A gas diffusion electrode for simultaneously enhancing O2 transmission and H2O2 selectivity, preparation method and application thereof

Abstract

The present invention relates to a gas diffusion electrode for synchronously enhancing O2 transmission and H2O2 selectivity, a preparation method and an application thereof. The preparation method is as follows: a conductive material, a polytetrafluoroethylene emulsion and polymethylhydrosiloxane are mixed in an organic solvent to obtain a mixed solution; the mixed solution is made into a viscous paste and coated on the surface of carbon cloth, and then hot pressing treatment is carried out to obtain an electrode intermediate; the electrode intermediate is subjected to calcination treatment to obtain a gas diffusion electrode for synchronously enhancing O2 transmission and H2O2 selectivity. The present invention also provides a gas diffusion electrode for synchronously enhancing O2 transmission and H2O2 selectivity prepared by the above preparation method. The present invention also provides an application of the gas diffusion electrode for synchronously enhancing O2 transmission and H2O2 selectivity in wastewater. The present invention solves the problem that in the existing electro-Fenton technology, the gas diffusion electrode has insufficient H2O2 production capacity due to high oxygen diffusion impedance and low H2O2 selectivity.

Description

Technical Field

[0001] The present invention relates to the technical field of wastewater treatment, and particularly relates to a gas diffusion electrode for synchronously enhancing O 2 transport and H 2 O 2 selectivity, a preparation method and an application thereof. Background Art

[0002] In recent years, persistent organic pollutants have become one of the major problems affecting the global ecosystem and human health. The complexity, severity and long-term nature of the water pollution caused by them far exceed those of ordinary pollutants, and their in-depth treatment has always been the key and difficult point of water treatment work. The existing technologies are difficult to achieve ideal effects in the treatment of persistent organic pollutants. For example, the biochemical process has low efficiency and long cycle, the physical and chemical methods are difficult to effectively mineralize pollutants, and some advanced oxidation technologies are prone to generate more toxic intermediate products during treatment. The electrochemical advanced oxidation technology represented by electro-Fenton can generate strongly oxidizing active hydroxyl radicals, which can degrade and mineralize most organic pollutants without selectivity, and has the characteristics of mild reaction conditions, high efficiency, environmental friendliness and strong controllability, and has important applications in the in-depth treatment of refractory organic pollutants.

[0003] Among them, the in-situ production of H 2 O 2 through a gas diffusion electrode and the addition of ferrous salt externally to obtain Fenton reagent is a widely recognized method for constructing an electro-Fenton system at home and abroad. O 2 Diffuses through the porous channels of the electrode into the carbon material medium and contacts the solution surface, and the two-electron oxygen reduction reaction occurs to continuously generate H 2 O 2 in-situ, effectively solving the problems of high cost and high risk during the transportation and storage of H 2 O 2 However, during the electro-Fenton process, competitive side reactions such as hydrogen evolution reaction and four-electron oxygen reduction reaction inevitably occur on the cathode surface, inhibiting the generation of H 2 O 2 At the same time, the OH - generated by the hydrogen evolution reaction on the cathode makes the solution form a local high-pH reaction zone, accelerating the self-decomposition of H 2 O 2 in the solution. These reactions all lead to a decrease in the production capacity of H 2 O 2 and it is difficult to meet the efficient operation of the system. Therefore, the preparation of an electro-Fenton cathode with high activity, high H 2 O 2 selectivity and strong stability is the focus of current research in this field. Precious metals such as platinum, gold, and lead and their alloys have a small overpotential for releasing O 2 through disproportionation and high H 2O 2 Selectivity to become H generated by electrochemical reaction 2 O 2 The preferred material of the catalyst, but the scarcity of precious metals limits its large-scale application as a cathode material in the electrochemical field.

[0004] In recent years, due to advantages such as rich reserves, low price, environmental friendliness, and easy modification, carbon materials have become the preferred materials for electro-Fenton cathodes. However, due to the inherent inert characteristics of carbon materials, their activity and selectivity are much lower than those of precious metals and transition metal catalysts under acidic / neutral conditions. In addition, gas diffusion electrodes prepared from carbon materials such as carbon black and carbon nanotubes have poor hydrophobic properties and are prone to the "water tipping" phenomenon, resulting in a decline in oxygen transport performance and being unfavorable for the generation of H 2 O 2 Therefore, the research and development of gas diffusion electrodes that simultaneously enhance O 2 transport and H 2 O 2 selectivity to improve H 2 O 2 production capacity is of great significance for the large-scale application of electro-Fenton wastewater treatment technology.

