A method of preparing a sulfur-doped nickel hydroxide-based self-supporting water electrolysis anode

Abstract

The application discloses a method for preparing a sulfur-doped nickel hydroxide-based self-supporting water electrolysis anode, and belongs to the technical field of water electrolysis catalyst electrode preparation, and comprises the following steps: S1, preparing an active solution by mixing a strong oxidizing salt, thiourea and a transition metal salt; S2, pretreating a nickel-containing metal substrate to obtain a precursor; and S3, immersing the precursor in the active solution, ultrasonic-impregnating and in-situ oxidizing to obtain the sulfur-doped nickel hydroxide-based self-supporting water electrolysis anode. The method for preparing the sulfur-doped nickel hydroxide-based self-supporting water electrolysis anode has the advantages that an oxidant-thiourea-transition metal salt synergistic reaction system is adopted, an ultrasonic auxiliary technology is combined, a high-performance catalytic layer is directly grown on the surface of a metal substrate in-situ at room temperature, high catalytic activity, excellent stability and mass production of the electrode are simultaneously achieved, and the core pain points of long process, high energy consumption and difficulty in amplification of the prior art are fundamentally solved.

Description

Technical Field

[0001] This invention relates to the field of preparation technology of catalytic electrodes for water electrolysis, and in particular to a method for preparing a sulfur-doped nickel hydroxide-based self-supporting anode for water electrolysis. Background Technology

[0002] With the rapid development of China's green hydrogen industry, alkaline electrolyzers, as the mainstream hydrogen production technology, face increasingly urgent requirements for their anode materials in terms of low overpotential and high stability. Nickel hydroxide (Ni(OH)2), with its Ni... 2+ / Ni 3+ / Ni 4+ Its reversible redox reaction makes it a promising candidate material for applications. However, its poor intrinsic conductivity and the tendency for lattice oxygen to dissolve during the reaction limit its catalytic activity and long-term operational stability.

[0003] Recent studies have shown that anion doping strategies such as sulfur (S) and nitrogen (N) can effectively modulate the electronic structure, narrow the band gap, and enhance the covalent nature of Ni–O bonds, thereby significantly improving the performance and stability of the oxygen evolution reaction (OER). However, existing synthesis methods (such as hydrothermal methods, high-temperature sulfidation, and nitriding processes) typically rely on high-temperature (≥400℃) and high-pressure environments, and may involve toxic gases. These methods suffer from high energy consumption, complex processes, poor batch consistency, and demanding equipment requirements, making it difficult to achieve continuous, large-scale fabrication of large-area electrodes.

[0004] Therefore, developing a large-scale fabrication process for sulfur-doped nickel hydroxide-based electrodes that can be achieved in situ on a self-supporting nickel substrate at room temperature in one step has become the key to breaking through the current technological bottleneck. Summary of the Invention

[0005] The purpose of this invention is to provide a method for preparing a sulfur-doped nickel hydroxide-based self-supporting electrolytic water anode. The method employs a synergistic reaction system of oxidant-thiourea-transition metal salt, combined with ultrasound-assisted technology, to directly grow a high-performance catalytic layer on the surface of a metal substrate at room temperature. This aims to simultaneously achieve high catalytic activity, excellent stability, and large-scale preparation of the electrode, fundamentally solving the core pain points of existing technologies such as long process, high energy consumption, and difficulty in scale-up.

[0006] To achieve the above objectives, the present invention provides a method for preparing a sulfur-doped nickel hydroxide-based self-supporting water electrolysis anode, comprising the following steps: S1. Prepare an active solution by mixing a strong oxidizing salt, thiourea, and a transition metal salt. S2. Pretreatment of nickel-containing metal substrate to obtain precursor; S3. The precursor is immersed in the active solution, ultrasonically impregnated, and oxidized in situ to obtain a sulfur-doped nickel hydroxide-based self-supporting water electrolysis anode.

[0007] Preferably, the specific operation of S1 is as follows: the strong oxidizing salt, thiourea and transition metal salt are added to deionized water in sequence and stirred evenly to obtain an active solution.

[0008] Preferably, in S1, the concentration of the strong oxidizing salt is 0.002-0.3 mol·L⁻¹. -1 The thiourea concentration was 0.005-0.25 mol·L⁻¹. -1 The concentration of transition metal salts is 0-0.5 mol·L⁻¹ -1 The molar ratio of strong oxidizing salts, thiourea and transition metal salts is (2-40):1:(0-100).

