte without a dispersed catalyst, labeled "Bare Ni." The above procedure was repeated 20 times for each test, for a total of 40,000 cycles.

[0060] Figure 6 shows the results of the accelerated durability test against the above-mentioned potential fluctuation. As shown in Figure 6, an increase in overvoltage was observed after 10,000 cycles for bare Ni, whereas the increase in overvoltage was suppressed in all cases for the examples using electrolyte with dispersed catalyst. This is thought to be due to the catalyst being redeposited (self-repaired) from the electrolyte by constant current electrolysis every 2,000 cycles. 61.5 Fe 38.5 -ns, Ni 11.5 Fe 70.5 Co 18 In the examples using Ni-hmh and Fe-hmh, the overvoltage was maintained lower than when bare Ni or Co-ns was used as the catalyst. 11.5 Fe 70.5 Co 18 When -hmh was used as the catalyst, the initial activity was the highest. Although a slight increase in overpotential was observed from 4000 to 8000 cycles, the increase in overpotential was then stably suppressed. 61.5 Fe 38.5 -ns and Ni 11.5 Fe 70.5 Co 18 Although the characteristics were inferior to those of -hmh, good characteristics were also obtained when Fe-hmh was used.

[0061] (Study example 2) Figure 7 shows the results of the current density test at 100 mA / cm with various catalyst components dispersed in the electrolyte. 2 The graph shows the change in overvoltage when electrolysis was performed continuously at 1000 kJ / s. The following catalysts were used as the catalysts dispersed in the electrolyte, and electrolysis was performed using the electrolyte obtained in the same manner as in Study Example 1. Specifically, Ni was used as a binary Ni-Fe sample (catalyst). 83.6 Fe 16.3 -ns, Ni 76.6 Fe 23.5 -ns, Ni 61.5 Fe 38.5 -ns and Ni 58.8 Fe 41.2 As a ternary sample (catalyst) of Ni-Fe-Co constituting the present invention, Ni 65.6 Fe 33.7Co 0.6 -hmh, Ni 11.5 Fe 70.5 Co 18 -hmh and Ni 8.2 Fe 85 Co 6.8 In addition, we also tested the case where Co-ns and Fe-hmh were used as catalysts.

[0062] As shown in FIG. 7, the smallest overvoltage was obtained for the Ni-Fe-Co ternary sample of the present invention. 11.5 Fe 70.5 Co 18 The results were obtained when using -hmh as a catalyst. Furthermore, when using the Ni-Fe-Co ternary samples of the present invention, all samples exhibited stable low overpotentials, and most samples exhibited lower overpotentials than those using Co-ns. Among the Ni-Fe-Co ternary samples, those with a low cobalt content of 0.6 exhibited slightly higher overpotentials than those using Co-ns, but the results were comparable. In contrast, when using Ni-Fe binary samples, although some samples exhibited stable low overpotentials compared to those using Co-ns, the resulting overpotentials tended to vary significantly depending on the sample. This suggests that the newly discovered Ni-Fe-Co ternary composite catalyst of the present invention can more easily achieve effective continuous electrolysis with stable low overpotentials than those using Ni-Fe binary catalysts.

[0063] (Study example 3) Next, a durability test based on shutdown was carried out according to the following procedure: First, the anode to be tested was (1) set at 0.6 A / cm 2 After oxygen generation for 1 minute at 0.1 A / cm, (2) the anode potential was shifted to 0.5 V vs. RHE at a rate of 500 mV / s, and then (3) the anode potential was held at 0.5 V vs. RHE for 1 minute. The steps (1) to (3) were repeated, and the current at this time was 0.1 A / cm. 2The change in oxygen evolution potential was measured as a characteristic value. The number of times the above process was repeated is called an ADT (Advanced Durability Test) cycle. It is known that this accelerated life test causes deterioration to progress in fewer cycles than the accelerated durability test for potential fluctuations, the results of which are shown in Figure 6.

[0064] Durability tests were conducted using the above procedure using four types of anodes: a Ni anode and three types of anodes with different catalytic layers formed on a Ni substrate. The results are shown in Figure 8. Specifically, four types of anodes were used: a Ni anode, a Ni anode with a Co-ns catalytic layer, an anode with a Ni-Co spinel oxide catalytic layer prepared by pyrolysis, and a Ni anode with an Fe-hmh catalytic layer (an example in which the effects of the present invention were achieved). As shown in Figure 8, an increase in the oxygen evolving potential was observed after only a few ADT cycles for the Ni anode. Even for the anode with the Ni-Co spinel oxide catalytic layer, an increase in the oxygen evolving potential was observed after 1,000 cycles. Furthermore, the Ni anode with the Co-ns catalytic layer showed a slight tendency for potential increase up to 2,700 cycles. In contrast to the above results, a stable potential was observed even after 4,000 cycles for the anode with the Fe-hmh catalytic layer formed on a Ni substrate (Ni anode), confirming its effectiveness as an anode.