[0005] CN 110386645 A discloses a gas diffusion electrode with high oxygen transport for electrocatalytic oxygen reduction to produce H 2 O 2 and its preparation method. The gas diffusion electrode uses titanium cloth as the substrate, ultrasonically mixes carbon black and polytetrafluoroethylene, dries to a paste state, and then hot-presses with the titanium mesh substrate to form a precursor, and is modified with a mixed solution of dimethyl silicone oil and n-hexane to obtain a gas diffusion electrode with high oxygen transport. This method only reduces the oxygen diffusion impedance from a physical perspective and does not improve the selectivity of H 2 O 2 from the mechanism. The prior art also discloses a method for a carbon material with high H 2 O 2 selectivity. This method uses hexamine as a nitrogen source to adjust the electronic structure of the catalyst, change the interaction of oxygen-containing intermediates, and thus improve the selectivity of H 2 O 2 However, this material is only applicable to pure electrocatalysis and does not prepare the corresponding gas diffusion electrode, and its H 2 O 2 output is not sufficient for the electro-Fenton reaction to degrade persistent organic pollutants.

[0006] Although the above patents have prepared catalysts or gas diffusion electrodes for electrocatalytic oxygen reduction to produce H 2 O 2 there are still relatively high oxygen diffusion impedance and low H 2 O 2Problems such as selectivity, high preparation cost, and difficulty in industrialization. In addition, so far, there has been no report on synchronously enhancing the O 2 transport performance and H 2 O 2 selectivity by the same modification method. Therefore, it is an urgent need for industrial applications to study gas diffusion electrodes with simple preparation processes, low costs, excellent performance, and applied to synchronously enhance O 2 transport and H 2 O 2 selectivity. Summary of the Invention

[0007] The object of the present invention is to provide a gas diffusion electrode, a preparation method, and an application for synchronously enhancing O 2 transport and H 2 O 2 selectivity, so as to solve the problem of insufficient H 2 O 2 production capacity caused by the high oxygen diffusion impedance and low H 2 O 2 selectivity of the gas diffusion electrode in the existing electro-Fenton technology.

[0008] In order to achieve the above object, the technical solution adopted by the present invention is as follows:

[0009] A preparation method of a gas diffusion electrode for synchronously enhancing O 2 transport and H 2 O 2 selectivity, comprising the following steps:

[0010] S1. Mix a conductive material, a polytetrafluoroethylene emulsion, and polymethylhydrogensiloxane in an organic solvent to obtain a mixed solution;

[0011] S2. Make the mixed solution into a viscous paste, coat it on the surface of carbon cloth, and then perform hot pressing treatment to obtain an electrode intermediate;

[0012] S3. Bake the electrode intermediate to obtain a gas diffusion electrode for synchronously enhancing O 2 transport and H 2 O 2 selectivity.

[0013] According to the above technical means, first, by selecting a conductive material with high conductivity, high specific surface area, and high porosity as the substrate, introducing polymethylhydrogensiloxane (PMHS) as a modifier, and by regulating the addition amounts of polytetrafluoroethylene (PTFE) emulsion and polymethylhydrogensiloxane (PMHS), the interfacial properties and electronic characteristics of the electrode are optimized, not only improving the hydrophobicity of the electrode interface, but also enhancing the catalytic activity of two-electron oxygen reduction and strengthening H 2 O2 Selectivity realizes synchronous enhancement of O 2 transport and H 2 O 2 selectivity.

[0014] Preferably, in S1, the conductive material is conductive carbon black, acetylene black or carbon nanotubes.

[0015] Preferably, in S1, the mass percentage of polytetrafluoroethylene in the polytetrafluoroethylene emulsion is 30% - 60%.

[0016] Preferably, in S1, the mass ratio of conductive carbon black to the added polytetrafluoroethylene emulsion is 1:1 - 5:1. That is, the volume addition amount of the polytetrafluoroethylene emulsion is 0.457 - 1.141 mL.

[0017] Preferably, in S1, the mass ratio of the polytetrafluoroethylene emulsion to the added polymethylhydrogensiloxane is 1:0.038 - 1:0.25. That is, the volume addition amount of the polymethylhydrogensiloxane is 0.038 - 0.25 mL.

[0018] By regulating the addition amounts of the polytetrafluoroethylene emulsion and the polymethylhydrogensiloxane, the interfacial properties and electronic characteristics of the electrode are optimized.

[0019] Preferably, in S1, the organic solvent is absolute ethanol.

[0020] Preferably, in S2, it specifically includes: drying the mixed solution to obtain a viscous paste, coating the viscous paste on the front and back of the carbon cloth, and then performing hot pressing treatment under the conditions of a temperature of 30°C - 60°C and a pressure of 0.5 MPa - 1.5 MPa to obtain an electrode intermediate.

[0021] Preferably, in S3, the temperature of the calcination treatment is between 300°C and 400°C, and the calcination time is 1 - 3 h.

[0022] By performing calcination treatment on the electrode intermediate, the electrolysis interface is further stabilized, effectively ensuring the stability of the modified electrode.

[0023] The present invention also provides a gas diffusion electrode for synchronously enhancing O 2 transport and H 2 O 2 selectivity, and the gas diffusion electrode is prepared by the preparation method described in the present invention.

