Three-dimensional oxygen reduction electrode and preparation method and application thereof

Abstract

The invention provides a three-dimensional oxygen reduction electrode and a preparation method and application thereof, and belongs to the technical field of electro-catalysis. According to the preparation method, the high-performance three-dimensional oxygen reduction cathode is successfully prepared by optimizing the material ratio and process parameters. Wherein the cationic functional group is effectively induced to form a local alkaline microenvironment, the hydrophobicity of the electrode and the stability of a three-phase interface are enhanced by the PTFE, and the reaction mass transfer is promoted by the three-dimensional porous structure of the graphite felt substrate, so that the comprehensive performance of electro-synthesis of hydrogen peroxide under the neutral condition is synergistically improved.

Description

Technical Field

[0001] This invention relates to the field of electrocatalysis technology, and in particular to a three-dimensional oxygen reduction electrode, its preparation method, and its application. Background Technology

[0002] Neutral pure hydrogen peroxide is directly synthesized by the two-electron oxygen reduction reaction. As a green alternative to the traditional high-energy-consuming anthraquinone process, solution electrolysis has attracted widespread attention in recent years. Early studies successfully prepared neutral pure solutions by drawing on the structural design of fuel cells (PEMFC) and proton exchange membranes (PEM) for water electrolysis. The anode serves as the proton source for the hydrogen oxidation / water oxidation reaction; under the influence of the electric field, protons are transferred to the cathode catalytic layer interface and react with oxygen to generate hydrogen peroxide (2H₂O₃). + +O2 + 2e - H2O2). However, at high operating current densities, due to the large amount of H... + Enrichment at the catalytic interface in the cathode region (a locally strong acid environment) readily triggers the hydrogen evolution reaction (HER), significantly suppressing the current efficiency of H2O2 electrosynthesis (<10%). Furthermore, the yield of hydrogen peroxide electrosynthesis is also limited by inherent defects in its reactor design. Specifically, due to the membrane electrode assembly (MEA) structure used, the product... Molecules accumulate at the interface between the cathode catalyst layer and the membrane (MEA cathodes use hydrophobic carbon paper, making it difficult for products to be discharged). Local high concentrations of hydrogen peroxide inhibit the two-electron oxygen reduction process and exacerbate side reactions (including hydrogen peroxide decomposition, secondary reduction of hydrogen peroxide to water, and hydrogen evolution), leading to decreased selectivity and further reduction in current efficiency.

[0003] Therefore, in order to address the problems of slow reaction kinetics, low selectivity, and low yield in existing PEM-type electrosynthesis hydrogen peroxide systems, developing a strategy that can overcome these limitations and achieve an electrosynthesis system with high current efficiency, high yield, and high H2O2 concentration has become a key challenge in this field. Summary of the Invention

[0004] The purpose of this invention is to provide a three-dimensional oxygen reduction electrode, its preparation method, and its application, which can solve the problems of slow reaction kinetics, low selectivity, and low yield in PEM-type electrosynthesis of hydrogen peroxide systems.

[0005] To achieve the above-mentioned objectives, the present invention provides the following technical solution: This invention provides a method for preparing a three-dimensional oxygen reduction electrode, comprising the following steps: Carbon powder, a polymer containing cationic functional groups, and a solvent are mixed and then subjected to stirring and ball milling processes in sequence. Under stirring conditions, a polytetrafluoroethylene aqueous dispersion is added to the resulting mixture to obtain a catalyst slurry. The catalyst slurry was coated onto the surface of a graphite felt using ultrasonic spraying and then cured to obtain a three-dimensional oxygen reduction electrode.

[0006] Preferably, the toner comprises one or more of conductive carbon black, acetylene black, Ketjen black, carbon nanotubes, and graphene.

[0007] Preferably, the cationic functional group in the cationic functional group polymer includes one or more of quaternary ammonium cations, imidazole cations, and guanidine salt cations; the polymer used in the cationic functional group polymer includes one or more of polyarylpiperidine, polyether ether ketone, and polystyrene.

