A method for preparing formic acid by electroreduction of supercritical carbon dioxide

Abstract

The present invention discloses a method for producing formic acid by supercritical carbon dioxide electroreduction. The method comprises: conducting a carbon dioxide electroreduction reaction to produce formic acid under supercritical conditions; wherein an electrode loaded with nanoflower-like Bi serves as the cathode; and the carbon dioxide electroreduction reaction is conducted at a pressure of 7.5 to 9.5 MPa and a temperature of 35 to 55°C. Compared to conventional CO₂RR, the present invention improves the problems of low current density and narrow electrochemical window, providing a process with high current density and a wide electrochemical window.

Description

Technical Field

[0001] The present invention belongs to the technical field of electrocatalysis, and more specifically, relates to a method for preparing formic acid by electroreduction of supercritical carbon dioxide. Background Art

[0002] The combustion of fossil fuels produces large amounts of carbon dioxide (CO2), significantly increasing atmospheric CO2 concentrations and causing numerous environmental problems. The CO2 electroreduction reaction (CO2RR), powered by clean energy sources such as wind and solar power, effectively reduces CO2 emissions.

[0003] Metallic Bi has high CO₂RR activity and offers unique advantages over other traditional metal catalysts due to its low price, low toxicity, environmental friendliness, and high stability. However, metallic Bi catalysts in the form of nanoparticles or two-dimensional nanosheets suffer from poor conductivity and limited exposure of active sites, which often results in low current density for CO₂RR.

[0004] At the same time, in practical applications, since the voltage of renewable energy sources that provide CO2RR electricity fluctuates greatly and the voltage gap provided by different renewable energy sources is also large, a reaction system with a wider electrochemical window with high selectivity for formate / formic acid is required; however, the electrochemical window of CO2RR carried out at room temperature and pressure is narrow. Summary of the Invention

[0005] The present invention aims to provide a method for preparing formic acid by electroreduction of supercritical carbon dioxide. The method of the present invention uses a catalyst nanoflower-shaped Bi and performs electroreduction under the condition that carbon dioxide is in a supercritical state, thereby increasing the current density of the reaction and expanding the electrochemical window.

[0006] To achieve the above-mentioned object, the present invention provides a method for preparing formic acid by supercritical carbon dioxide electroreduction, the method comprising: carrying out a carbon dioxide electroreduction reaction to prepare formic acid under the condition that the carbon dioxide is in a supercritical state; wherein an electrode loaded with Bi having a nanoflower-like morphology is used as a cathode; the carbon dioxide electroreduction reaction pressure is 7.5-9.5 MPa, and the temperature is 35-55°C.

[0007] The technical problem to be solved by the present invention is how to increase the current density of CO2RR and expand the electrochemical window. The present invention uses a catalyst nanoflower-shaped Bi and performs electroreduction under supercritical conditions of carbon dioxide (i.e., carbon dioxide is in a supercritical state under pressure of 7.5-9.5 MPa and temperature of 35-55°C). This improves the conductivity of the catalyst, increases the number of active sites, and also increases the solubility of carbon dioxide in the solution and the diffusion capacity of carbon dioxide from the solution to the electrode surface, thereby increasing the current density of the reaction and expanding the electrochemical window.

[0008] In the present invention, the electrode loaded with nanoflower-like Bi is preferably carbon paper loaded with nanoflower-like Bi. Furthermore, the electrode loaded with nanoflower-like Bi is preferably prepared by using BiOCl as a precursor and employing an electrochemical in-situ reduction method. The BiOCl precursor is synthesized using a solvothermal method: BiCl3 is dissolved in ethylene glycol, sodium dodecylbenzenesulfonate, a surfactant, is added, and the mixture is uniformly mixed. Deionized water is then added and mixed uniformly to obtain a mixed solution. The mixed solution is then subjected to a hydrothermal reaction, and the product is washed and dried to obtain the BiOCl precursor.

[0009] According to the present invention, preferably, in the method, the electrolyte used is a potassium bicarbonate aqueous solution, a mixed solution of an imidazole ionic liquid and water, or a mixed solution of an imidazole ionic liquid and methanol.

[0010] According to the present invention, preferably, the concentration of the potassium bicarbonate aqueous solution is 0.2 to 2.0 mol / L.