[0009] Preferably, in S1, the strong oxidizing salt is one of sodium persulfate, potassium persulfate, ammonium persulfate, and sodium perborate, and the transition metal salt is one or more of nitrate, sulfate, and acetate.

[0010] Preferably, in S1, the transition metal salt is one or more of the following: nickel nitrate, nickel sulfate, nickel acetate, ferric nitrate, ferric sulfate, ferric acetate, ferrous nitrate, ferrous sulfate, cobalt nitrate, cobalt sulfate, cobalt acetate, manganese nitrate, manganese sulfate, manganese acetate, copper nitrate, copper sulfate, copper acetate, chromium nitrate, chromium sulfate, cerium nitrate, and lanthanum nitrate.

[0011] Preferably, the specific operation of S2 is as follows: the nickel-containing metal substrate is washed sequentially with dilute hydrochloric acid, deionized water and anhydrous ethanol to obtain the precursor.

[0012] Preferably, in S2, the concentration of dilute hydrochloric acid is 0.5-3 mol·L⁻¹. -1 Clean for 3-10 minutes. The nickel-containing metal substrate is one of the following: nickel-containing foam metal, nickel-containing metal fiber felt, nickel-containing metal mesh, or nickel-containing metal foil.

[0013] Preferably, in S2, the nickel-containing metal substrate is one of Ni metal, NiMo alloy, NiCo alloy, NiFe alloy, and TiNi alloy.

[0014] Preferably, the specific operation of S3 is as follows: S31. Place the precursor in a container filled with an active solution, and completely immerse the precursor in the active solution. After the surface of the precursor is fully wetted, place it together with the container in an ultrasonic water bath for ultrasonic vibration. S32. After sonication, immediately remove the precursor from the container, leaving the surface liquid, spread the precursor evenly in a petri dish, and let it stand at room temperature to obtain a precursor with a surface covered with catalytically active substances. S33. Remove the precursor covered with catalytically active material from the culture dish, clean the soluble byproducts on the surface, and dry to obtain a sulfur-doped nickel hydroxide-based self-supporting water electrolysis anode.

[0015] Preferably, in S31, the ultrasonic vibration frequency is 25-40kHz and the ultrasonic time is 3-10min; In S32, the thickness of the residual liquid on the surface is 0.3-0.5 mm, and the standing time is 5-24 h; In S33, the specific operation of drying after cleaning the soluble byproducts on the surface is as follows: the precursor covered with catalytic active material on the surface is washed with deionized water and anhydrous ethanol for 5-8 minutes in sequence, and then air-dried at room temperature.

[0016] This invention also provides an application for preparing a sulfur-doped nickel hydroxide-based self-supporting water electrolysis anode, wherein the sulfur-doped nickel hydroxide-based self-supporting water electrolysis anode prepared by the above-described method is applied to water electrolysis.

[0017] The principle of this invention is as follows: a nickel-containing metal substrate is ultrasonically impregnated in a mixed solution of "strong oxidizing salt-thiourea-transition metal salt", then removed and placed in the air. The whole process can be divided into two steps: "oxidation-coordination in solution" and "secondary oxidation-sulfidation in air".

[0018] Dissolving a strong oxidizing salt containing persulfate or perborate, a small amount of thiourea, and transition metal salts such as nickel sulfate in water yields a product that possesses both strong oxidizing power and can provide Ni. 2+ An active solution containing S source was prepared; subsequently, the nickel substrate was sequentially cleaned with dilute hydrochloric acid-water-ethanol to remove the surface oxide layer. Next, the clean nickel-containing metal substrate was immersed in the active solution and subjected to ultrasonic vibration: ultrasonic cavitation instantly stripped surface bubbles and forced the solution into the microgrooves; simultaneously, localized heating caused the strong oxidizing salt to rapidly oxidize the nickel substrate to Ni. 2+ and Ni 3+ Trace amounts of thiourea are reacted with strong oxidizing free radicals (OH· / SO4·) in the strong oxidizing salt. - Oxidation forms •SC(=NH)NH2,SO3 - -R fragments, instantly interacting with Ni 2+ / Ni 3+ Bonding occurs, forming Ni–S–Ni bonds, thus completing S doping.

