A structural discontinuous air self-priming electrode with surface microcracks and anti-electrowetting properties, as well as a preparation method and use thereof

Abstract

The present invention relates to a method for preparing a structurally discontinuous air self-priming electrode with surface microcracks that resist electrowetting. A carbon black-polytetrafluoroethylene film prepared by coating forms a large number of irregular microcracks during the calcination process, thereby causing structural discontinuity. This structurally discontinuous air self-priming electrode can effectively avoid the electrowetting effect and the resulting electrolyte flooding during electrocatalytic service, maintain stable local water resistance and air self-diffusion channels, and achieve efficient and long-lasting electrochemical synthesis of H2O2. Due to the steric effect, the discontinuity of the electrode structure prevents electric field lines from reaching, resulting in a local low electric field region at the crack. This achieves the electrode's anti-electrowetting ability during long-cycle electrolysis, achieves stable hydrophobicity and rapid oxygen transmission channels under the electric field, and greatly improves the yield, current efficiency, and long-term stability of H2O2 electrosynthesis in air.

Description

Technical Field

[0001] The invention relates to a preparation method and application of a structural discontinuous air self-absorption electrode with surface microcracks and anti-electrowetting properties, belonging to the technical field of electrocatalytic electrode preparation. Background Art

[0002] In recent years, the synthesis of H2O2 through mild electrochemical oxygen reduction reaction is becoming a potential green alternative strategy to the traditional energy-intensive anthraquinone process. This process can directly use oxygen in the air and renewable electricity to produce H2O2 on-site, which is convenient for the decentralized integration of various downstream applications. In a typical electrochemical synthesis process, the yield of H2O2 depends largely on the properties of the electrode material. The most widely studied electrode materials to date can be divided into two categories according to the oxygen supply method: immersed electrodes and air diffusion electrodes. The former uses dissolved oxygen in the electrolyte to complete the ORR process. However, this type of electrode is usually only allowed at a small current density (<10mA / cm 2 ) maintains high H2O2 yield and current efficiency. However, as the applied potential increases, its efficiency is limited by slow oxygen mass transfer. To address this issue, researchers developed an air diffusion electrode, which allows oxygen to diffuse directly from the outside to the three-phase interface of the cathode catalyst layer to complete the ORR reaction, greatly improving oxygen utilization and opening up a new path for the large-scale application of H2O2 electrocatalytic synthesis.

[0003] To date, most of the research and development on air diffusion electrodes has focused on the selective modification of electrocatalysts for ORR. However, it is still difficult to achieve the performance of air diffusion electrodes at industrial high current densities (>100 mA / cm 2 ) remains a significant challenge. This is because as current density increases, the "flooding" of the catalyst layer caused by the electrowetting effect gradually intensifies, leading to a rapid increase in oxygen diffusion resistance. Therefore, ORR performance at high current density is largely affected by the oxygen concentration at the interface, that is, the oxygen mass transfer efficiency at the interface structure controlled by wetting behavior. Therefore, it is of great significance to develop a method for preparing air-absorption electrodes that are resistant to electrowetting. Summary of the Invention

[0004] The present invention relates to a method for preparing a structurally discontinuous air-absorbing electrode with surface microcracks that resist electrowetting. The carbon black-polytetrafluoroethylene film prepared by coating forms numerous irregular microcracks during calcination, leading to structural discontinuity. This structurally discontinuous air-absorbing electrode effectively avoids the electrowetting effect and the resulting electrolyte flooding during electrocatalytic service, maintains stable local water resistance and autonomous air diffusion channels, and achieves efficient and durable electrochemical synthesis of H2O2. The structurally discontinuous air-absorbing electrode is prepared according to the following steps: a stainless steel mesh modified with a polytetrafluoroethylene dispersion is used as a substrate, and a mixed paste of carbon black, polytetrafluoroethylene, and ethanol is uniformly coated on the substrate surface. Subsequently, during heat treatment, the rapid volatilization of the ethanol solvent causes volume shrinkage, thereby forming numerous irregular microcracks in the carbon black-polytetrafluoroethylene coating structure. Commercial carbon black is selected as the electrocatalyst due to its excellent two-electron oxygen reduction reaction (ORR) activity and low cost. Polytetrafluoroethylene serves as a binder and hydrophobic agent to form the coating while imparting basic hydrophobicity to the interface. Importantly, due to the steric effect, the discontinuity of the electrode structure prevents the electric field lines from reaching the cracks, resulting in a local low electric field area at the cracks. This enables the electrode to resist electrowetting during long-cycle electrolysis and achieves stable hydrophobicity and rapid oxygen transmission channels under the electric field, greatly improving the yield, current efficiency and long-term stability during the H2O2 electrosynthesis process in air.

