Method for preparing cathode material for alkaline electrolyzed water based on molten salt activation and cathode material prepared by method

Abstract

The invention provides a method for preparing a cathode material for alkaline electrolyzed water based on molten salt activation and the cathode material prepared by the method, and belongs to the technical field of electrolyzed water electrodes. The method comprises the steps that a metallic nickel substrate subjected to surface cleaning treatment is subjected to corrosion treatment based on solvothermal reaction in a mixed solution containing tungstate and fluoride, nickel tungstate of a smooth nanorod structure is formed on the surface of the metallic nickel substrate, and the nickel-based composite material is obtained; under the protection of inert atmosphere, the nickel-based composite material is placed in molten salt for a solid-liquid reaction, zinc, bismuth and chlorine in the molten salt are jointly doped into nickel tungstate, and the cathode material for alkaline electrolyzed water is obtained. The surface material of the cathode material for alkaline electrolysis of water is zinc, bismuth and chlorine doped rod-like nickel tungstate rich in nano-pores. Through verification, the alkaline electrolyzed water cathode electrode shows high-efficiency electro-catalysis water decomposition performance.

Description

Technical Field

[0001] The present invention belongs to the technical field of water electrolysis electrodes, and in particular relates to a method for preparing a cathode material for alkaline water electrolysis based on molten salt activation and the prepared cathode material. Background Art

[0002] Hydrogen is primarily obtained through fossil fuel conversion, including methane reforming and coal-to-hydrogen production. These processes are inherently high-emission and highly polluting. Currently, water electrolysis, which utilizes renewable energy sources (wind, solar, and hydropower), is gaining momentum and is expected to become the greenest hydrogen production method. Alkaline water electrolysis is expected to be the first to achieve large-scale hydrogen production. The cathode in alkaline water electrolysis involves a hydrogen evolution reaction, which is directly related to the performance of hydrogen produced by water electrolysis.

[0003] Currently, the predominant cathode surfactant in commercial alkaline water electrolysis is nickel-based nanoparticles. However, their intrinsic catalytic activity is severely limited, resulting in energy consumption that cannot meet increasingly stringent economic targets for water electrolysis. Further improving cathode performance within the non-precious metal category is a current research hotspot in the hydrogen energy materials field.

[0004] Nickel and tungsten are commonly used catalyst elements, and there has been considerable research on their use as cathodes in water electrolysis. However, the preparation process and catalytic performance of nickel-tungsten-based active materials currently do not meet the requirements for industrial water electrolysis.

[0005] In view of this, there are still severe challenges in how to successfully prepare highly active nickel-tungsten-based electrodes. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to provide a method for preparing a cathode material for alkaline water electrolysis based on molten salt activation and the cathode material prepared therefrom.

[0007] In order to solve the above technical problems, the technical solution adopted by the present invention is: In a first aspect, a method for preparing a cathode material for alkaline water electrolysis based on molten salt activation is provided, the preparation method comprising the following steps: S1. Tungstate etching treatment: A metal nickel substrate is subjected to a solvent thermal reaction-based etching treatment in a mixed solution containing tungstate and fluoride to form nickel tungstate with a nanorod-like structure on the surface of the metal nickel substrate to obtain a nickel-based composite material; the nanorod-like structure is a smooth nanorod-like structure.

[0008] S2. Molten salt activation treatment: Under the protection of an inert atmosphere, the nickel-based composite material is placed in a molten salt for a solid-liquid reaction, and the surface of the nickel tungstate of the nickel-based composite material is activated, so that the zinc, bismuth and chlorine in the molten salt are co-doped into the nickel tungstate to obtain the cathode material for alkaline water electrolysis.

[0009] In some preferred embodiments, the metal nickel substrate is a metal nickel substrate that has been surface cleaned.

[0010] In some embodiments, the surface cleaning treatment specifically includes: placing the metal nickel substrate in an acetone solution for ultrasonic cleaning for 10 to 30 minutes, and then repeatedly cleaning with ethanol to remove the grease layer on the metal surface; placing the metal nickel substrate after the grease layer on the metal surface is removed in a hydrochloric acid solution with a concentration of 1 to 6 mol / L for ultrasonic cleaning for 5 to 25 minutes, and letting it stand for 10 to 30 minutes, and then repeatedly cleaning with distilled water to remove the oxide layer on the metal surface, and drying to obtain the metal nickel substrate after surface cleaning treatment.

