A self-supporting oxygen evolution electrode and its preparation method and application

Abstract

The present application discloses an oxygen evolution electrode with a self-supporting structure and its preparation method and application. It belongs to the field of electrocatalysis technology. It includes a substrate and a porous catalytic layer supported on the surface of the substrate; the method does not require the use of an organic precipitant, thus avoiding pollution to the environment; does not use a strong alkaline precipitant, and utilizes a transient high-temperature process to allow the metal salt to quickly adhere to the surface of the metal skeleton, ensuring that the resulting metal active components are evenly distributed; does not require high-temperature and high-pressure equipment, the process is safe, the cost is low, and it is suitable for large-scale production. The prepared catalyst is supported on the foam metal in situ, has a strong bonding force, is not easy to fall off, and has a low contact resistance. The oxygen evolution electrode prepared by this method has the advantages of low overpotential, long life, strong catalyst stability, low cost, etc., and has good prospects for industrial application.

Description

Technical Field

[0001] The present application relates to a self-supporting oxygen evolution catalyst and a preparation method and application thereof, belonging to the field of electrocatalysis technology. Background Art

[0002] The oxygen evolution reaction (OER) is a crucial step in the electrolytic production of hydrogen from water. Its slow kinetics limit the overall reaction efficiency. To improve the efficiency of water electrolysis, the development of efficient OER catalysts has become a research priority. Currently, Ir- and Ru-based noble metals and their oxides are considered to be excellent OER catalysts. However, the scarcity and high cost of these noble metals limit their feasibility in large-scale industrial applications. Therefore, the development of low-cost, resource-abundant non-noble metal catalysts has become a research hotspot.

[0003] Among the many non-precious metal catalysts, transition metal oxides have attracted widespread attention due to their excellent catalytic activity and stability. These catalysts not only exhibit activity close to that of precious metal catalysts in the OER reaction but also possess excellent long-term stability. However, existing transition metal oxide catalysts are typically obtained through complex preparation processes such as co-precipitation, hydrothermal methods, or electrodeposition. These methods require strict experimental conditions and equipment control, limiting their application in large-scale industrial production.

[0004] To overcome these issues, researchers have recently focused on the application of free-standing electrodes in OER catalysis. Compared to traditional supported electrodes, free-standing electrodes not only significantly improve catalyst performance but also simplify the preparation process. By directly loading the metal oxide catalyst onto a conductive substrate, free-standing electrodes eliminate the need for binders or additional current collectors, reducing interfacial resistance and improving charge transfer efficiency, thereby accelerating the OER reaction kinetics.

[0005] Furthermore, the design of the self-supporting structure helps optimize the electrode's specific surface area and pore structure, increasing the contact area between the catalyst and the electrolyte, further promoting the OER reaction. This structure not only improves the catalyst's utilization efficiency but also enhances its mechanical stability, effectively preventing the catalyst from falling off or losing during long-term electrolysis. As a result, self-supporting metal oxide electrodes exhibit excellent electrocatalytic performance and long-term durability, showing broad application prospects. Summary of the Invention

[0006] By introducing a self-supporting structure, this invention optimizes the composition and preparation process of the metal oxide catalyst, further enhancing the catalyst's electrocatalytic water oxidation performance. This method is simple, economical, and environmentally friendly, suitable for practical application in large-scale hydrogen production, and has the potential to promote the industrialization of OER catalysts.

[0007] This invention addresses the drawbacks of existing self-supporting metal oxide electrodes, which suffer from complex preparation processes and difficulty in large-scale application. By immersing a metal foam in an ethanol solution of metal cations and then igniting and burning it, metal oxide nanoparticles rapidly attach and grow on the foam skeleton. This method offers the advantages of simplicity, low raw material costs, high catalytic activity, excellent selectivity, and suitability for large-scale production. It is expected to provide a highly efficient catalyst for the industrialization of hydrogen production from water electrolysis.

[0008] According to one aspect of the present application, a self-supporting oxygen evolution electrode is provided. The self-supporting oxygen evolution electrode comprises a substrate and a porous catalytic layer supported on a surface of the substrate.

[0009] The porous catalytic layer is composed of metal oxide nanoparticles.

