Anode for alkaline water electrolysis and method for manufacturing the same

Abstract

To provide an anode for alkaline water electrolysis which hardly causes deterioration in electrolysis performance and can stably maintain excellent catalytic activity for a long period of time even when a power with large output fluctuation such as renewable energy is used as a power source.SOLUTION: There is provided an anode 10 for alkaline water electrolysis which comprises a conductive substrate 2 at least a surface of which is composed of nickel or a nickel-based alloy and a catalysis 6 containing a metal composite oxide having a quadruple perovskite oxide structure arranged on the surface of the conductive substrate 2, wherein the metal composite oxide contains calcium (Ca), manganese (Mn) and nickel (Ni) and has a Ca / Mn / Ni / O atomic ratio of (1.0) / (6.6 to 7.0) / (0.1 to 0.4) / 12.0.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to an anode for alkaline water electrolysis and a method for manufacturing the same.

Background Art

[0002] Hydrogen is a secondary energy source that is suitable for storage and transportation and has a small environmental impact. Therefore, there is growing interest in hydrogen energy systems that use hydrogen as an energy carrier. Currently, hydrogen is mainly produced by steam reforming of fossil fuels. However, from the perspectives of global warming and fossil fuel depletion problems, among the basic technologies, it is important to produce hydrogen by water electrolysis using renewable energy such as solar power generation and wind power generation. Water electrolysis is suitable for large-scale production at low cost and is a promising technology for hydrogen production.

[0003] Among the members used in water electrolysis, the anode material often has an oxygen evolution overvoltage exceeding 0.3 V under actual operating conditions. This indicates that there is significant room for improvement compared to the overvoltage of hydrogen evolution and chlorine evolution, which is around 0.1 V, utilized in the current electrolysis industry. When using power with large output fluctuations such as renewable energy for power source water electrolysis, an anode that can stably maintain excellent catalytic activity over a long period is in the development stage and has not yet been put into practical use.

[0004] Current practical water electrolysis can be broadly divided into two types. One is alkaline water electrolysis, in which a high-concentration alkaline aqueous solution is used as the electrolyte. The other is solid polymer electrolyte water electrolysis, in which a solid polymer membrane (SPE) is used as the electrolyte. When performing large-scale hydrogen production by water electrolysis, alkaline water electrolysis using inexpensive materials such as iron-based metals like nickel is said to be more suitable than solid polymer electrolyte water electrolysis that uses electrodes with a large amount of expensive noble metals.

[0005] High-concentration alkaline aqueous solutions have a high conductivity as the temperature rises, but also have high corrosivity. Therefore, the upper limit of the operating temperature is suppressed to about 80-90°C. Through the development of constituent materials for electrolytic cells and various piping materials that can withstand high temperatures and high-concentration alkaline aqueous solutions, low-resistance diaphragms, and electrodes with an enlarged surface area and catalyst application, the electrolytic cell voltage at a current density of 0.6 A / cm -2 has been improved until it reaches 2 V or less.

[0006] As an anode for alkaline water electrolysis, nickel-based materials that are stable in high-concentration alkaline aqueous solutions are used. In the case of alkaline water electrolysis using a stable power source, nickel-based anodes are known to have a lifespan of several decades or more. However, when using renewable energy as a power source, severe conditions such as frequent start-stop and load fluctuations often occur, and performance degradation of nickel-based anodes has become a problem.

[0007] Both the formation reaction of nickel oxide and the reduction reaction of the formed nickel oxide proceed on the metal surface. Therefore, with these reactions, the desorption of the electrode catalyst formed on the metal surface is promoted. When the power supply for electrolysis stops, electrolysis ceases, 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 hydrogen evolution cathode (0.00 V vs. RHE) as the counter electrode. In the electrolytic cell, electromotive forces are generated by various chemical species, and the anode potential is maintained low as the battery reaction progresses, promoting the reduction reaction of nickel oxide.

[0008] The current generated by the battery reaction leaks through the pipes connecting the cells in the case of an electrolysis stack that combines a plurality of cells such as an anode chamber and a cathode chamber, for example. As a countermeasure to prevent such current leakage, there is, for example, a method of continuously flowing a minute current during stoppage. However, continuously flowing a minute current during stoppage requires special power control and also requires continuous generation of oxygen and hydrogen, resulting in excessive labor in operation management, and there are such problems. Also, in order to intentionally avoid the reverse current state, it is possible to drain the liquid immediately after stoppage to prevent the battery reaction, but in the case of operation with power having large output fluctuations such as renewable energy, it cannot be said to be an appropriate measure.