[0008] Preferably, the mass ratio of the cationic functional group polymer to the toner is 0 to 1:1 and not 0; the solvent is a mixture of isopropanol and water, and the volume ratio of isopropanol to water is 1 to 5:1.

[0009] Preferably, the stirring speed is 500~2000 rpm and the time is 0.5~2 h; the ball milling speed is 500~2000 rpm and the time is 2~5 h; and the stirring speed is 500~2000 rpm.

[0010] Preferably, the mass ratio of polytetrafluoroethylene to carbon powder in the polytetrafluoroethylene aqueous dispersion is 0~2:1 and not 0; the solid content of the catalyst slurry is 1~20wt%.

[0011] Preferably, during ultrasonic spraying, the catalyst loading on the graphite felt surface is 1~5 mg / cm². 2 .

[0012] Preferably, the curing temperature is 60~120 ℃ and the time is 1~12 h.

[0013] The present invention provides a three-dimensional oxygen reduction electrode prepared by the preparation method described in the above technical solution.

[0014] This invention provides the application of the three-dimensional oxygen reduction electrode described above as a cathode in PEM-type electrosynthesis of hydrogen peroxide.

[0015] This invention provides a method for preparing a three-dimensional oxygen reduction electrode. By combining carbon powder, a polymer containing cationic functional groups, and polytetrafluoroethylene (PTFE), and then uniformly loading these components onto the surface of a hydrophobic three-dimensional graphite felt using an ultrasonic spraying process, a high-performance cathode for the electrolytic synthesis of hydrogen peroxide via PEM was successfully prepared. The core innovation of this cathode lies in utilizing the electrostatic repulsion of hydrogen ions by the cationic functional groups in the polymer to effectively block hydrogen ions migrating from the anode to the cathode reaction interface, thereby constructing a dynamic alkaline microenvironment on the cathode surface and significantly improving the selectivity and reaction kinetics of the two-electron oxygen reduction reaction pathway. Simultaneously, the introduction of PTFE enhances the hydrophobicity of the electrode, effectively preventing water flooding and stabilizing the three-phase reaction interface; combined with the excellent structural characteristics of the three-dimensional porous graphite felt substrate, the mass transfer efficiency between reactants and products is further enhanced. This invention, through material design and structural control, constructs a dynamic alkaline microenvironment at the cathode catalytic layer interface, significantly improving the two-electron oxygen reduction reaction (2... The catalytic activity and selectivity of the ORR (oxygen reduction reaction) are enhanced, and the mass transfer process is strengthened, thereby significantly improving the energy consumption and yield of PEM-based electrosynthesis of hydrogen peroxide. Compared with the defects of existing PEM synthesis processes, which form a local acid environment and easily trigger hydrogen evolution side reactions, the three-dimensional oxygen reduction electrode of this invention has water vapor scouring of the membrane surface, which is conducive to product discharge, resulting in higher current efficiency, higher hydrogen peroxide production efficiency, and fewer hydrogen evolution side reactions.

[0016] The present invention has the following beneficial effects: (1) Construction of dynamic alkaline microenvironment: By introducing polymers containing cationic functional groups (such as quaternary ammonium and imidazole polymers), the electrostatic repulsion of hydrogen ions by these functional groups effectively blocks hydrogen ions from conducting from the anode to the cathode reaction interface, locally increasing the pH value at the cathode interface and forming a dynamic alkaline microenvironment. This environment significantly enhances the oxygen reduction reaction kinetics and greatly improves the selectivity for hydrogen peroxide generation via the two-electron pathway.

[0017] (2) Stable three-phase interface: By introducing polytetrafluoroethylene (PTFE) as a hydrophobic binder, a stable hydrophobic network structure is constructed inside the electrode, effectively controlling the distribution and stability of the gas-liquid-solid three-phase interface. The hydrophobic properties of PTFE prevent excessive electrolyte wetting of the pores, avoiding the submersion of active sites and ensuring efficient oxygen transport to the catalytic reaction sites.

