Preparation method of vanadium-containing transition metal hydroxide electro-catalysis electrode

Abstract

The invention discloses a preparation method of a vanadium-containing transition metal hydroxide electro-catalysis electrode, and relates to the technical field of electro-catalysis, and the preparation method specifically comprises the following steps: on a porous nickel or titanium electrode, by taking metavanadate as a V < 5 + > ion source, adding a reducing agent, mixing with an aqueous solution of nickel salt and iron salt, and carrying out cathode reduction electro-deposition to obtain NiFeV-OxHy and Ni (H2O) 2V2O6; the preparation method comprises the following steps of: performing electrochemical cyclic voltammetry scanning activation on an electrode for multiple times under an alkaline condition, so that vanadium ions are dissolved out and deposited for multiple times, low-valence V < 3 + > ions are gradually oxidized, a catalyst structure is reconstructed and optimized, and a small amount of V < 4 + > ions are doped into a NiOOH and / or FeOOH layer to replace Ni < 3 + > and / or Fe < 3 + > ions; and high-valence V < 5 + > ions are dissolved out, and a large number of oxygen vacancies are introduced into NiOOH and FeOOH layers, so that the catalyst can start an LOM mechanism when catalyzing an OER reaction, and shows very high electrochemical catalytic activity.

Description

Technical Field

[0001] The present invention relates to the technical field of electrocatalysis, and particularly to a preparation method of an electrocatalytic electrode of vanadium-containing transition metal hydroxide. Background Art

[0002] In the electrolysis of water to produce hydrogen in an alkaline aqueous solution, the oxygen evolution reaction (OER: 4OH -→ O2 + H2O + 4e, E o = +0.40V vs.SHE ) of the anode can use 3d transition metal hydroxides in the second half cycle to replace platinum-group-metal (PGM) as a catalyst, thus making the electrolytic water device show better cost advantages. The most common non-PGM catalyst is nickel-iron layered double metal hydroxide NiFe-LDHs. Layered double metal hydroxide (LDH) has a hydrotalcite-like structure of magnesium-aluminum carbonate Mg6Al2(OH) 16 CO3 2- ˙4H2O structure, and its chemical general formula is expressed as: , where the value of x (i.e., the molar ratio) is between 0.17 and 0.33, and a complete LDH structure cannot be obtained if x exceeds this range. In the LDH used as an OER catalyst, M 2+ is usually Ni 2+ , Co 2+ , Cu 2+ , Mg 2+ , and M 3+ is Fe 3+ , Al 3+ , Cr 3+ , etc. Usually, higher-valent metal elements, such as Mn (+4 valence), V (+5 valence), etc., are not common in LDH, but sometimes appear as doping elements in the LDH structure in small amounts.

[0003] During the electrochemical decomposition of water, the OER reaction involves a 4-electron transfer process and is the rate-determining step of the overall water electrolysis reaction. Therefore, improving the electrocatalytic activity of OER catalysts is the key to enhancing the energy efficiency of the entire electrolytic cell. Modifying the electronic states near the Fermi level of the active-site atoms of OER catalysts is crucial for achieving efficient electron transfer. Currently, there are two widely recognized OER electron transfer pathways: one is the reactant adsorption and desorption mechanism (*OH→*O→*OOH→*O2 process) with metal as the redox center (adsorbate evolution mechanism, AEM); the other is the redox and migration of the catalyst's own lattice oxygen under OER potential (lattice oxygen oxidation mechanism, LOM). Currently, the design of the vast majority of OER catalysts or the explanation of their electrocatalytic activity is based on the traditional AEM mechanism. Since AEM involves multiple oxygen reaction intermediates, such as *OH, *O, and *OOH, and the binding energies of the intermediates are linearly correlated and follow the proportional relationship ΔG OOH =ΔG OH +3.2±0.2 eV, that is, the binding energy of each intermediate cannot be independently adjusted. Therefore, a relatively high overpotential η is required to drive the reaction. The theoretical limit of η calculation is approximately 370±100 mV. For industrial water electrolysis hydrogen production devices, it is desired that the electrolytic cell can operate at a high current density and a low polarization potential. Therefore, it is necessary to break through this theoretical limit of the AEM mechanism, and thus the LOM mechanism has received attention. Due to the participation of lattice oxygen, the LOM mechanism can bypass the limitation of forming OOH*, and theoretically has faster reaction kinetics.

