Anode electrode for alkaline water electrolysis and method for manufacturing same

Abstract

Provided are: an anode electrode for alkaline water electrolysis, which can be manufactured at a lower cost and in a simpler process than ever before and with which oxygen evolution overpotential at the anode electrode can be reduced; and a method for manufacturing the same. In the method for manufacturing the anode electrode for alkaline water electrolysis, the anode electrode is manufactured by forming a catalyst layer on an Fe-Ni-based alloy substrate that contains 15-85 mass% of Ni and has a thickness of 1.0 mm or less. A catalyst layer 2 is formed by a catalyst layer formation step in which the Fe-Ni-based alloy substrate is immersed in an aqueous alkaline solution and a voltage is applied thereto. The catalyst layer 2 has an oxide layer or a hydroxide layer containing 10% or more of Ni, and has a thickness of greater than 0 nm but not greater than 400 nm.

Description

Anode electrode for alkaline water electrolysis and method for manufacturing the same

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

[0002] Hydrogen is attracting attention as a clean next-generation energy because it does not emit carbon dioxide during use and has a high energy density. As a method for producing this hydrogen, there is a method of electrolyzing water (electrolysis), and an alkaline water electrolysis method, a proton exchange membrane (hereinafter, PEM) type water electrolysis method, etc. have been known conventionally. Among them, the alkaline water electrolysis method tends to be suitable for large-scale production from the viewpoints of device life and power generation cost when compared with the PEM type water electrolysis method.

[0003] The alkaline water electrolysis method uses an alkaline aqueous solution in which an alkali metal hydroxide is dissolved as an electrolyte solution, and hydrogen is generated from the cathode electrode (cathode) and oxygen is generated from the anode electrode (anode). One of the factors that reduces the energy conversion efficiency of this alkaline water electrolysis method is overvoltage. Since this overvoltage is generally large on the anode side, various studies have been made on reducing the oxygen evolution overvoltage of the anode.

[0004] For example, in Patent Document 1, for the purpose of further reducing the voltage, it includes a conductive substrate at least the surface of which is made of nickel or a nickel-based alloy and an electrode catalyst layer formed on the surface of the conductive substrate, and the catalyst component constituting the electrode catalyst layer has a structural formula NiCo ２ O ４ A first catalyst component having a nickel cobalt spinel oxide represented by the formula, or a lanthanoid nickel cobalt perovskite oxide represented by the structural formula XNi ａ Co １－ａ O ３ (X is at least one metal selected from lanthanoids consisting of lanthanum, cerium and praseodymium, 0 <a <1), and a second catalyst component having at least one of iridium oxide and ruthenium oxide. An anode for alkaline water electrolysis characterized by comprising is disclosed.

[0005] Furthermore, Patent Document 2 discloses a method for manufacturing electrodes in which oxygen evolution reaction (OER) activity is improved without catalyst coating. Specifically, it describes a method for manufacturing electrodes comprising the steps of: heat-treating a conductive substrate made of a nickel alloy containing 30 to 70% by mass of Ni and 30 to 70% by mass of Fe (where Ni + Fe = 100% by mass); and etching the heat-treated conductive substrate with an etching solution containing at least one of an organic acid and a weak inorganic acid.

[0006] Japanese Patent Publication No. 2017-190476 Japanese Patent Publication No. 2023-011311

[0007] Alkaline water electrolysis is suitable for producing environmentally friendly green hydrogen that reduces carbon dioxide emissions by utilizing renewable energy sources such as solar and wind power. However, for large-scale hydrogen production, the equipment is expensive, so further cost reductions are desired, such as further cost reduction of electrode materials, in order to lower the equipment price. The electrode described in Patent Document 1 requires the formation of a catalyst layer having nickel cobalt spinel oxide or lanthanide nickel cobalt perovskite oxide on the substrate in order to achieve a reduction in overpotential, and also requires the formation of an oxide layer using expensive noble metal elements such as iridium and ruthenium. Furthermore, the electrode described in Patent Document 2 requires heat treatment and etching processes of the substrate, which can lead to high costs in electrode manufacturing. Therefore, the object of the present invention is to provide an anode electrode for alkaline water electrolysis and a method for manufacturing the same that can be manufactured at a lower cost and with a simpler process than conventional methods, and that can reduce the oxygen generation overpotential at the anode electrode.

[0008] The present invention has been made in view of the above-mentioned problems. That is, one aspect of the present invention is a method for manufacturing an anode electrode, wherein a catalyst layer is formed on an Fe-Ni alloy substrate with a thickness of 1.0 mm or less and containing Ni by mass% 15 to 85%, and the catalyst layer is formed by a catalyst layer formation step in which the Fe-Ni alloy substrate is immersed in an alkaline aqueous solution and a voltage is applied, thereby a method for manufacturing an anode electrode for alkaline water electrolysis.