[0018] (3) Three-dimensional electrode structure enhances mass transfer: By combining a hydrophobic three-dimensional graphite felt substrate with a uniform catalytic layer formed by ultrasonic spraying, a porous electrode structure with high specific surface area and excellent gas / liquid permeability was constructed. This greatly promoted oxygen mass transfer and hydrogen peroxide desorption, avoiding the occurrence of side reactions, thereby achieving high current density and high yield at a low overpotential.

[0019] (4) High-efficiency and stable operation: This method can use a PEM-type electrolyzer to directly electrolyze pure water and oxygen into neutral pure hydrogen peroxide, avoiding problems such as equipment corrosion and product purification difficulties caused by strong acid / strong alkali electrolytes. It also has the advantages of low energy consumption, high stability and simple operation. Attached Figure Description

[0020] Figure 1 A cross-sectional scanning electron microscope image of the three-dimensional oxygen reduction electrode prepared in Example 1; Figure 2 High-resolution scanning electron microscope image of carbon and polymer particles in the catalyst layer of the three-dimensional oxygen reduction electrode prepared in Example 1; Figure 3 This is a schematic diagram illustrating the PEM-type electrosynthesis of hydrogen peroxide process and mechanism in the test examples of this invention; Figure 4 Polarization curves of oxygen reduction reaction of conductive carbon black in electrolytes with different pH values; Figure 5 The electrolytic cell voltage for the electrosynthesis of hydrogen peroxide using the three-dimensional oxygen reduction electrode prepared in Examples 1-4 and Comparative Example 1; Figure 6 The current efficiency of hydrogen peroxide electrosynthesis by the three-dimensional oxygen reduction electrode prepared in Examples 1-4 and Comparative Example 1; Figure 7 The concentration of hydrogen peroxide electrosynthesized by the three-dimensional oxygen reduction electrode prepared in Examples 1-4 and Comparative Example 1 is denoted as . Detailed Implementation

[0021] In this invention, unless otherwise specified, the raw materials or reagents required for preparation are all commercially available products well known to those skilled in the art.

[0022] This invention provides a method for preparing a three-dimensional oxygen reduction electrode, comprising the following steps: Carbon powder, a polymer containing cationic functional groups, and a solvent are mixed and then subjected to stirring and ball milling processes in sequence. Under stirring conditions, a polytetrafluoroethylene aqueous dispersion is added to the resulting mixture to obtain a catalyst slurry. The catalyst slurry was coated onto the surface of a graphite felt using ultrasonic spraying and then cured to obtain a three-dimensional oxygen reduction electrode.

[0023] In this invention, the toner preferably includes one or more of conductive carbon black, acetylene black, Ketjen black, carbon nanotubes, and graphene.

[0024] In this invention, the cationic functional group in the cationic functional group polymer preferably includes one or more of quaternary ammonium cations, imidazole cations, and guanidine salt cations; the polymer used in the cationic functional group polymer preferably includes one or more of polyarylpiperidine, polyether ether ketone, and polystyrene. This invention does not impose any specific limitation on the type of polyarylpiperidine; any commercially available product well-known in the art is acceptable.

[0025] In this invention, the cationic functional group-containing polymer is preferably a quaternized polyarylpiperidine; the quaternized polyarylpiperidine is preferably PiperION-A5-HCO3-EtOH, NEXIONIC® QAPPT, or Pention-D35-5wt%.

[0026] In this invention, the mass ratio of the cationic functional group polymer to the toner is preferably 0 to 1:1 and not 0, more preferably 0.05 to 0.8:1, and even more preferably 0.25 to 0.5:1.

[0027] In this invention, the solvent is preferably a mixture of isopropanol and water, and the volume ratio of isopropanol to water is preferably 1 to 5:1, more preferably 2 to 3:1.

[0028] In this invention, the stirring speed is preferably 500~2000 rpm, more preferably 1000~1500 rpm, and the time is preferably 0.5~2 h, more preferably 1~1.5 h; the stirring process is preferably carried out in a high-speed mechanical stirrer.

[0029] In this invention, the ball milling speed is preferably 500-2000 rpm, more preferably 1000-1500 rpm, and the time is preferably 2-5 h, more preferably 3-4 h. Preferably, this invention uses a planetary ball mill with zirconia balls for the ball milling process.

