A nickel-iron-phosphorus-tungsten electrode material and its preparation method

Abstract

The present invention provides a nickel-iron phosphorus-tungsten electrode material and a preparation method thereof. The high-stability iron-nickel-phosphorus-tungsten electrode material is characterized in that it uses a nickel-iron mesh as a substrate, and a catalytic-protective composite layer of nickel-iron phosphate, tungstate, and hydroxide is in situ loaded on the nickel-iron surface. The nickel-iron phosphorus-tungsten electrode material is prepared by the following method: first, the nickel-iron mesh substrate is subjected to alkaline degreasing and pickling to remove oxides, and then electrochemical polarization treatment is performed in a solution containing a certain concentration of potassium phosphate, sodium tungstate, and potassium hydroxide to obtain a composite layer with insoluble tungstate, phosphate, and hydroxide loaded on the surface. The material shows that the nickel-iron hydroxide formed by electrochemical treatment improves the electrocatalytic oxygen evolution activity, while the insoluble tungstate and phosphate improve the corrosion resistance of the material, especially avoiding the dissolution of iron and nickel. As an electrolytic water electrode and oxygen evolution electrode, the material has the advantages of high electrocatalytic activity and good stability.

Description

Technical Field

[0001] The present invention relates to the field of hydrogen energy technology, and in particular to a nickel-iron-phosphorus-tungsten electrode material and a preparation method thereof. Background Art

[0002] Hydrogen production by water electrolysis is an important way to obtain green hydrogen in the future. There are four ways to produce hydrogen by water electrolysis: proton exchange membrane electrolysis, alkaline water electrolysis, alkaline anion exchange membrane electrolysis, and solid oxide electrolysis. In proton exchange membrane electrolysis, since the electrocatalyst works in a strongly acidic proton environment, corrosion-resistant precious metals such as Pt / Ir / Ru have to be used. However, the scarcity and high cost of these precious metal catalysts limit the large-scale utilization of proton exchange membrane electrolysis for hydrogen production. Alkaline water electrolysis is the main method for commercial hydrogen production at present. It has the significant advantages of not requiring precious metal catalysts, high scalability, and relatively low cost. However, the current density on the nickel electrodes commonly used in alkaline water electrolyzers is low, and the overpotential is relatively high, resulting in high power consumption and low hydrogen production rate per unit volume.

[0003] In order to further improve the oxygen evolution performance of nickel-based materials, adding iron into nickel-based materials is an effective way to improve oxygen evolution performance. Chinese patent CN202210686366.3 reports a method for preparing a nickel-iron alloy high-efficiency oxygen evolution electrode. This invention prepares a Ni-Fe oxygen evolution electrode with a uniform and stable structure and composition by optimizing the main salt concentration ratio, electrodeposition density, time and temperature parameters. Chinese invention patent CN202110090706.1 discloses an electrode treated with hydrothermal oxidation under alkaline conditions and its preparation method. It mainly hydrothermally oxidizes a metal nickel-iron alloy substrate under alkaline conditions to obtain an electrode with a surface of a nickel-iron combined oxidation state substance, thereby improving the oxygen evolution activity of the nickel-iron electrode. In addition, there is also a document (ACSSustainable Chem. Eng. 2018, 6, 6, 7206-7211) reporting that a nanostructured bimetallic phosphide NiFeP with a size of several nanometers was synthesized by pyrolysis of nickel salt, iron salt, graphene oxide and an organic phosphorus source at 850°C in a hydrogen atmosphere and exhibited no oxygen evolution activity.

