Efficient CO2 electroreduction method and device for anode and cathode acidic electrolyte connected in series

Abstract

The invention discloses an efficient CO2 electroreduction method and device for anode and cathode acid electrolyte connected in series, and the method comprises the following steps: pumping an acid electrolyte into an anode chamber, and enabling the acid electrolyte to react on the surface of an anode electrode to obtain an acid electrolyte containing dissolved oxygen; an acidic electrolyte containing dissolved oxygen is introduced into the cathode chamber, and the dissolved oxygen generates an OOH * intermediate at the cathode electrode; cO2 is introduced into the surface of the catalyst layer of the cathode gas diffusion electrode, the OOH * intermediate can reduce the energy barrier of CO2 molecule activation, and a stable * COOH intermediate and a stable * OCHO intermediate are obtained; and a * OCHO intermediate, the * OCHO intermediate continuing to be electrically reduced to form a product. The acidic electrolyte is introduced from the anode side, the coupling anode OER is driven by the acidic electrolyte from the anode side to the cathode side, the proton concentration on the two sides is effectively balanced, and continuous and stable operation of CO2 electroreduction is facilitated; the dissolved oxygen generated by the anode OER can participate in CO2 electroreduction, and the dissolved oxygen in the electrolyte is beneficial to adjusting the oxidation state of the catalyst in the CO2 electroreduction process, so that an efficient catalytic environment is maintained; meanwhile, the OOH * intermediate can reduce the energy barrier of CO2 molecule activation and stabilize the intermediate of the ECO2R product, so that the conversion efficiency of CO2 electroreduction is improved, and the efficient ECO2R process is realized.

Description

Technical Field

[0001] The present invention relates to the technical field of electro-reduction of CO2, and in particular to a method and a device for electro-reduction of CO2. Background Art

[0002] As global climate change and environmental problems become increasingly severe, carbon dioxide (CO2) emission reduction and resource utilization have become research hotspots. Electrochemical CO2 reduction (ECO2R) is an effective way to achieve CO2 resource utilization. It can use renewable electricity to convert CO2 into high-value-added chemicals and fuels, such as carbon monoxide (CO), methane (CH4), ethylene (C2H4), formic acid (HCOOH) and other compounds. These compounds can be used as fuels or chemical raw materials to replace fossil resources, thereby achieving carbon cycle and sustainable utilization of resources.

[0003] The electrolyte environment is an important part of the ECO2R process. It not only acts as a conductive medium for ions, but also directly affects the reaction environment on the catalyst surface, thereby affecting the efficiency of the reaction and the selectivity of the product. Therefore, the choice of electrolyte is crucial to the performance of ECO2R. The commonly used electrolytes in ECO2R are mainly neutral and alkaline environments, which can effectively inhibit the hydrogen evolution reaction (HER) side reaction, but CO2 combines with OH- to form carbonate (HCO3 - / CO3 2- ), blocking the micropores of the gas diffusion electrode (GDE) and causing a decrease in mass transfer efficiency, limiting the single-pass utilization efficiency (SPCE) of CO2, which is not conducive to industrial applications.

[0004] Therefore, it is a current research trend to conduct ECO2R based on acidic electrolytes to improve carbon conversion efficiency. When hydronium ions are used as proton donors for acidic ECO2R, the formation of carbonates can be inhibited; at the same time, when water is used as a proton source in the acidic medium, the carbonates produced in the diffusion layer can be converted into CO2 through abundant protons. However, due to the high proton concentration in the acidic electrolyte, the competitive HER is kinetically faster than the CO2 electrolysis process, which reduces the selectivity of the product, that is, reduces the yield of the product.

[0005] Therefore, the key to suppressing the competitive side reaction HER of the acidic ECO2R process is to regulate the local reaction environment on the catalyst surface. In the prior art, the following two methods are usually used to regulate the local reaction environment on the catalyst surface. One is catalyst selection and surface modification, that is, using catalysts with high CO2 reduction selectivity and low HER activity, such as indium, tin, and bismuth. These catalysts have high selectivity for CO2 reduction under acidic conditions; and by modifying organic molecules, ligands or metal oxides on the catalyst surface, such as by modifying nitrogen-doped carbon materials on the catalyst surface, the selectivity of the catalyst for CO2 reduction can be improved. The second is local pH regulation, that is, by adjusting the ion concentration in the electrolyte to design a microenvironment on the electrode surface, such as adding alkali metal cations, changing the distribution of the double-layer electric field, and suppressing the migration of hydronium ions to regulate the local pH value near the electrode, thereby suppressing HER.

