Oxygen evolution reaction catalyst, preparation method therefor, and use thereof

Abstract

The present application belongs to the technical field of hydrogen production by water electrolysis, and particularly relates to an oxygen evolution reaction catalyst, a preparation method therefor, and the use thereof. The present application uses the hydrolysis effect of metal positive ions in a hydrolysable metal salt solution to make a weakly-acidic heterogeneous soaking system, which slowly acts on the surface of a metal substrate, thereby partially etching the surface of the metal substrate while removing metal oxides on the surface; on the surface of the substrate, metal ions generated by the etching bind to metal ions generated by hydrolysis, so as to form an LDH catalyst structure, ensuring a relatively high catalytic activity thereof. Moreover, under an interface-confined effect, a compact transition layer structure is slowly formed at the interface between the metal substrate and the catalyst layer; as a bridge of the metal substrate and the catalyst layer, said transition layer has the same structure as that of the LDH, but exhibits a more compact appearance and totally covers the surface of the metal substrate, so as to firmly anchor the LDH catalytic structure layer onto the surface of the metal substrate, thereby allowing the OER catalyst to have high activity and high stability under the condition of an industrial-level current density.

Description

A water oxidation catalyst and its preparation method and application

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to the Chinese patent application filed with the Patent Office of China on January 30, 2024, with application number 202410131060.0, entitled “A water oxidation catalyst, its preparation method and application”, and the Chinese patent application filed with the Patent Office of China on July 19, 2024, with application number 202410973502.6, entitled “A water oxidation catalyst, its preparation method and application”, the entire contents of which are incorporated herein by reference. Technical Field

[0003] The present application belongs to the technical field of hydrogen production by electrolysis of water, and specifically relates to a water oxidation catalyst and its preparation method and application. Background Art

[0004] Hydrogen is a clean fuel with high energy density, widespread availability, no pollution, and storability. It is one of the key energy carriers for addressing the crisis of traditional energy demand and environmental pollution in the context of the "dual carbon" strategy. Compared with hydrogen produced from traditional fossil fuels (such as coal and oil) (gray hydrogen) and natural gas (blue hydrogen), hydrogen produced from water electrolysis (green hydrogen) using renewable energy sources (such as solar, wind, and nuclear energy) offers the advantages of a wide range of raw material sources, zero carbon emissions, and renewability. Existing industrial low-temperature water electrolysis hydrogen production technologies mainly use alkaline water electrolysis (AWE) and proton exchange membrane water electrolysis (PEM-WE). AWE has low material cost, high stability, and is easy to scale up industrially, but it suffers from hydrogen and oxygen crosstalk, low operating efficiency, and the use of high alkaline concentrations can easily cause corrosion. PEM-WE has a compact structure, high hydrogen production efficiency, and fast response time, but it has high investment costs, is dependent on precious metals (such as Pt), and has limited hydrogen production capacity. The newly developed anion exchange membrane water electrolysis (AEM-WE) in recent years combines the advantages of AWE and PEM-WE, namely low material cost, compact structure, high hydrogen production efficiency, etc., and has great development potential for water electrolysis hydrogen production. However, AEM-WE is still some distance away from large-scale industrial production of green hydrogen. The main reason is that it has a low current density (such as ≥1000mA cm) at industrial level. -2 ) still faces the problem of achieving both hydrogen production performance and stability.

[0005] The core parts of the electrolytic water hydrogen production reaction are water oxidation (OER) catalysts and hydrogen reduction (HER) catalysts. Among them, the OER catalytic process involving four-electron transfer has slow reaction kinetics, which restricts the entire water electrolysis reaction process more than the HER process. Therefore, the development of efficient and stable OER catalysts is particularly important for green hydrogen engineering. Studies have shown that precious metal compounds represented by IrO2 and RuO2 exhibit excellent water oxidation activity, but they are difficult to popularize due to the high price of precious metals. Therefore, the development of non-precious metal OER catalysts has gradually become a research trend. However, current reports on non-precious metal OER catalysts focus more on improving catalytic performance, but less on long-term stability (such as >8000h), especially stability under industrial-grade current density conditions and high-performance conditions.

[0006] Therefore, there is an urgent need to develop a preparation method that can firmly fix the catalyst structure on the surface of the metal substrate to ensure the stable and efficient operation of the OER reaction at industrial-level current density. Summary of the Invention

[0007] Therefore, the technical problem to be solved by the present application is to overcome the above-mentioned defects of the water oxidation catalyst in the process of hydrogen production by electrolysis of water in the prior art, thereby providing a water oxidation catalyst and its preparation method and application.

[0008] To this end, this application provides the following technical solutions:

[0009] The present application provides a method for preparing a water oxidation catalyst, comprising the following steps:

[0010] S1, preparing a hydrolyzable metal salt solution, and adjusting the pH of the hydrolyzable metal salt solution to 2.5-6.5;

[0011] S2, soaking the metal substrate with a hydrolyzable metal salt solution;

[0012] S3, adding an organic solvent to the system of step S2 to form a heterogeneous system, and reacting for 4-72 hours.

[0013] Optionally, in step S1, the concentration of the hydrolyzable metal salt solution is 20-400 mmol / L.

[0014] Optionally, the hydrolyzable metal salt includes but is not limited to at least one of nickel chloride, nickel sulfate, nickel nitrate, ferric sulfate, ferrous sulfate, ferric chloride, ferrous chloride, vanadium trichloride, vanadium oxysulfate, aluminum chloride, indium trichloride, cerium trichloride, cerium sulfate, and bismuth trichloride.

[0015] Optionally, in step S2, the soaking temperature is 5-50°C and the soaking time is 0-5h;

[0016] Optionally, the soaking time is 1-2 hours.

[0017] Optionally, in step S3, the organic solvent includes but is not limited to at least one of acetone, methanol, ethanol, propanol, isopropanol, allyl alcohol, butanol, 2-butanol, tert-butanol, ethylene glycol, propylene glycol, tetrahydrofuran, dimethyl ether, ethyl acetate, and N,N-dimethylformamide;

[0018] and / or, the volume ratio of the organic solvent to the hydrolyzable salt solution is in the range of (0.5-9):1;

[0019] And / or, the metal substrate includes but is not limited to at least one of nickel foam, iron foam, nickel-iron foam, nickel mesh, iron mesh, nickel-iron mesh, nickel felt, iron felt, nickel-iron felt, nickel electrode plate, and iron electrode plate. If the metal substrate contains only one metal element, in order to subsequently form a layered bimetallic compound (LDH), the metal element in the hydrolyzable metal salt solution must be different from the metal component in the substrate.