[0011] In some embodiments, the metal nickel substrate is one of a nickel mesh, nickel foam, and a nickel sheet.

[0012] In some embodiments, the metal nickel substrate is nickel foam.

[0013] In some embodiments, the solvent in the mixed solution containing tungstate and fluoride is a mixture of water and ethylene glycol, the concentration of tungstate is 12-76 mmol / L, and the concentration of fluoride is 9-52 mmol / L. Preferably, the volume ratio of water to ethylene glycol in the solvent is 1:(1-2).

[0014] In some embodiments, the tungstate is any one of ammonium tungstate, sodium tungstate and potassium tungstate, or any combination thereof; the fluoride is any one of ammonium fluoride, sodium fluoride and potassium fluoride, or any combination thereof; and the inert atmosphere is any one of nitrogen and argon, or any combination thereof.

[0015] In some embodiments, the molten salt is a mixture of bismuth chloride, zinc chloride, and metallic zinc, wherein the mass percentage of zinc element is 25% to 70%, and the mass percentage of bismuth element is 15 to 45%.

[0016] In some embodiments, the S1 step is specifically as follows: placing the metal nickel substrate in a hydrothermal kettle containing a mixed solution of tungstate and fluoride, the filling degree of the hydrothermal kettle is 50%~85%, heating the hydrothermal kettle to 90~180°C for reaction, and maintaining it for 0.5~13h.

[0017] In some embodiments, the smooth nanorod-like structures have a length in the range of 0.5-400 μm and a diameter in the range of 20-40 nm.

[0018] In some embodiments, the S2 step is specifically as follows: placing the nickel-based composite material in a molten salt under the protection of an inert atmosphere for a solid-liquid reaction, activating the nickel tungstate surface of the nickel-based composite material, and co-doping zinc, bismuth, and chlorine into the nickel tungstate. The temperature of the solid-liquid reaction is 200~480°C, and the time is 0.5~6.5h.

[0019] In some embodiments, the surface material of the alkaline water electrolysis cathode electrode is nickel tungstate co-doped with zinc, bismuth, and chlorine, with zinc doped at the nickel site, bismuth doped at the tungsten site, and chlorine doped at the oxygen site. The surface material presents a porous nanorod structure, and the pore size of the porous nanorod structure is in the range of 5 to 30 nm.

[0020] In a second aspect, a cathode material for alkaline water electrolysis prepared by the above method is provided.

[0021] Compared with the prior art, the method for preparing a cathode material for alkaline water electrolysis based on molten salt activation provided by the present invention and the cathode material prepared therefrom have at least one or at least part of the following advantages: 1) Based on a solid-liquid reaction, the surface material is co-doped with anions and cations, introducing anionic chloride and cations zinc and bismuth into nickel tungstate. Simultaneously, the nanostructure is modified, transforming the smooth nanorod structure into a porous nanorod structure, greatly improving the intrinsic catalytic activity. 2) The method is simple in process, does not require the introduction of external nickel ions, has low cost, and is suitable for production promotion. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] The technical solutions and beneficial effects of the present invention will be made apparent by describing in detail the specific embodiments of the present invention in conjunction with the accompanying drawings.

[0023] Figure 1 This is a flow chart of a method for molten salt activation of a cathode electrode for preparing alkaline water electrolysis according to one embodiment of the present invention; Figure 2 This is a scanning electron microscope image of a certain area of the final electrode surface material corresponding to Example 4; Figure 3 This is a transmission electron microscope image of a single nanorod in a certain area of the final electrode surface material corresponding to Example 4. DETAILED DESCRIPTION

[0024] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative work shall fall within the scope of protection of the present invention.