[0006] Although the hydrogen evolution side reaction (HER) of CO2 electroreduction in acidic electrolytes can be suppressed to some extent by catalyst selection and local pH regulation, the conversion and selectivity of products in acidic ECO2R are still limited at high current density. It is urgent to explore electrolysis processes to suppress HER and improve ECO2R performance in acidic environments to promote the development of CO2 electroreduction technology. Summary of the invention

[0007] The technical problem to be solved by the present invention is to provide a high-efficiency CO2 electroreduction method and device with an anode and a cathode acidic electrolyte connected in series, which can effectively improve the product conversion rate of CO2 electroreduction and reduce the overall overpotential energy consumption.

[0008] In order to solve the above technical problems, in the first aspect, the present invention provides a highly efficient CO2 electroreduction method with an anode and a cathode acidic electrolyte connected in series, which adopts the following technical solutions:

[0009] An efficient CO2 electroreduction method with an anode and a cathode acidic electrolyte connected in series comprises the following steps:

[0010] Pumping an acidic electrolyte into the anode chamber, wherein the acidic electrolyte contains alkali metal cations, and the acidic electrolyte undergoes an oxygen precipitation reaction on the surface of the anode electrode to obtain an acidic electrolyte containing dissolved oxygen;

[0011] Then, the acidic electrolyte containing dissolved oxygen is passed into the cathode chamber that only exchanges protons with the anode chamber, and the dissolved oxygen undergoes an oxygen reduction reaction on the surface of the catalyst layer of the cathode gas diffusion electrode to generate an OOH* intermediate;

[0012] CO2 is introduced into the surface of the catalyst layer of the cathode gas diffusion electrode, and the OOH* intermediate reduces the energy barrier for the activation of CO2 molecules. The CO2 is electro-reduced to generate *COOH intermediates and *OCHO intermediates. The *OCHO intermediates continue to be electro-reduced at the cathode gas diffusion electrode where the OOH* intermediates are distributed to form gaseous products, which are diffused, discharged and collected. The *COOH intermediates form liquid products at the cathode gas diffusion electrode where the OOH* intermediates are distributed, which escape into the acidic electrolyte, are discharged and collected.

[0013] Since the anode reaction corresponding to the electroreduction of CO2 is usually the oxygen evolution reaction (OER), dissolved oxygen and H* are generated through water oxidation. The OER technology is mature, with a lot of research and application experience, and the raw materials are easy to obtain and low-cost, but the OER process usually requires a higher overpotential (1.23V vs. RHE), resulting in higher energy consumption and reduced overall reaction efficiency. By adopting the above technical solution, the acidic electrolyte is introduced from the anode side, the anode OER produces dissolved oxygen, and then the acidic electrolyte containing dissolved oxygen is passed into the cathode chamber, so that the dissolved oxygen can participate in the electroreduction of CO2 at the cathode gas diffusion electrode. In the co-electrolysis with CO2, the low concentration of dissolved oxygen is conducive to regulating the oxidation state of the catalyst layer of the cathode gas diffusion electrode, maintaining an efficient catalytic environment, so as to improve the conversion efficiency of CO2 electroreduction. In addition, the OOH* intermediates produced by the oxygen reduction reaction can reduce the energy barrier for the activation of CO2 molecules, which is conducive to the realization of an efficient CO2 electroreduction process; the OOH* intermediates can also stabilize the *COOH intermediates and *OCHO intermediates of the CO2 electroreduction products, significantly improving the conversion efficiency of CO2 electroreduction; the OOH* intermediates and alkali metal cations jointly construct a microenvironment near the catalytic layer, driving protons away from the cathode gas diffusion electrode, and regulating the local pH value near the cathode gas diffusion electrode to more effectively inhibit the competitive side reaction HER.

[0014] At the same time, the above method introduces the acidic electrolyte from the anode side, and then drives the coupled anode OER process from the anode to the cathode through the acidic electrolyte to achieve efficient and stable CO2 electroreduction, thereby constructing a stable and efficient CO2 electroreduction process; and because the above method utilizes OER to effectively improve the conversion efficiency of CO2 electroreduction, when the same amount of product is obtained, the overpotential energy consumption required for CO2 electroreduction on the cathode side is reduced, which cleverly neutralizes the defect of high energy consumption of OER and improves the overall efficiency and economy of CO2 electroreduction.

[0015] Optionally, the pH of the obtained acidic electrolyte is 1.0-3.0.

[0016] By adopting the above technical scheme, the proton concentration in the acidic electrolyte in the above pH range can provide sufficient hydronium ions as proton donors for acidic CO2 electroreduction, so as to effectively inhibit the formation of carbonates and avoid clogging the micropores of the cathode gas diffusion electrode, resulting in a decrease in mass transfer efficiency.

