A carbon-based gas diffusion electrode and its preparation method and application

Abstract

The present invention belongs to the field of electrode material technology and provides a carbon-based gas diffusion electrode, its preparation method, and application. The method comprises the following steps: mixing multi-walled carbon nanotubes and an acid solution for functionalization treatment to obtain functionalized multi-walled carbon nanotubes; mixing the functionalized multi-walled carbon nanotubes, an alcohol solution, and a fluorine-containing emulsion for a first calcination to obtain a functionalized carbon nanotube current collector layer; mixing the functionalized multi-walled carbon nanotubes, a nitrogen-containing polycarboxylic acid ligand, an alcohol substance, and a cobalt source, and sequentially performing a hydrothermal reaction and a second calcination to obtain a catalytic layer of cobalt-nitrogen-doped functionalized carbon nanotubes; and laminating the catalytic layer, the current collector layer, and a polytetrafluoroethylene film in this order and pressing them to obtain a carbon-based gas diffusion electrode. The preparation process of the present invention not only imparts hydrophobicity and gas permeability to the electrode surface, but also imparts excellent electrochemical properties to the electrode, ensuring adsorption and desorption of reactants and products at the interface and increasing the generation rate of H2O2.

Description

Technical Field

[0001] The present invention relates to the technical field of electrode materials, and in particular to a carbon-based gas diffusion electrode and a preparation method and application thereof. Background Art

[0002] In recent years, the amount of organic pollutants in water bodies has been increasing, causing serious impacts on the ecological environment and human health. Traditional water treatment technologies such as physical adsorption, chemical oxidation, and biodegradation have problems such as low treatment efficiency, long cycle time, and easy formation of secondary pollution. Therefore, the development of a new, cost-effective and efficient water treatment technology is of great significance. Hydrogen peroxide (H2O2) itself has strong oxidizing properties and is an environmentally friendly compound. Excess H2O2 will slowly decompose into oxygen and water, and has broad application prospects in the field of organic pollutant treatment. However, to date, 95% of the world's H2O2 is obtained from the anthraquinone method. The anthraquinone method of preparing H2O2 inevitably produces side reactions, resulting in environmentally unfriendly products such as 2-ethylanthraquinone, trioctyl phosphate, and tert-butyl urea, which cause environmental pollution and energy waste.

[0003] At the same time, using electrochemical principles, oxygen and water are used as sources, and electrical energy is used as energy input to electrocatalytically synthesize H2O2, namely 2e - The oxygen reduction reaction (ORR) process is a potentially environmentally friendly method for generating H2O2. This process can effectively mineralize organic pollutants into small molecules such as H2O and CO2. However, its development is limited by the development of highly active and selective electrode materials. Summary of the Invention

[0004] The purpose of the present invention is to overcome the problems existing in the prior art and provide a carbon-based gas diffusion electrode and a preparation method and application thereof.

[0005] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0006] The present invention provides a method for preparing a carbon-based gas diffusion electrode, comprising the following steps:

[0007] Mixing multi-walled carbon nanotubes with an acid solution and performing functionalization treatment to obtain functionalized multi-walled carbon nanotubes;

[0008] The functionalized multi-walled carbon nanotubes, the alcohol solution and the fluorine-containing emulsion are mixed and subjected to a first calcination to obtain a functionalized carbon nanotube current collector layer;

[0009] The functionalized multi-walled carbon nanotubes, nitrogen-containing polycarboxylic acid ligands, alcohols and a cobalt source are mixed, and a hydrothermal reaction and a second calcination are performed in sequence to obtain a catalytic layer of cobalt-nitrogen doped functionalized carbon nanotubes;

[0010] The carbon-based gas diffusion electrode is obtained by stacking a catalyst layer of cobalt-nitrogen doped functionalized carbon nanotubes, a functionalized carbon nanotube current collector layer and a polytetrafluoroethylene film in this order and pressing them.

[0011] Preferably, the acid solution comprises one or more of a hydrochloric acid solution, a sulfuric acid solution and a nitric acid solution; the mass fraction of the hydrochloric acid solution is 10 to 37%, the mass fraction of the sulfuric acid solution is 60 to 98%, and the mass fraction of the nitric acid solution is 30 to 68%;

[0012] The mass volume ratio of the multi-walled carbon nanotubes and the acid solution is 1g:50-200mL.

[0013] Preferably, the functionalization treatment is carried out at a temperature of 70 to 150° C. and for a time of 1 to 5 hours.

[0014] Preferably, the alcohol solution comprises water and isopropyl alcohol, wherein the volume ratio of water to isopropyl alcohol is 1 to 6:1; the fluorine-containing emulsion is polytetrafluoroethylene emulsion and / or perfluorosulfonic acid solution; the mass fraction of the polytetrafluoroethylene emulsion is 10 to 60%, and the mass fraction of the perfluorosulfonic acid solution is 1 to 5%;

[0015] The mass volume ratio of the functionalized multi-walled carbon nanotubes, the alcohol solution and the fluorine-containing emulsion is 1-10 g: 100-500 mL: 0.1-5 g.