[0025] In one embodiment of the present invention, a method for preparing a cathode material for alkaline water electrolysis based on molten salt activation is provided, wherein the preparation method comprises the following steps: S1. Tungstate etching treatment: A metal nickel substrate is subjected to a solvent thermal reaction-based etching treatment in a mixed solution containing tungstate and fluoride to form a smooth nanorod-like structure of nickel tungstate on the surface of the metal nickel substrate to obtain a nickel-based composite material; S2. Molten salt activation treatment: Under the protection of an inert atmosphere, the nickel-based composite material is placed in a molten salt for a solid-liquid reaction, and the surface of the nickel tungstate of the nickel-based composite material is activated, so that the zinc, bismuth and chlorine in the molten salt are co-doped into the nickel tungstate to obtain the cathode material for alkaline water electrolysis.

[0026] In a specific embodiment of the present invention, Figure 1 As shown, a method for preparing a cathode material for alkaline water electrolysis based on molten salt activation is provided, comprising the following steps: S10 surface cleaning: performing surface cleaning on the metal nickel substrate to obtain a metal nickel substrate after surface cleaning.

[0027] Step S10 specifically includes the following steps: S11: placing a metal nickel substrate in an acetone solution and ultrasonically cleaning it for 10 to 30 minutes, and then repeatedly cleaning it with ethanol to remove the grease layer on the metal surface. The ultrasonic cleaning time is preferably 10 minutes, 15 minutes, 20 minutes, 25 minutes or 30 minutes. The metal nickel substrate is preferably any one of nickel mesh, nickel foam or nickel sheet, or any combination thereof; more preferably, the metal nickel substrate is nickel foam.

[0028] S12: The metal nickel substrate after removing the grease layer on the metal surface is placed in a hydrochloric acid solution with a concentration of 1 to 6 mol / L and ultrasonicated for 5 to 25 minutes, and then allowed to stand for 10 to 30 minutes, and then repeatedly washed with distilled water to remove the oxide layer on the metal surface. After drying, the metal nickel substrate after surface cleaning is obtained.

[0029] Preferably, the concentration of the hydrochloric acid solution is 1 mol / L, 2 mol / L, 3 mol / L, 4 mol / L, 5 mol / L or 6 mol / L, the ultrasonic time is preferably 5 min, 10 min, 15 min, 20 min or 25 min, and the standing time is preferably 10 min, 15 min, 20 min, 25 min or 30 min.

[0030] S20 tungstate etching treatment: The metal nickel substrate after surface cleaning is subjected to a solvent thermal reaction-based etching treatment in a mixed solution containing tungstate and fluoride.

[0031] In some embodiments of the present invention, step S20 specifically comprises placing the surface-cleaned nickel substrate in a hydrothermal reaction vessel containing a mixed solution of tungstate and fluoride, heating the vessel to 90-180°C for a solvothermal reaction for 0.5-13 hours to form nickel tungstate with smooth nanorod-like structures on the surface of the nickel substrate, thereby obtaining a nickel-based composite material. The smooth nanorod-like structures have a length of 50-150 nm and a diameter of 20-40 nm.

[0032] The fluoride in the mixed solution can promote the corrosion reaction between tungstate and nickel substrate in the solvothermal reaction.

[0033] Preferably, the length of the smooth nanorod-like structures is in the range of 0.5 to 400 μm, and the diameter is in the range of 20 to 40 nm.

[0034] Preferably, the heating temperature of the hydrothermal reactor is preferably 90°C, 120°C, 150°C or 180°C, and the corresponding reaction time is preferably 0.5h, 6.5h, 9.5h or 13h.

[0035] In some embodiments of the present invention, the filling degree of the hydrothermal reactor containing the mixed solution of tungstate and fluoride is 50% to 85%, preferably 50%, 60%, 75% or 85%. Preferably, in the mixed solution containing tungstate and fluoride, the solvent is a mixture of water and an organic solvent. The use of a mixed solvent can reduce the amount of water involved in the reaction. By selecting a suitable organic solvent and regulating the proportion of the organic solvent, the solvothermal growth process of nickel tungstate can be regulated, thereby controlling the nanostructure of nickel tungstate.