[0065] (Study example 4) As the component dispersed in the electrolyte, we investigated the case where Fe-hmh was used alone, and the case where Fe-hmh and Co-ns components were added to the electrolyte at a mass ratio of 1:1. When preparing an electrolyte containing both Fe-hmh and Co-ns components, the total amount of these components added was adjusted to a dispersion concentration of 8 mL / L, as in Study Example 1. Two types of electrolytes with different dispersed catalyst components were used, and the results were analyzed using a current of 800 mA / cm according to the method described in Study Example 1. 2 The composition of the latter electrode was determined to be Fe by ICP analysis of the aqueous solution in which the electrode was dissolved. 55 Co 45The composition ratio of the catalyst layer was -hmh. Figure 12 shows the current density of 100 mA / cm. 2 The graph shows the change in overpotential when electrolysis was performed continuously at 1000 kJ / cm². As shown in Figure 12, the electrode fabricated with the coexistence of the Fe-hmh component and the Co-ns component exhibited a smaller overpotential than the electrode fabricated with only Fe-hmh. In order to demonstrate the effect of the above composition, Figure 12 also shows the test results when the Co-ns component was dispersed alone in the electrolyte.

[0066] (Study example 5) As components to be dispersed in the electrolyte, Fe-hmh particles and Co-ns particles were used in the following different ratios, and electrolytes were prepared in which catalyst components were dispersed at the same concentrations as in Study Example 4. Electrolysis was performed with each of the obtained electrolytes, and the amount of Fe-hmh component (hereinafter also referred to as Fe) precipitated relative to the amount of Co-ns component (hereinafter also referred to as Co) precipitated after electrolysis and the electrolytic characteristics were examined. Specifically, electrolytes to which Fe-hmh component and Co-ns component were added were prepared so that Fe and Co coexisted in the following mass ratios: Fe:Co = 5:1 (Co / Fe = 0.2), Fe:Co = 10:1 (Co / Fe = 0.1), Fe:Co = 1:5 (Co / Fe = 5), and Fe:Co = 1:10 (Co / Fe = 10). Then, using multiple electrolytes with different composition ratios of the dispersed catalyst components, electrolysis was performed at 800 mA / cm according to the method described in Study Example 1. 2 Constant-current electrolysis was performed 10 times for 30 minutes at 1000 kJ / s. As a result, as shown in Figure 14, it was confirmed that the use of an electrolyte in which catalytic components containing coexisting Fe and Co were dispersed resulted in an increase in the amounts of Fe and Co deposited. Figure 14 also shows the amounts of deposition when electrolysis was performed using an electrolyte in which catalytic components were dispersed at an addition ratio of Fe:Co = 1:1 (Co / Fe = 1), as used in Study Example 4.

[0067] Figure 13 shows the relationship between the amount of Fe deposited relative to the amount of Co deposited after electrolysis and the amount of Fe deposited at a current density of 100 mA / cm. Electrodes were fabricated using electrolytes in which the two different catalyst components described above were dispersed at different addition ratios, and each electrode had a different catalyst layer deposited thereon. 2 The graph shows the change in overvoltage when electrolysis was performed at 1000 kJ / cm². The "○" in Figure 13 indicates the amount of Fe precipitated relative to the amount of Co precipitated, and the "□" in Figure 13 indicates the change in overvoltage. As shown in Figure 13, the electrode with a higher amount of Co-ns component precipitated also had a higher amount of Fe-hmh precipitate, and at the same time, the overvoltage decreased.

[0068] Example 1 The anode substrate used was a nickel expanded mesh (10 cm x 10 cm, LW x 3.7 SW x 0.9 ST x 0.8 T) that had been chemically etched by immersion in 17.5% by mass hydrochloric acid near its boiling point for 6 minutes. This expanded mesh was blasted (0.3 MPa) with 60-mesh alumina particles, then immersed in 20% by mass hydrochloric acid and chemically etched near its boiling point for 6 minutes. An aqueous solution containing a component that will become a precursor of lithium-containing nickel oxide was then applied to the surface of the anode substrate after the chemical etching treatment with a brush, followed by drying at 80°C for 15 minutes. This was then heat-treated at 600°C for 15 minutes in an air atmosphere. The above-mentioned process from application of the aqueous solution to heat treatment was repeated 20 times to form an intermediate layer (composition: Li 0.5 Ni 1.5 O2) was formed to give an intermediate.

