Preparation method of cathode catalyst with multilevel structure for electro-catalysis of carbon dioxide reduction

Abstract

The invention relates to a preparation method of a cathode catalyst with a multilevel structure for electro-catalysis of carbon dioxide reduction, and belongs to the field of new energy nano materials and the technical field of electro-catalysis. The invention aims to solve the problems of low selectivity in acidic electrolyte, salt deposition caused by introduction of excessive potassium ions and the like. According to the main scheme, an electrostatic spinning method is adopted for preparing a Zn < 2 + > / PAN nanofiber membrane, then the Zn < 2 + > / PAN nanofiber membrane is soaked in a solution containing nickel salt and 2-methylimidazole for in-situ growth of ZIF-8, meanwhile, adsorption of nickel can be promoted, and finally, high-temperature pyrolysis is conducted to obtain the nitrogen-doped carbon nanotube coated nickel nanoparticles (Ni-coated NCNT / HPNF) with the surfaces modified by hollow porous carbon nanofibers of a multilevel structure. Wherein the hollow porous carbon nanofiber is used as a'trunk ', the nitrogen-doped carbon nanotube is used as a'branch', and the nickel nanoparticles are embedded as a'fruit '. The hierarchical structure can enrich K < + > in the solution in the acidic electrolyte, so that side reaction hydrogen evolution can be inhibited, and the problem of salt deposition is also relieved.

Description

Technical Field

[0001] The present invention relates to a method for preparing a cathode catalyst for electrocatalytic carbon dioxide reduction with a multi-level structure, belonging to the field of new energy nanomaterials and electrocatalytic technology. Background Art

[0002] The electrocatalytic carbon dioxide reduction reaction (CO2RR) driven by renewable electricity to convert CO2 into high-value-added fuels and chemicals is an important approach to achieving a sustainable carbon cycle. Among the various reduction products, carbon monoxide (CO) has attracted much attention due to its industrial value as a key raw material for Fischer-Tropsch synthesis and its high efficiency synthesis with only two electron transfers. However, the practical application of current CO2RR technology still faces challenges. The key lies in how to construct an efficient catalytic system, which requires the simultaneous optimization of the synergistic effect of catalyst performance and electrolyte system.

[0003] In recent years, nickel-based catalysts have become a hot topic in CO₂RR research due to their cost advantages and excellent CO selectivity. Studies have shown that these catalysts can achieve high Faradaic efficiencies and current densities in alkaline and neutral electrolytes. Their excellent performance stems from the enrichment of hydroxide ions (OH) at the catalyst-electrolyte interface. This localized accumulation creates a significant pH gradient on the electrode surface, creating an alkaline microenvironment at the interface. This microenvironment effectively suppresses the competitive hydrogen evolution reaction (HER), significantly improving CO selectivity.

[0004] However, CO2RR under neutral and alkaline conditions still faces significant challenges, mainly due to the OH - Reacts with CO2 to form bicarbonate (HCO3 - ) and carbonate (CO3 2- ) ions. This process raises three key questions:

[0005] (1) Carbonate deposition will block the pores of the gas diffusion electrode and hinder CO2 mass transfer;

[0006] (2) Sediments will destroy the hydrophobicity of the electrode and aggravate the flooding phenomenon.

[0007] (3) Carbonate deposition will significantly reduce the utilization efficiency of CO2.

[0008] To circumvent the carbonate problem, researchers turned their attention to the acidic electrolyte system. Although this environment can effectively inhibit the formation of carbonate, it is + Too high a concentration will aggravate the hydrogen evolution reaction (HER) and inhibit the CO2 reduction kinetics. To solve this contradiction, alkali metal ions (such as K + ) becomes the key strategy: it weakens the cathode electric field through the electrostatic shielding effect, suppressing the H3O +migration, thereby reducing the HER competitive reaction activity and promoting CO2 reduction selectivity. However, high concentrations of K + It may cause salt deposition, so a balance solution needs to be designed - while maintaining the low K of the bulk electrolyte + While increasing the concentration, efficient K at the reaction interface can be achieved through local regulation strategies (such as interface engineering or microenvironment optimization). + This direction is crucial for achieving efficient and stable CO2 electroreduction.

