Oxygen-evolving anode and method for producing same

Abstract

Provided is an oxygen-evolving anode comprising a catalyst layer which, without using a precious metal, has low oxygen evolution overvoltage and is mechanically stable. An oxygen-evolving anode (10) comprises: a conductive base material (2) of which at least the surface is composed of nickel or a nickel-based alloy; and a catalyst layer (4) which is disposed on the surface of the base material (2) and has a porous structure formed using a nickel-iron alloy. In the nickel-iron alloy, the percentage of nickel is 35-95 mass%, the percentage of iron is 5-65 mass%, and the sum of the percentages of nickel and iron is 100 mass%.

Description

Anode for oxygen generation and method for manufacturing the same

[0001] The present invention relates to an anode for oxygen generation and a method for producing the same.

[0002] Hydrogen is a secondary energy source that is suitable for storage and transportation and has a low environmental impact, so 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 perspective of global warming and the depletion of fossil fuels, it is important to produce hydrogen through water electrolysis using renewable energy sources such as solar and wind power, among other fundamental technologies. Water electrolysis technology is a promising technology for hydrogen production because it is low-cost and suitable for large-scale production.

[0003] Among the components used in water electrolysis, the anode often exhibits an oxygen generation overvoltage exceeding 0.3V under actual operating conditions. This is significantly higher than the approximately 0.1V overvoltages used for hydrogen and chlorine generation in current electrolysis industries, indicating considerable room for improvement.

[0004] For alkaline water electrolysis, electrodes made of nickel alloys or the like that are stable in high-concentration alkaline aqueous solutions are used as anodes, or electrodes in which a conductive substrate is used and a catalyst layer or the like is provided on the surface of the substrate are used. Furthermore, in order to reduce the oxygen generation overpotential in alkaline water electrolysis applications, various electrodes with a catalyst layer or the like on the surface of the substrate have been proposed. For example, an electrode useful as an anode for alkaline water electrolysis has been proposed in which a porous catalyst layer containing nickel oxide is provided on the surface of a metal substrate (Patent Documents 1 and 2). In addition, regarding an anode for alkaline water electrolysis equipped with a Raney nickel catalyst obtained by dissolving and removing only aluminum from a Raney alloy composed of nickel and aluminum, a manufacturing method has been proposed in which nickel and aluminum powder is thermal sprayed onto the substrate of the anode (Patent Document 3). Also, since iron is more abundant than nickel and is generally cheaper, electrodes using nickel and iron as conductive substrates or catalyst layers are known (Patent Document 4).

[0005] Japanese Patent Publication No. 2023-543550, Japanese Patent Publication No. 2024-516075, International Publication No. 2023 / 111223, Japanese Patent Publication No. 2020-41185

[0006] However, even with the electrodes proposed in Patent Documents 1 to 3, the oxygen generation overpotential when used as an anode for alkaline water electrolysis was not necessarily sufficiently low, indicating room for improvement. Furthermore, there is a need for inexpensive catalyst metals that are more abundant than nickel.

[0007] Furthermore, it has been pointed out that when the electrode described in Patent Document 4 is used as an anode for alkaline water electrolysis, excessive iron dissolves due to the alkaline aqueous solution.

[0008] This invention has been made in view of the problems of the prior art, and its objective is to provide an oxygen-generating anode that does not use precious metals, has a low oxygen-generation overpotential, and has a mechanically stable catalyst layer. Another objective of this invention is to provide a method for manufacturing such an oxygen-generating anode.

[0009] In other words, the present invention provides the following oxygen-generating anode: [1] An oxygen-generating anode comprising a conductive substrate whose surface is at least made of nickel or a nickel-based alloy, and a catalyst layer having a porous structure formed of a nickel-iron alloy disposed on the surface of the substrate, wherein the nickel-iron alloy has a nickel ratio of 35 to 95% by mass, an iron ratio of 5 to 65% by mass, and the sum of the nickel ratio and the iron ratio is 100% by mass. [2] A capacitance per unit area of ​​20 to 1,100 mF / cm². ２ The oxygen-generating anode described in [1] above.

