Application of multi-scale coarse structure gas diffusion film in electrochemical reduction of carbon dioxide

Abstract

The invention discloses application of a multi-scale coarse structure gas diffusion film in electrochemical reduction of carbon dioxide. According to the invention, the gas diffusion membrane is utilized to construct the gas diffusion electrode, and stabilization of a gas-liquid-solid three-phase interface is realized in the flowing electrolytic tank; the gas diffusion membrane comprises a support layer with a three-dimensional through framework and a conductive hydrophobic microporous layer, the support layer is formed by melting polyvinylidene fluoride and NaCl particles with different particle sizes and washing to remove a template, the surface of the gas diffusion membrane is subjected to solvent heat treatment to form a scaly rough structure, and the gas diffusion membrane has super-hydrophobic performance. When the membrane is applied to a CO2 electrochemical reduction system, the electrolyte infiltration resistance and long-term operation stability of an electrode under high current density can be remarkably enhanced, hydrogen evolution side reaction is inhibited, the selectivity of C2 + products (such as ethylene) is effectively improved, the highest C2H4 Faraday efficiency can reach 43.49%, and the stability of a three-phase interface can still be maintained under the high potential of-2.0 V (vs. RHE).

Description

Technical Field

[0001] This invention relates to the application of a multi-scale rough structure gas diffusion membrane in the electrochemical reduction of carbon dioxide, belonging to the field of electrochemical technology. Background Technology

[0002] The greenhouse effect, a major challenge to human society, has led to global warming, which is the primary cause of climate change and biodiversity loss. CO2, a major greenhouse gas, is increasingly accumulated due to the imbalance in the carbon cycle caused by fossil fuel combustion and deforestation, resulting in severe ecological crises such as sea-level rise, ocean acidification, and glacial melting. The international community has established a coordinated emission reduction approach centered on energy structure transformation (developing renewable energy), carbon capture and storage (CFS), and CO2 resource utilization. Current CO2RR technologies encompass multiple pathways, including electrochemical catalysis, thermocatalysis, photocatalysis, and biocatalysis. Thermocatalysis is constrained by harsh reaction conditions and secondary emissions; biocatalysis suffers from insufficient enzyme activity and stringent anaerobic requirements affecting carbon fixation efficiency; photocatalysis faces bottlenecks in light energy utilization due to material bandgap defects; while electrochemical methods, with their mild reaction conditions, controllable reaction processes, and high product formation rates, demonstrate significant commercial potential.

[0003] Most current research on CO2RR is still in the laboratory stage, and the commonly used reactor is the traditional three-electrode H-cell electrolyzer. However, the relatively long mass transfer distance and the low solubility of CO2 in the aqueous electrolyte solution limit the reaction efficiency of CO2RR in the H-cell system, which is dominated by hydrogen evolution reaction at high current densities. Compared to the mass transfer of CO2 in the liquid phase, the diffusion coefficient of CO2 in the gas phase is -0.1 cm⁻¹. 2 s -1The diffusion coefficient of CO2 in the gas phase is about four orders of magnitude higher than that of CO2 in the liquid phase, making gaseous CO2 a more suitable reactant source for CO2RR. Since gaseous CO2 itself cannot participate in the electrochemical reaction due to the absence of an aqueous medium, researchers have focused on developing a gas-liquid-solid three-phase interface system for CO2RR based on the GDE (Flow-Cell) derived from fuel cell technology. The development of this three-phase interface system has shortened the mass transfer distance of CO2 in the aqueous electrolyte solution from about 50 μm to about 50 nm, significantly improving gas-phase mass transfer and mitigating, to some extent, the limitation of poor CO2 solubility in the electrolyte solution. The catalytic current density of the Flow-Cell system is also significantly higher than that of the H-Cell system. This is attributed to its support for a high-pH electrolyte to optimize CO2RR electron transfer kinetics, enabling direct contact between gaseous CO2 and the catalyst, and effectively suppressing hydrogen evolution side reactions. Therefore, the use of Flow-Cell is a necessary condition for the large-scale application of CO2RR technology to achieve industrial-scale CO2 electrolysis. Existing research focuses on the electrolyte effects (cation / anion effects, local pH, electrolyte type and concentration), morphology effects (tip effects, regio effects), and surface modifications (hydrophobicity control, chemical / electronic state modification) of catalysts, but their effects on improving electrode stability and durability remain limited. Recent studies have found that the decline in GDE catalytic performance is also closely related to changes in the interfacial properties of the gas diffusion layer (GDL) during electrocatalysis. However, due to the fact that commercial gas diffusion membranes have largely met the performance requirements of GDLs, comprehensive and in-depth research on the interfacial microenvironment of GDLs is still relatively scarce. It is worth noting that most commercial gas diffusion membranes tested so far are designed for fuel cells, and often exhibit insufficient stability and durability in CO2RR processes (especially for systems producing ethylene and ethanol). Therefore, to optimize the catalytic performance (activity, selectivity, stability) of GDEs, fundamental research on the GDL interfacial microenvironment should be as important as research on the inherent properties of the catalyst. Constructing a GDL suitable for CO2RR is a necessary condition for advancing CO2RR research.

[0004] This invention addresses the limitations of current commercial GDL processes, which are complex and cannot meet the requirements for membrane electrode permeability resistance to electrolyte solutions, long-term stability, and durability at high cathode potentials during long-term rinsing. Summary of the Invention

[0005] The purpose of this invention is to provide an application of a multi-scale roughened gas diffusion membrane (GDL) in the electrochemical reduction of carbon dioxide. The multi-scale roughened structure of the gas diffusion membrane significantly enhances the stability and durability of the gas diffusion membrane (GDE) in the CO2RR process. This invention also clarifies the hydrophobicity changes of the gas diffusion membrane (GDL) under external voltage application and long-term electrolyte solution scouring through electrowetting and scouring durability experiments, revealing the changes in electrolyte solution flow direction during GDL flooding. This is of great significance for the subsequent design of GDLs and the large-scale application of stable superhydrophobic GDLs in future CO2RR technology.