[0009] Studies have shown that K can be precisely controlled by catalyst morphology design. + The spatial distribution of ions at the reaction interface is achieved by utilizing the geometric field effect. This is specifically manifested in three mechanisms:

[0010] (1) The porous carbon framework increases the local basicity through geometric confinement, thereby inhibiting the HER while enhancing the CO2RR activity;

[0011] (2) Hollow nanostructures with surface channels can selectively adsorb K + and OH - , while hindering H + diffusion, thereby effectively inhibiting HER side reactions and promoting CO2 reduction;

[0012] (3) The nanoneedle array generates a local strong electric field through the tip effect, driving K + Directed aggregation forms highly active catalytic sites.

[0013] Although these structural designs have shown significant advantages, existing research is mostly limited to the independent effects of a single structure, and the systematic exploration of the synergistic effects of multi-level structures is still insufficient. This research gap mainly stems from the technical challenge - how to effectively integrate the above-mentioned geometric features (such as porous confinement, hollow channels and nanoneedle arrays) in a single catalyst system. In-depth analysis of the synergistic mechanism of these structures will provide new design ideas for the development of efficient CO2RR catalysts. Therefore, the present invention attempts to synthesize in situ grown nickel nanoparticles on the surface of hollow porous carbon nanofibers wrapped in nitrogen-doped carbon nanotubes Ni 3.4 The hierarchical structure of @NCNT / HPNF consists of hollow porous carbon nanofibers as the "trunk"; nitrogen-doped carbon nanotubes as the "branches" and nickel nanoparticles as the "fruits". This structure promotes the diffusion of CO2 to the reaction interface and improves the electrocatalytic efficiency. More importantly, this combined structure induces local K + Enrichment, effectively blocking H + migration, thereby inhibiting HER and enhancing CO2RR under acidic conditions. Summary of the Invention

[0014] The present invention aims to provide a simple and efficient catalyst synthesis method to solve the problem of K + The key contradiction in concentration control: too low a concentration will intensify the hydrogen evolution reaction (HER), while too high a concentration will easily cause salt deposition problems.

[0015] To this end, we designed a multi-level structure Ni 3.4 @NCNT / HPNF cathode catalyst has the following unique advantages:

[0016] 1) Through the synergistic effect of multi-scale structures, at low body K + Dynamic enrichment of K at the reaction interface is achieved under high concentration conditions;

[0017] 2) Achieve triple regulatory effects simultaneously: inhibit H + Migration to alleviate HER competition reactions; avoid salt crystallization caused by high electrolyte concentrations; maintain a highly active CO2 reduction interface microenvironment;

[0018] This design breaks through the limitations of traditional electrolyte concentration regulation and provides a new catalyst solution for CO2RR in acidic systems.

[0019] In order to solve the above problems, the present invention adopts the following technical solutions:

[0020] The present invention provides a method for preparing a cathode catalyst for electrocatalytic carbon dioxide reduction using a multi-level structure. First, Zn is prepared by electrospinning technology. 2+ / PAN nanofiber membrane, and the obtained nanofiber membrane was immersed in an aqueous solution containing nickel salt and 2-methylimidazole, and the uniform adsorption of nickel ions was achieved by in situ growth of ZIF-8 metal organic framework, thereby obtaining Ni 2+ / ZIF-8 / PAN precursor, and then the precursor is subjected to high-temperature carbonization treatment to finally obtain a catalyst with a multi-level structure of nitrogen-doped carbon nanotubes coated with nickel nanoparticles loaded on hollow porous nanofiber catalysts.