[0010] Furthermore, the present invention provides the following methods for manufacturing an oxygen-generating anode: [3] A method for manufacturing an oxygen-generating anode comprising the steps of: spraying a metal component containing a nickel-iron alloy and aluminum onto the surface of a conductive substrate whose surface is at least made of nickel or a nickel-based alloy to form a sprayed coating on the surface of the substrate; and contacting the sprayed coating with an alkaline component to dissolve and remove at least some of the aluminum from the sprayed coating to form a catalyst layer having a porous structure made of a nickel-iron alloy, wherein the nickel-iron alloy has a nickel ratio of 35 to 95% by mass, an iron ratio of 5 to 65% by mass, the sum of the nickel ratio and the iron ratio is 100% by mass, the aluminum ratio in the metal component is 1 to 30% by mass, and the sum of the nickel-iron alloy ratio and the aluminum ratio is 100% by mass. [4] The method for manufacturing an oxygen-generating anode according to [3], wherein the aluminum ratio in the metal component is 5 to 25% by mass.

[0011] According to the present invention, it is possible to provide an oxygen-generating anode having a catalyst layer that is mechanically stable and has a low oxygen-generation overpotential, without using precious metals. Furthermore, according to the present invention, it is possible to provide a method for manufacturing an oxygen-generating anode having a catalyst layer that is mechanically stable and has a low oxygen-generation overpotential, without using precious metals.

[0012] This is a schematic cross-sectional view showing one embodiment of the oxygen-generating anode of the present invention. This is an electron microscope image of a cross-section of the oxygen-generating anode manufactured in Example 1. This is an electron microscope image of a cross-section of the oxygen-generating anode manufactured in Example 3. This is a scatter plot of oxygen generation overpotential against Al ratio. This is a scatter plot of oxygen generation overpotential against Fe ratio. This is a graph plotting Fe retention rate (%) against test time (h).

[0013] <Oxygen-Generating Anode> The embodiments of the present invention will be described below, but the present invention is not limited to the embodiments described below. When numerical ranges are given, the values ​​at both ends are included unless otherwise specified. Figure 1 is a schematic cross-sectional view showing one embodiment of the oxygen-generating anode of the present invention. As shown in Figure 1, the oxygen-generating anode 10 of this embodiment is an electrode suitable as an oxygen-generating anode, comprising a conductive substrate 2 and a catalyst layer 4 disposed on the surface of the substrate 2. The details of the oxygen-generating anode of the present invention will be described below.

[0014] (Base Material) The base material 2 is a conductor that conducts electricity for electrolysis and functions as a carrier for supporting the catalyst layer 4. At least the surface of the base material 2 (the surface on which the catalyst layer 4 is formed) is made of nickel or a nickel-based alloy. That is, the entire base material 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 base material 2 may be a metal material such as iron, stainless steel, aluminum, or titanium, on which a coating of nickel or a nickel-based alloy is formed by plating or the like.

[0015] The thickness of the substrate is preferably 0.05 to 5 mm. The shape of the substrate is preferably such that it has openings for removing bubbles such as oxygen and hydrogen that are generated. For example, expanded mesh or porous expanded mesh can be used as the conductive substrate. If the substrate has an opening, the opening ratio of the substrate is preferably 10 to 95%.

[0016] (Catalyst Layer) The catalyst layer 4 is a catalytic layer placed on the surface of the substrate 2 and has a porous structure containing numerous voids. This porous structure increases the actual surface area, resulting in a lower oxygen evolution overvoltage (O.O.V.) compared to a catalyst layer without a porous structure.