[0017] Optionally, the acidic electrolyte includes sulfuric acid and alkali metal cation sulfate, wherein the concentration of the sulfuric acid is 0.0025-0.005%, and the concentration of the alkali metal cation is 0.5-1.5 mol / L.

[0018] By adopting the above technical scheme, the sulfuric acid concentration in the above range can adjust the pH of the acidic electrolyte to between 1-3, and the alkali metal cation concentration in the above range cooperates with the OOH* intermediate to better inhibit the migration of hydronium ions and regulate the local pH value near the electrode, thereby better inhibiting the competitive hydrogen evolution side reaction, thereby further improving the conversion efficiency of CO2 electroreduction.

[0019] Optionally, the method for preparing the acidic electrolyte comprises the following steps:

[0020] First, take an appropriate amount of concentrated sulfuric acid and dissolve it in deionized water to prepare a 0.0025-0.005% sulfuric acid aqueous solution, then weigh an appropriate amount of alkali metal cation sulfate and dissolve it in the above solution to prepare an acidic electrolyte with an alkali metal cation concentration of 0.5-1.5 mol / L.

[0021] Optionally, the acid electrolyte is pumped into the anode chamber at a flow rate of 1.0-5.0 mL / min, and the CO2 is introduced at a flow rate of 3-100 sccm.

[0022] By adopting the above technical scheme, the pumping flow rate of the above-mentioned acidic electrolyte and the introduction flow rate range of CO2 can make the amount of dissolved oxygen obtained after the OER reaction of the anode electrode moderate, so that the dissolved oxygen at the cathode gas diffusion electrode is adjusted to be maintained at a low concentration state, so as to better adjust the oxidation state of the catalytic layer of the cathode gas diffusion electrode; and the OOH* intermediate generated at the cathode gas diffusion electrode can better stabilize the *COOH intermediate and *OCHO intermediate.

[0023] Optionally, the current density applied during the electroreduction process is 50-300 mA / cm 2 .

[0024] By adopting the above technical solution, the above current density range can stably drive the CO2 electroreduction reaction to achieve efficient and stable CO2 electroreduction.

[0025] Optionally, the cathode gas diffusion electrode uses a catalytic material of at least one of Bi, Bi2S3, Bi2O3, Bi2S3@CNTs, Bi2O3@CNTs, Bi-Bi2O2CO3@CNTs, Bi-Bi2O2CO3, and CNTs.

[0026] By adopting the above technical solution, the above catalyst material has a high selectivity for CO2 reduction under acidic conditions, that is, it has a high catalytic activity for CO2 reduction and effectively inhibits the competitive hydrogen evolution side reaction.

[0027] Optionally, the preparation process of the cathode gas diffusion electrode comprises the following steps:

[0028] The cathode catalyst material is dispersed in a mixed solvent of ethanol and isopropanol, and an appropriate amount of adhesive is added to form an ink solution; the ink solution is subjected to room temperature ultrasonic treatment, and then the ink solution is uniformly deposited on one side of a porous hydrophobic carbon paper substrate to form a catalyst layer, and the catalyst loading is 1-5 mg / cm 2 , a gas diffusion electrode with one side as a diffusion layer and the other side as a catalyst layer is made, and then dried for use.

[0029] Optionally, the ratio of ethanol to isopropanol in the mixed solvent is (2-4):1, and the volume of the adhesive is 0.03-0.05% of the mixed solvent.

[0030] Optionally, the material of the anode electrode is at least one of foamed nickel, foamed copper, and a nickel mesh loaded with IrOx.

[0031] In the second aspect, the present invention provides a highly efficient CO2 electroreduction device with an anode and a cathode acid electrolyte connected in series, which adopts the following technical solutions:

[0032] A high-efficiency CO2 electroreduction method device with an anode and a cathode acidic electrolyte connected in series, comprising a support block, an anode electrode fixed on a support plate in sequence and overlapped, an anode press block, a proton exchange membrane, a cathode press block, a cathode gas diffusion electrode and a ventilation block, wherein the anode press block is provided with an anode chamber and is provided with a first liquid inlet and a first liquid outlet connected to the anode chamber, the cathode press block is provided with a cathode chamber and is provided with a second liquid inlet and a second liquid outlet connected to the cathode chamber, a connecting pipe is connected between the first liquid outlet and the second liquid inlet, the anode electrode is located in the anode chamber, the cathode gas diffusion electrode is located in the cathode chamber, the diffusion layer of the cathode gas diffusion electrode faces the ventilation block and the catalyst layer faces the cathode chamber, and the proton exchange membrane spans between the anode chamber and the cathode chamber.

