Method for catalyzing electrochemical reduction of carbonate into formate by bismuth-based material and application

Abstract

The invention provides a method for catalyzing electrochemical reduction of carbonate into formate by a bismuth-based material and application. The method comprises the following steps: (1) assembling a working electrode, a reference electrode, a counter electrode and an electrolyte into a three-electrode system, the working electrode being an electrode loaded with a bismuth-based material, and the electrolyte being a carbonate aqueous solution; (2) applying a potential of-0.8 to 0.4 V to the working electrode to realize adsorption of the carbonate by the working electrode, and then adjusting the potential to-2.0 to-1.2 V to realize reduction of the carbonate; and (3) taking the step (2) as a cycle, and carrying out the cycle in sequence. According to the method, the bismuth-based material can be kept relatively stable under the pulse potential, the conversion efficiency can be improved, the cost can be reduced, and industrialization can be better achieved in the future.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of electrocatalysis, and particularly relates to a method for catalyzing electrochemical reduction of carbonates to formates by using a bismuth-based material and application thereof. BACKGROUND

[0002] With the acceleration of human activities and industrialization process, the concentration of CO2 in the atmosphere has increased dramatically in recent decades, triggering the greenhouse effect and many climate problems. Under this background, CO2 reduction technology has gradually developed, and its principle is that CO2 obtains electrons through photochemistry or electrochemistry and is converted into high-value organic matter. In order to avoid the occurrence of hydrogen evolution side reaction, many CO2 reduction systems are carried out in alkaline solution, which will cause part of CO2 to be converted into carbonate, resulting in carbon loss. If carbonate can be reduced to organic matter, it will not only help to solve the problem of carbon loss in the process of CO2 reduction, but also help to provide a new carbon sequestration approach. However, carbonate is generally considered to be catalytically inert, and has lower efficiency compared with CO2 reduction technology. Therefore, it is of great significance to develop a carbonate reduction technology with high efficiency, high stability and low cost.

[0003] Reference (Haibin Ma, et al. Direct Electroreduction of Carbonate to Formate. J. Am. Chem. Soc. 2023, 145, 24707-24716) discloses that in the process of eCO2RR from 0.2 to-1.0 V, carbonate intermediates will be adsorbed on the copper electrode in the KHCO3 electrolyte. At-0.4 V and more negative potentials, these intermediates can be reduced to formate; in addition, in the pulse electrolysis experiment, the copper electrode is immersed in the K2CO3 electrolyte purged with nitrogen, and the carbonate anions therein can be adsorbed at-0.05 V, and then directly reduced to formate at-0.5 V (overpotential is 0.28 V), and the Faraday efficiency is 0.61%. The Faraday efficiency of this method is low.

[0004] Patent application with publication number CN119592970A discloses a method for preparing formate salt by electro-reduction of carbonate, comprising the following steps: 1) assembling a three-electrode system with a tin-based oxygen-containing compound loaded electrode as a working electrode, an Ag / AgCl electrode or a Hg / HgO electrode as a reference electrode, a platinum electrode as a counter electrode, and a carbonate solution as an electrolyte, and loading the electrolyte into a gas diffusion electrochemical reaction cell; 2) passing oxygen-containing gas into the gas diffusion electrochemical reaction cell, and then applying electricity to locally reduce the tin-based oxygen-containing compound at a potential range of-0.8 V~0 V, adjusting the potential to electro-reduce the carbonate at a potential range of-1.0 V~-0.8 V, and adjusting the potential to regenerate the tin-based oxygen-containing compound at a potential range of-0.4 V~0.4 V, and repeating the above steps. The tin-based oxygen-containing compound used in the method is also reduced during the electro-reduction process at-1.0 V~-0.8 V, and a regeneration process of the tin-based oxygen-containing compound is required. SUMMARY

[0005] To solve the above technical problems in the prior art, the present application provides a method for catalyzing electrochemical reduction of carbonate to formate salt by using a bismuth-based material and application thereof.

