Electrochemical etching method of a porous electrode and an electrolytic water electrode

Abstract

The application relates to an electrochemical etching method of a porous electrode and an electrolytic water electrode. The electrochemical etching method comprises the following steps: using a nickel-iron metal salt containing a pore-forming agent as an electroplating solution, using a nickel mesh as a working electrode and a platinum sheet as a counter electrode, performing constant-current electrodeposition in the electroplating solution, ensuring that the deposition rate remains unchanged, obtaining a nickel mesh material loaded with a porous nickel-iron alloy deposition layer; cleaning and drying; using a high-temperature furnace to perform fast firing treatment to improve the stability of the catalyst layer; in a two-electrode system, using prepared hydrochloric acid as an etching solution, using the obtained electrode as a working electrode and a platinum sheet as a counter electrode, performing constant-current etching, ensuring that the etching rate remains unchanged, and obtaining a porous electrode finished product after etching. Compared with the prior art, the application solves the problems of insufficient catalytic area of a traditional porous electrode and poor bubble release structure on the surface; is suitable for industrial large-scale production, has a simple preparation process, good repeat stability and low cost.

Description

TECHNICAL FIELD

[0001] The present application relates to a preparation method of an electrolytic water electrode, in particular to an electrochemical etching method of a porous electrode and an electrolytic water electrode. BACKGROUND

[0002] With the reduction of global dependence on fossil fuels and the increasing demand for renewable energy, hydrogen as a clean energy carrier is increasingly valued. Alkaline water electrolysis hydrogen production technology does not produce greenhouse gas emissions, which helps to reduce the impact on the environment. Electrolytic water technology can use renewable energy such as wind and solar power to convert these unstable and difficult to store energy into hydrogen, which is easy to store and transport. In particular, in recent years, technological advances and innovations in electrode materials, catalysts and electrolytic cell design have helped to improve the efficiency of water electrolysis and reduce costs. However, the existing structure of the electrolytic water electrode is still relatively simple, and the efficiency still has certain room for improvement. By using reasonable methods to further improve the active area of the electrode and improve the bubble release structure, the electrolytic efficiency can be effectively improved, and the hydrogen and oxygen evolution overpotential can be reduced.

[0003] Depositing porous nickel on commercial nickel mesh is a relatively common technology at present. This method can effectively increase the active area of the electrode, thereby improving the catalytic efficiency. This method mainly uses nickel salt and ammonium chloride as the electrodeposition precursor solution. During the electrodeposition process, nickel is continuously deposited on the surface of the nickel mesh substrate, and due to the addition of ammonium salt, hydrogen is continuously generated on the nickel mesh substrate, which ultimately leads to the formation of a porous nickel deposition layer on the nickel mesh, i.e. porous nickel. Porous nickel already has a large active area, but from a microscopic structural perspective, the porous structure still has room for optimization, and the active area can be further improved.

[0004] Considering that the pore structure of porous nickel is actually in the macroscopic category, it can be observed under a low magnification (such as 200-500 times) microscope. In the actual OER process, the pores of the porous nickel electrode do not significantly help the release of bubbles, but actually increase the active area of the electrode to improve the electrolytic efficiency. In view of this idea, it can be reasonably speculated that further improving the active area of the electrode and optimizing the bubble release structure under microscopic conditions can achieve better water electrolysis performance.

[0005] In summary, the existing porous nickel electrode still has certain room for improvement and optimization in terms of catalytic active surface area, bubble release structure, etc. In view of this problem, there is an urgent need for a new type of electrode that can improve the intrinsic active area while optimizing the bubble release structure to achieve efficient water electrolysis for hydrogen production. SUMMARY

[0006] The present application aims at overcoming the defects of the prior art, and provides an electrochemical etching method of a porous electrode and an electrolytic water electrode, which solves the problems of insufficient catalytic area and poor bubble release structure of a traditional porous electrode, is suitable for industrial large-scale production, has a simple preparation process, good repeatability and low cost.

[0007] The object of the present application can be achieved by the following technical solutions.

[0008] The present application provides an electrochemical etching method of a porous electrode, comprising the following steps:

[0009] S1: In a two-electrode system, a nickel-iron metal salt containing a pore-forming agent is used as an electroplating solution, a nickel mesh is used as a working electrode and a platinum sheet is used as a counter electrode, constant current electrodeposition is carried out in the electroplating solution, the deposition rate is kept unchanged, and a nickel mesh material loaded with a porous nickel-iron alloy deposition layer is obtained;

[0010] S2: The nickel mesh material loaded with the porous nickel-iron alloy deposition layer obtained in S1 is cleaned and dried;

[0011] S3: Based on the nickel mesh material loaded with the porous nickel-iron alloy deposition layer treated in S2, fast firing treatment is carried out using a high-temperature furnace to improve the stability of the catalyst layer;

[0012] S4: In a two-electrode system, a prepared hydrochloric acid is used as an etching solution, the electrode obtained in S3 is used as a working electrode, and a platinum sheet is used as a counter electrode, constant current etching is carried out, the etching rate is kept unchanged, and a porous electrode finished product is obtained.