[0009] Conventionally, as the catalyst for oxygen generation at the anode (anode catalyst) used in alkaline water electrolysis, platinum group metals, platinum group metal oxides, valve metal oxides, iron group oxides, lanthanide group metal oxides, etc. have been used. Other anode catalysts include alloy systems based on nickel such as Ni-Co and Ni-Fe; nickel with an enlarged surface area; conductive oxides (ceramic materials) such as spinel-based Co3O4, NiCo2O4, perovskite-based LaCoO3, LaNiO3, etc.; noble metal oxides; oxides composed of lanthanide group metals and noble metals are also known.

[0010] In recent years, as the anode for oxygen generation (anode) used in high-concentration alkaline water electrolysis, an anode for alkaline water electrolysis (Patent Document 1) in which a lithium-containing nickel oxide catalyst layer containing lithium and nickel in a predetermined molar ratio is formed on the surface of a nickel substrate, and an anode for alkaline water electrolysis (Patent Document 2) in which a catalyst layer containing a nickel cobalt-based oxide and an iridium oxide or a ruthenium oxide is formed on the surface of a nickel substrate have been proposed. Also, a catalyst for oxygen generation of A-site ordered perovskite oxide catalyst AMn3Mn4O 12 (A = La or Ca) has been proposed (Patent Document 3). Furthermore, CaMn3O6, CaMn4O8, and CaMn7O used as oxygen reduction catalysts 12 have been proposed (Patent Documents 4 and 5).

[0011] In addition, it has been reported that LiNi having a layered rock salt structure 0.8 Al 0.2 O2 exhibits high oxygen evolution activity (Non-Patent Document 1). Al is presumed to play a role in stabilizing the structure during polarization due to its synergistic effect with Ni. The layered rock salt structure has been developed by heat treatment in oxygen gas. Ni in the LiNiO2 layer 3+ is stabilized, and Li + layer Ni 2+ mixing is suppressed, and attention is paid to Al 3+ doping. Furthermore, it has been reported that LiNi having a layered rock salt structure 0.8 Fe 0.2 O2 exhibits high oxygen evolution activity (Non-Patent Document 2).

Prior Art Documents

Patent Documents

[0012]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Patent Document 5

Non-Patent Documents

[0013]

Non-Patent Document 1

Non-Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0014] However, even for the anodes for alkaline water electrolysis proposed in Patent Documents 1 and 2, when power with large output fluctuations such as renewable energy is used as the power source, the performance is likely to deteriorate, and it has been difficult to use stably over a long period of time. In addition, Patent Document 3 does not describe any effects obtained by controlling the amount of Ni. Furthermore, Patent Documents 4 and 5 do not describe anything regarding oxygen generation. Also, LiNi reported in Non-Patent Document 1 0.8 Al 0.2 O2 and LiNi reported in Non-Patent Document 2 0.8 Fe 0.2 O2 are not necessarily highly active enough, and there is room for further improvement.

[0015] The present invention has been made in view of such problems of the prior art, and the problem to be solved is to provide an anode for alkaline water electrolysis in which the electrolysis performance is less likely to deteriorate and excellent catalytic activity is stably maintained over a long period of time even when power with large output fluctuations such as renewable energy is used as the power source. Another problem to be solved by the present invention is to provide a method for manufacturing the anode for alkaline water electrolysis.

Means for Solving the Problems

[0016] As a result of intensive research aimed at solving the above problems, the inventors discovered that reaction activation occurs by controlling the Ni content in a metal composite oxide having a quadruple perovskite oxide structure and changing the Mn(A')-Mn(B) bond distance, and thus completed the present invention. 12 It has been reported that ABO3 exhibits higher oxygen evolution catalytic activity than the simple perovskite oxide ABO3, which has the same B-site element. One of the reasons for this is that ABO3 has a new adsorption site that is favorable for the reaction because it is missing one oxygen atom in the structure. ABO3 removes electrons from the hydroxide ion adsorbed on this adsorption site to form an OO dimer as an intermediate. It is presumed that the reduction in bond length caused by partial replacement of Mn(B) with Ni changes the stability of the OO bond at the A'-B site, making it easier for oxygen to be released.