[0020] Optionally, the reaction temperature in step S3 is 20-60° C., and the reaction time is 10-72 h.

[0021] The present application also provides a water oxidation catalyst prepared by the above preparation method.

[0022] The present application also provides an application of the above-mentioned water oxidation catalyst in hydrogen production by water electrolysis.

[0023] Optionally, the current density for hydrogen production by water electrolysis is 500-4000 mA cm -2 This application is particularly suitable for industrial-grade current densities of 1000-4000mA cm -2 Hydrogen production by water electrolysis.

[0024] Optionally, it is suitable for electrolysis of alkaline water systems, including but not limited to alkaline water, alkaline seawater, alkaline mineral water, etc.

[0025] The present application provides a water oxidation catalyst, which includes a metal substrate and a catalyst layer. There is also a transition layer attached to the surface of the metal substrate between the metal substrate and the catalyst layer. The catalyst layer and the transition layer have the same lamellar structure, and the morphology of the transition layer is denser than that of the catalyst layer.

[0026] It should be noted that the "lamellar structure" in this application means that the main structure of the catalyst layer and the transition layer is a lamellar structure. These lamellar structures in the transition layer are tightly stacked, and these lamellar structures in the catalyst layer can also form more delicate structures such as petal-shaped, honeycomb-shaped, cluster-shaped, and bundle-shaped.

[0027] It should also be noted that the meaning of "dense" is that the area of ​​the lamellar structure is smaller and the density of the lamellar structure arrangement is higher.

[0028] It should also be noted that the smaller the gap between the transition layer and the metal substrate, the more suitable the water oxidation catalyst is for stable and efficient operation under industrial-grade current density. The reason is that the water oxidation catalyst of the present application can achieve stable and efficient operation under industrial current density because the water oxidation catalyst of the present application includes a dense transition layer, and the dense transition layer enables the catalytic layer to be firmly anchored to the surface of the metal substrate, that is, the presence of the transition layer enables the water oxidation catalyst of the present application to have good mechanical stability, so the water oxidation catalyst of the present application can withstand higher industrial-grade current density. In this way, the smaller the gap between the transition layer and the metal substrate, the more firmly the catalyst is combined with the metal substrate, and the more stable and efficient operation of the water oxidation catalyst can be achieved under industrial-grade current density.

[0029] In some embodiments, there is no gap between the substrate and the transition layer at most locations, wherein the majority of locations refers to more than 80% of the locations.

[0030] Optionally, the thickness of the transition layer is 0.2-4 μm;

[0031] Optionally, the thickness of the transition layer is 0.2-3 μm;

[0032] Optionally, the thickness of the transition layer is 1-3 μm;

[0033] Optionally, the thickness of the transition layer is 2-3 μm.

[0034] It should be noted that in the present application, the thickness of transition layer in water oxidation catalyst is not completely consistent in every position, and some places have larger thickness, and some places have smaller thickness.Wherein, the thickness of transition layer in water oxidation catalyst is relevant to the position of metal reaction site in metal substrate, for example, when metal substrate is nickel foam, because nickel foam is honeycomb structure, therefore the nickel reaction site in nickel foam is towards all directions, when nickel reaction site in nickel foam is towards the same direction as gravity, because hydrolyzable salt solution is located above metal substrate, therefore the nickel reaction site reaction contact surface of this part and gravity is smaller, the nickel reaction site of this part and gravity is etched slower, the catalyst layer generated by the nickel reaction site position of this part and gravity is thinner, so transition layer thickness is smaller.On the contrary, when nickel reaction site in nickel foam is towards the opposite direction with gravity, then transition layer thickness is larger.

[0035] It should also be noted that the thickness of the transition layer refers to the thickness range of the transition layer at most locations. For example, the thickness of the transition layer refers to the thickness range of at least 50% of the transition layer. In most cases, the thickness of the transition layer refers to the thickness range of at least 60% of the transition layer. In other words, the thickness range of the transition layer at most locations can generally be used as the transition layer thickness, but this does not exclude the possibility that the thickness at individual locations is lower or higher than the transition layer thickness range.

[0036] It should be noted that, in the water oxidation catalyst of the present application, the method for measuring the thickness of the transition layer includes the following steps:

[0037] S11, obtaining a cross-sectional scanning electron microscope image of the water oxidation catalyst to be tested (using FIG. 19 as an example for illustration);

[0038] S12, as shown in FIG23 , determining the boundary line 4 between the metal substrate and the transition layer according to the location where the morphology of the metal substrate 3 and the transition layer 2 changes significantly, and determining the boundary line 5 between the catalyst layer 1 and the transition layer 2 according to the location where the density of the lamellar structure changes significantly;

[0039] S13, a trend line 6 is determined based on the boundary line 4, and the distance between the trend line 6 and the dividing line 5 is measured along the perpendicular direction of the trend line at the position to be measured, which is the thickness of the transition layer at the position to be measured; FIG24 is another schematic diagram of the transition layer thickness test in the water oxidation catalyst. For portions in the figure that significantly deviate from the trend line (circled portions in the figure), they will be discarded in the process of determining the trend line 6 based on the boundary line 4;

[0040] S14, selecting a number of different positions to measure thickness according to the method of step S13, and the range consisting of the thickness at at least more than 50% of the positions is the thickness of the water oxidation catalyst transition layer.

[0041] Optionally, the metal substrate comprises at least one of nickel foam, iron foam, nickel-iron foam, nickel mesh, iron mesh, nickel-iron mesh, nickel felt, iron felt, nickel-iron felt, nickel plate, and iron plate;

[0042] And / or, the catalyst layer and the transition layer are both composed of layered bimetallic compounds.

[0043] Optionally, the metal substrate is foamed nickel or foamed iron;

[0044] The catalyst layer and the transition layer are composed of at least one of a nickel-iron layered bimetallic compound, a nickel-vanadium layered bimetallic compound, a nickel-aluminum layered bimetallic compound, and a nickel-cerium layered bimetallic compound.

[0045] The reaction principle of this application is as follows:

[0046] In step S1, the metal salt undergoes hydrolysis in water, generating a large amount of hydrogen ions. In steps S2 and S3, these hydrogen ions come into contact with the metal substrate and first etch away the loose metal oxides on the surface; as time goes on, some of the surface metal is slowly etched away. In addition to cleaning the surface of the metal substrate, the etching process also releases a certain amount of base metal ions (such as Ni 2+ 、Fe 2+ 、Fe 3+ The released ions can serve as raw materials for the subsequent formation of layered bimetallic compounds (LDHs). This mild etching method avoids the environmental pollution, structural damage, and low metal ion source utilization that can occur with conventional acid-washing of metal substrates. The etched metal ions can then be used as raw materials for the formation of LDH catalysts in a subsequent heterogeneous system. The ions involved in the hydrolysis reaction are typically metal ions with a higher valence (e.g., +3 valence). While completing the hydrolysis reaction, they can also participate in the subsequent formation of the LDH catalyst.