[0033] By adopting the above technical solution, CO2 is introduced into the device through the gas chamber, and CO2 diffuses to the catalyst layer through the diffusion layer of the cathode gas diffusion electrode to perform the electro-reduction reaction of CO2. At the same time, an acidic electrolyte is introduced into the anode chamber through the first liquid inlet end, and the acidic electrolyte undergoes an OER reaction with the anode motor in the anode chamber to obtain an acidic electrolyte containing dissolved oxygen. The acidic electrolyte containing dissolved oxygen enters the cathode chamber through the connecting pipe and participates in the electro-reduction reaction of CO2. Since the proton exchange membrane spans between the anode chamber and the cathode chamber, proton exchange can be performed between the anode chamber and the cathode chamber, so that the protons displaced by the OOH* intermediate and the alkali metal cation can pass through the proton exchange membrane away from the anode gas diffusion electrode, so as to better regulate the local pH value near the cathode gas diffusion electrode. The gaseous products generated by the electrochemical reduction of CO2 are discharged from the ventilation block, and the liquid products and the acidic electrolyte are discharged from the second liquid outlet together.

[0034] In summary, the present invention includes at least one of the following beneficial technical effects:

[0035] 1. An acidic electrolyte is introduced from the anode side, and the anode OER produces dissolved oxygen. The acidic electrolyte containing dissolved oxygen is then passed into the cathode chamber, so that the dissolved oxygen can participate in the CO2 electroreduction at the cathode gas diffusion electrode. In the co-electrolysis with CO2, the low concentration of dissolved oxygen is conducive to regulating the oxidation state of the catalyst layer of the cathode gas diffusion electrode and maintaining an efficient catalytic environment to improve the conversion efficiency of CO2 electroreduction. The anode OER process is coupled through the acidic electrolyte drive from the anode to the cathode to achieve efficient and stable CO2 electroreduction;

[0036] 2. In addition, the anode OER is combined with CO2 electrocatalysis, and the OOH* intermediates generated by dissolved oxygen at the cathode gas diffusion electrode are used to help regulate and maintain the microenvironment of the catalytic surface in the acidic electrolyte, reducing the energy barrier for the activation of CO2 molecules; at the same time, the activation energy barrier of CO2 is reduced and the intermediates of the ECO2R product are stabilized, thus constructing a stable and efficient ECO2R process;

[0037] 3. The use of OER effectively improves the conversion efficiency of CO2 electroreduction. When obtaining the same amount of products, the overpotential energy consumption required for CO2 electroreduction on the cathode side is reduced, which cleverly neutralizes the high energy consumption defect of OER and improves the overall efficiency and economy of CO2 electroreduction. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 It is a three-dimensional assembly diagram of a high-efficiency CO2 electric reduction device of the present invention with an anode and a cathode acid electrolyte connected in series.

[0039] Explanation of the accompanying drawings: 1. Support block; 2. Anode electrode; 3. Anode press block; 31. Anode chamber; 32. First liquid inlet end; 33. First liquid outlet end; 4. Proton exchange membrane; 5. Cathode press block; 51. Cathode chamber; 52. Second liquid inlet end; 53. Second liquid outlet end; 6. Cathode gas diffusion electrode; 7. Ventilation block; 71. Gas chamber; 72. Gas inlet end; 73. Gas outlet end; 8. Connecting pipe; 9. Reference electrode. DETAILED DESCRIPTION

[0040] The following is combined with Figure 1 The present invention is described in further detail.

[0041] The embodiment of the present invention discloses a highly efficient CO2 electroreduction device with an anode and a cathode acidic electrolyte connected in series. Figure 1 The CO2 electroreduction device driven by anode-cathode acidic electrolyte flow includes a support block 1, an anode electrode 2 fixed on a support plate in sequence, an anode pressing block 3, a proton exchange membrane 4, a cathode pressing block 5, a cathode gas diffusion electrode 6 and a ventilation block 7.

[0042] Reference Figure 1 The anode block 3 is provided with an anode chamber 31, which is arranged to penetrate in a direction perpendicular to the anode block 3, and the two ends of the anode block 3 are respectively provided with a first liquid inlet 32 ​​and a first liquid outlet 33, which are both connected to the anode chamber 31. The anode electrode 2 is located at the anode chamber 31 and covers the opening surface of the anode chamber 31. The anode material is at least one of foamed nickel, foamed copper, and a nickel mesh loaded with IrOx.

[0043] Reference Figure 1 The cathode block 5 is provided with a cathode chamber 51, which is arranged in a direction perpendicular to the cathode block 5. The cathode block 5 is provided with a second liquid inlet 52 and a second liquid outlet 53 at both ends, respectively. The second liquid inlet 52 and the second liquid outlet 53 are both connected to the cathode chamber 51. A connecting pipe 8 is connected between the first liquid outlet 33 and the second liquid inlet 52. The cathode block 5 is provided with a reference electrode 9, and the material of the reference electrode 9 is at least one of Ag / AgCl, Hg / HgSO4, and a saturated calomel electrode.