[0021] In the above technical solution, the preparation method comprises the following steps:

[0022] Step 1: Add zinc acetate Zn(CH3COO)2 and polyacrylonitrile PAN into N,N-dimethylformamide DMF solution and stir to dissolve.

[0023] Step 2: electrospin the above solution to obtain Zn 2+ / PAN nanofiber membrane;

[0024] Step 3: Zn 2+ / PAN nanofiber membrane was vacuum dried;

[0025] Step 4: Immerse the nanofiber membrane obtained above in an aqueous solution containing nickel salt and 2-methylimidazole and heat it to in situ grow ZIF-8 on the nanofiber and adsorb nickel ions to obtain Ni 2+ / ZIF-8 / PAN;

[0026] Step 5: Ni 2+ / ZIF-8 / PAN washing and drying.

[0027] Step 6: Ni 2+ / ZIF-8 / PAN composite was carbonized at high temperature to obtain nickel nanoparticles Ni@NCNT / HPNF coated with nitrogen-doped carbon nanotubes on the surface of hollow porous carbon nanofibers;

[0028] In the above technical solution, in step 1, the mass ratio of Zn(CH3COO)2 to PAN is 1.1:1, the mass percentage concentration of PAN in DMF solution is 7.9wt%, and the stirring time at room temperature is 24h.

[0029] In the above technical solution, in step 2, the electrospinning voltage is 15 kV and the pushing speed is 0.03 mL min -1 , the spinning temperature was 40 °C, and the distance between the syringe needle tip and the collector was 18 cm.

[0030] In the above technical solution, in step 3, the vacuum drying temperature is 60°C.

[0031] In the above technical solution, in step 4, 2-methylimidazole, Zn 2+ / PAN nanofiber membrane and nickel acetylacetonate were added into the aqueous solution in a mass ratio of 65:3:1 and heated to 80°C for 3 h.

[0032] In the above technical solution, in step 5, deionized water is used for washing, and the drying temperature is 60°C.

[0033] In the above technical solution, in step 6, the carbonization temperature is 900°C, the heating rate is 2°C / min, the heat treatment time is 2h, and the atmosphere is Ar.

[0034] The present invention has the following advantages:

[0035] 1) Using electrospinning technology to 2+ The ZnO2 is evenly distributed on the nanofibers. Then, in a solution containing 2-methylimidazole, 2-methylimidazole can react with the ZnO2 on the surface of the nanofiber membrane. 2+ The coordination in situ forms ZIF-8, which further promotes the formation of Ni 2+During the subsequent high-temperature treatment, the precursor undergoes the following structural evolution: the wrapping of the surface ZIF-8 layer leads to the formation of a hollow structure; the volatilization of the Zn component inside the fiber creates a porous structure; the adsorbed Ni 2+ It is reduced to metallic Ni nanoparticles; these Ni nanoparticles catalyze the carbon layer on the surface to form nitrogen-doped carbon nanotubes, thus forming a multi-level structure composed of hollow porous carbon nanofibers; nitrogen-doped carbon nanotubes serve as "branches" and the wrapped nickel nanoparticles serve as "fruits".

[0036] 2) Hollow, porous, and carbon tube structures each have their own effects on K in solution + This multi-level structure integrates three structures, even in the presence of low K + In the bulk solution, due to this multi-level structure, K + enrichment, so that K + The high concentration creates a slightly alkaline environment, which can significantly inhibit HER and enhance CO2RR. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 Ni prepared in Example 1 3.4 Detailed characterization results of the @NCNT / HPNF catalyst, including (a, b) HAADF-STEM images and (c) EDX elemental mapping distribution.

[0038] Figure 2 Ni prepared in Example 2 3.4 Detailed characterization results of the @NF catalyst, including (a) TEM image and (b) EDX elemental mapping distribution.