[0013] Further, the nickel mesh is a pretreated nickel mesh, and the pretreatment process comprises:

[0014] The nickel mesh is ultrasonically treated in dilute hydrochloric acid to remove the surface oxides, then ultrasonically treated in anhydrous ethanol to remove the surface hydrochloric acid and organic matter, and finally ultrasonically treated in deionized water to remove other residual impurities on the surface.

[0015] Further, the concentration of the dilute hydrochloric acid is 0.1-2 mol / L, and the ultrasonic treatment time is 15 min.

[0016] Further preferably, the concentration of the dilute hydrochloric acid is 1 mol / L.

[0017] Further, the nickel wire diameter of the nickel mesh is 50-300 μm, and the mesh number of the nickel mesh is 40-200.

[0018] Further, in S1, the pore-forming agent in the nickel-iron metal salt electroplating solution is ammonium chloride, the solvent is water, the concentration of nickel chloride is 0.02-0.2 mol / L, the concentration of ferrous chloride is 0-0.1 mol / L, and the concentration of the pore-forming agent is 0.5-3 mol / L.

[0019] Further preferably, the concentration of nickel chloride is 0.1 mol / L, the concentration of ferrous chloride is 0.04 mol / L, and the concentration of the pore-forming agent ammonium chloride is 3 mol / L.

[0020] Further, in S1, the time of electrodeposition is 10 min, the current density is 0.5 A / cm 2 -2 A / cm 2 , and the control temperature is 20-30 DEG C.

[0021] Further, in S2, the cleaning process is to first wash the surface impurities with deionized water and then wash with anhydrous ethanol.

[0022] The drying temperature is room temperature.

[0023] Further, in S3, a super-fast high-temperature furnace is used for fast firing to improve the stability of the catalyst layer, wherein: the fast firing temperature is set to 800-1200 DEG C, the heating rate is 400 DEG C / s, and the fast firing is carried out in an inert atmosphere.

[0024] The catalyst structure deposited on the nickel mesh material loaded with the porous nickel-iron alloy deposition layer is solidified by fast firing sintering, and the oxygen in the catalyst layer is eliminated at the same time, thereby improving the durability and stability of the electrode.

[0025] The high-temperature fast firing time is 1-3 s, and the cooling time is 3 s, so that the temperature is rapidly reduced to room temperature.

[0026] Further, in S4, the concentration of the hydrochloric acid etching solution is 0.5-2 M, the electrochemical etching time is 1-10 min, the current density is 0.02-0.5 A / cm 2 , and the temperature is maintained at 20-30 DEG C.

[0027] The material obtained after etching is cleaned and dried to obtain a porous electrode product.

[0028] The cleaning process is to first wash the surface impurities with deionized water and then wash with anhydrous ethanol, and the drying temperature is room temperature.

[0029] The second application of the application provides an electrolytic water electrode obtained by the electrochemical etching method.

[0030] Compared with the prior art, the application has the following beneficial effects:

[0031] 1) Improve the efficiency of electrolytic water: The porous electrode etching method provided by the present application can effectively improve the efficiency of electrolytic water, help to improve the energy utilization efficiency in the application scenario related to electrolytic water, realize more efficient water electrolysis reaction, and then play a positive role in the field such as hydrogen production.

[0032] 2) Optimize the shortcomings of traditional porous electrodes: In view of the problems of insufficient catalytic area and poor surface bubble release structure of traditional deposited porous electrodes, the present application provides an effective optimization solution. Through subsequent electrochemical etching treatment, the microstructure of the electrode surface is improved, the defects of the traditional method are made up, and the performance of the electrode is significantly improved.

[0033] 3) Suitable for industrial large-scale production: The present application, whether it is electrodeposition process or subsequent electrochemical etching process, has good characteristics suitable for industrial large-scale production. This means that the application can be stably applied in industrial production environment, meet the demand of large-scale and batch production of electrodes, and provide strong technical support for the scale development of related industries.

[0034] 4) Simple preparation process, good stability and low cost: The preparation process is simple and easy to operate, without complex process equipment and cumbersome operation process, easy to popularize and implement. At the same time, the repeated stability is good, which ensures that high-quality porous electrodes with similar performance can be stably produced in multiple preparation processes, and the cost is low, which can effectively reduce the economic cost of electrode production, improve production efficiency, and enhance the competitiveness of products in the market.