[0024] The present invention also provides a gas diffusion electrode for synchronously enhancing O 2 transport and H 2 O 2Application of a selective gas diffusion electrode, which serves as O in the electro-Fenton treatment of refractory organic compounds 2 transport and H 2 O 2 A selective gas diffusion electrode, where the refractory organic compounds include bisphenol A, naproxen, ciprofloxacin, amoxicillin, diclofenac sodium, rhodamine B, methyl orange, and 2,4-dichlorophenol.

[0025] Advantages of the present invention:

[0026] 1) The synchronous enhancement of O 2 transport and H 2 O 2 Preparation method of a selective gas diffusion electrode. First, a conductive material with high conductivity, high specific surface area, and high porosity is selected as the substrate, and polymethylhydrosiloxane is introduced as a modifier. By regulating the addition amounts of polytetrafluoroethylene emulsion and polymethylhydrosiloxane, the interfacial properties and electronic characteristics of the electrode are optimized, not only improving the hydrophobicity of the electrode interface but also enhancing the catalytic activity of two-electron oxygen reduction, strengthening the H 2 O 2 selectivity, thereby achieving the synchronous enhancement of O 2 transport and H 2 O 2 selectivity. Moreover, this preparation method has the advantages of simple process, low cost, easy operation and control of conditions, which is conducive to large-scale preparation and industrial application;

[0027] 2) The synchronous enhancement of O 2 transport and H 2 O 2 A selective gas diffusion electrode for the production of H 2 O 2 by oxygen reduction. After reacting for 6 h, the cumulative concentration of H 2 O 2 is as high as 1874.8 mg / L, while the cumulative concentration of H 2 O 2 of the conventional gas diffusion electrode is 1087.4 mg / L. The H 2 O 2 production capacity of the modified electrode is increased by 1.7 times. The synchronous enhancement of O 2 transport and H 2 O 2 The selectivity of the selective gas diffusion electrode remains above 80.0% in the voltage range of -0.4 to -1.0 V, and the number of electron transfers is about 2.3. While the H 2 O 2 selectivity of the conventional gas diffusion electrode remains above 80.0% in the voltage range of -0.4 to -1.0 V, and the number of electron transfers is about 2.3. While the H 2 O 2The selectivity is maintained between 64.5% and 74.0%, and the number of electron transfers is about 2.7; moreover, the synchronous enhancement of O 2 transport and H 2 O 2 After the selective gas diffusion electrode is recycled ten times, the cumulative concentration of H 2 O 2 only decreases by 22.6%. Compared with the existing conventional gas diffusion electrodes, the synchronous enhancement of O 2 transport and H 2 O 2 The selective gas diffusion electrode has higher two-electron oxygen reduction catalytic activity, higher H 2 O 2 selectivity, better stability, no secondary pollution and other advantages;

[0028] 3) The synchronous enhancement of O 2 transport and H 2 O 2 The selective gas diffusion electrode is used for electro-Fenton treatment of micro-pollutants. Under the same conditions, the removal efficiency of micro-pollutants is significantly better than that of the conventional gas diffusion electrode, and it shows a high H 2 O 2 cumulative concentration, and has the value of popularization and application in the field of wastewater treatment technology. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 is the SEM image of the gas diffusion electrode prepared in Example 2;

[0030] Figure 2 is the contact angle image of the gas diffusion electrode prepared in Example 2;

[0031] Figure 3 is the contact angle image of the conventional gas diffusion electrode prepared in Comparative Example 2;

[0032] Figure 4 is the electrochemical impedance spectroscopy image of the gas diffusion electrodes prepared in Example 2 and Comparative Example 2;

[0033] Figure 5 is the H 2 O 2 selectivity and number of electron transfers image of the gas diffusion electrodes prepared in Example 2 and Comparative Example 2;

[0034] Figure 6 is the relationship image between the cumulative concentration of H 2 O 2 and reaction time in the oxygen reduction reaction of the gas diffusion electrodes prepared in Example 2, Comparative Example 2 and Comparative Example 5;

[0035] Figure 7 For the graph showing the relationship between the cumulative concentration of H 2 O 2 and the reaction time in the oxygen reduction reaction for the conventional gas diffusion electrodes prepared in Comparative Examples 1 to 4;

[0036] Figure 8 For the graph showing the relationship between the cumulative concentration of H 2 O 2 and the reaction time in the oxygen reduction reaction for the gas diffusion electrodes prepared in Examples 1 to 4;

[0037] Figure 9 For the graph showing the relationship between the cumulative concentration of H 2 O 2 and the reaction time in the oxygen reduction reaction for the gas diffusion electrode prepared in Recycling Example 2;

[0038] Figure 10 For the degradation effect diagram of micropollutants in the electro-Fenton reaction for the gas diffusion electrodes prepared in Example 2 and Comparative Example 2. Detailed implementation manners

[0039] The following will illustrate the implementation manners of the present invention with reference to the drawings and preferred embodiments. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through different specific implementation manners. Various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention. It should be understood that the preferred embodiments are only for illustrating the present invention, rather than for limiting the protection scope of the present invention.

