High-performance self-optimizing stainless steel oxygen evolution electrode and application thereof

Abstract

The application discloses a high-performance self-optimization stainless steel oxygen evolution electrode and application, and the electrode is obtained through acid etching, annealing and electrochemical oxidation treatment. The stainless steel is a self-optimization electrode, through improving electrochemical activity area and conductivity, optimizing OER reaction mechanism and simplifying production process, remarkable improvement of the performance of the stainless steel electrode is realized, and a solid foundation is laid for actual industrial application.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of new energy, in particular to a high-performance self-optimizing stainless steel oxygen evolution electrode and application. BACKGROUND

[0002] With the rapid development of industry, excessive carbon emissions have exacerbated global warming. In order to cope with the threat of climate change, it is crucial to find clean energy to replace non-fossil energy. Among them, hydrogen energy is considered as the most potential clean energy. Water electrolysis hydrogen production technology is a low-carbon and environmentally friendly way to produce green hydrogen, but it still faces difficult problems in popularization and application. The main reason is that reducing the high operating cost caused by catalyst price and low electrolysis efficiency has always been a big problem. Therefore, developing low-cost, high-activity and high-stability water decomposition electrocatalysts is the core of efficient and sustainable production of hydrogen.

[0003] Oxygen evolution reaction (OER) under alkaline conditions is considered as a key anodic reaction for renewable energy systems. Although noble metal oxides such as RuO2 and IrO2 have been widely used for OER in alkaline media, they are too expensive for large-scale industrial applications. Nickel-iron (Ni-Fe) based electrocatalysts have become an outstanding choice in the past decade, becoming the preferred catalyst for OER in alkaline environments. These NiFe catalyst layers are mostly grown on nickel foam, stainless steel and carbon cloth, etc., but under industrial high current operation, the catalytic layer is easy to be separated or leached, resulting in poor stability. In addition, the catalyst prepared under laboratory conditions has the problems of small production and complicated preparation process, and it is difficult to realize its large-scale synthesis, thereby restricting the wide application of these catalysts in industrial production.

[0004] Currently, alkaline electrolysis systems have been widely used, but due to the direct contact between stainless steel bipolar plates and anode catalysts, the potential difference caused by the difference in materials easily leads to corrosion of the catalyst. Stainless steel has abundant transition metal elements such as Fe, Ni, Cr, Mo, etc., which can be used as a source for in-situ growth of OER catalysts, making it a suitable candidate for OER electrodes. Secondly, its good electrical conductivity makes it an ideal substrate for electrochemical processes such as OER. In addition, stainless steel is a ubiquitous and inexpensive material. Therefore, active and low-cost OER electrodes made of stainless steel are likely to have great prospects. In the prior art, CN2024103820025 proposes a preparation method for a stainless steel-based anode oxygen evolution electrode for seawater electrolysis, which involves immersing a stainless steel substrate in an aqueous solution containing halogen-containing oxyacid salts and alkali metal hydroxides for hydrothermal corrosion. The resulting electrode exhibits low overpotential, high catalytic activity, long-term stability, and excellent corrosion resistance. CN2021108561930 discloses a preparation method for a stainless steel-based catalyst, which involves anodizing stainless steel in a solution containing NaCl to increase its catalytic activity and expose more active sites. This method is simple and easy to operate, and exhibits excellent activity and good durability at high current densities. CN2024103284865 provides a preparation method for a stainless steel-based oxygen evolution electrode, which involves etching the surface of stainless steel in an acid solution using an electrochemical etching method, and then using a hydrothermal method to form a basic electrolytic water oxygen evolution catalyst electrode. CN2024102728657 describes a preparation method for a high-performance self-optimized stainless steel oxygen evolution electrode, which involves anodic corrosion in a chloride solution combined with subsequent secondary electrolysis in an alkaline solution to modify the electrode. CN2022116061739 introduces a method for modifying the surface of stainless steel, which involves combining hydrothermal corrosion and hydrothermal sulfidation processes to obtain a stainless steel surface with good catalytic activity.

[0005] However, the above methods generally rely on complex hydrothermal synthesis steps, which not only require high equipment and operating conditions, making it difficult to meet the needs of large-scale industrial production, but also lack sufficient testing and research on the stability of the electrode under long-term industrial conditions, and lack sufficient verification of its long-term performance in actual application environments, which undoubtedly affects the practical application of the electrode. SUMMARY

[0006] In view of the above-mentioned deficiencies of the prior art, the purpose of the present application is to provide a high-performance self-optimizing stainless steel oxygen evolution electrode and application. The electrode is obtained after coupling corrosion, annealing and electrochemical activation treatment. The process significantly simplifies the preparation process, and the modified stainless steel as an OER anode follows the OPM reaction mechanism, thereby greatly improving the catalytic activity and long-term stability of the electrode. Finally, the problem of the need for surface modification, high overpotential and difficulty in meeting the industrial alkaline water electrolysis demand of stainless steel for water electrolysis catalysis in the prior art is solved.

[0007] In order to solve the above technical problems, the technical scheme adopted by the present application is as follows:

[0008] A high-performance self-optimizing stainless steel oxygen evolution electrode is prepared by the following steps:

[0009] Step 1: pretreat the surface of the stainless steel to remove impurities on the surface thereof;

[0010] Step 2: place the stainless steel treated in step 1 in an acid solution and corrode for 1-4h at 25-50℃, and then clean and dry the stainless steel to obtain an acid-etched stainless steel electrode; wherein the concentration in the acid solution is 10-40wt%;

[0011] Step 3: anneal the stainless steel treated in step 2 in an air atmosphere to obtain an air-annealed stainless steel electrode; wherein the annealing temperature is 400-900℃, and the annealing holding time is 1-4h;

[0012] Step 4: place the stainless steel electrode treated in step 3 in an alkali solution and electrolyze the stainless steel as an anode to obtain the stainless steel oxygen evolution electrode; wherein the concentration of alkali in the alkali solution is 1-2mol / L, the current density during electrolysis is 400-600mA / cm 2 , and the electrolysis time is 100-1600h.