[0010] The metal oxide is selected from at least one of oxides of Ni, Fe, Co, Mn, Ce, W, V, and Mo.

[0011] The loading amount of the metal oxide in the self-supporting oxygen evolution electrode is 0.1-100 mg / cm 2 .

[0012] The particle size of the metal oxide nanoparticles is 10-30 nm.

[0013] The thickness of the porous catalytic layer is 50-300 nm.

[0014] The thickness of the substrate is 0.1-5 mm.

[0015] The substrate is selected from at least one of foamed nickel, foamed copper, foamed iron or foamed iron-nickel alloy.

[0016] According to another aspect of the present application, a method for preparing the above-mentioned self-supporting oxygen evolution electrode is provided, comprising the following steps:

[0017] The substrate is immersed in an ethanol solution containing a metal salt, the substrate is taken out, and ignited to obtain the self-supporting oxygen evolution electrode.

[0018] The metal salt is selected from at least one of nickel nitrate, iron nitrate, cobalt nitrate, manganese nitrate, cerium nitrate, tungsten chloride, vanadium chloride, and molybdenum chloride.

[0019] The concentration of the ethanol solution containing the metal salt is 0.01-1 mol / L.

[0020] The immersion time is 1 to 60 minutes.

[0021] The ignition atmosphere is an oxygen atmosphere or an air atmosphere.

[0022] The obtained substrate is cleaned.

[0023] The cleaning is carried out by sequentially using hydrochloric acid, ethanol and water.

[0024] When the self-supporting oxygen evolution electrode contains multiple metal oxides, the preparation method thereof comprises the following steps:

[0025] The substrate is immersed in an ethanol solution containing a first metal salt, the substrate is taken out, ignited, and then immersed in an ethanol solution containing a second metal salt, the substrate is taken out, ignited, and so on.

[0026] The further specific steps are:

[0027] Step 1) Cut the foam metal substrate into 10×10 cm 2 The blocks were ultrasonically cleaned with 1-3 mol / L hydrochloric acid solution for 30 minutes, and then repeatedly washed with ethanol and deionized water.

[0028] Step 2) Dissolve the metal salt in an ethanol solution. Once the metal salt is completely dissolved, soak the treated metal foam substrate in the solution for 5 minutes. After the reaction is complete, remove the metal foam substrate and ignite and ignite it under ambient conditions. After cooling, rinse with deionized water and ethanol, then dry in an oven at 60°C overnight to obtain a self-supporting metal oxide catalyst.

[0029] Electrocatalytic Water Oxidation Performance: In a standard three-electrode electrolytic cell system, the prepared metal oxide catalyst served as the working electrode, with a Hg / HgO electrode and a carbon rod as the reference and counter electrodes, respectively. A 1 M KOH solution was used as the electrolyte. All electrochemical performance tests were performed using a Chenhua 760E electrochemical workstation. Cyclic voltammetry (CV) electrochemical activation was performed before testing, with a voltage range of 0-1.5 V (vs. Hg / HgO) at a scan rate of 100 mV / s and 40 scans. After the CV scan curve stabilized, linear sweep voltammetry (LSV) polarization curves were performed, with a potential range of 0-1.5 V (vs. Hg / HgO) at a scan rate of 10 mV / s, and iR compensation set to 85%. Finally, the catalyst stability was evaluated by potentiostatic method.

[0030] According to another aspect of the present application, there is provided an application of the above-mentioned self-supporting oxygen evolution electrode for alkaline oxygen evolution reaction.

[0031] The key to the present invention lies in the precise selection of metal salts and solvents. First, compared to other metal salts, metal nitrates have unique combustion-supporting properties, readily decomposing and releasing oxidizing gases under high temperature conditions. This not only increases the temperature during the calcination process but also reduces the need to convert the metal salt from its ionic state to a solid state through steps such as roasting in the traditional preparation process. Furthermore, anhydrous ethanol, as a solvent, exhibits excellent solubility for metal nitrates and chlorides, significantly greater than other common alcohol solutions. This ensures the uniformity of the reaction. Ethanol's flammability further simplifies the process flow, and the heat released by combustion allows the required temperature to be quickly reached, thereby facilitating the efficient preparation of the metal oxide layer. Compared to the liquid-phase ion exchange strategy described in existing patents, although this method can produce self-supporting structured electrodes, the process generally requires a longer impregnation time and the loading of the catalytic active components is still limited. By optimizing the metal salt and solvent system, the present invention achieves a more efficient metal oxide preparation pathway, overcoming bottlenecks in the prior art.