[0004] Industrial alkaline water electrolysis requires more stringent operating conditions than laboratory research, requiring nickel-iron oxygen evolution electrodes to operate at high current densities for extended periods in strong alkaline solutions above 30% at temperatures exceeding 80°C. Current electrode materials, typically in the form of nickel-iron oxides, metals, or hydroxides, particularly high-surface-area nanopowders, suffer from slow dissolution of the iron element under actual electrolysis conditions, leading to electrolyte degradation and reduced hydrogen production performance in the electrolyzer. Iron and nickel dissolution is particularly pronounced in weakly alkaline solutions with a pH between 7 and 13. Summary of the Invention

[0005] In light of this, the present invention provides a nickel-iron-phosphorus-tungsten electrode material and a preparation method thereof. The electrode material is characterized by a nickel-iron mesh as a substrate, with an in-situ composite catalytic-protective layer of nickel-iron phosphate, tungstate, and hydroxide loaded on the nickel-iron surface. The nickel-iron composite hydroxide enhances the oxygen evolution activity of the nickel-iron mesh material, while the insoluble tungstate and phosphate enhance the material's corrosion resistance, significantly preventing the dissolution of the iron and nickel catalytic elements and improving oxygen evolution stability.

[0006] The nickel-iron mesh is a nickel-iron alloy woven mesh, a nickel-iron foam mesh, or an iron-nickel-plated mesh, and is a commercial base material. The nickel content of the nickel-iron mesh as the base material is ≥50%.

[0007] The nickel-iron surface is in situ loaded with a nickel-iron phosphate, tungstate, and hydroxide catalytic-protective composite layer. In this layer, the phosphate is iron phosphate and nickel phosphate; the tungstate is nickel tungstate and iron tungstate; the composite hydroxide is nickel-iron composite hydroxide, and the total mass content of nickel in the substrate and the surface layer is ≥45%.

[0008] In order to achieve the above-mentioned purpose of the invention, the nickel-iron-phosphorus-tungsten electrode material is prepared by the following method:

[0009] 1) First, alkaline degreasing and pickling of the nickel-iron mesh are performed. Use acetone or sodium carbonate-sodium hydroxide as the degreasing solution for 10-30 minutes at room temperature to 80°C. Pickling is performed with 0.1-1M HCl at room temperature for 5-30 minutes to remove surface oxides.

[0010] 2) The degreased and pickled nickel-iron mesh is then subjected to electrochemical polarization treatment in a mixed solution of potassium phosphate, sodium tungstate, and potassium hydroxide, wherein the potassium phosphate concentration ranges from 0.05 to 2 M, the sodium tungstate concentration ranges from 0.01 to 0.5 M, and the potassium hydroxide concentration ranges from 0.05 to 5 M. The electrochemical polarization treatment employs cyclic voltammetry or square wave amperometry; the cyclic voltammetry method employs a voltage range of -1.0 V ≤ U ≤ 1.0 V relative to a saturated calomel electrode; the scan rate range is 5 to 100 mV / s, and the number of cycles is 10 to 30; the current density range of the square wave amperometry method is 10 to 200 mA / cm 2 , the number of cycles is 5 to 30, and the single cycle time is 1 to 10 minutes;

[0011] 3) The electrode after the electrochemical treatment is rinsed with deionized water and then dried at 30-90° C. to obtain the nickel-iron-phosphorus-tungsten electrode material prepared by the present invention.

[0012] In this preparation method, the concentration of one of potassium phosphate and sodium tungstate in step 2 is ≤ 0.1M. In this way, in the prepared material, one of nickel phosphate, iron phosphate, or nickel tungstate, or iron tungstate is the main component of the composite layer protective component. In step 2, only one of potassium phosphate and sodium tungstate can also be added. In this way, in the prepared material, one of nickel phosphate, iron phosphate, or nickel tungstate, or iron tungstate is the protective component of the composite layer.

[0013] In this preparation method, potassium phosphate can be replaced by dipotassium hydrogen phosphate, potassium dihydrogen phosphate, sodium phosphate, disodium hydrogen phosphate, or sodium dihydrogen phosphate. Sodium tungstate can be replaced by potassium tungstate. Potassium hydroxide can be replaced by sodium hydroxide.