[0040] It should be noted that the drawings provided in the following embodiments only illustrate the basic concept of the present invention in a schematic manner. Therefore, only the components related to the present invention are shown in the drawings, rather than being drawn according to the number, shape, and size of the components in actual implementation. The type, quantity, and ratio of each component in actual implementation can be arbitrarily changed, and the component layout type may also be more complex.

[0041] Example 1

[0042] A preparation method of a gas diffusion electrode for synchronously enhancing O 2 transport and H 2 O 2 selectivity, comprising the following steps:

[0043] S1. Add 0.2 g of conductive carbon black, 0.685 mL of polytetrafluoroethylene emulsion, and 0.038 mL of polymethylhydrosiloxane into 10 mL of absolute ethanol, and ultrasonically mix to obtain a uniform mixed solution;

[0044] S2. Dry the mixed solution to a viscous paste, evenly coat it on the front and back of the carbon cloth, and then perform hot pressing under the conditions of a temperature of 50 °C and a pressure of 0.5 MPa to ensure uniform hot pressing, obtaining an electrode intermediate;

[0045] S3. Place the electrode intermediate in a muffle furnace and calcine it at a temperature of 350 °C for 2 h to obtain a gas diffusion electrode with synchronous enhanced O 2 transport and H 2 O 2 selectivity.

[0046] Example 2

[0047] A method for preparing a gas diffusion electrode with synchronous enhanced O 2 transport and H 2 O 2 selectivity, comprising the following steps:

[0048] S1. Add 0.2 g of conductive carbon black, 0.685 mL of polytetrafluoroethylene emulsion, and 0.075 mL of polymethylhydrosiloxane to 10 mL of absolute ethanol and ultrasonically mix to obtain a uniform mixed solution;

[0049] S2. Dry the mixed solution to a viscous paste, evenly coat it on the front and back of the carbon cloth, and then perform hot pressing under the conditions of a temperature of 50 °C and a pressure of 0.5 MPa. Repeat the above steps 5 times to ensure uniform hot pressing, obtaining an electrode intermediate;

[0050] S3. Place the electrode intermediate in a muffle furnace and calcine it at a temperature of 350 °C for 2 h to obtain a gas diffusion electrode with synchronous enhanced O 2 transport and H 2 O 2 selectivity.

[0051] Example 3

[0052] A method for preparing a gas diffusion electrode with synchronous enhanced O 2 transport and H 2 O 2 selectivity, comprising the following steps:

[0053] S1. Add 0.2 g of conductive carbon black, 0.685 mL of polytetrafluoroethylene emulsion, and 0.125 mL of polymethylhydrosiloxane to 10 mL of absolute ethanol and ultrasonically mix to obtain a uniform mixed solution;

[0054] S2. Dry the mixed solution to a viscous paste, evenly coat it on the front and back of the carbon cloth, and then perform hot pressing under the conditions of a temperature of 50 °C and a pressure of 0.5 MPa. Repeat the above steps 5 times to ensure uniform hot pressing, obtaining an electrode intermediate;

[0055] S3. Place the electrode intermediate in a muffle furnace and calcine it at a temperature of 350 °C for 2 h to obtain a gas diffusion electrode with synchronous enhanced O 2 transport and H 2 O 2 selective gas diffusion electrode.

[0056] Example 4

[0057] A method for preparing a gas diffusion electrode with synchronous enhanced O 2 transport and H 2 O 2 selective gas diffusion electrode, comprising the following steps:

[0058] S1. Add 0.2 g of conductive carbon black, 0.685 mL of polytetrafluoroethylene emulsion and 0.250 mL of polymethylhydrosiloxane to 10 mL of absolute ethanol and ultrasonically mix to obtain a homogeneous mixed solution;

[0059] S2. Dry the mixed solution to a viscous paste, evenly coat the front and back of the carbon cloth, and then perform hot pressing under the conditions of a temperature of 50 °C and a pressure of 0.5 MPa to ensure uniform hot pressing to obtain an electrode intermediate;

[0060] S3. Place the electrode intermediate in a muffle furnace and calcine it at a temperature of 350 °C for 2 h to obtain a gas diffusion electrode with synchronous enhanced O 2 transport and H 2 O 2 selective gas diffusion electrode.

[0061] Control Example 1

[0062] A method for preparing a conventional gas diffusion electrode, comprising the following steps:

[0063] S1. Add 0.2 g of conductive carbon black and 0.457 mL of polytetrafluoroethylene emulsion to 10 mL of absolute ethanol and ultrasonically mix to obtain a homogeneous mixed solution;

[0064] S2. Dry the mixed solution to a viscous paste, evenly coat the front and back of the carbon cloth, and then perform hot pressing under the conditions of a temperature of 50 °C and a pressure of 0.5 MPa to ensure uniform hot pressing to obtain an electrode intermediate;

[0065] S3. Place the electrode intermediate in a muffle furnace and calcine it at a temperature of 350 °C for 2 h to obtain a conventional gas diffusion electrode.