[0030] After the ball milling process is completed, the present invention preferably returns the obtained slurry to a high-speed mechanical stirrer, and adds polytetrafluoroethylene aqueous dispersion dropwise using a drop pump under stirring conditions. The dropwise addition is completed within 30 minutes, and stirring is continued for another 30 minutes to obtain the catalyst slurry.

[0031] In this invention, the stirring conditions include a stirring speed of 500-2000 rpm, more preferably 1000-1500 rpm.

[0032] In this invention, the mass concentration of the polytetrafluoroethylene aqueous dispersion is preferably 1-10%, more preferably 5-10%; the polytetrafluoroethylene aqueous dispersion is prepared by dispersing commercially available polytetrafluoroethylene emulsion (mass fraction 60%) in water.

[0033] In this invention, the mass ratio of polytetrafluoroethylene to carbon powder in the polytetrafluoroethylene aqueous dispersion is preferably 0~2:1 and not 0, more preferably 1~1.5:1, and even more preferably 1.2:1; the solid content of the catalyst slurry is preferably 1~20wt%, more preferably 4.68~15wt%, and even more preferably 5~10wt%.

[0034] The present invention does not impose any special limitations on the specifications and source of the graphite felt; commercially available products well known in the art are acceptable.

[0035] In this invention, during ultrasonic spraying, the catalyst loading on the graphite felt surface is preferably 1~5 mg / cm². 2 More preferably 2~3 mg / cm 2 This loading amount represents the total loading density of all solid substances in the catalyst slurry. The present invention does not impose any special limitations on the size of the graphite felt, as long as the above loading amount is met; in the embodiments of the present invention, the graphite felt size is specifically 5 cm × 5 cm × 0.39 cm.

[0036] This invention does not impose any particular limitation on the ultrasonic spraying process; the required loading amount can be achieved by following a process well-known in the art. This invention uses ultrasonic spraying to ensure a uniform distribution of the catalyst layer and a strong bond with the substrate.

[0037] In this invention, the curing temperature is preferably 60~120℃, more preferably 80~100℃, and the curing time is preferably 1~12 h, more preferably 3~8 h, and even more preferably 6 h. This invention cures the catalyst coating to form an electrode with a stable three-dimensional porous structure.

[0038] The present invention provides a three-dimensional oxygen reduction electrode prepared by the preparation method described in the above technical solution.

[0039] This invention provides the application of the three-dimensional oxygen reduction electrode described above as a cathode in PEM-type electrosynthesis of hydrogen peroxide. This invention does not specifically limit the method of application; any method well-known in the art can be used to apply the three-dimensional oxygen reduction electrode as a cathode in PEM-type electrosynthesis of hydrogen peroxide.

[0040] The specific embodiments of the present invention are described in detail below, but it should be understood that the scope of protection of the present invention is not limited to the specific embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0041] Unless otherwise specified, the experimental methods described in the various embodiments of this invention are conventional methods; unless otherwise specified, the reagents and raw materials described below are all commercially available.

[0042] Example 1

[0043] 1.0 g of conductive carbon black (XC-72R), 5.0 g of 5 wt.% quaternized polyarylpiperidine solution (PiperION-A5-HCO3-EtOH dispersion, solvent ethanol) and 40 mL of solvent (isopropanol / water volume ratio of 2:1) were mixed in a beaker. The beaker was placed under a high-speed mechanical stirrer and stirred at 1500 rpm for 1 h. The resulting mixture was transferred to a planetary ball mill, zirconia balls were added, and the mixture was ball-milled at 1000 rpm for 3 h to obtain a slurry. The slurry was returned to the high-speed mechanical stirrer, and 12.0 g of 10wt.% polytetrafluoroethylene aqueous dispersion was added dropwise using a drop pump while stirring at 1500 rpm. The addition was completed within 30 min, and stirring was continued for another 30 min to obtain a catalyst slurry with a solid content of 4.68wt%. The catalyst slurry was uniformly applied to the surface of the graphite felt (5 cm × 5 cm × 0.39 cm) using ultrasonic spraying, and the number of sprayings was controlled to ensure that the catalyst loading was 3.0 mg / cm². The coated electrode was placed in a forced-air drying oven and cured at 80°C for 6 hours. After naturally cooling to room temperature, a three-dimensional oxygen reduction electrode was obtained.