[0032] The beneficial effects of this application include:

[0033] Environmental protection: The present invention does not use organic precipitants, thus avoiding environmental pollution. In addition, no strong alkaline precipitants are used, and the high temperature environment generated by the natural process of ethanol is utilized to make the catalyst particles evenly adhere to the foam metal skeleton, thereby reducing the environmental burden.

[0034] Economical and safe: The method of the present invention does not rely on high-temperature and high-pressure equipment, is safe to operate and low-cost, and is suitable for large-scale amplification and batch preparation.

[0035] Excellent catalytic performance: The catalyst is in situ loaded on the support, providing strong binding, reducing the risk of catalyst detachment, and providing low electrode contact resistance. The resulting oxygen evolution electrode exhibits high catalytic activity and low overpotential, with low internal resistance and catalyst resistance, extending the electrode's service life. Furthermore, it offers the advantages of low cost and ease of industrial production.

[0036] Advantages of self-supporting electrodes: As self-supporting electrodes, the present invention eliminates the need for a binder, which improves electron transport and reduces interfacial resistance. The surface nanostructure provides a rich pore structure and good hydrophilicity, which not only promotes the exposure of active sites but also improves electrolyte permeability.

[0037] Highly efficient catalytic performance: The iron oxide-tungsten oxide catalyst prepared by the present invention exhibits excellent catalytic activity and stability in the alkaline water oxidation process. In a 1 mol / L KOH solution, the catalyst can achieve 1 A / cm2 at a potential of only 1.65-1.75 V (vs. RHE). 2 industrial current density, and is capable of 0.5 A / cm 2 It maintains stability for more than 1000 hours at a current density that meets commercial requirements and provides a reliable catalyst for the development of water electrolysis hydrogen production systems. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 This is a scanning electron microscope (SEM) image of the FeO / NF catalyst in Example 1, with a scale of 50 μm.

[0039] Figure 2 This is the SEM image of the FeO-WO / NF catalyst in Example 2, with a scale of 50 μm.

[0040] Figure 3 is a linear sweep voltammetry (LSV) curve of the FeO-WO / NF catalyst in Example 2.

[0041] Figure 4 This is the stability test curve of the FeO-WO / NF catalyst in Example 2. DETAILED DESCRIPTION

[0042] The present invention will be further described below with reference to the following examples. The following examples are non-limiting implementation measures and are intended to enable those skilled in the art to more fully understand the technical content of the present invention, but are not intended to limit the scope of the present invention in any way.

[0043] Unless otherwise specified, the experimental methods described in the following examples are conventional methods; the reagents and materials described are commercially available unless otherwise specified.

[0044] Example 1:

[0045] The preparation method of the self-supporting iron oxide catalyst for oxygen evolution reaction in an alkaline environment is as follows:

[0046] Step 1) Cut the nickel foam substrate into 10*10 cm 2 The size was ultrasonically cleaned with 2 mol / L hydrochloric acid for 30 min and then repeatedly rinsed with ethanol and deionized water to remove the surface oxide layer.

[0047] Step 2) Prepare a 0.5 mol / L ferric nitrate ethanol solution; soak the treated nickel foam in the solution for 5 minutes; after the reaction is complete, remove the nickel foam, ignite it, and burn it under ambient conditions; after cooling, rinse it with deionized water and ethanol, and dry it in an oven overnight to obtain a self-supporting iron oxide catalyst (named FeO / NF).

[0048] The material morphology was characterized by scanning electron microscopy, and the results showed that the iron oxide catalyst had a granular stacking structure and grew on the skeleton of the nickel foam matrix ( Figure 1 In a standard three-electrode electrolytic cell system, the above catalyst was used directly as the working electrode, Hg / HgO and carbon rod were used as the reference electrode and counter electrode, respectively. The electrolyte was 1.0 mol / L KOH. All electrochemical performance tests were performed using a Chenhua 760E electrochemical workstation. Electrochemical tests showed that this type of catalyst requires an anode potential of 1.77 V (vs. RHE) to achieve 1 A / cm 2 industrial current density.