[0004] For NiFe-LDH catalysts, the main body is the NiOOH layered structure, and Fe 3+ is the catalytic active site. The method to improve the activity of NiFe-LDH catalysts is to adjust the d-orbital electronic states of the active metals (such as Fe 3+ ) by doping and creating defects. Vanadium has multiple valence states such as +2, +3, +4, and +5. Replacing Fe 3+ ions in NiFe-LDH catalysts with V 3+ ions can also obtain highly active catalysts with a layered double metal hydroxide structure, such as Ni 0.75 V 0.25-LDH catalyst. However, according to the Eh-pH diagram (Pourbaix diagram) of vanadium, V 3+ ions cannot exist stably at the anodic oxygen evolution potential (> +0.40 V vs.SHE ), and are easily oxidized to V 4+ and V 5+ ions. Under medium to strong alkaline (pH > 10) conditions, V 4+ ions can exist in the form of [HV2O 5 - , and V 5+ ions will form complex ions [VO(OH)3] – and dissolve (Literature 2: J. Krakowiak, D. Lundberg, I. Persson, A Coordination Chemistry Study of Hydrated and Solvated Cationic Vanadium Ions in Oxidation States +III, +IV, and +V in Solution and Solid State, Inorg. Chem. 2012, 51, 18, 9598–9609). Some studies have shown that in the vanadium-doped β-FeOOH catalyst, V exists stably in the +4 valence state under strong alkaline conditions (Literature 3: F.N.I. Sari, H.S. Chen, A.K. Anbalagan, et al., V-doped, divacancy-containing β-FeOOH electrocatalyst for high performance oxygen evolution reaction, Chem. Eng. J. 2022, 438, 135515).

[0005] When preparing a vanadium-doped OER electrocatalyst with an LDH structure, generally +3-valent vanadium salts are used. A large number of studies have shown that the decline in the activity of the NiFe-LDH catalyst is related to the cycle of dissolution and precipitation of Fe at the anodic oxygen evolution potential, which causes irreversible dynamic reconstruction of the LDH structure, leading to the destruction of the LDH structure and the decline in the performance of the catalyst. The preliminary experiment of the present invention found that under alkaline conditions, V 3+ ions in the NiV-LDH catalyst are easily lost due to dissolution. Although the initial activity of the NiV-LDH catalyst is higher than that of the NiFe-LDH catalyst, the decline is faster than that of the traditional NiFe-LDH catalyst.

[0006] ​Based on the above knowledge, the present invention adopts a new method for preparing a catalytic electrode: starting from a vanadium salt with a valence of +5, first performing cathodic reduction under weak acid conditions to obtain V 3+ and V 4+ ions, and co-depositing them together with Ni 2+ , Fe 3+ and other ions to obtain a metal hydroxide catalyst co-doped with vanadium ions of +5, +4, and +3 valence in-situ grown on a metal cathode. Due to the presence of +4 and +5 valence vanadium ions, the deposit generally does not have the LDH structure and is often a hydrate of various metal ion oxides and hydroxides. Subsequently, this primary electrodeposit is activated by cyclic voltammetry multiple times under medium-strong base conditions to oxidize vanadium, increase its valence state, and at the same time lose low-valence vanadium ions V 3+ , generating an intermediate product similar to Fe5 III V3 IV V 12 V O 39 (OH)9∙9H2O. Continuing the activation, V 5+ ions become soluble complex ions and dissolve out, and the catalyst structure is reconstructed to form microcrystals with a structure similar to iron hydroxide (FeOOH) or nickel hydroxide (NiOOH) with a large number of oxygen vacancies. This V 4+ -doped catalyst with a large number of oxygen vacancies (denoted as V O ) has high electrochemistry activity. Summary of the Invention

[0007] The purpose of the present invention is to provide a method for preparing an electrocatalytic electrode of a vanadium-containing transition metal hydroxide.

[0008] To solve the problems raised in the above background technology, the present invention provides the following technical solution: A method for preparing an electrocatalytic electrode of a vanadium-containing transition metal hydroxide, the preparation method of the electrocatalytic electrode specifically includes the following steps: Step 1: Prepare an electrodeposition solution using a metavanadate containing VO 3- and a transition metal salt; Step 2: Use a strong reducing agent to reduce VO 3- to V 3+ ; Step 3: Add an appropriate amount of dilute acid solution to make the electrodeposition solution acidic; Step 4: Use a conductive substrate material as the working electrode, and use a three-electrode system to perform cathodic electrodeposition on the working electrode. After the deposition is completed, take out the working electrode loaded with the deposit, wash it with deionized water for more than 10 seconds, and obtain a self-supporting three-dimensional vanadium-containing transition metal hydroxide electrocatalytic electrode after drying; Step 5: Use the prepared self-supporting three-dimensional vanadium-containing transition metal hydroxide electrocatalytic electrode as the working electrode, and use a three-electrode system to electrochemically activate the working electrode. After the electrochemical activation is completed, take out the working electrode, wash it with deionized water for more than 10 seconds, and obtain the activated self-supporting three-dimensional vanadium-containing transition metal hydroxide electrocatalytic electrode after drying.