[0016] Preferably, the temperature of the first calcination is 300-500° C., and the time is 20-180 min.

[0017] Preferably, the nitrogen-containing polycarboxylic acid ligand is one or more of 2-methylimidazole, p-aminobenzoic acid and 4-nitrobenzoic acid, the alcohol substance is methanol and / or ethanol, the cobalt source is cobalt chloride hexahydrate, cobalt nitrate hexahydrate, cobalt sulfate hexahydrate or cobalt acetylacetonate, and the dosage ratio of the functionalized multi-walled carbon nanotubes, nitrogen-containing polycarboxylic acid ligand, alcohol substance and cobalt source is 100-500 mg:1-10 mmol:20-100 mL:1-6 mmol.

[0018] Preferably, the temperature of the hydrothermal reaction is 80-130°C and the time is 4-18 hours;

[0019] The second calcination temperature is 500-900° C., and the time is 20-200 minutes.

[0020] Preferably, the mass ratio of the cobalt-nitrogen doped functionalized carbon nanotube catalyst layer, the functionalized carbon nanotube current collector layer, and the polytetrafluoroethylene film is 0.1-2.0:0.05-1.0:0.02-0.3;

[0021] The pressing pressure is 0.1-50 MPa, the temperature is 20-250° C., and the pressing time is 5-30 min.

[0022] The present invention also provides a carbon-based gas diffusion electrode prepared by the preparation method, comprising a catalyst layer of cobalt-nitrogen doped functionalized carbon nanotubes, a functionalized carbon nanotube current collector layer and a polytetrafluoroethylene film hydrophobic layer stacked in sequence.

[0023] The present invention also provides the use of the carbon-based gas diffusion electrode in the degradation of organic pollutants. The method of the application comprises the following steps: subjecting the carbon-based gas diffusion electrode to a weak alkaline aqueous solution containing a strong base and a weak acid salt as a medium for 2e - ORR reaction to generate H2O2;

[0024] The 2e - The relationship between the interfacial oxygen demand and time of the ORR reaction is:

[0025]

[0026] 2e - The relationship between the concentration of H2O2 produced by ORR and time is:

[0027]

[0028] D O2 2e per unit time - ORR interface oxygen demand, mol·s -1 ; Q is the charge required for the reaction, C; n is 2e - The electron transfer number of ORR, F is the Faraday constant, 96486 C·mol -1 ; t is the reaction time, h; j is the current density, mA·cm -2 ; A is the area of ​​the electrode, cm 2 ; C H2O2 is the H2O2 concentration, mg·L -1 ;K g is the rate constant for H2O2 formation, mg·L -1 min -1 ;K d is the rate constant of H2O2 decomposition, min -1 .

[0029] The beneficial effects of the present invention are:

[0030] (1) The present invention provides a method for preparing a carbon-based gas diffusion electrode, wherein a catalyst layer of cobalt-nitrogen doped functionalized carbon nanotubes, a functionalized carbon nanotube current collector layer, and a polytetrafluoroethylene film hydrophobic layer are pressed into a carbon-based gas diffusion electrode. On the one hand, the electrode surface is made hydrophobic and breathable, and on the other hand, the electrode has good electrochemical properties, thereby ensuring the adsorption and desorption of reactants and products at the interface and increasing the generation rate of H2O2.

[0031] (2) The present invention effectively improves the barrier of surface charge transfer kinetics in alkaline media by doping cobalt, nitrogen and oxygen elements in the carbon-based gas diffusion electrode, optimizes the adsorption energy of oxygen-containing species in the reaction process, and breaks through the existing 2e - The ORR pathway has a bottleneck of poor activity and selectivity. Therefore, the prepared carbon-based gas diffusion electrode enhances the conductivity of the solution under the action of strong base and weak acid salt as electrolyte, obtains a wide range of gas-solid-liquid three-phase interface, and transfers O2 through 2e - Path reduction to generate H2O2, showing excellent 2e - ORR activity, giving full play to the intrinsic activity of the electrocatalyst, improving the reaction rate and significantly accelerating the degradation rate of organic pollutants. At the same time, the alkaline environment has a great influence on the degradation of 2e - The ORR pathway is more favorable, the overpotential of the first electron transfer step is significantly reduced, and the energy conversion efficiency is higher. The results of the embodiment show that the carbon-based gas diffusion electrode can produce 48 mg / L of H2O2 in 0.1 mol / L sodium carbonate electrolyte in 20 minutes. 2- For example, the H2O2 obtained after electrochemical oxidation will complex with it to form an intermediate medium percarbonate, thereby effectively improving the selectivity of the reaction to produce H2O2.