[0013] Preferably, the content of Cr in the stainless steel is >20%, and the content of Ni is >20% by weight percentage.

[0014] Preferably, the stainless steel comprises the following components by weight percentage: 23-25% of Cr, 21-23% of Ni, 0.04-0.05% of Si, 2-4% of Mn, and the balance of Fe.

[0015] Preferably, in step 1, the stainless steel is placed in deionized water and ultrasonically cleaned for 10-20min.

[0016] Preferably, in step 2, the acid solution comprises one of HF, H2SO4 or HNO3.

[0017] Preferably, in step 3, the temperature rising rate is 2℃ / min.

[0018] Preferably, in step 4, the base is one of KOH, NaOH.

[0019] The application also provides an application of the high-performance self-optimizing stainless steel oxygen evolution electrode to electrolysis of water for oxygen evolution.

[0020] Preferably, the stainless steel oxygen evolution electrode is used as an anode for oxygen evolution in the process of electrolysis of water.

[0021] Compared with the prior art, the application has the following beneficial effects:

[0022] 1. In the application, the stainless steel is used as a base material, and the specific surface area and porosity of the stainless steel electrode can be significantly increased through acid etching treatment. This surface modification not only helps to remove surface impurities, but also creates more active sites, thereby improving the electrochemical active surface area (ECSA). Subsequently, air annealing treatment can generate oxides with strong crystallinity, such as Fe2O3, on the surface of the stainless steel, further improving the electronic properties of the electrode and increasing the electrical conductivity of the material. Under the combined action of these treatment steps, the stainless steel electrode exhibits more excellent catalytic performance when used as an anode for oxygen evolution in the process of electrolysis of water.

[0023] 2. Through a series of treatment steps for the stainless steel, the application further converts oxides into active OER substances such as hydroxyl oxides, ultimately inducing the OER reaction mechanism of the stainless steel electrode to be the OPM mechanism with higher catalytic activity and stronger stability. Under the OPM mechanism, there is no generation of *OOH intermediate, and no direct participation of lattice oxygen, which breaks the limitation of the AEM scaling relationship and reduces the overpotential in the OER process. At the same time, the problem of catalyst structure collapse caused by the evolution of lattice oxygen is avoided, ensuring the structural stability and durability of the electrode during long-term operation, and fundamentally improving the self-optimizing performance of the stainless steel electrode during long-term operation.

[0024] 3、Compared with the complex hydrothermal synthesis method, the preparation process of the present application is more simple and easy to control, does not need complex equipment or harsh operating conditions, and has lower energy consumption, which is very suitable for large-scale industrial production; the stainless steel substrate selected by the present application has good electrical conductivity and mechanical strength, and combined with the optimized preparation process, the final obtained electrode has both high efficient catalytic performance and economy; this provides the possibility for realizing efficient and low-cost electrolytic water hydrogen production in industry; in summary, the present application realizes the significant improvement of the performance of stainless steel electrode by improving the electrochemical activity area and electrical conductivity, optimizing the OER reaction mechanism and simplifying the production process, and lays a solid foundation for practical industrial application. BRIEF DESCRIPTION OF DRAWINGS

[0025] Figure 1 The scanning electron microscope photograph of the untreated stainless steel is shown in Figure 1.

[0026] Figure 2 The scanning electron microscope photograph of the stainless steel oxygen evolution electrode obtained in the present application Comparative Example 1 is shown in Figure 2.

[0027] Figure 3 The scanning electron microscope photograph of the stainless steel oxygen evolution electrode obtained in the present application Comparative Example 2 is shown in Figure 3.

[0028] Figure 4 The scanning electron microscope photograph of the stainless steel oxygen evolution electrode obtained in the present application Example 1 is shown in Figure 4.

[0029] Figure 5 The LSV curves of the stainless steel oxygen evolution electrodes obtained in the present application Comparative Example 1, Comparative Example 2, Example 1, Example 15, Example 16, Example 17, Example 18 and the untreated stainless steel are shown in Figure 5.

[0030] Figure 6 The stability test graph of the stainless steel oxygen evolution electrode obtained in the present application Example 18 at 500 mA / cm 2

[0031] Figure 7 The electrochemical impedance spectrograms of the stainless steel oxygen evolution electrodes obtained in the present application Comparative Example 1, Comparative Example 2, Example 1, Example 15, Example 16, Example 17, Example 18 and the untreated stainless steel are shown in Figure 6.

[0032] Figure 8 The electrochemical specific surface area graphs of the stainless steel oxygen evolution electrodes obtained in the present application Comparative Example 1, Comparative Example 2, Example 1, Example 15, Example 16, Example 17, Example 18 and the untreated stainless steel are shown in Figure 7.

[0033] Figure 9 ​Polarization curves of Example 1 with and without TMA+.

[0034] Figure 10 Raman spectra of Example 1 after OER reaction in TMAOH.

[0035] Figure 11 ATR-SEIRAS spectra of Example 1 at various applied potentials in the range of 1000-1400 cm -1

[0036] Figure 12 CV curves of SSEAE recorded with and without 0.1 M methanol at a scan rate of 50 mV s -1

[0037] Figure: SSE is Comparative Example 1; SSEA is Comparative Example 2; SSEAE / 800 is Example 1; SS is a control sample; SSEAE / 100 is Example 15, SSEAE / 200 is Example 16, SSEAE / 400 is Example 17, SSEAE / 1600 is Example 18. DETAILED DESCRIPTION

[0038] The technical solutions in the embodiments of the present application will be described clearly and completely in the present application with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only some of the embodiments of the present application, but not all the embodiments. All other embodiments obtained by a person of ordinary skill in the art based on the present application are within the scope of protection of the present application.