[0006] The multi-scale rough structure gas diffusion membrane used in this invention includes: The support layer is a three-dimensional through-frame structure formed by melting polyvinylidene fluoride and NaCl particles of the first size and then removing the NaCl. This ensures low-resistance transmission of CO2 gas. The three-dimensional through-frame provides excellent mechanical strength and toughness, preventing structural collapse under high voltage. A microporous layer, disposed on the support layer, is a conductive and hydrophobic layer formed by melting and molding polyvinylidene fluoride, multi-walled carbon nanotubes, and second-sized NaCl particles, followed by NaCl removal. This layer serves as the main bearing area of ​​the gas-liquid-solid three-phase interface, and its pore size distribution precisely matches the requirements for CO2 mass transfer and electrolyte barrier. The surface of the gas diffusion membrane is subjected to solvent thermal treatment to form a fish-scale-like rough structure, which gives it superhydrophobic properties.

[0007] Preferably, the particle size of the NaCl particles in the support layer ranges from 150 to 300 μm; The NaCl particles in the microporous layer have a particle size range of 50-100 μm.

[0008] Preferably, in the microporous layer, the mass ratio of the polyvinylidene fluoride, the multi-walled carbon nanotubes, and the NaCl particles is 1:0.05-0.4:7, more preferably 1:0.3:7.

[0009] Preferably, the solvent used in the solvothermal treatment includes an alcohol solvent, a co-solvent, and water.

[0010] The alcohol solvent is an alcohol with 3-7 carbon atoms, preferably pentanol; When the size of the gas diffusion membrane is 2.5 × 2.5 cm 2 In the treatment solution, the content of the alcohol solvent is 3-5.5 mL, preferably 4 mL, the co-solvent is dilute HCl with a content of 12-17 mL, and the content of water is 15 mL.

[0011] Preferably, the solvent heat treatment is performed at a temperature of 100-200°C for 1-10 hours, and preferably at 150°C for 5 hours.

[0012] The gas diffusion membrane of this invention has a water contact angle greater than 160°, a roll-off angle less than 5°, and a CO2 flux greater than 1.8 mL·cm⁻¹. -2 ·min -1 ·Pa -1 .

[0013] The gas diffusion membrane can be prepared according to the following method: Polyvinylidene fluoride is mixed with NaCl particles of the first size, melted and molded, and then washed with water to remove NaCl, forming a support layer. Polyvinylidene fluoride, multi-walled carbon nanotubes and second-size NaCl particles are mixed, melted and shaped, and then washed with water to remove NaCl, forming a microporous layer on the support layer to obtain a composite membrane. The composite membrane is subjected to solvent heat treatment, cleaned and dried to obtain a gas diffusion membrane with a fish-scale-like surface structure.

[0014] This invention utilizes a multi-scale rough structure gas diffusion membrane in CO2 electrochemical reduction. The multi-scale rough structure gas diffusion membrane is used to construct a gas diffusion electrode. The multi-scale rough structure gas diffusion membrane provides a CO2 gas phase transport channel while blocking the electrolyte solution, thereby stabilizing the gas-liquid-solid three-phase interface in a flow electrolyzer. Commercial GDLs (such as carbon paper and carbon cloth) are mostly designed for fuel cells, and are prone to flooding (electrolyte permeation leading to interface collapse) in CO2 RR.

[0015] Specifically, the electrochemical reduction method for carbon dioxide provided by the present invention includes the following steps: A gas diffusion electrode is obtained by loading a catalyst onto the surface of a multi-scale rough gas diffusion film. The gas diffusion electrode is placed in a flowing electrolytic cell, and electrochemical reduction is performed by applying a potential using CO2 gas as the reaction source.

[0016] Preferably, the nano-copper catalyst is dispersed in isopropanol, water (such as ultrapure water), and Nafion solution to form an ink, and the ink is drop-coated onto the surface of the scale-rough structured gas diffusion membrane to obtain a gas diffusion electrode. The isopropanol improves dispersibility and prevents catalyst agglomeration, and the Nafion solution provides a proton conduction channel and enhances the electrode-membrane interface bonding. For example, 20 mg of nano-copper was used as a catalyst and dispersed in a mixed solvent containing 70 μL isopropanol, 430 μL ultrapure water and 30 μL 5% Nafion solution. The mixture was then ultrasonically treated for 45 min until a uniform ink was formed.

[0017] Preferably, the conditions for the electrochemical reduction are as follows: The electrolyte is a 1 mol / L KOH alkaline electrolyte solution; The gas flow rate is 100-300 mL / min to ensure that CO2 is evenly distributed on the electrode surface and to avoid local concentration polarization. Voltage ranges from -0.6 to 2 V (vs. RHE), current density ranges from 50 to 300 mA·cm. -2 .

[0018] The present invention analyzes the structure of SPM-M by SEM and finds that the surface of the multi-scale rough structure gas diffusion membrane (SPM-M) used in the present invention has a multi-scale rough structure composed of fiber network, fish scale wrinkles and MWCNT. The synergistic effect of this multi-scale structure ensures the hydrophobic stability of the SPM-M surface and effectively reduces the roll-off angle of droplets on the SPM-M surface. This is the key to the superhydrophobic properties of SPM-M and endows the SPM-M surface with excellent anti-electrowetting ability.

