A phase-conversion gas diffusion electrode under room temperature and light pressure, and its preparation method and application

Abstract

A phase-conversion gas diffusion electrode under light pressure at room temperature, and its preparation method and application, including a gas diffusion layer made of a hydrophobic breathable membrane that has been cross-linked to enhance the electrode's resistance to organic solvents and water pressure; a catalytic layer made of a mixture of cheap activated carbon, carbon black and a polymer binder. The above mixture is coated on a support layer, and the cross-linked hydrophobic breathable membrane is covered on top of the mixture, and rolled to ensure uniform distribution of the catalyst. The rolled electrode is placed in water for phase conversion and dried to obtain the phase-conversion gas diffusion electrode under light pressure at room temperature. The raw materials of the gas diffusion electrode of the present invention are cheap and easy to obtain, the method is simple, easy to prepare, and has the potential for large-scale production. The gas diffusion electrode synthesized by this method can be used for in-situ electrosynthesis of H 2 O 2 and environmental pollution remediation.

Description

Technical Field

[0001] The invention belongs to the technical field of electrochemical synthesis, and in particular relates to a phase-conversion gas diffusion electrode under normal temperature and light pressure, and a preparation method and application thereof. Background Art

[0002] Gas diffusion electrode is a porous membrane electrode with electrical conductivity, waterproof permeability and high activity. Due to its low cost and easy production, it has been widely used in fuel cells, chemical synthesis and wastewater treatment. Gas diffusion electrode is generally composed of gas diffusion layer, catalyst layer and support layer. The gas diffusion layer mainly provides a fast and efficient transmission channel for oxygen participating in the electrode reaction. The solid catalyst can contact with the electrolyte and air or oxygen at the same time, so that the catalyst layer forms a structure with a stable solid, liquid and gas three-phase interface. The support layer serves as the supporting skeleton of the gas diffusion electrode to enhance the mechanical strength of the gas diffusion electrode. The gas diffusion electrode can be applied to the anode or cathode. Among them, the gas diffusion electrode applied to the cathode can directly utilize the oxygen in the air and make it act quickly on the cathode active center, thereby reducing the energy consumption of the electrochemical oxygen reduction reaction process.

[0003] Traditional gas diffusion electrodes are synthesized by directly coating a paste mixture of catalyst and binder onto a support layer. In actual applications, the traditional direct coating method will cause the electrode catalyst layer to be unevenly distributed, thereby reducing the electrode performance. Prior Art 1 In order to solve the problem of uneven electrode preparation by the direct coating method, a roller method is used to prepare gas diffusion electrodes. In the traditional roller method, a press equipment is required to roll the electrode under high pressure during the preparation process, which has a high failure rate and high cost. In addition, the traditional roller method uses polytetrafluoroethylene as the binder, but polytetrafluoroethylene needs to be hot-pressed (i.e., high temperature and high pressure) to form a uniform waterproof gas diffusion layer, and heating and pressurizing increase energy consumption.

[0004] Prior art 2 uses polyvinylidene difluoride (PVDF) as a binder to form a gas diffusion layer by phase inversion. However, this method has three disadvantages: first, due to its stable chemical properties, polyvinylidene fluoride is only soluble in a few organic solvents, and the organic solvent will be released during the phase inversion process to dissolve the gas diffusion layer; second, the gas diffusion layer formed by this method is uneven, and the uneven gas diffusion layer will cause the gas diffusion channel to be buried due to the migration of the electrolyte, the gas mass transfer is limited, the three-phase interface disappears, and the reaction active sites are reduced; third, with the migration of the electrolyte in the reactor, the electrode is subjected to uneven pressure from the electrolyte, which easily causes excessive pressure at the defect, resulting in leakage. Summary of the invention

[0005] The purpose of the present invention is to overcome the shortcomings of the existing gas diffusion electrode, such as low mechanical strength of the gas diffusion layer, uneven distribution of the catalyst layer, complex preparation process and high energy consumption, and provide a preparation method of a phase-conversion gas diffusion electrode under light pressure at room temperature, wherein a cross-linked polymer membrane is used as the gas diffusion layer, and a cheap and readily available carbon material is used as the catalyst layer, and the catalyst layer and the gas diffusion layer are uniformly covered on one side of the conductive support layer by a roller method. The electrode can be prepared on a large scale at room temperature and pressure, and the mechanical properties of the gas diffusion layer are improved, the catalyst layer is evenly distributed, and it has the ability to generate hydrogen peroxide in situ; and the raw materials used are economical and readily available, the process operation is convenient, and it is easy to mass produce, which is suitable for industrial application.

