A nanosheet heterostructure based on alkali etching, its preparation method and application in electrochemical oxygen evolution reaction
The heterostructure of nickel-iron-cobalt aluminum nanosheets was prepared by alkali etching, which solved the problem of slow oxygen evolution reaction, improved catalytic activity and current density, simplified the preparation process, and was suitable for electrochemical oxygen evolution reactions.
Patent Information
- Application Number
- CN202510227196.6
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- Filing Date
- 2025-02-27
- Publication Date
- 2025-08-12
- Estimated Expiration
- 2045-02-27
AI Technical Summary
The prior art is difficult to effectively solve the problem of slow oxygen evolution reaction, which leads to the electrolytic water reaction requiring large reaction overpotentials and high power consumption, and the high cost and scarcity of precious metal catalysts limit their large-scale application.
The heterostructure of nickel, iron, cobalt, aluminum layered bimetallic hydroxide nanosheets was prepared by alkali etching method, and porous structures were formed through element doping and alkali etching, increasing the specific surface area and active sites of the catalyst, and optimizing the electronic structure and surface properties.
It improves the catalytic activity of the catalyst, reduces the overpotential, increases the current density, simplifies the preparation process, and facilitates laboratory research and industrial production.
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Figure CN119800412B_ABST
Abstract
Description
Technical Field
[0001] The present invention belongs to the technical field of electrolytic water catalytic materials, and in particular relates to a nanosheet heterostructure based on alkali etching, a preparation method thereof, and an application thereof in an electrochemical oxygen evolution reaction. Background Art
[0002] The combustion of fossil fuels releases large amounts of greenhouse gases, causing environmental pollution and threatening human health. Developing renewable energy can reduce fossil fuel use. Clean energy sources such as solar and wind power offer inexhaustible resources, effectively reducing greenhouse gas emissions and protecting the environment. Hydrogen, due to its high calorific value and pollution-free properties, is considered a green alternative to fossil fuels.
[0003] With the rapid development of renewable energy (such as wind power and solar energy), the use of excess electricity to electrolyze water to produce hydrogen has become the main way to achieve green hydrogen energy. The water electrolysis reaction is divided into the hydrogen evolution reaction (HER) at the cathode and the oxygen evolution reaction (OER) at the anode. However, due to the slow kinetics of the oxygen evolution reaction, water electrolysis requires a large reaction overpotential, which leads to excessive power consumption and high hydrogen production costs. Precious metal-based catalysts such as IrO2 and RuO2 exhibit excellent OER activity, but their high cost and scarcity limit their large-scale application. Therefore, it is urgent to develop low-cost, highly catalytically active oxygen evolution reaction catalysts as alternatives. Among transition metals, nickel-iron elements and layered double hydroxides have shown great potential in oxygen evolution electrocatalytic performance due to their unique layered structure. However, their poor intrinsic conductivity and low basal catalytic activity restrict their electrocatalytic performance.
[0004] Nanosheet heterostructures can be rationally designed and combined to optimize the electronic structure and surface properties of catalysts, thereby improving their catalytic activity for the oxygen evolution reaction (OER). However, the preparation of nanosheet heterostructures typically requires complex synthesis methods and process conditions, making it difficult to precisely control the composition, morphology, and size of the heterostructures, which can lead to variations and uncertainties in catalyst performance.
[0005] Fabricating nanosheet heterostructures through alkaline etching creates a porous structure on the nanosheet surface, significantly increasing the specific surface area and number of active sites on the catalyst, thereby optimizing the nanosheet microstructure. This facilitates the adsorption and diffusion of reactants, accelerating chemical reactions such as the oxygen evolution reaction (OER), thereby enhancing the catalyst's catalytic activity.