[0009] In an embodiment of the present invention: in the said Step 1, the metavanadate is selected from NaVO3, the transition metal salts are selected from two transition metal salts other than V salts, and the molar concentration of the transition metal salts in the electrodeposition solution is greater than 50 mmol / L. In 100 ml of the electrodeposition solution, the electrodeposition solution VxAyBz composed of x mmol of metavanadate V and y mmol of a certain transition metal salt A other than V and z mmol of another transition metal salt B other than V, x + y + z > 5.

[0010] In an embodiment of the present invention: in the said Step 2, the selection of the strong reducing agent includes but is not limited to NaBH4, NH3BH3, H3BO3, and the molar mass of the strong reducing agent is more than 0.1 mmol more than the molar mass of the metavanadate.

[0011] In an embodiment of the present invention: in the said Step 3, dilute hydrochloric acid is selected as the dilute acid, and the concentration of the dilute acid is preferably 3 mol / L.

[0012] In an embodiment of the present invention: in the said Step 3, first prepare a solution of metavanadate, then add a dilute acid solution, and then add a strong reducing agent. After the solution reaction is stable, add the transition metal salt. The amount of the added dilute acid solution is 2-5% of the total volume of the electrodeposition solution (excluding the volume of the dilute acid), specifically based on the fact that the solution is clear and transparent after adding the transition metal salt and no precipitation occurs.

[0013] In an embodiment of the present invention: in the said Step 4, the preferred conductive porous material is metal nickel or metal titanium, in the form of foam, paper, or felt, net, porous sintered sheet. Non-metallic conductive materials that are not easily reactive with dilute acid solutions such as carbon paper and carbon cloth can also be selected. Foam nickel is preferred, and the maximum projected plane area of the conductive substrate material should be less than the maximum projected plane area of the counter electrode.

[0014] In one embodiment of the present invention: in the fourth step, the method of cathodic electrodeposition on the working electrode can be one of potentiostatic deposition or galvanostatic deposition. The current density or potential set for cathodic electrodeposition on the working electrode should be determined according to cyclic voltammetry. The reduction peak current of the cyclic voltammogram is selected to determine the lower limit of the current density, and the upper limit is determined by the current without violent side reactions such as hydrogen evolution. The corresponding potential in the cyclic voltammogram is the potential required for electrodeposition. Specifically, it is based on the appearance of an obvious deposit on the surface of the conductive substrate material after a certain deposition time. Preferably, the current density ranges from -20 mA / cm 2 to -200 mA / cm 2 is used as the electrodeposition current density, and the corresponding potential in the cyclic voltammogram is used as the electrodeposition potential.

[0015] In one embodiment of the present invention: in the fourth step, the self-supporting three-dimensional vanadium-containing transition metal hydroxide electrocatalytic electrode is prepared according to the preparation method described in any one of claims 1 to 7. The three-electrode system includes a working electrode, a counter electrode, and a reference electrode. The counter electrode is preferably a platinum sheet electrode, and the reference electrode is preferably a saturated calomel electrode.

[0016] In one embodiment of the present invention: in the fifth step, the method of electrochemically activating the working electrode is as follows: using cyclic voltammetry in an alkaline solution with a pH of 13 to 14, the potential set for electrochemically activating the working electrode is preferably 0.4 V (relative to the mercury / mercuric oxide reference electrode), and it is cycled at a speed of 100 m / s for no less than 30 times.