[0006] The present application provides a method for catalyzing electrochemical reduction of carbonate to formate salt by using a bismuth-based material, comprising the following steps: (1) assembling a three-electrode system with a working electrode, a reference electrode, a counter electrode, and an electrolyte, wherein the working electrode is a bismuth-based material loaded electrode, and the electrolyte is an aqueous carbonate solution; (2) applying a potential of-0.8~0.4 V to the working electrode to realize adsorption of carbonate on the working electrode, and then adjusting the potential to-2.0~-1.2 V to realize reduction of the carbonate; (3) taking step (2) as a cycle and repeating the cycle.

[0007] The present application adopts pulse potential method, first partially reduces the bismuth-based material in a potential range of-0.8~0.4 V, so that more active sites of the working electrode are exposed, which is conducive to adsorption of carbonate on the working electrode; then switches the potential to a potential range of-2.0~-1.2 V, in which the carbonate is converted to formate by receiving electrons; continues to switch the potential back to the potential range of-0.8~0.4 V to continue adsorption of carbonate on the electrode, while avoiding repulsion of the double-layer effect on the carbonate. In general, the pulse potential and the duration at each potential can well control the adsorption and reduction behavior of carbonate on the bismuth-based material electrode, so as to realize efficient conversion of carbonate.

[0008] Preferably, in step (1), the bismuth-based material comprises at least one of metallic bismuth, bismuth oxide, bismuth sulfide, bismuth acetate and bismuth subcarbonate.

[0009] Further preferably, the bismuth-based material is bismuth subcarbonate, which has a higher Faraday efficiency in electrochemical reduction of carbonates.

[0010] Preferably, in step (1), the solute in the aqueous carbonate solution is at least one of potassium carbonate, sodium carbonate and lithium carbonate.

[0011] Preferably, in step (1), the concentration of the aqueous carbonate solution is 0.01-7 mol / L, which can ensure sufficient supply of carbonate ions and avoid side reactions such as hydrogen generation in electrolysis of water, and the concentration of 7 mol / L is close to the solubility limit of carbonates in water.

[0012] Preferably, in step (1), the pH of the aqueous carbonate solution is 8-14, in which range carbonate ions can exist stably in the aqueous solution, as shown in the following equation: Figure 1 Further preferably, the pH of the aqueous carbonate solution is 12, which has a higher Faraday efficiency in electrochemical reduction of carbonates.

[0013] Preferably, in step (2), a potential of -0.8 V is first applied to the working electrode to realize adsorption of carbonates on the working electrode, and then the potential is adjusted to -1.2 V to realize reduction of carbonates. Under this pulsed potential, the Faraday efficiency of electrochemical reduction of carbonates is higher.

[0014] Preferably, in step (2), the time for applying a potential of -0.8-0.4 V to the working electrode is 0.1-50 s, and the time for applying a potential of -2.0- -1.2 V to the working electrode is 0.1-50 s.

[0015] Further preferably, in step (2), the time for applying a potential of -0.8-0.4 V to the working electrode is 20 s, and the time for applying a potential of -2.0- -1.2 V to the working electrode is 10 s. In this way, the current curve is basically stable when the potential is switched, indicating that the adsorption or reduction process is just completed, so that the electric charge can be effectively utilized, and too long time can easily cause side reactions.

[0016] Preferably, in step (1), the substrate of the working electrode is at least one of carbon paper, carbon fiber cloth, glassy carbon, FTO glass, metal foil, PVDF film and non-woven fabric.

[0017] Preferably, in step (1), the reference electrode is a Hg / HgO or Ag / AgCl electrode, and the counter electrode is a platinum electrode or a graphite rod.

[0018] The application further provides application of the method for catalyzing electrochemical reduction of carbonates to formate by the bismuth-based material in preparation of formate.