[0047] Due to the different solubility of metal compounds in water and organic solvents, the addition of organic solvent to S3 leads to the precipitation of a large number of nanoparticles. These nanoparticles are evenly dispersed in the liquid phase and readily adsorb onto the surface of a metal substrate (such as nickel foam), thereby reducing the adsorption energy of the metal surface. Due to the acidic nature of the liquid phase (caused by the hydrolysis of metal ions), acid etching of the metal substrate continues, significantly increasing the metal ion concentration at the solid-liquid interface. These etched ions and metal ions in the liquid, with the adsorbed nanoparticles on the metal surface as cores (or seeds), gradually grow into the LDH catalytic structure. As the catalytic structure slowly grows, the metal substrate surface is gradually covered, and acid etching gradually weakens (the rate slows but still occurs). At this point, metal ions are concentrated only at the interface between the metal substrate surface and the catalytic structure. Due to interfacial confinement, a dense transition layer (with slow growth kinetics) gradually forms at this interface over time. When the transition layer completely covers the metal substrate, the etching process ceases, the surrounding metal ion concentration decreases, and the growth of the catalytic structure and the transition layer ceases, thus ending the catalyst growth process. Since the growth of the transition layer is accompanied by the etching of the metal on the substrate surface, when the catalyst stops growing, the metal surface has been completely covered by the transition layer. Due to the presence of the dense transition layer, the LDH catalyst layer with a good three-dimensional structure is firmly anchored on the surface of the metal substrate. The catalyst obtained in this application has both high OER activity and high stability under industrial-grade current density conditions, and because the transition layer completely covers the metal substrate surface, it can effectively protect the metal substrate from harmful ions (such as Cl - The catalyst can be used not only for hydrogen production from alkaline water, but also for hydrogen production from alkaline seawater and alkaline mineral water.

[0048] The technical solution of this application has the following advantages:

[0049] The preparation method of the water oxidation catalyst provided by the present application comprises the following steps: S1, preparing a hydrolyzable metal salt solution, and regulating the pH of the hydrolyzable metal salt solution to 2.5-6.5; S2, soaking a metal substrate with the hydrolyzable metal salt solution; S3, adding an organic solvent to the system of step S2 to form a heterogeneous system, and reacting for 4-72 hours. The present application utilizes the hydrolysis of metal cations in the hydrolyzable metal salt solution to manufacture a weakly acidic heterogeneous immersion system, slowly acting on the surface of a metal substrate (such as foamed nickel, foamed iron, etc.), while removing the surface metal oxide, it also partially etches the surface of the metal substrate; these etched metal ions combine with the hydrolyzed metal ions on the substrate surface to form an LDH catalyst structure, ensuring its high catalytic activity; at the same time, under the effect of interface confinement, a dense transition layer structure (low growth kinetics) is slowly formed at the interface between the metal substrate and the catalyst layer. This transition layer serves as a bridge between the metal substrate and the catalyst layer. Its structure is the same as that of LDH, but its morphology is denser and it is fully covered on the surface of the metal substrate, thereby achieving the firm anchoring of the LDH catalytic structure layer on the surface of the metal substrate. The resulting 3D self-supporting catalyst outer layer (catalyst layer) is responsible for high OER activity, the metal substrate is responsible for support and electron transport, and the intermediate dense transition layer is responsible for firmly anchoring the catalyst layer on the surface of the metal substrate, thereby achieving high activity and high stability of the material in OER water oxidation catalysis under industrial current density conditions. In addition, the present application utilizes the weak acid effect of cationic hydrolysis to etch the surface of the metal substrate (without adding or adding only a very small amount of acid to adjust the pH value), avoiding the environmental pollution that may be caused by conventional pickling and other means; the cations etched out of the metal substrate surface participate in the formation of the catalyst layer, avoiding the addition of a substrate metal ion source, and saving costs; the method has low raw material cost, mild treatment conditions, simple operation, high repeatability, high OER activity, strong OER stability, and easy large-scale application.

[0050] The preparation method of the water oxidation catalyst provided in the present application can increase the thickness of the transition layer by further optimizing the reaction time, and can further improve the operating stability of the catalyst at industrial-grade current density.

[0051] The water oxidation catalyst provided by the application, the water oxidation catalyst includes a metal substrate, a catalyst layer, a transition layer attached to the surface of the metal substrate between the metal substrate and the catalyst layer, the catalyst layer and the transition layer are both sheet structures, and the morphology of the transition layer is denser than the catalyst layer. The metal substrate surface of the water oxidation catalyst has been completely covered by the transition layer, due to the presence of the transition layer, and the catalyst layer and the transition layer are the same sheet structure, the LDH catalyst layer with a good three-dimensional structure can be firmly anchored to the metal substrate surface, because the morphology of the transition layer is denser than the catalyst layer, this multi-stage structure can make the catalyst distributed in depth on the metal substrate surface, which is conducive to mass transfer process in the catalytic process, responsible for providing OER high activity, metal substrate is responsible for support and electron transport, the catalyst obtained by the application has both OER high activity and high stability under industrial grade current density conditions, and due to the complete coverage of the metal substrate surface by the transition layer, the metal substrate can be effectively protected from harmful ions (such as Cl - The catalyst has anti-corrosion function. In addition to being used for hydrogen production from alkaline water, it can also be used for hydrogen production from alkaline seawater and alkaline mineral water. BRIEF DESCRIPTION OF THE DRAWINGS

[0052] In order to more clearly illustrate the specific implementation methods of the present application or the technical solutions in the prior art, the following is a brief introduction to the drawings required for use in the specific implementation methods or the description of the prior art. Obviously, the drawings described below are some implementation methods of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0053] FIG1 is a spherical aberration electron microscopy (STEM) image of nanoparticles in the heterogeneous system formed in Example 1;

[0054] FIG2 is a scanning electron microscope (SEM) image of the catalyst on the surface of the nickel foam substrate obtained in Example 1;

[0055] FIG3 is a diagram showing the growth process of the LDH catalyst layer and the dense transition layer on the surface of the nickel foam substrate in Example 2;

[0056] FIG4 is a photograph of a large-size (20 cm×20 cm) nickel foam substrate catalyst provided in Example 3;