[0014] In this preparation method, the nickel and iron in the catalytic layer originate from the nickel-iron metal mesh substrate itself. During electrochemical polarization treatment of the nickel-iron metal mesh, phosphate, tungstate, and hydroxide react with the nickel and iron in the matrix to form iron phosphate, nickel phosphate, nickel tungstate, iron tungstate, and nickel-iron composite hydroxide. The nickel-iron composite hydroxide enhances the oxygen evolution activity of the nickel-iron metal mesh material, while the sparingly soluble phosphates and tungstates improve the material's corrosion resistance, particularly by significantly preventing the dissolution of the iron and nickel catalytic elements and enhancing its stability in weakly alkaline and strongly alkaline electrolytes.

[0015] The nickel-iron-phosphorus-tungsten electrode material prepared by the present invention can be used as an oxygen evolution anode in weakly alkaline and strongly alkaline electrolytes with a pH greater than 7. This includes oxygen evolution reactions in solutions with a pH greater than 7, such as sodium carbonate, sodium bicarbonate, potassium phosphate, and dipotassium hydrogen phosphate. The nickel-iron-phosphorus-tungsten electrode material prepared by the present invention can improve the activity of the oxygen evolution reaction in these electrolytes, particularly improving the long-term stability of the nickel-iron electrode. DETAILED DESCRIPTION

[0016] The technical solutions of the present invention will be described clearly and completely below in conjunction with the embodiments of the present invention, but they should not be understood as limiting the scope of protection of the present invention.

[0017] Example 1

[0018] A 100mm x 100mm nickel-iron alloy mesh was ultrasonically degreased in a mixed solution of 40g / L sodium carbonate and 20g / L sodium hydroxide at room temperature for 15 minutes. The residual degreasing solution was then rinsed with deionized water. The degreased nickel-iron alloy mesh was then pickled in a 1M HCl solution at room temperature for 5 minutes. After pickling, the twill iron mesh was rinsed with deionized water and air-dried. Using the degreased and pickled nickel-iron alloy mesh as the working electrode and a nickel mesh as the counter electrode, a square wave current of ±50mAcm⁻² was applied in a mixture of 1M potassium phosphate, 0.2M sodium tungstate, and 0.1M potassium hydroxide for 20 cycles. After the square wave current treatment, the mesh was rinsed with deionized water and then dried at 60°C to obtain the nickel-iron-phosphorus-tungsten-nickel-iron alloy mesh electrode material.

[0019] The nickel-iron-phosphorus-tungsten-nickel-iron alloy mesh electrode material prepared in this example was used to evaluate oxygen evolution performance. In a 1M potassium carbonate-0.1M dipotassium hydrogen phosphate solution, the reference saturated calomel electrode potential was 1.0V, and the current density was >550mA / cm 2 , and the current density is maintained at >96% over time in a 200-hour experiment; in a 1M potassium hydroxide solution, when the reference saturated calomel electrode potential is 1.0V, the current density is >1000mA / cm 2 , and the current density retention rate over time is >96% in a 200-hour experiment; this shows that the nickel-iron-phosphorus-tungsten electrode material prepared in this embodiment exhibits the characteristics of high current density and high stability in both weakly alkaline and strongly alkaline electrolytes.

[0020] Example 2

[0021] A nickel-iron foam mesh with a size of 100 mm * 100 mm was used as the substrate. The degreasing and pickling were consistent with Example 1. The nickel-iron foam after degreasing and pickling was used as the working electrode and the nickel mesh was used as the auxiliary electrode. In a mixed solution containing 0.1 M potassium phosphate-0.1 M sodium tungstate-1 M potassium hydroxide, a cyclic voltammetric scan was performed with a reference saturated calomel electrode at -0.7 to 0.7 V, with a scan rate of 10 mVs -1 , cycle number 20; after the cyclic voltammetry treatment, the material was rinsed with deionized water and then dried at 60°C to obtain a nickel-iron-phosphorus-tungsten-foam nickel-iron electrode material.