[0032] (3) The carbon-based gas diffusion electrode of the present invention is used to electrosynthesize H2O2, and the electro-Fenton-like degradation of organic pollutants is achieved in a weakly alkaline medium through a "self-production and self-sales" model, effectively reducing large-molecule organic pollutants to small molecules, and even mineralizing them into inorganic substances. Not only does it not require additional H2O2, it eliminates the cost of H2O2 storage and transportation, and reduces the risk of explosion caused by concentrated H2O2 operations; it also avoids the degradation of H2O2 itself in alkaline media, which can accelerate the degradation rate of organic pollutants; at the same time, it also breaks the disadvantage of traditional electro-Fenton degradation reactions that rely on acidic solutions, avoiding Fe 3+ The accumulation of iron sludge in the electrolyte eliminates the generation of iron sludge. The results of the embodiment show that the carbon-based gas diffusion electrode prepared by the present invention can achieve a decolorization rate of 91.35% of malachite green when it is operated in 0.1 mol / L sodium carbonate electrolyte for 20 minutes. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1The graph is a graph showing the relationship between the concentration and time of H2O2 produced by the carbon-based gas diffusion electrode prepared in Example 1 in different electrolytes;

[0034] Figure 2 The graph is a graph showing the relationship between the absorbance of malachite green and time of the carbon-based gas diffusion electrode prepared in Example 1 in different electrolytes;

[0035] Figure 3 The graph is a graph showing the relationship between the concentration and time of H2O2 produced by the carbon-based gas diffusion electrodes prepared in Examples 1 to 3 in a 0.1 mol / L sodium carbonate electrolyte. DETAILED DESCRIPTION

[0036] The present invention provides a method for preparing a carbon-based gas diffusion electrode, comprising the following steps:

[0037] Mixing multi-walled carbon nanotubes with an acid solution and performing functionalization treatment to obtain functionalized multi-walled carbon nanotubes;

[0038] The functionalized multi-walled carbon nanotubes, the alcohol solution and the fluorine-containing emulsion are mixed and subjected to a first calcination to obtain a functionalized carbon nanotube current collector layer;

[0039] The functionalized multi-walled carbon nanotubes, nitrogen-containing polycarboxylic acid ligands, alcohols and a cobalt source are mixed, and a hydrothermal reaction and a second calcination are performed in sequence to obtain a catalytic layer of cobalt-nitrogen doped functionalized carbon nanotubes;

[0040] The carbon-based gas diffusion electrode is obtained by stacking a catalyst layer of cobalt-nitrogen doped functionalized carbon nanotubes, a functionalized carbon nanotube current collector layer and a polytetrafluoroethylene film in this order and pressing them.

[0041] In the present invention, the acid solution comprises one or more of a hydrochloric acid solution, a sulfuric acid solution and a nitric acid solution; the mass fraction of the hydrochloric acid solution is preferably 10-37%, more preferably 15-35%, and more preferably 20-30%; the mass fraction of the sulfuric acid solution is preferably 60-98%, more preferably 70-95%, and more preferably 80-90%; the mass fraction of the nitric acid solution is preferably 30-68%, more preferably 40-65%, and more preferably 50-60%.

[0042] In the present invention, the mass volume ratio of the multi-walled carbon nanotubes to the acid solution is preferably 1 g: 50 to 200 mL, more preferably 1 g: 70 to 180 mL, and even more preferably 1 g: 90 to 160 mL.

[0043] In the present invention, the functionalization treatment is specifically to mix the multi-walled carbon nanotubes and the acid solution and then perform a reflux treatment in a round-bottom flask.

[0044] In the present invention, the temperature of the functionalization treatment is preferably 70-150° C., more preferably 90-130° C., and more preferably 100-120° C.; the time is preferably 1-5 h, more preferably 2-4 h, and more preferably 2.5-3.5 h.

[0045] In the present invention, after the functionalization treatment is completed, the obtained mixed solution is centrifuged, and then the obtained solid product is collected, washed with water until neutral, and finally dried to obtain functionalized multi-walled carbon nanotubes; the centrifugal speed is preferably 800-10000 rpm, more preferably 1000-8000 rpm, more preferably 2000-4000 rpm; the centrifugal time is preferably 5-60 min, more preferably 10-40 min, more preferably 20-30 min; the drying temperature is preferably 40-80°C, more preferably 45-75°C, more preferably 50-70°C; the drying time is preferably 5-10 h, more preferably 6-9 h, more preferably 7-8 h.

[0046] In the present invention, the alcohol solution comprises water and isopropyl alcohol, and the volume ratio of water to isopropyl alcohol is preferably 1-6:1, more preferably 2-5:1, and more preferably 3-4:1; the fluorine-containing emulsion is a polytetrafluoroethylene emulsion and / or a perfluorosulfonic acid solution; the mass fraction of the polytetrafluoroethylene emulsion is preferably 10-60%, more preferably 15-50%, and more preferably 20-40%; the mass fraction of the perfluorosulfonic acid solution is preferably 1-5%, more preferably 2-4%, and more preferably 2.5-3.5%.