[0019] This invention uses a combination of SEM and EDS to study the changes in electrolyte solution flow direction across the SPM-M cross-section, revealing the flooding process, which is of great significance for the subsequent optimization and design of SPM-M. Under applied voltage, the contact angle of this material can remain stable above 145° for 300 min, and its contact angle change rate is significantly lower than that of Sigracet 22BB carbon paper in the same time period, exhibiting excellent anti-electrowetting ability. -2 It can operate stably for over 4000 min at current density, and its membrane flux is significantly better than that of commonly used GDLs. The SPM-M used in this invention has a Faraday efficiency of less than 35% for H2 in the range of -0.6 to -2.0 V (vs. RHE), and a maximum Faraday efficiency of 43.49% for C2H4. It maintains a stable gas-liquid-solid three-phase interface even at a high voltage of -2.0 V (vs. RHE) until flooding occurs at -2.2 V, exhibiting superior high voltage stability compared to other GDLs. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of the GDL membrane flux experimental setup.

[0021] Figure 2 This is a schematic diagram of the electrowetting test method.

[0022] Figure 3 It is the difference in membrane flux between different GDLs.

[0023] Figure 4The images show the surface microstructure and water contact angle of PM before and after modification, as well as PM-M before and after modification. (a) is the water contact angle and surface microstructure of PM magnified 500 times; (b) is the water contact angle and surface microstructure of modified PM magnified 500 times; (c) is the water contact angle and surface microstructure of PM-M magnified 500 times; (d) is the water contact angle and surface microstructure of modified PM-M magnified 500 times; (e) is the surface microstructure of PM magnified 2000 times; (f) is the surface microstructure of modified PM magnified 2000 times; (g) is the surface microstructure of PM-M magnified 2000 times; and (h) is the surface microstructure of modified PM-M magnified 2000 times.

[0024] Figure 5 The SPM-M electrowetting changes are shown in 1 mol / L solutions of KHCO3 (a), K2CO3 (b), KOH (c), and KCl (d).

[0025] Figure 6 It is the rate of change of contact angle of different electrolyte solutions under different voltages.

[0026] Figure 7 The dielectric wettability changes of SPM-M (a) and Sigrette 22 BB carbon paper (b) under high voltage over long periods. Figure 8 This is GDL's high cathode potential durability test.

[0027] Figure 9 The changes in SEM and K element distribution at different scouring times are: (a) 0h; (b) 10h; (c) 40h; (d) 70h.

[0028] Figure 10 These are the LSV curves for SPM-M, Sigracet 22 BB, AvCarb P75T, and HCP330P.

[0029] Figure 11 The CO2RR product distributions under different cathode potentials are: (a) SPM-M; (b) Sigracet 22 BB; (c) AvCarb P75T; (d) HCP330P.

[0030] Figure 12 The product Faradaic efficiencies of GDE under different voltages are: (a) Faradaic efficiency of H2 products; (b) Faradaic efficiency of total C products; (c) Faradaic efficiency of total C. 2+ Product Faraday efficiency. Detailed Implementation

[0031] Unless otherwise specified, the experimental methods used in the following examples are conventional methods.

[0032] Unless otherwise specified, all materials and reagents used in the following examples are commercially available.

[0033] The measurement methods in the following embodiments are as follows: Method for measuring gas diffusion layer membrane flux: Using CO2 as the test medium, the membrane flux of the GDL under different reaction conditions is measured. The schematic diagram of the experimental setup is shown below. Figure 1 As shown (1. pressure gauge; 2. Flow-Cell; 3. outlet flow meter; 4. inlet flow meter). The gas cylinder is connected to the inlet flow meter to set the gas flow rate through the GDL. The inlet flow meter is connected to the carrier device of the GDL, and the outlet flow meter is connected to the outlet flow meter. The gas flow rate released at the inlet is set to 100 mL / min, 200 mL / min and 300 mL / min. The pressure difference across the membrane is measured by a U-tube pressure gauge. The GDL membrane flux under different gas flow rates is calculated by formula (1). The sample membrane flux is obtained by calculating the average membrane flux under these flow rates.

[0034] (1) Where Q is the membrane flux (mL / cm²) 2 min Pa); q is the gas flow rate (mL / min); A is the GDL area ( / cm²). 2 ); ΔP is the pressure difference (Pa) across the membrane.

[0035] Electrowetting test: A schematic diagram of the electrowetting test experimental setup is shown below. Figure 2 As shown. The GDL connected to the copper foil was fixed on the platform of the contact angle measuring instrument. A stainless steel needle was used as the counter electrode, and the GDL as the working electrode. 10 μL of electrolyte solution was squeezed out from the injector and placed on the surface of the GDL to form a closed loop. The contact angle changes of 1 mol / L KOH solution, 1 mol / L K2CO3 solution, 1 mol / L KHCO3 solution, and 1 mol / L KCl solution were measured at -1 V, -2 V, and -3 V, respectively. The voltage was applied to the droplet by chronoamperometry (it test), and the test duration was set to 300 min. The contact angle change was recorded every 10 min. This experiment was also carried out in a closed instrument.

[0036] CO2RR stability test of high concentration salt solution: The CO2RR stability of high-concentration salt solutions was tested using a potentiostatic method (CP). A 1 mol / L KOH solution was used to continuously flush the GDL at the applied potential, and the test current density was set to 200 mA cm⁻¹. -2 Test different GDLs at 200mA cm -2Breakthrough time at current density was determined, and the changes in electrolyte flow direction at the SPM-M interface were revealed by combining SEM and EDS.

[0037] Example 1: Preparation of PM-M First, a mixture of 7 g of PVDF powder and NaCl particles with a particle size range of 150-300 μm was filled into a 75 mm glass dish as the GDL support layer. Then, a mixture of 3 g of PVDF powder, conductive filler multi-walled carbon nanotubes (MWCNTs), and NaCl particles with a particle size range of 50-100 μm was used as the GDL microporous layer. This mixture was heated to 200 °C for 30 min to melt the mixture, followed by immersion in water for 24 h to remove the NaCl, thus constructing a hydrophobic composite GDL with a multi-scale porous structure. For ease of description, the GDL without filler will be referred to as a PVDF composite gas diffusion membrane, abbreviated as PM, and the GDL with added MWCNTs will be referred to as a PVDF / PVDF-MWCNT composite gas diffusion membrane, abbreviated as PM-M.