[0019] After ultrasound, the substrate, still containing residual liquid, was left to stand in room temperature air for several hours: Ni in the residual liquid on the surface... 2+ Continued to be affected by O2 and residual S2O8 in the air 2- Oxidation and hydrolysis occur simultaneously, with thiourea in the residual liquid continuously providing S atoms as a S source: Ni 2 + / Ni 3+ +(2–x)OH - + x / 2O2→ NiO x Hy (S) + H₂O. Due to the extremely thin residual liquid and limited diffusion, oxidation and dehydration occur simultaneously, resulting in the formation of S-doped nickel hydroxide (NiO) on the electrode surface. x H y (S) Electrocatalytic active layer. High-valence Ni 3+ And S doping makes NiO x H y The Fermi level shifts upward, the band gap narrows, resulting in a black appearance. After washing with deionized water and anhydrous ethanol to remove soluble salts, a sulfur-doped nickel hydroxide-based electrocatalytic electrode that is tightly bonded to the substrate and self-supporting is obtained.

[0020] The introduction of S can improve NiO x H y The electronic conductivity of NiO is significantly enhanced. x H y The high charge transport efficiency ensures rapid charge migration during the OER process, thereby increasing the reaction rate. Furthermore, the incorporation of S atoms can lead to lattice distortion or the generation of defects. These defect sites themselves can serve as active centers and can modulate the local electronic structure, enhancing the reaction rate with reactants (such as OH groups). - The adsorption of ) enhances NiO. x H y catalytic activity.

[0021] Therefore, the method for preparing a sulfur-doped nickel hydroxide-based self-supporting electrolytic water anode described above has the following beneficial effects: (1) The preparation conditions of this invention are mild and the preparation process is simple: the entire preparation process is carried out at room temperature and normal pressure, without the need for high temperature furnaces or high pressure vessels, which simplifies the complex process of traditional multi-step doping (such as synthesis followed by sulfidation). The process consists of only three steps: "ultrasonic impregnation - room temperature reaction - air drying". The reaction is mild, the process is extremely simple, and the efficiency is doubled.

[0022] (2) The present invention has low raw material and equipment investment costs and good economic benefits: the whole process does not require precious metals (such as Ir, Ru), and is mainly based on non-precious metals such as nickel, which significantly reduces the cost of raw materials. Thiourea and other materials are used as dopant sources, which has a low cost; and the reaction can be completed at room temperature with ultrasonic assistance, without relying on complex equipment, which greatly reduces energy consumption and avoids the safety risks and equipment investment costs caused by high temperature and high pressure.

[0023] (3) This invention is energy-saving and emission-reducing, green and low-carbon: This invention reduces the preparation temperature from the traditional high temperature range of 400~800℃ to room temperature, completely eliminating the generation of toxic byproducts such as H2S, NH3, SO2, etc., and eliminating the need for tail gas washing, adsorption or incineration devices; at the same time, energy consumption is reduced by more than 70%; the whole process can be completed in an open container, without high pressure or risk of combustion and explosion, making the operation safer; the waste liquid is only a weakly acidic salt solution, which can be reused or discharged in compliance with standards after simple precipitation, truly achieving green and low-carbon manufacturing with "zero tail gas and zero hazardous waste".

[0024] (4) The preparation method of the present invention has controllability and wide window adjustability: The present invention takes "room temperature doping" as the core. The amount of S doping can be precisely controlled by adjusting the thiourea concentration in the same process. At the same time, different metal elements such as Fe, Co, Mn, Cu, Cr, Ce, and La can be introduced arbitrarily by changing the transition metal salt, so as to achieve wide window adjustability of Ni-MS multi-component composition. This "dual-dimensional adjustable" mechanism allows the electrocatalytic activity, stability and cost structure to be customized as needed without changing the equipment. It truly realizes the rapid switching of multiple formulations on the same process platform, which significantly improves the controllability of technology and market adaptability.