[0057] Figure 5 is a diagram showing the homogenization distribution of the catalyst obtained in Example 4: (a) a 5 cm × 5 cm photo of the catalyst, and (b) a comparison of linear scan performance curves at different points (25°C, 1 M KOH);

[0058] FIG6 is a stability curve of the nickel-based foam catalyst of Example 4 in 1M KOH electrolyte (25° C., 1000 mA cm -2);

[0059] FIG7 is a linear sweep performance curve (25° C.) of the nickel-based foam catalyst obtained in Example 4 in alkaline simulated seawater containing 1 M KOH and real seawater;

[0060] FIG8 is a stability curve of the nickel-based foam catalyst obtained in Example 4 in an alkaline seawater electrolyte containing 1M KOH (25° C., 1000 mA cm -2 );

[0061] FIG9 is a cross-sectional scanning electron microscope (SEM) image of the foamed iron-based catalyst obtained in Example 8;

[0062] FIG10 is a surface scanning electron microscope (SEM) image of the foamed iron-based catalyst obtained in Example 8;

[0063] FIG11 is a linear sweep performance curve of the foamed iron-based catalyst obtained in Example 8 (25° C., 1 M KOH);

[0064] FIG12 is a linear sweep performance curve of the catalyst obtained in Example 10 (25° C., 1 M KOH);

[0065] FIG13 is a cross-sectional scanning electron microscope (SEM) image of the catalyst obtained in Comparative Example 1;

[0066] Figure 14 is the stability curve of the catalyst obtained in Comparative Example 1 in 1M KOH electrolyte (25°C, 1000mA cm -2 );

[0067] Figure 15 is the stability curve of the catalyst obtained in Comparative Example 1 in 1M KOH alkaline seawater electrolyte (25°C, 1000mA cm -2 );

[0068] FIG16 is a cross-sectional scanning electron microscope (SEM) image of the catalyst obtained in Comparative Example 3;

[0069] FIG17 is a cross-sectional scanning electron microscope (SEM) image of the catalyst obtained in Comparative Example 5;

[0070] FIG18 is a cross-sectional scanning electron microscope (SEM) image of the catalyst obtained in Example 3;

[0071] FIG19 is a cross-sectional scanning electron microscope (SEM) image of the catalyst obtained in Example 4;

[0072] FIG20 is a cross-sectional scanning electron microscope (SEM) image of the catalyst obtained in Example 5;

[0073] FIG21 is a cross-sectional scanning electron microscope (SEM) image of the catalyst obtained in Example 7;

[0074] FIG22 is a cross-sectional scanning electron microscope (SEM) image of the catalyst obtained in Example 9;

[0075] FIG23 is a schematic diagram of a transition layer thickness test in a water oxidation catalyst;

[0076] FIG24 is another schematic diagram of the transition layer thickness test in the water oxidation catalyst;

[0077] Reference numerals: 1. catalyst layer; 2. transition layer; 3. metal substrate; 4. boundary line; 5. dividing line; 6. trend line. DETAILED DESCRIPTION

[0078] The following examples are provided to further better understand the present application, but are not limited to the best implementation mode described herein, and do not limit the content and protection scope of the present application. Any product identical or similar to the present application obtained by anyone under the inspiration of the present application or by combining the features of the present application with other prior arts shall fall within the scope of protection of the present application.

[0079] If no specific experimental steps or conditions are specified in the examples, the conventional experimental steps or conditions described in the literature in this field can be used. If the manufacturer of the reagents or instruments is not specified, they are all commercially available conventional reagents.

[0080] It should be noted that in the embodiments of the present application, the metal substrate, the transition layer and the catalyst layer are distinguished by the SEM image of the cross section of the water oxidation catalyst, wherein in the SEM image of the cross section, the metal substrate is located at the bottom of the image, and its morphology is significantly different from the flaky morphology of the transition layer and the catalyst layer, and the transition layer is located between the catalyst layer and the metal substrate. The position where the morphological structure changes significantly is used as the dividing line between the transition layer and the metal substrate. For example, when the metal substrate is nickel foam, it can be seen that the metal substrate is a porous structure and the transition layer is a flaky structure. The position where the density of the flaky morphology changes significantly is used as the dividing line between the transition layer and the catalyst layer. In the following embodiments and comparative examples, the thickness of the transition layer refers to the range where the thickness of the transition layer exceeds 50%, which is determined based on the thickness of the transition layer at multiple different positions measured in the SEM image.

[0081] Example 1

[0082] This embodiment provides a water oxidation catalyst, and its preparation steps and operating parameters are as follows:

[0083] S1: Preparation of weak acid hydrolysis solution: Dissolve a certain amount of easily hydrolyzed ferrous chloride metal salt in water, stir to form a solution with a metal ion concentration of 100 mol / L, and adjust the pH to 3.5 with sulfuric acid;

[0084] S2: Etching of oxides on the metal substrate: immerse nickel foam (Suzhou Christie's Company, 80 ppi, the same below, size 2 cm × 2 cm) in the weak acid solution of S1 and let it stand at 30°C for 4 h;

[0085] S3: In situ growth of catalyst: Under ultrasonic stirring conditions, ethanol was slowly added to the S2 system, wherein the volume ratio of ethanol to ferrous chloride solution was 3:1, to form a heterogeneous liquid phase system. The system was allowed to stand at 40°C for 24 hours, and then rinsed with water and dried.

[0086] A heterogeneous liquid phase system refers to a liquid phase system (suspension, emulsion) containing insoluble solid particles (including nano- or micron-sized particles). Heterogeneous liquid phase systems are formed by taking advantage of the solubility differences of metal inorganic salts in different solvents. For example, FeCl2 is soluble in water but insoluble in ethanol. Therefore, adding ethanol to a stirred FeCl2 aqueous solution produces many uniform but insoluble particles, forming a heterogeneous liquid phase system.

[0087] Figure 1 is a TEM image of insoluble nanoparticles in the liquid phase system after adding ethanol in step S3 of this embodiment. It can be seen that these nanoparticles are in an amorphous state with a uniform size distribution (nanometer level); these particles are easily adsorbed on the surface of the metal substrate in the liquid phase environment to reduce its surface energy, and then act as cores (or seeds), bypassing the nucleation process that the LDH new phase formation and growth process originally needs to go through, and assisting the rapid formation of the LDH structure. Figure 2 is an SEM image of the catalyst obtained in this embodiment. It can be seen from the figure that the catalyst is mainly composed of a tightly packed sheet layer (i.e., a transition layer) at the bottom and an upper secondary sheet structure (catalyst layer). This multi-level structure can make the catalyst distributed in depth on the surface of the metal substrate, which is beneficial to the mass transfer process during the catalytic process.