[0011] In the present invention, the concentration of the imidazole ionic liquid in the mixed solution of the imidazole ionic liquid and water is preferably 5 to 30 mmol / L; the concentration of the imidazole ionic liquid in the mixed solution of the imidazole ionic liquid and methanol is preferably 5 to 30 mmol / L.

[0012] According to the present invention, preferably, the imidazolium ionic liquid is at least one of 1-butyl-3-methylimidazolium hexafluorophosphate ([Bmim]PF6), 1-ethyl-3-methylimidazolium tetrafluoroborate ([Emim]BF4) and 1-ethyl-3-methylimidazolium bistrifluoromethanesulfonyl imide ([Emim]NTF2).

[0013] According to the present invention, preferably, in the method, platinum is used as the anode; and an Ag / AgCl electrode is used as the reference electrode.

[0014] According to the present invention, preferably, the reaction device is a diaphragm electrolyzer.

[0015] According to the present invention, preferably, the diaphragm of the diaphragm electrolyzer is a cation exchange membrane.

[0016] In the present invention, as a specific preferred embodiment, the method includes: carrying out a reaction in a diaphragm electrolyzer, adding an electrolyte to the cathode chamber and the anode chamber of the diaphragm electrolyzer; using an electrode loaded with Bi having a nanoflower-like morphology as a cathode; using a Pt sheet as an anode; and using an Ag / AgCl electrode as a reference electrode, which is arranged in the cathode chamber; introducing carbon dioxide into the cathode chamber and the anode chamber of the diaphragm electrolyzer, wherein the pressure in the cathode chamber and the anode chamber is 7.5 to 9.5 MPa and the temperature is 35 to 55° C., applying a negative potential to the cathode for constant potential electrolysis, and thus producing formic acid.

[0017] The technical solution of the present invention has the following beneficial effects:

[0018] Compared with the traditional CO2RR, the present invention improves the problems of low current density and narrow electrochemical window, and provides a process with high current density and wide electrochemical window.

[0019] Other features and advantages of the present invention will be described in detail in the following detailed description. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] The above and other objects, features and advantages of the present invention will become more apparent through a more detailed description of exemplary embodiments of the present invention with reference to the accompanying drawings, wherein like reference numerals generally represent like components throughout the exemplary embodiments of the present invention.

[0021] Figure 1 The figure shows a scanning electron microscope image of Bi on an electrode loaded with Bi having a nanoflower-like morphology used in accordance with one embodiment of the present invention.

[0022] Figure 2 The figure shows a scanning electron microscope image of Bi on an electrode loaded with Bi having a nano-particle morphology used in Comparative Example 1 of the present invention. DETAILED DESCRIPTION

[0023] The preferred embodiments of the present invention will be described in more detail below. Although the preferred embodiments of the present invention are described below, it should be understood that the present invention can be implemented in various forms and should not be limited by the embodiments set forth herein. Instead, these embodiments are provided to make the present invention more thorough and complete and to fully convey the scope of the present invention to those skilled in the art.

[0024] The present invention is further described below by way of examples:

[0025] In the following embodiments and comparative examples:

[0026] The Bi-loaded nanoflower-like electrode was prepared by the following method:

[0027] (1) The synthesis of BiOCl precursor adopts solvent thermal technology. The specific operation process is as follows: 0.12g BiCl3 is weighed and dissolved in 30mL ethylene glycol, and it is completely dissolved by ultrasonic treatment for 10 minutes. Then 0.1g sodium dodecylbenzenesulfonate (SDBS) is added to the solution and ultrasonic treatment is continued for 10 minutes until it is evenly dispersed. Then 0.6mL deionized water is added and ultrasonic dispersion treatment is carried out for 10 minutes to mix it evenly. The mixed solution is transferred to a 100mL polytetrafluoroethylene-lined reactor and hydrothermally reacted at 200℃ for 4h. After the reaction is completed, the reactor is naturally cooled to room temperature. The reaction solution is filtered to obtain a white precipitate, which is washed three times with ethanol solvent. Finally, the washed precipitate is vacuum dried at 60℃ for 12h to obtain BiOCl precursor powder.