[0019] Compared with the prior art, the application has the following beneficial effects: (1) The application utilizes pulse potential to realize the method for catalyzing electrochemical reduction of carbonates to formate by the bismuth-based material, wherein the bismuth-based material can be kept relatively stable under the pulse potential, which is beneficial to improving conversion efficiency and reducing cost, and better realizing industrialization in the future; (2) The application utilizes pulse potential to realize the method for catalyzing electrochemical reduction of carbonates to formate by the bismuth-based material, wherein the carbonates react at the interface between the solution and the electrode, which is beneficial to removing the carbonates generated in the CO2 reduction system in situ. BRIEF DESCRIPTION OF DRAWINGS

[0020] Figure 1 is a graph of the concentration of carbonate in an aqueous solution varying with pH; Figure 2 is a schematic diagram of the device in Example 1; Figure 3 is a cyclic voltammetry test diagram of the bismuth oxy carbonate working electrode in Example 1; Figure 4 is a graph of the pulse potential varying with time in Example 1; Figure 5 is a graph of the pulse current varying with time in Example 1; Figure 6 is a graph of the in-situ Raman test result of the working electrode in Example 1, wherein Figure 6 a is the change of the Raman peaks of the carbonate and reaction intermediates on the surface of the bismuth oxy carbonate working electrode under different potentials, Figure 6 b is a partial enlarged view of a; Figure 7 is an ion chromatography test result diagram of the solution after the test in Example 1. DETAILED DESCRIPTION

[0021] Example 1: A method for catalyzing electrochemical reduction of carbonates to formate by a bismuth-based material by utilizing pulse potential, steps are as follows: Preparation part: (1) 20 mg of bismuth oxy carbonate is added to 1 mL of isopropyl alcohol, and a few drops of 5% by mass Nafion solution are dropped in, and a uniformly dispersed bismuth-based material slurry is prepared under ultrasonic conditions, then the slurry is drop-coated on carbon paper by drop-coating method, and after natural air drying, it is transferred to a 60 ℃ oven for further drying, to obtain a working electrode loaded with the bismuth-based material; in addition, 0.05 mol / L of potassium carbonate solution is prepared as the carbonate solution for testing, and the pH of the solution is adjusted to 12; (2) Insert the working electrode and Hg / HgO reference electrode into the cathode chamber, and insert the platinum plate counter electrode into the anode chamber. The cathode chamber and the anode chamber are separated by a proton exchange membrane. After assembling the three-electrode electrolytic cell, add the prepared potassium carbonate solution into the cathode chamber and the anode chamber, respectively. The volume of the added potassium carbonate solution is determined according to the actual capacity of the electrolytic cell, which is 9 mL in this case. The device schematic diagram is shown in Figure 2 .

[0022] Test section: Before the pulse test, the working electrode is soaked in the carbonate solution for 30 minutes to achieve pre-enrichment of carbonate on the surface of the working electrode. Then, several cyclic voltammetry tests are performed to fully activate the surface of the working electrode, with the potential range being the redox interval of bismuth carbonate oxide, i.e. -1.5 V~0.5 V, as shown in Figure 3 . After sufficient activation, the working electrode is first applied with a potential of -0.8 V for 20 s (in this process, carbonate is adsorbed to the electrode surface); then the potential is switched to -1.2 V for 10 s (in this process, carbonate is reduced to formate by receiving electrons), which is one pulse cycle. The cycle number is set to 60 to achieve sufficient conversion of carbonate. The potential change during the pulse test is shown in Figure 4 , and the current change is shown in Figure 5 .

[0023] Product detection section: The three-electrode electrolytic cell used in this embodiment is placed on a Raman test table. Through the light window of the cathode chamber, the adsorption and reduction of carbonate on the working electrode under pulse potential can be in-situ characterized. The test results are shown in Figure 6 .

[0024] Raman spectroscopy can characterize the characteristic vibration of functional groups. Using this principle, the adsorption and reduction of carbonate on the bismuth-based material can be observed. As shown in Figure 6 , within the potential range of 0~-1.2 V, the characteristic Raman peak of carbonate appears at 1065 cm -1 , and the Raman peak intensity gradually increases, indicating the adsorption of carbonate on the electrode; when the potential becomes more negative, the carbonate Raman peak intensity gradually decreases, and a characteristic Raman peak of CO2· -1 , which is a key intermediate of the reduction of carbonate to formate, appears at 1530 cm - , indicating that the reduction of carbonate on the electrode and the conversion to formate have occurred.

[0025] At the same time, the solution in the cathode chamber after the reaction is collected and diluted for ion chromatography test. The test results are shown in Figure 7 . The standard formate chromatographic peak appears at a retention time of 3.5 min, indicating the formation of formate.