[0006] The preparation of nanosheet heterostructures usually requires more complex synthesis methods and process conditions, and it is difficult to precisely control the composition, morphology, and size of the heterostructures, which may lead to certain differences and uncertainties in the performance of the catalyst. Summary of the Invention
[0007] In view of the shortcomings of the existing technology, the present invention provides a nanosheet heterostructure based on alkaline etching, its preparation method and application in electrochemical oxygen evolution reaction. The present invention adopts the following technical solutions:
[0008] In one aspect, the present invention provides a method for preparing a nanosheet heterostructure based on alkaline etching, comprising the following steps:
[0009] S1, preparation of nickel-iron-cobalt-aluminum layered double hydroxide precursor: weighing metal salts, including cobalt salt, iron salt, nickel salt, and aluminum salt; adding water, and then adding urea, and vigorously stirring; transferring the resulting product to a polytetrafluoroethylene-lined container, sealing it, and placing it in a stainless steel autoclave, heating and reacting; cooling it, taking it out, and washing and drying the resulting product;
[0010] S2, preparation of nickel-iron-cobalt-aluminum layered double hydroxide: etching with alkaline solution.
[0011] Preferably, in step S1, the metal salt is a metal chloride, nitrate, sulfate or phosphate.
[0012] Preferably, in step S1, the cobalt salt is cobalt chloride hexahydrate, the aluminum salt is aluminum chloride hexahydrate, the iron salt is ferric chloride hexahydrate, and the nickel salt is nickel chloride hexahydrate.
[0013] Preferably, in step S1, the relatively weak alkalinity of urea is utilized, and the precursor is relatively easy to synthesize under this condition.
[0014] Preferably, in step S1, the reaction temperature is 90°C to 120°C.
[0015] Preferably, in step S1, when preparing the precursor, the added reactants CoCl2·6H2O and AlCl3·6H2O account for 90% in total, and NiCl2·6H2O and FeCl3·6H2O account for 10% in total.
[0016] Furthermore, in step S1, the ratio of CoCl2·6H2O to AlCl3·6H2O is 3:1, and the ratio of NiCl2·6H2O to FeCl3·6H2O is 3:1.
[0017] Preferably, in step S2, the alkaline solution is a strong alkaline solution selected from potassium hydroxide or sodium hydroxide. Since aluminum is amphoteric, it can form tetrahydroxyaluminate with the strong base, dissolve in water, and use the strong base to etch the aluminum ions.
[0018] Preferably, in step S2, the concentration of the alkaline solution is 8M, and etching is performed at room temperature.
[0019] Preferably, in step S2, the alkaline etching is performed at room temperature.
[0020] Due to the amphoteric nature of aluminum ions, they can generate tetrahydroxyaluminum ions at high alkali concentrations. Therefore, the purpose of both aluminum ions and etching is to etch aluminum in the form of ions in the second step, freeing up sites for the doping of elements such as Ni, Fe, and Co that are more likely to form active sites into the catalyst. Essentially, the goal is to create more active sites.
[0021] In a second aspect, the present invention also provides a product obtained by a method for preparing a nanosheet heterostructure based on alkali etching.
[0022] In a third aspect, the present invention further provides an application of a product obtained by a method for preparing a nanosheet heterostructure based on alkali etching in an electrochemical oxygen evolution reaction, wherein the product is used as a catalyst in the electrochemical oxygen evolution reaction.
[0023] Compared with the prior art, the present invention has the following beneficial effects:
[0024] (1) Based on layered metal hydroxides (LDHs) materials, the present invention uses element doping to synthesize a water electrolysis catalyst with better performance. Experimental comparisons show that it has a lower overpotential and a higher current density (LSV).
[0025] (2) The present invention provides a nanosheet heterostructure prepared by an alkaline etching method, which has a unique layered structure of layered metal hydroxide and can provide a large specific surface area. This means that there are more active sites available for adsorption of reactants (such as water molecules and ions), promoting the occurrence of water electrolysis reaction.
[0026] By alkali etching the nanosheet heterostructure, the nanosheet structure is made thinner and lighter, which increases the specific surface area and the number of active sites of the catalyst, making the reactants easier to adsorb and diffuse, accelerating chemical reactions such as the oxygen evolution reaction (OER), and improving the catalytic activity of the catalyst.
[0027] (3) The present invention can reduce the activation energy of the water electrolysis reaction to a certain extent by doping different metal ions and utilizing the synergistic effect between ions.
[0028] (4) The preparation process of the present invention is relatively simple, does not require complicated equipment and operation steps, is convenient for laboratory research and industrial production, and can quickly prepare nanosheet heterostructures. BRIEF DESCRIPTION OF THE DRAWINGS
[0029] The accompanying drawings, which constitute a part of the present invention, are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute improper limitations on the present invention.