[0066] Control Example 2

[0067] A method for preparing a conventional gas diffusion electrode, comprising the following steps:

[0068] S1. Add 0.2 g of conductive carbon black and 0.685 mL of polytetrafluoroethylene emulsion into 10 mL of absolute ethanol, and ultrasonically mix them to obtain a uniform mixed solution;

[0069] S2. Dry the mixed solution to a viscous paste, and evenly coat it on the front and back of the carbon cloth. Then, perform hot pressing under the conditions of a temperature of 50 °C and a pressure of 0.5 MPa to ensure uniform hot pressing, and obtain an electrode intermediate;

[0070] S3. Place the electrode intermediate in a muffle furnace and calcine it at a temperature of 350 °C for 2 h to obtain a conventional gas diffusion electrode.

[0071] Control Example 3

[0072] A preparation method of a conventional gas diffusion electrode, comprising the following steps:

[0073] S1. Add 0.2 g of conductive carbon black and 0.913 mL of polytetrafluoroethylene emulsion into 10 mL of absolute ethanol, and ultrasonically mix them to obtain a uniform mixed solution;

[0074] S2. Dry the mixed solution to a viscous paste, and evenly coat it on the front and back of the carbon cloth. Then, perform hot pressing under the conditions of a temperature of 50 °C and a pressure of 0.5 MPa to ensure uniform hot pressing, and obtain an electrode intermediate;

[0075] S3. Place the electrode intermediate in a muffle furnace and calcine it at a temperature of 350 °C for 2 h to obtain a conventional gas diffusion electrode.

[0076] Control Example 4

[0077] A preparation method of a conventional gas diffusion electrode, comprising the following steps:

[0078] S1. Add 0.2 g of conductive carbon black and 1.141 mL of polytetrafluoroethylene emulsion into 10 mL of absolute ethanol, and ultrasonically mix them to obtain a uniform mixed solution;

[0079] S2. Dry the mixed solution to a viscous paste, and evenly coat it on the front and back of the carbon cloth. Then, perform hot pressing under the conditions of a temperature of 50 °C and a pressure of 0.5 MPa to ensure uniform hot pressing, and obtain an electrode intermediate;

[0080] S3. Place the electrode intermediate in a muffle furnace and calcine it at a temperature of 350 °C for 2 h to obtain a conventional gas diffusion electrode.

[0081] Control Example 5

[0082] A preparation method of a conventional gas diffusion electrode, comprising the following steps:

[0083] S1. Add 0.2 g of conductive carbon black and 0.728 mL of polytetrafluoroethylene emulsion (i.e., convert 0.075 mL of polymethylhydrogensiloxane into an equal amount of polytetrafluoroethylene emulsion) to 10 mL of absolute ethanol and mix ultrasonically to obtain a uniform mixed solution;

[0084] S2. Dry the mixed solution to a viscous paste, evenly coat it on the front and back of the carbon cloth, and then perform hot pressing under the conditions of a temperature of 50 °C and a pressure of 0.5 MPa to ensure uniform hot pressing and obtain an electrode intermediate;

[0085] S3. Place the electrode intermediate in a muffle furnace and calcine it at a temperature of 350 °C for 2 h to obtain a conventional gas diffusion electrode.

[0086] Detection and analysis

[0087] 1) SEM analysis

[0088] Perform SEM analysis on the simultaneously enhanced O 2 transport and H 2 O 2 selective gas diffusion electrode prepared in Example 2, and the results are as Figure 1 shown.

[0089] From Figure 1 analysis, it can be seen that the simultaneously enhanced O 2 transport and H 2 O 2 selective gas diffusion electrode prepared in Example 2 mainly includes a catalytic layer and a carbon cloth substrate. Among them, the catalytic layer modified with polymethylhydrogensiloxane is about 547.1 µm.

[0090] 2) Contact angle characterization

[0091] Perform contact angle analysis on the simultaneously enhanced O 2 transport and H 2 O 2 selective gas diffusion electrode prepared in Example 2 and the conventional gas diffusion electrode prepared in Comparative Example 2, and the results are successively as Figure 2 and Figure 3 shown.

[0092] From Figure 2 analysis, it can be seen that the contact angle of the simultaneously enhanced O 2 transport and H 2 O 2 selective gas diffusion electrode prepared in Example 2 is 148.31º; while from Figure 3Analysis shows that the contact angle of the conventional gas diffusion electrode prepared in Comparative Example 2 is 104.47°. It is proved that the introduction of polymethylhydrosiloxane endows the gas diffusion electrode with superhydrophobicity, thus strengthening the 2 transport at the electrode interface.

[0093] 3) EIS Characterization

[0094] The simultaneously strengthened O 2 transport and H 2 O 2 selective gas diffusion electrode prepared in Example 2 and the conventional gas diffusion electrode prepared in Comparative Example 2 were subjected to contact angle analysis. The results are as Figure 4 shown.