[0017] The catalyst layer 4 is formed of a nickel-iron alloy (Ni-Fe alloy). That is, the catalyst layer 4 contains iron along with nickel. By forming the catalyst layer with a Ni-Fe alloy that contains iron in addition to nickel, the mechanical stability of the porous structure can be improved, and the peeling of the catalyst layer from the substrate can be suppressed. Furthermore, by including iron in the catalyst layer, the oxygen evolution overpotential can be reduced compared to a catalyst layer that does not contain iron. Note that at least a portion of the nickel and iron in the catalyst layer may be oxidized. That is, nickel and iron may exist in the catalyst layer in the form of nickel oxide and iron oxide. In addition, when an oxygen-evolving anode is manufactured by the method described later, trace amounts of aluminum (Al) may be present in the formed catalyst layer.

[0018] In the Ni-Fe alloy forming the catalyst layer, the proportion of nickel (Ni) is 35 to 95 mass%, and the proportion of iron (Fe) is 5 to 65 mass%, with the sum of the nickel and iron proportions being 100 mass%. By setting the proportions of nickel and iron in the Ni-Fe alloy within the above ranges, the oxygen evolution overpotential can be reduced while increasing the mechanical stability of the porous structure. From the viewpoint of further reducing the oxygen evolution overpotential, the proportion of nickel in the Ni-Fe alloy is preferably 58 to 85 mass%. Furthermore, the proportion of iron in the Ni-Fe alloy is preferably 15 to 42 mass%.

[0019] Because the catalyst layer has a porous structure, its actual surface area is increased compared to a catalyst layer without a porous structure. The actual surface area of ​​the catalyst layer can be defined, for example, by the capacitance per unit area of ​​the catalyst layer. Specifically, the oxygen-generating anode of this embodiment preferably has a capacitance per unit area of ​​20 to 1,100 mF / cm². ２ And more preferably 100 to 700 mF / cm ２ That is the case.

[0020] The thickness of the catalyst layer is preferably 30 to 400 μm, and more preferably 50 to 200 μm. If the thickness of the catalyst layer is less than 30 μm, the effect of reducing the oxygen evolution overpotential may be somewhat insufficient. On the other hand, if the thickness of the catalyst layer exceeds 400 μm, the voltage loss due to resistance becomes large, and it may be somewhat disadvantageous in terms of manufacturing costs, etc.

[0021] (Use of Oxygen-Generating Anode) The oxygen-generating anode of this embodiment is useful as an electrode when electrolyzing alkaline water because it has a low oxygen-generating overpotential. In other words, by using the oxygen-generating anode of this embodiment, an electrolytic cell such as an alkaline water electrolysis cell can be constructed. The type and configuration of the cathode and diaphragm used with the above-mentioned oxygen-generating anode are not particularly limited, and cathodes and diaphragms used in conventional alkaline water electrolysis can be used.

[0022] <Method for Manufacturing an Oxygen-Generating Anode> Next, the method for manufacturing an oxygen-generating anode of the present invention will be described. The method for manufacturing an oxygen-generating anode described below is a suitable method for manufacturing the oxygen-generating anode described above. One embodiment of the method for manufacturing an oxygen-generating anode of the present invention comprises a thermal spray coating formation step and a catalyst layer formation step. In the thermal spray coating formation step, a metal component including nickel-iron alloy and aluminum is thermal sprayed onto the surface of a conductive substrate whose surface is at least made of nickel or a nickel-based alloy to form a thermal spray coating on the surface of the substrate. In the catalyst layer formation step, an alkaline component is brought into contact with the thermal spray coating to dissolve and remove at least some of the aluminum from the thermal spray coating, forming a catalyst layer having a porous structure.

