A constant rate gas diffusion electrode for generating hydrogen peroxide and a method of using the same

Abstract

The invention discloses a constant-speed gas diffusion electrode for generating hydrogen peroxide and a method for using the same. The gas diffusion electrode comprises a carbon-based electrode sheet, an air chamber, an air guide tube, a sealing member and a wire, wherein the carbon-based electrode sheet is embedded in the air chamber; one end of the air guide tube is connected to the air chamber, and the other end is an air inlet connected to an external air supply device, and gas flows into the air chamber through the air guide tube; one end of the wire passes through a sealing device and is connected to the carbon-based electrode sheet, and the other end is connected to an external power source; the constant-speed gas diffusion electrode is installed in an electrolytic cell as a cathode, air is introduced into the air guide tube, and the air flow rate is adjusted according to the cathode current density; the constant-speed gas diffusion electrode controls the degree of electrolyte penetration by controlling the air flow rate to be constant, thereby improving the three-phase interface state inside the catalyst layer and improving the oxygen mass transfer efficiency.

Description

Technical Field

[0001] The invention relates to an electrode, in particular to a constant-rate gas diffusion electrode for generating hydrogen peroxide and a use method thereof. Background Art

[0002] Refractory organic pollutants cause serious environmental pollution, and it is difficult to completely degrade them by traditional water treatment processes. Electro-Fenton catalytic technology has recently attracted widespread attention due to its high efficiency and environmental friendliness. Electro-Fenton catalytic technology mainly relies on hydrogen peroxide and metal ions (Fe 2+ ,Cu + ) Hydroxyl radicals generated by the Fenton reaction, at this time, hydrogen peroxide can be generated in situ at the cathode through a two-electron oxygen reduction reaction. The hydroxyl radicals generated by the Fenton reaction have strong oxidizing properties (E -0 =2.80V vs.SHE), which can non-selectively degrade organic pollutants. Electro-Fenton catalysis technology can be combined with other technologies such as photocatalysis to develop into various advanced oxidation technologies such as photoelectric Fenton catalysis technology and solar photoelectric Fenton catalysis technology. The electro-Fenton reaction has many advantages such as mild reaction conditions and simple operation. It is an energy-saving and environmentally friendly technology. The key to the electro-Fenton technology based on the in-situ generation of Fenton reagents at the electrode is to improve the oxygen reduction catalytic performance of the cathode. In the two-electron oxygen reduction reaction (2e - In the process of ORR, the activity of the catalyst, the mass transfer of the reactants and the transfer of electrons are the three key factors to ensure the efficient generation of hydrogen peroxide. Among them, oxygen reduction catalysts have been studied in depth and great progress has been made. However, due to the low solubility of oxygen in water at room temperature and pressure (~8 mg / L), oxygen mass transfer becomes an important factor limiting the reaction rate during the oxygen reduction reaction. Therefore, modifying and optimizing the electrode preparation method to improve the oxygen mass transfer performance of the electro-Fenton cathode has become one of the research focuses.

[0003] In recent years, gas diffusion electrodes have attracted extensive attention from researchers due to their excellent mass transfer performance. The developed network structure of the gas diffusion electrode is conducive to the mass transfer of reactants and products, so it can improve the hydrogen peroxide production and current efficiency. However, in the gas diffusion electrode, electrolyte penetration occurs as the reaction time passes, and part or all of the catalyst layer is submerged by the electrolyte, resulting in a decrease in oxygen mass transfer performance. At present, there are some studies aimed at solving the penetration of electrolyte, among which document 1 (Y. Zheng, J. He, S. Qiu, D. Yu, Y. Zhu, H. Pang, J. Zhang, Boosting hydrogen peroxide accumulation by a novel air-breathing gas diffusion electrode in electro-Fenton system, Appl. Catal. B Environ., 316, 2022) and patent CN114774959A disclose a hydrophobic gas diffusion electrode, which forms a relatively stable three-phase interface in the catalyst layer by adjusting the hydrophobicity of the catalyst layer, and air reaches the catalytic active site through the pores of the electrode. This electrode does not require aeration equipment, so its energy consumption is relatively low, but this type of electrode still has electrolyte penetration at high current density, so the hydrogen peroxide production of the electrode is not high. Reference 2 (J.An, N.Li, Q.Zhao, Y.Qiao, S.Wang, C.Liao, L.Zhou, T.Li, X.Wang, Y.Feng, Highly efficient electro-generation of H2O2 by adjusting liquid-gas-solid threephase interfaces of porous carbonaceous cathode during oxygen reduction reaction, Water Res., 164, 2019) uses 20kPa high-pressure air to promote oxygen mass transfer in the catalytic layer, and the hydrogen peroxide production is increased by 45%. However, the thickness of the electrode catalytic layer is large, so the mass transfer resistance is also large, resulting in high aeration energy consumption, which is equivalent to the energy consumption required for the oxygen reduction reaction. Moreover, the oxygen utilization rate of most gas diffusion electrodes is very low, sometimes even less than 0.1%. Summary of the invention