[0044] Example 2

[0045] The only difference from Example 1 is that the quaternized polyarylepiperidine solution is replaced with commercially available anion exchange resin Pention-D35-5wt%, otherwise it is the same as Example 1.

[0046] Example 3

[0047] The only difference from Example 1 is that the mass of the quaternized polyarylpiperidine solution added is 1.0 g, otherwise it is the same as Example 1.

[0048] Example 4

[0049] The only difference from Example 1 is that the mass of the quaternized polyarylpiperidine solution added is 10.0 g, otherwise it is the same as Example 1.

[0050] Comparative Example 1

[0051] The only difference from Example 1 is that no polymer containing cationic functional groups is added; otherwise, it is the same as Example 1.

[0052] Structural characterization

[0053] Figure 1 A cross-sectional scanning electron microscope image of the three-dimensional oxygen reduction electrode prepared in Example 1; Figure 2Here is a high-resolution scanning electron microscope (SEM) image of carbon and polymer particles in the catalyst layer of the three-dimensional oxygen reduction electrode prepared in Example 1; from Figure 1 As can be seen, the catalyst layer is uniformly distributed on the electrode surface, with a thickness of approximately 1 mm. The microstructure of the catalyst layer was further observed using high-resolution scanning electron microscopy. Figure 2 It can be seen that the toner particles and polymers (including quaternized polyarylepiperidine and PTFE) form nanoscale clusters and are distributed in an interwoven network, which helps to form an efficient reaction interface.

[0054] Test case

[0055] PEM electrolytic cell performance test: 1) The three-dimensional oxygen reduction electrodes prepared in different cases were assembled as cathodes in a PEM-type electrolytic cell (see Figure 3 ); The anode uses Ir / Ti electrode; anode and cathode are separated by a proton exchange membrane; 2) Pure water is introduced into the anode (circulating electrolysis, flow rate of 30 mL / min); a pure water / oxygen mixture is introduced into the cathode (flow electrolysis, water flow rate of 4 mL / min, oxygen flow rate of 500 mL / min). 3) Run at a constant current density of 200 mA / cm², record the electrolysis voltage (V) and product hydrogen peroxide concentration (mg / L) every half hour, and calculate the corresponding current efficiency; 4) The concentration of hydrogen peroxide in the cathode electrolyte was determined by potassium titanium oxalate spectrophotometry.

[0056] Figure 4 The polarization curves of the oxygen reduction reaction of conductive carbon black in electrolytes of different pH values ​​are shown. The acidic electrolyte is 0.5M sulfuric acid aqueous solution, the neutral electrolyte is 0.5M sodium sulfate aqueous solution, and the alkaline electrolyte is 1M sodium hydroxide aqueous solution. Figure 4 The results showed that its oxygen reduction catalytic performance was poor under acidic conditions; however, when the electrolyte was converted to neutral or alkaline, the higher the pH, the significantly improved the catalytic activity, indicating that carbon materials are more suitable for oxygen reduction reactions in neutral and alkaline environments.

[0057] Figure 5 The electrolytic cell voltage for the electrosynthesis of hydrogen peroxide using the three-dimensional oxygen reduction electrode prepared in Examples 1-4 and Comparative Example 1; Figure 6 The current efficiency of hydrogen peroxide electrosynthesis by the three-dimensional oxygen reduction electrode prepared in Examples 1-4 and Comparative Example 1; Figure 7 The concentration of hydrogen peroxide electrosynthesized by the three-dimensional oxygen reduction electrode prepared in Examples 1-4 and Comparative Example 1 is denoted as .