[0030] Figure 1This is the XRD diffraction pattern of the 10% alkali-etched nickel-iron-cobalt-aluminum layered double hydroxide material prepared in Example 1 of Experimental Example 1;
[0031] Figure 2 The scanning electron microscope image and transmission electron microscope image of the 10% alkali-etched nickel-iron-cobalt-aluminum layered double hydroxide material prepared in Example 1 of Experimental Example 1 are shown, wherein (a) is a scanning electron microscope image and (b) is a transmission electron microscope image;
[0032] Figure 3 This is a comparison chart of the LSV properties of the samples of Examples 1 to 5 in Experimental Example 2;
[0033] Figure 4 CV property comparison chart of samples of Examples 1 to 5 in Experimental Example 2;
[0034] Figure 5 This is the LSV property diagram of the samples of Example 6, Comparative Example 1, Comparative Example 2 and Example 1 in Experimental Example 2. DETAILED DESCRIPTION
[0035] It should be noted that the following detailed descriptions are exemplary and intended to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which the present invention belongs.
[0036] Explanation of terms:
[0037] Nanosheet heterostructures are materials systems with unique properties and structures, formed by combining nanosheets of two or more different materials in a specific manner. The complementary and synergistic properties of each component material give the heterostructure superior overall performance compared to a single material. They can serve as highly efficient catalysts in chemical reactions.
[0038] Alkali etching: It is a material surface treatment technology that uses alkaline solution to react with the material, selectively dissolving part of it and changing the surface morphology, structure or performance.
[0039] Layered metal hydroxides (LDHs) are generally composed of divalent and trivalent metal hydroxides, forming octahedral, two-dimensional layers. The metal ion is located at the center of the octahedron, surrounded by hydroxide ions. The layers are connected by sharing edges or corners to form a two-dimensional plane. The structural characteristics of LDHs allow the interlayer anions to exchange with various anions. This property can be exploited to synthesize different types of LDHs by adjusting the type of interlayer anions and imparting different properties, thereby creating a new class of materials with diverse functionalities.
[0040] Example 1
[0041] The first step is to prepare a 10% nickel-iron-cobalt-aluminum layered double hydroxide precursor: Using a 1 / 10,000th balance, CoCl2·6H2O (0.81 mmol), AlCl3·6H2O (0.27 mmol), FeCl3·6H2O (0.03 mmol), and NiCl2·6H2O (0.09 mmol) are weighed into a beaker, with the iron salt weighed last. 80 ml of deionized water and 3.2 mmol of urea (0.192 g) are then added, stirring vigorously for 30 minutes. After stirring for 30 minutes, the solution is transferred to a 100 mL polytetrafluoroethylene-lined container, sealed, and placed in a stainless steel autoclave. The reaction is then heated at 100°C for 24 hours. After cooling to room temperature, the autoclave is removed and the resulting product is rinsed several times with deionized water and anhydrous ethanol, then dried in a vacuum oven.
[0042] The second step involved 10% alkaline etching of nickel-iron-cobalt-aluminum layered double hydroxide (main product) using 8M NaOH at room temperature. Specifically, 30 mg of sample was placed in a beaker, 10 ml of water was added, and stirred. A large magnetic particle was added, stirred thoroughly, and then mixed with 30 ml of NaOH solution, resulting in a total of 40 ml of solution with a total concentration of 8M NaOH. Etching was performed vigorously at room temperature for 12 hours.
[0043] Example 2
[0044] The first step is the preparation of a 10% nickel-cobalt-aluminum layered double hydroxide precursor (NiCoAl-e 10% Ni 90% CoAl): NiCl2·6H2O (0.12 mmol), AlCl3·6H2O (0.27 mmol), and CoCl2·6H2O (0.81 mmol) are placed in a beaker, 80 ml of deionized water is added, and 3.2 mmol of urea (0.192 g) is added. The mixture is stirred vigorously for 30 minutes. After stirring for 30 minutes, the solution is transferred to a 100 mL polytetrafluoroethylene-lined container, sealed, and placed in a stainless steel autoclave. The reaction is continued at 100°C for 24 hours. After cooling to room temperature, the autoclave is removed and the resulting product is washed several times with deionized water and anhydrous ethanol, respectively, and finally dried in a vacuum drying oven.