[0028] (2) Prepare an electrode loaded with nanoflower-like morphology of Bi by electrochemical in-situ reduction process. The specific operation process is as follows: weigh 3 mg of BiOCl precursor and disperse it into a mixed solution consisting of 270 μL of ethanol and 30 μL of DuPont's Nafion solution with a mass concentration of 5%, ultrasonically treat for 20 minutes to obtain a uniform dispersion, take 100 μL of the dispersion and coat it on a 1 cm*1 cm hydrophobic carbon paper and dry it; in a standard three-electrode system, use the above carbon paper as the working electrode, the platinum mesh as the counter electrode, the Ag / AgCl electrode as the reference electrode, and the 0.5 M (mol / L) KHCO3 aqueous solution as the electrolyte, and reduce it at a constant potential of -0.9 V (vs. RHE) for 1 hour at room temperature and normal pressure to finally obtain an electrode loaded with nanoflower-like morphology of Bi (the morphology of the catalyst Bi is shown in FIG). Figure 1 shown).

[0029] The diaphragm of the diaphragm electrolyzer used is Nafion 117 cation exchange membrane.

[0030] In the following examples and comparative examples, the ion chromatograph used for analysis was ICS-1100, Dionex Corporation, the mobile phase was 20 mM KOH aqueous solution, the flow rate was 1.0 mL / min (anion analysis column: IonPac AS15, guard column: AG15, suppressor: ADRS 600-4 mm, suppression current: 60 mA).

[0031] Example 1

[0032] 80 mL of 0.5 M KHCO₃ aqueous solution was added to each of the cathode and anode chambers of a diaphragm electrolyzer. A nanoflower-shaped Bi electrode was used as the cathode; a Pt sheet was used as the anode; and an Ag / AgCl electrode was used as the reference electrode, both placed in the cathode chamber. The reaction temperature in both chambers was set to 35°C. CO₂ was introduced into both chambers, and the pressure in both chambers was adjusted to 7.5 MPa. After the temperature and pressure in both chambers reached the set values, constant potential electrolysis was performed at electrode potentials of -2.0, -2.5, -3.0, -3.5, and -4.0 V (vs. Ag / AgCl), respectively, with the negative potentials applied to the cathode. After the electrolysis was completed, the valves in both the cathode and anode chambers were opened simultaneously to release the remaining pressure in the electrolytic cell. Liquid samples from the cathode side were collected and analyzed by ion chromatography. The results showed that the formic acid Faradaic efficiencies were higher than 70% at electrode potentials of -2.0, -2.5, -3.0, and -3.5 V (vs. Ag / AgCl), respectively, reaching 71.67%, 76.92%, 91.72%, and 72.57%. The formic acid separation current density was 35.57 mA cm-3, respectively. -2 、81.70mA cm -2 、178.98mA cm -2 、184.04mAcm -2 .

[0033] Example 2

[0034] 80 mL of 0.5 M KHCO₃ aqueous solution was added to each of the cathode and anode chambers of a diaphragm electrolyzer. A nanoflower-shaped Bi electrode was used as the cathode; a Pt sheet was used as the anode; and an Ag / AgCl electrode was used as the reference electrode, both placed in the cathode chamber. The reaction temperature in both chambers was set to 35°C. CO₂ was introduced into both chambers, and the pressure in both chambers was adjusted to 8.5 MPa. After the temperature and pressure in both chambers reached the set values, constant potential electrolysis was performed at electrode potentials of -2.0, -2.5, -3.0, -3.5, and -4.0 V (vs. Ag / AgCl), respectively, with the negative potentials applied to the cathode. After the electrolysis was completed, the valves of the cathode and anode chambers were opened simultaneously to release the residual pressure in the electrolytic cell. Liquid samples from the cathode side were collected and analyzed by ion chromatography. Calculations showed that the Faradaic efficiency of formic acid at electrode potentials of -2.0, -2.5, -3.0, -3.5, and -4.0 V (vs. Ag / AgCl) was higher than 70%, namely 70.71%, 85.44%, 92.29%, 93.00%, and 70.86%, respectively. The formic acid separation current density was 43.84 mA cm-3, respectively. -2 、81.50mA cm -2 、139.22mAcm-2 、212.28mA cm -2 、199.26mA cm -2 .