[0058] from Figure 5It can be seen that in Examples 1 and 2, which added two quaternized polymers, the cell voltage was reduced by approximately 50% compared to Comparative Example 1, which did not add polymers. This performance improvement is attributed to the shielding effect of the cationic functional groups on hydrogen ions migrating from the anode, creating a locally alkaline microenvironment at the cathode interface, and promoting the two-electron oxygen reduction pathway (2... O + +2 → + 2O This significantly improved reaction kinetics. Correspondingly, the current efficiency for hydrogen peroxide generation increased dramatically from approximately 8% to 90%. Figure 6 The concentration of hydrogen peroxide can reach up to approximately 12,000 mg / L. Figure 7 The yield can reach approximately 1.14 kg / (m²·h).

[0059] The results of Examples 3 and 4 show that the content of the cationic polymer has a significant impact on cathode performance, and there is an optimal range: when the content is too low, an alkaline microenvironment cannot be effectively constructed; when the content is moderate, the interfacial environment can be optimized without blocking pores; when the content is too high, the performance deteriorates because the polymer covers the active sites and hinders mass transfer. A comparison with Comparative Example 1 demonstrates that adding an appropriate amount of cationic functional group-containing polymer can effectively shield hydrogen ions, significantly improving the cathode's oxygen reduction reaction activity and hydrogen peroxide selectivity.

[0060] In summary, this invention successfully fabricated a high-performance oxygen reduction cathode by optimizing material ratios and process parameters. Specifically, the cationic functional groups effectively induce the formation of a localized alkaline microenvironment, PTFE enhances the electrode's hydrophobicity and the stability of the three-phase interface, and the three-dimensional porous structure of the graphite felt substrate promotes reaction mass transfer, thereby synergistically improving the overall performance of hydrogen peroxide electrosynthesis under neutral conditions.

[0061] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a three-dimensional oxygen reduction electrode, characterized in that, Includes the following steps: Carbon powder, a polymer containing cationic functional groups, and a solvent are mixed and then subjected to stirring and ball milling processes in sequence. Under stirring conditions, a polytetrafluoroethylene aqueous dispersion is added to the resulting mixture to obtain a catalyst slurry. The catalyst slurry was coated onto the surface of a graphite felt using ultrasonic spraying and then cured to obtain a three-dimensional oxygen reduction electrode.

2. The preparation method according to claim 1, characterized in that, The toner includes one or more of conductive carbon black, acetylene black, Ketjen black, carbon nanotubes, and graphene.

3. The preparation method according to claim 1, characterized in that, The cationic functional group in the polymer containing cationic functional groups includes one or more of quaternary ammonium cations, imidazole cations, and guanidine salt cations; the polymer used in the polymer containing cationic functional groups includes one or more of polyarylpiperidine, polyether ether ketone, and polystyrene.

4. The preparation method according to claim 2 or 3, characterized in that, The mass ratio of the cationic functional group polymer to the toner is 0 to 1:1 and not 0; the solvent is a mixture of isopropanol and water, and the volume ratio of isopropanol to water is 1 to 5:

1.

5. The preparation method according to claim 1, characterized in that, The stirring process is carried out at a speed of 500-2000 rpm for 0.5-2 h; the ball milling process is carried out at a speed of 500-2000 rpm for 2-5 h; and the stirring conditions include a stirring speed of 500-2000 rpm.

6. The preparation method according to claim 1 or 5, characterized in that, The mass ratio of polytetrafluoroethylene to carbon powder in the polytetrafluoroethylene aqueous dispersion is 0~2:1 and not 0; the solid content of the catalyst slurry is 1~20wt%.

7. The preparation method according to claim 6, characterized in that, During ultrasonic spraying, the catalyst loading on the graphite felt surface is 1~5 mg / cm². 2 .

8. The preparation method according to claim 7, characterized in that, The curing temperature is 60~120 ℃, and the time is 1~12 h.

9. The three-dimensional oxygen reduction electrode prepared by the preparation method according to any one of claims 1 to 8.

10. The application of the three-dimensional oxygen reduction electrode of claim 9 as a cathode in PEM-type electrosynthesis of hydrogen peroxide.

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