[0022] The nickel-iron-phosphorus-tungsten-nickel-iron foam electrode material prepared in this example was used to evaluate its oxygen evolution performance. In a 1M potassium bicarbonate-0.1M dipotassium hydrogen phosphate mixed weak alkaline solution, the reference saturated calomel electrode potential was 1.0V, and the current density was >420mA / cm 2 , and the current density is maintained at >96% over time in a 200-hour experiment; in a 1M potassium hydroxide solution, when the reference saturated calomel electrode potential is 1.0V, the current density is >980mA / cm2 , and the current density retention rate over time is >96% in a 200-hour experiment; this shows that the nickel-iron-phosphorus-tungsten electrode material prepared in this embodiment exhibits the characteristics of high current density and high stability in both weakly alkaline and strongly alkaline electrolytes.

[0023] Example 3

[0024] This embodiment is a comparative example. The nickel-iron foam is commercially available nickel-iron foam. A nickel-iron foam alloy with a size of 100mm*100mm is degreased and pickled. The oxygen evolution performance of the nickel-iron foam electrode after degreasing and pickling is evaluated. In a 1M potassium bicarbonate-0.1M dipotassium hydrogen phosphate solution, when the reference saturated calomel electrode potential is 1.0V, the current density is less than 300mA / cm2, and the current density decreases by more than 10% over time in a 200-hour experiment; in a 1M potassium hydroxide solution, when the reference saturated calomel electrode potential is 1.0V, the current density is less than 780mA / cm2, and the current density retention rate is about 95% over time in a 200-hour experiment; by comparing implementations 1 and 2 with this embodiment, it is shown that the nickel-iron phosphorus tungsten electrode material prepared by the present invention exhibits the advantages of higher current density and stronger stability than commercial nickel-iron electrodes in both weakly alkaline and strongly alkaline electrolytes.

[0025] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for preparing a nickel-iron-phosphorus-tungsten electrode material, wherein the material is based on a nickel-iron mesh and a catalytic-protective composite layer of nickel-iron phosphate, tungstate, and hydroxide is in situ loaded on the nickel-iron surface; the method for preparing the nickel-iron-phosphorus-tungsten electrode material is characterized by: 1) First, the nickel iron mesh is alkaline degreasing and pickling to remove surface oxides; 2) subjecting the nickel-iron mesh to an electrochemical polarization treatment in a mixed solution of potassium phosphate, sodium tungstate, and potassium hydroxide to form a catalytic-protective composite layer, wherein the electrochemical polarization treatment is cyclic voltammetry or square wave current method; 3) After the electrochemical treatment is completed, the nickel-iron-phosphorus-tungsten electrode material is washed with water and dried.

2. The method for preparing a nickel-iron-phosphorus-tungsten electrode material according to claim 1, characterized in that: The nickel-iron mesh is a nickel-iron alloy woven mesh, a foamed nickel-iron mesh or an iron-nickel-plated mesh, and is a commercial base material. The nickel content of the nickel-iron mesh as the base material is ≥50%.

3. The method for preparing a nickel-iron-phosphorus-tungsten electrode material according to claim 1, characterized in that: The phosphate is iron phosphate or nickel phosphate; the tungstate is nickel tungstate or iron tungstate; the composite hydroxide is nickel-iron composite hydroxide, and the total mass percentage of nickel in the substrate and the surface layer is ≥45%.

4. The method for preparing a nickel-iron-phosphorus-tungsten electrode material according to claim 1, characterized in that: In step 2 of the preparation method, the concentration range of potassium phosphate is 0.05-2M, the concentration range of sodium tungstate is 0.01-0.5M, and the concentration range of potassium hydroxide is 0.05-5M.

5. The method for preparing a nickel-iron-phosphorus-tungsten electrode material according to claim 1, characterized in that: The cyclic voltammetry method is based on a voltage range of -1.0V≤U≤1.0V for the reference saturated calomel electrode; a scan rate range of 5-100mV / s, and a cycle number of 10-30; and a current density range of 10-200mA / cm 2 , the number of cycles is 5 to 30, and the single cycle time is 1 to 10 minutes.

6. The method for preparing a nickel-iron-phosphorus-tungsten electrode material according to claim 1, characterized in that: The electrode material can be used as an oxygen evolution anode in electrolyzing weakly alkaline or strongly alkaline electrolytes with a pH greater than 7.