[0036] Among organic solvents, ethanol has a small molecular weight, while ethylene glycol has a larger molecular weight but is much smaller than other organic solvents. Therefore, ethylene glycol is preferably used as the organic solvent, which can well regulate the nanostructure of nickel tungstate.

[0037] In the mixture of water and organic solvent, the volume ratio of water to ethylene glycol is preferably 1: (1-2), which can further regulate the nanostructure of nickel tungstate.

[0038] Preferably, the concentration of the tungstate is 12 to 76 mmol / L, preferably 12 mmol / L, 36 mmol / L, 56 mmol / L or 76 mmol / L. The tungstate is preferably any one of ammonium tungstate, sodium tungstate, potassium tungstate or any combination thereof.

[0039] Preferably, the concentration of the fluoride is 9 to 52 mmol / L, preferably 9 mmol / L, 23 mmol / L, 38 mmol / L or 52 mmol / L. The fluoride is preferably any one of ammonium fluoride, sodium fluoride and potassium fluoride or any combination thereof.

[0040] S30 molten salt activation treatment: the metal nickel substrate after corrosion treatment is subjected to solid-liquid reaction in molten salt under the protection of an inert atmosphere, the surface material of the substrate is co-doped with anions and cations, and the nanostructure is modified at the same time to obtain the cathode material for alkaline water electrolysis.

[0041] In some preferred embodiments of the present invention, step S30 of the molten salt activation treatment is specifically as follows: the metal nickel substrate (i.e., nickel-based composite material) after corrosion treatment is subjected to a solid-liquid reaction in a molten salt under the protection of an inert atmosphere, and the surface material of the substrate is co-doped with anions and cations, so that zinc, bismuth, and chlorine in the molten salt are co-doped into the nickel tungstate, zinc is doped at the nickel site, bismuth is doped at the tungsten site, and chlorine is doped at the oxygen site. At the same time, nanostructured structure modification is performed to transform the smooth nanorod-like structure into a porous nanorod-like structure with a pore size of 5 to 30 nm, thereby obtaining the cathode material for alkaline water electrolysis.

[0042] Preferably, the inert atmosphere is any one of nitrogen and argon, or any combination thereof.

[0043] Preferably, the temperature of the solid-liquid reaction is 200-480°C, preferably 200°C, 260°C, 340°C or 480°C, and maintained at this temperature for 0.5-6.5h, preferably 0.5h, 2.8h, 5.4h or 6.5h.

[0044] Preferably, the molten salt consists of bismuth chloride, zinc chloride and metallic zinc. The mass percentage of zinc element in the molten salt is 25% to 70%, preferably the mass percentage of zinc element is 25%, 48%, 64% or 70%, and the mass percentage of bismuth element is 15% to 45%, preferably the mass percentage of bismuth element is 15%, 22%, 34% or 45%.

[0045] Another embodiment of the present invention also provides a cathode material for alkaline water electrolysis prepared using the above method, comprising a metal nickel substrate and a porous nanorod-like structure arranged on the metal nickel substrate, wherein the porous nanorod-like structure or the surface material is nickel tungstate co-doped with zinc at the nickel site, bismuth at the tungsten site, and chlorine at the oxygen site.

[0046] The present invention will be further described below through specific embodiments; Example 1 The method for preparing an electrode using nickel mesh as a metal nickel substrate is as follows: S11: Place a 40-mesh plain nickel mesh in an acetone solution for ultrasonic cleaning for 20 minutes, and then repeatedly clean it with ethanol to remove the grease layer on the metal surface; S12: The nickel mesh after the grease layer on the metal surface is removed is placed in a hydrochloric acid solution with a concentration of 4 mol / L and ultrasonicated for 15 minutes, and then allowed to stand for 20 minutes. It is then repeatedly washed with distilled water to remove the oxide layer on the metal surface. After drying, the nickel mesh after surface cleaning is obtained.