[0017] Adopting the above technical solution, compared with the prior art, the beneficial effects of the present invention are as follows: 1. The present invention uses foams, felts, meshes or porous sintered sheets of metallic nickel or titanium as the cathode, and uses readily available vanadates as the vanadium source. Compared with trivalent vanadium salts, they are not only cheap and easy to obtain, but also can be stably stored in the atmospheric environment. After being reduced by a strong reducing agent, they form a metal salt electrodeposition solution with transition metal ions, and an oxygen evolution catalytic electrode containing vanadium transition metal hydroxide is electrodeposited on the cathode to obtain a self-supporting three-dimensional porous structure for use in devices for electrolyzing water to produce hydrogen or oxygen under alkaline conditions. Since the vanadium-containing transition metal hydroxide electrocatalyst grows in-situ on the porous electrode of nickel or titanium, different from the traditional electrode preparation process of first making a catalyst powder into an ink together with a polymer binder and spraying it on a metal electrode or a diaphragm, the method of the present invention does not require a polymer binder, and the catalyst powder grows directly on the metal electrode, greatly improving the electron transport ability during the electrocatalytic process, enabling the electrode to still have a very low ohmic polarization potential when operating at a high current density, and having the characteristics of short preparation time, mild reaction conditions, simple operation and low cost. The obtained catalyst electrode has a low internal resistance, high activity, strong binding force between the catalyst and the electrode metal matrix, and is not easy to fall off; 2. In the present invention, a strong reducing agent is used to reduce VO 3- , which can not only avoid the reaction of oxidizing vanadate with Fe, Co, Mn transition metal salts to form vanadate precipitates, but also enable vanadium to exist in the electrodeposition solution in the forms of V 3+ and V 4+ , and together with other transition metal ions, synthesize vanadium-containing transition metal hydroxides; in addition, there are a large number of +4-valent metal vanadium ions in the in-situ electrodeposited catalyst, increasing the oxygen vacancies in the catalyst, improving the current density limit of the catalyst, and reducing the reaction polarization. The catalytic electrode prepared by the method of the present invention has very high catalytic activity and very long service life, and can work at a high current density for a long time; 3. The present invention conducts electrodeposition under weak acid conditions, so it is necessary to add dilute acid to the vanadate solution to adjust the pH value. In an acidic solution, V 5+ is yellow, V 4+ is blue, and V 3+ is green. When adding hydrochloric acid, the valence state of V ions can be judged according to the solution color. The cathode electrodeposition preparation technology has simple operation, short preparation time, easy control of the catalyst morphology, low requirements for the preparation environment, and the characteristics of low energy consumption, low time consumption and low cost, and has good industrial application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 It is a schematic diagram for evaluating the oxygen evolution performance of electrolyzed water of the self-supporting three-dimensional vanadium-containing transition metal hydroxide electrocatalytic electrode obtained in Examples 1-5 of the present invention and the RuO2-coated nickel foam electrocatalytic material obtained in Comparative Example 1, using 1 mol / L KOH aqueous solution as the electrolyte; Figure 2 Schematic diagram of the electrochemical impedance spectra of the self-supported three-dimensional vanadium-containing transition metal hydroxide electrocatalytic electrodes obtained in Examples 1-5 of the present invention and the RuO2-coated nickel foam electrocatalytic material obtained in Comparative Example 1 in a 1 mol / L KOH aqueous solution; Figure 3 Schematic diagram of the X-ray diffraction spectrum of the self-supported three-dimensional vanadium-containing transition metal hydroxide electrocatalytic electrodes obtained in Examples 4-6 of the present invention; Figure 4 Scanning electron microscope photograph of the Ni3V electrocatalyst electrodeposited on a nickel foam cathode under weakly acidic conditions in Example 4 of the present invention; Figure 5 Scanning electron microscope photograph of the FeV electrocatalytic material electrodeposited on a nickel foam cathode under weakly acidic conditions in Example 5 of the present invention; Figure 6 High-resolution transmission electron microscope photograph of the Ni3V self-supported three-dimensional electrocatalytic material obtained in Example 4 of the present invention after CV activation under alkaline conditions; Figure 7 High-resolution transmission electron microscope photograph of the FeV self-supported three-dimensional electrocatalytic material obtained in Example 5 of the present invention after CV activation under alkaline conditions. Detailed implementation manners

[0019] The following further describes the detailed implementation manners of the present invention with reference to the accompanying drawings. It should be noted here that the description of these implementation manners is used to help understand the present invention, but does not limit the present invention. In addition, the technical features involved in the various implementation manners of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0020] As shown in the attached Figure 1 - attached Figure 7 As shown, a preparation method of a vanadium-containing transition metal hydroxide electrocatalytic electrode, the preparation method of the electrocatalytic electrode specifically includes the following steps: Step 1. Prepare an electrodeposition solution using a vanadate containing VO 3- and a transition metal salt; Step 2. Use a strong reducing agent to reduce VO 3- to V 3+ ; Step 3. Add an appropriate amount of dilute acid solution to make the electrodeposition solution acidic; Step 4. Use a conductive substrate material as the working electrode, and use a three-electrode system to perform cathodic electrodeposition on the working electrode. After the deposition is completed, take out the working electrode loaded with the deposit, wash it with deionized water for more than 10 seconds, and dry it to obtain a self-supported three-dimensional vanadium-containing transition metal hydroxide electrocatalytic electrode; Step 5: Use the prepared self-supporting three-dimensional vanadium-containing transition metal hydroxide electrocatalytic electrode as the working electrode, and utilize a three-electrode system to electrochemically activate the working electrode. After the electrochemical activation is completed, take out the working electrode, wash it with deionized water for more than 10 seconds, and obtain the activated self-supporting three-dimensional vanadium-containing transition metal hydroxide electrocatalytic electrode after drying.