[0025] (5) The electrode material prepared by this invention exhibits excellent OER catalytic activity, with an OER overpotential ≤220mV@10mA cm⁻¹ at a current density. -2 Superior to existing commercial Raney nickel anodes with a voltage of 300~400mV: The catalytic active layer on the electrode surface is directly chemically bonded to the nickel substrate without the need for a binder. The active material grows directly on the conductive substrate, forming an integrated and seamless conductive network. This structure not only eliminates interface failure caused by binder aging, but also effectively buffers the volume expansion and stress concentration during the OER reaction process, enabling the electrode to exhibit excellent stability during long-term service, with an activity decay of <5% after 50 hours of continuous operation.

[0026] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0027] Figure 1 The image shows the morphology and elemental distribution of the sulfur-doped nickel hydroxide-based self-supporting water electrolysis anode prepared in Example 1 of this invention. Figure 2 The microstructure and elemental distribution of the sulfur-doped nickel hydroxide-based self-supporting water electrolysis anode prepared in Example 2 of this invention are shown in the figure. Figure 3 The polarization curves are shown for the sulfur-doped nickel hydroxide-based self-supporting water electrolysis anodes prepared in Examples 1 and 2 of this invention. Figure 4This is a Ni2p XPS peak fitting diagram of the sulfur-doped nickel hydroxide-based self-supporting water electrolysis anode prepared in Example 1 of the present invention; Figure 5 This is the S2p XPS peak fitting diagram of the sulfur-doped nickel hydroxide-based self-supporting water electrolysis anode prepared in Example 1 of the present invention; Figure 6 The 10 mA cm of the sulfur-doped nickel hydroxide-based self-supporting water electrolysis anode prepared in Example 1 of this invention. -2 Timing potential analysis diagram under current density; Figure 7 This is a physical image of the sulfur-doped nickel hydroxide-based self-supporting water electrolysis anode prepared in Example 1 of the present invention. Detailed Implementation

[0028] The technical solution of the present invention will be further described below with reference to the accompanying drawings and embodiments.

[0029] Unless otherwise defined, the technical or scientific terms used in this invention shall have the ordinary meaning as understood by one of ordinary skill in the art to which this invention pertains.

[0030] In this invention, unless otherwise specified, all other test materials and instruments are conventional test materials in the field and can be purchased through commercial channels.

[0031] Example 1 This invention provides a method for preparing a sulfur-doped nickel hydroxide-based self-supporting water electrolysis anode, comprising the following steps: S1. Preparation of active solution: Strong oxidizing salt, thiourea, and transition metal salt were added sequentially to deionized water and stirred until homogeneous to obtain an active solution.

[0032] The molar ratio of the strong oxidizing salt, thiourea, and transition metal salt is 5:1:2, and the strong oxidizing salt is 0.25 mol·L⁻¹. -1 Ammonium persulfate, a transition metal salt, is 0.1 mol·L⁻¹. -1 Nickel sulfate, thiourea concentration is 0.05 mol·L⁻¹ -1 .

[0033] S2. Pretreatment of the nickel-containing metal substrate yields the precursor: The precursor was obtained by sequentially cleaning the nickel-containing metal substrate with dilute hydrochloric acid, deionized water, and anhydrous ethanol.

[0034] The nickel-containing metal substrate is a nickel-containing foam metal, and the concentration of dilute hydrochloric acid is 3 mol·L⁻¹. -1 The cleaning time is 5 minutes.

[0035] S3, Ultrasonic impregnation and room temperature in-situ oxidation: S31. Place the precursor in a container filled with an active solution, ensuring the precursor is completely submerged in the active solution. After the surface of the precursor is fully wetted, place it together with the container in an ultrasonic water bath for ultrasonic vibration.

[0036] The ultrasonic vibration frequency was 25 kHz, and the ultrasonic vibration time was 5 min.

[0037] S32. After sonication, immediately remove the precursor, retain the residual liquid on the surface, and spread it evenly in a petri dish. Let it stand at room temperature to obtain a precursor with a surface covered with catalytically active substances.

[0038] The thickness of the residual liquid on the surface is 0.3 mm, and the standing time is 24 h.

[0039] S33. Remove the precursor covered with catalytically active material from the petri dish, clean the soluble byproducts on the surface and dry it to obtain the sulfur-doped nickel hydroxide-based self-supporting electrocatalytic anode.

[0040] The specific steps for cleaning soluble byproducts from the surface and drying are as follows: the precursor covered with catalytically active substances is washed sequentially with deionized water and anhydrous ethanol for 5 minutes, and then air-dried at room temperature.