[0095] From Figure 4 the analysis, it can be seen that the semi-circular radius of the simultaneously strengthened O 2 transport and H 2 O 2 selective gas diffusion electrode prepared in Example 2 is smaller, while that of the conventional gas diffusion electrode prepared in Comparative Example 2 is larger. And the semi-circular radius is related to the electron transfer resistance, thus proving that the simultaneously strengthened O 2 transport and H 2 O 2 selective gas diffusion electrode has a higher electron transfer rate and electrode activity, that is, the introduction of polymethylhydrosiloxane strengthens the electron transfer rate of the gas diffusion electrode.

[0096] 4) H 2 O 2 Selectivity and Electron Transfer Number Analysis

[0097] The simultaneously strengthened O 2 transport and H 2 O 2 selective gas diffusion electrode prepared in Example 2 and the conventional gas diffusion electrode prepared in Comparative Example 2 were subjected to H 2 O 2 selectivity and electron transfer number analysis. The results are as Figure 5 shown.

[0098] From Figure 5 the analysis, it can be seen that the H 2 O 2 selectivity of the conventional gas diffusion electrode prepared in Comparative Example 2 remains between 64.5% and 74.0% in the voltage range of -0.4 to -1.0 V, and the electron transfer number is about 2.7, while the simultaneously strengthened O 2 transport and H 2 O 2The selective gas diffusion electrode has a selectivity of over 80.0% in the voltage range of -0.4 to -1.0 V for H 2 O 2 The electron transfer number is about 2.3, which is closer to the theoretical electron number of 2 for the two-electron oxygen reduction. It can be seen that the introduction of polymethylhydrosiloxane (PMHS) improves the selectivity of H 2 O 2 , promotes the oxygen reduction reaction to be more inclined to two electrons, and is beneficial to the generation of H 2 O 2 .

[0099] 5) Evaluation of the oxygen reduction performance of the gas diffusion electrode

[0100] The specific operation steps are as follows: Add 160 mL of deionized aqueous solution (50 mM Na 2 SO 4 ) to a self-made single-chamber glass reactor. The anode is a commercial IrO 2 electrode plate (DSA, 3 cm 2 ), and the cathode is a self-made gas diffusion electrode. The two electrodes are installed 1 cm apart; Air is introduced at a flow rate of 1 L / min for the generation of H 2 O 2 ; Then turn on the power supply, the current is 80 mA, and 0.5 mL of the sample is taken from the reaction solution at regular intervals. The concentration of H 2 O 2 in the sample solution is measured using a UV spectrophotometer.

[0101] 5.1. Using the gas diffusion electrodes prepared in Example 2, Comparative Example 2, and Comparative Example 5 as the cathode respectively, the relationship between the cumulative concentration of H 2 O 2 and the reaction time in the oxygen reduction reaction is as Figure 6 shown.

[0102] It can be analyzed from Figure 6 that using the conventional gas diffusion electrode prepared in Comparative Example 2 as the cathode, the cumulative concentration of H 2 O 2 is 1087.4 mg / L after 6 h of reaction. Using the gas diffusion electrode with synchronous enhanced O 2 transport and H 2 O 2 selectivity prepared in Example 2 as the cathode, the cumulative concentration of H 2 O 2 is 1874.8 mg / L after 6 h of reaction, and H 2 O 2The production capacity has increased by about 1.7 times. To compare the influence of the introduction of polymethylhydrogensiloxane, it was converted into an equivalent amount of polytetrafluoroethylene emulsion, that is, using the conventional gas diffusion electrode prepared in Comparative Example 5 as the cathode. It was found that after 6 h of reaction, the cumulative concentration of H 2 O 2 was only 1039.2 mg / L. It can be seen that the introduction of polymethylhydrogensiloxane simultaneously enhanced the O 2 transport and H 2 O 2 selectivity, and thus significantly improved the H 2 O 2 production capacity.

[0103] 5.2 Using the conventional gas diffusion electrodes prepared in Comparative Examples 1 to 4 as cathodes respectively, the relationship between the cumulative concentration of H 2 O 2 and the reaction time in the oxygen reduction reaction was obtained as shown in Figure 7 shown.

[0104] It can be analyzed from Figure 7 that under the conditions of different polytetrafluoroethylene emulsion addition amounts, the H 2 O 2 yield will change significantly. As the polytetrafluoroethylene emulsion addition amount decreased from 1.141 mL to 0.457 mL, the H 2 O 2 yield increased from 212.6 mg / L to 1483.7 mg / L. Although the decrease in the polytetrafluoroethylene liquid amount increased the H 2 O 2 production capacity, it would lead to a decrease in the O 2 transport performance of the gas diffusion electrode, resulting in a significant decrease in the electrode stability and the reuse effect. Considering various factors comprehensively, when the polytetrafluoroethylene emulsion addition amount was 0.685 mL, the performance of the conventional gas diffusion electrode reached the best.