[0006] The first aspect of the present invention provides a method for preparing a phase-conversion gas diffusion electrode under room temperature and light pressure, comprising the following steps:

[0007] The hydrophobic porous polymer membrane undergoes a cross-linking reaction in the presence of a cross-linking agent to obtain a hydrophobic breathable membrane resistant to organic solvents;

[0008] mixing a binder with a carbon material to obtain a paste-like mixture;

[0009] After applying the paste mixture on a support, covering it with the organic solvent-resistant hydrophobic breathable membrane, and rolling it evenly with a roller at a low pressure to obtain a preliminary gas diffusion electrode;

[0010] The preliminary gas diffusion electrode is immersed in deionized water to induce phase conversion, and then dried to obtain a phase conversion gas diffusion electrode under light pressure at room temperature.

[0011] Optionally, the hydrophobic porous polymer membrane is a PVDF membrane or a PTFE membrane.

[0012] Optionally, the cross-linking agent is one or more of ethylenediamine, bisphenol, peroxide and thiol.

[0013] Optionally, the reaction temperature of the cross-linking reaction is 40 to 100° C., and the reaction time is 5 to 180 seconds.

[0014] Optionally, the carbon material includes activated carbon and carbon black, and the mass ratio of the activated carbon to the carbon black is 1 to 50:1.

[0015] Optionally, the binder is one or more of PVDF solution, PSF solution and PES solution, the concentration of PVDF in the PVDF solution is 5-30% (w / v), and the mass ratio of the activated carbon to the PVDF is 1-10:1.

[0016] Optionally, the phase conversion time is 10 to 60 minutes.

[0017] Optionally, the support body is one or more of a stainless steel mesh, a titanium mesh, a carbon cloth, a carbon felt and a carbon paper.

[0018] The second aspect of the present invention provides a phase-conversion gas diffusion electrode prepared by the preparation method of the first aspect at room temperature and under light pressure.

[0019] The third aspect of the present invention provides a use of a phase-conversion gas diffusion electrode under room temperature and light pressure prepared by the preparation method of the first aspect as a cathode in the preparation of hydrogen peroxide.

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] (1) The present invention prepares the gas diffusion electrode at room temperature and under light pressure, using cheap and readily available carbon materials as raw materials. The preparation process is simple, easy to operate and control, and is conducive to large-scale production.

[0022] (2) The present invention prepares the gas diffusion electrode by the roller method, the catalyst layer is evenly distributed, and a stable solid-liquid-gas three-phase interface is formed, which solves the problem of electrode leakage caused by uneven catalyst coating.

[0023] (3) The present invention pre-treats the hydrophobic porous gas diffusion layer through a cross-linking reaction, thereby enhancing the mechanical strength of the gas diffusion layer and making it resistant to organic solvents, so that the gas diffusion electrode can remain stable during the phase conversion process.

[0024] (4) The room temperature and light pressure phase transformation gas diffusion electrode synthesized by the present invention can generate hydrogen peroxide in situ without the need for additional reagents. It can generate a higher concentration of hydrogen peroxide at a lower current density only through active mass transfer of oxygen in the air. The raw materials and products are green and environmentally friendly, which reduces the cost of the reaction.

[0025] In summary, the present invention optimizes the electrode composition, such as the materials of the gas diffusion layer and the catalyst layer, and improves the preparation process to develop a gas diffusion electrode that is resistant to organic solvents, low in cost, simple in process and excellent in performance, so that it can achieve the ability to produce hydrogen peroxide efficiently and stably. The present invention synthesizes a room temperature and light pressure phase conversion gas diffusion electrode and uses it for in-situ production of hydrogen peroxide, thereby obtaining an efficient and stable electrode material, providing research ideas and theoretical support for the development of promising electrochemical synthesis. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 A is the SEM characterization result of the PVDF membrane provided in the embodiment of the present invention, and B is the SEM characterization result of the PVDF membrane after the cross-linking reaction;

[0027] Figure 2A is the SEM characterization result of the tolerance of the PVDF membrane to organic solvents provided by the embodiment of the present invention, and B is the SEM characterization result of the tolerance of the PVDF membrane to organic solvents after the cross-linking reaction;

[0028] Figure 3 This is a comparison chart of XPS characterization results of PVDF membranes before and after the cross-linking reaction provided in an embodiment of the present invention;

[0029] Figure 4 A schematic diagram of the change in current density concentration and the change in current density and current efficiency when the gas diffusion electrode provided by an embodiment of the present invention is used as a cathode to generate hydrogen peroxide;

[0030] Figure 5 This is a schematic diagram of the structure of a gas diffusion electrode prepared in an embodiment of the present invention. DETAILED DESCRIPTION

[0031] The present application is further described below in conjunction with the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solution of the present invention, and cannot be used to limit the protection scope of the present application.