[0035] Example 3

[0036] 80 mL of 0.5 M KHCO₃ aqueous solution was added to each of the cathode and anode chambers of a diaphragm electrolyzer. A nanoflower-shaped Bi electrode was used as the cathode; a Pt sheet was used as the anode; and an Ag / AgCl electrode was used as the reference electrode, both placed in the cathode chamber. The reaction temperature in both chambers was set to 35°C. CO₂ was introduced into both chambers, and the pressure in both chambers was adjusted to 9.5 MPa. After the temperature and pressure in both chambers reached the set values, constant potential electrolysis was performed at electrode potentials of -2.0, -2.5, -3.0, -3.5, and -4.0 V (vs. Ag / AgCl), respectively, with the negative potentials applied to the cathode. After the electrolysis was completed, the valves in both the cathode and anode chambers were opened simultaneously to release the residual pressure in the electrolytic cell. Liquid samples from the cathode side were collected and analyzed by ion chromatography. The results showed that the formic acid Faradaic efficiencies were all above 70% at electrode potentials of -2.0, -2.5, and -3.0 V (vs. Ag / AgCl), namely 71.04%, 86.70%, and 79.05%, respectively. The formic acid separation current densities were 41.59 mA cm-3, respectively. -2 、88.16mA cm -2 、127.54mA cm -2 .

[0037] Example 4

[0038] 80 mL of 0.5 M KHCO₃ aqueous solution was added to each of the cathode and anode chambers of a diaphragm electrolyzer. A nanoflower-shaped Bi electrode was used as the cathode; a Pt sheet was used as the anode; and an Ag / AgCl electrode was used as the reference electrode, both placed in the cathode chamber. The reaction temperature in both chambers was set to 45°C. CO₂ was introduced into both chambers, and the pressure in both chambers was adjusted to 7.5 MPa. After the temperature and pressure in both chambers reached the set values, constant potential electrolysis was performed at electrode potentials of -2.0, -2.5, -3.0, -3.5, and -4.0 V (vs. Ag / AgCl), respectively, with the negative potentials applied to the cathode. After the electrolysis was completed, the valves in both the cathode and anode chambers were opened simultaneously to release the remaining pressure in the electrolytic cell. Liquid samples from the cathode side were collected and analyzed by ion chromatography. The results showed that the formic acid Faradaic efficiency was higher than 70% at electrode potentials of -2.5, -3.0, and -3.5 V (vs. Ag / AgCl), reaching 75.25%, 90.29%, and 74.85%, respectively. The formic acid separation current density was 93.97 mA cm-3, respectively. -2 、188.77mA cm -2 、219.09mA cm -2 .

[0039] Example 5

[0040] 80 mL of 0.5 M KHCO₃ aqueous solution was added to each of the cathode and anode chambers of a diaphragm electrolyzer. A nanoflower-shaped Bi electrode was used as the cathode; a Pt sheet was used as the anode; and an Ag / AgCl electrode was used as the reference electrode, both placed in the cathode chamber. The reaction temperature in both chambers was set to 55°C. CO₂ was introduced into both chambers, and the pressure in both chambers was adjusted to 7.5 MPa. After the temperature and pressure in both chambers reached the set values, constant potential electrolysis was performed at electrode potentials of -2.0, -2.5, -3.0, -3.5, and -4.0 V (vs. Ag / AgCl), respectively, with the negative potentials applied to the cathode. After the electrolysis was completed, the valves in both the cathode and anode chambers were opened to release the remaining pressure in the electrolytic cell. Liquid samples from the cathode side were collected and analyzed by ion chromatography. The results showed that the formic acid Faradaic efficiencies were higher than 70% at electrode potentials of -2.5 and -3.0 V (vs. Ag / AgCl), respectively, at 77.95% and 73.62%. The formic acid separation current densities were 111.67 mA cm-1, respectively. -2 、164.98mA cm -2 .

[0041] Example 6

[0042] 80 mL of 0.2 M KHCO₃ aqueous solution was added to each of the cathode and anode chambers of a diaphragm electrolyzer. A nanoflower-shaped Bi electrode was used as the cathode; a Pt sheet was used as the anode; and an Ag / AgCl electrode was used as the reference electrode, both placed in the cathode chamber. The reaction temperature in both chambers was set to 35°C. CO₂ was introduced into both chambers, and the pressure in both chambers was adjusted to 7.5 MPa. After the temperature and pressure in both chambers reached the set values, constant potential electrolysis was performed at electrode potentials of -2.0, -2.5, -3.0, -3.5, and -4.0 V (vs. Ag / AgCl), respectively, with the negative potentials applied to the cathode. After the electrolysis was completed, the valves in both the cathode and anode chambers were opened to release the remaining pressure in the electrolytic cell. Liquid samples from the cathode side were collected and analyzed by ion chromatography. The results showed that the formic acid Faradaic efficiencies were higher than 70% at electrode potentials of -2.5 and -3.0 V (vs. Ag / AgCl), respectively, at 75.34% and 78.83%, and the formic acid separation current densities were 30.26 mA cm-3. -2 、74.23mA cm -2 .