[0039] Unless otherwise specified in specific cases, the numerical ranges listed in the present application include the upper and lower limits, and all integers and fractions within the range, but are not limited to the specific values listed in the defined range.

[0040] One. A high-performance self-optimizing stainless steel oxygen evolution electrode

[0041] Step 1: pretreat the surface of the stainless steel to remove impurities on the surface of the stainless steel;

[0042] Step 2: place the stainless steel treated in step 1 in an acid solution and corrode at 25-50°C for 1-4h, and then clean and dry the stainless steel to obtain an acid-etched stainless steel electrode; wherein the concentration in the acid solution is 10-40wt%;

[0043] Step 3: anneal the stainless steel treated in step 2 in an air atmosphere to obtain an air-annealed stainless steel electrode; wherein the annealing temperature is 400-900°C, the holding time is 1-4h, and the heating rate is 2°C / min; ​​

[0044] Step 4: placing the stainless steel electrode treated in step 3 in an alkaline solution, electrolyzing the stainless steel as an anode to obtain the stainless steel oxygen evolution electrode; wherein the concentration of alkali in the alkaline solution is 1-2 mol / L, the current density during electrolysis is 400-600 mA / cm 2 , and the electrolysis time is 100-1600 h.

[0045] The present application considers that the prior art often relies on a complex hydrothermal synthesis step, which not only has high requirements for equipment and operating conditions, but also is difficult to meet the requirements in actual large-scale industrial production due to its high energy consumption. At the same time, the electrolysis of water to produce hydrogen often needs long-time operation, which also puts higher requirements on the stability of the electrode. Based on the limitations of the prior art, the present application considers improving the preparation method of the electrode. The stainless steel prepared by coupling corrosion, air annealing and electrochemical oxidation process is first etched by acid to greatly increase the specific surface area and porosity of the stainless steel electrode, then the strong crystallinity Fe2O3 and other oxides are generated on the surface of the stainless steel by air annealing method, and finally the oxides are further converted into active OER substances such as hydroxyl oxide by electrochemical oxidation method. The OER reaction mechanism of the stainless steel electrode is finally induced to the OPM mechanism with higher catalytic activity and stronger stability. Because there is no *OOH generated in the OPM mechanism process, and no lattice oxygen participates in the reaction, the AEM scaling relationship limit can be broken, so that the prepared electrode not only has a theoretical high intrinsic activity, but also can avoid the collapse of the catalyst structure caused by the precipitation of lattice oxygen, ensuring that the electrode can maintain structural stability during the long-time electrolysis of water. After in-depth research on the surface of the stainless steel oxygen evolution electrode, the present application finds that the method of the present application improves the electronic properties and surface structure of the stainless steel surface, increases its specific surface area and porosity, and also improves the electron conduction efficiency. These improvements endow the stainless steel electrode with better electrical conductivity, enhanced electrochemical active area and electrocatalytic performance, making it exhibit excellent comprehensive performance in the electrolysis of water to produce hydrogen.

[0046] In some embodiments of the present application, when etching the stainless steel in step 2, the temperature control can be achieved by using a water bath to heat the solution to a temperature slightly higher than room temperature, i.e. 25-50 °C. The stainless steel is then immersed in the reaction vessel so that the acid solution submerges the stainless steel. The stainless steel is etched under this condition for 1-4 hours, and then cleaned and dried to obtain the etched stainless steel electrode. The concentration and type of acid solution can affect the performance of the final electrode. When the concentration of the acid solution is low, the etching rate is slow, which can not achieve the purpose of effectively removing surface impurities or changing the surface structure. When the concentration of the acid solution is too high, it can cause excessive etching, which can damage the stability of the material itself and affect the stability and catalytic performance of the electrode in the long-term electrolysis of water to produce hydrogen. Therefore, the concentration of the acid solution is controlled between 10-40 wt%, preferably 20 wt%, such as 10 wt%, 20 wt%, 30 wt%, 40 wt%, etc., as well as all ranges and sub-ranges between the above values. The acid solution includes one of hydrofluoric acid (HF), sulfuric acid (H2SO4), or nitric acid (HNO3). Different types of acid have different effects on stainless steel, and the selection of the appropriate acid type can be determined according to the desired final electrode characteristics. The etching time should be controlled between 1-4 hours. When the etching time is short, it can not be enough to achieve the desired surface modification effect. When the etching time is too long, it can cause unnecessary excessive etching, which can affect the performance and stability of the electrode. Therefore, the etching time is further preferably 2 hours, such as 1 hour, 2 hours, 3 hours, 4 hours, etc., as well as all ranges and sub-ranges between the above values. It should be understood that in embodiments, any of the above ranges can be combined with any other range in other embodiments to optimize the preparation process of the stainless steel electrode to ensure that it has excellent electrochemical performance and stability.