[0047] In the present invention, the mass volume ratio of the functionalized multi-walled carbon nanotubes, alcohol solution and fluorine-containing emulsion is preferably 1-10 g:100-500 mL:0.1-5 g, more preferably 2-9 g:150-400 mL:0.3-3 g, and more preferably 3-8 g:180-350 mL:0.5-2 g.

[0048] In the present invention, during the mixing of the functionalized multi-walled carbon nanotubes, alcohol solution and fluorine-containing emulsion, the functionalized multi-walled carbon nanotubes and alcohol solution are preferably first ultrasonically dispersed to obtain a uniform dispersion; and then the fluorine-containing emulsion is added dropwise and stirred.

[0049] In the present invention, the frequency of the ultrasonic dispersion is preferably 20 to 60 kHz, more preferably 30 to 50 kHz, and more preferably 32 to 40 kHz; the time of the ultrasonic dispersion is preferably 20 to 40 min, more preferably 25 to 35 min, and more preferably 27 to 33 min; the stirring speed is preferably 200 to 700 r / min, more preferably 300 to 600 r / min, and more preferably 400 to 500 r / min; the stirring time is preferably 30 to 150 min, more preferably 40 to 120 min, and more preferably 60 to 90 min.

[0050] In the present invention, after the stirring is completed, the obtained system is sequentially subjected to vacuum filtration and drying, and then subjected to the first calcination to obtain a functionalized carbon nanotube current collector layer; the vacuum filtration can be completed according to conventional technical means in the art; the drying temperature is preferably 40 to 80°C, more preferably 45 to 75°C, and more preferably 50 to 70°C; the drying time is preferably 5 to 10 hours, more preferably 6 to 9 hours, and more preferably 7 to 8 hours.

[0051] In the present invention, the temperature of the first calcination is preferably 300-500°C, more preferably 350-450°C, more preferably 370-430°C; the time is preferably 20-180 min, more preferably 50-150 min, more preferably 70-130 min.

[0052] In the present invention, the nitrogen-containing polycarboxylic acid ligand is preferably one or more of 2-methylimidazole, p-aminobenzoic acid and 4-nitrobenzoic acid, the alcohol substance is preferably methanol and / or ethanol, the cobalt source is preferably cobalt chloride hexahydrate, cobalt nitrate hexahydrate, cobalt sulfate hexahydrate or cobalt acetylacetonate, and the amount ratio of the functionalized multi-walled carbon nanotubes, nitrogen-containing polycarboxylic acid ligand, alcohol substance and cobalt source is preferably 100-500 mg:1-10 mmol:20-100 mL:1-6 mmol, more preferably 200-400 mg:2-9 mmol:30-90 mL:2-5 mmol, and more preferably 250-350 mg:3-8 mmol:65-80 mL:2.5-4.5 mmol.

[0053] In the present invention, in the process of mixing the functionalized multi-walled carbon nanotubes, nitrogen-containing polycarboxylic acid ligands, alcohol substance and cobalt source, it is preferred to first mix the nitrogen-containing polycarboxylic acid ligands and the first portion of the alcohol substance to obtain a mixed solution of the nitrogen-containing polycarboxylic acid ligands and the alcohol substance, then disperse the functionalized multi-walled carbon nanotubes in the mixed solution and stir it once, and finally add the cobalt source and the remaining portion of the alcohol substance mixed solution and stir it a second time, and then perform a hydrothermal reaction after the stirring is completed.

[0054] In the present invention, the volume ratio of the first part of alcohol substance to the remaining part of alcohol substance is preferably 10-40:10-60, more preferably 15-35:20-50, and even more preferably 25-32:30-45.

[0055] In the present invention, the rotation speed of the primary stirring is preferably 200-700 r / min, more preferably 300-600 r / min, more preferably 400-500 r / min; the time of the primary stirring is preferably 5-60 min, more preferably 10-50 min, more preferably 20-30 min; the rotation speed of the secondary stirring is preferably 200-700 r / min, more preferably 300-600 r / min, more preferably 400-500 r / min; the time of the secondary stirring is preferably 5-60 min, more preferably 10-50 min, more preferably 20-30 min.

[0056] In the present invention, the temperature of the hydrothermal reaction is preferably 80-130° C., more preferably 90-120° C., and more preferably 100-110° C.; the time is preferably 4-18 h, more preferably 6-16 h, and more preferably 9-12 h.

[0057] In the present invention, after the hydrothermal reaction is completed, the process preferably further comprises: naturally cooling the obtained system, then sequentially performing suction filtration separation, washing, drying, and finally performing a second calcination to obtain a catalytic layer of cobalt-nitrogen doped functionalized carbon nanotubes.

[0058] In the present invention, the target temperature of the natural cooling is preferably 20-30°C, more preferably 22-28°C, and more preferably 24-26°C; the suction filtration separation is carried out according to conventional technical means in the art; the drying temperature is preferably 40-80°C, more preferably 45-75°C, and more preferably 50-70°C; the drying time is preferably 5-10h, more preferably 6-9h, and more preferably 7-8h.