[0049] Example 2:

[0050] The preparation method of a self-supporting oxide catalyst for oxygen evolution reaction in an alkaline environment mentions that a multi-component metal oxide composite catalyst can be prepared to achieve better catalytic effects. Here, chloride is used for corresponding research as follows:

[0051] Step 1) Cut the nickel foam substrate into 10*10 cm 2 The size was ultrasonically cleaned with 2 mol / L hydrochloric acid for 30 min, and then rinsed repeatedly with ethanol and deionized water.

[0052] Step 2) Prepare a 0.5 mol / L ferric nitrate-ethanol solution; soak the treated nickel foam in this solution for 5 minutes. After the reaction is complete, remove the nickel foam, ignite and ignite it under ambient conditions. After cooling, rinse with deionized water and ethanol, and dry in an oven overnight to obtain a self-supporting iron oxide catalyst. Furthermore, soak the obtained iron oxide catalyst in a 0.5 mol / L tungsten chloride-ethanol solution for 5 minutes. After the reaction is complete, remove the substrate, ignite and ignite it under ambient conditions. After cooling, rinse with deionized water and ethanol, and dry in an oven overnight to obtain a self-supporting iron oxide-tungsten oxide catalyst (named FeO-WO / NF). Furthermore, by replacing tungsten chloride with molybdenum chloride and vanadium chloride, the resulting catalysts are iron oxide-molybdenum oxide (FeO-MoO / NF) and iron oxide-vanadium oxide (FeO-VO / NF).

[0053] From the perspective of morphology, this secondary calcination process has little effect on the morphology of the catalyst, and it still presents a uniform nanoparticle structure ( Figure 2 ), the catalytic performance of the two catalysts was further evaluated by electrochemical testing in the same manner. Compared with the iron oxide catalyst, the performance of the prepared two-component oxide catalyst was improved, and an anode potential of 1.69 V (vs. RHE) was required to achieve 1 A / cm 2 Industrial current density ( Figure 3 ); FeO-WO / NF catalyst at 0.5 A / cm 2 It can operate stably for more than 1000 hours at a current density of Figure 4 ).

[0054] Example 3:

[0055] The preparation method of a self-supporting electrocatalyst for oxygen evolution reaction in an alkaline environment mentions that the ratio of metal salt precursors can be adjusted. The corresponding research is as follows:

[0056] Step 1) Cut the nickel foam substrate into 10*10 cm 2 The size was ultrasonically cleaned with 2 mol / L hydrochloric acid for 30 min and then repeatedly rinsed with ethanol and deionized water to remove the surface oxide layer.

[0057] Step 2) Prepare an ethanol solution of 0.5 mol / L ferric nitrate and 0.5 mol / L tungsten chloride. Separately, prepare two solutions with varying Ni:W ratios: one containing 1.0 mol / L ferric nitrate and 0.3 mol / L tungsten chloride, and the other containing 0.3 mol / L ferric nitrate and 1.0 mol / L tungsten chloride. Immerse the treated nickel foam in each of these solutions for 5 minutes. After the reaction is complete, remove the nickel foam, ignite it, and ignite it under ambient conditions. After cooling, rinse with deionized water and ethanol, and dry in an oven overnight to obtain the self-supporting structures of FeO-WO / NF-1, FeO-WO / NF-2, and FeO-WO / NF-3.

[0058] Electrochemical tests showed that the three catalysts exhibited different catalytic activities for oxygen evolution, among which FeO-WO / NF-1 had the best catalytic performance, achieving 1 A / cm at an electrode potential of only 1.69 V (vs. RHE). 2 The other two require 1.72 V (vs.RHE) and 1.74 V (vs.RHE).