[0047] In some embodiments of the present application, in step 3, the stainless steel after step 2 treatment is subjected to air annealing treatment to form strong crystalline Fe2O3 and other oxides on the surface of the stainless steel. The stainless steel after step 2 treatment is placed in a horizontal furnace and subjected to annealing treatment in an air atmosphere to obtain an air-annealed stainless steel electrode. The annealing treatment temperature is controlled between 400-900°C. When the annealing treatment temperature is too low, it may not be sufficient to promote the full reorganization of the surface structure and the conversion of inactive substances. When the annealing treatment temperature is too high, it may cause changes in the internal structure of the material or excessive oxidation of the surface, affecting the performance of the final electrode. Therefore, the annealing treatment temperature is further preferably 700°C, for example, it can be 400°C, 500°C, 600°C, 700°C, 800°C, 900°C, etc., and all ranges and sub-ranges between the above-mentioned values. The holding time of the annealing treatment is controlled between 1-4 hours. Because a shorter holding time may not provide enough time for the necessary structural changes and chemical reactions to occur on the surface, and a longer holding time will result in unnecessary energy waste and may trigger adverse side reactions. Therefore, the holding time of the annealing treatment is further preferably 2 hours, for example, it can be 1 hour, 2 hours, 3 hours, 4 hours, etc., and all ranges and sub-ranges between the above-mentioned values.

[0048] In some embodiments of the present application, in step 3, the heating rate during annealing treatment is set to 2°C / min. This rate helps to ensure uniform heating of the sample, reduce the impact of thermal stress on the material structure, and avoid potential defects caused by rapid heating. By precisely controlling the annealing conditions, the reorganization of the stainless steel surface structure can be effectively promoted, the oxygen vacancy concentration can be increased, and the transition of the OER (oxygen evolution reaction) mechanism can be induced, thereby improving the catalytic activity and durability of the electrode. It should be understood that in embodiments, any of the above ranges can be combined with any other range in other embodiments to optimize the preparation process of the stainless steel electrode and ensure its excellent electrochemical performance and stability.

[0049] In some embodiments of the present application, electrochemical oxidation is performed in step 4 to further restructure the surface of the air-annealed stainless steel. This process can use a two-electrode system, with the air-annealed stainless steel as the anode, a graphite rod as the cathode, and an alkaline solution as the electrolyte. The concentration of the alkali in the alkaline solution is controlled between 1-2 mol / L. When the alkali concentration is low, the current transfer efficiency can be insufficient; when the alkali concentration is too high, the solution viscosity can increase and the conductivity can decrease, both of which can adversely affect the oxygen evolution performance of the electrode. Therefore, the concentration of the alkali in the alkaline solution is further preferably 1 mol / L, such as 1 mol / L, 1.5 mol / L, 2 mol / L, and the like, as well as all ranges and sub-ranges between the aforementioned values. The alkali is one of KOH and NaOH. The current density during this electrolysis process affects the restructuring of the stainless steel surface. When the current density is low, the oxidation rate is slow, making it difficult to effectively promote the restructuring of the electrode surface; when the current density is too high, the electrode surface can be excessively corroded, thereby reducing the oxygen evolution performance of the electrode. Therefore, the current density during electrolysis is controlled between 400-600 mA / cm 2 , preferably 500 mA / cm 2 , such as 400 mA / cm 2 , 500 mA / cm 2 , 600 mA / cm 2 , and the like, as well as all ranges and sub-ranges between the aforementioned values. At the same time, the electrolysis time also needs to be controlled. A shorter electrolysis time is insufficient to dissolve the inactive substances, the oxides on the electrode surface cannot be fully converted to hydroxides, the oxygen vacancy concentration cannot be effectively increased, and the OER reaction mechanism of the stainless steel electrode cannot be induced to change, which will reduce the oxygen evolution performance of the electrode. On the other hand, a longer electrolysis time will unnecessarily increase the energy consumption of the entire preparation process, thereby increasing the preparation cost. Therefore, the electrolysis time is controlled between 100-1600 hours, preferably 800 hours, such as 100 hours, 200 hours, 400 hours, 800 hours, 1600 hours, and the like, as well as all ranges and sub-ranges between the aforementioned values. It should be understood that in embodiments, any of the aforementioned ranges can be combined with any other range in other embodiments to optimize the preparation process of the stainless steel oxygen evolution electrode, ensuring that it has excellent electrochemical performance and stability.

[0050] The present application can effectively promote the restructuring of the stainless steel electrode surface, increase the oxygen vacancy concentration, induce the change of the OER (oxygen evolution reaction) mechanism, and thereby improve the catalytic activity and durability of the electrode by precisely controlling the concentration of the alkaline solution, the current density, and the electrolysis time.

[0051] In some embodiments of the present application, the stainless steel contains Cr > 20% and Ni > 20% by weight. The present application is applicable to almost all stainless steels with mass fraction of Cr and Ni greater than 20%. When the content of Ni in the stainless steel is low, it is impossible to form the key OER active substance Ni on the surface of the electrode x Fe 1-x OOH. When the content of Cr in the stainless steel is low, there will be no phenomenon of dissolution of non-active element Cr in the second electrolysis process, and the ratio of Ni and Fe will not change, which may not induce a change in the OER reaction mechanism of the stainless steel electrode. In the examples, the stainless steel contains the following components: 23-25% Cr, 21-23% Ni, 0.04-0.05% Si, 2-4% Mn, and the balance Fe by weight.

[0052] In some embodiments of the present application, in step 1, the stainless steel sample is ultrasonically cleaned in deionized water to remove loose contaminants, dust and other tiny impurities on the surface, and to ensure the effectiveness of the subsequent treatment steps. The time control of ultrasonic cleaning is crucial to achieve good cleaning effect: too short time may not completely remove the surface contaminants, affecting the quality of the subsequent treatment; while too long time may cause unnecessary energy waste, and may cause slight damage to the sample surface. Therefore, the time of ultrasonic cleaning can be controlled at 10 minutes, 15 minutes, 20 minutes, etc., and all ranges and sub-ranges between the above-mentioned values. It should be understood that in embodiments, any of the above-mentioned ranges can be combined with any other range in other embodiments to optimize the pretreatment process of the stainless steel sample, to ensure that its surface cleanliness is in the best state, thereby providing an ideal starting condition for the subsequent anodic corrosion or other treatment steps. In addition, in order to ensure the cleaning effect while avoiding any potential adverse effects on the stainless steel sample, it is recommended to use deionized water as the cleaning medium, because deionized water does not contain minerals and other impurities, which can reduce the risk of secondary pollution. By strictly controlling the time of ultrasonic cleaning and using appropriate cleaning medium, the surface quality of the stainless steel sample and the effect of subsequent treatment can be effectively improved.