[0032] An embodiment of the present invention provides a method for preparing a phase-conversion gas diffusion electrode under room temperature and light pressure. The method comprises steps S1 to S4.

[0033] S1. The hydrophobic porous polymer membrane undergoes a cross-linking reaction in the presence of a cross-linking agent to obtain a hydrophobic breathable membrane resistant to organic solvents.

[0034] The embodiment of the present invention pre-treats the hydrophobic porous gas diffusion layer through a cross-linking reaction, thereby enhancing the mechanical strength of the gas diffusion layer and making it resistant to organic solvents, so that the gas diffusion electrode can remain stable during the phase inversion process. The hydrophobic porous polymer membrane is a PVDF membrane or a PTFE membrane, the cross-linking agent is one or a combination of at least two of ethylenediamine, bisphenol, peroxide and thiol, the reaction temperature of the cross-linking reaction is 40 to 100°C, and the reaction time is 5 to 180s.

[0035] In some preferred embodiments, after the cross-linking reaction, the film is washed three times with deionized water and then dried in an oven to obtain a hydrophobic and breathable film resistant to organic solvents.

[0036] S2. Mixing the binder with the carbon material to obtain a paste-like mixture.

[0037] The binder is one or more of PVDF solution, polysulfone (PSF) solution and polyethersulfone (PES) solution, and the carbon material includes activated carbon and carbon black.

[0038] In some preferred embodiments, the binder is a PVDF solution, the concentration of PVDF in the PVDF solution is 5-30% (w / v), the mass ratio of activated carbon to carbon black in the carbon material is 1-50:1, and the mass ratio of activated carbon to solute PVDF in the PVDF solution is 1-10:1. The PVDF solution and the carbon material are fully stirred to form a paste mixture.

[0039] S3. After applying the paste mixture on a support, covering it with the organic solvent-resistant hydrophobic breathable membrane, rolling it evenly with a roller at a low pressure to obtain a preliminary gas diffusion electrode.

[0040] The paste mixture is poured onto a support, covered with a hydrophobic porous polymer membrane after cross-linking reaction, i.e., a hydrophobic breathable membrane resistant to organic solvents, and then lightly pressed and flattened by a roller to obtain a preliminary gas diffusion electrode with a three-layer structure. The support is one or a combination of at least two of a stainless steel mesh, a titanium mesh, a carbon cloth, a carbon felt, and a carbon paper.

[0041] It should be noted that the binder used in the traditional roller method must first be melted at high temperature and subjected to high pressure to stabilize the gas-liquid-solid three-phase interface together. The binder used in the embodiment of the present application and the gas diffusion layer (hydrophobic porous polymer membrane) can be directly bonded together through subsequent phase transformation. Therefore, unlike the traditional roller method, which requires a press equipment to perform high-pressure rolling on the electrode during the preparation process, the embodiment of the present application only needs to apply slight pressure when rolling using the roller method, which is simple and effective.

[0042] S4. Soaking the preliminary gas diffusion electrode in deionized water to induce phase conversion, and then drying to obtain a phase conversion gas diffusion electrode under light pressure at room temperature.

[0043] The preliminary gas diffusion electrode is placed in deionized water at room temperature for phase conversion for 10 to 60 minutes, and then dried to obtain a phase conversion gas diffusion electrode at room temperature and under light pressure.

[0044] Unlike suspensions such as PTFE, which require high temperature and high pressure to process the electrodes to bond them together, the binders in the embodiments of the present application, such as PVDF solution, are viscous fluids that can be formed by phase transformation after being lightly pressed by a roller, thereby allowing the electrodes to directly obtain a stable gas-liquid-solid three-phase interface.

[0045] The embodiment of the present invention also provides the use of the phase-conversion gas diffusion electrode under room temperature and light pressure prepared by the above preparation method as a cathode in the preparation of hydrogen peroxide. The application method comprises:

[0046] (1) The above-mentioned gas diffusion electrode is used as a cathode and an electrolyte solution is added.