[0026] Example 2 A method for realizing electrochemical reduction of carbonates to formate by bismuth-based material catalysis using pulse potential, the steps are as follows: Preparation part: (1) 20 mg of bismuth subcarbonate was added to 1 mL of isopropyl alcohol, and a few drops of 5% Nafion solution were added at the same time. A uniformly dispersed slurry of bismuth-based material was prepared under ultrasonic conditions, and then the slurry was drop-coated onto carbon paper. After natural air drying, it was transferred to a 60 ℃ oven for further drying to obtain a working electrode loaded with bismuth-based material. In addition, 0.05 mol / L potassium carbonate solution was prepared as the test carbonate solution, and the solution pH was adjusted to 12; (2) The working electrode and Hg / HgO reference electrode were inserted into the cathode chamber, and the platinum sheet counter electrode was inserted into the anode chamber. The cathode chamber and the anode chamber were separated by a proton exchange membrane. After assembling the three-electrode electrolytic cell, the same amount of potassium carbonate solution was added to the cathode chamber and the anode chamber.

[0027] Test part: Before pulse testing, the working electrode was soaked in the carbonate solution for 30 minutes, and then several cyclic voltammetry tests were performed to fully activate the surface of the working electrode, with a potential range of -1.5 V~0.5 V. After sufficient activation, the working electrode was first applied with a potential of -0.8 V for 50 s (in this process, carbonate ions are adsorbed onto the electrode surface); then the potential was switched to -2.0 V for 50 s (in this process, carbonate ions are reduced to formate ions), which is one pulse cycle. The number of cycles was set to 60 to achieve sufficient conversion of carbonates.

[0028] Example 3 A method for realizing electrochemical reduction of carbonates to formate by bismuth-based material catalysis using pulse potential, the steps are as follows: Preparation part: (1) 20 mg of bismuth subcarbonate was added to 1 mL of isopropyl alcohol, and a few drops of 5% Nafion solution were added at the same time. A uniformly dispersed slurry of bismuth-based material was prepared under ultrasonic conditions, and then the slurry was drop-coated onto carbon paper. After natural air drying, it was transferred to a 60 ℃ oven for further drying to obtain a working electrode loaded with bismuth-based material. In addition, 0.05 mol / L potassium carbonate solution was prepared as the test carbonate solution, and the solution pH was adjusted to 12; (2) The working electrode and Hg / HgO reference electrode were inserted into the cathode chamber, and the platinum sheet counter electrode was inserted into the anode chamber. The cathode chamber and the anode chamber were separated by a proton exchange membrane. After assembling the three-electrode electrolytic cell, the same amount of potassium carbonate solution was added to the cathode chamber and the anode chamber.

[0029] Test section: Before the pulse test, the working electrode is soaked in carbonate solution for 30 minutes, and then several cyclic voltammetry tests are performed to fully activate the surface of the working electrode, with a potential range of -1.5 V~0.5 V. After full activation, a potential of -0.8 V is first applied to the working electrode for a duration of 5 s (during which carbonate is adsorbed onto the electrode surface); the potential is then switched to -1.2 V for a duration of 0.1 s (during which the carbonate is reduced to formate by electron transfer). This is one pulse cycle. The number of cycles is set to 60 to achieve full conversion of the carbonate.

[0030] Example 4: A method for using pulse potential to catalyze the electrochemical reduction of carbonate to formate by bismuth-based materials, the steps are as follows: Preparation section: (1) 20 mg of bismuth subcarbonate is added to 1 mL of isopropyl alcohol, and a few drops of 5% by mass Nafion solution are added. A uniform dispersion of bismuth-based material slurry is prepared under ultrasonic conditions, and then the slurry is drop-cast onto carbon paper using a drop-casting method. After natural air drying, the working electrode loaded with bismuth-based material is transferred to a 60°C oven for further drying. In addition, a 0.05 mol / L potassium carbonate solution is prepared as the test carbonate solution, and the pH of the solution is adjusted to 12; (2) The working electrode and Hg / HgO reference electrode are inserted into the cathode chamber, and the platinum sheet counter electrode is inserted into the anode chamber. The cathode chamber and anode chamber are separated by a proton exchange membrane. After assembling the three-electrode electrolytic cell, the same amount of potassium carbonate solution is added to the cathode chamber and anode chamber.