[0017] That is, according to the present invention, there is provided an anode for alkaline water electrolysis as described below. [1] An anode for alkaline water electrolysis comprising: a conductive substrate, at least a surface of which is made of nickel or a nickel-based alloy; and a catalytic layer disposed on the surface of the conductive substrate, the catalytic layer containing a metal composite oxide having a quadruple perovskite oxide structure, the metal composite oxide containing calcium (Ca), manganese (Mn), and nickel (Ni), and the atomic ratio of Ca / Mn / Ni / O is (1.0) / (6.6-7.0) / (0.1-0.4) / 12.0. [2] The anode for alkaline water electrolysis according to [1], wherein the Mn(A')-Mn(B) bond distance is 3.18 to 3.19 Å. [3] A compound having the formula Li disposed between the conductive substrate and the catalyst layer. x Ni 2-x The anode for alkaline water electrolysis according to [1] or [2], further comprising an intermediate layer made of a lithium-containing nickel oxide represented by O2 (0.02≦x≦0.5).

[0018] Furthermore, according to the present invention, there is provided the following method for producing an anode for alkaline water electrolysis. [4] A step of heat-treating a precursor containing a calcium component, a manganese component, and a nickel component at 400 to 900 °C in an oxygen-containing atmosphere to obtain a metal composite oxide having a quadruple perovskite oxide structure; and a step of forming a catalyst layer containing the metal composite oxide on the surface of a conductive substrate at least the surface of which is made of nickel or a nickel-based alloy. The metal composite oxide contains calcium (Ca), manganese (Mn), and nickel (Ni), and the atomic ratio of Ca / Mn / Ni / O is (1.0) / (6.6 - 7.0) / (0.1 - 0.4) / 12.0. A method for manufacturing an anode for alkaline water electrolysis. [5] The method for manufacturing an anode for alkaline water electrolysis according to [4], wherein the precursor is heat-treated in an oxygen-containing atmosphere having an oxygen partial pressure of 0.2 atm or more.

Advantages of the Invention

[0019] According to the present invention, even when power with large output fluctuations such as renewable energy is used as a power source, it is possible to provide an anode for alkaline water electrolysis in which the electrolysis performance is less likely to deteriorate and excellent catalytic activity is stably maintained over a long period. Further, according to the present invention, it is possible to provide a method for manufacturing the anode for alkaline water electrolysis.

Brief Description of the Drawings

[0020]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Mode for Carrying Out the Invention

[0021] <Anode for Alkaline Water Electrolysis> FIG. 1 is a cross-sectional view schematically showing an embodiment of the anode for alkaline water electrolysis of the present invention. As shown in FIG. 1, the anode 10 for alkaline water electrolysis of the present embodiment includes a conductive substrate 2, an intermediate layer 4 formed on the surface of the conductive substrate 2, and a catalyst layer 6 formed on the surface of the intermediate layer 4. Hereinafter, details of the anode for alkaline water electrolysis of the present invention (hereinafter, also simply referred to as "anode") will be described.

[0022] (Conductive Substrate) The conductive substrate 2 is a conductor for passing electricity for electrolysis and is a member having a function as a carrier for supporting the intermediate layer 4 and the catalyst layer 6. At least the surface of the conductive substrate 2 (the surface on which the intermediate layer 4 and the catalyst layer 6 are formed) is formed of nickel or a nickel-based alloy. That is, the entire conductive substrate 2 may be formed of nickel or a nickel-based alloy, or only the surface may be formed of nickel or a nickel-based alloy. Specifically, the conductive substrate 2 may be one in which a coating of nickel or a nickel-based alloy is formed on the surface of a metal material such as iron, stainless steel, aluminum, or titanium by plating or the like.

[0023] The thickness of the conductive substrate is preferably 0.05 to 5 mm. The shape of the conductive substrate is preferably a shape having an opening for removing bubbles such as generated oxygen and hydrogen. For example, expanded mesh or porous expanded mesh can be used as the conductive substrate. When the conductive substrate has a shape with an opening, the opening ratio of the conductive substrate is preferably 10 to 95%.

[0024] (Intermediate Layer) The anode of the present invention preferably includes an intermediate layer disposed between the conductive substrate and the catalyst layer. As shown in FIG. 1, the intermediate layer 4 is a layer formed on the surface of the conductive substrate 2. The intermediate layer 4 suppresses corrosion of the conductive substrate 2 and stably adheres the catalyst layer 6 to the conductive substrate 2. Further, the intermediate layer 4 also serves to promptly supply current to the catalyst layer 6. The intermediate layer 4 is composed of a lithium-containing nickel oxide represented by the composition formula Li x Ni 2-x O2 (0.02 ≤ x ≤ 0.5). When x in the above composition formula is less than 0.02, the conductivity may be slightly insufficient. On the other hand, when x exceeds 0.5, the physical strength and chemical stability may be slightly reduced. The intermediate layer 4 formed of the lithium-containing nickel oxide represented by the above composition formula has sufficient conductivity for electrolysis and exhibits excellent physical strength and chemical stability even when used for a long period of time.