[0038] Example 2: Preparation of SPM-M A treatment solution containing 15 mL of dilute HCl, 15 mL of deionized water, and 4 mL of pentanol was prepared in a high-temperature, high-pressure autoclave with a PTFE liner. A 2.5 × 2.5 cm piece of material was then placed in the autoclave. 2 The PM-M was immersed in the solution. It was then subjected to solvothermal treatment in an oven at 150°C for 5 hours. Afterward, the PM-M was removed from the autoclave and rinsed three times with ethanol and deionized water in an ultrasonic cleaner to remove residual treatment solution. Finally, it was dried in an oven at 60°C for 24 hours.

[0039] Example 3: Electrocatalysis Experiment 20 mg of nano-copper was used as a catalyst and dispersed in a mixed solvent containing 70 μL isopropanol, 430 μL ultrapure water, and 30 μL 5% Nafion solution. The mixture was sonicated for 45 min until a uniform ink was formed. The nano-copper ink was then uniformly drop-coated onto the GDL surface and dried by N2 to prepare the working electrode. The three-electrode system constructed in Flow-Cell was measured using the IT method of an electrochemical workstation. A 1 mol / L KOH solution was used as the electrolyte solution; 3PK-130 was used as the ion exchange membrane separating the anode and cathode chambers; an Ag / AgCl electrode (potassium chloride salt, salt bridge) was used as the reference electrode; a 3 × 1 cm iridium oxide mesh was used as the counter electrode; and the working electrode was the diffusion electrode prepared in Examples 1 and 2. The CO2 flow rate and electrolyte flow rate were consistent with the parameters set for the high-salt solution scouring durability test. Gas-phase products generated on the GDL surface were sampled at fixed time intervals (15 min) and quantitatively analyzed by gas chromatography. Electrochemical reaction data were collected using a CHI760E electrochemical workstation, and the Faraday efficiency of the liquid and gaseous products was calculated based on the collected charge information. All electrochemical tests were IR-compensated, and all potentials were converted to reversible hydrogen electrode (RHE) values ​​using formula (2): (2) Among them, E RHE E is the RHE potential. Ag / AgCl The potential of Ag / AgCl was determined by linear sweep voltammetry (LSV) in the potential range of -0.2V to -1.2V (vs RHE) at 10 mV / s. -1 The sample was scanned at a certain rate. Gaseous products were continuously injected and analyzed in the gas chromatograph. Gaseous products were analyzed every 15 minutes, and the Faraday efficiency of a certain gaseous product was calculated based on equation (3): (3) Where ν (vol %) is the volume concentration of the gaseous product (GC data); V is the gas flow rate measured by a flow meter; I is the steady-state total current of the Flow-Cell, n is the number of electrons transferred in the products; and F is the Faraday constant, 96485 C mol. -1 P is one atmosphere, 1.013 × 10⁻⁶ 5 Pa.

[0040] Example 4: Membrane flux of different gas diffusion layers Figure 3The membrane flux of SPM-M was compared with that of three other commonly used GDLs. Sigracet 22 BB is a hydrophobic carbon paper with a microporous layer on its surface, AvCarb P75T is a hydrophobic carbon paper without a microporous layer on its surface, and HCP330P is a PTFE-modified hydrophobic carbon cloth.

[0041] Experiments revealed significant differences in membrane flux among different GDLs. The modified PM-M (SPM-M) had a membrane flux of 1.86 mL / cm². -2 min -1 Pa -1 The membrane flux of Sigracet 22 BB is 0.13 mL cm⁻¹. -2 min -1 Pa -1 The membrane flux of AvCarb P75T is 0.17 mL cm⁻¹. -2 min -1 Pa -1 The membrane flux of HCP330P is 0.24 mL cm⁻¹. -2 min -1 Pa -1 It is evident that the modified PM-M used in this invention has a significantly higher membrane flux than the other three commonly used GDLs. This results in superior CO2 mass transfer and redistribution capabilities on the PM-M surface, ensuring rapid CO2 transfer to the catalyst surface and promoting uniform CO2 distribution on the electrode surface. This effectively avoids the problems of limited reaction rates due to insufficient reactant supply and the aggravated hydrogen evolution reaction caused by excessively low local concentrations. Based on its preparation process and microstructure, the excellent membrane flux is attributed to the abundant pore structure generated by the salt template.

[0042] Example 5: Formation Mechanism of PM-M Superhydrophobic Behavior Studies have shown that the wettability of droplets on solid surfaces is mainly determined by the combined effects of surface chemical functional groups and surface morphology. Modifying surface chemical functional groups alone has limited impact on the wettability of solid surfaces. Although PVDF surfaces are rich in fluorine (F), giving them hydrophobic properties, the water contact angle of PVDF without a rough surface structure cannot exceed 120°. Therefore, it is necessary to combine the regulation of solid surface functional groups and microstructure to construct superhydrophobic surfaces. To reveal the influence of microstructures at different scales on the superhydrophobic behavior of modified PM-M, this invention used a contact angle meter and SEM to test the contact angles and microstructures of PM, modified PM (with the same modification method as SPM-M), PM-M, and modified PM-M, respectively. The results are as follows: Figure 4 As shown.