[0023] (Thermal spray coating formation process) In the thermal spray coating formation process, a thermal spray coating made of metal components is formed on the surface of the substrate by thermal spraying metal components onto the substrate surface. The metal components used for thermal spraying include Ni-Fe alloy and aluminum (Al). In the Ni-Fe alloy, the ratio of nickel (Ni) is 35 to 95 mass%, the ratio of iron (Fe) is 5 to 65 mass%, and the sum of the two ratios is 100 mass%. By using a Ni-Fe alloy in which the ratios of nickel and iron are within the above ranges, it is possible to form a catalyst layer with low oxygen generation overpotential, which is less likely to peel off from the substrate and has excellent mechanical stability. From the viewpoint of further reducing the oxygen generation overpotential, it is preferable that the ratio of nickel in the Ni-Fe alloy is 58 to 85 mass%. It is also preferable that the ratio of iron in the Ni-Fe alloy is 15 to 42 mass%.

[0024] In the metal component used for thermal spraying, the proportion of aluminum (Al) is 1 to 30% by mass, and the sum of the proportion of nickel-iron alloy and the proportion of aluminum is 100% by mass. Preferably, the proportion of aluminum is 5 to 25% by mass. By thermal spraying a metal component with an aluminum proportion within the above range, at least some of the aluminum can be dissolved and removed from the thermal spray coating in the subsequent catalyst layer formation process, thereby forming a catalyst layer having a porous structure formed of the desired nickel-iron alloy. If the proportion of aluminum in the metal component exceeds 30% by mass, the proportion of voids in the formed porous structure becomes excessive. As a result, the capacitance per unit area increases, while the mechanical stability of the catalyst layer decreases and it becomes brittle, making it easy to peel off from the substrate.

[0025] Thermal spraying can be carried out according to conventionally known thermal spraying methods. Examples of thermal spraying methods include plasma spraying, in which Ni-Fe alloy powder and aluminum powder are heated, melted, and accelerated using a plasma jet generated by a plasma spray gun, and then sprayed onto the surface of the substrate; and arc spraying, in which a DC arc discharge is generated at the tip of a Ni-Fe alloy wire and an aluminum wire, and the molten metal component is blown off with compressed air and sprayed onto the surface of the substrate. These thermal spraying methods are preferred because the ratio of metal in the metal component and the thickness of the thermal spray coating that is formed can be arbitrarily set.

[0026] (Catalyst layer formation process) In the catalyst layer formation process, an alkaline component is brought into contact with the thermal spray coating to dissolve and remove at least some of the aluminum from the thermal spray coating. This creates voids where the aluminum was present, forming a catalyst layer with a porous structure.

[0027] Various alkaline aqueous solutions can be used as the alkaline component to be brought into contact with the thermal spray coating. For example, inorganic alkalis such as sodium hydroxide or potassium hydroxide can be used. The substrate on which the thermal spray coating has been formed on its surface is immersed in an alkaline aqueous solution, or an alkaline aqueous solution is sprayed or applied to the substrate to bring the alkaline component into contact with the thermal spray coating. If necessary, the thermal spray coating is heated appropriately to dissolve and remove at least some of the aluminum, forming a porous catalyst layer. Furthermore, by washing with water and drying, the desired oxygen-generating anode can be obtained.

[0028] The present invention will be described in detail below based on examples, but the present invention is not limited to these examples. In the examples and comparative examples, "parts" and "%" are based on mass unless otherwise specified.

[0029] <Manufacturing of an Oxygen Generating Anode (1)> (Example 1) A nickel substrate (100 mm x 100 mm x 0.9 mm) was prepared as a conductive substrate by chemical etching by immersing it in 17.5% hydrochloric acid heated to near its boiling point for 6 minutes. This substrate was then subjected to blast treatment by spraying 60 mesh alumina particles at a pressure of 0.3 MPa, and then chemical etching by immersing it in 20% hydrochloric acid heated to near its boiling point for 6 minutes. In addition, a Ni-Fe alloy powder (Ni: 90%, Fe: 10%) was prepared as metal powder (1). Furthermore, an Al powder was prepared as metal powder (2). Metal powder (1) and metal powder (2) were used in a mass ratio of (1):(2) = 90:10, and a thermal spray coating was formed on the surface of the substrate after chemical etching by plasma spraying according to the conditions shown below. • Spray supply rate: 50 g / min • Main gas: Argon • Gas pressure: 100 Psi • Gas flow rate: 80 L / min • Secondary gas: Nitrogen • Secondary gas pressure: 100 Psi • Secondary gas flow rate: 17 L / min • Cooling air pressure: 60 Psi • Voltage: 65 V • Current: 500 A • Output: 32.5 kW • Nozzle model: 3M7-GE-S • Pass speed: 400 mm / sec • Gun angle: 90° • Operating direction: Horizontal • Jump: 4 mm • Distance between nozzle and substrate: 152 mm