[0005] A discontinuous air self-priming electrode with surface microcracks and anti-electrowetting structure comprises a support material, a diffusion layer loaded on the surface of the support material, and an electrode material loaded on the surface of the diffusion layer. The electrode material comprises carbon and a polymer, and microcracks exist on the surface of the electrode material.

[0006] The diffusion layer includes polymer.

[0007] The polymer in the electrode material and / or the polymer in the diffusion layer has a water drop contact angle greater than 90°; preferably, it is polytetrafluoroethylene.

[0008] The supporting material is a conductive porous material, which is one of stainless steel mesh, foam nickel and graphite felt.

[0009] The weight ratio of carbon to polymer in the electrode material is 0.5-1.5:1.

[0010] The width of the microcracks is 40-500 μm.

[0011] The method for preparing the above-mentioned surface microcrack anti-electrowetting structural discontinuous air self-absorption electrode comprises the following steps:

[0012] Step 1: immerse the support material in a dispersion containing a polymer, take it out and dry it to load the diffusion layer on the surface;

[0013] Step 2: adding carbon black and an alcohol solvent to the dispersion containing the polymer, mixing them evenly, and then evaporating the solvent from the mixture to form a paste, which is then applied to the surface of the support material obtained in step 1;

[0014] Step 3: After calcination, an electrode is obtained.

[0015] In the step 1, the drying condition is 50-120° C. for 1-20 hours.

[0016] In the step 1, the concentration of the dispersion containing the polymer is 2-10 wt %, and the polymer is polytetrafluoroethylene.

[0017] In the step 2, the concentration of the polymer-containing dispersion is 40-70 wt %; and the mass ratio of carbon black, the polymer-containing dispersion and the alcohol solvent is 1:0.2-2:50-200.

[0018] In the step 3, the calcination conditions are to increase the temperature to 330-400°C at a heating rate of 1-10°C / min, continue to calcine for 10-100 minutes, and then cool down to room temperature at a cooling rate of 1-10°C / min.

[0019] A method for synthesizing H2O2 by electrochemical oxygen reduction reaction uses the above-mentioned self-absorption electrode to carry out catalytic reaction.

[0020] In the method described, 10-500 mM sodium sulfate is used as the supporting electrolyte, and the current intensity is 10-100 mA / cm 2 .

[0021] In the method, the electrode material is used to maintain interfacial hydrophobicity.

[0022] Beneficial effects

[0023] The surface microcrack anti-electrowetting structural discontinuous air self-priming electrode of the present invention is obtained by coating and calcining a stainless steel mesh substrate / carbon black-polytetrafluoroethylene to naturally form microcracks. Commercial carbon black is selected as the electrocatalyst due to its excellent ORR activity and low cost. Polytetrafluoroethylene is used as a binder and hydrophobic agent to form the coating while giving the interface basic hydrophobicity. Importantly, due to the steric hindrance effect, the discontinuity of the electrode structure prevents the electric field lines from reaching the local low electric field area at the crack, which realizes the anti-electrowetting ability of the electrode during long-cycle electrolysis and achieves the stable hydrophobicity and rapid oxygen transmission channel of the electrode under the electric field, greatly improving the yield, current efficiency and long-term stability during the electrosynthesis of H2O2 in air. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 Graph showing the hydrogen peroxide production and current efficiency of the non-continuous air self-priming electrode and the conventional continuous air diffusion electrode in Example 1 of the present invention under no aeration conditions;

[0025] Figure 2 This is a photograph of the wettability evolution of the non-continuous air self-absorption electrode and the traditional continuous air diffusion electrode during the reaction process in Example 1 of the present invention;

[0026] Figure 3 This is a photograph of the contact angle evolution during the reaction of the discontinuous air self-absorption electrode and the traditional continuous air diffusion electrode in Example 1 of the present invention;