[0088] In Example 1, a transition layer was generated in the S3 system with a thickness of 1-2 μm. The obtained catalyst was used for industrial-grade current density (1000 mA cm -2 ) under alkaline water (1M KOH) oxidation stability test, it can run stably for more than 4500h.

[0089] Example 2

[0090] This embodiment provides a water oxidation catalyst, and its preparation steps and operating parameters are as follows:

[0091] S1: Preparation of weak acid hydrolysis solution: Dissolve a certain amount of easily hydrolyzed ferrous chloride metal salt in water, stir to form a solution with a metal ion concentration of 200 mol / L, and adjust the pH to 3.5 with hydrochloric acid;

[0092] S2: Etching of oxides on the metal substrate: 8 pieces of nickel foam (size 2 cm × 2 cm) were immersed in the weak acid solution of S1 and allowed to stand at 30°C for 4 h.

[0093] S3: In situ growth of catalyst: Under ultrasonic stirring conditions, ethanol was slowly added to the S2 system, wherein the volume ratio of ethanol to ferrous chloride solution was 3:1, to form a heterogeneous liquid phase system. The system was allowed to stand at 25°C, and one piece was taken out at 1h, 2h, 4h, 8h, 16h, 24h, 36h and 72h of soaking, respectively. After taking out, the system was rinsed with water and dried.

[0094] Figure 3 is a cross-sectional SEM image of the catalyst obtained in this embodiment. It can be seen from the figure that a clear lamellar structure (catalyst layer) can be obtained by soaking in the S3 system for 1 hour. As time goes on, the lamellar structure grows. When the soaking time in step S3 reaches 4 hours or more, a dense transition layer is generated between the catalyst layer and the foam nickel substrate (the portion between the dotted lines in the figure is the transition layer, the lamellar structure with a hydrophobic morphology above the dotted line is the catalyst layer, and the metal substrate below the dotted line does not have a lamellar structure). The thickness is about 0.2-0.5 μm, and the thickness gradually increases with time (when the soaking time is 8 hours, the thickness of the transition layer is 0.5-0.8 μm; when the soaking time is 16 hours, the thickness of the transition layer is 1-2 μm; when the soaking time is 24 hours, the thickness of the transition layer is 1.5-2.5 μm). When the time is extended to 36 hours or more, the thickness of the transition layer no longer increases, and the thickness is finally maintained at 2-3 μm. The catalyst obtained after the reaction for 36 hours was used for industrial-grade current density (1000 mA cm -2 ) under alkaline water (1M KOH) oxidation stability test, it can run stably for more than 6800h.

[0095] Example 3

[0096] This embodiment provides a water oxidation catalyst, and its preparation steps and operating parameters are as follows:

[0097] S1: Preparation of weak acid hydrolysis solution: Dissolve a certain amount of easily hydrolyzed ferrous chloride metal salt in water, stir to form a solution with a metal ion concentration of 30 mol / L, and adjust the pH to 6.5 with hydrochloric acid;

[0098] S2: Etching of oxides on the metal substrate: Immerse nickel foam (size 20 cm × 20 cm) in the weakly acidic solution of S1 and let it stand at 5°C for 0.1 h;

[0099] S3: In situ growth of catalyst: Under ultrasonic stirring conditions, ethanol was slowly added to the S2 system, wherein the volume ratio of ethanol to ferrous chloride solution was 0.5:1, to form a heterogeneous liquid phase system. The system was allowed to stand at 20°C for 6 hours, and then rinsed with water and dried.

[0100] As shown in Figure 4, the obtained catalyst grows well on the surface of the nickel foam substrate, indicating that even under relatively low growth conditions (such as lower metal ion concentration, higher pH value and shorter immersion time), the catalyst can still be grown relatively uniformly on the surface of a larger size (20 cm × 20 cm) of foam metal.

[0101] As can be seen from Figure 5, in the case of a large metal substrate size in this embodiment, the potential difference between different points is extremely small. It can be seen that in the water oxidation catalyst prepared in this embodiment, the performance gap between various locations is small. In this way, in the actual industrial use process, the catalytic effect of each location on the water oxidation catalyst is similar, and the effective area of ​​the water oxidation catalyst participating in the reaction is very small compared to the area of ​​the water oxidation catalyst. That is, in the actual industrial use process, the proportion of the water oxidation catalyst participating in the reaction is extremely high, which can greatly improve industrial production efficiency. In Example 3, in the S3 system, a transition layer is generated, as shown in Figure 18, and the thickness of the transition layer is 0.2-0.3 μm. The resulting catalyst is used for industrial-grade current density (1000mA cm -2 ) under alkaline water (1M KOH) oxidation stability test, it can run stably for more than 1500h.

[0102] The metal substrate in this method can be replaced with a larger metal plate, so that a transition layer and a catalyst layer can be grown on the surface of the metal plate to protect the metal plate and avoid corrosion of the metal plate.

[0103] Example 4

[0104] This embodiment provides a water oxidation catalyst, and its preparation steps and operating parameters are as follows:

[0105] S1: Preparation of weak acid hydrolysis solution: Dissolve a certain amount of easily hydrolyzed ferrous chloride metal salt in water, stir to form a solution with a metal ion concentration of 400 mol / L, and adjust the pH to 2.6 with hydrochloric acid;

[0106] S2: Etching of oxides on the metal substrate: immerse nickel foam (5 cm × 5 cm) in the weakly acidic solution of S1 and let it stand at 50 °C for 5 h;

[0107] S3: In situ growth of catalyst: Under ultrasonic stirring conditions, ethanol was slowly added to the S2 system, wherein the volume ratio of ethanol to ferrous chloride solution was 8:1, to form a heterogeneous liquid phase system. The system was allowed to stand at 60°C for 70 hours, and then rinsed with water and dried.

[0108] In Example 4, in the S3 system, a transition layer is generated, as shown in FIG19 , and the thickness of the transition layer is 3-4 μm.