[0021] As a further solution of the present invention: In step 1, the metavanadate is selected from NaVO3, and the transition metal salts are selected from two transition metal salts other than V salts. The molar concentration of the transition metal salts in the electrodeposition solution is greater than 50 mmol / L. In a 100 ml electrodeposition solution, the electrodeposition solution VxAyBz composed of x mmol of metavanadate V, y mmol of a certain transition metal salt A other than vanadium, and z mmol of another transition metal salt B other than vanadium, where x + y + z > 5.

[0022] As a further solution of the present invention: In step 2, the selection of the strong reducing agent includes but is not limited to NaBH4, NH3BH3, H3BO3, and the molar mass of the strong reducing agent is more than 0.1 mmol higher than that of the metavanadate.

[0023] As a further solution of the present invention: In step 3, dilute acid is selected as dilute hydrochloric acid, and the concentration of the dilute acid is preferably 3 mol / L.

[0024] As a further solution of the present invention: In step 3, first prepare a solution of metavanadate, then add the dilute acid solution, then add the strong reducing agent, and after the solution reaction is stable, add the transition metal salt. The amount of the added dilute acid solution is 2 - 5% of the total volume of the electrodeposition solution (excluding the volume of the dilute acid), specifically based on the fact that the solution is clear and transparent after adding the transition metal salt and no precipitation occurs.

[0025] As a further solution of the present invention: In step 4, the preferred conductive porous materials are metal nickel or metal titanium, in the form of foam, paper, or felt, mesh, porous sintered sheet. Non-metallic conductive materials that are not easily reactive with dilute acid solutions such as carbon paper and carbon cloth can also be selected. Foam nickel is preferred. The maximum projected plane area of the conductive substrate material should be smaller than the maximum projected plane area of the counter electrode.

[0026] As a further solution of the present invention: In step 4, the method of cathodic electrodeposition on the working electrode can be one of potentiostatic deposition or galvanostatic deposition. The set current density or potential for cathodic electrodeposition on the working electrode should be determined according to cyclic voltammetry. The reduction peak current of the cyclic voltammogram is selected to determine the lower limit of the current density, and the upper limit is determined by the current without violent side reactions such as hydrogen evolution. The corresponding potential in the cyclic voltammogram is the potential required for electrodeposition. Specifically, after depositing for a certain time, a distinct deposit appears on the surface of the conductive substrate material. Preferably from -20 mA / cm2 to -200 mA / cm 2 The current density of up to -200 mA / cm is used as the electrodeposition current density, and the corresponding potential in the cyclic voltammetry curve is used as the electrodeposition potential.

[0027] As a further solution of the present invention: in step five, the method for electrochemically activating the working electrode is to use cyclic voltammetry in an alkaline solution with a pH of 13 to 14. The potential set for electrochemically activating the working electrode is preferably 0.4 V (relative to a mercury / mercuric oxide reference electrode applicable to alkaline media). The specific setting range of the potential is 0 to 0.8 V, and it is cycled at a speed of 100 m / s for no less than 30 times, with the speed range being 10 to 150 m / s.

[0028] As a further solution of the present invention: in step four, the self-supporting three-dimensional vanadium-containing transition metal hydroxide electrocatalytic electrode is prepared according to the preparation method of any one of claims 1 to 7. The three-electrode system includes a working electrode, a counter electrode, and a reference electrode. The counter electrode is preferably a platinum sheet electrode, and the reference electrode is preferably a saturated calomel electrode.

[0029] Example 1. Preparation of Ni3CoV self-supporting three-dimensional electrocatalytic electrode Weigh 1.5 mmol of sodium metavanadate and dissolve it in 100 ml of deionized water. Then, add 2 ml of 3 mol / L dilute hydrochloric acid dropwise, and then slowly add 1.6 mmol of sodium borohydride. After stirring well, add 1.5 mmol of cobalt nitrate and 4.5 mmol of nickel nitrate in sequence. After stirring well, an electrodeposition solution is obtained. Using a 1 cm × 1 cm nickel foam as the working electrode, a 1.5 cm × 1.5 cm platinum sheet electrode as the counter electrode, and a calomel electrode as the reference electrode, with the assistance of an electrochemical workstation, under the condition of -2 V, potentiostatic deposition is carried out for 600 s. After the deposition is completed, the nickel foam sheet loaded with the deposit is taken out, washed with deionized water for 10 s, and dried to obtain a self-supporting three-dimensional vanadium-containing transition metal hydroxide electrocatalytic electrode, denoted as Ni3CoV.