[0044] Reference Figure 1 The cathode gas diffusion electrode 6 is located at the cathode chamber 51 and covers the opening surface of the cathode chamber 51 . The diffusion layer of the cathode gas diffusion electrode 6 faces the ventilation block 7 , and the catalyst layer of the cathode gas diffusion electrode 6 faces the cathode chamber 51 .

[0045] Reference Figure 1A gas chamber 71 is provided on the side wall of the ventilation block 7 facing the cathode diffusion electrode, and the opening direction of the gas chamber 71 faces the cathode gas diffusion electrode 6, and the cathode gas diffusion electrode 6 covers the opening surface of the gas chamber 71. An inlet end 72 and an outlet end 73 are respectively provided at both ends of the ventilation block 7, and both the inlet end 72 and the outlet end 73 are connected to the gas chamber 71.

[0046] Part I: Effect of different potassium ion concentrations on the electroreduction of CO2

[0047] Embodiment 1:

[0048] An efficient CO2 electroreduction method with an anode and a cathode acidic electrolyte connected in series comprises the following steps:

[0049] 1. Preparation of cathode gas diffusion electrode 6:

[0050] Bi-Bi2O2CO3@CNTs were dispersed in a mixed solvent of ethanol and isopropanol, and an appropriate amount of Nafion (5wt%) solution was added as an adhesive to form an ink solution; the volume ratio of ethanol and isopropanol in the mixed solvent was 3:1, the volume of the adhesive was 0.04% of the ink solution, and the concentration of Bi-Bi2O2CO3@CNTs in the ink solution was 3wt%.

[0051] The ink solution was subjected to ultrasonic treatment at room temperature, with an ultrasonic time of 1 h and a temperature of 10°C. The ink solution was evenly deposited on the porous hydrophobic carbon paper substrate using a spray gun to form a catalytic layer, with a catalyst loading of 3 mg / cm 2 A gas diffusion electrode with one side being a diffusion layer and the other side being a catalyst layer is made, and dried at 40-55°C for later use.

[0052] 2. Prepare acid electrolyte:

[0053] Take an appropriate amount of concentrated sulfuric acid and dissolve it in deionized water to prepare a sulfuric acid aqueous solution, then weigh an appropriate amount of potassium sulfate and dissolve it in the above solution to prepare an acidic electrolyte with a potassium ion concentration of 1 mol / L and a pH of 3.

[0054] 3. CO2 electroreduction:

[0055] The material of the anode electrode 2 is a nickel mesh loaded with IrOx, the material of the reference electrode 9 is Ag / AgCl, and the current density applied during the electroreduction process is 100 mA / cm 2 ;

[0056] The acidic electrolyte is pumped into the anode chamber 31 from the first liquid inlet end 32 at a pumping rate of 3 mL / min. The acidic electrolyte undergoes an oxygen evolution reaction (OER) on the surface of the anode electrode 2 to obtain an acidic electrolyte containing dissolved oxygen;

[0057] Then, the acidic electrolyte containing dissolved oxygen is introduced into the cathode chamber 51 through the connecting pipe 8, and the acidic electrolyte containing dissolved oxygen comes into contact with the catalyst layer of the cathode gas diffusion electrode 6, and the dissolved oxygen undergoes an oxygen reduction reaction on the catalyst layer surface of the cathode gas diffusion electrode 6 to generate an OOH* intermediate;

[0058] CO2 is introduced through the air inlet 72 with a flow rate of 56 sccm. CO2 enters the gas chamber 71 of the ventilation block 7, and diffuses from the diffusion layer of the cathode gas diffusion electrode 6 to the surface of the catalyst layer. CO2 is electro-reduced on the surface of the catalyst layer to generate *COOH intermediates and *OCHO intermediates. The gaseous product formed by the continued electro-reduction of the *OCHO intermediate is discharged and collected through the air outlet 73 of the ventilation block 7, and the liquid product formed by the *COOH intermediate escapes into the acidic electrolyte, and is discharged and collected through the second liquid outlet 53.

[0059] Embodiment 2:

[0060] A highly efficient CO2 electroreduction method with an anode and a cathode acidic electrolyte connected in series, which is different from Example 1 in that the potassium ion concentration in the acidic electrolyte is 0.5 mol / L.

[0061] Embodiment 3:

[0062] A highly efficient CO2 electroreduction method with an anode and a cathode acidic electrolyte connected in series, which is different from Example 1 in that the potassium ion concentration in the acidic electrolyte is 1.5 mol / L.