[0004] Purpose of the invention: The first purpose of the present invention is to provide a constant-rate gas diffusion electrode that can efficiently produce hydrogen peroxide, has a high oxygen utilization rate, and has a low aeration energy consumption, in order to solve the problem in the prior art that the oxygen mass transfer performance is reduced, the oxygen utilization rate is low, and the aeration energy consumption is high due to the electrolyte penetration of the gas diffusion electrode; the second purpose of the present invention is to provide a method for using the electrode.

[0005] Technical solution: The constant-rate gas diffusion electrode for producing hydrogen peroxide described in the present invention includes a carbon-based electrode sheet, an air chamber, an air duct, a seal and a wire, wherein the carbon-based electrode sheet is embedded in the air chamber; one end of the air duct is connected to the air chamber, and the other end is an air inlet connected to an external air supply device, and the gas flows into the air chamber through the air duct; one end of the wire passes through the sealing device and is connected to the carbon-based electrode sheet, and the other end is connected to an external power supply.

[0006] Preferably, the carbon-based electrode sheet comprises a base carbon cloth and a carbon-based catalyst coated on the carbon cloth; preferably, the catalyst loading on the carbon-based electrode sheet is 0.5 to 6 mg / cm 2 ; Preferably, the thickness of the catalytic layer of the carbon-based electrode sheet is 5 to 60 μm. The carbon-based electrode sheet eliminates the diffusion layer of the traditional gas diffusion electrode and only has a catalytic layer with gas diffusion and catalytic functions. The thickness is 5 to 60 μm, which is much smaller than that of the traditional gas diffusion electrode. Therefore, the air diffusion resistance is very small, which can reduce the aeration energy consumption, avoid the uneven oxygen mass transfer, and improve the hydrogen peroxide production and current efficiency.

[0007] The preparation method of the carbon-based electrode sheet is as follows: carbon-based catalyst powder, adhesive and solvent are mixed, a dispersion is obtained by ultrasonic treatment, the dispersion is evenly coated on the carbon cloth, and the carbon-based electrode sheet is obtained by annealing. Preferably, the annealing temperature is 300-360°C, and the annealing time is 1-2h. Preferably, the mass ratio of the carbon-based catalyst to the adhesive is 1:(0.5-1).

[0008] Preferably, the carbon-based catalyst is selected from one or more of carbon black, graphene, carbon nanotubes, activated carbon or graphite.

[0009] Preferably, the gas chamber is cylindrical, and the carbon-based electrode sheet is embedded in a circle outside the cylindrical gas chamber. The carbon-based electrode sheet is embedded in a circle on the cylindrical gas chamber, and the electrolyte flow rate distribution and pressure distribution on the surface of the electrode sheet are uniform, which is conducive to the mass transfer of reactants and products.

[0010] The method for using the gas diffusion electrode of the present invention comprises the following steps: installing the constant-speed gas diffusion electrode as a cathode into an electrolytic cell, introducing air through an air guide pipe, and adjusting the air flow rate according to the cathode current density.

[0011] The air flow rate supplied to the constant-rate gas diffusion electrode depends on the current density of the electrode and remains constant during the reaction. The air pressure inside the electrode gas chamber changes with the change in the degree of electrolyte penetration inside the catalyst layer. That is to say, when the electrolyte penetrates excessively, the air pressure rises accordingly, pushing the penetrated electrolyte into the electrolytic cell. On the contrary, when the permeated electrolyte is too little, the air pressure decreases, allowing the electrolyte to penetrate deeply, thereby achieving the purpose of controlling the electrolyte penetration, improving the three-phase interface state inside the catalyst layer, and improving the oxygen mass transfer efficiency, which can ensure the efficient production of hydrogen peroxide.

[0012] Preferably, the electrode current density is 10 to 200 mA / cm 2 .