[0069] Next, the same NiFeCo-hmh dispersion as described in Examination Example 1 was used, and the dispersion was adjusted so that the dispersion concentration relative to the electrolyte described in Examination Example 1 was 1 mL / L to prepare an electrolyte in which the catalyst used in this example was dispersed. Then, using this electrolyte, the same electrolysis operation as described in Examination Example 1 was performed to deposit Ni x Fe y Co zA Ni anode (oxygen generating anode) was obtained on which a catalytic layer made of -hmh was formed. A small-sized zero-gap electrolysis cell using a neutral diaphragm was fabricated using the obtained Ni anode, a diaphragm Zirfon (trade name, manufactured by AGFA), and an active cathode on which a catalytic layer made of Ru and Pr oxide was formed. The electrode area was 19 cm. 2 It was decided.

[0070] Alkaline water electrolysis was carried out using the zero-gap electrolytic cell obtained as described above. The NiFeCo-hmh dispersion used to form the catalytic layer of the Ni anode was added to a 25 mass% KOH aqueous solution at a concentration of 1 mL / L. The electrolytic solution was then supplied to the anode and cathode chambers constituting the electrolytic cell, and electrolysis was carried out at a current density of 6 kA / m. 2 Then, the anode and cathode were short-circuited (0 kA / m 2 ) and stopped for 15 hours. A shutdown test was conducted, with the above procedure from electrolysis to shutdown being one cycle. As a result, it was confirmed that the voltage was maintained stable over 20 shutdown tests.

[0071] (Comparative Example 1) The electrolytic solution supplied to each of the anode and cathode chambers constituting the zero-gap electrolytic cell prepared in Example 1 contained Ni x Fe y Co z Alkaline water electrolysis was carried out in the same manner as in Example 1, except that an electrolyte solution containing no -hmh was used. Specifically, a shutdown test similar to that carried out in Example 1 was carried out using the same electrolytic cell as used in Example 1. As a result, it was confirmed that the cell voltage gradually increased with an increase in the number of shutdowns. From this, it can be seen that the Ni x Fe y Co z The superiority of alkaline water electrolysis using an electrolyte solution with dispersed -hmh was confirmed. [Industrial Applicability]

[0072] As an example of the application of this invention, a hybrid nickel-iron-cobalt hydroxide (Ni x Fe y Co z The oxygen generating anode has a unique structure using Ni x Fe y Co z This extremely simple method of supplying an electrolyte solution containing dispersed Fe-hmh to at least the anode chamber and performing electrolysis using a conventional method allows for the deposition of a large amount of catalyst in a short period of time, thereby effectively restoring the catalytic activity of the catalyst layer. This is expected to lead to the realization of an alkaline water electrolysis method with high industrial practical value, in which electrolysis performance is less likely to deteriorate and can be maintained more stably over a longer period of time, even when using electricity with large output fluctuations, such as renewable energy, as the power source. Furthermore, an example of the use of the present invention is an oxygen generating anode in which a catalyst layer is formed using an electrolyte solution containing dispersed Fe-hmh made from a very common material, or an electrolyte solution containing dispersed Fe-hmh and Co-ns, which has been confirmed to result in a large deposition amount of Fe-hmh. [Explanation of symbols]

[0073] 2: Conductive substrate 4: Middle class 6: Catalyst layer 10: Anode for alkaline water electrolysis

Claims

1. The hybrid nickel-iron-cobalt hydroxide (Ni) is a metal hydroxide-organic complex with a complex structure in which a tripodal ligand of Tris-NH 2 is covalently fixed. ｘ Fe ｙ Co ｚ an electrolytic solution containing a dispersed catalyst comprising: a Ni / Fe / Co complex; and a cathode chamber comprising an electrolytic cell, the anode chamber and the cathode chamber being supplied with the dispersed catalyst; and the electrolyte being used in common for electrolysis in each chamber.