[0030] Example 2. Preparation of Ni3CrV self-supporting three-dimensional electrocatalytic electrode Weigh 1.5 mmol of sodium metavanadate and dissolve it in 100 ml of deionized water. Then, add 2 ml of 3 mol / L dilute hydrochloric acid dropwise. Next, slowly add 1.6 mmol of sodium borohydride. After stirring well, add 1.5 mmol of chromium nitrate and 4.5 mmol of nickel nitrate in sequence. After sufficient stirring, an electrodeposition solution is obtained. Using a 1 cm × 1 cm nickel foam as the working electrode, a 1.5 cm × 1.5 cm platinum sheet electrode as the counter electrode, and a calomel electrode as the reference electrode, with the assistance of an electrochemical workstation, under the condition of -2 V, perform potentiostatic deposition for 600 s. After the deposition is completed, take out the nickel foam sheet loaded with the deposit, wash it with deionized water for 10 s, and after drying, a self-supporting three-dimensional vanadium-containing transition metal hydroxide electrocatalytic electrode is obtained, denoted as Ni3CrV.

[0031] Example 3: Preparation of Ni3MnV self-supporting three-dimensional electrocatalytic electrode; Weigh 1.5 mmol of sodium metavanadate and dissolve it in 100 ml of deionized water. Then, add 2 ml of 3 mol / L dilute hydrochloric acid dropwise. Next, slowly add 1.6 mmol of sodium borohydride. After stirring well, add 1.5 mmol of manganese nitrate and 4.5 mmol of nickel nitrate in sequence. After sufficient stirring, an electrodeposition solution is obtained. Using a 1 cm × 1 cm nickel foam as the working electrode, a 1.5 cm × 1.5 cm platinum sheet electrode as the counter electrode, and a calomel electrode as the reference electrode, with the assistance of an electrochemical workstation, under the condition of -2 V, perform potentiostatic deposition for 600 s. After the deposition is completed, take out the nickel foam sheet loaded with the deposit, wash it with deionized water for 10 s, and after drying, a self-supporting three-dimensional vanadium-containing transition metal hydroxide electrocatalytic electrode is obtained, denoted as Ni3MnV.

[0032] Example 4: Preparation of Ni3V self-supporting three-dimensional electrocatalytic electrode Weigh 2 mmol of sodium metavanadate and dissolve it in 100 ml of deionized water. Then, add 2 ml of 3 mol / L dilute hydrochloric acid dropwise. Next, slowly add 2.1 mmol of sodium borohydride. After stirring well, continue to add 6 mmol of nickel nitrate. After sufficient stirring, an electrodeposition solution is obtained. Using a 1 cm × 1 cm nickel foam as the working electrode, a 1.5 cm × 1.5 cm platinum sheet electrode as the counter electrode, and a calomel electrode as the reference electrode, with the assistance of an electrochemical workstation, under the condition of -1.5 V, perform potentiostatic deposition for 600 s. After the deposition is completed, take out the nickel foam sheet loaded with the deposit, wash it with deionized water for 10 s, and after drying, a self-supporting three-dimensional vanadium-containing transition metal hydroxide electrocatalytic electrode is obtained, denoted as Ni3V.

[0033] Example 5: Preparation of FeV self-supporting three-dimensional electrocatalytic electrode Weigh 3.5 mmol of sodium metavanadate and dissolve it in 100 ml of deionized water. Then, add 4.5 ml of 3 mol / L dilute hydrochloric acid dropwise. Next, slowly add 3.1 mmol of sodium borohydride. After stirring well, continue to add 3.5 mmol of iron nitrate. After sufficient stirring, the electrodeposition solution is obtained. Using a 1 cm × 1 cm nickel foam as the working electrode, a 1.5 cm × 1.5 cm platinum sheet electrode as the counter electrode, and a calomel electrode as the reference electrode, with the assistance of an electrochemical workstation, under the condition of -1.5 V, potentiostatic deposition is carried out for 600 s. After the deposition is completed, take out the nickel foam sheet loaded with the deposit, wash it with deionized water for 10 s, and obtain a self-supporting three-dimensional vanadium-containing transition metal hydroxide electrocatalytic electrode after drying, denoted as FeV.

[0034] Example 6. Preparation of Ni3FeV self-supporting three-dimensional electrocatalytic electrode; Weigh 1.5 mmol of sodium metavanadate and dissolve it in 100 ml of deionized water. Then, add 2 ml of 3 mol / L dilute hydrochloric acid dropwise. Next, slowly add 1.6 mmol of sodium borohydride. After stirring well, add 1.5 mmol of iron nitrate and 4.5 mmol of nickel nitrate in sequence. After sufficient stirring, the electrodeposition solution is obtained. Using a 1 cm × 1 cm nickel foam as the working electrode, a 1.5 cm × 1.5 cm platinum sheet electrode as the counter electrode, and a calomel electrode as the reference electrode, with the assistance of an electrochemical workstation, under the condition of -2 V, potentiostatic deposition is carried out for 600 s. After the deposition is completed, take out the nickel foam sheet loaded with the deposit, wash it with deionized water for 10 s, and obtain a self-supporting three-dimensional vanadium-containing transition metal hydroxide electrocatalytic electrode after drying, denoted as Ni3NiV.