[0063] Comparative Example 1:

[0064] A highly efficient CO2 electroreduction method with an anode and a cathode acidic electrolyte connected in series, which is different from Example 1 in that the potassium ion concentration in the acidic electrolyte is 0.2 mol / L.

[0065] Comparative Example 1:

[0066] The difference from Example 1 is that an acidic electrolyte is introduced into the cathode chamber and the anode chamber respectively, the potassium ion concentration in the acidic electrolyte is 1 mol / L, and the current density is 100 mA / cm 2 , the catalytic material is Bi-Bi2O2CO3@CNTs.

[0067] Comparative Example 2:

[0068] The difference from Comparative Example 1 is that the potassium ion concentration in the acidic electrolyte is 0.5 mol / L.

[0069] Comparative Example 3:

[0070] The difference from Comparative Example 1 is that the potassium ion concentration in the acidic electrolyte is 1.5 mol / L.

[0071] Comparative Example 4:

[0072] The difference from Comparative Example 1 is that the potassium ion concentration in the acidic electrolyte is 0.2 mol / L.

[0073] Performance test method:

[0074] 1) Overpotential energy loss:

[0075] The cathode applied current is constant, and the electrochemical workstation has an output voltage corresponding to it. The calculation results are shown in Table 1 based on the average value of the output voltage.

[0076] ΔE Cathode =z HCOOH Fn HCOOH where z HCOOH is the number of electron transfers of HCOOH, and F is the Faraday constant (96485 mol -1 ),η HCOOH is the overpotential for the generation of formic acid at a certain current density.

[0077] in, is the equilibrium potential of CO2 reduction to formic acid (-0.2VvsRHEforpH<4), is the output potential at a certain current density.

[0078] 2) Faraday efficiency of the product (taking formic acid as an example):

[0079] The calculation formula of the Faraday efficiency of formic acid and the calculation results are shown in Table 1:

[0080] Among them, z HCOOH is the number of electrons transferred to HCOOH, C HCOOH is the molar concentration of formic acid in the product stream, V liquid is the volume of electrolyte and Q is the total charge.

[0081] 3) 80h long-term stability test:

[0082] The device of the present invention was used to carry out continuous electrolysis for 80 hours, and the Faraday efficiency change of the product was tested and calculated. Finally, the Faraday efficiency decrease rate was calculated. The calculation results are shown in Table 1.

[0083] 4) Electroreduction environmental stability test:

[0084] The potassium ion concentration of the acidic electrolyte on the cathode side and the anode side of Examples 1-3 and Comparative Example 1 was tested;

[0085] The pH of the acidic electrolyte on the cathode side of Examples 1-3, Comparative Example 1 and Comparative Examples 1-4 was tested.

[0086] Table 1:

[0087]

[0088] As can be seen from Table 1, the overpotential energy loss of Examples 1-3 and Comparative Example 1 is reduced by about 44.5% compared with Comparative Examples 1-4, which means that within the potassium ion concentration range of the present invention, the electro-reduction method of the present invention can cleverly neutralize the defect of high energy consumption of OER, reduce the overpotential energy loss of CO2 electro-reduction, and improve the overall efficiency and economy of CO2 electro-reduction.

[0089] It can also be seen from Table 1 that the Faraday efficiency of the product of Example 1 is significantly higher than that of Comparative Example 1, the Faraday efficiency of the product of Example 2 is significantly higher than that of Comparative Example 2, the Faraday efficiency of the product of Example 3 is significantly higher than that of Comparative Example 3, and the Faraday efficiency of the product of Comparative Example 1 is significantly higher than that of Comparative Example 4; while the Faraday efficiency of the product of Example 1 is significantly higher than that of Examples 2-3, and the Faraday efficiency of the product of Comparative Example 1 is significantly lower than that of Examples 1-3. It can be seen from the above that the electro-reduction method of the present invention significantly improves the conversion efficiency of the CO2 electro-reduction product, and within the potassium ion concentration range of the present invention, the conversion efficiency is relatively better.

[0090] As can be seen from Table 1, the potassium ion concentrations of the electrolytes on both sides of Examples 1-3 and Comparative Example 1 are consistent with the initial concentrations, the pH on the cathode side is also maintained at 2.7-2.9, and the 80h Faraday drop rate is maintained at about 4%, indicating that the electro-reduction process of the present invention is stable and efficient. The pH on the cathode side of Comparative Examples 1-4 rises to about 7, and the 80h Faraday drop rate is as high as 6.5%-7.0%. It can be seen that the short-term and long-term stability of the electro-reduction method of the present application are significantly improved.