[0027] Figure 4 This is a graph showing the production of hydrogen peroxide by the discontinuous air self-priming electrode in Example 2 of the present invention under conditions ranging from low laboratory current density to high industrial current density without aeration;

[0028] Figure 5 This is a long-term stability diagram of the discontinuous air self-priming electrode structure in Example 3 of the present invention producing hydrogen peroxide under industrial current density and no aeration conditions. DETAILED DESCRIPTION

[0029] The carbon black-polytetrafluoroethylene film prepared by coating forms a large number of irregular microcracks during the calcination process. These microcracks can effectively avoid the electrowetting effect and the resulting electrolyte flooding during electrocatalytic service, maintain stable hydrophobicity and autonomous air diffusion channels, and achieve efficient and long-lasting electrochemical synthesis of H2O2. In a typical preparation process, the preparation process of the electrode material in this patent is as follows:

[0030] The stainless steel mesh modified with polytetrafluoroethylene dispersion is used as the base, a mixed paste of carbon black, polytetrafluoroethylene and ethanol is evenly coated on the stainless steel mesh base, and then calcined to form a large number of micro cracks to obtain the product.

[0031] Here are the steps:

[0032] Step 1: Clean a 60-mesh stainless steel mesh with deionized water and ethanol to remove surface grease and then dry it for later use;

[0033] Step 2: Soaking the stainless steel mesh obtained in step 1 in a polytetrafluoroethylene dispersion and then drying it to serve as a support and diffusion layer;

[0034] Step 3, ultrasonically dispersing the carbon black and polytetrafluoroethylene dispersion in an ethanol solution to obtain a mixed solution;

[0035] Step 4: Place the mixture obtained in step 3 in a constant temperature water bath and stir to evaporate the ethanol until it becomes a paste;

[0036] Step 5: evenly coating the mixed paste obtained in step 4 on one side of the stainless steel mesh to form a catalyst thin film layer;

[0037] In step 6, the film obtained in step 5 is placed in a muffle furnace for high-temperature calcination. During this process, the film volume shrinks due to the rapid volatilization of the ethanol solution, and a large number of micron-sized cracks are naturally formed in the structure.

[0038] The concentration of the polytetrafluoroethylene dispersion in step 2 is 2-10 wt %.

[0039] The drying condition in step 2 is to stand in an oven at 100° C. for 3 hours.

[0040] The concentration of the polytetrafluoroethylene dispersion in step 3 is 60 wt%.

[0041] In step 3, the mass ratio of carbon black, polytetrafluoroethylene dispersion and ethanol is 1:1:100.

[0042] The ultrasonic treatment time in step 3 is 60 minutes.

[0043] The water bath condition in step 4 is 80° C. and stirring for 60 minutes.

[0044] The muffle furnace calcination conditions in step 6 are as follows: heating from room temperature to 360° C. at a heating rate of 3° C. / min, calcining for 30 minutes, and then cooling to room temperature at a cooling rate of 3° C. / min.

[0045] The physical characteristics of the microcracks in step 6 can be dynamically controlled by the loading amounts of carbon black and polytetrafluoroethylene. As the carbon black loading amount increases, the number of microcracks formed after calcination decreases, while the width and depth increase.

[0046] Example 1

[0047] A 60-mesh stainless steel mesh was cleaned with deionized water and ethanol to remove impurities such as surface grease, then immersed in a 10wt% polytetrafluoroethylene dispersion for 30 minutes, and then dried as a support and diffusion layer; carbon black, polytetrafluoroethylene dispersion and ethanol were mixed by ultrasonic treatment for 60 minutes until uniform dispersion to obtain a mixed solution; the mixed solution was placed in a constant temperature water bath at 80°C and stirred for 60 minutes until it became a paste; the obtained mixed paste was evenly coated on one side of the stainless steel mesh as a catalyst film layer; the electrode was placed in a muffle furnace and heated from room temperature to 360°C at a heating rate of 3°C / min. After calcination for 30 minutes, it was cooled to room temperature at a cooling rate of 3°C / min. During the calcination process, the rapid volatilization of ethanol caused the film layer to shrink in volume, and a large number of irregular microcracks were formed in the electrode film structure, thereby obtaining a structurally discontinuous air self-priming electrode.