[0025] 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. When the thickness of the intermediate layer is less than 0.01 μm, the above-described functions are not exhibited. On the other hand, even if the thickness of the intermediate layer exceeds 100 μm, the voltage loss due to the resistance in the intermediate layer increases, making it difficult to exhibit the above-described functions, and it may be somewhat disadvantageous in terms of manufacturing cost and the like.

[0026] (Catalyst layer) The catalyst layer 6 is a layer having catalytic ability formed on the surface of the intermediate layer 4. By interposing the intermediate layer 4, the catalyst layer 6 is more firmly fixed on the conductive substrate 2.

[0027] The catalyst layer is a layer containing a metal composite oxide having a quadruple perovskite oxide structure, preferably a layer substantially formed of a metal composite oxide having a quadruple perovskite oxide structure. And this metal composite oxide contains calcium (Ca), manganese (Mn), and nickel (Ni), and the atomic ratio of Ca / Mn / Ni / O is (1.0) / (6.6 - 7.0) / (0.1 - 0.4) / 12.0. By providing a catalyst layer containing a metal composite oxide with the composition represented by the above ratio of Ca, Mn, Ni, and O, even when using power with large output fluctuations such as renewable energy as a power source, the electrolysis performance is less likely to deteriorate, and excellent catalytic activity can be stably maintained over a long period of time.

[0028] The thickness of the catalyst 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 catalyst layer is less than 0.01 μm, the above-described functions will not be exhibited. On the other hand, even if the thickness of the catalyst layer exceeds 100 μm, the voltage loss due to the resistance in the catalyst layer increases, making it difficult to exhibit the above-described functions, and it may be somewhat disadvantageous in terms of manufacturing cost and the like.

[0029] <Method for manufacturing an anode for alkaline water electrolysis> Next, the method for manufacturing the anode for alkaline water electrolysis of the present invention will be described. The method for manufacturing the anode described below is a method for suitably manufacturing the above-described anode for alkaline water electrolysis. The method for manufacturing the anode of the present invention has a step of preparing a metal composite oxide and a step of forming a catalyst layer. The step of preparing a metal composite oxide is a step of heat-treating a precursor containing a calcium component, a manganese component, and a nickel component at 400 to 900°C in an oxygen-containing atmosphere to obtain a metal composite oxide having a quadruple perovskite oxide structure. The step of forming a catalyst layer is a step of forming a catalyst layer containing a metal composite oxide on the surface of a conductive substrate.

[0030] As described above, an intermediate layer can be disposed between the conductive substrate and the catalyst layer as needed. A method for manufacturing an anode provided with an intermediate layer includes, before the first coating step described above, a step of applying an aqueous solution containing lithium ions and nickel ions to the surface of the conductive substrate (coating step), and heat-treating the conductive substrate to which the aqueous solution has been applied to form an intermediate layer composed of lithium-containing nickel oxide represented by the composition formula Li x Ni 2-x O2 (0.02 ≤ x ≤ 0.5) on the surface of the conductive substrate (intermediate layer forming step).

[0031] (Pretreatment step) Before forming the intermediate layer or the catalyst layer, it is preferable to subject the conductive substrate to chemical etching treatment in advance to remove contaminant particles such as metals and organic substances on the surface. The consumption amount of the conductive substrate by the chemical etching treatment is preferably about 30 g / m 2 or more and 400 g / m 2 or less. Further, in order to enhance the adhesion to the intermediate layer and the catalyst layer, it is preferable to roughen the surface of the conductive substrate in advance. Examples of the means for roughening treatment include blasting treatment for spraying powder, etching treatment using an acid soluble in the substrate, and plasma spraying.