[0030] A substrate coated with a thermal spray film was immersed in an alkaline aqueous solution (20% sodium hydroxide (NaOH) aqueous solution, 60°C) for approximately 8 hours until no more bubbles were formed. After washing with water, it was dried in a 60°C oven for approximately 3 hours to obtain an oxygen-evolving anode with a porous catalyst layer formed on its surface. The thickness of the catalyst layer, measured using a digital caliper, was approximately 150 μm. Figure 2 shows an electron microscope image of the cross-section of the obtained oxygen-evolving anode.

[0031] (Examples 2 and 3, Comparative Examples 1 to 3) An oxygen generation anode having a catalyst layer formed on the surface was obtained in the same manner as in Example 1 described above, except that the types and ratios of the metal powders (1) and (2) were as shown in Table 1. The catalyst layers of the oxygen generation anodes obtained in Examples 2 and 3 and Comparative Examples 2 and 3 had a porous structure. On the other hand, the catalyst layer of the oxygen generation anode obtained in Comparative Example 1 did not have a porous structure. An electron micrograph of the cross section of the oxygen generation anode obtained in Example 3 is shown in Fig. 3.

[0032] <Evaluation (1)> (Measurement of Oxygen Generation Overpotential (O.O.V.)) Using the manufactured oxygen generation anode and using a reversible hydrogen electrode as a reference electrode, an electrolytic cell was fabricated. A 30% potassium hydroxide (KOH) aqueous solution at 80 °C was used as the electrolyte, and preliminary electrolysis was carried out at a current density of 10 kA / m ２ for 2 hours. Then, electrolysis was carried out at a current density of 10 kA / m ２ for 2 hours to measure the oxygen generation overpotential (O.O.V. (mV)). The measured potential was corrected for iR before conversion to O.O.V. The measurement results are shown in Table 1. Also, a scatter diagram plotting the oxygen generation overpotential against the Al ratio is shown in Fig. 4.

[0033] (Measurement and Calculation of Capacitance per Unit Area) The charging current (I ｃ ) of the manufactured oxygen generation anode was measured by cyclic voltammetry scanning within the range of open circuit potential (Open Circuit Potential, OCP) ± 50 mV and scanning speed (ν) 0.005 to 0.2 V / s. Next, a graph plotting the charging current against the scanning speed was created, and the capacitance (C ｄｌ ) corresponding to the slope of the graph was calculated from the following formula (1). Then, the value of the obtained capacitance (C ｄｌ ) was divided by the area of the catalyst layer to calculate the capacitance per unit area (mF / cm ２ ). The results are shown in Table 1. C ｄｌ = △I ｃ / △ν ・・・(1) C ｄｌ : Capacitance (F) I ｃ : Charging current (A) ν: Scanning speed (V / s)

[0034] (Tape peeling test) The manufactured anode for oxygen generation was placed on a horizontal surface, and a mending tape (manufactured by 3M) was attached to the catalyst layer so that no air bubbles were trapped. After pressing the mending tape for about 10 seconds, one end of the tape was pinched with a finger and quickly pulled vertically to peel it off. The amount of the catalyst layer attached to the tape was visually confirmed, and the mechanical stability (adhesive strength) of the catalyst layer was evaluated according to the evaluation criteria shown below. Note that this evaluation criterion is a relative evaluation and not a strict one, but it is a sufficiently reasonable criterion for evaluating the mechanical stability of the catalyst layer. The results are shown in Table 1. Note that Evaluation A is the most preferable, and up to Evaluation B is within the acceptable range. A: No peeling B: Some peeling C: Overall peeling