[0059] Example 4:

[0060] The preparation method of a self-supporting electrocatalyst for oxygen evolution reaction in an alkaline environment mentions that the concentration of the metal salt in step 2 is 0.01-1.0 mol / L. The corresponding research is as follows:

[0061] Step 1) Cut the nickel foam substrate into 10*10 cm 2 The size was ultrasonically cleaned with 2 mol / L hydrochloric acid for 30 min and then repeatedly rinsed with ethanol and deionized water to remove the surface oxide layer.

[0062] Step 2) Prepare 0.1, 0.5, and 1.0 mol / L ferric nitrate ethanol solutions, respectively. Immerse the treated nickel foam in these solutions for 5 minutes. After the reaction is complete, remove the nickel foam, ignite it, and burn it under ambient conditions. After cooling, rinse it with deionized water and ethanol, and dry it in an oven overnight to obtain FeO / NF catalysts prepared with solutions containing different metal salt concentrations.

[0063] In the metal salt solution of step 2, it was found that the prepared solution had limited solubility for the metal salt, and the excess metal salt was difficult to completely dissolve in ethanol. According to the results of scanning electron microscopy, the morphology of the catalysts showed stacked particles, but the stacked particles were relatively sparse at low concentrations. Therefore, it is more appropriate to control the metal salt concentration of this type of self-supporting structure catalyst synthesized at 0.5 mol / L.

[0064] Example 5:

[0065] The preparation method of a self-supporting electrocatalyst for oxygen evolution reaction in an alkaline environment mentions that the type of metal salt in step 2 can be adjusted. The corresponding research is as follows:

[0066] Step 1) Cut the nickel foam substrate into 10*10 cm 2 The surface oxide layer was removed by ultrasonic cleaning with 2 mol / L hydrochloric acid for 30 min and then repeatedly rinsed with ethanol and deionized water.

[0067] Step 2) Prepare 0.5 mol / L ethanol solutions of metal salts, including ferric nitrate, nickel nitrate, cobalt nitrate, manganese nitrate, cerium nitrate, tungsten chloride, vanadium chloride, and molybdenum chloride. Immerse the treated nickel foam in these solutions for 5 minutes. After the reaction is complete, remove the nickel foam, ignite it, and burn it under ambient conditions. After cooling, rinse it with deionized water and ethanol, and dry it in an oven overnight to obtain metal oxide catalysts prepared with different metal salt solutions.

[0068] According to the results of scanning electron microscopy, the morphology of the catalysts all appeared to be stacked particles without significant changes. However, there were large differences in the oxygen evolution activity of the catalysts. Among them, the self-supporting structure catalyst prepared from ferric nitrate had the best catalytic activity.

[0069] Example 6:

[0070] The preparation method of a self-supporting electrocatalyst for oxygen evolution reaction in an alkaline environment mentions that the substrate immersion time in step 2 is 1 to 60 minutes. The corresponding research is as follows:

[0071] Step 1) Cut the nickel foam substrate into 10*10 cm 2 The surface oxide layer was removed by ultrasonic cleaning with 2 mol / L hydrochloric acid for 30 min and then repeatedly rinsed with ethanol and deionized water.

[0072] Step 2) preparing a 0.5 mol / L ferric nitrate ethanol solution; immersing the treated nickel foam in the above mixture for 1 minute, 5 minutes, and 60 minutes, respectively; after the reaction is completed, removing the nickel foam, igniting and burning it under ambient conditions; after cooling, washing it with deionized water and ethanol, and drying it in an oven overnight to obtain iron oxide catalysts prepared with different immersion times.

[0073] In terms of morphology, the immersion time in step 2 had little effect on the catalyst's morphology. In terms of catalytic activity, the activity of the catalyst obtained with a shorter immersion time was lower, while a longer immersion time had no significant effect on catalytic activity. Overall analysis showed that a substrate immersion time of 5 minutes was optimal.

[0074] Example 7:

[0075] The preparation method of a self-supporting electrocatalyst for oxygen evolution reaction in an alkaline environment mentions that the ignition atmosphere in step 2 is pure oxygen or atmospheric environment, and the corresponding research is as follows:

[0076] Step 1) Cut the nickel foam substrate into 10*10 cm 2 The surface oxide layer was removed by ultrasonic cleaning with 2 mol / L hydrochloric acid for 30 min and then repeatedly rinsed with ethanol and deionized water.