[0047] S21: placing the surface-cleaned nickel mesh in a hydrothermal reactor containing a mixed solution of 6 mmol / L ammonium tungstate, 6 mmol / L potassium tungstate, and 23 mmol / L potassium fluoride, wherein the solvent comprises water and ethylene glycol in a volume ratio of 1:1.5, and the reactor is filled to 85%. The hydrothermal reactor is heated to 120° C. and maintained for 9.5 hours. S22 rinses the nickel mesh after the hydrothermal reaction with distilled water and dries it to obtain the nickel mesh after tungstate corrosion treatment. The surface of the metal nickel substrate after tungstate corrosion treatment is a smooth nanorod-like structure with a length of 0.5~400µm and a diameter of 20~40nm, and its material property is nickel tungstate.

[0048] S31: activating the nickel substrate after tungstate etching in a molten salt of bismuth chloride, zinc chloride, and metallic zinc under an inert atmosphere, wherein the mass percentage of zinc is 48%, the mass percentage of bismuth is 22%, and the molten salt temperature is 260°C, and maintained at this temperature for 5.4 hours; S32 rinses the metal nickel substrate after molten salt activation treatment with ethanol and vacuum dries it to obtain the final electrode. The surface of the final electrode is a porous nanorod structure with a pore size of 5~30nm. Its material properties are nickel tungstate co-doped with zinc, bismuth and chlorine, with zinc doped at the nickel site, bismuth doped at the tungsten site, and chlorine doped at the oxygen site.

[0049] Example 2 The method for preparing an electrode using nickel foam as a metal nickel substrate is as follows: S11: The nickel foam was ultrasonically cleaned in an acetone solution for 30 min, and then repeatedly cleaned with ethanol to remove the grease layer on the metal surface; S12: The nickel foam after removing the grease layer on the metal surface is placed in a hydrochloric acid solution with a concentration of 6 mol / L and ultrasonicated for 5 minutes, and then allowed to stand for 30 minutes, and then repeatedly washed with distilled water to remove the oxide layer on the metal surface. After drying, the nickel foam after the surface cleaning treatment is obtained.

[0050] S21: placing the surface-cleaned nickel foam in a hydrothermal reactor containing a mixed solution of 30 mmol / L ammonium tungstate, 46 mmol / L sodium tungstate, and 9 mmol / L ammonium fluoride, wherein the solvent comprises water and ethylene glycol in a volume ratio of 1:1.5, and the filling degree of the reactor is 50%. The hydrothermal reactor is heated to 180° C. and maintained for 13 hours. S22 rinses the nickel foam after the hydrothermal reaction with distilled water and dries it to obtain nickel foam after tungstate corrosion treatment. The surface of the metal nickel substrate after tungstate corrosion treatment is a smooth nanorod-like structure with a length of 0.5~400µm and a diameter of 20~40nm, and its material property is nickel tungstate.

[0051] S31: activating the nickel substrate after tungstate etching in a molten salt of bismuth chloride, zinc chloride, and metallic zinc under inert atmosphere, wherein the mass percentage of zinc element is 70%, the mass percentage of bismuth element is 15%, and the molten salt temperature is 480° C., and maintained at this temperature for 0.5 h; S32 rinses the metal nickel substrate after molten salt activation treatment with ethanol and vacuum dries it to obtain the final electrode. The surface of the final electrode is a porous nanorod structure with a pore size of 5~30nm. Its material properties are nickel tungstate co-doped with zinc, bismuth and chlorine, with zinc doped at the nickel site, bismuth doped at the tungsten site, and chlorine doped at the oxygen site.

[0052] Example 3 The method for preparing an electrode using a nickel sheet as a metal nickel substrate is as follows: S11: ultrasonically clean the nickel sheet in acetone solution for 10 minutes, and then repeatedly clean it with ethanol to remove the grease layer on the metal surface; S12: The nickel sheet after the grease layer on the metal surface is removed is placed in a hydrochloric acid solution with a concentration of 1 mol / L and ultrasonicated for 25 minutes, and then allowed to stand for 10 minutes. The nickel sheet is then repeatedly washed with distilled water to remove the oxide layer on the metal surface. After drying, the nickel sheet with a clean surface is obtained.