[0039] Figure 3 Ni prepared in Example 1 and Example 2 3.4 Electrochemical performance diagram of @NCNT / HPNF catalyst under alkaline conditions, including (a) linear sweep voltammetry curve and (b) CO and H2 Faraday effect bar graph;

[0040] Figure 4 Ni prepared in Example 1 3.4 Practical issues with NCNT / HPNF catalysts under alkaline conditions. (a) Photo of white crystals precipitated in the flow cell gas channel and on the gas diffusion electrode; (b) XRD pattern of the white crystals.

[0041] Figure 5 Ni prepared in Examples 1 and 2 3.4 @NCNT / HPNF and Ni 3.4 Electrochemical performance of @NF catalyst in acidic environment in flow cell. (a) Ni 3.4@NCNT / HPNF with or without K + Faraday effect bar graph of CO and H2 in (b)Ni 3.4 @NCNT / HPNF and Ni 3.4 Linear sweep voltammetry curve of @NF catalyst, (c) the corresponding CO and H2 Faraday effect bar graph, (d) the single-pass conversion efficiency at different OO2 flow rates.

[0042] Figure 6 Ni prepared in Example 1 3.4 Contact angle of the gas diffusion electrode of the NCNT / HPNF catalyst before and after acidic electrochemical performance testing. (a) Contact angle of the gas diffusion electrode before and after electrochemical performance testing. (b) Contact angle of the gas diffusion electrode after the electrochemical performance testing.

[0043] Figure 7 The influence characteristics of different catalyst structures on the spatial distribution of K+ are presented in detail. DETAILED DESCRIPTION

[0044] The present invention will be further described below with reference to specific implementation examples.

[0045] First, Zn was prepared by electrospinning 2+ / PAN nanofiber membrane, when the membrane is immersed in an aqueous solution containing nickel salt and 2-methylimidazole, ZIF-8 can be grown in situ on the surface of the nanofiber membrane, while also promoting the growth of Ni 2+ Uniform adsorption, followed by high-temperature carbonization treatment, to obtain a multi-level structure Ni 3.4 @NCNT / HPNF catalyst.

[0046] The principle is to use electrostatic spinning technology to 2+ The Zn 2+ Coordinated with 2-methylimidazole and in situ generated ZIF-8. The formation of the ZIF-8 layer can effectively promote the Ni 2+ During the subsequent high-temperature heat treatment, the precursor undergoes the following structural evolution:

[0047] 1) The surface ZIF-8 layer promotes the formation of a hollow structure;

[0048] 2) The Zn component inside the fiber evaporates to produce a porous structure;

[0049] 3) Adsorbed Ni 2+ Reduced to metallic Ni nanoparticles;

[0050] 4) Ni nanoparticles catalyze the carbon layer to form nitrogen-doped carbon nanotubes in situ.

[0051] Finally, a hierarchical structure consisting of hollow porous carbon nanofibers ("trunk"), nitrogen-doped carbon nanotubes ("branches"), and Ni nanoparticles embedded therein ("fruits") was obtained.

[0052] The preparation process of the cathode catalyst for the multi-level structure electrocatalytic carbon dioxide reduction is as follows:

[0053] Step 1) zinc acetate (Zn(CH3COO)2) and polyacrylonitrile (PAN) are added to N,N-dimethylformamide solution (DMF) and stirred to dissolve;

[0054] Step 2) electrospinning the above solution to obtain Zn 2+ / PAN nanofiber membrane;

[0055] Step 3) Zn 2+ / PAN nanofiber membrane was vacuum dried;

[0056] Step 4) The nanofiber membrane obtained above is immersed in an aqueous solution containing nickel salt and 2-methylimidazole, heated, and in situ ZIF-8 is grown on the nanofiber and nickel ions are adsorbed to obtain Ni 2+ / ZIF-8 / PAN;

[0057] Step 5) Ni 2+ / ZIF-8 / PAN washing and drying.