[0035] Comparative Example 1. Preparation of RuO2-coated nickel foam electrocatalytic electrode Weigh 5 mg of ruthenium dioxide powder and disperse it in a mixed solution of 300 ml of ethanol, 700 μl of deionized water, and 20 ml of 5 wt% Nafion solution. Ultrasonicate the suspension for 30 min to form a uniform suspension. Then, drop 250 ml of the suspension onto the surface of a 1 cm × 1 cm nickel foam. After drying, the RuO2-coated nickel foam electrocatalytic electrode is obtained, denoted as RuO2 / NF.

[0036] Example 7. Evaluation of the oxygen evolution performance of electrocatalytic materials for water electrolysis Using the self-supported three-dimensional vanadium-containing transition metal hydroxide electrocatalytic electrodes obtained from Examples 1 to 5 and the RuO₂-coated nickel foam electrocatalytic material obtained from Comparative Example 1 as the working electrodes, a 1 cm × 1 cm platinum sheet electrode as the counter electrode, a mercury / mercuric oxide electrode as the reference electrode, and a 1 mol / L aqueous KOH solution as the electrolyte, with the assistance of an electrochemical workstation, the current density value I was measured in the potential range from 0 to 1.5 V relative to the reference electrode, and the internal resistance R of each working electrode was measured by the electrochemical workstation.

[0037] The potential V1 relative to the reference electrode was converted to the potential V2 relative to the reversible hydrogen electrode by the formula V2 = V1 + 0.059×pH + 0.098, where pH is the pH value of the electrolyte, and 85% IR compensation was performed using the formula V3 = V2 - I×R×85%. The obtained potential V3 was plotted against I, and Figure 1 it can be seen from the figure that at the same current density, the working potential required for the obtained self-supported three-dimensional vanadium-containing transition metal hydroxide electrocatalytic electrode is lower than that of the RuO₂-coated nickel foam electrocatalytic electrode of Comparative Example 1.

[0038] Example VIII. Evaluation of the Conductive Performance of the Electrocatalytic Material Using the self-supported three-dimensional vanadium-containing transition metal hydroxide electrocatalytic electrodes obtained from Examples 1 to 5 and the RuO₂-coated nickel foam electrocatalytic material obtained from Comparative Example 1 as the working electrodes, a 1 cm × 1 cm platinum sheet electrode as the counter electrode, a mercury / mercuric oxide electrode as the reference electrode, and a 1 mol / L aqueous KOH solution as the test solution, with the assistance of an electrochemical workstation, the electrochemical impedance spectrum of the working electrode at the open circuit potential was measured.

[0039] Using Figure 2 the shown simulation circuit to analyze the obtained electrochemical impedance spectrum curve, the electron conduction impedance of the working electrode can be obtained. The results are as shown in the Figure 2 table in. It can be seen that the RuO₂-coated nickel foam electrocatalytic material of Comparative Example 1 has the largest electron conduction impedance of 26.95 Ω·cm 2 , indicating that its conductivity is the worst.

[0040] The embodiments of the present invention have been described in detail above in conjunction with the accompanying drawings, but the present invention is not limited to the described embodiments. For those skilled in the art, without departing from the principles and spirits of the present invention, various changes, modifications, substitutions, and variations to these embodiments still fall within the protection scope of the present invention.

[0041] In the description of the specification, the descriptions referring to terms such as "one embodiment", "example", "specific example", etc. mean that the specific features, structures, materials or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic expressions of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in a suitable manner in any one or more embodiments or examples.

[0042] The above are only examples and explanations of the present invention. Those skilled in the art of this technology can make various modifications or supplements to the specific embodiments described or use similar ways to replace them. As long as they do not deviate from the invention or exceed the scope defined by the claims of the present invention, they should fall within the protection scope of the present invention.

[0043] As mentioned above, it is only a preferred specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art within the technical scope disclosed by the present invention, according to the technical solution and inventive concept of the present invention, makes equivalent replacements or changes, and should be covered by the protection scope of the present invention.