[0053] S21: placing the nickel sheet after surface cleaning in a hydrothermal reactor containing a mixed solution of 36 mmol / L ammonium tungstate and 52 mmol / L ammonium fluoride, wherein the solvent comprises water and ethylene glycol in a volume ratio of 1:1.5, and the filling degree of the reactor is 75%. The hydrothermal reactor is heated to 90° C. and maintained for 0.5 h. S22 rinses the nickel sheet after the hydrothermal reaction with distilled water and dries it to obtain a nickel sheet after tungstate corrosion treatment. The surface of the metal nickel substrate after tungstate corrosion treatment is a smooth nanorod-like structure with a length of 0.5~400µm and a diameter of 20~40nm, and its material property is nickel tungstate.

[0054] S31: activating the nickel substrate after tungstate etching in a molten salt of bismuth chloride, zinc chloride, and metallic zinc under inert atmosphere, wherein the mass percentage of zinc element is 64%, the mass percentage of bismuth element is 45%, and the molten salt temperature is 340°C, and maintained at this temperature for 2.8 hours; S32 rinses the metal nickel substrate after molten salt activation treatment with ethanol and vacuum dries it to obtain the final electrode. The surface of the final electrode is a porous nanorod structure with a pore size of 5~30nm. Its material properties are nickel tungstate co-doped with zinc, bismuth and chlorine, with zinc doped at the nickel site, bismuth doped at the tungsten site, and chlorine doped at the oxygen site.

[0055] Example 4 The method for preparing an electrode using nickel foam as a metal nickel substrate is as follows: S11: The nickel foam was ultrasonically cleaned in an acetone solution for 25 min, and then repeatedly cleaned with ethanol to remove the grease layer on the metal surface; S12: The nickel foam after removing the grease layer on the metal surface is placed in a hydrochloric acid solution with a concentration of 3 mol / L and ultrasonicated for 10 minutes, and then allowed to stand for 25 minutes, and then repeatedly washed with distilled water to remove the oxide layer on the metal surface. After drying, the nickel foam after the surface cleaning treatment is obtained.

[0056] S21: placing the surface-cleaned nickel foam in a hydrothermal reactor containing a mixed solution of 40 mmol / L ammonium tungstate, 16 mmol / L potassium tungstate, 24 mmol / L potassium fluoride, and 14 mmol / L ammonium fluoride, wherein the solvent comprises water and ethylene glycol in a volume ratio of 1:1.5, and the filling degree of the reactor is 60%. The hydrothermal reactor is heated to 150° C. and maintained for 6.5 hours. S22 rinses the nickel foam after the hydrothermal reaction with distilled water and dries it to obtain a nickel mesh after tungstate corrosion treatment. The surface of the metal nickel substrate after tungstate corrosion treatment is a smooth nanorod-like structure with a length of 0.5~400µm and a diameter of 20~40nm, and its material property is nickel tungstate.

[0057] S31: activating the nickel substrate after tungstate etching in a molten salt of bismuth chloride, zinc chloride, and metallic zinc under an inert atmosphere, wherein the mass percentage of zinc is 25%, the mass percentage of bismuth is 34%, and the temperature of the molten salt is 200° C., and maintaining the molten salt at this temperature for 6.5 hours; S32 The nickel substrate after molten salt activation was rinsed with ethanol and vacuum dried to obtain the final electrode. The scanning electron microscope image of a certain area of the electrode surface material is as follows: Figure 2 As shown, the transmission electron microscope image of a single nanorod in a certain area of the surface material is as follows Figure 3The electrode surface finally obtained is a porous nanorod-like structure with a pore size of 5 to 30 nm. Its material properties are nickel tungstate co-doped with zinc, bismuth, and chlorine, with zinc doped at nickel sites, bismuth doped at tungsten sites, and chlorine doped at oxygen sites.

[0058] Comparative Example 1 This comparative example 1 directly uses 40 mesh plain nickel mesh as the electrode: A 40-mesh plain nickel mesh was ultrasonically cleaned in acetone solution for 20 minutes, and then repeatedly cleaned with ethanol to remove the grease layer on the surface of the nickel mesh; S12: The nickel mesh after removing the surface grease layer is placed in a 4 mol / L hydrochloric acid solution for ultrasonic treatment for 15 minutes, and allowed to stand for 20 minutes. The mesh is then repeatedly washed with distilled water to remove the oxide layer on the metal surface, and dried to obtain a clean nickel mesh.