[0058] Step 6) Ni 2+ / ZIF-8 / PAN composite was carbonized at high temperature to obtain nickel nanoparticles Ni@NCNT / HPNF coated with nitrogen-doped carbon nanotubes on the surface of hollow porous carbon nanofibers;

[0059] In the above step 1), the mass ratio of Zn(CH3COO)2 to PAN is 1.1:1, the mass percentage concentration of PAN in DMF solution is 7.9wt%, and the stirring time at room temperature is 24h.

[0060] In step 2), the electrospinning voltage was 15 kV and the pushing speed was 0.03 mL min -1 , the spinning temperature was 40 °C, and the distance between the syringe needle tip and the collector was 18 cm.

[0061] In the above step 3), the vacuum drying temperature is 60°C.

[0062] In the above step 4), 2-methylimidazole, Zn 2+ / PAN nanofiber membrane and nickel acetylacetonate were added into the aqueous solution at a mass ratio of 65:3:1 and heated at 80 °C for 3 h.

[0063] In the above step 5), deionized water is used for washing and the drying temperature is 60°C.

[0064] In the above step 4), the carbonization temperature is 900° C., the heating rate is 2° C. / min, the heat treatment time is 2 h, and the atmosphere is Ar.

[0065] Example 1

[0066] The specific preparation steps are as follows:

[0067] 1) Add 660 mg Zn(CH3COO)2 and 600 mg PAN to 8 mL DMF solution and stir at room temperature for 24 h to form a homogeneous solution;

[0068] 2) The mixed solution was placed in a 10 mL graduated cylinder. The inner diameter of the needle was 0.4 mm, the outer diameter was 0.7 mm, the electrospinning voltage was 15 kV, and the pushing speed was 0.03 mL min -1 , the spinning temperature was 40 °C, and the distance between the syringe needle tip and the collector was 18 cm;

[0069] 3) Vacuum drying at 60°C overnight to obtain Zn 2+ / PAN nanofiber membrane;

[0070] 4) 3.25g of 2-methylimidazole solution was added to 50mL of 3.4mM nickel acetylacetonate solution and stirred until completely dissolved. Then 150mg of the above-obtained Zn 2+ / PAN nanofiber membranes were immersed in the above three solutions respectively, and they were heated to 80℃ and kept for 3h;

[0071] 5) The nanofibers were washed by immersing in an aqueous solution and dried at 60°C to obtain Ni 3.4 / ZIF-8 / PAN;

[0072] 6) Get Ni 3.4 The Ni / ZIF-8 / PAN composite was carbonized at 900℃ at a heating rate of 2℃ / min under Ar atmosphere for 2h to obtain a hierarchical structure. 3.4 @NCNT / HPN catalyst;

[0073] 7) Figure 1 (a) shows the prepared Ni 3.4 @NCNT / HPNF presents a multi-level structure, forming a "trunk" composed of hollow porous carbon nanofibers; nitrogen-doped carbon nanotubes as "branches", and nickel nanoparticles wrapped therein as "fruits". Figure 1 A clear core-shell structure was observed in (b), confirming that the nanoparticles were encapsulated in the carbon layer. Figure 2The EDX element mapping in (c) further confirms that the nitrogen element is successfully doped on the carbon fibers and carbon nanotubes, and the nickel metal particles are also uniformly dispersed on the fibers and inside the carbon nanotubes.

[0074] Example 2

[0075] The steps of Example 2 are similar to those of Example 1, except that 2-methylimidazole is not added in step 4), and other conditions remain unchanged.

[0076] Figure 2 The prepared Ni 3.4 / NF presents a nanofibrous structure of carbon-coated nickel nanoparticles without forming carbon nanotubes and hollow structures. Figure 2 The EDX elemental mapping in (b) confirms that Ni metal nanoparticles are dispersed on the fibers and N is mainly doped on the carbon nanofibers.