[0077] Step 2) Prepare a 0.5 mol / L ferric nitrate ethanol solution; soak the treated nickel foam in the above mixture for 5 minutes; after the reaction is completed, remove the nickel foam, ignite and burn it under ambient conditions or pure oxygen conditions; wait for it to cool, wash it with deionized water and ethanol, and dry it in an oven overnight to obtain iron oxide catalysts prepared with different ignition environments.

[0078] In terms of morphology, the different ignition environments in step 2 have little effect on the catalyst, but in terms of catalytic activity, the catalyst prepared under pure oxygen conditions shows a slightly increased oxygen evolution catalytic activity.

[0079] Example 8:

[0080] The preparation method of self-supporting electrocatalyst for oxygen evolution reaction in alkaline environment mentioned that the substrate can be replaced, which can also achieve good results. Here, copper foam and iron foam are selected as the research substrates as follows:

[0081] Step 1) Cut the foam copper and foam iron into 10*10 cm 2 The size was ultrasonically cleaned with 2 mol / L hydrochloric acid for 30 min, and then rinsed repeatedly with ethanol and deionized water.

[0082] Step 2) Prepare a 0.5 mol / L ferric nitrate ethanol solution; soak the treated copper foam or iron foam in the solution for 5 minutes; after the reaction is complete, remove the copper foam or iron foam, ignite and burn it under ambient conditions; wait for it to cool, then rinse it with deionized water and ethanol, and dry it in an oven overnight to obtain a self-supporting iron oxide catalyst.

[0083] In terms of morphology, replacing the matrix with copper foam or iron foam has little effect on the morphology of the catalyst, which still presents a uniform nanoparticle structure. The catalytic performance of the two catalysts was further evaluated through electrochemical tests in the same way. Compared with the matrix based on nickel foam, the performance of both catalysts was reduced, among which the catalyst based on iron foam had relatively outstanding performance.

[0084] The above descriptions are merely a few embodiments of the present application and do not constitute any form of limitation to the present application. Although the present application discloses the preferred embodiments as above, they are not intended to limit the present application. Any technical personnel familiar with the present profession, without departing from the scope of the technical solution of the present application, using the technical content disclosed above to make slight changes or modifications are equivalent to equivalent implementation cases and fall within the scope of the technical solution.

Claims

1. Application of a self-supporting oxygen evolution electrode, characterized in that: Used for alkaline oxygen evolution reaction; The method for preparing the oxygen evolution electrode of the self-supporting structure comprises the following steps: Immersing the substrate in an ethanol solution containing a metal salt, taking out the substrate, and igniting it to obtain the self-supporting oxygen evolution electrode; When the self-supporting oxygen evolution electrode contains multiple metal oxides, the preparation method thereof comprises the following steps: The substrate is immersed in an ethanol solution containing a first metal salt, the substrate is removed, ignited, and then immersed in an ethanol solution containing a second metal salt, the substrate is removed, ignited, and so on; The metal salt is ferric nitrate, or ferric nitrate and tungsten chloride; When the first metal salt is ferric nitrate, the second metal salt is tungsten chloride; the concentration of the ethanol solution containing the metal salt is 0.01~1mol / L The self-supporting oxygen evolution electrode comprises a substrate and a porous catalytic layer supported on the surface of the substrate; The porous catalytic layer is composed of metal oxide nanoparticles; The metal oxide is selected from at least one of Fe and W oxides; The loading amount of the metal oxide in the self-supporting oxygen evolution electrode is 0.1-100 mg / cm 2 ; The particle size of the metal oxide nanoparticles is 10 to 30 nm; The thickness of the porous catalytic layer is 50-300 nm; The thickness of the substrate is 0.1-5 mm.

2. The use according to claim 1, characterized in that The substrate is selected from at least one of foamed nickel, foamed copper, foamed iron or foamed iron-nickel alloy.

3. The use according to claim 1, characterized in that The dipping time is 1 to 60 minutes; The ignition atmosphere is an oxygen atmosphere or an air atmosphere.

4. The use according to claim 1, characterized in that The obtained substrate is cleaned; The cleaning is carried out by sequentially using hydrochloric acid, ethanol and water.

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