[0045] The second step involved 10% alkaline etching of nickel-cobalt-aluminum layered double hydroxides using 8M NaOH at room temperature. Specifically, 30mg of sample was placed in a beaker, and 10ml of water was added and stirred. A large magnetic particle was added, stirred thoroughly, and then mixed with 30ml of NaOH solution, resulting in a total of 40ml of solution with a total concentration of 8M NaOH. Etching was performed vigorously at room temperature for 12 hours.
[0046] Example 3
[0047] The first step is the preparation of a 10% iron-cobalt-aluminum layered double hydroxide precursor (FeCoAl-e 10% Fe90% CoAl): FeCl3·6H2O (0.12 mmol), AlCl3·6H2O (0.27 mmol), and CoCl2·6H2O (0.81 mmol) are placed in a beaker, 80 ml of deionized water is added, and 3.2 mmol of urea (0.192 g) is added. The mixture is stirred vigorously for 30 minutes. After stirring for 30 minutes, the solution is transferred to a 100 mL polytetrafluoroethylene-lined container, sealed, and placed in a stainless steel autoclave. The reaction is continued at 100°C for 24 hours. After cooling to room temperature, the autoclave is removed and the resulting product is washed several times with deionized water and anhydrous ethanol, respectively, and finally dried in a vacuum drying oven.
[0048] The second step involved 10% alkaline etching of the Fe-Co-Al layered double hydroxide using 8M NaOH at room temperature. Specifically, 30mg of sample was placed in a beaker, and 10ml of water was added and stirred. A large magnetic particle was added, stirred thoroughly, and then mixed with 30ml of NaOH solution, resulting in a total of 40ml of solution with a total concentration of 8M NaOH. Etching was performed vigorously at room temperature for 12 hours.
[0049] Example 4
[0050] The first step is the preparation of a 10% nickel-iron-aluminum layered double hydroxide precursor (NiFeAl-e 10% NiFe90% Al): AlCl3·6H2O (1.08 mmol), FeCl3·6H2O (0.03 mmol), and NiCl2·6H2O (0.09 mmol) are placed in a beaker, 80 ml of deionized water is added, and 3.2 mmol of urea (0.192 g) is added. The mixture is stirred vigorously for 30 minutes. After stirring for 30 minutes, the solution is transferred to a 100 mL polytetrafluoroethylene-lined container, sealed, and placed in a stainless steel autoclave. The reaction is continued at 100°C for 24 hours. After cooling to room temperature, the autoclave is removed and the resulting product is washed several times with deionized water and anhydrous ethanol, respectively, and finally dried in a vacuum drying oven.
[0051] The second step involved 10% alkaline etching of nickel-iron-aluminum layered double hydroxides using 8M NaOH at room temperature. Specifically, 30mg of sample was placed in a beaker, and 10ml of water was added and stirred. A large magnetic particle was added, stirred thoroughly, and then mixed with 30ml of NaOH solution, resulting in a total of 40ml of solution with a total concentration of 8M NaOH. Etching was performed vigorously at room temperature for 12 hours.
[0052] Example 5
[0053] The first step is the preparation of the cobalt-aluminum layered double hydroxide precursor (CoAl-e 75% Co 25% Al): AlCl3·6H2O (0.3mmol) and CoCl2·6H2O (0.9mmol) are placed in a beaker, 80ml of deionized water is added, and 3.2mmol of urea (0.192g) is added. The mixture is stirred vigorously for 30min. After stirring for 30min, the solution is transferred to a 100mL polytetrafluoroethylene-lined container, sealed, and placed in a stainless steel autoclave. The reaction is carried out at 100°C for 24h. After cooling to room temperature, the autoclave is removed, and the resulting product is washed several times with deionized water and anhydrous ethanol, and finally dried in a vacuum drying oven.
[0054] The second step involves alkaline etching of the cobalt-aluminum layered double hydroxide using 8M NaOH at room temperature. Specifically, 30mg of sample was placed in a beaker, and 10ml of water was added and stirred. The largest magnet was then added, stirred thoroughly, and then mixed with 30ml of NaOH solution, resulting in a total of 40ml of solution with a total concentration of 8M NaOH. Etching was performed vigorously at room temperature for 12 hours.