[0059] Comparative Example 2 Comparative Example 2 directly uses nickel foam as the electrode: The nickel foam was placed in an acetone solution for ultrasonic cleaning for 30 min, and then repeatedly cleaned with ethanol to remove the grease layer on the surface of the nickel foam; S12: The nickel foam after removing the surface grease layer is placed in a hydrochloric acid solution with a concentration of 6 mol / L and ultrasonicated for 5 minutes, and then allowed to stand for 30 minutes, and then repeatedly washed with distilled water to remove the metal surface oxide layer, and dried to obtain a clean nickel foam.

[0060] Comparative Example 3 This comparative example 3 directly uses nickel sheets as electrodes: The nickel sheet was ultrasonically cleaned in acetone solution for 10 min, and then repeatedly cleaned with ethanol to remove the grease layer on the surface of the nickel sheet; S12: The nickel sheet after removing the surface grease layer is placed in a hydrochloric acid solution with a concentration of 1 mol / L and ultrasonicated for 25 minutes, and then allowed to stand for 10 minutes. It is then repeatedly washed with distilled water to remove the oxide layer on the metal surface, and dried to obtain a clean nickel sheet.

[0061] Comparative Example 4 In this comparative example 4, nickel foam was used as the metal nickel substrate, and only surface cleaning and tungstate etching were performed to prepare the electrode: S11: The nickel foam was ultrasonically cleaned in an acetone solution for 25 min, and then repeatedly cleaned with ethanol to remove the grease layer on the metal surface; S12: The nickel foam after removing the grease layer on the metal surface is placed in a hydrochloric acid solution with a concentration of 3 mol / L and ultrasonicated for 10 minutes, and then allowed to stand for 25 minutes, and then repeatedly washed with distilled water to remove the oxide layer on the metal surface. After drying, the nickel foam after the surface cleaning treatment is obtained.

[0062] S21: placing the surface-cleaned nickel foam in a hydrothermal reactor containing a mixed solution of 40 mmol / L ammonium tungstate, 16 mmol / L potassium tungstate, 24 mmol / L potassium fluoride, and 14 mmol / L ammonium fluoride, wherein the solvent comprises water and ethylene glycol in a volume ratio of 1:1.5, and the filling degree of the reactor is 60%. The hydrothermal reactor is heated to 150° C. and maintained for 6.5 hours. S22 rinses the nickel foam after the hydrothermal reaction with distilled water and dries it to obtain a nickel mesh after tungstate corrosion treatment. The surface of the metal nickel substrate after tungstate corrosion treatment is a smooth nanorod-like structure with a length of 0.5~400µm and a diameter of 20~40nm, and its material property is nickel tungstate.

[0063] Analysis of electrode catalytic performance: The electrodes obtained in Examples 1 to 4 and Comparative Examples 1 to 4 were tested for hydrogen evolution in alkaline water electrolysis using a linear voltammetric sweep test method. The test used a three-electrode system, with the electrodes obtained in each Example and Comparative Example as the working electrode, mercury / mercuric oxide as the reference electrode, and a graphite sheet as the auxiliary electrode. The electrolyte used was 1 mol / L potassium hydroxide, and the scan rate was 5 mV / s over a scan range of -0.8 volts to -1.75 volts. The hydrogen evolution electrocatalytic performance was tested on an electrochemical workstation (CHI760E, Shanghai Chenhua Instrument Co., Ltd.). The test results correspond to Table 1.