[0105] 5.3 Using the gas diffusion electrodes prepared in Examples 1 to 4 that simultaneously enhanced O 2 transport and H 2 O 2 selectivity as cathodes respectively, the relationship between the cumulative concentration of H 2 O 2 and the reaction time in the oxygen reduction reaction was obtained as shown in Figure 8 shown.

[0106] It can be analyzed from Figure 8 that for the gas diffusion electrodes prepared by adding 0.038 mL, 0.075 mL, 0.125 mL, and 0.250 mL of polymethylhydrogensiloxane and simultaneously enhancing O 2 transport and H 2 O2 Selective gas diffusion electrode, after 6 h of reaction, the cumulative concentration of H 2 O 2 is 1345.0 mg / L, 1874.8 mg / L, 1561.3 mg / L and 1293.0 mg / L respectively, all higher than that of the conventional gas diffusion electrode for H 2 O 2 production. It can be seen that under the conditions of different addition amounts of polymethylhydrogensiloxane, the H 2 O 2 production will change significantly. Only when an appropriate amount of polymethylhydrogensiloxane is added can the H 2 O 2 production capacity be maximized, and the simultaneous enhancement of O 2 transport and H 2 O 2 selectivity can be achieved.

[0107] 6) Stability evaluation of gas diffusion electrode

[0108] The gas diffusion electrode prepared in Example 2 with simultaneous enhancement of O 2 transport and H 2 O 2 selectivity was used for cyclic reaction by the oxygen reduction method, and the H 2 O 2 production capacity results are as Figure 9 shown. It can be analyzed from Figure 9 that after 10 cycles of utilization, the cumulative concentration of H 2 O 2 has been maintained in the range of 1419.2 - 1874.8 mg / L, only decreasing by 22.6%. Compared with the existing conventional gas diffusion electrode, the gas diffusion electrode prepared by the present invention with simultaneous enhancement of O 2 transport and H 2 O 2 selectivity has the advantages of higher two-electron oxygen reduction catalytic activity and better stability.

[0109] 7) Electro-Fenton performance evaluation of gas diffusion electrode

[0110] The specific operation steps are as follows: 160 mL of deionized aqueous solution (50 mM Na 2 SO 4 ) was added to a self-made single-chamber glass reactor. The anode was a commercial IrO 2 electrode plate (DSA, 3 cm 2 ), and the cathode was the self-made gas diffusion electrode. The two electrodes were installed 1 cm apart; air was introduced at a flow rate of 1 L / min for H 2 O 2Generation; 20 mg / L of pollutants (bisphenol A: BPA; naproxen: NPX; ciprofloxacin: CIP; amoxicillin: AMX; diclofenac sodium: DCF; rhodamine B: RhB; methyl orange: MO; 2,4-dichlorophenol: 2,4 - DCP) and 0.2 mol / L of FeSO 4 were added respectively, the pH was adjusted to 3, then the power supply was turned on, the current was 80 mA, 1 mL of sample was taken from the reaction solution at regular intervals, and the concentration of H 2 O 2 in the sample solution was measured using an ultraviolet spectrophotometer; after filtering with a microporous membrane with a pore size of 0.22 μm, the concentration of the remaining trimethoprim in the filtered sample solution was measured using high performance liquid chromatography.

[0111] The simultaneously enhanced O 2 transport and H 2 O 2 selective gas diffusion electrode prepared in Example 2 and the conventional gas diffusion electrode prepared in Comparative Example 2 were used as the cathode respectively, and electro-Fenton method was used for wastewater treatment, and the degradation results are as Figure 10 shown.

[0112] It can be analyzed from Figure 10 that using the simultaneously enhanced O 2 transport and H 2 O 2 selective gas diffusion electrode prepared in Example 2 as the cathode for electro-Fenton reaction, except for 2,4-DCP and DCF, the removal rates of the other 6 kinds of micropollutants can reach about 90% within 20 min. The simultaneously enhanced O 2 transport and H 2 O 2 selective gas diffusion electrode prepared in Example 2 is significantly better than the conventional gas diffusion electrode prepared in Comparative Example 2 in all cases and shows a higher H 2 O 2 cumulative concentration.

[0113] In summary, for the preparation method of the simultaneously enhanced O 2 transport and H 2 O 2 selective gas diffusion electrode of the present invention, first, conductive carbon black with high conductivity, high specific surface area and high porosity is selected as the substrate, polymethylhydrosiloxane (PMHS) is introduced as a modifier, and by regulating the addition amounts of polytetrafluoroethylene emulsion and polymethylhydrosiloxane, the interfacial properties and electronic characteristics of the electrode are optimized, which not only improves the hydrophobicity of the electrode interface, but also improves the catalytic activity of two-electron oxygen reduction, and enhances H 2 O 2Selectivity, realizing synchronous enhancement of O 2 transmission and H 2 O 2 Selectivity. This preparation method has the advantages of simple process, low cost, easy operation and control of conditions, which is conducive to large-scale preparation and industrial application.