[0047] The electrode is powered by external power supply, and the electrolyte solution is selected from any one of sodium sulfate, sodium chloride, sodium perchlorate, PBS, sulfuric acid and sodium hydroxide or a combination of at least two thereof, and the concentration of the electrolyte solution is 10-2000mM.

[0048] (2) 3-50mA / cm 2 The hydrogen peroxide solution can be obtained by reacting for 5 to 480 minutes at the current density.

[0049] The following examples will further illustrate the present invention.

[0050] Example 1

[0051] A commercial PVDF membrane with a diameter of 3.8 cm was immersed in a 100% ethylenediamine solution and cross-linked at 80°C for 1 minute. After the cross-linking reaction, it was washed with deionized water 3 times and then dried to obtain a hydrophobic, breathable membrane resistant to organic solvents. 300 mg of activated carbon and 30 mg of carbon black were added to 1 mL of 10% (w / v) PVDF solution and stirred thoroughly to form a paste mixture. The paste mixture was poured onto a stainless steel mesh, covered with the PVDF membrane after the cross-linking reaction, and the mixture was flattened with a roller to obtain a preliminary gas diffusion electrode with a three-layer structure. The preliminary gas diffusion electrode was immersed in deionized water at room temperature for phase inversion for 15 minutes, and then dried at room temperature for 6 hours to obtain a phase inversion gas diffusion electrode under light pressure at room temperature.

[0052] Comparative Example 1

[0053] A commercial PVDF membrane with a diameter of 3.8 cm was washed three times with deionized water and then dried. 300 mg of activated carbon and 30 mg of carbon black were added to 1 mL of 10% (w / v) PVDF solution and stirred thoroughly to form a paste mixture. The paste mixture was poured onto a stainless steel mesh, covered with a PVDF membrane, and the mixture was flattened with a roller to obtain a preliminary electrode with a three-layer structure. The electrode was immersed in deionized water at room temperature for phase conversion for 15 minutes, and then dried at room temperature for 6 hours to obtain the gas diffusion electrode of Comparative Example 1.

[0054] Example 2

[0055] In a 50 mM Na2SO4 solution, the gas diffusion electrode prepared in Example 1 was used as the cathode. An external power supply was used to power the gas diffusion electrode system. The constant current mode was adopted. The constant currents were 35, 70, 105, 140, and 175 mA, respectively. The reaction time was 1 h. The potassium titanium oxalate spectrophotometry was used to determine the H2O2 concentration.

[0056] The experimental results and analysis are as follows:

[0057] See also Figure 1 , Figure 1A is the SEM characterization result of the PVDF membrane provided in Comparative Example 1 of the present invention, and B is the SEM characterization result of the PVDF membrane after cross-linking reaction in Example 1 of the present invention. Figure 1 It can be seen that the surface of the PVDF membrane is in a mesh-like shape with a porous structure. The surface properties of the PVDF membrane after the cross-linking reaction have not changed significantly compared with those before the cross-linking. The surface is porous and has a continuous mesh-like structure.

[0058] See also Figure 2 , A is the SEM characterization result of the organic solvent tolerance of the PVDF membrane provided in Comparative Example 1 of the present invention, and B is the SEM characterization result of the organic solvent tolerance of the PVDF membrane after the cross-linking reaction in Example 1 of the present invention. It can be seen from the figure that the PVDF membrane of Comparative Example 1 will be dissolved by the organic solvent and generate irregular holes, while the PVDF membrane after the cross-linking reaction in Example 1 can withstand the corrosion of organic solvents.

[0059] See also Figure 3 , the dotted line is the XPS characterization result of the PVDF membrane provided in Comparative Example 1 of the present invention, and the solid line is the XPS characterization result of the PVDF membrane after the cross-linking reaction provided in Example 1 of the present invention. It can be seen that after the cross-linking reaction, the nitrogen peak of the PVDF membrane appears and the fluorine peak intensity decreases, proving that the PVDF membrane is successfully cross-linked.

[0060] See also Figure 4 , wherein the columnar portion is a current density-concentration variation diagram of the gas diffusion electrode for generating hydrogen peroxide provided in Example 2, and the broken line portion is a current density-current efficiency variation diagram of the gas diffusion electrode for generating hydrogen peroxide provided in Example 2. It can be seen from the figure that at a current density of 25 mA / cm 2 In the case of , the amount of hydrogen peroxide generated is 420.4mg / L; at a current density of 15mA / cm 2 Under the condition of , the efficiency of the two-electron oxidation reaction to generate hydrogen peroxide is 46.6%. This shows that the gas diffusion electrode can be used in the field of electrochemical synthesis of hydrogen peroxide.