[0013] Preferably, the air flow rate supplied to the constant-rate gas diffusion electrode is 3 to 6 times the theoretical amount, and the air pressure supplied to the cathode varies with the state of the electrode and is in the range of 0.5 to 2 kPa.

[0014] Invention mechanism: The present invention adopts a constant speed operation mode. In order to achieve constant speed operation, the air outlet is cancelled and the air flow is controlled by a flow meter. At this time, the air pressure inside the electrode air chamber changes with the change of the electrolyte penetration degree inside the catalyst layer. That is to say, when the electrolyte is excessively penetrated, the air pressure rises accordingly, pushing the penetrated electrolyte into the electrolytic cell. On the contrary, when the electrolyte is too little, the air pressure decreases, allowing the electrolyte to penetrate deeply. Therefore, the purpose of controlling the electrolyte penetration is achieved, the three-phase interface state inside the catalyst layer is improved, and the oxygen mass transfer efficiency is improved.

[0015] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages: (1) The constant-rate gas diffusion electrode controls the degree of electrolyte penetration by controlling the air flow rate to be constant, thereby improving the three-phase interface state inside the catalyst layer and improving the oxygen mass transfer efficiency; (2) The carbon-based electrode sheet of the electrode eliminates the diffusion layer and only has a catalyst layer with gas diffusion and catalytic functions, the thickness of which is 5 to 60 μm, which is much smaller than that of the traditional gas diffusion electrode. Therefore, the air diffusion resistance is very small, which can reduce the aeration energy consumption, avoid the uneven oxygen mass transfer, and improve the hydrogen peroxide production and current efficiency; (3) The cylindrical air chamber makes the electrolyte flow rate distribution and pressure distribution on the surface of the carbon-based electrode sheet embedded in the air chamber surface uniform, which is conducive to the uniform mass transfer of reactants and products, and the mechanical strength of the cylindrical electrode is higher than that of the flat electrode under the same material and size, which is conducive to engineering; (4) The constant-rate gas diffusion electrode has a flow rate of 10 to 200 mA / cm 2Under neutral conditions, the current efficiency reaches 60-95%. At the same time, compared with the existing gas diffusion electrodes, the constant-rate gas diffusion electrode provided by the present invention has a high oxygen utilization rate and extremely low aeration energy consumption, which does not exceed 1 / 1000 of the energy consumption required for the oxygen reduction reaction. In addition, the electrode has a simple structure, low manufacturing and operating costs, and is conducive to promotion; (5) The method of using the gas diffusion electrode is simple and easy to operate. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 A schematic diagram of the structure of a constant-rate gas diffusion electrode prepared by the present invention;

[0017] Figure 2 The scanning electron microscope (SEM) image and the surface contact angle measurement result image of the constant rate gas diffusion electrode prepared in Example 5;

[0018] Figure 3 The linear sweep voltammetry (LSV) curves of the constant rate gas diffusion electrodes prepared in Examples 1 to 4 and Comparative Example 1 at a pH value of 3.0;

[0019] Figure 4 The linear sweep voltammetry (LSV) curves of the constant rate gas diffusion electrodes prepared in Examples 1 to 4 and Comparative Example 1 at a pH value of 5.8;

[0020] Figure 5 The hydrogen peroxide production and current efficiency results of the constant rate gas diffusion electrodes prepared in Examples 1 to 4 and Comparative Example 1 are shown;

[0021] Figure 6 The hydrogen peroxide production results of the constant rate gas diffusion electrodes prepared in Examples 2, 5 to 7 are shown;

[0022] Figure 7 This is a graph showing the hydrogen peroxide production results of the constant rate gas diffusion electrode prepared in Example 5;

[0023] Figure 8 This is a graph showing the cycle test results of the constant rate gas diffusion electrode prepared in Example 5. DETAILED DESCRIPTION

[0024] The technical solution of the present invention is further described below in conjunction with embodiments.

[0025] Example 1

[0026] The constant-rate gas diffusion electrode of the present invention is as follows Figure 1As shown, it includes a carbon-based electrode sheet 1, an air chamber 2, an air guide tube 3, a seal 4 and a wire 5. The carbon-based electrode sheet 1 is embedded in the air chamber 2; one end of the air guide tube 3 is connected to the air chamber 2, and the other end is an air inlet connected to an external air supply device, and the gas flows into the air chamber 2 through the air guide tube 3; one end of the wire 5 passes through the sealing device 4 and is connected to the carbon-based electrode sheet 1, and the other end is connected to an external power supply. In this embodiment, the electrode area is 3cm 2 (3cm x 1cm), the air chamber 2 is made of plastic, with an outer diameter of 15mm, and the air guide tube 3 is made of glass, with an outer diameter of 6mm.