[0032] (Coating step) In the coating process, an aqueous solution containing lithium ions and nickel ions is coated on the surface of a conductive substrate. The intermediate layer is formed by a so-called thermal decomposition method. When forming the intermediate layer by the thermal decomposition method, first, an aqueous precursor solution of the intermediate layer is prepared. As the precursor containing a lithium component, known precursors such as lithium nitrate, lithium carbonate, lithium chloride, lithium hydroxide, and lithium carboxylate can be used. Examples of lithium carboxylate include lithium formate and lithium acetate. As the precursor containing a nickel component, known precursors such as nickel nitrate, nickel carbonate, nickel chloride, and nickel carboxylate can be used. Examples of nickel carboxylate include nickel formate and nickel acetate. In particular, it is particularly preferable to use at least one of lithium carboxylate and nickel carboxylate as the precursor because a dense intermediate layer can be formed even when fired at a low temperature as described later.

[0033] (Intermediate layer formation process) In the intermediate layer formation process, the conductive substrate coated with the aqueous solution is heat-treated. Thereby, an intermediate layer made of a lithium-containing nickel oxide represented by the composition formula Li x Ni 2-x O2 (0.02 ≦ x ≦ 0.5) can be formed on the surface of the conductive substrate. The heat treatment temperature when forming the intermediate layer by the thermal decomposition method can be set as appropriate. Considering the decomposition temperature of the precursor and the production cost, the heat treatment temperature is preferably 450 to 600 °C, and more preferably 450 to 550 °C. For example, the decomposition temperature of lithium nitrate is about 430 °C, and the decomposition temperature of nickel acetate is about 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 tends to proceed, the electrode resistance increases, and an increase in voltage loss may occur. The heat treatment time may be set as appropriate considering the reaction rate, productivity, oxidation resistance of the intermediate layer surface, etc.

[0034] By appropriately setting the number of times of applying the aqueous solution in the above-described coating step, the thickness of the formed intermediate layer can be controlled. Note that the application and drying of the aqueous solution may be repeated for each layer, and after forming the uppermost layer, the whole may be heat-treated. Also, the application and heat treatment (pretreatment) of the aqueous solution may be repeated for each layer, and after forming the uppermost layer, the whole may be heat-treated. The temperature of the pretreatment and the temperature of the overall heat treatment may be the same or different. Also, it is preferable that the time of the pretreatment is shorter than the time of the overall heat treatment.

[0035] (Preparation step of metal composite oxide) In the preparation step of the metal composite oxide, a precursor containing a calcium component, a manganese component, and a nickel component is heat-treated at 400 to 900 °C in an oxygen-containing atmosphere to prepare a metal composite oxide. As the calcium component, known compounds such as calcium nitrate, calcium carbonate, calcium chloride, calcium hydroxide, and calcium carboxylate can be used. Examples of the calcium carboxylate include calcium formate and calcium acetate. As the nickel component, known compounds such as nickel nitrate, nickel carbonate, nickel chloride, and nickel carboxylate can be used. Examples of the nickel carboxylate include nickel formate and nickel acetate. In particular, it is preferable to use at least one of lithium carboxylate and nickel carboxylate because a denser catalyst layer can be formed. As the manganese component, known compounds such as manganese nitrate, manganese carbonate, manganese chloride, and manganese carboxylate can be used. Examples of the manganese carboxylate include manganese formate and manganese acetate.

[0036] The target substance, metal composite oxide (CaMn 7-x Ni x O 12) can be prepared by the citrate complexation method. For example, after dissolving a predetermined amount of calcium component, manganese component, and nickel component in nitric acid, a large excess of citric acid and a stoichiometric amount of 1,2-ethanediol are added with stirring. By heating the obtained solution to around 300 °C and holding it for a certain period of time, a precursor dry powder can be obtained. By heat-treating the obtained precursor (dry powder) in an oxygen-containing atmosphere at 400 - 900 °C, preferably 700 - 900 °C for 2 - 50 hours, a metal composite oxide (hereinafter also referred to as "CMO"), which is the target substance, can be obtained.

[0037] When heat-treating the precursor, the oxygen partial pressure in the oxygen-containing atmosphere is preferably 0.2 atm or more, and more preferably 0.5 atm or more. Also, the gas flow rate of the gas containing the supplied oxygen is preferably controlled to 5 mL / min or less as oxygen, and more preferably 2.5 mL / min or less. If the gas flow rate is too high (too fast), the formation of the oxide may be excessively promoted, so the composition of the CMO may easily deviate from the target composition. Whether the obtained metal composite oxide (CMO) has a quadruple perovskite oxide structure can be confirmed by XRD crystal structure analysis.