[0059] In the present invention, the atmosphere of the second calcination is preferably nitrogen or argon, the temperature is preferably 500-900°C, more preferably 600-800°C, more preferably 650-750°C; the time is preferably 20-200 min, more preferably 50-180 min, more preferably 80-150 min.

[0060] In the present invention, the mass ratio of the cobalt-nitrogen doped functionalized carbon nanotube catalyst layer, the functionalized carbon nanotube current collector layer, and the polytetrafluoroethylene film is preferably 0.1-2.0: 0.05-1.0: 0.02-0.3, more preferably 0.2-1.5: 0.1-0.8: 0.05-0.2, and more preferably 0.5-1.0: 0.3-0.5: 0.06-0.15.

[0061] In the present invention, the pressing pressure is preferably 0.1 to 50 MPa, more preferably 5 to 45 MPa, and more preferably 15 to 35 MPa; the temperature is preferably 20 to 250°C, more preferably 50 to 230°C, and more preferably 100 to 150°C; and the time is preferably 5 to 30 min, more preferably 15 to 25 min, and more preferably 17 to 20 min.

[0062] The present invention also provides a carbon-based gas diffusion electrode prepared by the preparation method described in the above technical solution, comprising a catalyst layer of cobalt-nitrogen-doped functionalized carbon nanotubes, a functionalized carbon nanotube current collector layer and a polytetrafluoroethylene film hydrophobic layer stacked in sequence.

[0063] The present invention also provides the use of the carbon-based gas diffusion electrode in the degradation of organic pollutants. The present invention does not specifically limit the method of the application, and the carbon-based gas diffusion electrode can be used to generate H2O2 for degradation of organic pollutants according to methods well known in the art.

[0064] In the present invention, the carbon-based gas diffusion electrode is placed in a weak alkaline aqueous solution with a strong base and a weak acid salt as a medium to generate H2O2. The concentration of the strong base and weak acid salt in the weak alkaline aqueous solution is preferably 0.01 to 1.5 mol / L, more preferably 0.3 to 1.2 mol / L, and more preferably 0.5 to 1.0 mol / L. The strong base and weak acid salt is preferably carbonate, bicarbonate, monohydrogen phosphate or borate, more preferably carbonate or bicarbonate, and more preferably sodium carbonate or sodium bicarbonate.

[0065] In the present invention, the steps of electrosynthesizing H2O2 by placing the carbon-based gas diffusion electrode in a weakly alkaline aqueous solution with sodium carbonate as the medium are as follows:

[0066] O2+H2O+e - →OOH*+OH -

[0067] OOH*+H2O+e - →H2O2+OH -

[0068] H2O2+NaCO3→NaCO3·1.5H2O2

[0069] Overall reaction: O2+2H2O+2e - →H2O2+2OH - (pH<11.6).

[0070] In the present invention, 2e - The relationship between the oxygen demand at the ORR interface and time is:

[0071]

[0072] 2e - The relationship between the concentration of H2O2 produced by ORR and time is:

[0073]

[0074] Among them, D O2 2e per unit time - ORR interface oxygen demand, mol·s -1 ; Q is the charge required for the reaction, C; n is 2e - The electron transfer number of ORR, F is the Faraday constant, 96486 C·mol -1 ; t is the reaction time, h; j is the current density, mA·cm -2 ; A is the area of ​​the electrode, cm 2 ; C H2O2 is the H2O2 concentration, mg·L -1 ;K g is the rate constant for H2O2 formation, mg·L -1 min -1 ;K d is the rate constant of H2O2 decomposition, min -1 .

[0075] In the present invention, when the carbon-based gas diffusion electrode is used to degrade organic pollutants, it is preferred to place the organic pollutants in a weak alkaline aqueous solution with a strong base and a weak acid salt as the medium, and degrade the organic pollutants while generating H2O2, or to pass the H2O2 generated at the end of the reaction into the organic pollutants for degradation. It is more preferred to place the organic pollutants in a weak alkaline aqueous solution with a strong base and a weak acid salt as the medium, and degrade the organic pollutants while generating H2O2.

[0076] The technical solutions provided by the present invention are described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0077] Example 1