[0035] 5) Refine the grain and improve the surface structure: The etching method can further refine the spherical grains obtained by deposition in order, increase the surface area of the electrode, and create a rough surface structure conducive to bubble release. Larger surface area means more active sites participating in catalytic reaction, and structure conducive to bubble release can reduce the adhesion and accumulation of bubbles on the electrode surface, so that the electrode reaction can continue smoothly, further enhancing the catalytic performance of the electrode. BRIEF DESCRIPTION OF DRAWINGS

[0036] Figure 1 is the low-power scanning electron microscope (SEM) image of the porous nickel-iron in Example 1 of the present application;

[0037] Figure 2 is the low-power (200 times) SEM image of the etched porous nickel-iron electrode in Example 1 of the present application;

[0038] Figure 3 is the high-power (20000 times) SEM image of the porous nickel-iron in Example 1 of the present application;

[0039] Figure 4High magnification (20000 times) SEM image of the porous nickel-iron electrode after etching in Example 1 of the present application;

[0040] Figure 5 Electrochemically active surface area curve of the porous nickel-iron electrode and after etching in Example 1 of the present application;

[0041] Figure 6 Linear sweep voltammetry curve of the oxygen evolution reaction in Example 1 of the present application. DETAILED DESCRIPTION

[0042] Overall, to solve the problems of insufficient catalytic activity and bubble release structure of the existing alkaline water hydrogen production electrode, a new type of water electrolysis electrode is designed. The electrode includes a basic porous catalyst layer electrodeposition, sintering and curing of the deposited catalyst layer, and further electrochemical etching of the porous layer, wherein the etching treatment is the main content of the present application. At the same time, the present application provides an etching method for a porous electrode, which effectively improves the efficiency of water electrolysis. The present application is mainly an optimization method for traditional deposition porous electrodes, which solves the problems of insufficient catalytic area and poor bubble release structure of the surface of the traditional porous electrode. The present application further performs electrochemical etching on the basis of electrodeposition, which is suitable for industrial large-scale production, and the preparation process is simple, the repeatability is good, and the cost is low. The present application faces different deposition conditions and sets corresponding etching parameters to realize precise etching of the porous catalyst layer with different pore sizes and different deposition layer thicknesses, so as to improve the overall electrode electrolysis performance. The etching method of the present application can further refine the spherical grains obtained by deposition in order, obtain a rough surface structure with larger surface area and facilitate bubble release. The present application as a whole makes the electrode have higher catalytic performance, and guides the electrode preparation method to develop in the direction of etching.

[0043] The present application will be described in detail below with reference to the accompanying drawings and specific examples. In the technical solution, if the preparation means, materials, structure or composition ratio and other features are not explicitly stated, they are regarded as common technical features disclosed in the prior art.

[0044] Example 1

[0045] 1) Pretreatment of nickel mesh:

[0046] The 50-mesh nickel mesh is ultrasonically treated in 1 mol / L dilute hydrochloric acid to remove the surface oxides, then ultrasonically treated in anhydrous ethanol to remove the surface hydrochloric acid and organic matter, and finally ultrasonically treated in deionized water to remove other residual impurities, to obtain the pretreated nickel mesh;

[0047] 2) Electrodeposition of porous catalyst layer:

[0048] The nickel-iron metal salt plating solution includes nickel chloride, ferrous chloride, ammonium chloride and deionized water;

[0049] The concentration of nickel chloride in the nickel-iron metal salt electroplating solution is 0.1 mol / L, the concentration of ferrous chloride is 0.04 mol / L, and the concentration of the pore-forming agent ammonium chloride is 3 mol / L.

[0050] In the two-electrode system, the nickel-iron metal salt electroplating solution prepared in the above step is arranged in the deposition tank, the pretreated nickel mesh is used as the working electrode, and the platinum sheet is used as the counter electrode. A current density of 0.5 A / cm 2 is applied for 600 s, the temperature is maintained at 20-30°C, and a nickel mesh electrode loaded with a porous nickel-iron catalyst layer is obtained. The obtained composite electrode is taken out of the deposition tank, cleaned with deionized water and anhydrous ethanol, and naturally dried, and is named "porous nickel-iron" and used as a subsequent comparative sample.

[0051] 3) Sintering of the porous electrode:

[0052] After obtaining the porous catalyst layer electrode prepared in step 2), in order to improve the stability of the catalyst layer, solidification of the catalyst layer, i.e., fast firing treatment, is needed, and an ultrafast high-temperature furnace is used for the treatment.