[0043] Example 7

[0044] 80 mL of 0.3 M KHCO₃ aqueous solution was added to each of the cathode and anode chambers of a diaphragm electrolyzer. A nanoflower-shaped Bi electrode was used as the cathode; a Pt sheet was used as the anode; and an Ag / AgCl electrode was used as the reference electrode, both placed in the cathode chamber. The reaction temperature in both chambers was set to 35°C. CO₂ was introduced into both chambers, and the pressure in both chambers was adjusted to 7.5 MPa. After the temperature and pressure in both chambers reached the set values, constant potential electrolysis was performed at electrode potentials of -2.0, -2.5, -3.0, -3.5, and -4.0 V (vs. Ag / AgCl), respectively, with the negative potentials applied to the cathode. After the electrolysis was completed, the valves in both the cathode and anode chambers were opened simultaneously to release the remaining pressure in the electrolytic cell. Liquid samples from the cathode side were collected and analyzed by ion chromatography. The results showed that the formic acid Faradaic efficiencies were higher than 70% at electrode potentials of -2.5, -3.0, and -3.5 V (vs. Ag / AgCl), namely 73.77%, 85.36%, and 75.99%, respectively. The formic acid separation current densities were 43.89 mA cm-3, respectively. -2 、109.91mA cm -2 、127.06mA cm -2 .

[0045] Example 8

[0046] 80 mL of 0.4 M KHCO₃ aqueous solution was added to each of the cathode and anode chambers of a diaphragm electrolyzer. A nanoflower-shaped Bi electrode was used as the cathode; a Pt sheet was used as the anode; and an Ag / AgCl electrode was used as the reference electrode, both placed in the cathode chamber. The reaction temperature in both chambers was set to 35°C. CO₂ was introduced into both chambers, and the pressure in both chambers was adjusted to 7.5 MPa. After the temperature and pressure in both chambers reached the set values, constant potential electrolysis was performed at electrode potentials of -2.0, -2.5, -3.0, -3.5, and -4.0 V (vs. Ag / AgCl), respectively, with the negative potentials applied to the cathode. After the electrolysis was completed, the valves in both the cathode and anode chambers were opened simultaneously to release the residual pressure in the electrolytic cell. Liquid samples from the cathode side were collected and analyzed by ion chromatography. The results showed that the formic acid Faradaic efficiencies were higher than 70% at electrode potentials of -2.5, -3.0, and -3.5 V (vs. Ag / AgCl), namely 76.43%, 87.22%, and 78.93%, respectively. The formic acid separation current densities were 58.29 mA cm-3, respectively. -2 、119.16mA cm -2 、140.54mA cm -2 .

[0047] Comparative Example 1

[0048] 80 mL of 0.5 M KHCO3 aqueous solution was added to the cathode chamber and the anode chamber of the diaphragm electrolyzer; an electrode loaded with nano-particle-shaped Bi was used as the cathode. The electrode loaded with nano-particle-shaped Bi was purchased from Shanghai Mairui Biochemical Technology Co., Ltd. with the product number B802618. The morphology of the catalyst Bi is as shown in FIG. Figure 2 As shown in the figure, a Pt sheet was used as the anode, and an Ag / AgCl electrode was used as the reference electrode, both placed in the cathode chamber. The reaction temperature in the cathode and anode chambers was set to 35°C. CO2 was introduced into the cathode and anode chambers, and the pressure in both the cathode and anode chambers of the electrolytic cell was adjusted to 7.5 MPa. After the temperature and pressure in the cathode and anode chambers reached the set values, constant potential electrolysis was carried out at electrode potentials of -2.0, -2.5, -3.0, -3.5, and -4.0 V (vs. Ag / AgCl), respectively. The above negative potentials were applied to the cathode. After the electrolysis was completed, the valves in the cathode and anode chambers were opened simultaneously to release the residual pressure in the electrolytic cell. The cathode liquid sample was collected and analyzed by ion chromatography. It was calculated that the formic acid Faradaic efficiency at electrode potentials of -2.5 and -3.0 V (vs. Ag / AgCl) was higher than 70%, 70.95% and 72.68%, respectively, and the formic acid separation current density was 61.32 mA cm -2 、89.93mA cm -2 .