[0078] 1g of multi-walled carbon nanotubes was mixed with 120mL of 68% nitric acid solution, refluxed at 110°C in a round-bottom flask for 3h, and the resulting mixed solution was centrifuged at 4000rpm for 30min. The solid product was then collected, washed with water until neutral, and finally dried at 70°C for 8h to obtain functionalized multi-walled carbon nanotubes. 16mL of water and 4mL of isopropanol were mixed to obtain an alcohol solution. 0.5g of functionalized multi-walled carbon nanotubes was mixed with the alcohol solution and ultrasonically dispersed at 32kHz for 30min. min to obtain a uniform dispersion; then, 0.5 g of 20% polytetrafluoroethylene emulsion was added dropwise and stirred at 400 r / min for 90 min. After the stirring was completed, the obtained system was vacuum filtered and dried at 70 ° C for 8 h, and then placed in a tube furnace and calcined at 350 ° C for 120 min to obtain a functionalized carbon nanotube current collector layer; 6 mmol 2-methylimidazole, 2 mmol p-aminobenzoic acid and 30 mL methanol were mixed to obtain a mixture of nitrogen-containing polycarboxylic acid ligands and alcohol substances. 250 mg of functionalized multi-walled carbon nanotubes were dispersed in a mixed solution of nitrogen-containing polycarboxylic acid ligands and alcohols, stirred at 400 r / min for 30 min, and then a mixed solution of 4 mmol of cobalt chloride hexahydrate and 35 mL of methanol was added, and stirred at 400 r / min for 30 min. After the stirring was completed, the mixture was transferred to a reactor and hydroheated at 120 ° C for 12 h. The obtained system was naturally cooled to 25 ° C, and then filtered and separated, washed, and then dried at 70 ° C for 8 h. Finally, the mixture was heated in an argon atmosphere. The carbon-based gas diffusion electrode was obtained by laminating the cobalt-nitrogen doped functional carbon nanotube catalytic layer, calcining at 700°C for 120 minutes, and stacking the cobalt-nitrogen doped functional carbon nanotube catalytic layer, the functional carbon nanotube current collector layer, and the polytetrafluoroethylene film in the order of stacking (the mass ratio of the cobalt-nitrogen doped functional carbon nanotube catalytic layer, the functional carbon nanotube current collector layer, and the polytetrafluoroethylene film was 1:0.5:0.15). The carbon-based gas diffusion electrode was obtained by pressing at a pressure of 20 MPa and a temperature of 120°C for 20 minutes.

[0079] The carbon-based gas diffusion electrode prepared in this embodiment was used as the cathode and the Pt sheet as the anode. The H2O2 content was detected under a 5V DC power supply and different electrolytes. The organic pollutant, malachite green, was selected as an example to detect its decolorization behavior. Sodium sulfate was used as a representative neutral electrolyte, and sodium carbonate was used as a representative strong base weak acid salt electrolyte (the concentration of both electrolytes was 0.1 mol / L). The relationship curves of the H2O2 concentration and time generated by the carbon-based gas diffusion electrode prepared in this embodiment in different electrolytes were obtained, as shown in FIG. Figure 1 shown; from Figure 1It can be seen that the carbon-based gas diffusion electrode prepared in this example increases the concentration of H2O2 over time, regardless of the medium used. Notably, 48 mg / L of H2O2 can be produced in 20 minutes in a 0.1 mol / L sodium carbonate electrolyte (the hydrogen peroxide concentration in the sodium carbonate electrolyte tested after 20 minutes is 48 mg / L), which is 1.41 times that of a sodium sulfate electrolyte. This indicates that the addition of a strong acid and weak base electrolyte improves the selectivity of H2O2 generation.

[0080] The absorbance and time relationship curves of malachite green in different electrolytes of the carbon-based gas diffusion electrode prepared in this embodiment are as follows: Figure 2 shown; from Figure 2 It can be seen that the absorbance of malachite green decreases over time in the carbon-based gas diffusion electrode prepared in this example, regardless of the medium. Compared to the 56.18% decolorization rate of malachite green achieved after 20 minutes in a 0.1 mol / L sodium sulfate electrolyte, the decolorization rate reached 91.35% in a sodium carbonate electrolyte under the same conditions, demonstrating that H2O2 can maintain high activity in a weakly alkaline environment with a strong base and a weak acid salt as the electrolyte.

[0081] Example 2

[0082] 1g of multi-walled carbon nanotubes was mixed with 50mL of 98% sulfuric acid solution and 100mL of 68% nitric acid solution, and refluxed at 90°C in a round-bottom flask for 2h. The obtained mixed solution was centrifuged at 5000rpm for 25min, and then the obtained solid product was collected, washed with water until neutral, and finally dried at 50°C for 8h to obtain functionalized multi-walled carbon nanotubes; 15mL of water and 5mL of isopropanol were mixed to obtain an alcohol solution; 0.6g of functionalized multi-walled carbon nanotubes was taken and mixed with the alcohol solution. Mix and ultrasonically disperse at 40kHz for 30min to obtain a uniform dispersion; then, add 0.8g of 40% polytetrafluoroethylene emulsion dropwise and stir at 500r / min for 90min. After stirring, the obtained system is vacuum filtered and dried at 50℃ for 8h, and then placed in a tube furnace and calcined at 400℃ for 120min to obtain a functionalized carbon nanotube current collector layer; 2mmol of p-aminobenzoic acid and 20mL of methanol are mixed to obtain p-aminobenzoic acid and alcohol. 100 mg of functionalized multi-walled carbon nanotubes were dispersed in a mixed solution of p-aminobenzoic acid and alcohols, stirred at 450 r / min for 30 min, then a mixed solution of 4 mmol of cobalt sulfate hexahydrate and 50 mL of methanol was added, and stirred at 450 r / min for 30 min. After the stirring was completed, the mixture was transferred to a reactor and hydroheated at 120 ° C for 6 h. The obtained system was naturally cooled to 27 ° C, and then filtered and separated, washed, and then dried at 50 ° C for 8 h. Finally, the mixture was heated under nitrogen atmosphere. The carbon-based gas diffusion electrode was obtained by calcining at 650°C for 150 minutes under an atmosphere of 1% CO and 25°C. Finally, the catalytic layer of cobalt-nitrogen-doped functionalized carbon nanotubes, the functionalized carbon nanotube current collector layer and the polytetrafluoroethylene film were stacked in this order (the mass ratio of the catalytic layer of cobalt-nitrogen-doped functionalized carbon nanotubes, the functionalized carbon nanotube current collector layer and the polytetrafluoroethylene film was 0.8:0.3:0.2). The carbon-based gas diffusion electrode was obtained by pressing at a pressure of 30 MPa and a temperature of 25°C for 15 minutes.