[0091] Part II: Effect of different current densities on the electroreduction of CO2

[0092] Embodiment 4:

[0093] A highly efficient CO2 electroreduction method with an anode and a cathode acid electrolyte connected in series, which is different from Example 1 in that the current density applied during the electroreduction process is 50 mA / cm 2 .

[0094] Embodiment 5:

[0095] A highly efficient CO2 electroreduction method with an anode and a cathode acid electrolyte connected in series, which is different from Example 1 in that the current density applied during the electroreduction process is 300 mA / cm 2 .

[0096] Comparative Example 5:

[0097] The difference from Comparative Example 1 is that the applied current density is 50 mA / cm 2 .

[0098] Comparative Example 6:

[0099] The difference from Comparative Example 1 is that the applied current density is 300 mA / cm 2 .

[0100] Performance test method:

[0101] The overpotential energy loss, product Faraday efficiency, and 80h Faraday drop rate of Examples 4-5 and Comparative Examples 5-6 were tested according to the above method. The test results are shown in Table 2.

[0102] Table 2:

[0103]

[0104] It can be seen from Table 2 that the overpotential energy loss of Examples 4-5 is significantly reduced compared with that of Comparative Examples 5-6, indicating that the electro-reduction method of the present invention can cleverly neutralize the defect of high energy consumption of OER and improve the overall efficiency and economy of CO2 electro-reduction.

[0105] It can be seen from Table 2 that the Faraday efficiency of the product of Example 1 is significantly higher than that of Comparative Example 1, the Faraday efficiency of the product of Example 4 is significantly higher than that of Comparative Example 5, and the Faraday efficiency of the product of Example 5 is significantly higher than that of Comparative Example 6; and the Faraday efficiency of the product of Example 1 is significantly higher than that of Examples 4-5. It can be seen from the above that the electro-reduction method of the present invention significantly improves the conversion efficiency and electro-reduction stability of the CO2 electro-reduction product, and the conversion efficiency is the highest within the current density range of the present invention.

[0106] Part III: Effects of different catalytic materials on electroreduction of CO2

[0107] Embodiment 6:

[0108] A highly efficient CO2 electroreduction method with an anode and a cathode acidic electrolyte connected in series is different from Example 1 in that the catalytic material used in the cathode gas diffusion electrode is Bi2O3@CNTs.

[0109] Embodiment 7:

[0110] A highly efficient CO2 electroreduction method with an anode and a cathode acidic electrolyte connected in series is different from Example 1 in that the catalytic material used in the cathode gas diffusion electrode is Bi2S3@CNTs.

[0111] Embodiment 8:

[0112] A highly efficient CO2 electroreduction method with an anode and a cathode acidic electrolyte connected in series is different from Example 1 in that the catalytic material used in the cathode gas diffusion electrode is Bi-Bi2O2CO3.

[0113] Performance test method:

[0114] The overpotential energy loss, product Faraday efficiency, and 80h Faraday drop rate of Examples 6-8 were tested according to the above method. The test results are shown in Table 3.

[0115] Table 3:

[0116]

[0117]

[0118] As can be seen from Table 3, the overpotential energy loss of Examples 6-8 is significantly reduced compared to Comparative Example 1, indicating that the electro-reduction method of the present invention can cleverly neutralize the defect of high energy consumption of OER and improve the overall efficiency and economy of CO2 electro-reduction. The Faraday efficiency of Examples 6-8 is maintained at more than 80%, and the 80h Faraday decrease rate is maintained at about 4%, which is better than Comparative Example 1. It can be seen from the above that the electro-reduction method of the present invention significantly improves the conversion efficiency and electro-reduction stability of the CO2 electro-reduction product, and the catalyst material within the scope of this application can maintain a high conversion efficiency.

[0119] The above are all preferred embodiments of the present invention, and are not intended to limit the protection scope of the present invention. Therefore, any equivalent changes made based on the structure, shape, and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. An efficient CO2 electroreduction method with an anode and a cathode acidic electrolyte connected in series, characterized in that: The following steps are involved: Pumping an acidic electrolyte into the anode chamber (31), wherein the acidic electrolyte contains alkali metal cations, and the acidic electrolyte undergoes an oxygen precipitation reaction on the surface of the anode electrode (2) to obtain an acidic electrolyte containing dissolved oxygen; Then, the acidic electrolyte containing dissolved oxygen is passed into the cathode chamber (51) that performs only proton exchange with the anode chamber (31), and the dissolved oxygen undergoes an oxygen reduction reaction on the surface of the catalyst layer of the cathode gas diffusion electrode (6) to generate an OOH* intermediate; CO2 is introduced into the surface of the catalyst layer of the cathode gas diffusion electrode (6), and the OOH* intermediate reduces the energy barrier for the activation of CO2 molecules. The CO2 is electro-reduced to generate *COOH intermediates and *OCHO intermediates. The *OCHO intermediates and *OCHO intermediates continue to be electro-reduced on the cathode gas diffusion electrode (6) where the OOH* intermediates are distributed to form products, which are then discharged and collected.