2. The hybrid nickel-iron-cobalt hydroxide (Ni) is a metal hydroxide-organic complex with a complex structure in which a tripodal ligand of Tris-NH 2 is covalently fixed. ｘ Fe ｙ Co ｚ an electrolytic solution containing a dispersed catalyst (Ni / Fe / Co) of 8.2 to 65.6 / 33.7 to 85 / 0.6 to 18) is supplied to at least the anode chamber constituting the electrolytic cell, and during operation, the Ni ｘ Fe ｙ Co ｚ The electrolytic deposition of Ni-hmh is carried out in the electrolytic cell, and the Ni-hmh is deposited on the surface of a conductive substrate having a catalyst layer formed on the surface thereof, which constitutes an anode for oxygen generation. ｘ Fe ｙ Co ｚ An alkaline water electrolysis method characterized by electrolytically depositing -hmh.

3. The supply of the electrolytic solution to the anode chamber is carried out when the performance of the oxygen generating anode is deteriorated due to operation, and the Ni ｘ Fe ｙ Co ｚ The alkaline water electrolysis method according to claim 2, wherein -hmh is electrolytically deposited to restore and improve electrolysis performance.

4. The Ni ｘ Fe ｙ Co ｚ The alkaline water electrolysis method according to claim 1 or 2, wherein -hmh comprises at least one of a sheet-like substance having a layered molecular structure, a needle-shaped substance having a tunnel structure, and a particulate substance having an amorphous structure.

5. The Ni ｘ Fe ｙ Co ｚ The alkaline water electrolysis method according to claim 3, wherein -hmh is electrolytically deposited on the surface of the conductive substrate under conditions that the conductive substrate is maintained at a potential range of 1.2 V to 1.8 V vs. RHE.

6. The Ni ｘ Fe ｙ Co ｚ -Hmh is dispersed in an electrolyte solution having a concentration of 5 to 100 g / L. ｘ Fe ｙ Co ｚ -hmh dispersion liquid, ｘ Fe ｙ Co ｚ The alkaline water electrolysis method according to claim 1 or 2, wherein the -hmh dispersion is added to the electrolytic solution at a concentration adjusted to be within a range of 0.1 to 8 mL / L.

7. The Ni ｘ Fe ｙ Co ｚ The alkaline water electrolysis method according to claim 1 or 2, wherein -hmh is at least any one selected from Ni 11.5 Fe 70.5 Co 18 -hmh, Ni 65.6 Fe 33.7 Co 0.6 -hmh, and Ni 8.2 Fe 85 Co 6.8 -hmh.

8. a conductive substrate having a surface made of nickel or a nickel-based alloy; The electrolytic deposit formed on the surface of the conductive substrate is a hybrid nickel-iron-cobalt hydroxide (Ni) which is a composite of a metal hydroxide and an organic substance and has a composite structure in which a tripodal ligand of Tris-NH 2 is covalently fixed. ｘ Fe ｙ Co ｚ -hmh, in which the atomic ratio x / y / z of Ni / Fe / Co is 8.2 to 65.6 / 33.7 to 85 / 0.6 to 18), and An anode for alkaline water electrolysis that generates oxygen, comprising:

9. The anode for alkaline water electrolysis which generates oxygen according to claim 8, wherein the Ni x Fe y Co z -hmh is at least one selected from Ni 11.5 Fe 70.5 Co 18 -hmh, Ni 65.6 Fe 33.7 Co 0.6 -hmh, and Ni 8.2 Fe 85 Co 6.8 -hmh.

10. a conductive substrate having a surface made of nickel or a nickel-based alloy; A conductive substrate having the formula Li ｘ Ni ２－ｘ O ２ an intermediate layer made of a lithium-containing nickel oxide represented by (0.02≦x≦0.5); The electrolytic deposit formed on the surface of the intermediate layer is a hybrid nickel-iron-cobalt hydroxide (Ni) which is a composite of a metal hydroxide and an organic substance and has a composite structure in which a tripodal ligand of Tris-NH 2 is covalently fixed. ｘ Fe ｙ Co ｚ -hmh, where the atomic ratio x / y / z of Ni / Fe / Co is 8.2 to 65.6 / 33.7 to 85 / 0.6 to 18; and An anode for alkaline water electrolysis that generates oxygen, comprising:

11. The anode for alkaline water electrolysis which generates oxygen according to claim 10, wherein the Ni x Fe y Co z -hmh is at least one selected from Ni 11.5 Fe 70.5 Co 18 -hmh, Ni 65.6 Fe 33.7 Co 0.6 -hmh, and Ni 8.2 Fe 85 Co 6.8 -hmh.

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