[0114] Proved by experiments, the synchronous enhancement of O 2 transmission and H 2 O 2 selective gas diffusion electrode prepared by the invention, after reacting for 6 h, the cumulative concentration of H 2 O 2 reaches as high as 1874.8 mg / L, while that of the conventional gas diffusion electrode is only 1087.4 mg / L. The H 2 O 2 production capacity of the modified electrode is increased by 1.7 times. At the same time, the H 2 O 2 selectivity of the conventional gas diffusion electrode remains between 64.5% and 74.0% in the voltage range of -0.4~-1.0 V, and the number of electron transfers is about 2.7, while the synchronous enhancement of O 2 transmission and H 2 O 2 selective gas diffusion electrode prepared by modifying with polymethylhydrosiloxane has an H 2 O 2 selectivity of more than 80.0% in the voltage range of -0.4~-1.0 V, and the number of electron transfers is about 2.3. And after recycling ten times, the cumulative concentration of H 2 O 2 only decreases by 22.6%. In the electro-Fenton reaction of multiple pollutants, for the removal efficiency of micro-pollutants, the synchronous enhancement of O 2 transmission and H 2 O 2 selective gas diffusion electrode is significantly superior to the conventional gas diffusion electrode in all cases, and shows a higher cumulative concentration of H 2 O 2 Compared with the existing conventional gas diffusion electrode, the synchronous enhancement of O 2 transmission and H 2 O 2 selective gas diffusion electrode prepared by the invention has higher two-electron oxygen reduction catalytic activity, higher H 2 O 2 selectivity, better stability and no secondary pollution, etc., and has the value of popularization and application in the field of wastewater treatment technology.

[0115] The above embodiments are only preferred embodiments given to fully illustrate the present invention, and the protection scope of the present invention is not limited thereto. Equivalent substitutions or transformations made by those skilled in the art in the technical field on the basis of the present invention are all within the protection scope of the present invention.

Claims

1. A method for preparing a gas diffusion electrode for simultaneously enhancing O2 transmission and H2O2 selectivity, characterized in that: The following steps are involved: S1, mixing a conductive material, a polytetrafluoroethylene emulsion and polymethylhydrogensiloxane in an organic solvent to obtain a mixed solution; S2, making the mixed solution into a viscous paste, coating it on the surface of the carbon cloth, and then performing a hot pressing process to obtain an electrode intermediate; S3, calcining the electrode intermediate to obtain a gas diffusion electrode with simultaneous enhanced O2 transmission and H2O2 selectivity; In S1, the conductive material is conductive carbon black.

2. The method for preparing a gas diffusion electrode for simultaneously enhancing O2 transmission and H2O2 selectivity according to claim 1, characterized in that: In the S1, the mass fraction of polytetrafluoroethylene in the polytetrafluoroethylene emulsion is 30% to 60%.

3. The method for preparing a gas diffusion electrode for simultaneously enhancing O2 transmission and H2O2 selectivity according to claim 1, characterized in that: In the S1, the mass ratio of the conductive carbon black to the polytetrafluoroethylene emulsion is 1:1 to 5:

1.

4. The method for preparing a gas diffusion electrode for simultaneously enhancing O2 transmission and H2O2 selectivity according to claim 1, characterized in that: In S1, the mass ratio of the added polytetrafluoroethylene emulsion to the added polymethylhydrogensiloxane is 1:0.038 to 1:0.

25.

5. The method for preparing a gas diffusion electrode for simultaneously enhancing O2 transmission and H2O2 selectivity according to claim 1, characterized in that: In the above-mentioned S1, the organic solvent is anhydrous ethanol.

6. The method for preparing a gas diffusion electrode for simultaneously enhancing O2 transport and H2O2 selectivity according to claim 1, characterized in that: The S2 specifically includes: drying the mixed solution to obtain a viscous paste, coating the viscous paste on the front and back sides of the carbon cloth, and then performing hot pressing at a temperature of 30° C. to 60° C. and a pressure of 0.5 MPa to 1.5 MPa to obtain an electrode intermediate.

7. The method for preparing a gas diffusion electrode for simultaneously enhancing O2 transport and H2O2 selectivity according to claim 1, characterized in that: In S3, the calcination temperature is between 300° C. and 400° C., and the calcination time is 1 to 3 hours.

8. A gas diffusion electrode for simultaneously enhancing O2 transport and H2O2 selectivity, characterized in that: The gas diffusion electrode is made by the preparation method described in any one of claims 1 to 7.

9. An application of a gas diffusion electrode for simultaneously enhancing O2 transmission and H2O2 selectivity obtained by the preparation method according to any one of claims 1 to 7, characterized in that: The gas diffusion electrode is used as a gas diffusion electrode for O2 transmission and H2O2 selectivity in the electro-Fenton treatment of refractory organic matter, and the refractory organic matter includes bisphenol A, naproxen, ciprofloxacin, amoxicillin, diclofenac sodium, rhodamine B, methyl orange and 2,4-dichlorophenol.

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