[0035] The experimental results shown in Table 1 and Figure 4 indicate the performance of the anode for oxygen generation when Ni:Fe in the Ni-Fe alloy was fixed at 90:10 and the Al ratio was increased while maintaining the thickness of the catalyst layer. As the Al ratio increases, the structure of the catalyst layer becomes more porous, resulting in an increase in the actual surface area. However, when the thickness of the catalyst layer is constant, the amount of catalyst metal in the catalyst layer is considered to decrease. Therefore, as shown by the approximate curve in Figure 4, the O.O.V. of the anode for oxygen generation decreases with the increase in the Al ratio and then increases. In addition, as the Al ratio increases, the structure of the catalyst layer becomes more porous, so it is considered that the mechanical stability of the catalyst layer decreases as shown in the tape peeling test in Table 1. Considering the above, the Al ratio is preferably 1 to 30%. In particular, if the Al ratio is 5% or more, the O.O.V. is generally less than 200 mV, so 5 to 40% is more preferable. Furthermore, based on the results of the tape peeling test shown in Table 1, the Al ratio is more preferably 25% or less, and even more preferably 17% or less. Therefore, the Al ratio is preferably 1 to 30%, more preferably 5 to 25%, and even more preferably 5 to 17%.

[0036] <Manufacture of Anode for Oxygen Generation (2)> (Examples 4 to 10, Comparative Example 4) An oxygen generation anode having a catalytic layer with a porous structure formed on its surface was obtained in the same manner as in Example 1 described above, except that the types and ratios of the metal powders (1) and (2) were as shown in Table 2. However, the thickness of the catalytic layer was set to approximately 300 μm only in Example 10.

[0037] <Evaluation (2)> In the same manner as in the aforementioned "Evaluation (1)", the O.O.V. (mV) of the manufactured oxygen generation anode was measured, and the capacitance per unit area (mF / cm ２ ) was measured and calculated. Furthermore, a tape peeling test was conducted in the same manner as in the aforementioned "Evaluation (1)" to evaluate the mechanical stability (adhesion strength) of the catalytic layer. The results are shown in Table 2. Also, a scatter diagram plotting the oxygen generation overvoltage against the Fe ratio is shown in FIG. 5.

[0038] The experimental results shown in Table 2 and FIG. 5 indicate the performance of the oxygen generation anode when the Fe ratio in the Ni-Fe alloy was increased while fixing the Al ratio, that is, when the Ni ratio was decreased. When the Fe ratio is 5% or more, that is, when the Ni ratio is 95% or less, it can be seen that the O.O.V. is lower than that of Comparative Example 4 which does not contain any Fe. On the other hand, from the results of the tape peeling test, it is considered that the mechanical stability of the catalytic layer begins to decrease when the Fe ratio reaches about 64%, that is, when the Ni ratio reaches about 36%. Therefore, it is preferable that the Ni ratio is 35 to 95% and the Fe ratio is 5 to 65%, and it is more preferable that the Ni ratio is 58 to 85% and the Fe ratio is 15 to 42% (however, in both cases, the sum of the two ratios is 100%).

[0039] <Evaluation (3)> (Accelerated Life Test) Using the oxygen generation anode manufactured in Example 4, an aqueous solution of 30% KOH at 88°C was used at a current density of 30 kA / m ２An accelerated life test was conducted using electrolysis. The residual rate of iron in the catalyst layer (Fe residual rate (%)) was measured and calculated over time using X-ray fluorescence elemental analysis (XRF). Figure 6 shows a graph plotting the Fe residual rate (%) against the test time (h). As shown in Figure 6, it was found that even when electrolysis was performed at a high current density in an alkaline aqueous solution, not much iron (Fe) leached out of the catalyst layer. Furthermore, the Fe residual rate was approximately 90% even after 1,500 hours, and remained stable with almost no change even after 2,000 hours.