Claims

1. A method for preparing a vanadium-containing transition metal hydroxide electrocatalytic electrode, characterized in that: The method for preparing the electrocatalytic electrode specifically comprises the following steps: Step 1: Use VO3 - Metavanadate and transition metal salt are used to prepare an electrodeposition solution; Step 2: Use a strong reducing agent to reduce VO3 - Restore to V 3+ ; Step 3, adding an appropriate amount of dilute acid solution to make the electrodeposition solution acidic; Step 4: Using the conductive substrate material as the working electrode, using a three-electrode system, cathode electrodeposition is performed on the working electrode. After the deposition is completed, the working electrode loaded with the deposit is taken out, washed with deionized water for more than 10 seconds, and dried to obtain a self-supporting three-dimensional vanadium-containing transition metal hydroxide electrocatalytic electrode; Step 5: Use the prepared self-supporting three-dimensional vanadium-containing transition metal hydroxide electrocatalytic electrode as the working electrode, and use a three-electrode system to electrochemically activate the working electrode. After the electrochemical activation is completed, take out the working electrode, wash it with deionized water for more than 10 seconds, and dry it to obtain the activated self-supporting three-dimensional vanadium-containing transition metal hydroxide electrocatalytic electrode.

2. The method for preparing a vanadium-containing transition metal hydroxide electrocatalytic electrode according to claim 1, characterized in that: In the step 1, the metavanadate is selected from NaVO3, the transition metal salt is selected from two transition metal salts other than V salt, and the molar concentration of the transition metal salt in the electrodeposition solution is greater than 50 mmol / L. In 100 ml of the electrodeposition solution, the electrodeposition solution V is composed of x mmol of the metavanadate V, y mmol of a transition metal salt A other than vanadium, and z mmol of another transition metal salt B other than vanadium. x A y B z , x+y+z﹥5.

3. The method for preparing a vanadium-containing transition metal hydroxide electrocatalytic electrode according to claim 1, characterized in that: In the step 2, the strong reducing agent includes but is not limited to NaBH4, NH3BH3, H3BO3, and the molar mass of the strong reducing agent is at least 0.1 mmol greater than the molar mass of the metavanadate.

4. The method for preparing a vanadium-containing transition metal hydroxide electrocatalytic electrode according to claim 1, characterized in that: In the step 3, dilute hydrochloric acid is used as the dilute acid, and the concentration of the dilute acid is preferably 3 mol / L.

5. The method for preparing a vanadium-containing transition metal hydroxide electrocatalytic electrode according to claim 1, characterized in that: In the step 3, a metavanadate solution is first prepared, and then a dilute acid solution is added, followed by a strong reducing agent. After the solution reacts and stabilizes, a transition metal salt is added. The amount of the added dilute acid solution is 2-5% of the total volume of the electrodeposition solution (excluding the volume of the dilute acid), and the specific amount is based on the solution being clear and transparent after the transition metal salt is added, and no precipitation is generated.

6. The method for preparing a vanadium-containing transition metal hydroxide electrocatalytic electrode according to claim 1, characterized in that: In the step 4, the conductive porous material is preferably metal nickel or metal titanium in the form of foam, paper or felt, mesh, porous sintered sheet, and non-metallic conductive materials such as carbon paper and carbon cloth that do not easily react with dilute acid solutions can also be selected. Foam nickel is preferred, and the maximum projected plane area of ​​the conductive base material should be smaller than the maximum projected plane area of ​​the counter electrode.

7. The method for preparing a vanadium-containing transition metal hydroxide electrocatalytic electrode according to claim 1, characterized in that: In the step 4, the method of cathode electrodeposition of the working electrode can be one of constant potential deposition or constant current deposition. The current density or potential set for cathode electrodeposition of the working electrode should be determined according to cyclic voltammetry. The reduction peak current of the cyclic voltammetry curve is selected to determine the lower limit of the current density, and the upper limit is determined by the current without violent hydrogen evolution and other side reactions. The corresponding potential in the cyclic voltammetry curve is the potential required for electrodeposition. Specifically, after a certain period of deposition, a layer of obvious sediment appears on the surface of the conductive substrate material. Preferably, from -20mA / cm 2 To -200mA / cm 2 The current density was taken as the electrodeposition current density, and the corresponding potential in the cyclic voltammetry curve was taken as the electrodeposition potential.

8. The method for preparing a vanadium-containing transition metal hydroxide electrocatalytic electrode according to claim 1, characterized in that: In step 4, the self-supporting three-dimensional vanadium-containing transition metal hydroxide electrocatalytic electrode is prepared according to the preparation method according to any one of claims 1 to 7, and the three-electrode system includes a working electrode, a counter electrode and a reference electrode. The counter electrode is preferably a platinum sheet electrode, and the reference electrode is preferably a saturated calomel electrode.

9. The method for preparing a vanadium-containing transition metal hydroxide electrocatalytic electrode according to claim 1, characterized in that: In step 5, the method for electrochemically activating the working electrode is: using cyclic voltammetry in an alkaline solution with a pH of 13 to 14 to electrochemically activate the working electrode. The potential is preferably set to 0.4 V (relative to a mercury / mercuric oxide reference electrode), and the cycle is repeated at a speed of 100 m / s for not less than 30 times.

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