[0041] Example 2 The only difference between this embodiment and Embodiment 1 is that the transition metal salt in S1 is 0.1 mol·L⁻¹. -1 Cerium nitrate, all other conditions are the same.

[0042] Figure 1 The image shows the morphology and elemental distribution of the sulfur-doped nickel hydroxide-based self-supporting water electrolysis anode prepared in Example 1; Figure 1 As can be seen, a catalyst layer covers the surface of the nickel-containing foam metal skeleton. The catalyst layer surface exhibits a typical mud-crack-like morphology, manifested as an irregular polygonal network of cracks. The crack walls and tips expose a large number of low-coordination steps / edge sites, which easily become highly intrinsic active centers. During the oxygen evolution reaction, if bubbles generated on the electrode surface are trapped, they will cover the active sites. The specific crack structure can limit bubble growth and accelerate their detachment, thereby reducing the bubble shielding effect, lowering the overpotential, and improving the electrolysis efficiency. The uniform distribution of Ni, O, and S elements on the catalyst layer proves that the method of this invention can realize the preparation of multi-component Ni-SO catalysts.

[0043] Figure 2The microstructure and elemental distribution of the sulfur-doped nickel hydroxide-based self-supporting water electrolysis anode prepared in Example 2 are shown. The surface morphology of the electrocatalytic electrode is still a catalyst layer with a cracked structure, and the Ni, Ce, O, and S elements in the catalyst layer are uniformly distributed, confirming that this method can realize the preparation of multi-element Ni-MSO catalysts.

[0044] Figure 3 The figures show the polarization curves of the sulfur-doped nickel hydroxide-based self-supporting water electrolysis anodes prepared in Examples 1 and 2. As can be seen from the figures, with a carbon rod as the counter electrode and a 1 mol·L⁻¹ hydrochloric acid concentration, the polarization curves are... -1 In a three-electrode testing system using KOH solution as the electrolyte, the electrocatalytic electrode prepared in Example 1 exhibited an oxygen evolution half-reaction (OER) at 10 mA cm⁻¹ during water electrolysis. -2 The overpotential corresponding to the current density is 240 mV. The electrocatalytic electrode prepared in Example 2 exhibits an oxygen evolution half-reaction (OER) at 10 mA cm⁻¹ during water electrolysis. -2 The overpotential at the current density is only 201 mV, which indicates that it has outstanding electrocatalytic activity.

[0045] Figure 4 The image shows the Ni2p XPS peak fitting diagram of the sulfur-doped nickel hydroxide-based self-supporting water electrolysis anode prepared in Example 1. As can be seen from the figure, the catalyst layer on the surface of the electrocatalytic electrode prepared in Example 1 contains a large amount of highly active Ni. 3+ Ni 3+ The presence of electrons helps generate more electronic states near the Fermi level, reduces the charge transport resistance of the catalyst itself, and ensures that electrons can be quickly transferred to the electrode during the reaction, thereby improving the overall catalytic efficiency.

[0046] Figure 5 The image shows the S2p XPS peak fitting diagram of the sulfur-doped nickel hydroxide-based self-supporting water electrolysis anode prepared in Example 1. The figure shows that the catalyst layer on the surface of the electrocatalytic electrode prepared in Example 1 contains S... 2- This confirms that S does indeed enter NiO in a doped state. x H y In the crystal lattice.

[0047] Figure 6 The 10 mA cm-type sulfur-doped nickel hydroxide-based self-supporting water electrolysis anode prepared in Example 1 -2 Chronopotential analysis at current density. Catalytic electrode performance at 1 mol·L⁻¹ -1 KOH electrolyte, 10 mA cm -2 After 12 hours at a constant current density, the catalytic activity increased by only 2 mV, indicating good stability.

[0048] Figure 7This is a photograph of the sulfur-doped nickel hydroxide-based self-supporting water electrolysis anode prepared in Example 1. Figure 7 It is known that the electrocatalytic electrode is 5cm×5cm in size, with three-dimensional porous nickel foam as the current collector skeleton, and the whole has a regular macroscopic network structure. After being loaded with the catalyst layer, the surface is uniformly black and has no metallic luster.