[0053] II. Use of a high-performance self-optimized stainless steel oxygen evolution electrode

[0054] The high-performance self-optimized stainless steel oxygen evolution electrode described in the present application can be used for electrolytic water oxygen evolution. In specific implementation, the stainless steel oxygen evolution electrode acts as an anode for oxygen evolution during electrolytic water process.

[0055] III. Examples and comparative examples

[0056] Example 1

[0057] Step 1: Pretreatment of stainless steel material:

[0058] Take 654S stainless steel and cut it into a rectangle, the untreated 654S stainless steel is marked as SS. Then the stainless steel sample is ultrasonically cleaned in deionized water for 10 min to remove impurities on the surface of the stainless steel. After slow flushing with deionized water for 3 minutes, dry for 6 hours to obtain a rectangular stainless steel sheet.

[0059] Step 2: Preparation of acid-etched stainless steel electrode:

[0060] The stainless steel sample is placed in a 20% HF solution and etched at 30°C for 2 hours. Then the stainless steel is cleaned and dried to obtain the HF etched stainless steel sample.

[0061] Step 3: Preparation of air annealed stainless steel electrode:

[0062] The stainless steel is placed in a horizontal furnace and annealed in an air atmosphere, the temperature is raised to 700°C at a rate of 2°C / min, and the holding time is 2h, to obtain the air annealed stainless steel electrode.

[0063] Step 4: Preparation of electrochemically oxidized stainless steel electrode:

[0064] A two-electrode system is used, the anodically etched stainless steel electrode as the anode and the graphite rod as the cathode, and the electrolyte is KOH solution. The anodically etched stainless steel electrode is placed in the KOH solution for secondary electrolysis for 800 hours to obtain the final stainless steel oxygen evolution electrode. Among them, the current density during structure reconstruction is 500 mA / cm 2 , and the electrolyte concentration during structure reconstruction is 1 mol / L.

[0065] Example 2

[0066] Based on Example 1, the improvement is that in Step 2, the concentration of HF is 10%.

[0067] Example 3

[0068] Based on Example 1, the improvement is that in Step 2, the concentration of HF is 30%.

[0069] Example 4

[0070] Based on Example 1, the improvement is that in Step 2, the concentration of HF is 40%.

[0071] Example 5

[0072] Based on Example 1, the improvement is that in Step 2, the concentration of HNO3 is 20%.

[0073] Example 6

[0074] Improvement based on Example 1, different from which lies in that in Step 2, the concentration of H2SO4 is 20%.

[0075] Example 7

[0076] Improvement based on Example 1, different from which lies in that in Step 2, the time of water bath heating is 1 h.

[0077] Example 8

[0078] Improvement based on Example 1, different from which lies in that in Step 2, the time of water bath heating is 3 h.

[0079] Example 9

[0080] Improvement based on Example 1, different from which lies in that in Step 2, the time of water bath heating is 4 h.

[0081] Example 10

[0082] Improvement based on Example 1, different from which lies in that in Step 3, the holding temperature is 400℃.

[0083] Example 11

[0084] Improvement based on Example 1, different from which lies in that in Step 3, the holding temperature is 500℃.

[0085] Example 12

[0086] Improvement based on Example 1, different from which lies in that in Step 3, the holding temperature is 600℃.

[0087] Example 13

[0088] Improvement based on Example 1, different from which lies in that in Step 3, the holding temperature is 800℃.

[0089] Example 14

[0090] Improvement based on Example 1, different from which lies in that in Step 3, the holding temperature is 900℃.

[0091] Example 15

[0092] Improvement based on Example 1, different from which lies in that in Step 4, the electrolysis time is 100 h.

[0093] Example 16

[0094] Improvement based on Example 1, different from it in that in Step 4, the electrolysis time is 200 h.

[0095] Example 17

[0096] Improvement based on Example 1, different from it in that in Step 4, the electrolysis time is 400 h.

[0097] Example 18

[0098] Improvement based on Example 1, different from it in that in Step 4, the electrolysis time is 1600 h.

[0099] Comparative Example 1

[0100] Step 1: Pretreatment of stainless steel material:

[0101] Take 654S stainless steel and cut it into a rectangle, and the untreated 654S stainless steel is marked as SS. Then the stainless steel sample is ultrasonically cleaned in deionized water for 10 min to remove impurities on the surface of the stainless steel. After slow flushing with deionized water for 3 minutes, dry for 6 hours to obtain a rectangular stainless steel sheet.

[0102] Step 2: Preparation of acid-etched stainless steel electrode:

[0103] The stainless steel sample is placed in a 20% HF solution and etched at 30°C for 2 hours. Then the stainless steel is cleaned and dried to obtain a stainless steel sample treated by HF etching.

[0104] Comparative Example 2

[0105] Step 1: Pretreatment of stainless steel material:

[0106] Take 654S stainless steel and cut it into a rectangle, and the untreated 654S stainless steel is marked as SS. Then the stainless steel sample is ultrasonically cleaned in deionized water for 10 min to remove impurities on the surface of the stainless steel. After slow flushing with deionized water for 3 minutes, dry for 6 hours to obtain a rectangular stainless steel sheet.