[0043] Figure 4(a) and (e) show the surface microstructure and water contact angle of PM before modification. Figure 4 In (a) and (e), it can be seen that the PM surface before modification only has a micron-scale single-scale rough structure generated by NaCl powder, which improves the surface roughness of PVDF to a certain extent, so that the water contact angle reaches 136.60°. Figure 4 Figures (b) and (f) show the surface microstructure and water contact angle of the modified PM. Figure 4 As can be seen from (b) and (f), after solvothermal treatment, PM undergoes asymmetric shrinkage of its surface, resulting in the development of micro- and nano-scale fish-scale rough structures along the micron-scale single-scale rough structure of PM, forming a dual-scale rough structure. The generation of micro- and nano-scale rough structures plays an important role in improving the hydrophobicity of the high static contact angle hydrophobic surface, significantly improving the overall hydrophobicity of PM. At this time, the water contact angle is 151.85°. Figure 4 (c) and (g) represent the surface microstructure and water contact angle of the modified PM. Figure 4 As can be seen in (c) and (g), after the conductive filler MWCNT is filled, a large number of MWCNTs wrapped by PVDF can be found on the surface of GDL. The MWCNTs are intertwined with each other to form a loose network structure with micron-scale roughness. At the same time, due to the nanoscale roughness structure generated by the exposure of MWCNTs, it is consistent with the modified PM and also has a dual-scale roughness structure. The water contact angle result is similar to the water contact angle result of the modified PM, which is 147.66°. Figure 4 (d) and (h) represent the surface microstructure and water contact angle of the modified PM, respectively. Figure 4 As shown in (d) and (h), the modified PM-M forms a multi-scale rough structure on its surface due to the combined effects of NaCl powder, solvothermal treatment, and MWCNT. This makes the modified PM-M more hydrophobic than the other three types of GDL prepared, with a water contact angle of 167.30°.

[0044] Example 6: Electrowetting stability of gas diffusion layer under high voltage over long period of time Figure 5 The changes in electrowetting properties of SPM-M surfaces under different voltages were demonstrated using 1 mol / L KOH solution, 1 mol / L K2CO3 solution, 1 mol / L KHCO3 solution, and 1 mol / L KCl solution. It should be noted that the experimental method used a stainless steel needle as the counter electrode to form a closed loop. The insertion of the stainless steel needle will cause a change in the radius of curvature of the contact angle. Therefore, the contact angle measured in this invention will be slightly smaller than the actual contact angle.

[0045] Depend on Figure 5It can be seen that within 300 min, after applying voltages of -1 V, -2 V, and -3 V to different electrolyte solutions, the contact angle of SPM-M gradually decreased with the extension of voltage application time, but the overall change was not significant. The contact angle of all four electrolyte solutions remained above 145° after 300 min of voltage application, indicating that SPM-M exhibits excellent electrowetting stability for different electrolyte solutions. To further illustrate the effect of voltage on the surface wettability of SPM-M, Figure 6 This demonstrates the rate of change of contact angle for different electrolyte solutions under different voltages. Figure 6 It can be seen that the contact angle change rate of the four different electrolyte solutions on the SPM-M surface gradually increases with the increase of voltage. This experimental result is usually described by the Young-Lippmann equation, as shown in Equation 4.

[0046] (4) Where: U is the magnitude of the applied voltage; θ V θ is the static contact angle after voltage is applied. e The static contact angle before voltage is applied; γ lg For liquid-gas surface tension; C H This represents the electric double layer formed by the solution on the surface of the GDL microporous layer. For the Young-Lippmann equation, the cosine of the static contact angle of the GDL is related to U... 2 The positive correlation indicates that increased voltage exacerbates electrowetting on the SPM-M surface, which is the primary cause of flooding and disruption of the three-phase interface stability at the GDE surface. On the other hand, due to the accumulation of charge on the surface of the GDL microporous layer under high cathode potential, the accumulated charge on the PVDF surface attracts ions and polar molecules with opposite charges from the water, thereby increasing the charge density of the electric double layer at the GDL liquid-solid interface. This significantly reduces the interfacial tension, further intensifying wetting. [ Furthermore, the charge accumulation on the PVDF surface also intensifies the formation of O–H···F hydrogen bonds between F atoms on the PVDF surface and water molecules in the droplet, thereby increasing the interaction between the droplet and the GDL surface and ultimately leading to a decrease in the contact angle.

[0047] Meanwhile, the experiment found that when the voltage was -1 V, the contact angle change rate of the four electrolyte solutions was almost the same, all remaining below 2.6%. This is almost the same as the contact angle change rate of the four electrolyte solutions when no voltage was applied. This is because of the existence of the multi-level rough structure. The droplet needs to overcome additional energy to break the gas-liquid interface and pore capillary pressure to perform electrowetting. At this time, the applied voltage failed to break this additional resistance to drive electrowetting. Therefore, the change in hydrophobic angle is mainly caused by droplet evaporation. When the applied voltage was increased to -2 V, bubbles were continuously generated at the tip of the stainless steel needle, indicating that the voltage had reached the initiation potential of the electrochemical reaction, and the oxygen evolution reaction at the cathode began. Comparing the contact angles of the four electrolyte solutions, it was found that the 1 mol / L KOH solution had the largest contact angle change rate, followed by the 1 mol / L K2CO3 and KHCO3 solutions, while the 1 mol / L KCl solution had the smallest contact angle change rate. This trend increased with increasing voltage, becoming even more pronounced at -3 V. At this voltage, the contact angle change rate was 6.70% for the 1 mol / L KOH solution, 4.89% for the 1 mol / L K2CO3 solution, 4.79% for the 1 mol / L KHCO3 solution, and 3.95% for the 1 mol / L KCl solution. This is because, compared to the other three electrolyte solutions, 1 mol / L KOH solution... A mol / L KOH solution is more alkaline. Under the prolonged action of a high-concentration alkaline environment and a high cathode potential, on the one hand, according to the Young-Lippmann equation, the application of a high cathode potential exacerbates electrowetting; on the other hand, the PVDF on the SPM-M surface exposed to the KOH solution is affected by OH... - Modification leads to a decrease in hydrophobicity. Therefore, electrowetting and prolonged exposure to high-concentration alkaline environments at high cathode potentials are important reasons for the loss of hydrophobicity and decreased durability of GDL surfaces.