[0038] (Catalyst layer formation step) In the catalyst layer formation step, a catalyst layer containing a metal composite oxide (CMO) as a catalyst is formed on the surface of the conductive substrate. Thereby, the target anode for alkaline water electrolysis can be obtained. To form a catalyst layer on the surface of the conductive substrate, a conventionally known method can be appropriately adopted and is not particularly limited. For example, a catalyst (CMO) is added to a solvent containing a specific resin (Nafion (registered trademark), etc.) to prepare a catalyst ink. Then, the prepared catalyst ink is applied to the surface of the conductive substrate or the surface of an intermediate layer formed on the conductive substrate, and dried by heating etc. as necessary, whereby a catalyst layer can be formed on the surface of the conductive substrate.

[0039] <Use of the anode for alkaline water electrolysis> The anode for alkaline water electrolysis of the present invention can be used as an anode for oxygen generation when electrolyzing alkaline water. That is, by using the anode of the present invention, an electrolytic cell such as an alkaline water electrolysis cell can be constructed. The type and configuration of the cathode (cathode) and diaphragm used together with the above anode are not particularly limited, and cathodes and diaphragms used in conventional alkaline water electrolysis can be used.

[0040] (Cathode) As the cathode, it is preferable to select and use a substrate made of a material resistant to 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. Examples of the shape of the cathode substrate include a plate shape, expanded mesh, and porous expanded mesh.

[0041] Examples of the cathode material include porous nickel with a large surface area and Ni-Mo-based materials. In addition, there are 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 Ti2Ni. As the catalyst, those having properties such as low hydrogen overvoltage, high short-circuit stability, and high poisoning resistance are preferable. Other catalysts preferably include metals such as platinum, palladium, ruthenium, and iridium, and oxides thereof.

[0042] (Diaphragm) As the diaphragm for electrolysis, asbestos, non-woven fabric, ion exchange membrane, polymer porous membrane, composite membrane of inorganic substance and organic polymer, etc. can be used. Specifically, an ion-permeable diaphragm in which an organic fiber cloth is incorporated in a mixture of a hydrophilic inorganic material such as calcium phosphate compound and calcium fluoride, and an organic binding material such as polysulfone, polypropylene, and polyvinylidene fluoride can be used. Further, an ion-permeable diaphragm in which an extended organic fiber cloth is incorporated in a film-forming mixture of a granular inorganic hydrophilic substance such as an oxide and hydroxide of antimony or zirconium, and an organic binder such as fluorocarbon polymer, polysulfone, polypropylene, polyvinyl chloride, and polyvinyl butyral can be used.

[0043] If an alkaline water electrolysis cell having the anode of the present invention as a component is used, a high-concentration alkaline aqueous solution can be electrolyzed. As the alkaline aqueous solution used as the electrolyte, an aqueous solution of an alkali metal hydroxide such as potassium hydroxide (KOH) and sodium hydroxide (NaOH) is preferable. The concentration of the alkaline aqueous solution is preferably 1.5 mass% or more and 40 mass% or less. Further, the concentration of the alkaline aqueous solution being 15 mass% or more and 40 mass% or less is preferable because the electric conductivity is large and the power consumption can be suppressed. Furthermore, considering cost, corrosiveness, viscosity, operability, etc., the concentration of the alkaline aqueous solution is preferably 20 mass% or more and 30 mass% or less.

Examples

[0044] Hereinafter, the present invention will be specifically described based on examples, but the present invention is not limited to these examples. In addition, "parts" and "%" in the examples and comparative examples are based on mass unless otherwise specified.

[0045] <Production of Catalyst for Alkaline Water Electrolysis> (Production Example 1) The stoichiometric amounts of CaCO3, Mn(NO3)2·6H2O, and Ni(NO3)2·6H2O were dissolved in nitric acid. While stirring, 5-fold molar excess of citric acid and the stoichiometric amount of 1,2-ethanediol were added, and then heated to 300 °C to obtain a powdery precursor. The obtained precursor was calcined using a heating furnace at 400 °C for 1 hour and at 675 °C for 12 hours in air. Then, it was calcined at 900 °C for 12 hours in air to obtain a powdery target substance (CMO). A solution obtained by dissolving a part of the obtained standard substance in an acid was used as a sample, and its composition was analyzed by inductively coupled plasma (ICP) optical emission spectrometry. As the inductively coupled plasma optical emission analyzer, the product name "ICPS-8100CL" (manufactured by Shimadzu Corporation) was used. As a result, it was confirmed that the chemical composition of the obtained target substance (CMO) was represented by "CaMn 7-x Ni x O 12 " (five types with x = 0.0, 0.1, 0.2, 0.3, and 0.4).