[0107] Step 2: Preparation of acid-etched stainless steel electrode:

[0108] The stainless steel sample is placed in a 20% HF solution and etched at 30°C for 2 hours. Then the stainless steel is cleaned and dried to obtain a stainless steel sample treated by HF etching.

[0109] Step 3: Preparation of air-annealed stainless steel electrode:

[0110] The stainless steel is placed in a horizontal furnace and annealed in an air atmosphere, heated to 700°C at a rate of 2°C / min, and held for 2 h to obtain an air-annealed stainless steel electrode.

[0111] Comparative Example 3

[0112] Step 1: Pretreatment of stainless steel material:

[0113] Take 654S stainless steel and cut it into a rectangle, and the untreated 654S stainless steel is marked as SS. Then the stainless steel sample is ultrasonically cleaned in deionized water for 10 min to remove impurities on the surface of the stainless steel. After slow flushing with deionized water for 3 min, dry for 6 h to obtain a rectangular stainless steel sheet.

[0114] Step 2: Preparation of acid-etched stainless steel electrode:

[0115] The stainless steel sample is placed in a 20% HF solution and etched at 30°C for 2 hours. Then the stainless steel is cleaned and dried to obtain the HF etched stainless steel sample.

[0116] Step 3: Preparation of electrochemically oxidized stainless steel electrode:

[0117] An anodic etching stainless steel electrode is used as the anode and a graphite rod is used as the cathode in a two-electrode system, and the electrolyte is a KOH solution. The anodic etching stainless steel electrode is placed in the KOH solution for secondary electrolysis for 800 hours to obtain the final stainless steel oxygen evolution electrode. The current density during structure reconstruction is 500 mA / cm 2 , and the electrolyte concentration during structure reconstruction is 1 mol / L.

[0118] Comparative Example 4

[0119] Step 1: Pretreatment of stainless steel material:

[0120] Take 654S stainless steel and cut it into a rectangle, and the untreated 654S stainless steel is marked as SS. Then the stainless steel sample is ultrasonically cleaned in deionized water for 10 min to remove impurities on the surface of the stainless steel. After slow flushing with deionized water for 3 min, dry for 6 h to obtain a rectangular stainless steel sheet.

[0121] Step 2: Preparation of air-annealed stainless steel electrode:

[0122] The stainless steel is placed in a horizontal furnace and annealed in an air atmosphere, heated to 700°C at a rate of 2°C / min, and held for 2 h to obtain the air-annealed stainless steel electrode.

[0123] Step 3: Preparation of electrochemically oxidized stainless steel electrode:

[0124] A two-electrode system was used, in which the anodically corroded stainless steel electrode was used as the anode and a graphite rod was used as the cathode, and the electrolyte was a KOH solution. The anodically corroded stainless steel electrode was placed in the KOH solution for secondary electrolysis for 800 hours to obtain the final stainless steel oxygen evolution electrode. The current density during the structural reconstruction was 500 mA / cm 2 , and the electrolyte concentration during the structural reconstruction was 1 mol / L.

[0125] Comparative Example 5

[0126] Step 1: Pretreatment of the stainless steel material

[0127] The 654S stainless steel was cut into a rectangular shape, and the untreated 654S stainless steel was marked as SS. Then, the stainless steel sample was ultrasonically cleaned in deionized water for 10 min to remove impurities on the surface of the stainless steel. After being slowly rinsed with deionized water for 3 min, the stainless steel sample was dried for 6 hours to obtain a rectangular stainless steel sheet.

[0128] Step 2: Preparation of the electrochemically oxidized stainless steel electrode

[0129] A two-electrode system was used, in which the anodically corroded stainless steel electrode was used as the anode and a graphite rod was used as the cathode, and the electrolyte was a KOH solution. The anodically corroded stainless steel electrode was placed in the KOH solution for secondary electrolysis for 800 hours to obtain the final stainless steel oxygen evolution electrode. The current density during the structural reconstruction was 500 mA / cm 2 , and the electrolyte concentration during the structural reconstruction was 1 mol / L.

[0130] IV. Performance analysis

[0131] 1. Micro-morphology

[0132] The example, the comparative examples, and the untreated stainless steel (control sample) were all placed on a JSM-7800F scanning electron microscope produced by JEOL for micro-morphology observation.

[0133] As can be seen from Figure 1 , the surface of the initial stainless steel was relatively flat and smooth. As can be seen from Figure 2 , the stainless steel obtained in Comparative Example 1 was corroded into a porous structure, which greatly facilitated the increase in the active specific surface area. As can be seen from Figure 3 , the porous structure of the stainless steel obtained in Comparative Example 2 grew many dense grains, and these fine grains showed a hexagonal shape. As can be seen from Figure 4It can be seen that the stainless steel surface mass obtained in Example 1 is further decomposed, and the surface is loose and porous, like a sponge, greatly increasing the active specific surface area. This phenomenon shows that long-time electro-oxidation not only changes the composition of the material, but also affects its microstructure, which may be due to the continuous oxidation reaction, which destroys the original structure and recombines it into a new amorphous or low-crystallinity hydroxyl compound.

[0134] 2. Measurement of overpotential

[0135] The examples and comparative examples, as well as the untreated stainless steel (control sample), were placed on a CHI1140C electrochemical workstation produced by Shanghai Chenhua Instrument Co., Ltd. to measure the LSV curve. A three-electrode system was used for oxygen evolution performance test, the stainless steel electrode was used as the anode, the graphite rod was used as the cathode, the Hg / HgO was used as the reference electrode, and the electrolyte was 1 mol / L KOH solution. This method is different from the second electrolysis.