[0048] Figure 7 The changes in the contact angle of 1 mol / L KOH solution on the surfaces of Sigrette 22 BB carbon paper and SPM-M under different voltages over a period of 60 min are shown. Figure 7As shown, when the voltage is -1 V, the contact angle change rate of Sigracet 22 BB carbon paper and SPM-M are almost identical, both remaining at around 0.9%. When the applied voltage is increased to -2 V, the contact angle change rate of SPM-M only increases slightly, reaching 1.32%, while the contact angle change rate of Sigracet 22 BB carbon paper increases to nearly twice that of SPM-M, at 2.63%. When the applied voltage is further increased to -3 V, the contact angle change rate of Sigracet 22 BB carbon paper increases rapidly, reaching 6.65%, while the contact angle change rate of SPM-M is only 1.42%. The experimental results show that SPM-M exhibits superior anti-electrowetting ability compared to Sigracet 22 BB carbon paper. The reasons are analyzed as follows: On the one hand, the hydrophobic reinforcing agent on the surface of Sigracet 22BB carbon paper is PTFE. Compared with PVDF, PTFE has more exposed F atoms on its surface. After accumulating electrons on the surface, the interaction force between PTFE and water molecules is stronger, which exacerbates the loss of hydrophobicity on the surface of Sigracet 22BB carbon paper. On the other hand, the unique multi-scale rough structure of SPM-M results in a significant air film between the SPM-M surface and the KOH solution, which reduces the liquid-solid contact area, allowing it to maintain high hydrophobicity even under long-term high cathode potential.

[0049] Example 7: CO2RR Stability Test of High-Concentration Salt Solutions At 200 mA cm -2 High cathode potential durability tests were conducted on different GDLs with supported catalysts at current densities, and the results are as follows: Figure 8 As shown. Figure 8 The results showed that HCP330P hydrophobic carbon cloth and AvCarb P75T carbon paper, lacking a microporous layer, experienced flooding after 40 min and 160 min, respectively. Sigracet 22 BB carbon paper, with a microporous layer, followed, with a flooding time of 830 min. This was significantly longer than the operating time of HCP330P and AvCarb P75T, nearly five times that of AvCarb P75T. This is because the Laplace pressure difference meant that the pressure the solution had to overcome to enter the GDL channels with a microporous layer was much greater than the pressure to enter the GDL channels without a microporous layer. This indicates that the presence of a microporous layer is crucial for preventing the electrode from being flooded by the electrolyte solution and for maintaining the stability of the three-phase interface at high cathode potentials. Compared to the other four materials, SPM-M showed better performance at 200 mA cm⁻¹. -2It can maintain its resistance to electrolyte solution penetration for more than 4140 minutes at current density without flooding, which is nearly 5 times that of AvCarbP75T carbon paper. This indicates that SPM-M has a much greater resistance to electrolyte solution penetration at high cathode potential than the other three materials.

[0050] To clarify the microscopic mechanism of electrolyte intrusion into SPM-M, SEM and EDS were used in combination. SEM was used to assist EDS in mapping the distribution of K element, thus clarifying the entire flooding process of SPM-M. Throughout the experiment, 1 mol / L KOH was used as the electrolyte solution, consistent with the high cathode potential durability test of SPM-M. The experiment was conducted at 200 mA cm⁻¹. -2 Performed at current density, Figure 9 The images, from top to bottom, show the SEM and K-element distributions of the SPM-M cross-section after 0 h, 10 h, 40 h, and 70 h of scouring.

[0051] like Figure 9 As shown in (a), the SPM-M section showed almost no K element distribution before scouring. After 10 h of scouring, as... Figure 9 As shown in (b), due to the excellent hydrophobicity of SPM-M, the K element is only distributed on the surface of SPM-M. With further extension of the rinsing time, the accumulation of triboelectric charges generated by the applied voltage and the sliding of the electrolyte solution on the SPM-M surface leads to changes in the local wettability of the SPM-M surface. This causes the alkaline electrolyte solution to penetrate into the interior of the SPM-M along the less hydrophobic areas. Simultaneously, the carbonate deposition produced by the continuous reaction of the alkaline electrolyte solution with CO2 further damages the hydrophobicity of the SPM-M surface, allowing the electrolyte solution to penetrate deeper into the SPM-M, such as... Figure 9 As shown in (c). After 70 hours of SPM-M flushing, the results are as follows. Figure 9 As shown in (d), the surface of SPM-M is almost completely covered by K elements. The electrolyte is immersed in the interior of GDL and migrates in both the longitudinal and transverse directions. In addition, a more obvious cone-shaped distribution of K elements is also found at the bottom, which is consistent with the seepage phenomenon of the electrode.

[0052] Example 8: Effect of different gas diffusion layers on electrocatalytic reduction of CO2 To investigate the effects of different GDL materials on CO2RR catalytic performance, the CO2RR catalytic performance of copper-loaded GDLs was evaluated using Flow-Cell in a 1 mol / L KOH alkaline electrolyte solution. Figure 10 To construct different GDE linear sweep voltammetry (LSV) curves.

[0053] from Figure 10As can be seen, the onset potential of SPM-M is -0.47 V, which is significantly higher than that of AvCarb P75T, Sigracet 22 BB, and HCP330P. Meanwhile, when the potential is less than -0.7 V, the current density of SPM-M is significantly lower than that of Sigracet 22 BB and HCP330P. This is because SPM-M has a slightly higher resistance, meaning that at the same potential, the electrochemical kinetics of SPM-M are weaker than those of Sigracet 22 BB and HCP330P. Therefore, SPM-M requires more energy to overcome the system resistance in the GDE composed of SPM-M components. This amplifies the effect of this internal resistance on the current density at low potentials. When the cathode potential is greater than -0.7 V, the current density of SPM-M is higher at the same potential. This is because SPM-M not only provides a stable three-phase interface, but its abundant pore structure and high membrane flux ensure rapid CO2 mass transfer in the GDE, promoting CO2RR.