[0053] The fast firing temperature is set to 1000°C, the heating rate is 400°C / s, and the specific calcination temperature is determined by parameters such as the thickness of the catalyst layer;

[0054] The fast firing is carried out under nitrogen to prevent oxidation of the electrode;

[0055] The fast firing high temperature is maintained for 1 s, and the cooling time is 3 s, and the temperature is quickly reduced to room temperature. At this time, it is still the "porous nickel-iron" electrode.

[0056] 4) Etching treatment of the porous electrode:

[0057] The porous nickel-iron electrode obtained in step 3) is further subjected to electrochemical etching treatment, which aims to further increase the surface area of the porous catalyst layer and etch rough structures on the catalyst grains to facilitate bubble release.

[0058] In the two-electrode system, 1M hydrochloric acid is used as the etching solution, the porous nickel-iron electrode obtained in step (2) is used as the working electrode, and the platinum sheet is used as the counter electrode. Each electrode is immersed in the etching solution for constant current etching at 0.5 A / cm 2 for 400 s, the temperature is maintained at 20-30°C, and the surrounding environment is ventilated.

[0059] The obtained material is cleaned and dried. The cleaning process is to first rinse the surface impurities with deionized water, and then rinse with anhydrous ethanol. The drying condition is room temperature drying, and the porous catalyst layer electrode after etching is obtained and named "porous nickel-iron-etching" electrode.

[0060] 5) Electrode testing

[0061] A standard three-electrode system was used, with mercury / mercury oxide (Hg / HgO) as the reference electrode, 2×2cm. 2 The platinum sheet is used as the counter electrode, 1*1cm 2 The porous nickel-iron electrode and the porous nickel-iron-etched electrode prepared in Example 1 were used as working electrodes. Electrochemical tests were performed on a Corrtest electrochemical workstation using a 1 mol / L KOH solution as the electrolyte and the test temperature was controlled at 25°C to carry out the oxygen evolution reaction.

[0062] Electrochemical active surface area test: Cyclic voltammetry was performed at five scan rates of 20mV / s, 40mV / s, 60mV / s, 80mV / s, and 100mV / s in the non-Radida range (corresponding to actual voltage of about 1.0-1.1V). The electrode active surface area data were obtained by plotting the data and fitting the slope.

[0063] Linear scan voltammetry curve test: The scan rate was 5 mV / s, and the electrode potentials were all compensated with 90% iR and converted into electrode potentials relative to the reversible hydrogen potential (RHE). The calculation formula is shown in Equation (1):

[0064] Overpotential (V) = electrode potential + 0.059 × pH + Hg / HgO electrode potential - 1.23 (1)

[0065] In the formula (1), pH is the pH value of the electrolyte.

[0066] Figure 1 and Figure 3 The image shows a porous catalyst layer, named "Porous Nickel-Iron", obtained after step 3) by conventional electrodeposition.

[0067] Figure 2 and Figure 4 This is a SEM image of the "porous nickel-iron-etched" electrode after etching in step 3).

[0068] Depend on Figure 1 and Figure 2 The comparison shows that after etching, the aggregated particle structure of the electrodeposited catalytic layer is differentiated to some extent, increasing the inter-particle space, which helps to improve the catalytic active area of ​​the porous nickel electrode. Meanwhile, due to... Figure 3 and Figure 4 The comparison shows that, under high-magnification SEM observation, compared to the relatively smooth grain surface of traditional "porous nickel-iron" (…), Figure 3 The grains of the "porous nickel-iron-etched" electrode have a distinctly rough surface. Figure 4), which can significantly optimize the process of bubble detachment from the surface of the particles and is also an important factor for the increase of the electrochemically active surface area, which can be verified by the active surface area characterization test of Figure 5 The active surface area of the etched electrode (16.64 mF·cm -2 ) is nearly doubled compared with that of the original "porous nickel-iron" electrode (8.78 mF·cm -2 ), which shows that etching has a significant effect on the increase of the active surface area.

[0069] Figure 6 The oxygen evolution reaction current-voltage curve of the "porous nickel-iron-etching" electrode also shows that the "porous nickel-iron-etching" electrode has better performance than the "porous nickel-iron" electrode. At a small current, the "porous nickel-iron-etching" electrode can start to generate current at a lower potential, which is related to the more active sites. At a large current, the "porous nickel-iron-etching" electrode also has better performance than the "porous nickel-iron" electrode, because the etched electrode has a rough bubble detachment surface, which can quickly detach the bubbles from the surface of the catalyst layer at a large current and many bubbles, reduce the solution impedance and the coverage of the active sites, and achieve the effect of reducing the potential.