[0009] Another aspect of the present invention is an anode electrode in which a catalyst layer is formed on an Fe-Ni alloy substrate containing 15 to 85% Ni by mass%, wherein the thickness of the substrate is 1.0 mm or less, and the catalyst layer has an oxide layer or hydroxide layer containing 10% or more Ni, and the thickness of the catalyst layer is greater than 0 nm and less than or equal to 400 nm.

[0010] According to the present invention, it is possible to manufacture the product at a lower cost and with a simpler process than conventional methods, reduce the oxygen generation overvoltage of the anode electrode for alkaline water electrolysis, and suppress the amount of Fe eluted into the alkaline aqueous solution (electrolyte) that inhibits electrode characteristics.

[0011] This is a transmission electron microscope image (magnification ×100k) showing a cross-section of the catalyst layer of a comparative example sample. This is a transmission electron microscope image (magnification ×2500k) showing a cross-section of the catalyst layer of a sample according to the present invention example. This is a transmission electron microscope image (magnification ×250k) showing a cross-section of the catalyst layer of another sample according to the present invention example.

[0012] Embodiments of the present invention will be described below. First, the Fe-Ni alloy substrate in the present invention will be described. As the Fe-Ni alloy substrate in the present invention, a thin alloy sheet cut from a strip of cold-rolled material or an alloy member having multiple through holes can be used. For example, as a member having through holes, examples include a thin alloy sheet that has been processed (e.g., expanded metal or perforated metal) or a mesh made by weaving alloy wires together (e.g., mesh or wire mesh).

[0013] The alloy composition of the Fe-Ni alloy substrate in this invention contains 15-85% Ni by mass. The preferred lower limit for Ni content is 30%, and the more preferred lower limit is 35%. The preferred upper limit for Ni content is 70%, the more preferred upper limit is 60%, and the even more preferred upper limit is 55%. By adjusting the Ni content within the above range, it is possible to reduce the amount of Ni used in the electrode material without impairing the oxygen generation overpotential of commonly used pure Ni (Ni: 99% or more) electrode materials, thereby contributing to cost reduction and conservation of Ni resources. In this invention, elements other than Ni can be Fe and unavoidable impurities. However, in order to improve the thermal expansion characteristics and mechanical strength of the electrode substrate without impairing the effects of this invention, one or more elements from groups 2 to 16 of periods 2 to 5 of the periodic table, either metallic (including metalloids) or nonmetallic, may be included in addition to the above alloy components, up to a maximum of 10% by mass in total. A more preferred alloy composition is an Fe-Ni alloy consisting of C: ≤0.01%, Si: ≤0.5%, Mn: ≤1.0%, Ni: 15-85%, with the remainder being Fe and unavoidable impurities.

[0014] Next, an example of a manufacturing method for obtaining the above-mentioned Fe-Ni alloy substrate will be described with the help of embodiments. In this embodiment, a strip-shaped intermediate material having the composition of the above-mentioned Fe-Ni alloy is prepared. This intermediate material can be obtained, for example, by mechanically or chemically removing the oxide layer from a hot-rolled material having the aforementioned composition. In addition, the edges of the cold-rolled material may be trimmed or otherwise smoothed to prevent defects such as cracks from occurring at the edges during cold rolling. Next, the intermediate material is cold-rolled one or more times. In this embodiment, the case in which cold rolling is introduced will be described, but if the desired plate thickness can be adjusted after hot rolling, cold rolling may be omitted. In addition, the thin plate after cold rolling may be annealed once or more at a temperature of, for example, 800°C or higher in order to soften the work-hardened material and remove processing distortion. The heating and holding time at this time should be appropriately adjusted according to the composition of the material and the plate thickness. The above-mentioned annealing can be performed by continuously passing the thin plate after cold rolling through a heating furnace set to the desired temperature. For example, this can be done by taking out a thin sheet of material that has been cold-rolled and wound into a roll, passing it through a heating furnace, and then winding it into a roll again.

[0015] By the manufacturing process that includes the cold rolling process described above, a strip of cold-rolled material can be obtained, and then by cutting it into the desired shape (including press working, laser processing, etc.), a thin alloy sheet-like Fe-Ni alloy substrate can be obtained. Furthermore, by subjecting the obtained strip of cold-rolled material to mesh-like stretch cutting or punching, expanded metal or perforated metal can be obtained.