[0054] To compare the catalytic performance of GDEs constructed from four different GDLs, the product distribution of the four different GDEs at different cathode potentials was determined by electrochemical workstation coupled with gas chromatography. The results are shown below. Figure 11 The Faraday efficiency of GDE for H2, CO, CH4, C2H4 and C2H6 was tested respectively.

[0055] Figure 11 In Figure (a), the CO2RR product distribution of the GDE constructed by SPM-M under different cathode potentials is shown. For SPM-M, within the potential range of -0.6 V to -2 V (vs. RHE), the H2 Faradaic efficiency of the GDE constructed by SPM-M is less than 35%, and the generated C products are mainly CO and C2H4, while CH4 and C2H6 account for a small proportion of the overall carbon product distribution. When the applied voltage is -0.6 V (vs. RHE), the Faradaic efficiency of C2H4 is 27.07%, which is significantly lower than that of CO. As the voltage increases, the CC coupling path becomes dominant, the Faraday efficiency of CO decreases, and the Faraday efficiency of C2H4 increases. When the applied voltage increases to -1.4 V (vs. RHE), the selectivity of the GDE constructed by SPM-M for C2H4 reaches its maximum, at which point the Faraday efficiency of C2H4 is 43.49%. Thereafter, as the voltage increases, the total Faraday efficiency of C products decreases, while the Faraday efficiency of H2 products gradually increases until flooding occurs when the voltage increases to -2.2 V (vs. RHE). Figure 11 (b) shows the CO2RR product distribution of the GDE constructed from Sigracet 22 BB at different cathode potentials, as shown in Figure 1. Figure 11As shown in (b), the product distribution trend of the diffusion electrode constructed with Sigracet 22 BB carbon paper is basically consistent with that of the diffusion electrode constructed with SPM-M. The selectivity for C2H4 reaches its highest when the applied voltage is increased to -1.2 V (vs. RHE). After that, the Faraday efficiency of H2 products gradually increases with increasing voltage, while the total Faraday efficiency of C products continuously decreases. However, compared with the GDE constructed with SPM-M, the stability of the GDE constructed with Sigracet 22 BB at high voltage is worse. Flooding occurs when the voltage is increased to -1.8 V (vs. RHE). Figure 11 (c) and (d) show the CO2RR product distribution of the GDE constructed with HCP330P carbon cloth and AvCarb P75T carbon paper, respectively. It is worth noting that in the potential range of -0.6 V to -1.2 V (vs. RHE), there is significant CH4 formation in the C product of the GDE constructed with HCP330P. In contrast, the Faraday efficiency of C2H4 remains at around 17%, indicating that the GDE constructed with HCP330P carbon cloth has better CH4 selectivity than the GDE constructed with SPM-M and Sigracet 22 BB. At the same time, the CH4 selectivity of the GDE constructed with HCP330P gradually increases with increasing voltage. When the voltage rises to -1.2 V (vs. RHE), the Faraday efficiency of CH4 is 27.78%, at which point the CH4 selectivity reaches its highest level. The GDE constructed with AvCarb P75T exhibits a minimum Faraday efficiency of 42.12% in the potential range of -0.6 V to -1.2 V (vs. RHE), which is significantly higher than the other three GDEs. Meanwhile, the GDE constructed with AvCarb P75T carbon paper and HCP330P carbon cloth shows significantly lower stability at high voltages compared to the GDEs constructed with SPM-M and Sigracet 22 BB. When the voltage is increased to -1.4 V (vs. RHE), the GDE constructed with AvCarb P75T carbon paper and HCP330P carbon cloth rapidly undergoes flooding.

[0056] To further investigate the effect of GDL on the catalytic performance of CO2RR, the Faradaic efficiency of GDE products under different voltages was calculated. The results are shown in [Figure number missing]. Figure 12 .from Figure 12 It can be seen that within the range of -0.6 V to -1.2 V (vs. RHE), the AvCarb P75T carbon paper exhibits the highest Faraday efficiency for H2 products, consistently maintaining above 40%. 2+The Faradaic efficiency of the product and total C product was significantly lower than that of the other three GDLs. This is mainly due to the lack of hydrophobic reinforcement on the surface of the AvCarb P75T carbon paper, which leads to the disruption of the three-phase interface due to electrowetting when voltage is applied. The electrolyte solution then floods the catalyst and comes into contact with the carbon fibers on the carbon paper surface, resulting in severe hydrogen evolution. HCP330P carbon cloth, Sigrette 22 BB carbon paper, and SPM-M all have excellent hydrophobicity, and compared to AvCarb P75T carbon paper, they all exhibited lower Faradaic efficiency for H2 products and higher Faradaic efficiency for C products during the catalytic process. However, despite this, from... Figure 12 In (a), it can be observed that the Faraday efficiency of H2 products of HCP330P carbon cloth increases rapidly with increasing voltage. Therefore, although superhydrophobicity is the key to ensuring the three-phase interface on the GDL surface, the lack of a microporous layer still results in its ability to block electrolytes and prevent flooding being far lower than that of Sigracet 22 BB carbon paper and SPM-M. Figure 12 As shown in (c), it is worth noting that although HCP330P carbon cloth exhibits a high total C product Faradaic efficiency, as Figure 12 In (b), we can find its C. 2+ The product's Faraday efficiency is significantly lower than that of Sigracet 22 BB carbon paper and SPM-M. 2+ The product's Faraday efficiency remained at around 15%, further indicating that the microporous layer controlled the carbon content. 2+ It also plays an important role in the selectivity of gaseous products. The presence of the microporous layer increases the contact area between CO2 and the catalyst layer, thereby promoting mass transfer and ultimately promoting the production of C. 2+ Product formation.