[0031] Test section: Before the pulse test, the working electrode is soaked in carbonate solution for 30 minutes, and then several cyclic voltammetry tests are performed to fully activate the surface of the working electrode, with a potential range of -1.5 V~0.5 V. After full activation, a potential of -0.8 V is first applied to the working electrode for a duration of 0.1 s (during which carbonate is adsorbed onto the electrode surface); the potential is then switched to -1.2 V for a duration of 0.1 s (during which the carbonate is reduced to formate by electron transfer). This is one pulse cycle. The number of cycles is set to 60 to achieve full conversion of the carbonate.

[0032] Example 5: A method for using pulse potential to catalyze the electrochemical reduction of carbonate to formate by bismuth-based materials, the steps are as follows: Preparation section: (1) 20 mg bismuth carbonate was added to 1 mL isopropyl alcohol, and a few drops of 5% Nafion solution were added dropwise. A uniformly dispersed bismuth-based material slurry was prepared under ultrasonic conditions, and then the slurry was drop-casted onto carbon paper by drop-casting. After natural air drying, it was transferred to a 60°C oven for further drying to obtain a working electrode loaded with a bismuth-based material. In addition, a 0.05 mol / L potassium carbonate solution was prepared as a carbonate salt solution for testing, and the solution pH was adjusted to 12; (2) The working electrode and the Hg / HgO reference electrode were inserted into the cathode chamber, and the platinum sheet counter electrode was inserted into the anode chamber. The cathode chamber and the anode chamber were separated by a proton exchange membrane. After assembling the three-electrode electrolytic cell, the same amount of potassium carbonate solution was added to the cathode chamber and the anode chamber.

[0033] Test section: Before pulse testing, the working electrode was soaked in the carbonate solution for 30 minutes, and then several cyclic voltammetry tests were performed to fully activate the surface of the working electrode, with a potential range of -1.5 V to 0.5 V. After sufficient activation, the working electrode was first applied with a potential of 0.4 V for 20 s (in this process, carbonate ions are adsorbed onto the electrode surface); then the potential was switched to -1.2 V for 10 s (in this process, carbonate ions are reduced to formate ions), which is one pulse cycle. The number of cycles was set to 60 to achieve sufficient conversion of carbonate.

[0034] Example 6: A method for catalyzing the electrochemical reduction of carbonate to formate by a bismuth-based material using pulse potential, the steps are as follows: Preparation section: (1) 20 mg bismuth carbonate was added to 1 mL isopropyl alcohol, and a few drops of 5% Nafion solution were added dropwise. A uniformly dispersed bismuth-based material slurry was prepared under ultrasonic conditions, and then the slurry was drop-casted onto carbon paper by drop-casting. After natural air drying, it was transferred to a 60°C oven for further drying to obtain a working electrode loaded with a bismuth-based material. In addition, a 0.05 mol / L potassium carbonate solution was prepared as a carbonate salt solution for testing, and the solution pH was adjusted to 12; (2) The working electrode and the Hg / HgO reference electrode were inserted into the cathode chamber, and the platinum sheet counter electrode was inserted into the anode chamber. The cathode chamber and the anode chamber were separated by a proton exchange membrane. After assembling the three-electrode electrolytic cell, the same amount of potassium carbonate solution was added to the cathode chamber and the anode chamber.

[0035] Test section: Before the pulse test, the working electrode was immersed in the carbonate solution for 30 minutes, and then several cyclic voltammetry tests were performed to fully activate the surface of the working electrode, with a potential range of -1.5 V~0.5 V. After full activation, a potential of -0.8 V was first applied to the working electrode for a duration of 20 s (during which process carbonate was adsorbed onto the electrode surface); then the potential was switched to -2.0 V for a duration of 10 s (during which process carbonate was reduced to formate by electron transfer), which was one pulse cycle. The number of cycles was set to 60 to achieve full conversion of carbonate.