[0016] Another example of a manufacturing method for obtaining the above-mentioned Fe-Ni alloy substrate will be described. A columnar intermediate material having the composition of the above-mentioned Fe-Ni alloy is prepared. This intermediate material can be obtained, for example, by mechanically or chemically removing the oxide layer from a hot-drawn wire rod produced by hot working having the aforementioned composition. Subsequently, the intermediate material is subjected to cold drawing one or more times. After cold drawing, the wire rod may be annealed one or more times at a temperature of, for example, 800°C or higher to soften the work-hardened material and remove processing strain. The heating and holding time at this time can be appropriately adjusted according to the material composition and plate thickness. The above-mentioned annealing can be performed by continuously passing the cold-drawn wire rod through a heating furnace set to a desired temperature. By weaving the alloy wire rods obtained by the above manufacturing process into a mesh, an Fe-Ni alloy substrate having through holes can be obtained.

[0017] The manufacturing method of the present invention involves immersing the aforementioned Fe-Ni alloy substrate in an alkaline aqueous solution and applying a voltage to form a catalyst layer, thereby forming a catalyst layer containing Ni eluted from the substrate on the Fe-Ni alloy substrate to serve as an anode electrode. Generally, the catalyst layer at the anode of alkaline water electrolysis is formed by coating the substrate with metal oxides or metals using physical vapor deposition or plating methods. In the present invention, by passing an electric current through the Fe-Ni alloy substrate as an anode in an alkaline aqueous solution, a layer of oxide or hydroxide is formed on the substrate to create the catalyst layer. Therefore, a catalyst layer that contributes to reducing overvoltage can be formed using a simple method without the need for vapor deposition or plating. The alkaline aqueous solution can be any solution commonly used in alkaline water electrolysis; for example, an alkali metal hydroxide solution or an alkaline earth metal hydroxide solution can be used. Preferably, a strongly alkaline sodium hydroxide solution or potassium hydroxide solution is used, and more preferably, a potassium hydroxide solution is used. The concentration of the alkaline aqueous solution is not particularly limited, but for example, 5 to 50% by mass is preferred.

[0018] By using an Fe-Ni alloy substrate as the anode electrode in this way, a catalyst layer is formed on the Fe-Ni alloy substrate under the operating environment of alkaline water electrolysis. In other words, operating as alkaline water electrolysis also serves as the catalyst layer formation step of the present invention. To form the catalyst layer more stably, it is preferable to place the Fe-Ni alloy substrate in an alkaline aqueous solution and sweep the potential under conditions that will form the desired catalyst layer before operating as alkaline water electrolysis. The voltage application conditions are not limited to any particular numerical range, as long as the amount of Ni and thickness of the catalyst layer, as described later, can be obtained.

[0019] The alkaline water electrolysis anode electrode of the present invention, obtained by the manufacturing method of the present invention described above, comprises an oxide layer or hydroxide layer containing 10% or more Ni on an Fe-Ni alloy substrate. This makes it possible to improve the overvoltage characteristics of the electrode and suppress the amount of Fe eluted.

[0020] The catalyst layer thickness of the alkaline water electrolysis anode electrode of the present invention is greater than 0 nm and less than or equal to 400 nm. This improves the overpotential characteristics of the electrode and suppresses the amount of Fe elution. When the catalyst layer thickness is 0 nm (none), the amount of Fe elution tends to increase, and when the catalyst layer thickness exceeds 400 nm, there is a risk that the overpotential characteristics of the electrode will increase (deteriorate). The preferred lower limit of the catalyst layer thickness is 5 nm, the more preferred lower limit is 10 nm, and the preferred upper limit of the catalyst layer thickness is 300 nm. In this invention, the thickness of the catalyst layer and the amount of Ni in the catalyst layer can be measured by observing the cross-sectional portion of the electrode surface layer of the sample using a transmission electron microscope (TEM), scanning electron microscope (SEM), or energy-dispersive X-ray spectrometer (EDX).

[0021] The Fe-Ni alloy substrate in this invention has a thickness of 1.0 mm or less. This is expected to reduce the amount of expensive Ni used in the electrode material without impairing the overvoltage characteristics or lifespan of the electrode. The preferred lower limit of thickness is 0.1 mm, and the more preferred lower limit of thickness is 0.2 mm. Furthermore, the preferred upper limit of thickness is 0.8 mm, and the more preferred upper limit of thickness is 0.5 mm.

[0022] As a base material, intermediate Fe-Ni alloys with varying Ni compositions as shown in Table 1 were cold-rolled to prepare cold-rolled sheets with a thickness of 0.2 mm. Subsequently, 12 mm square test specimens were taken from the cold-rolled material by wire cutting. To prepare the evaluation conditions, the non-evaluation surface of the test specimen was polished with #800 abrasive paper, and the evaluation surface was polished with abrasive paper and then finished to a mirror finish using diamond abrasive grains.