[0048] Comparative Example 1

[0049] A 60-mesh stainless steel mesh was cleaned with deionized water and ethanol to remove surface grease, then immersed in a 10wt% polytetrafluoroethylene dispersion for 30 minutes and dried to serve as a support and diffusion layer. Carbon black, polytetrafluoroethylene dispersion and ethanol were mixed and ultrasonicated for 60 minutes until uniformly dispersed to obtain a mixed solution. The obtained mixed solution was placed in a constant temperature water bath at 80°C and stirred for 60 minutes to evaporate to a mixed paste. The obtained mixed paste was evenly coated on one side of the stainless steel mesh and cold-pressed at 18MPa for 10 minutes to serve as a catalyst thin film layer. After drying, the mixture was placed in a muffle furnace and heated from room temperature to 360°C at a heating rate of 3°C / min. After calcination for 30 minutes, the mixture was cooled to room temperature at a cooling rate of 3°C / min to obtain a conventional continuous air diffusion electrode with a flat surface.

[0050] like Figure 2 As shown, cracks with a width of about 40-500 μm are evenly distributed on the surface of the diffusion electrode prepared in Example 1, while the surface of the electrode in Comparative Example 1 is relatively smooth.

[0051] refer to Figure 1 , using 50mM sodium sulfate as the supporting electrolyte, a DC power supply was applied to the discontinuous air self-absorption electrode and the traditional continuous air diffusion electrode at 30mA / cm 2 The constant current is set at 1 hour as one cycle. It can be seen that within 10 cycles, the structural non-continuous air self-absorption electrode maintains a high H2O2 production and current efficiency; the traditional structural continuous air diffusion electrode has a continuous decrease in H2O2 production and current efficiency as the number of cycles increases. Specifically, after the first cycle, the H2O2 production of the structural non-continuous air self-absorption electrode was 1307.5 mg / L and the current efficiency was 98.2%. After the tenth cycle, its H2O2 production was 1291.2 mg / L and the current efficiency was 96.9%. After the first cycle, the H2O2 production of the structural continuous air diffusion electrode was 1296.1 mg / L and the current efficiency was 97.3%. After the tenth cycle, its H2O2 production was 637.8 mg / L and the current efficiency was 47.9%. This shows that the structural non-continuous air self-absorption electrode can maintain high yield and stability under long-term operating conditions. Reference Figure 2, the real-time wettability photos of the structural discontinuous air self-absorption electrode and the structural continuous air diffusion electrode after the 0th, 1st, and 10th cycles were monitored. It can be seen that the dense areas of the two electrodes are gradually wetted by the electrolyte as the reaction time increases, while the microcracks of the structural discontinuous air self-absorption electrode still show a "mirror" effect with hydrophobic characteristics, indicating that it can effectively slow down the electrowetting phenomenon and maintain a high underwater hydrophobicity, which is beneficial to the oxygen mass transfer in the ORR reaction. Figure 3 , the real-time contact angle photos of the structural discontinuous air self-absorption electrode and the structural continuous air diffusion electrode after the 0th, 1st, and 10th cycles were monitored. It can be seen that the contact angles of the dense areas of the two electrodes gradually changed from hydrophobic to hydrophilic with the extension of the reaction time, while the microcracks of the structural discontinuous air self-absorption electrode maintained a relatively stable hydrophobicity. Specifically, after the structural discontinuous air self-absorption electrode was electrolyzed 10 times, the contact angles of its dense areas decreased from 120.1° to 63.9°, and after the structural continuous air diffusion electrode was electrolyzed 10 times, the contact angles of its dense areas decreased from 122.5° to 52.3°. After the microcracks of the structural discontinuous air self-absorption electrode were electrolyzed 10 times, the contact angles slowly decreased from 111.7° to 91.4°.