[0136] Table 1 shows the overpotential measurement results of different stainless steel electrodes

[0137]

[0138] From Figure 5 , Figure 6 and Table 1, it can be seen that:

[0139] (1) The overpotential of all examples of the present application has been greatly reduced, and is significantly lower than that of the comparative examples and the control sample. Even under the condition of higher current density, the overpotential of the electrode prepared by the examples of the present application is still low, which shows that after acid etching, annealing and electrochemical oxidation treatment, the overpotential of the stainless steel electrode can be significantly reduced, thereby improving its efficiency as an oxygen evolution reaction (OER) catalyst.

[0140] (2) Comparative Example 1 only acid-etched the stainless steel, Comparative Example 2 used acid etching + annealing, Comparative Example 3 used acid etching + electrochemical oxidation, Comparative Example 4 used annealing + electrochemical oxidation, and Comparative Example 5 only used electrochemical oxidation. Compared with the control sample, the overpotential of the stainless steel electrode can be reduced to a certain extent by the comparative examples, but the reduction effect is still significantly different from that of Example 1.

[0141] (3) The control sample is the initial stainless steel, and the overpotential (η) thereof is 368 mV to achieve a current density (j) of 10 mA·cm -2 . Comparative Example 1 only acid-etched the stainless steel, and the overpotential (η) thereof was 345 mV to achieve a current density (j) of 10 mA·cm -2 . Comparative Example 2 used acid etching + annealing, and the overpotential (η) thereof was 341 mV to achieve a current density (j) of 10 mA·cm -2Example 15 adopts corrosion + annealing treatment + electrochemical oxidation for 100h, and the overpotential (η) of 300mV can reach the current density (j) of 10mA·cm -2 Example 16 adopts corrosion + annealing treatment + electrochemical oxidation for 200h, and the overpotential (η) of 288mV can reach the current density (j) of 10mA·cm -2 Example 17 adopts corrosion + annealing treatment + electrochemical oxidation for 400h, and the overpotential (η) of 277mV can reach the current density (j) of 10mA·cm -2 Example 1 adopts corrosion + annealing treatment + electrochemical oxidation for 800h, and the overpotential (η) of 188mV can reach the current density (j) of 10mA·cm -2 Example 18 adopts corrosion + annealing treatment + electrochemical oxidation for 1600h, and the overpotential (η) of 198mV can reach the current density (j) of 10mA·cm -2 Meanwhile, the electrode material prepared by the same process as above shows a gradually improved performance under different current densities, which indicates that the electrode material has a self-optimization performance.

[0142] (4) In general, the behavior of the electrode material prepared in Example 18 in the 1600-hour stability test shows two trends: in the first 800 hours, the performance of the electrode material is in a very gentle rising stage, and its performance is slowly and continuously improved; then in the last 800 hours, the performance of the electrode material enters a stable period, and this stable period lasts for 800 hours; this indicates that the electrode material has excellent stability when performing oxygen evolution reaction (OER) for a long time.

[0143] 3. Electrochemical impedance measurement

[0144] The examples and comparative examples, as well as the untreated stainless steel (control sample), were placed on a CHI1140C electrochemical workstation produced by Shanghai Chenhua Instrument Co., Ltd. to measure the electrochemical impedance (EIS).

[0145] Table 2 Electrochemical impedance measurement results of different stainless steel electrodes

[0146]

[0147]

[0148] From Figure 7 and Table 2, it can be seen that:

[0149] (1) The Nyquist plots obtained by electrochemical impedance spectroscopy tests of the stainless steel oxygen evolution electrodes prepared by the embodiments, the comparative examples and the untreated stainless steel are all approximately semicircular. Since the smaller the radius of the semicircle of the Nyquist plot (i.e. impedance plot) is, the lower the impedance of the material is; therefore, the impedances of the stainless steel oxygen evolution electrodes prepared by the embodiments are all lower than those of the comparative examples and the control sample, while the impedances of the comparative examples are generally higher, which indicates that the stainless steel electrodes described in the present application have lower impedance, i.e. more excellent electrical conductivity.

[0150] (2) The comparative examples 3-5 adopt the method of combination of two by two, which can reduce the impedance to a certain extent, but the effect is still lower than that of the coupling of the three processes, i.e. the impedance of the embodiment 1, and the difference is large.

[0151] (3) The control sample is the initial stainless steel, and the Rct value is 8.223. The comparative example 1 only performs acid etching treatment on the stainless steel, and the Rct value is 7.45. The comparative example 2 adopts acid etching + annealing treatment, and the Rct value is 7.334. The embodiment 15 adopts etching + annealing treatment + electrochemical oxidation for 100 h, and the Rct value is 2.232. The embodiment 16 adopts etching + annealing treatment + electrochemical oxidation for 200 h, and the Rct value is 1.977. The embodiment 17 adopts etching + annealing treatment + electrochemical oxidation for 400 h, and the Rct value is 1.491. The embodiment 1 adopts etching + annealing treatment + electrochemical oxidation for 800 h, and the Rct value is 0.861. The embodiment 18 adopts etching + annealing treatment + electrochemical oxidation for 1600 h, and the Rct value is 0.936. With the advancement of the process, the stainless steel has continuously improved charge transfer kinetics, which can be attributed to the excellent electrical conductivity of the stainless steel and the in-situ development of the active material on the surface thereof.

[0152] 4. Measurement of electrochemical specific surface area

[0153] The embodiments, the comparative examples and the untreated stainless steel (control sample) are all placed on a CHI1140C type electrochemical workstation produced by Shanghai Chenhua Instrument Co., Ltd. to measure the cyclic voltammetry curve (CV curve), and the electrochemical specific surface area (C dl ) of each sample is obtained by fitting the cyclic voltammetry curve.