[0049] Therefore, the present invention adopts the above-mentioned method for preparing sulfur-doped nickel hydroxide-based self-supporting electrolytic water anode, using an oxidant-thiourea-transition metal salt synergistic reaction system, combined with ultrasonic-assisted technology, to directly grow a high-performance catalytic layer on the surface of a metal substrate at room temperature. The aim is to simultaneously achieve high catalytic activity, excellent stability and large-scale preparation of the electrode, fundamentally solving the core pain points of existing technologies such as long process, high energy consumption and difficulty in scale-up.

[0050] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the technical solutions of the present invention, and these modifications or equivalent substitutions cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A method for preparing a sulfur-doped nickel hydroxide-based self-supporting water electrolysis anode, characterized in that: Includes the following steps: S1. Prepare an active solution by mixing a strong oxidizing salt, thiourea, and a transition metal salt. In S1, the concentration of the strong oxidizing salt is 0.25-0.3 mol·L⁻¹. -1 The thiourea concentration was 0.005-0.25 mol·L⁻¹. -1 The concentration of transition metal salts is 0.1-0.5 mol·L⁻¹. -1 ; In S1, the strong oxidizing salt is one of sodium persulfate, potassium persulfate, ammonium persulfate, and sodium perborate; In S1, the transition metal salt is one or more of the following: nickel nitrate, nickel sulfate, nickel acetate, ferric nitrate, ferric sulfate, ferric acetate, ferrous nitrate, ferrous sulfate, cobalt nitrate, cobalt sulfate, cobalt acetate, and cerium nitrate. S2. Pretreatment of nickel-containing metal substrate to obtain precursor; S3. The precursor was immersed in the active solution, ultrasonically impregnated, and oxidized in situ to obtain a sulfur-doped nickel hydroxide-based self-supporting water electrolysis anode. The specific operation of S3 is as follows: S31. Place the precursor in a container filled with an active solution, and completely immerse the precursor in the active solution. After the surface of the precursor is fully wetted, place it together with the container in an ultrasonic water bath for ultrasonic vibration. S32. After sonication, immediately remove the precursor from the container, leaving the surface liquid, spread the precursor evenly in a petri dish, and let it stand at room temperature to obtain a precursor with a surface covered with catalytically active substances. S33. Remove the precursor covered with catalytically active material from the culture dish, clean the soluble byproducts on the surface, and dry to obtain a sulfur-doped nickel hydroxide-based self-supporting water electrolysis anode.

2. The method for preparing a sulfur-doped nickel hydroxide-based self-supporting electrolytic water anode according to claim 1, characterized in that: The specific operation of S1 is as follows: add the strong oxidizing salt, thiourea and transition metal salt to deionized water in sequence, stir evenly, and obtain an active solution.

3. The method for preparing a sulfur-doped nickel hydroxide-based self-supporting electrolytic water anode according to claim 1, characterized in that: The specific operation of S2 is as follows: the nickel-containing metal substrate is washed sequentially with dilute hydrochloric acid, deionized water and anhydrous ethanol to obtain the precursor.

4. The method for preparing a sulfur-doped nickel hydroxide-based self-supporting water electrolysis anode according to claim 3, characterized in that: In S2, the concentration of dilute hydrochloric acid is 0.5-3 mol·L⁻¹. -1 Clean for 3-10 minutes. The nickel-containing metal substrate is one of the following: nickel-containing foam metal, nickel-containing metal fiber felt, nickel-containing metal mesh, or nickel-containing metal foil.

5. The method for preparing a sulfur-doped nickel hydroxide-based self-supporting water electrolysis anode according to claim 3, characterized in that: In S2, the nickel-containing metal substrate is one of Ni metal, NiMo alloy, NiCo alloy, NiFe alloy, and TiNi alloy.

6. The method for preparing a sulfur-doped nickel hydroxide-based self-supporting water electrolysis anode according to claim 1, characterized in that: In S31, the ultrasonic vibration frequency is 25-40kHz, and the ultrasonic time is 3-10min; In S32, the thickness of the residual liquid on the surface is 0.3-0.5 mm, and the standing time is 5-24 h; In S33, the specific operation of drying after cleaning the soluble byproducts on the surface is as follows: the precursor covered with catalytic active material on the surface is washed with deionized water and anhydrous ethanol for 5-8 minutes in sequence, and then air-dried at room temperature.

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