[0052] Example 2:

[0053] refer to Figure 4 , using 50mM sodium sulfate as the supporting electrolyte, an external power supply was applied to the discontinuous air self-absorption electrode at 5mA / cm 2 、30mA / cm 2 , 70mA / cm 2 , 100mA / cm 2 , 200mA / cm 2 、300mA / cm 2 When the current density is constant, the H2O2 accumulation concentration in the reaction device is linearly related to time, and the hydrogen peroxide accumulation concentration is positively correlated with the current density. Specifically, when the current density is 5mA / cm 2 Increased to 300mA / cm 2 When the reaction is carried out for 1 hour, the H2O2 accumulation concentration in the system can be increased from 222.92 mg / L to 11718.39 mg / L. At the same time, the current efficiency of the H2O2 produced by the discontinuous air self-absorption electrode with different current densities can be observed. It can be observed that with the increase of current density, the current efficiency shows a slight downward trend, but even at the industrial-grade high current density of 100, 200 and 300 mA / cm 2Under the conditions of high current density, the current efficiency still maintains a high level, which are 97.54%, 94.35% and 88.62% respectively within 1 hour; while the current efficiency under the lower laboratory small current density is almost maintained at a level close to 100%, indicating that the discontinuous air self-priming electrode with this structure maintains its hydrophobicity under the electric field due to the unique anti-electrowetting effect at its cracks. At the same time, the cracks have low oxygen diffusion resistance, and the sufficient oxygen supply makes full use of electrons, reducing the occurrence of hydrogen evolution side reaction.

[0054] Example 3:

[0055] Using 50mM sodium sulfate as the supporting electrolyte, an external power supply was applied to the discontinuous air self-absorption electrode at 100mA / cm 2 The long-term stability of the discontinuous air self-absorption electrode with this structure was investigated at a constant current density of . Figure 5 , when applying 100mA / cm 2 At a constant current density of 1.5 GHz, the discontinuous air-diffusion electrode can operate stably for 100 hours without aeration, and the hourly H2O2 production remains above 4000 mg / L, with the current efficiency remaining above 90%. This indicates that the unique anti-electrowetting phenomenon at the cracks of the discontinuous air-diffusion electrode effectively maintains the hydrophobicity of the electrode under the electric field and ensures a stable oxygen transmission channel, enabling the electrode to autonomously breathe / diffuse oxygen in the air in the atmospheric environment, greatly improving the production, current efficiency, and long-term stability of the H2O2 electrosynthesis process.

Claims

1. A surface microcracked anti-electrowetting structured discontinuous air self-priming electrode for electrochemical oxygen reduction reaction to synthesize H2O2, characterized in that: The self-priming electrode includes a support material, a diffusion layer loaded on the surface of the support material, and an electrode material loaded on the surface of the diffusion layer, wherein the electrode material includes carbon and polymer, and microcracks exist on the surface of the electrode material; The diffusion layer includes a polymer; The polymer in the electrode material is polytetrafluoroethylene; The weight ratio of carbon to polymer in the electrode material is 0.5-1.5:1; the width of the microcracks is 40-500 μm; The preparation method of the self-priming electrode comprises the following steps: Step 1: immerse the support material in a dispersion containing a polymer, take it out and dry it to load the diffusion layer on the surface; Step 2: adding carbon black and an alcohol solvent to the dispersion containing the polymer, mixing them evenly, and then evaporating the solvent from the mixture to form a paste, which is then applied to the surface of the support material obtained in step 1; the alcohol solvent is ethanol; and the support material is one of stainless steel mesh, nickel foam, and graphite felt; Step 3: After calcination, an electrode is obtained; In the step 1, the concentration of the dispersion containing the polymer is 2-10wt%; In step 2, the concentration of the polymer-containing dispersion is 40-70 wt %; and the mass ratio of carbon black, the polymer-containing dispersion, and the alcohol solvent is 1:0.2-2:50-200; In step 3, the calcination conditions are as follows: heating the temperature to 330-400 °C at a heating rate of 1-10 °C / min, maintaining the calcination for 10-100 minutes, and then cooling the temperature to room temperature at a cooling rate of 1-10 °C / min.

2. The surface microcrack anti-electrowetting structural discontinuous air self-priming electrode according to claim 1, characterized in that: In the step 1, the drying condition is 50-120 ° C for 1-20 hours.

3. A method for synthesizing H2O2 by electrochemical oxygen reduction reaction, characterized in that: The self-absorption electrode according to claim 1 is used to carry out a catalytic reaction.

4. The method for synthesizing H2O2 by electrochemical oxygen reduction reaction according to claim 3, characterized in that In the method described, 10-500 mM sodium sulfate is used as the supporting electrolyte, and the current intensity is 10-100 mA / cm 2 .

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