2. The method for efficient CO2 electroreduction with an anode and a cathode acidic electrolyte connected in series according to claim 1, characterized in that: The pH of the resulting acidic electrolyte is 1.0-3.

0.

3. The method for efficient CO2 electroreduction with an anode and a cathode acidic electrolyte connected in series according to claim 2, characterized in that: The acidic electrolyte includes sulfuric acid and alkali metal cation sulfate, wherein the concentration of the sulfuric acid is 0.0025-0.005%, and the concentration of the alkali metal cation is 0.5-1.5 mol / L.

4. The method for efficient CO2 electroreduction with an anode and a cathode acidic electrolyte connected in series according to claim 3, characterized in that: The preparation method of the acid electrolyte comprises the following steps: First, take an appropriate amount of concentrated sulfuric acid and dissolve it in deionized water to prepare a 0.0025-0.005% sulfuric acid aqueous solution, then weigh an appropriate amount of alkali metal cation sulfate and dissolve it in the above solution to prepare an acidic electrolyte with an alkali metal cation concentration of 0.5-1.5 mol / L.

5. A highly efficient CO2 electroreduction method with an anode and a cathode acidic electrolyte connected in series according to any one of claims 1 or 2, characterized in that: The acid electrolyte is pumped into the anode chamber (31) at a flow rate of 1.0-5.0 mL / min, and the CO2 is introduced at a flow rate of 3-100 sccm.

6. A highly efficient CO2 electroreduction method with an anode and a cathode acidic electrolyte connected in series according to any one of claims 1 or 2, characterized in that: The current density applied during the electroreduction process is 50-300 mA / cm 2 .

7. A highly efficient CO2 electroreduction method with an anode and a cathode acidic electrolyte connected in series according to any one of claims 1 or 2, characterized in that: The cathode gas diffusion electrode (6) adopts a catalytic material of at least one of Bi, Bi2S3, Bi2O3, Bi2S3@CNTs, Bi2O3@CNTs, Bi-Bi2O2CO3@CNTs, Bi-Bi2O2CO3, and CNTs.

8. A highly efficient CO2 electroreduction method with an anode and a cathode acidic electrolyte connected in series according to any one of claims 1 or 2, characterized in that: The preparation process of the cathode gas diffusion electrode (6) comprises the following steps: The cathode catalyst material is dispersed in a mixed solvent of ethanol and isopropanol, and an appropriate amount of adhesive is added to form an ink solution; the ink solution is subjected to room temperature ultrasonic treatment, and then the ink solution is uniformly deposited on one side of a porous hydrophobic carbon paper substrate to form a catalyst layer, and the catalyst loading is 1-5 mg / cm 2 , a gas diffusion electrode with one side as a diffusion layer and the other side as a catalyst layer is made, and then dried for use.

9. The method for efficient CO2 electroreduction with an anode and a cathode acidic electrolyte connected in series according to claim 8, characterized in that: The ratio of ethanol to isopropanol in the mixed solvent is (2-4):1, and the volume of the adhesive is 0.03-0.05% of the mixed solvent.

10. A high-efficiency CO2 electroreduction device based on the anode and cathode acid electrolyte connected in series according to any one of claims 1 to 9, characterized in that: The invention comprises a support block (1), an anode electrode (2) fixedly overlapped on a support plate in sequence, an anode pressing block (3), a proton exchange membrane (4), a cathode pressing block (5), a cathode gas diffusion electrode (6) and a venting block (7), wherein the anode pressing block (3) is provided with an anode chamber (31) and is provided with a first liquid inlet end (32) and a first liquid outlet end (33) connected to the anode chamber (31), and the cathode pressing block (5) is provided with a cathode chamber (51) and is provided with a second liquid inlet end (32) and a first liquid outlet end (33) connected to the cathode chamber (51). The invention relates to a liquid-liquid-discharging device comprising a first liquid outlet (52) and a second liquid outlet (53), wherein a connecting pipe (8) is connected between the first liquid outlet (33) and the second liquid inlet (52), the anode electrode (2) is located at the anode chamber (31), the cathode gas diffusion electrode (6) is located at the cathode chamber (51), the diffusion layer of the cathode gas diffusion electrode (6) faces the ventilation block (7) and the catalyst layer faces the cathode chamber (51), and the proton exchange membrane (4) spans between the anode chamber (31) and the cathode chamber (51).

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