[0064] Table 1 Overpotential of hydrogen evolution reaction at different test electrodes at a certain current density Test electrocatalyst preparation source Overpotential at a current density of 100 mA / cm² (unit: volts, relative to the reversible hydrogen electrode) Potential increase after 80 hours of continuous hydrogen evolution reaction at a current density of 100 mA / cm² (unit: millivolts, relative to the reversible hydrogen electrode) Example 1 0.211 35 Example 2 0.196 33 Example 3 0.303 43 Example 4 0.161 3 Comparative Example 1 0.522 129 Comparative Example 2 0.432 96 Comparative Example 3 0.771 147 Comparative Example 4 0.362 80 The data in Table 1 show that the hydrogen evolution reaction performance of the electrodes prepared using various nickel substrates in the relevant examples was significantly improved compared to the comparative electrodes based on pristine metal substrates. In particular, the electrodes prepared using nickel foam exhibited an overpotential of only 0.161 volts at a current density of 100 milliamperes per square centimeter, a decrease of 0.271 volts compared to the pure nickel foam electrode and 0.201 volts compared to the electrode prepared only after surface cleaning and tungstate etching. Furthermore, the overpotential of the electrode prepared using nickel foam increased by only 3 millivolts after 80 hours of continuous oxygen evolution reaction.

[0065] Compared with the prior art, the method for preparing a cathode material for alkaline water electrolysis based on molten salt activation provided by the present invention and the cathode material prepared therefrom have at least one or at least part of the following advantages: 1) Based on the solid-liquid reaction, the surface material is co-doped with anions and cations, and anions of chlorine and cations of zinc and bismuth are introduced into nickel tungstate. At the same time, nanostructure modification is performed, which greatly improves the intrinsic catalytic activity.

[0066] 2) The method is simple in process, does not require the introduction of external nickel ions, has low cost, and is suitable for production promotion.

[0067] While embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions, and variations may be made to these embodiments without departing from the principles and spirit of the invention, and that the scope of the invention is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a cathode material for alkaline water electrolysis based on molten salt activation, characterized in that: The preparation method comprises the following steps: S1. Tungstate etching treatment: A metal nickel substrate is subjected to a solvent thermal reaction-based etching treatment in a mixed solution containing tungstate and fluoride to form a smooth nanorod-like structure of nickel tungstate on the surface of the metal nickel substrate to obtain a nickel-based composite material; S2. Molten salt activation treatment: Under the protection of an inert atmosphere, the nickel-based composite material is placed in a molten salt for a solid-liquid reaction, so that the zinc, bismuth and chlorine in the molten salt are co-doped into the nickel tungstate to obtain the cathode material for alkaline water electrolysis.

2. The method according to claim 1, characterized in that The metal nickel substrate is one of nickel mesh, nickel foam and nickel sheet.

3. The method according to claim 1, characterized in that In the mixed solution containing tungstate and fluoride, the solvent is a mixed solution of water and ethylene glycol, the concentration of tungstate is 12-76 mmol / L, and the concentration of fluoride is 9-52 mmol / L.

4. The method according to claim 1, wherein The tungstate is any one of ammonium tungstate, sodium tungstate and potassium tungstate, or any combination thereof; The fluoride is any one of ammonium fluoride, sodium fluoride and potassium fluoride or any combination thereof; The inert atmosphere is any one of nitrogen and argon or any combination thereof.

5. The method according to claim 1, wherein The molten salt is formed by mixing bismuth chloride, zinc chloride and metallic zinc, wherein the mass percentage of zinc element is 25% to 70% and the mass percentage of bismuth element is 15% to 45%.

6. The method according to claim 1, characterized in that The S1 step specifically includes placing a metal nickel substrate in a hydrothermal kettle containing a mixed solution of tungstate and fluoride, wherein the filling degree of the hydrothermal kettle is 50% to 85%, heating the hydrothermal kettle to 90 to 180° C. for reaction, and the reaction time is 0.5 to 13 hours.

7. The method according to claim 1, characterized in that The length of the smooth nanorod-like structure is in the range of 0.5-400 μm, and the diameter is in the range of 20-40 nm.

8. The method according to claim 1, characterized in that The temperature of the solid-liquid reaction is 200-480° C., and the time is 0.5-6.5 h.

9. The method according to claim 1, characterized in that The surface material of the cathode material for alkaline water electrolysis presents a porous nanorod-like structure, and the pore diameter of the porous nanorod-like structure is in the range of 5 to 30 nm.

10. A cathode material for alkaline water electrolysis prepared by the method according to any one of claims 1 to 9.

Images