[0057] from Figure 12 It can be seen that both Sigracet 22 BB carbon paper and SPM-M exhibit excellent selectivity at low voltages. Within the potential range of -0.6 V to -1.6 V (vs. RHE), the product Faradaic efficiency changes of Sigracet 22 BB carbon paper and SPM-M are essentially consistent. 2+The Faraday efficiency of both the product and the total C product showed a trend of first increasing and then decreasing. Although the Faraday efficiency of the H2 product gradually increased with increasing voltage, it remained below 30% within this range, indicating that the three-phase interface could exist stably. With further increases in cathode potential, SPM-M exhibited significantly better stability at higher cathode potentials than Sigracet 22 BB carbon paper. When the cathode potential exceeded -1.6 V (vs. RHE), Sigracet 22 BB carbon paper rapidly flooded, while SPM-M only experienced flooding when the cathode potential exceeded -2.0 V (vs. RHE). This demonstrates that SPM-M's high-potential stability is significantly superior to that of Sigracet 22 BB carbon paper. The excellent high-voltage stability of SPM-M is mainly due to its unique multi-scale rough structure and multi-scale pore distribution. The multi-scale rough structure on the SPM-M surface effectively suppresses the influence of external applied voltage and electrolyte solution slippage on the electrowetting of the SPM-M surface. At the same time, the multi-scale channel structure forms a microporous layer on the SPM-M surface, increasing the pressure required for the solution to break through GDL. This promotes mass transfer while effectively blocking the electrolyte solution and preventing flooding. The combined effect of these two factors significantly improves the stability of the three-phase interface and catalytic performance during the CO2RR process.

Claims

1. Application of multi-scale rough structure gas diffusion membranes in the electrochemical reduction of CO2; The multi-scale rough structure gas diffusion membrane is used to construct the gas diffusion electrode and to stabilize the gas-liquid-solid three-phase interface in the flow electrolysis cell. The multi-scale rough structure gas diffusion membrane includes: The support layer is a three-dimensional through-frame structure formed by melting polyvinylidene fluoride and NaCl particles of the first size and then removing the NaCl. A microporous layer, disposed on the support layer, is a conductive and hydrophobic layer formed by melting and molding polyvinylidene fluoride, multi-walled carbon nanotubes and second-sized NaCl particles and then removing the NaCl. The surface of the gas diffusion membrane is subjected to solvent thermal treatment to form a fish-scale-like rough structure, which gives it superhydrophobic properties.

2. A method for electrochemically reducing carbon dioxide, comprising the following steps: A gas diffusion electrode is obtained by loading a catalyst onto the surface of a multi-scale rough gas diffusion film. The gas diffusion electrode is placed in a flowing electrolytic cell, and electrochemical reduction is performed by applying a potential using CO2 gas as the reaction source. The multi-scale rough structure gas diffusion membrane includes: The support layer is a three-dimensional through-frame structure formed by melting polyvinylidene fluoride and NaCl particles of the first size and then removing the NaCl. A microporous layer, disposed on the support layer, is a conductive and hydrophobic layer formed by melting and molding polyvinylidene fluoride, multi-walled carbon nanotubes and second-sized NaCl particles and then removing the NaCl. The surface of the gas diffusion membrane is subjected to solvent thermal treatment to form a fish-scale-like rough structure, which gives it superhydrophobic properties.

3. The application according to claim 1 or the method according to claim 2, characterized in that: The particle size range of the NaCl particles in the support layer is 150-300 μm; The NaCl particles in the microporous layer have a particle size range of 50-100 μm.

4. The application according to claim 1 or 3, or the method according to claim 2 or 3, characterized in that: In the microporous layer, the mass ratio of the polyvinylidene fluoride, the multi-walled carbon nanotubes, and the NaCl particles is 1:0.05-0.4:

7.

5. The application according to claim 1, 3, or 4, or the method according to claim 2, 3, or 4, characterized in that: The solvent heat treatment uses a treatment solution including alcohol solvents, co-solvents, and water; The alcohol solvent is an alcohol with 3-7 carbon atoms; In the treatment solution, the content of the alcohol solvent is 3-5.5 mL, the content of the co-solvent is dilute HCl, which is 12-17 mL, and the content of water is 15 mL.

6. The application according to any one of claims 1 or 3-5, or the method according to any one of claims 2 or 3-5, characterized in that: The solvent heat treatment is performed at a temperature of 100-200℃ for 1-10 hours.

7. The application according to any one of claims 1 or 3-6, or the method according to any one of claims 2 or 3-6, characterized in that: A nano-copper catalyst is dispersed in isopropanol, water and Nafion solution to form an ink, and the ink is drop-coated onto the surface of the scale-roughened gas diffusion film to obtain a gas diffusion electrode.

8. The application according to any one of claims 1 or 3-7, or the method according to any one of claims 2 or 3-7, characterized in that: The conditions for the electrochemical reduction are as follows: The electrolyte is a KOH alkaline electrolyte solution; The gas flow rate is 100-300 mL / min; Voltage ranges from -0.6 to 2 V (vs. RHE), current density ranges from 50 to 300 mA·cm. -2 .

9. A gas diffusion electrode, comprising: Multi-scale rough structure gas diffusion membrane; And the electrocatalyst supported on its surface; The multi-scale rough structure gas diffusion membrane includes: The support layer is a three-dimensional through-frame structure formed by melting polyvinylidene fluoride and NaCl particles of the first size and then removing the NaCl. A microporous layer, disposed on the support layer, is a conductive and hydrophobic layer formed by melting and molding polyvinylidene fluoride, multi-walled carbon nanotubes and second-sized NaCl particles and then removing the NaCl. The surface of the gas diffusion membrane is subjected to solvent thermal treatment to form a fish-scale-like rough structure, which gives it superhydrophobic properties.

10. A system for the electrochemical reduction of carbon dioxide, comprising: The gas diffusion electrode according to claim 9; Flow electrolytic cell; Electrolyte solution; CO2 gas supply device.

Images