[0109] As shown in Figure 5, the catalyst grew more uniformly on the surface of nickel foam, and the linear scan curves measured at at least three locations on the surface almost overlapped, indicating that the catalytic activity of the catalyst was uniform at multiple sites. The catalyst was used for industrial-grade current density (1000 mA cm -2 ) under alkaline water (1M KOH) oxidation stability test, as shown in Figure 6, during the test process of more than 8760h (one year), the potential did not increase significantly, indicating that the material has excellent catalytic stability in alkaline water. The catalyst was used to simulate alkaline seawater and alkaline real seawater electrolysis to produce hydrogen. As shown in Figure 7, in 1M KOH + 0.5M NaCl simulated seawater (chloride ion concentration is consistent with seawater) and 1M KOH + real seawater, the catalyst showed excellent catalytic activity at 1000mA cm -2 The overpotentials under the conditions of 1000 mA cm-1 and 203 mV respectively are higher than those reported in most of the previous studies. -2 The electrolytic solution can operate stably for over 2000 hours at industrial-grade current densities (see Figure 8; based on its stable operating trend, it is expected to achieve a stable operating time similar to that of alkaline water). This excellent seawater electrolysis stability stems primarily from two aspects: first, a dense transition layer that thoroughly encapsulates the metal substrate, protecting it from corrosive chloride ions; and second, the anion exchange capacity of the catalyst's LDH structure. After absorbing some chloride ions, it acts as a like-charge ion to repel more chloride ions from the seawater, protecting the catalyst.

[0110] Example 5

[0111] This embodiment provides a water oxidation catalyst, and its preparation steps and operating parameters are as follows:

[0112] S1: Preparation of weak acidic hydrolysis solution: dissolve a certain amount of easily hydrolyzed vanadium trichloride metal salt in water, stir to form a solution with a concentration of 200 mol / L, and adjust the pH to 3.5 with sulfuric acid;

[0113] S2: Etching of oxides on the metal substrate: immerse nickel foam (2 cm × 2 cm) in the weakly acidic solution of S1 and let it stand at 30 °C for 4 h;

[0114] S3: In situ growth of catalyst: Under ultrasonic stirring conditions, ethanol was slowly added to the S2 system, wherein the volume ratio of ethanol to vanadium trichloride solution was 3:1, to form a heterogeneous liquid phase system. The system was allowed to stand at 40°C for 24 hours, and then rinsed with water and dried.

[0115] In Example 5, a transition layer was generated in the S3 system, as shown in FIG20 , and the thickness of the transition layer was 0.5-1 μm. The obtained catalyst was used for industrial-grade current density (1000 mA cm -2) under alkaline real seawater oxidation (containing 1M KOH, 25 ° C), and it can operate stably for 1200h; the obtained catalyst is used for industrial-grade current density (1000mA cm -2 ) under alkaline water oxidation (1M KOH) stability test, it can run stably for more than 2100h.

[0116] Example 6

[0117] This embodiment provides a water oxidation catalyst, and its preparation steps and operating parameters are as follows:

[0118] S1: Preparation of weak acid hydrolysis solution: Dissolve a certain amount of easily hydrolyzed aluminum chloride metal salt in water, stir to form a solution with a concentration of 200 mol / L, and adjust the pH to 3.5 with sulfuric acid;

[0119] S2: Etching of oxides on the metal substrate: immerse nickel foam (2 cm × 2 cm) in the weakly acidic solution of S1 and let it stand at 30 °C for 4 h;

[0120] S3: In situ growth of catalyst: Under ultrasonic stirring conditions, ethanol was slowly added to the S2 system, wherein the volume ratio of ethanol to aluminum chloride solution was 3:1, to form a heterogeneous liquid phase system. The system was allowed to stand at 40°C for 24 hours, and then rinsed with water and dried.

[0121] In Example 6, a transition layer was generated in the S3 system with a thickness of 0.2-0.5 μm. The obtained catalyst was used for industrial-grade current density (1000 mA cm -2 The stability test of alkaline real seawater oxidation (containing 1M KOH, 25°C) was carried out, and the catalyst could operate stably for 1000h. The obtained catalyst was used for industrial-grade current density (1000mA cm -2 ) under alkaline water (1M KOH) oxidation stability test, it can run stably for more than 1200h.

[0122] Example 7

[0123] This embodiment provides a water oxidation catalyst, and its preparation steps and operating parameters are as follows:

[0124] S1: Preparation of weak acid hydrolysis solution: dissolve a certain amount of easily hydrolyzed cerium sulfate metal salt in water, stir to form a solution with a concentration of 200 mol / L, and adjust the pH to 3.5 with sulfuric acid;

[0125] S2: Etching of oxides on the metal substrate: immerse nickel foam (2 cm × 2 cm) in the weakly acidic solution of S1 and let it stand at 30 °C for 4 h;

[0126] S3: In situ growth of catalyst: Under ultrasonic stirring conditions, ethanol was slowly added to the S2 system, wherein the volume ratio of ethanol to cerium sulfate solution was 3:1, to form a heterogeneous liquid phase system. The system was allowed to stand at 40°C for 24 hours, and then rinsed with water and dried.

[0127] In Example 7, a transition layer was generated in the S3 system, as shown in FIG21 , and the thickness of the transition layer was 1-2 μm. The obtained catalyst was used for industrial-grade current density (1000 mA cm -2 The stability test of alkaline real seawater oxidation (containing 1M KOH, 25°C) was carried out, and the catalyst could operate stably for 1000h. The obtained catalyst was used for industrial-grade current density (1000mA cm -2 ) under alkaline water (1M KOH) oxidation stability test, it can run stably for more than 3200h.

[0128] Example 8

[0129] This embodiment provides a water oxidation catalyst, and its preparation steps and operating parameters are as follows:

[0130] S1: Preparation of weak acid hydrolysis solution: Dissolve a certain amount of easily hydrolyzed ferrous sulfate and nickel nitrate in water, stir to form a solution with a concentration of 200 mol / L, the molar ratio of iron to nickel being 1:3.5, and adjust the pH to 3.5 with sulfuric acid;

[0131] S2: Etching of oxides on the metal substrate: Immerse the foamed iron (2 cm × 2 cm) in the weakly acidic solution of S1 and let it stand at 30 °C for 4 h;

[0132] S3: In situ growth of catalyst: Under ultrasonic stirring conditions, ethanol was slowly added to the S2 system, wherein the volume ratio of ethanol to ferrous sulfate and nickel nitrate solution was 3:1, to form a heterogeneous liquid phase system. The system was allowed to stand at 40°C for 24 hours, and then rinsed with water and dried.

[0133] In Example 8, in the S3 system, a transition layer is generated, and the thickness of the transition layer is 1-2 μm. As shown in the cross-sectional SEM image of Figure 9, the obtained catalyst contains a three-layer structure: an upper sheet structure, a middle transition layer structure and a bottom foam iron structure. As shown in the top view SEM image of Figure 10, the water oxidation catalyst is also composed of a tightly packed sheet layer (transition layer) at the bottom and a large petal secondary sheet layer structure (catalyst layer). A linear scanning curve test was performed on it, as shown in Figure 11, at 1000mA cm -2 The lower overpotential is 240 mV.