[0070] In summary, the "porous nickel-iron-etching" electrode has better oxygen evolution catalytic performance.

[0071] The above description of the embodiments is for the convenience of the ordinary skilled in the art to understand and use the application. Those skilled in the art can easily make various modifications to these embodiments and apply the general principles described herein to other embodiments without creative labor. Therefore, the application is not limited to the above embodiments, and the improvements and modifications made by those skilled in the art according to the disclosure of the application without departing from the scope of the application should be within the protection scope of the application.

Claims

1. An electrochemical etching method of a porous electrode, characterized by, The method comprises the following steps: S1: In a two-electrode system, a nickel-iron metal salt containing a pore-forming agent is used as an electroplating solution, a nickel mesh is used as a working electrode, and a platinum sheet is used as a counter electrode, constant current electrodeposition is carried out in the electroplating solution, the deposition rate is kept unchanged, and a nickel mesh material loaded with a porous nickel-iron alloy deposition layer is obtained; S2: The nickel mesh material loaded with the porous nickel-iron alloy deposition layer obtained in S1 is cleaned and dried; S3: Based on the nickel mesh material loaded with the porous nickel-iron alloy deposition layer treated in S2, a high-temperature furnace is used for fast firing to improve the stability of the catalyst layer; S4: In a two-electrode system, a prepared hydrochloric acid is used as an etching solution, the electrode obtained in S3 is used as a working electrode, and a platinum sheet is used as a counter electrode, constant current etching is carried out, the etching rate is kept unchanged, and a porous electrode product after etching is obtained; In S1, in the nickel-iron metal salt electroplating solution containing a pore-forming agent, the pore-forming agent is ammonium chloride, the solvent is water, the concentration of nickel chloride is 0.02-0.2 mol / L, the concentration of ferrous chloride is 0-0.1 mol / L, and the concentration of the pore-forming agent is 0.5-3 mol / L; In S3, an ultrafast high-temperature furnace is used for fast firing to improve the stability of the catalyst layer, wherein the fast firing temperature is set to 800-1200℃, the temperature rising rate is 400℃ / s, and the fast firing is carried out in an inert atmosphere.

2. The method of claim 1, wherein the porous electrode is a porous copper electrode. In S1, the nickel mesh is a pretreated nickel mesh, and the pretreatment process comprises: The nickel mesh is ultrasonically treated in dilute hydrochloric acid to remove oxides on the surface, then ultrasonically treated in anhydrous ethanol to remove hydrochloric acid and organic matter on the surface, and finally ultrasonically treated in deionized water to remove other residual impurities on the surface.

3. The method of claim 2, wherein the porous electrode is a porous copper electrode. The concentration of the dilute hydrochloric acid is 0.1-2 mol / L, and the ultrasonic treatment time is 15 min.

4. The method of claim 2, wherein the porous electrode is a porous copper electrode. The nickel wire diameter of the nickel mesh is 50-300 μm, and the mesh number of the nickel mesh is 40-200 meshes.

5. The method of claim 1, wherein the porous electrode is a porous copper electrode. In S1, the time of electrodeposition is 10 min, the current density is 0.5 A / cm 2 - 2 A / cm 2 , and the control temperature is 20 - 30 °C.

6. The method of claim 1, wherein the porous electrode is a porous copper electrode. In S2, the cleaning process is to first wash the surface impurities with deionized water and then wash with anhydrous ethanol; The drying temperature is room temperature.

7. The method of claim 1, wherein the porous electrode is a porous copper electrode. In S3, an ultrafast high-temperature furnace is used for fast firing to improve the stability of the catalyst layer, wherein the catalyst structure deposited on the surface of the nickel mesh material loaded with the porous nickel-iron alloy deposition layer is sintered and solidified by fast firing, and the oxygen in the catalyst layer is eliminated at the same time, thereby improving the durability and stability of the electrode; The fast firing high-temperature holding time is 1-3 s, and the cooling time is 3 s, so that the temperature is rapidly reduced to room temperature.

8. The method of claim 1, wherein the porous electrode is a porous copper electrode. In S4, the concentration of the hydrochloric acid etching solution is 0.5-2 M, the electrochemical etching time is 1-10 min, the current density is 0.02-0.5 A / cm², and the temperature is kept at 20-30℃; The material obtained after etching is cleaned and dried to obtain a porous electrode product; The cleaning process is to first wash the surface impurities with deionized water and then wash with anhydrous ethanol, and the drying temperature is room temperature.

9. An electrolytic water electrode obtained by the electrochemical etching method according to any one of claims 1 to 8.

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