[0055] Example 6,
[0056] The reaction temperature was changed to 200° C., and the other conditions were the same as in Example 1.
[0057] Comparative Example 1:
[0058] (1) Preparation and alkaline etching of 20% NiFe:CoAl layered double hydroxide:
[0059] Using a 1 / 10,000 balance, CoCl2·6H2O (0.72 mmol), AlCl3·6H2O (0.24 mmol), FeCl3·6H2O (0.06 mmol), and NiCl2·6H2O (0.18 mmol) were weighed into a beaker, with the iron salt weighed last. 80 ml of deionized water and 3.2 mmol of urea (0.192 g) were added, and the mixture was stirred vigorously for 30 minutes. After stirring for 30 minutes, the solution was transferred to a 100 mL polytetrafluoroethylene-lined container, sealed, and placed in a stainless steel autoclave. The reaction was allowed to proceed at 100°C for 24 hours. After cooling to room temperature, the autoclave was removed, and the resulting product was rinsed several times with deionized water and anhydrous ethanol, then dried in a vacuum oven.
[0060] Take 30 mg of sample in a beaker, add 10 ml of water and stir first, add the largest size magnet, stir evenly, and then mix with 30 ml of NaOH solution, a total of 40 ml of solution, with a total concentration of 8M NaOH, and etch vigorously at room temperature for 12 hours.
[0061] Comparative Example 2:
[0062] (1) Preparation and alkaline etching of 5% NiFe:CoAl layered double hydroxide:
[0063] Using a 1 / 10,000 balance, CoCl2·6H2O (0.855 mmol), AlCl3·6H2O (0.285 mmol), FeCl3·6H2O (0.015 mmol), and NiCl2·6H2O (0.045 mmol) were weighed into a beaker, with the iron salt weighed last. 80 ml of deionized water and 3.2 mmol of urea (0.192 g) were added, and the mixture was stirred vigorously for 30 minutes. After stirring for 30 minutes, the solution was transferred to a 100 mL polytetrafluoroethylene-lined container, sealed, and placed in a stainless steel autoclave. The reaction was allowed to proceed at 100°C for 24 hours. After cooling to room temperature, the autoclave was removed and the resulting product was rinsed several times with deionized water and anhydrous ethanol, then dried in a vacuum oven.
[0064] Take 30 mg of sample in a beaker, add 10 ml of water and stir first, add the largest size magnet, stir evenly, and then mix with 30 ml of NaOH solution, a total of 40 ml of solution, with a total concentration of 8M NaOH, and etch vigorously at room temperature for 12 hours.
[0065] Test Example 1
[0066] Figure 1 The X-ray diffraction patterns of the nanosheet heterostructure materials prepared in this embodiment and the comparative example show that CoO(OH) is detected, indicating that metal ions with higher valence are generated, which means that there are more active sites.
[0067] Through transmission electron microscopy and scanning electron microscopy tests, such as Figure 2 As shown in (a) and (b), the nanosheet heterostructure prepared by the present invention is sheet-shaped and thin, which makes it have better catalytic activity.
[0068] Test Example 2
[0069] The products prepared in the Examples and Comparative Examples were used in water electrolysis tests using a typical three-electrode system and linear sweep voltammetry on a Chenhua electrochemical workstation. The working electrode was an electrode coated with the nanosheet heterostructured nanomaterial, the counter electrode was a platinum electrode, and the reference electrode was a Hg / HgO electrode. 1 mol / L potassium hydroxide was used as the electrolyte, and the reaction apparatus was a glass electrolytic cell.
[0070] Comparison of LSV properties of samples from Example 1 to Example 5 Figure 3 As shown, the CV property comparison is Figure 4The electrochemical properties of the product of Example 1 of the present invention show that the main product 10% NiFe:CoAl is 10mAcm -2 At a current density of 1.50 V vs. RHE, the potential is close to 240 mA cm -2 The current density, overpotential and maximum current density are all higher than those of the control sample, indicating excellent properties and improved catalytic efficiency. The overpotential values (mV) of NiFe:CoAl measured in Examples 1 to 6, Comparative Example 1 and Comparative Example 2 are shown in Table 1.