[0134] The obtained catalyst was used for industrial-grade current density (1000 mA cm -2) under alkaline real seawater oxidation (containing 1M KOH, 25 ° C), and it can operate stably for 1500h; the obtained catalyst is used for industrial-grade current density (1000mA cm -2 ) under alkaline water (1M KOH) oxidation stability test, it can run stably for more than 2500h.

[0135] Example 9

[0136] This embodiment provides a water oxidation catalyst, and its preparation steps and operating parameters are as follows:

[0137] S1: Preparation of weak acid hydrolysis solution: Dissolve a certain amount of easily hydrolyzed ferrous sulfate metal salt in water, stir to form a solution with a concentration of 200 mol / L, and adjust the pH to 3.5 with sulfuric acid;

[0138] S2: Etching of oxides on the metal substrate: immerse nickel foam (2 cm × 2 cm) in the weakly acidic solution of S1 and let it stand at 30 °C for 4 h;

[0139] S3: In situ growth of catalyst: Under ultrasonic stirring conditions, isopropanol was slowly added to the S2 system, wherein the volume ratio of isopropanol to ferrous sulfate solution was 3:1, to form a heterogeneous liquid phase system. The system was allowed to stand at 40°C for 24 hours, and then rinsed with water and dried.

[0140] In Example 9, in the S3 system, a transition layer was generated, as shown in FIG22 , and the thickness of the transition layer was 2-3 μm. The obtained catalyst was used for industrial-grade current density (1000 mA cm -2 ) under alkaline real seawater oxidation (containing 1M KOH, 25 ° C), and it can operate stably for 1800h; the obtained catalyst is used for industrial-grade current density (1000mA cm -2 ) under alkaline water (1M KOH) oxidation stability test, and can run stably for more than 5500h.

[0141] Example 10

[0142] This embodiment provides a water oxidation catalyst, and its preparation steps and operating parameters are as follows:

[0143] S1: Preparation of weak acid hydrolysis solution: Dissolve a certain amount of easily hydrolyzed ferrous sulfate metal salt in water, stir to form a solution with a concentration of 200 mol / L, and adjust the pH to 3.5 with sulfuric acid;

[0144] S2: In situ growth of catalyst: Under ultrasonic stirring conditions, ethanol was slowly added to the S1 system, where the volume ratio of ethanol to ferrous sulfate solution was 3:1, forming a heterogeneous liquid phase system in which the metal substrate was immersed. The nickel foam (2cm×2cm) was immersed in it and allowed to stand at 40°C for 36 hours. After being taken out, it was rinsed with water and dried.

[0145] In Example 10, a transition layer was generated in the S3 system, and the thickness of the transition layer was 0.5-1.5 μm. The obtained catalyst was subjected to a linear scanning curve test in 1 M KOH alkaline aqueous electrolyte (25°C). As shown in Figure 12, at 1000 mA cm -2 The overpotential was 225 mV. The obtained catalyst was used for industrial-grade current density (1000 mA cm -2 ) Stability test of alkaline water oxidation (1M KOH), stable operation for more than 2500h.

[0146] Comparative Example 1

[0147] This comparative example provides a water oxidation catalyst, the preparation steps and operating parameters of which are as follows:

[0148] S1: Acid pickling pretreatment of metal foam: nickel foam (2 cm × 2 cm) was ultrasonically washed in 2 M hydrochloric acid for 30 min, and then cleaned with anhydrous ethanol, acetone and deionized water in sequence;

[0149] S2: Preparation of metal salt suspension: nickel nitrate was dissolved in ethanol and ferrous sulfate was dissolved in deionized water in a volume ratio of ethanol to water of 2:1. The mixture was thoroughly mixed to form a metal salt suspension with a metal ion concentration of 200 mol / L.

[0150] S3: In-situ growth of catalyst: soak the pretreated metal foam in a metal salt suspension at 30°C for 24 hours, take it out and rinse it repeatedly with anhydrous ethanol and deionized water for 2-5 times, and then dry it for use.

[0151] In step S2 of this comparative example, the addition of a metal ion source required for LDH structure growth enabled rapid growth of the catalytic layer. Furthermore, without adjusting the system pH, there was little or no etching of the metal substrate surface, preventing the formation of a transition layer due to interfacial confinement. As shown in Figure 13, the catalytic layer structure of the comparative catalyst is similar to that of the catalyst layer obtained in this application, consisting of a multi-level lamellar structure, but no obvious transition layer was observed, and a small gap existed between the catalytic layer and the metal substrate.

[0152] The stability of the obtained catalyst was tested in 1M KOH alkaline aqueous electrolyte (25°C). As shown in Figure 14, at 1000 mA cm -2The potential increased by about 400 mV around 1000 h, indicating that the catalytic activity gradually decreased with time.

[0153] The stability of the obtained catalyst was tested in 1M KOH alkaline seawater electrolyte (25°C). As shown in Figure 15, at 1000 mA cm -2 The potential increased by about 1000 mV in the next 5 hours, indicating that the catalyst could hardly operate stably in alkaline seawater.

[0154] Comparative Example 2

[0155] This comparative example provides a water oxidation catalyst, which differs from Example 2 only in that the reaction time of step S3 is 2 h.

[0156] The obtained catalyst was electrochemically tested in 1 M KOH alkaline seawater electrolyte (25 °C, 1000 mA cm -2 ), ran stably for 3 hours, and then the potential rose rapidly. Figure 3 shows that a 2-hour catalyst growth time does not produce a transition layer. Therefore, although the catalyst has a multi-layer structure, it cannot be used in alkaline seawater due to the lack of protection from the transition layer.

[0157] Comparative Example 3

[0158] This comparative example provides a water oxidation catalyst, which differs from Example 1 only in that no organic solvent is added in step S3.

[0159] The obtained catalyst was electrochemically tested in 1 M KOH alkaline seawater electrolyte (25 °C, 1000 mA cm -2 ), running stably for about 3 hours, after which the potential rapidly increased. The primary function of the organic solvent is to induce the formation of nanoparticles. In aqueous systems lacking nanoparticles, the resulting catalyst transition layer is not significant (as shown in Figure 16), and therefore lacks the ability to stabilize the catalyst in alkaline seawater.

[0160] Comparative Example 4

[0161] This comparative example provides a water oxidation catalyst, which differs from Example 1 only in that a non-hydrolyzable metal salt NaCl is used.