[0046] Figure 2 is a diagram schematically showing the crystal structure (tetragonal perovskite oxide structure) of the metal composite oxide (catalyst). As shown in Figure 2, when Mn(B) at the Mn(A’)-Mn(B) bond distance in the tetragonal perovskite oxide structure is partially replaced with Ni, it can be seen that Ni is incorporated into the B site of the host matrix without any change in the states of Mn and O. 12 When Mn(B) at the Mn(A’)-Mn(B) bond distance in the tetragonal perovskite oxide structure is partially replaced with Ni, it can be seen that Ni is incorporated into the B site of the host matrix without any change in the states of Mn and O.

[0047] Figure 3 is a diagram showing the synchrotron radiation X-ray diffraction pattern of the metal composite oxide (catalyst). As shown in Figure 3, it can be seen that Ni doping clearly causes a phase transition in the crystal structure. The disappearance of some diffraction peaks of Ni-doped CMO suggests that a change in the crystal structure occurred at x = 0.2. According to the Rietveld refinement analysis, at x = 0.0, a distorted perovskite structure with trigonal symmetry, R3 - space group is shown, and for x ≥ 0.2, a cubic symmetry, Im3 - space group is shown. In the case of x = 0.1, R3 - and Im3 -Both phases were observed. Since impurities were present, samples were not prepared for x ≥ 0.5.

[0048] Figure 4 is a diagram showing the XANES spectra of the K-edge of Mn ((a)) and the K-edge of Ni ((b)) of the metal composite oxide (catalyst). As shown in Figure 4, regardless of the Ni doping level, the state of Mn was constant. And the absorption edge position was higher than that of NiO, and it was inferred that the valence electron state of Ni was "+3" in all samples. Note that the O K-edge spectrum did not change. For this reason, it is considered that neither the state of Mn nor the O 2p band center, which are factors related to oxygen generation ability, has changed.

[0049] 10 mg of each catalyst, 2 mg of acetylene black (manufactured by Denka), 40 μL of 5% Nafion (registered trademark) solution, and 20 μL of 0.1 mol / L KOH aqueous solution were mixed to obtain a suspension. 1.94 mL of tetrahydrofuran was added to the obtained suspension and sonicated for 30 minutes to obtain a catalyst ink, which is a uniform suspension. 10 μL of the catalyst ink was dropped onto a polished glassy carbon (GC) rotating disk electrode (RDE, manufactured by Hokuto Denko, diameter 5 mm, 0.196 cm 2 ) and then vacuum dried at room temperature for 12 hours to obtain a working electrode. Then, an electrolysis operation was carried out using a three-electrode cell with the following configuration connected to a potentiostat-galvanostat (trade name "MPG-205-NUC", manufactured by Bio-Logic). Note that linear sweep voltammetry (LSV) was carried out as a pretreatment, and the current was measured at a potential of 1.2 to 1.8 V and a sweep rate of 5 mV / s while rotating the electrode at 1,600 rpm. Also, all electrochemical experiments were carried out in a nitrogen atmosphere, and iR correction (R ~ 12 Ω) was performed on all the measured data. The measurement results of linear sweep voltammetry (LSV curve) ((a)), Tafel plot ((b)), and a graph showing the correlation between the Mn(A')-Mn(B) bond distance and the current density ((c)) are shown in Figure 5. [Three-electrode cell]: · Working electrode: Catalyst-coated GC · Reference electrode: Reversible hydrogen electrode (RHE) ·Counter electrode: Pt wire ·Electrolyte: 0.1 mol / L KOH aqueous solution

[0050] As shown in Fig. 5(a), there is a correlation between the catalytic activity and the Ni doping amount, and it can be seen that the best activity is shown at x = 0.4. Note that the decreasing trend of the OER activity corresponds to the decrease of x. Also, as shown in Fig. 5(b), the Tafel slope (gradient) is approximately 94 mV dec -1 in all cases regardless of x(Ni). It is suggested that the catalytic activity of the Ni-doped CMO is due to the increase in the reaction rate of the rate-determining step rather than the change in the reaction path. As shown in Fig. 5(c), the catalytic activity of oxygen generation was clearly correlated with the Mn(A’)-Mn(B) bond distance.