[0154] Table 3 Measurement results of electrochemical specific surface area of different stainless steel electrodes

[0155]

[0156]

[0157] From the above data, it can be seen that the electrochemical specific surface area of the stainless steel electrode prepared by the embodiment 1 is 0. 1 1 1 1 m2 / g, which is much larger than that of the untreated stainless steel (control sample) and the stainless steel electrodes prepared by the comparative examples, and the difference is large. Figure 8As can be seen from Table 3, the oxygen evolution electrodes of stainless steel prepared by the embodiments and the comparative examples of the present application and the untreated stainless steel can obtain the electrochemical specific surface area (C dl ) of each sample by fitting the cyclic voltammetry curves of each sample. Comparative Example 1, Comparative Example 2 and Comparative Example 6 only perform one step of the method described in the present application, and such treatment is quite limited for the improvement of the electrochemical specific surface area, while Comparative Example 3, Comparative Example 4 and Comparative Example 5 adopt the method combination of two methods each, and it is found that the effect is still not good. However, the embodiments of the present application greatly improve the electrochemical specific surface area of the electrode after coupling the acid etching, air annealing and electrochemical oxidation treatment, so that the electrochemical specific surface area is increased to 30.9 mF cm -2 .

[0158] The control is the initial stainless steel, and the double-layer capacitance value is 1.8 mF cm -2 . Comparative Example 1 only performs acid etching treatment on the stainless steel, and the double-layer capacitance value is 3.3 mF cm -2 . Comparative Example 2 adopts acid etching + annealing treatment, and the double-layer capacitance value is 3.5 mF cm -2 . Example 15 adopts etching + annealing treatment + electrochemical oxidation for 100 h, and the double-layer capacitance value is 13.9 mF cm -2 . Example 16 adopts etching + annealing treatment + electrochemical oxidation for 200 h, and the double-layer capacitance value is 15.7 mF cm -2 . Example 17 adopts etching + annealing treatment + electrochemical oxidation for 400 h, and the double-layer capacitance value is 20.6 mF cm -2 . Example 1 adopts etching + annealing treatment + electrochemical oxidation for 800 h, and the double-layer capacitance value is 30.9 mF cm -2 . Example 18 adopts etching + annealing treatment + electrochemical oxidation for 1600 h, and the double-layer capacitance value is 28.4 mF cm -2 . The process flow of etching, annealing and electrochemical oxidation contributes to the increase of the overall active sites of the catalyst, and after the electrochemical oxidation treatment time reaches 800 h, the effect brought by such contribution gradually tends to be stable.

[0159] 5. Evolution of catalytic mechanism

[0160] The control experiment (with or without TMA+) and no change in polarization curve is detected, which proves that there is no O 2- intermediate produced in the catalytic process. The Raman spectrum after 800 H of OER condition in 1 m TMAOH solution shows weak vibration peaks of TMA+, which may be TMA+ ions and O 2-Weak binding of intermediates or residual TMAOH solution remaining after the OER reaction. These experimental results surface the OER reaction mechanism of the stainless steel oxygen evolution electrode as the oxide pathway mechanism (OPM) through analysis of attenuated total reflectance (ATR-SEIRAS) and experiments of reacting intermediates with methanol.

[0161] Finally, it should be noted that the above examples are only intended to illustrate the technical solutions of the present application and not to limit the technical solutions. Those of ordinary skill in the art should understand that modifications or equivalent replacements to the technical solutions of the present application without departing from the purpose and scope of the technical solutions should be covered in the scope of claims of the present application.

Claims

1. A high performance self-optimizing stainless steel oxygen evolution electrode characterized in that, The electrode is prepared by the following steps: Step 1: pretreating the surface of the stainless steel to remove impurities therefrom; Step 2: placing the stainless steel treated in step 1 in an acid solution and etching the stainless steel at 25-50℃ for 1-4h, and then cleaning and drying the stainless steel to obtain an acid-etched stainless steel electrode; wherein the concentration of the acid solution is 10-40wt%; Step 3: annealing the stainless steel treated in step 2 in an air atmosphere to obtain an air-annealed stainless steel electrode; wherein the annealing temperature is 400-900℃, and the annealing time is 1-4h; Step 4: placing the stainless steel electrode treated in step 3 in an alkali solution and electrolyzing the stainless steel as an anode to obtain the oxygen-evolving electrode; wherein the concentration of the alkali in the alkali solution is 1-2mol / L, the current density during electrolysis is 400-600mA / cm2, and the electrolysis time is 100-1600h; In step 2, the acid solution comprises one of HF, H2SO4 or HNO3. In step 4, the alkali is one of KOH and NaOH.

2. The high performance self-optimizing stainless steel oxygen evolution electrode according to claim 1, characterized in that, According to the weight percentage, The content of Cr in the stainless steel is >20%, and the content of Ni is >20%.

3. The high performance self-optimizing stainless steel oxygen evolution electrode according to claim 2, characterized in that, According to the weight percentage, the stainless steel comprises the following components: 23-25% of Cr, 21-23% of Ni, 0.04-0.05% of Si, 2-4% of Mn, and the balance of Fe.

4. The high performance self-optimizing stainless steel oxygen evolution electrode of claim 1, wherein, In step 1, the stainless steel is ultrasonically cleaned in deionized water for 10-20min.

5. The high performance self-optimizing stainless steel oxygen evolution electrode according to claim 1, wherein, In step 3, the heating rate is 2℃ / min.

6. Use of a high performance self-optimizing stainless steel oxygen evolution electrode, characterized in that, The high-performance self-optimized oxygen-evolving electrode of stainless steel according to any one of claims 1-5 is used for electrolysis of water to evolve oxygen.

7. Use of a high performance self-optimizing stainless steel oxygen evolution electrode according to claim 6, characterized in that The oxygen-evolving electrode of stainless steel is used as an anode to evolve oxygen during electrolysis of water.

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