[0061] The beneficial effects of the present invention are as follows:

[0062] (1) The present invention prepares the gas diffusion electrode at room temperature and under light pressure, using cheap and readily available carbon materials as raw materials. The preparation process is simple, easy to operate and control, and is conducive to large-scale production.

[0063] (2) The present invention prepares the gas diffusion electrode by the roller method, the catalyst layer is evenly distributed, and a stable solid-liquid-gas three-phase interface is formed, which solves the problem of electrode leakage caused by uneven catalyst coating.

[0064] (3) The present invention pre-treats the hydrophobic porous gas diffusion layer through a cross-linking reaction, thereby enhancing the mechanical strength of the gas diffusion layer and making it resistant to organic solvents, so that the gas diffusion electrode can remain stable during the phase conversion process.

[0065] (4) The room temperature and light pressure phase transformation gas diffusion electrode synthesized by the present invention can generate hydrogen peroxide in situ without the need for additional reagents. It can generate a higher concentration of hydrogen peroxide at a lower current density only through active mass transfer of oxygen in the air. The raw materials and products are green and environmentally friendly, which reduces the cost of the reaction.

[0066] In summary, the embodiments of the present invention optimize the electrode composition, such as the materials of the gas diffusion layer and the catalyst layer, and improve the preparation process to develop a gas diffusion electrode that is resistant to organic solvents, low in cost, simple in process and excellent in performance, so that it can achieve the ability to produce hydrogen peroxide efficiently and stably. The present invention synthesizes a room temperature and light pressure phase conversion gas diffusion electrode and uses it to produce hydrogen peroxide in situ, thereby obtaining an efficient and stable electrode material, providing research ideas and theoretical support for the development of promising electrochemical synthesis.

[0067] The applicant of the present invention has made a detailed explanation and description of the implementation examples of the present invention in conjunction with the drawings in the specification. However, those skilled in the art should understand that the above implementation examples are only preferred implementation schemes of the present invention, and the detailed description is only to help readers better understand the spirit of the present invention, but not to limit the scope of protection of the present invention. On the contrary, any improvements or modifications based on the inventive spirit of the present invention should fall within the scope of protection of the present invention.

Claims

1. A method for preparing a phase-change gas diffusion electrode at room temperature and light pressure, characterized in that: The following steps are involved: The hydrophobic porous polymer membrane undergoes a cross-linking reaction in the presence of a cross-linking agent to obtain a hydrophobic breathable membrane resistant to organic solvents; the reaction temperature of the cross-linking reaction is 40-100° C., and the reaction time is 5-180 seconds; The cross-linking agent is one or more of ethylenediamine, bisphenol, peroxide and thiol; The binder is mixed with the carbon material to obtain a paste mixture; the carbon material includes activated carbon and carbon black, and the mass ratio of the activated carbon to the carbon black is 1-50:1; the binder is one or more of PVDF solution, PSF solution and PES solution, the concentration of the binder in the binder solution is 5-30% (w / v), and the mass ratio of the activated carbon to the binder is 1-10:1; After applying the paste mixture on a support, covering it with the organic solvent-resistant hydrophobic breathable membrane, and gently pressing and rolling it evenly with a roller to obtain a preliminary gas diffusion electrode; The preliminary gas diffusion electrode is immersed in deionized water to induce phase conversion, the phase conversion time is 10 to 60 minutes, and then dried to obtain a phase conversion gas diffusion electrode under light pressure at room temperature.

2. The method for preparing a phase-change gas diffusion electrode at room temperature and light pressure according to claim 1, characterized in that: The hydrophobic porous polymer membrane is a PVDF membrane or a PTFE membrane.

3. The method for preparing a phase-conversion gas diffusion electrode at room temperature and light pressure according to claim 1, characterized in that: The support body is one or more of a stainless steel mesh, a titanium mesh, a carbon cloth, a carbon felt and a carbon paper.

4. A phase-change gas diffusion electrode under room temperature and light pressure prepared by the preparation method described in any one of claims 1 to 3.

5. Use of a phase-conversion gas diffusion electrode under room temperature and light pressure prepared by the preparation method according to any one of claims 1 to 3 as a cathode in the preparation of hydrogen peroxide.

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