[0049] Comparative Example 2

[0050] 80 mL of 0.5 M KHCO₃ aqueous solution was added to each of the cathode and anode chambers of a diaphragm electrolyzer. A nanoflower-shaped Bi electrode was used as the cathode; a Pt sheet was used as the anode; and an Ag / AgCl electrode was used as the reference electrode, both placed in the cathode chamber. The reaction temperature in both chambers was set to 35°C. CO₂ was introduced into both chambers, and the pressure in both chambers was adjusted to atmospheric pressure. After the temperature and pressure in both chambers reached the set values, constant potential electrolysis was performed at electrode potentials of -1.4, -1.5, -1.6, -1.7, -1.8, and -2.0 V (vs. Ag / AgCl), with the negative potentials applied to the cathode. After the electrolysis, cathode liquid samples were collected and analyzed by ion chromatography. The results showed that the formic acid Faradaic efficiency was higher than 70% at electrode potentials of -1.5 and -1.6 V (vs. Ag / AgCl), which were 76.82% and 70.11%, respectively. The formic acid separation current density was 13.82 mA cm-3, respectively. -2 , 22.23mAcm -2 , while when the electrode potential was -2.0 V (vs. Ag / AgCl), no formic acid was generated.

[0051] Comparative Example 3

[0052] 80 mL of 0.5 M KHCO₃ aqueous solution was added to each of the cathode and anode chambers of a diaphragm electrolyzer. A nanoflower-shaped Bi electrode was used as the cathode; a Pt sheet was used as the anode; and an Ag / AgCl electrode was used as the reference electrode, both placed in the cathode chamber. The reaction temperature in both chambers was set to 65°C. CO₂ was introduced into both chambers, and the pressure in both chambers was adjusted to 7.5 MPa. After the temperature and pressure in both chambers reached the set values, constant potential electrolysis was performed at electrode potentials of -2.0, -2.5, -3.0, -3.5, and -4.0 V (vs. Ag / AgCl), respectively, with the negative potentials applied to the cathode. After the electrolysis was completed, the valves in both the cathode and anode chambers were opened simultaneously to release the remaining pressure in the electrolytic cell. Liquid samples from the cathode side were collected and analyzed by ion chromatography. Calculations showed that the formic acid Faradaic efficiency was less than 70% at all the aforementioned electrode potentials. The highest formic acid Faradaic efficiency, 48.01%, was achieved at an electrode potential of -2.5 V (vs. Ag / AgCl), with a formic acid separation current density of 51.56 mA cm -2 .

[0053] While various embodiments of the present invention have been described above, the above description is intended to be illustrative, not exhaustive, and not limited to the disclosed embodiments. Many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the described embodiments.

Claims

1. A method for preparing formic acid by electroreduction of supercritical carbon dioxide, characterized in that: The method comprises: preparing formic acid by conducting a carbon dioxide electroreduction reaction in an electrolyte under the condition that carbon dioxide is in a supercritical state; wherein an electrode loaded with Bi having a nanoflower-like morphology is used as a cathode; and the pressure of the carbon dioxide electroreduction reaction is 7.5-9.5 MPa and the temperature is 35-55°C.

2. The method according to claim 1, wherein In the method, the electrolyte used is a potassium bicarbonate aqueous solution, a mixed solution of an imidazole ionic liquid and water, or a mixed solution of an imidazole ionic liquid and methanol.

3. The method according to claim 2, wherein: The concentration of the potassium bicarbonate aqueous solution is 0.2-2.0 mol / L.

4. The method according to claim 2, wherein: The imidazolium ionic liquid is at least one of 1-butyl-3-methylimidazolium hexafluorophosphate, 1-ethyl-3-methylimidazolium tetrafluoroborate and 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide.

5. The method according to claim 1, wherein In the method, platinum is used as the anode; and an Ag / AgCl electrode is used as the reference electrode.

6. The method according to claim 1, wherein The reaction device is a diaphragm electrolyzer.

7. The method according to claim 6, wherein: The diaphragm of the diaphragm electrolyzer is a cation exchange membrane.

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