[0083] Example 3

[0084] 1g of multi-walled carbon nanotubes was mixed with 150mL of 98% sulfuric acid solution, refluxed at 75°C in a round-bottom flask for 5h, and the obtained mixed solution was centrifuged at 3500rpm for 35min. The solid product was then collected, washed with water until neutral, and finally dried at 60°C for 8h to obtain functionalized multi-walled carbon nanotubes; 14mL of water and 6mL of isopropanol were mixed to obtain an alcohol solution; 0.5g of functionalized multi-walled carbon nanotubes was mixed with the alcohol solution and ultrasonically dispersed at 45kHz for 30mi n, to obtain a uniform dispersion; then, 0.8 g of 30% polytetrafluoroethylene emulsion was added dropwise, and stirred at 600 r / min for 60 min. After the stirring was completed, the obtained system was vacuum filtered, and then dried at 60 ° C for 8 h, and then placed in a tube furnace and calcined at 400 ° C for 150 min to obtain a functionalized carbon nanotube current collector layer; 3 mmol of p-aminobenzoic acid, 2 mmol of 4-nitrobenzoic acid and 25 mL of ethanol were mixed to obtain a mixture of nitrogen-containing polycarboxylic acid ligands and alcohol substances. Solution; 300 mg of functionalized multi-walled carbon nanotubes were dispersed in a mixed solution of nitrogen-containing polycarboxylic acid ligands and alcohols, stirred at 300 r / min for 30 min, then a mixed solution of 5 mmol of cobalt nitrate hexahydrate and 45 mL of ethanol was added, and stirred at 300 r / min for 30 min. After the stirring was completed, it was transferred to a reactor and hydroheated at 125 ° C for 12 h. The obtained system was naturally cooled to 23 ° C, and then filtered and separated, washed, and then dried at 60 ° C for 8 h. Finally, under an argon atmosphere, , calcined at 750℃ for 120min to obtain a catalytic layer of cobalt-nitrogen-doped functionalized carbon nanotubes; finally, the catalytic layer of cobalt-nitrogen-doped functionalized carbon nanotubes, the functionalized carbon nanotube current collector layer and the polytetrafluoroethylene film were stacked in this order (the mass ratio of the catalytic layer of cobalt-nitrogen-doped functionalized carbon nanotubes, the functionalized carbon nanotube current collector layer and the polytetrafluoroethylene film was 1.6:0.8:0.25), and pressed at a pressure of 15Mpa and a temperature of 110℃ for 25min to obtain the carbon-based gas diffusion electrode.

[0085] The carbon-based gas diffusion electrodes prepared in Examples 1 to 3 were used as cathodes and the Pt sheet was used as anodes. The H2O2 content was detected under a 5V DC power supply and a 0.1mol / L sodium carbonate electrolyte. The relationship between the concentration and time of H2O2 produced by the carbon-based gas diffusion electrodes prepared in Examples 1 to 3 in a 0.1mol / L sodium carbonate electrolyte was obtained, as shown in FIG. Figure 3 shown; from Figure 3 It can be concluded that the carbon-based gas diffusion electrode prepared in Example 2 can produce 23 mg / L of H2O2 in 0.1 mol / L sodium carbonate electrolyte for 20 minutes, and the carbon-based gas diffusion electrode prepared in Example 3 can produce 36 mg / L of H2O2 in 0.1 mol / L sodium carbonate electrolyte for 20 minutes.

[0086] As can be seen from the above examples, the present invention provides a carbon-based gas diffusion electrode. By compressing a three-layer structure consisting of a catalyst layer of cobalt-nitrogen-doped functionalized carbon nanotubes, a functionalized carbon nanotube current collector layer, and a polytetrafluoroethylene film hydrophobic layer, the electrode surface is rendered hydrophobic and breathable. Furthermore, the electrode exhibits excellent electrochemical properties, ensuring interfacial adsorption and desorption of reactants and products, thereby increasing the rate of H2O2 generation. The carbon-based gas diffusion electrode prepared in this example can produce 48 mg / L of H2O2 in 0.1 mol / L sodium carbonate electrolyte for 20 minutes, and achieves a 91.35% decolorization rate of malachite green after 20 minutes in 0.1 mol / L sodium carbonate electrolyte.