[0027] The carbon-based electrode sheet 1 comprises a base carbon cloth and a carbon-based catalyst coated on the carbon cloth, and the preparation method thereof comprises the following steps:

[0028] (1) Carbon cloth pretreatment: The carbon cloth was cut, washed with acetone and deionized water for three times, and then immersed in 15% polytetrafluoroethylene (PTFE) emulsion after vacuum drying. Then, it was dried at 120 °C for 30 min. The soaking and drying were repeated three times. Then, it was transferred to a muffle furnace and annealed at 360 °C for 2 h to obtain a hydrophobic carbon cloth.

[0029] (2) Preparation of electrode sheet: Reduced graphene oxide powder and anhydrous ethanol were mixed, ultrasonically treated for 2 h, and after being evenly mixed, PTFE emulsion (60%) was mixed with the mixture, and then ultrasonically treated for 1 h to obtain a uniform mixed solution; wherein the mass ratio of reduced graphene oxide, polytetrafluoroethylene and ethanol was 1:0.6:100, and the mixed solution was evenly coated on one side of the above-mentioned carbon cloth, and dried in an oven at 100°C for 20 min. The above steps were repeated until the catalyst reduced graphene oxide loading reached 1 mg / cm 2 After drying, the mixture was transferred to a muffle furnace and annealed at 360°C for 2h to obtain an electrode sheet.

[0030] When performing the hydrogen peroxide synthesis reaction, Na2SO4 solution was added to the electrolytic cell as the electrolyte, a platinum electrode was used as the anode, and the constant rate gas diffusion electrode prepared in this embodiment was used as the cathode. The current density was set to 60 mA / cm 2 , air flow rate is 8mL / cm 2 ·min, the reaction time is 60min.

[0031] Example 2

[0032] On the basis of Example 1, the carbon-based catalyst material was replaced with boron-doped graphene powder, and other conditions remained unchanged.

[0033] Example 3

[0034] Based on Example 1, the carbon-based catalyst material was replaced with annealed reduced graphene oxide powder, and the catalyst loading was 3 mg / cm2 , other conditions remain unchanged.

[0035] Example 4

[0036] Based on Example 1, the carbon-based catalyst material was replaced with annealed boron-doped graphene powder, and the catalyst loading was 3 mg / cm 2 , other conditions remain unchanged.

[0037] Example 5

[0038] Based on Example 1, the carbon-based catalyst material was replaced with boron-doped graphene powder, and the catalyst loading was 2 mg / cm 2 , other conditions remain unchanged.

[0039] Example 6

[0040] Based on Example 1, the carbon-based catalyst material was replaced with boron-doped graphene powder, and the catalyst loading was 3 mg / cm 2 , other conditions remain unchanged.

[0041] Example 7

[0042] Based on Example 1, the carbon-based catalyst material was replaced with boron-doped graphene powder, and the catalyst loading was 0.5 mg / cm 2 , other conditions remain unchanged.

[0043] Comparative Example 1

[0044] The difference between this embodiment and embodiment 1 is that no catalyst material is used.

[0045] Structural characterization of carbon-based electrode sheets

[0046] Figure 2 This is a scanning electron microscope image of the carbon-based electrode sheet prepared in Example 5. Figure 2 It can be seen that the thickness of the electrode catalyst layer is about 25 μm, and the surface contact angle is about 130.9°, which is a hydrophobic electrode.

[0047] Electrochemical Performance Test of Constant Rate Gas Diffusion Electrode

[0048] Figure 3 and 4 The linear sweep voltammetry (LSV) curves of the carbon-based electrode sheets prepared in Examples 1 to 4 at pH values ​​of 3.0 and 5.8 are shown respectively. It can be seen from the figures that the current response of the prepared constant-rate gas diffusion electrodes is very large, indicating that the mass transfer performance of the electrode is excellent.

[0049] Performance test of constant rate gas diffusion electrode for preparing hydrogen peroxide

[0050] (1) The constant-rate gas diffusion electrode provided in Examples 1 to 4 and Comparative Example 1 was used as the cathode, the platinum electrode was used as the anode, and Na2SO4 solution was used as the electrolyte. The current density was 60 mA / cm 2 , air flow rate is 8mL / cm 2 ·min, the reaction time under neutral conditions is 60min, the experimental results are as follows Figure 5 shown.