[0162] The catalyst surface was hardly observed to have any catalyst structure attached. In 1M KOH alkaline seawater electrolyte (25℃, 1000mA cm -2 ), and stable operation is less than 1h. This indicates that non-hydrolyzable metal salts cannot meet the requirements of etching the metal substrate and forming the catalyst structure, making it difficult to use them for seawater electrolysis to produce hydrogen.

[0163] Comparative Example 5

[0164] This comparative example provides a water oxidation catalyst, which is different from Example 1 only in that step S1 does not include a pH adjustment step.

[0165] The obtained catalyst sheet structure is small, with an overall thickness of only 1-2μm. Although a dense transition layer can be observed, there is a significant peeling phenomenon between the transition layer and the nickel foam substrate. The transition layer is not tightly attached to the metal substrate, so the catalyst layer cannot be firmly anchored to the metal substrate surface (see Figure 17). This may be related to the high pH of the immersion system. The stability test of the obtained catalyst was carried out in 1M KOH alkaline aqueous electrolyte (25℃). -2 The potential rises by about 300 mV after about 500 h; while in 1 M KOH alkaline seawater electrolyte (25 ° C, 1000 mA cm -2 ), and the potential rose rapidly after 5 hours of stable operation. This indicates that adjusting the mother liquor to a reasonable pH range is crucial for metal substrate etching and catalyst formation. Without a suitable weakly acidic mother liquor environment, catalyst formation (morphology, structure, and adhesion to the substrate) is inhibited to varying degrees, hindering its stable electrocatalysis in alkaline water and alkaline seawater.

[0166] In order to facilitate comparison between data, some parameters and test results of the water oxidation catalysts provided in the examples and comparative examples are summarized as follows:

[0167] Table 1

[0168] Note: “ / ” in the table means that the test was not conducted.

[0169] It can be seen from the test data in the above table that an increase in the thickness of the transition layer can significantly improve the stable operation time of the catalyst. This may be because the transition layer can play a certain anti-corrosion function, thereby extending the service life of the catalyst; from the comparison of the embodiments and the comparative examples, it can be seen that the transition layer is tightly attached to the surface of the metal substrate, and the catalyst layer can be firmly anchored on the surface of the metal substrate, significantly extending the stable operation time of the catalyst; if the thickness of the transition layer is almost zero or the transition layer and the metal substrate are not tightly attached, the adhesion of the catalyst layer to the metal substrate is very unstable, and it cannot play an anti-corrosion function, and it can hardly operate stably in alkaline real seawater.

[0170] Obviously, the above embodiments are merely examples for clarity of explanation and are not intended to limit the implementation methods. Those skilled in the art will appreciate that other variations or modifications can be made based on the above description. It is not necessary and impossible to enumerate all implementation methods here. Obvious variations or modifications arising therefrom remain within the scope of protection of the present invention.

Claims

1. A method for preparing a water oxidation catalyst, characterized in that: The steps include: S1, preparing a hydrolyzable metal salt solution, and adjusting the pH of the hydrolyzable metal salt solution to 2.5-6.5; S2, soaking the metal substrate with a hydrolyzable metal salt solution; S3, adding an organic solvent to the system of step S2 to form a heterogeneous system, and reacting for 4-72 hours.

2. The method for preparing a water oxidation catalyst according to claim 1, wherein In step S1, the concentration of the hydrolyzable metal salt solution is 20-400 mmol / L.

3. The method for preparing a water oxidation catalyst according to claim 1, wherein The hydrolyzable metal salt includes at least one of nickel chloride, nickel sulfate, nickel nitrate, ferric sulfate, ferrous sulfate, ferric chloride, ferrous chloride, vanadium trichloride, vanadium oxysulfate, aluminum chloride, indium trichloride, cerium trichloride, cerium sulfate, and bismuth trichloride.

4. The method for preparing a water oxidation catalyst according to claim 1, wherein In step S2, the soaking temperature is 5-50°C and the soaking time is 0-5h; Optionally, the soaking time is 1-2 hours.

5. The method for preparing a water oxidation catalyst according to claim 1, wherein In step S3, the organic solvent includes at least one of acetone, methanol, ethanol, propanol, isopropanol, allyl alcohol, butanol, 2-butanol, tert-butanol, ethylene glycol, propylene glycol, tetrahydrofuran, dimethyl ether, ethyl acetate, and N,N-dimethylformamide; and / or, the volume ratio of the organic solvent to the hydrolyzable salt solution is in the range of (0.5-9):1; And / or, the metal substrate includes at least one of foamed nickel, foamed iron, foamed nickel-iron, nickel mesh, iron mesh, nickel-iron mesh, nickel felt, iron felt, nickel-iron felt, nickel plate, and iron plate.

6. The method for preparing a water oxidation catalyst according to any one of claims 1 to 5, characterized in that: The reaction temperature in step S3 is 20-60° C., and the reaction time is 10-72 h.

7. A water oxidation catalyst prepared by the preparation method according to any one of claims 1 to 6.

8. Use of the water oxidation catalyst according to claim 7 in producing hydrogen by electrolysis of water.

9. The use according to claim 8, characterized in that The current density of water electrolysis to produce hydrogen is 500-4000 mA cm -2 .

10. The use according to claim 8 or 9, characterized in that: Suitable for electrolysis of alkaline water system; Optionally, the alkaline water system includes alkaline water, alkaline seawater or alkaline mineral water.

11. A water oxidation catalyst, characterized in that The water oxidation catalyst includes a metal substrate and a catalyst layer. A transition layer attached to the surface of the metal substrate is provided between the metal substrate and the catalyst layer. The catalyst layer and the transition layer have the same lamellar structure, and the morphology of the transition layer is denser than that of the catalyst layer.

12. The water oxidation catalyst according to claim 11, characterized in that The thickness of the transition layer is 0.2-4 μm; Optionally, the thickness of the transition layer is 0.2-3 μm; Optionally, the thickness of the transition layer is 1-3 μm; Optionally, the thickness of the transition layer is 2-3 μm.

13. The water oxidation catalyst according to claim 11 or 12, characterized in that The metal substrate comprises at least one of nickel foam, iron foam, nickel-iron foam, nickel mesh, iron mesh, nickel-iron mesh, nickel felt, iron felt, nickel-iron felt, nickel plate, and iron plate; And / or, the catalyst layer and the transition layer are both composed of layered bimetallic compounds.

14. The water oxidation catalyst according to claim 13, characterized in that The metal substrate is foamed nickel or foamed iron; The catalyst layer and the transition layer are composed of at least one of a nickel-iron layered bimetallic compound, a nickel-vanadium layered bimetallic compound, a nickel-aluminum layered bimetallic compound, and a nickel-cerium layered bimetallic compound.

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