[0087] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as within the scope of protection of the present invention.

Claims

1. A method for preparing a carbon-based gas diffusion electrode, characterized in that: It includes the following steps: Mixing multi-walled carbon nanotubes with an acid solution and performing functionalization treatment to obtain functionalized multi-walled carbon nanotubes; The functionalized multi-walled carbon nanotubes, the alcohol solution and the fluorine-containing emulsion are mixed and subjected to a first calcination to obtain a functionalized carbon nanotube current collector layer; The functionalized multi-walled carbon nanotubes, one or more of 2-methylimidazole, p-aminobenzoic acid and 4-nitrobenzoic acid, an alcohol and a cobalt source are mixed, and a hydrothermal reaction and a second calcination are performed in sequence to obtain a catalytic layer of cobalt-nitrogen doped functionalized carbon nanotubes; The carbon-based gas diffusion electrode is obtained by stacking a catalyst layer of cobalt-nitrogen-doped functionalized carbon nanotubes, a functionalized carbon nanotube current collector layer, and a polytetrafluoroethylene film in this order and pressing them. The alcohol substance is methanol and / or ethanol, the cobalt source is cobalt chloride hexahydrate, cobalt nitrate hexahydrate, cobalt sulfate hexahydrate or cobalt acetylacetonate, the functionalized multi-walled carbon nanotubes, one or more of 2-methylimidazole, p-aminobenzoic acid and 4-nitrobenzoic acid, and the usage ratio of the alcohol substance to the cobalt source is 100-500 mg:1-10 mmol:20-100 mL:1-6 mmol; The hydrothermal reaction temperature is 80-130°C and the time is 4-18 hours; The second calcination temperature is 500-900° C., and the time is 20-200 min.

2. The preparation method according to claim 1, wherein The acid solution comprises one or more of hydrochloric acid solution, sulfuric acid solution and nitric acid solution; the mass fraction of the hydrochloric acid solution is 10-37%, the mass fraction of the sulfuric acid solution is 60-98%, and the mass fraction of the nitric acid solution is 30-68%; The mass volume ratio of the multi-walled carbon nanotubes to the acid solution is 1g:50-200mL.

3. The preparation method according to claim 1 or 2, wherein The temperature of the functionalization treatment is 70-150° C., and the time is 1-5 hours.

4. The preparation method according to claim 3, wherein The alcohol solution comprises water and isopropyl alcohol, wherein the volume ratio of water to isopropyl alcohol is 1 to 6:1; the fluorine-containing emulsion is polytetrafluoroethylene emulsion and / or perfluorosulfonic acid solution; the mass fraction of the polytetrafluoroethylene emulsion is 10 to 60%, and the mass fraction of the perfluorosulfonic acid solution is 1 to 5%; The mass volume ratio of the functionalized multi-walled carbon nanotubes, the alcohol solution and the fluorine-containing emulsion is 1-10 g: 100-500 mL: 0.1-5 g.

5. The preparation method according to claim 4, wherein The temperature of the first calcination is 300-500° C., and the time is 20-180 minutes.

6. The preparation method according to claim 5, wherein The mass ratio of the cobalt-nitrogen doped functionalized carbon nanotube catalyst layer, the functionalized carbon nanotube current collector layer, and the polytetrafluoroethylene film is 0.1-2.0: 0.05-1.0: 0.02-0.3; The pressing pressure is 0.1-50 MPa, the temperature is 20-250° C., and the pressing time is 5-30 min.

7. The carbon-based gas diffusion electrode prepared by the preparation method according to any one of claims 1 to 6, characterized in that: The invention comprises a catalyst layer of cobalt-nitrogen doped functionalized carbon nanotubes, a functionalized carbon nanotube current collector layer and a polytetrafluoroethylene film hydrophobic layer which are stacked in sequence.

8. Use of the carbon-based gas diffusion electrode according to claim 7 in the degradation of organic pollutants, characterized in that: The application method comprises the following steps: subjecting the carbon-based gas diffusion electrode to a weak alkaline aqueous solution with a strong base and a weak acid salt as a medium for 2e - ORR reaction to generate H2O2; The 2e - The relationship between the interfacial oxygen demand and time of the ORR reaction is: ； 2e - The relationship between the concentration of H2O2 produced by ORR and time is: ； D O2 2e per unit time - ORR interface oxygen demand, mol·s -1 ; Q is the charge required for the reaction, C; n is 2e - The electron transfer number of ORR, F is the Faraday constant, 96486 C·mol -1 ; t is the reaction time, h; j is the current density, mA·cm -2 ; A is the area of ​​the electrode, cm 2 ; C H2O2 is the H2O2 concentration, mg·L -1 ;K g is the rate constant for H2O2 formation, mg·L -1 min -1 ; Kd is the rate constant of H2O2 decomposition, min -1 .

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