[0023] Subsequently, the electrode area of ​​the test specimen evaluation surface was 0.5 cm². ２ A test specimen coated with insulating resin was mounted in a Teflon® H-type cell, and in a 30% potassium hydroxide solution (7M KOH) at a solution temperature of 20±1°C, the potential of the reference electrode was measured relative to a chemical hydrogen electrode. A catalyst layer formation process was carried out by sweeping the potential under the conditions of a potential of 0.5-1.8V relative to a hydrogen electrode, a potential velocity of 1V / s, and 20,000 cycles, thereby forming a catalyst layer on the electrode surface.

[0024]

[0025] The polarization curves before and after the formation of the catalyst layer were measured using the evaluation apparatus described above, and the oxygen evolution overpotential was evaluated. In addition, the amount of Fe eluted in the solution after the catalyst layer formation was analyzed using inductively coupled plasma mass spectrometry (ICP-MS). For both oxygen evolution overpotential and Fe elution, two tests were conducted, and the average value was calculated. The results are shown in Table 2.

[0026]

[0027] As shown in Table 2, it was confirmed that in the present invention examples No. 4, 6, 8, 10, 12, 14, and 16, in which the amount of Ni was adjusted using Fe as a balance component as defined in the present invention and the catalyst layer formation treatment was performed, the oxygen generation overpotential was reduced compared to comparative examples No. 3, 5, 7, 9, 11, 13, and 15 with the same amount of Ni and no catalyst layer, while suppressing the amount of Fe elution. Furthermore, it was confirmed that the present invention examples obtained superior oxygen generation overpotential characteristics even when compared with reference examples No. 17 (without catalyst layer) and 18 (with catalyst layer), in which the Ni amount was 99.1%. Comparative examples No. 1 (without catalyst layer) and 2 (with catalyst layer), which contained almost no Ni in the substrate, had a larger overpotential than the present invention examples, and the amount of Fe eluted was extremely large even after the catalyst layer formation treatment was performed, making them unsuitable as anode electrodes for alkaline water electrolysis.

[0028] For Comparative Example No. 2, Invention Examples No. 4, 6, 10, 12, 14, and Reference Example No. 18, which were samples in which a catalyst layer was formed, the cross-section of the sample (electrode surface layer) was observed using a JEOL transmission electron microscope, and the thickness of the catalyst layer was measured. Furthermore, the components in the catalyst layer were analyzed using an energy-dispersive X-ray analyzer. The results are shown in Table 3. Also, TEM observation images of the cross-sections of the catalyst layers of Comparative Example No. 2, Invention Example No. 12, and Reference Example No. 18 are shown in Figures 1 to 3. In Table 3, "Other" indicates the total amount of Si, K, and Mn detected in the analysis of the catalyst layer.

[0029]

[0030] As shown in Table 3, the catalyst layer of Comparative Example No. 2 (reference numeral 1 in Figure 1) had a film thickness of 1730 nm and a Ni content of 0.0%, the catalyst layers of Invention Examples No. 4, 6, 10, 12, and 14 (reference numeral 2 in Figure 2 for Invention Example No. 12) had a film thickness of 11 to 262 nm and a Ni content of 19.3 to 72.0%, and the catalyst layer of Reference Example No. 18 (reference numeral 3) had a film thickness of 524 nm and a Ni content of 77.4%. Of these, the catalyst layers of Invention Examples No. 4, 6, 10, 12, and 14, which are excellent in oxygen generation overpotential and Fe elution amount, are suitable as catalyst layers for anode electrodes for alkaline water electrolysis. On the other hand, Comparative Example No. 2, which contains almost no Ni in the substrate... The catalyst layer of No. 2 had a thicker film thickness and a lower Ni content than the present invention example, resulting in high oxygen evolution overpotential and Fe elution, making it unsuitable as a catalyst layer for an anode electrode for alkaline water electrolysis. Furthermore, the catalyst layer of Comparative Example No. 18, with a Ni content of 99.1% in the substrate, had approximately the same Ni content as the catalyst layer of the present invention example, but its thicker film thickness resulted in a high oxygen evolution overpotential, making it unsuitable as a catalyst layer for an anode electrode for alkaline water electrolysis.

[0031] 1, 2, 3 catalyst layer

Claims

1. A method for manufacturing an anode electrode for alkaline water electrolysis, comprising forming a catalyst layer on an Fe-Ni alloy substrate with a thickness of 1.0 mm or less and containing Ni by mass% 15 to 85%, wherein the catalyst layer is formed by a catalyst layer formation step of immersing the Fe-Ni alloy substrate in an alkaline aqueous solution and applying a voltage.

2. An anode electrode for alkaline water electrolysis, comprising an Fe-Ni alloy substrate containing 15-85% Ni by mass, wherein a catalyst layer is formed on the substrate, the thickness of the substrate is 1.0 mm or less, the catalyst layer has an oxide layer or hydroxide layer containing 10% or more Ni, and the thickness of the catalyst layer is greater than 0 nm and less than or equal to 400 nm.

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