[0051] Depend on Figure 5 It can be seen that the hydrogen peroxide yield of the constant rate gas diffusion electrode prepared in Example 1 is 23.53 mg / cm 2 h, the current efficiency was 61.8%, and the hydrogen peroxide yield of the constant-rate gas diffusion electrode prepared in Example 2 was 30.78 mg / cm 2 h, the current efficiency was 80.8%, and the hydrogen peroxide yield of the constant-rate gas diffusion electrode prepared in Example 3 was 20.22 mg / cm 2 h, the current efficiency was 53.1%, and the hydrogen peroxide yield of the constant-rate gas diffusion electrode prepared in Example 4 was 30.24 mg / cm 2 ·h, and the current efficiency is 79.4%.

[0052] (2) The constant rate gas diffusion electrode prepared in Examples 2 and 5 to 7 was used as the cathode, the platinum electrode was used as the anode, and Na2SO4 solution was used as the electrolyte. The current density was 60 mA / cm 2 , air flow rate is 8mL / cm 2 ·min, the reaction time under neutral conditions is 60min, the experimental results are as follows Figure 6 shown.

[0053] Depend on Figure 6 It can be seen that with the increase of catalyst loading, the hydrogen peroxide yield first increases and then decreases. There is an optimal loading. The hydrogen peroxide yield of the constant-rate gas diffusion electrode provided in Example 2 is 30.78 mg / cm 2 ·h, and the current efficiency is as high as 80.8%, which is better than other embodiments.

[0054] (3) The constant-rate gas diffusion electrode provided in Example 5 was used as the cathode, the platinum electrode was used as the anode, and the Na2SO4 solution was used as the electrolyte. The current density was 30-200 mA / cm 2 , the reaction time under neutral conditions is 60min, the experimental results are as follows Figure 7 shown.

[0055] Depend on Figure 7 It can be seen that the hydrogen peroxide production of the electrode increases with the increase of current density, reaching up to 73.64 mg / cm 2 ·h.

[0056] (4) The constant-rate gas diffusion electrode provided in Example 5 was used as the cathode, the platinum electrode was used as the anode, and the Na2SO4 solution was used as the electrolyte. The operation was continued for 10 times, and the reaction time for each time was 60 minutes. The experimental results are shown in FIG. Figure 8 shown.

[0057] Depend on Figure 8 It can be seen that the hydrogen peroxide production of the electrode is maintained at 29-30 mg / cm 2 ·h, the average current efficiency remains at 77-78%, indicating that the cyclic performance of the electrode is stable.

Claims

1. A constant rate gas diffusion electrode for producing hydrogen peroxide, characterized in that: The invention comprises a carbon-based electrode sheet (1), an air chamber (2), an air guide tube (3), a sealing member (4) and a wire (5), wherein the carbon-based electrode sheet (1) is embedded in the air chamber (2); one end of the air guide tube (3) is connected to the air chamber (2), and the other end is an air inlet connected to an external air supply device, and gas flows into the air chamber (2) through the air guide tube (3); one end of the wire (5) passes through the sealing member (4) and is connected to the carbon-based electrode sheet (1), and the other end is connected to an external power source; the carbon-based electrode sheet (1) comprises a base carbon cloth and a carbon-based catalyst coated on the carbon cloth; the carbon-based catalyst is selected from one or more of carbon black, graphene, carbon nanotubes, activated carbon or graphite.

2. The gas diffusion electrode according to claim 1, characterized in that The catalyst loading on the carbon-based electrode sheet (1) is 0.5-6 mg / cm 2 .

3. The gas diffusion electrode according to claim 1, characterized in that The thickness of the catalytic layer of the carbon-based electrode sheet (1) is 5 to 60 μm.

4. The gas diffusion electrode according to claim 1, characterized in that The gas chamber (2) is cylindrical, and the carbon-based electrode sheet is embedded outside the cylindrical gas chamber (2) to form a circle.

5. A method for using the gas diffusion electrode according to claim 1, characterized in that: The constant-rate gas diffusion electrode is installed as a cathode in an electrolytic cell, and air is introduced into an air guide pipe (3), and the air flow rate is adjusted according to the cathode current density.

6. The method for using the gas diffusion electrode according to claim 5, characterized in that: The cathode current density is 10-200 mA / cm 2 .

7. The method for using a gas diffusion electrode according to claim 5, characterized in that: The air flow rate is 3 to 6 times the required theoretical air volume.

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