[0036] Example 7: A method for realizing the electrochemical reduction of carbonate to formate by bismuth-based materials using pulse potential, the steps are as follows: Preparation part: (1) 20 mg of bismuth subcarbonate was added to 1 mL of isopropyl alcohol, and a few drops of 5% Nafion solution were added. A uniform dispersion of bismuth-based material slurry was prepared under ultrasonic conditions, and then the slurry was drop-casted onto carbon paper. After natural air drying, it was transferred to a 60 ℃ oven for further drying, obtaining a working electrode loaded with bismuth-based materials. In addition, 0.05 mol / L potassium carbonate solution was prepared as the test carbonate solution, and the solution pH was adjusted to 14; (2) The working electrode and Hg / HgO reference electrode were inserted into the cathode chamber, and the platinum sheet counter electrode was inserted into the anode chamber. The cathode chamber and anode chamber were separated by a proton exchange membrane. After assembling the three-electrode electrolytic cell, the same amount of potassium carbonate solution was added to the cathode chamber and anode chamber.

[0037] Test part: Before the pulse test, the working electrode was immersed in the carbonate solution for 30 minutes, and then several cyclic voltammetry tests were performed to fully activate the surface of the working electrode, with a potential range of -1.5 V~0.5 V. After full activation, a potential of -0.8 V was first applied to the working electrode for a duration of 20 s (during which process carbonate was adsorbed onto the electrode surface); then the potential was switched to -1.2 V for a duration of 10 s (during which process carbonate was reduced to formate by electron transfer), which was one pulse cycle. The number of cycles was set to 60 to achieve full conversion of carbonate.

[0038] Example 8: A method for realizing the electrochemical reduction of carbonate to formate by bismuth-based materials using pulse potential, the steps are as follows: Preparation part: (1) 20 mg bismuth carbonate was added to 1 mL isopropyl alcohol, and a few drops of 5% Nafion solution were added dropwise. A uniformly dispersed bismuth-based material slurry was prepared under ultrasonic conditions, and then the slurry was drop-casted onto carbon paper by drop-casting. After natural air drying, it was transferred to a 60°C oven for further drying to obtain a working electrode loaded with a bismuth-based material. In addition, 0.05 mol / L potassium carbonate solution was prepared as the carbonate solution for testing, and the solution pH was adjusted to 8; (2) The working electrode and the Hg / HgO reference electrode were inserted into the cathode chamber, and the platinum sheet counter electrode was inserted into the anode chamber. The cathode chamber and the anode chamber were separated by a proton exchange membrane. After assembling the three-electrode electrolytic cell, the same amount of potassium carbonate solution was added to the cathode chamber and the anode chamber.

[0039] Test section: Before the pulse test, the working electrode was soaked in the carbonate solution for 30 minutes, and then several cyclic voltammetry tests were performed to fully activate the surface of the working electrode, with a potential range of -1.5 V to 0.5 V. After sufficient activation, the working electrode was first applied with a potential of -0.8 V for 20 s (in this process, carbonate ions are adsorbed onto the electrode surface); then the potential was switched to -1.2 V for 10 s (in this process, carbonate ions are reduced to formate ions), which is one pulse cycle. The number of cycles was set to 60 to achieve sufficient conversion of carbonate.

[0040] Example 9: A method for catalyzing the electrochemical reduction of carbonate to formate by a bismuth-based material using pulse potential, the steps are as follows: Preparation section: (1) 20 mg bismuth carbonate was added to 1 mL isopropyl alcohol, and a few drops of 5% Nafion solution were added dropwise. A uniformly dispersed bismuth-based material slurry was prepared under ultrasonic conditions, and then the slurry was drop-casted onto carbon paper by drop-casting. After natural air drying, it was transferred to a 60°C oven for further drying to obtain a working electrode loaded with a bismuth-based material. In addition, 0.05 mol / L potassium carbonate solution was prepared as the carbonate solution for testing, and the solution pH was adjusted to 8; (2) The working electrode and the Hg / HgO reference electrode were inserted into the cathode chamber, and the platinum sheet counter electrode was inserted into the anode chamber. The cathode chamber and the anode chamber were separated by a proton exchange membrane. After assembling the three-electrode electrolytic cell, the same amount of potassium carbonate solution was added to the cathode chamber and the anode chamber.