[0071] Table 1 NiFe:CoAl overpotential values (mV) measured in Examples 1 to 6, Comparative Example 1, and Comparative Example 2
[0072]
[0073] The LSV properties of Example 6, Comparative Example 1 and Comparative Example 2 and the sample of Example 1 are as follows: Figure 5 As shown, the LSV curve measured in Example 6 decreases. This is presumably due to the fact that the temperature control is set to 200°C. At high temperatures, the layered double hydroxide morphology becomes non-uniform, and the sheet structure becomes thicker, reducing the exposure of edge active sites. Alternatively, excessive particle growth and agglomeration reduce the specific surface area, thereby reducing the number of active sites available for catalytic reactions.
[0074] From the comparison of Comparative Example 1, Comparative Example 2 and Example 1, it can be seen that the LSV curves of the main product 20% NiFe:CoAl and the main product 5% NiFe:CoAl are lower than those of the main product 10% NiFe:CoAl. The samples prepared with the ion ratios provided in Example 1 have better catalytic properties. 2+ and Co 2+ The ratio of Ni has a significant effect on the catalytic performance of the material (especially the electrolytic water performance). 2+ and Co 2+ The proportion of Ni will directly affect the electronic structure, number of active sites, conductivity and catalytic reaction kinetics of the material. The excellent amphoteric properties of Al are essential for alkaline etching. 2+ Provide active sites, Co 2+ Enhance electrical conductivity, the synergistic effect of the two improves catalytic efficiency. Fe3+ has rich redox properties and can enhance the redox ability of the material. The introduction of Fe3+ can adjust the electronic structure of layered double hydroxides and improve electrical conductivity. It is usually used as an auxiliary metal ion and is combined with other metal ions (such as Ni 2 +, Co2+) synergistically improve catalytic performance. Aluminum ions have excellent amphoteric properties and play an important role in alkaline etching. They can form tetrahydroxyaluminate with strong bases and dissolve in water.
[0075] The foregoing description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention are intended to be within the scope of protection of the present invention.
Claims
1. A method for preparing a nanosheet heterostructure based on alkali etching, characterized in that: The steps include: S1, preparation of nickel-iron-cobalt-aluminum layered double hydroxide precursor: weighing metal salts, including cobalt salt, iron salt, nickel salt, and aluminum salt; adding water, and then adding urea, and vigorously stirring; transferring the resulting product to a polytetrafluoroethylene-lined container, sealing it, and placing it in a stainless steel autoclave, heating and reacting; cooling it, taking it out, and washing and drying the resulting product; S2, preparation of nickel-iron-cobalt-aluminum layered double hydroxide: etching the nickel-iron-cobalt-aluminum layered double hydroxide precursor prepared in step S1 with an alkaline solution; In step S1, when the precursor is prepared, the cobalt salt is CoCl2•6H2O, the aluminum salt is AlCl3•6H2O, the iron salt is FeCl3•6H2O, and the nickel salt is NiCl2•6H2O; the added CoCl2•6H2O and AlCl3•6H2O account for 90% by mole, and the added NiCl2•6H2O and FeCl3•6H2O account for 10% by mole; In step S1, the molar ratio of CoCl2•6H2O to AlCl3•6H2O is 3:1, and the molar ratio of NiCl2•6H2O to FeCl3•6H2O is 3:1; In step S1, the reaction temperature is 90°C to 120°C.
2. The method for preparing a nanosheet heterostructure based on alkali etching according to claim 1, characterized in that: In step S2, the alkaline solution is a strong alkaline solution selected from potassium hydroxide or sodium hydroxide.
3. The method for preparing nanosheet heterostructures based on alkali etching according to claim 2, characterized in that: In step S2, the concentration of the alkaline solution is 8M.
4. The method for preparing nanosheet heterostructures based on alkali etching according to claim 1, characterized in that: In step S2, the alkaline etching is performed at room temperature.
5. A product obtained by the method for preparing a nanosheet heterostructure based on alkali etching according to any one of claims 1 to 4.
6. Use of the product obtained by the method for preparing nanosheet heterostructures based on alkali etching according to claim 5 in an electrochemical oxygen evolution reaction.