[0051] <Manufacture of Anode> (Example 1) As the anode substrate, an expanded mesh made of nickel (10 cm × 10 cm, LW × 3.7 SW × 0.9 ST × 0.8 T) that was chemically etched by immersion in 17.5% hydrochloric acid heated to near the boiling point for 6 minutes was prepared. This expanded mesh was blast-treated (0.3 MPa) with 60-mesh alumina particles, and then immersed in 20% hydrochloric acid heated to near the boiling point and immersed for 6 minutes for chemical etching treatment. After the surface of the anode substrate after the chemical etching treatment was coated with an aqueous solution containing a component that becomes a precursor of lithium-containing nickel oxide with a brush, it was dried at 80 °C for 15 minutes. Next, it was heat-treated at 600 °C for 15 minutes in an oxygen atmosphere. The treatment from the application of the aqueous solution to the heat treatment was repeated 20 times to obtain an intermediate in which an intermediate layer (composition: Li 0.5 Ni 1.5 O2) was formed.

[0052] Next, using the catalyst ink of the metal composite oxide (catalyst) (x = 0.4) obtained in Production Example 1, in the same manner as in Production Example 1 described above, a catalyst layer (composition: CaMn 6.6 Ni 0.4 O 12 ) was formed on the surface of the intermediate layer to obtain an anode.

[0053] The obtained anode, a diaphragm (trade name: "Zirfon", manufactured by AGFA), and an active cathode formed with a catalyst layer composed of Ru and Pr oxides were used to fabricate a small zero-gap type electrolytic cell using a neutral diaphragm. The electrode area was 19 cm 2 2. The electrolytic solution (25% aqueous KOH solution) was supplied to the anode chamber and the cathode chamber constituting the electrolytic cell, and electrolysis was carried out at a current density of 6 kA / m 2 2 for 6 hours each. The overvoltage at this time was 250 mV. Next, the anode and the cathode were set in a short-circuited state (0 kA / m 2 ) and stopped for 15 hours. A shutdown test was conducted with one cycle being the operation from electrolysis to stop. As a result, it was confirmed that the voltage was stably maintained in 16 shutdown tests.

Industrial Applicability

[0054] The anode for alkaline water electrolysis of the present invention is suitable as an anode for alkaline water electrolysis constituting an electrolysis facility, etc., which uses power with large output fluctuations such as renewable energy as a power source.

Explanation of Signs

[0055] 2: Conductive substrate 4: Intermediate layer 6: Catalyst layer 10: Anode for alkaline water electrolysis

Claims

1. A conductive substrate at least the surface of which is made of nickel or a nickel-based alloy, and a catalyst layer including a metal composite oxide having a quadruple perovskite oxide structure disposed on the surface of the conductive substrate, wherein the metal composite oxide contains calcium (Ca), manganese (Mn), and nickel (Ni), and the atomic ratio of Ca / Mn / Ni / O is (1.0) / (6.6 - 7.0) / (0.1 - 0.4) / 12.0, an anode for alkaline water electrolysis.

2. The anode for alkaline water electrolysis according to claim 1, wherein the quadruple perovskite oxide structure is represented as AA’3B4O12, and when Mn at the A’ site is represented as Mn(A’) and Mn at the B site is represented as Mn(B), respectively, the Mn(A’) - Mn(B) bond distance is 3.18 to 3.19 Å.

3. An intermediate layer made of a lithium-containing nickel oxide represented by the composition formula Li ｘ Ni ２－ｘ O ２ (0.02 ≦ x ≦ 0.5), further provided between the conductive substrate and the catalyst layer, the anode for alkaline water electrolysis according to claim 1 or 2.

4. A step of heat-treating a precursor containing a calcium component, a manganese component, and a nickel component at 400 to 900 °C in an oxygen-containing atmosphere to obtain a metal composite oxide having a quadruple perovskite oxide structure, and a step of forming a catalyst layer containing the metal composite oxide on the surface of a conductive substrate at least the surface of which is made of nickel or a nickel-based alloy, and having a method for manufacturing an anode for alkaline water electrolysis, wherein the metal composite oxide contains calcium (Ca), manganese (Mn), and nickel (Ni), and the atomic ratio of Ca / Mn / Ni / O is (1.0) / (6.6 - 7.0) / (0.1 - 0.4) / 12.

0.

5. The method for manufacturing an anode for alkaline water electrolysis according to claim 4, wherein the precursor is heat-treated in an oxygen-containing atmosphere having an oxygen partial pressure of 0.2 atm or more.

Images