[0077] Figure 3 Ni prepared in Examples 1 and 2 3.4 @NCNT / HPNF and Ni 3.4 Electrochemical performance testing of the @NF catalyst under alkaline conditions in a flow cell. Figure 3 The linear sweep voltammetry curve in (a) was tested under the following conditions: in a CO2-saturated 1 M KOH electrolyte, the scan rate was 5 mV s -1 , confirmed that Ni 3.4 The multi-level structure of NCNT / HPNF has a current density of up to 420 mA cm at a voltage of -1.2 V. -2 , Ni 3.4 @NF only 90mA cm -2 , indicating that this multi-level structure can increase the activity of CO2RR. Figure 3 The Faraday efficiency test range of (b) is from -0.3V to -1.0V, Ni 3.4 @NCNT / HPNF CO selectivity (FE) in a wide voltage range CO ) is close to 100%, but Ni 3.4 @NF is less than 50%. This multi-level structure is proven to promote CO production.

[0078] Figure 4 Ni prepared in Example 1 3.4 The main problem of electrochemical testing of NCNT / HPNF under alkaline conditions. Figure 4 (a) shows that white crystals appear on the gas channels and gas diffusion electrodes during long-term electrolysis. Figure 4 The XRD pattern of (b) confirms that the white crystals are mainly a mixture of potassium bicarbonate and potassium carbonate, with potassium bicarbonate as the main component. This may be due to CO2+OH-=HCO3- .

[0079] Figure 5 Ni prepared in Examples 1 and 2 3.4 @NCNT / HPNF and Ni 3.4 The electrochemical performance test results of @NF catalyst in acidic environment. Figure 5 In the Faraday efficiency test in (a), the voltage range was -0.8V to -1.0V, and a phytic acid solution with pH = 1.5 was used as the electrolyte. The addition of 0M and 1M KCl was investigated. The results show that the introduction of KCl under acidic conditions + After that, the hydrogen evolution side reaction was significantly suppressed and CO2RR was promoted. Therefore, the subsequent tests used a phytic acid solution with pH = 1.5 containing 1M KCl as the electrolyte. Figure 5 Linear sweep voltammetry curve (scan rate: 5 mV s) -1 ) shows that Ni 3.4 NCNT / HPNF has a current density of up to 500 mA cm at -1.6 V. -2 , and Ni 3.4 @NF is only 67mA cm -2 . Figure 5 The Faraday efficiency test (voltage range: -0.8V to -1.5V) in (c) further shows that Ni 3.4 The FEc0 of @NCNT / HPNF remains at 100%, while Ni 3.4 @NF is only 20%, confirming the multi-level structure of Ni 3.4 @NCNT / HPNF has excellent selectivity for CO in acidic electrolyte. In addition, Figure 5 (d) Tests were performed on the single-pass CO conversion efficiency (SPCE) at various gas flow rates (2, 5, 10, 15, and 20 sccm). The results show that as the flow rate increases, the FEc0 gradually increases, but the SPCE gradually decreases. At the lowest flow rate of 2 sccm, the SPCE reaches a maximum of 74.2%.

[0080] Figure 6 Ni prepared in Example 1 3.4 @Contact angle of gas diffusion electrode before and after NCNT / HPNF test, Figure 6 The results in (a) show that the contact angle before the test is 137.3°. Figure 6 The result in (b) shows that after the test, there is 135.1°, indicating that Ni 3.4 After the @NCNT / HPNF catalyst was tested under acidic conditions, the hydrophobicity of the gas diffusion electrode did not change significantly, and no obvious carbonate deposition was observed.

[0081] Figure 7 The effects of hollow structure, porous structure, tip structure and their composite structure on K + The impact of distribution. Figure 7 In (a), it can be clearly observed that the pore area appears red (representing high K + concentration), while the non-porous area is white (representing low K + concentration), confirming that the porous structure is beneficial to K + enrichment. Figure 7 (b) shows that the tip of the carbon nanotube K + The concentration increased significantly, indicating that the tip structure can promote K + adsorption. Figure 7 Further comparison in (c) reveals that the K + The concentration is significantly higher than that of the solid part of the outer surface, indicating that the hollow structure can effectively concentrate K + . Figure 7 (d) shows that when the porous, hollow and pointed structures are combined, K + The enrichment in the pores, hollow cavities and tip regions is enhanced, and these effects have a synergistic effect. 3.4 The multi-level structure design of NCNT / HPNF can significantly improve K + enrichment capacity, thereby optimizing the catalytic performance.