[0040] <Evaluation (4)> (Comparison with pyrolysis method) (Comparative Example 5) The same substrate as the one used in Example 1 above was prepared. An oxygen-generating anode (Comparative Example 5) was prepared by a conventionally known pyrolysis method in which a catalyst layer containing nickel and iron was formed by applying a precursor solution to the surface of the prepared substrate and then pyrolyzing it. Nickel nitrate (Ni(NO)) was used as the precursor. ３ ) ２ ) and iron nitrate (Fe(NO) ３ ) ３ ) was used. The mass ratio of Ni to Fe in the catalyst layer of the oxygen-evolving anode of Comparative Example 5 was 90:10, as shown in Table 3. In addition, aluminum was not used when forming the catalyst layer of the oxygen-evolving anode of Comparative Example 5, as in the above-described examples. Therefore, the catalyst layer does not have a porous structure like the above-described examples.

[0041] The 0.0.V. (mV) of the oxygen-generating anode produced in Comparative Example 5 was measured in the same manner as in "Evaluation (1)" described above. Furthermore, the Fe retention rate (%) after 2 hours was calculated using the oxygen-generating anodes produced in Comparative Example 5 and Example 5, in the same manner as in "Evaluation (3)" described above. The results are shown in Table 3.

[0042] As shown in Table 3, although Example 5 and Comparative Example 5 have the same Ni-Fe ratio, the O.O.V. of Example 5 is lower than that of Comparative Example 5. Furthermore, in Example 5, where the catalyst layer was formed by thermal spraying, the Fe retention rate after 2 hours was an excellent 99%. On the other hand, in Comparative Example 5, where the catalyst layer was formed by pyrolysis, the Fe retention rate after 2 hours decreased to 71%. This suggests that in the catalyst layer formed by pyrolysis, more iron is leached out due to the influence of the alkaline aqueous solution compared to the catalyst layer formed by thermal spraying. Therefore, when the catalyst layer of an oxygen-evolving anode used in an alkaline aqueous solution contains iron, it can be said that it is preferable for the catalyst layer to be formed by thermal spraying.

[0043] The oxygen-generating anode of the present invention is useful as an oxygen-generating anode used in alkaline water electrolysis.

Claims

1. An oxygen-evolving anode comprising: a conductive substrate whose surface is at least made of nickel or a nickel-based alloy; and a catalyst layer having a porous structure formed of a nickel-iron alloy, disposed on the surface of the substrate, wherein the nickel-iron alloy has a nickel ratio of 35 to 95% by mass, an iron ratio of 5 to 65% by mass, and the sum of the nickel ratio and the iron ratio is 100% by mass.

2. Capacitance per unit area is 20 to 1,100 mF / cm² ２ The oxygen-generating anode according to claim 1.

3. A method for producing an oxygen-generating anode, comprising the steps of: thermal spraying a metal component containing a nickel-iron alloy and aluminum onto the surface of a conductive substrate whose surface is at least made of nickel or a nickel-based alloy to form a thermal spray coating on the surface of the substrate; and contacting the thermal spray coating with an alkaline component to dissolve and remove at least some of the aluminum from the thermal spray coating to form a catalyst layer having a porous structure formed of a nickel-iron alloy, wherein the nickel-iron alloy has a nickel ratio of 35 to 95% by mass, an iron ratio of 5 to 65% by mass, the sum of the nickel ratio and the iron ratio is 100% by mass, and the aluminum ratio in the metal component is 1 to 30% by mass, the sum of the nickel-iron alloy ratio and the aluminum ratio is 100% by mass.

4. The method for producing an oxygen-generating anode according to claim 3, wherein the proportion of aluminum in the metal component is 5 to 25% by mass.

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