Claims

1. A method for preparing a cathode catalyst for electrocatalytic carbon dioxide reduction with a multi-level structure, characterized by: Preparation of Zn by electrospinning 2+ / PAN nanofiber membrane, which was then immersed in an aqueous solution containing nickel salt and 2-methylimidazole, and ZIF-8 was in situ grown on the nanofibers. Finally, high-temperature carbonization treatment was performed and high-temperature pyrolysis was performed to obtain nitrogen-doped carbon nanotubes wrapped with nickel nanoparticles on the surface of hollow porous carbon nanofibers with a multi-level structure.

2. The method for preparing a cathode catalyst for electrocatalytic carbon dioxide reduction with a multi-level structure according to claim 1, characterized in that: The steps include: Step 1, adding zinc acetate Zn(CH3COO)2 and polyacrylonitrile PAN to N,N-dimethylformamide DMF solution, stirring and dissolving; Step 2: electrospin the above solution to obtain Zn 2+ / PAN nanofiber membrane; Step 3: Zn 2+ / PAN nanofiber membrane was vacuum dried; Step 4: Immerse the nanofiber membrane obtained above in an aqueous solution containing nickel salt and 2-methylimidazole and heat it to in situ grow ZIF-8 on the nanofiber and adsorb nickel ions to obtain Ni 2+ / ZIF-8 / PAN; Step 5: Ni 2+ / ZIF-8 / PAN washing and drying; Step 6: Ni 2+ / ZIF-8 / PAN composite was carbonized at high temperature to obtain nickel nanoparticles Ni@NCNT / HPNF coated with nitrogen-doped carbon nanotubes on the surface of hollow porous carbon nanofibers.

3. The method for preparing a cathode catalyst for electrocatalytic carbon dioxide reduction with a multi-level structure according to claim 2, characterized in that: In step 1, the mass ratio of Zn(CH3COO)2 to PAN is 1.1:1, the mass percentage concentration of PAN in DMF solution is 7.9wt%, and the stirring time at room temperature is 24h.

4. The method for preparing a cathode catalyst for electrocatalytic carbon dioxide reduction with a multi-level structure according to claim 2, characterized in that: In step 2, the electrospinning voltage was 15 kV and the flow rate was 0.03 mL min -1 , the distance between the needle and the receiver is 18 cm, thus obtaining Zn 2+ / PAN nanofiber membrane.

5. The method for preparing a cathode catalyst for electrocatalytic carbon dioxide reduction with a multi-level structure according to claim 2, characterized in that: In step 3, the vacuum drying temperature is 60°C.

6. The method for preparing a cathode catalyst for electrocatalytic carbon dioxide reduction with a multi-level structure according to claim 2, characterized in that: In step 4, 2-methylimidazole, Zn 2+ / PAN nanofiber membrane and nickel acetylacetonate were added into the aqueous solution at a mass ratio of 65:3:1 and heated at 80 °C for 3 h.

7. The method for preparing a cathode catalyst for electrocatalytic carbon dioxide reduction with a multi-level structure according to claim 2, characterized in that: In step 5, Ni is washed with deionized water. 2+ The solution of / ZIF-8 / PAN nanofiber membrane changed from turbid white to colorless, and the drying temperature was 60℃.

8. The method for preparing a cathode catalyst for electrocatalytic carbon dioxide reduction with a multi-level structure according to claim 2, characterized in that: In step 6, the carbonization temperature is 900° C., the heating rate is 2° C. / min, the heat treatment time is 2 h, and the atmosphere is Ar.

Images