[0041] Test section: Before the pulse test, the working electrode is immersed in the carbonate solution for 30 minutes, and then several cyclic voltammetry tests are performed to fully activate the surface of the working electrode, with a potential range of -1.5 V~0.5 V. After full activation, a potential of -0.8 V is first applied to the working electrode for a duration of 20 s (during which process carbonate is adsorbed to the electrode surface); then the potential is switched to -1.2 V for a duration of 10 s (during which process carbonate is reduced to formate by electron transfer), which is one pulse cycle. The number of cycles is set to 60 to achieve full conversion of carbonate.

[0042] Example 10: A method for realizing the electrochemical reduction of carbonate to formate by bismuth-based materials using pulse potential, the steps are as follows: Preparation part: (1) 20 mg of bismuth subcarbonate is added to 1 mL of isopropyl alcohol, and a few drops of 5% Nafion solution are added dropwise. A uniform dispersion of bismuth-based material slurry is prepared under ultrasonic conditions, and then the slurry is drop-casted onto carbon paper using a drop-casting method. After natural air drying, it is transferred to a 60 °C oven for further drying to obtain a working electrode loaded with bismuth-based materials. In addition, a 7 mol / L potassium carbonate solution is prepared as the test carbonate solution, and the solution pH is adjusted to 12; (2) The working electrode and Hg / HgO reference electrode are inserted into the cathode chamber, and the platinum sheet counter electrode is inserted into the anode chamber. The cathode chamber and anode chamber are separated by a proton exchange membrane. After assembling the three-electrode electrolytic cell, the same amount of potassium carbonate solution is added to the cathode chamber and anode chamber.

[0043] Test part: Before the pulse test, the working electrode is immersed in the carbonate solution for 30 minutes, and then several cyclic voltammetry tests are performed to fully activate the surface of the working electrode, with a potential range of -1.5 V~0.5 V. After full activation, a potential of -0.8 V is first applied to the working electrode for a duration of 20 s (during which process carbonate is adsorbed to the electrode surface); then the potential is switched to -1.2 V for a duration of 10 s (during which process carbonate is reduced to formate by electron transfer), which is one pulse cycle. The number of cycles is set to 60 to achieve full conversion of carbonate.

[0044] Example 11: A method for realizing the electrochemical reduction of carbonate to formate by bismuth-based materials using pulse potential, the steps are as follows: Preparation part: (1) 20 mg bismuth powder was added into 1 mL isopropyl alcohol, and a few drops of 5% mass fraction Nafion solution were added dropwise, and a uniformly dispersed bismuth-based material slurry was prepared under ultrasonic conditions, and then the slurry was drop-coated on carbon paper by drop-coating method, and after natural air drying, it was transferred to a 60°C oven for further drying to obtain a working electrode loaded with bismuth-based material; in addition, 0.05 mol / L potassium carbonate solution was prepared as a carbonate solution for testing, and the solution pH was adjusted to 12; (2) The working electrode and the Hg / HgO reference electrode were inserted into the cathode chamber, and the platinum sheet counter electrode was inserted into the anode chamber. The cathode chamber and the anode chamber were separated by a proton exchange membrane. After assembling the three-electrode electrolytic cell, the same amount of potassium carbonate solution was added to the cathode chamber and the anode chamber.

[0045] Test section: Before the pulse test, the working electrode was soaked in the carbonate solution for 30 minutes, and then several cyclic voltammetry tests were performed to fully activate the surface of the working electrode, with a potential range of -1.5 V~0.5 V. After sufficient activation, the working electrode was first applied with a potential of -0.8 V for 20 s (in this process, carbonate ions are adsorbed on the electrode surface); then the potential was switched to -1.2 V for 10 s (in this process, carbonate ions are converted to formate ions), which is one pulse cycle. The cycle number was set to 60 to achieve sufficient conversion of carbonate.

[0046] Detection Example 1 The Faraday efficiency of the conversion of carbonate to formate was calculated by the following formula: Faraday efficiency = (number of electrons transferred * formate concentration * volume * Faraday constant * 0.1) / (charge amount * formate molar mass), wherein the number of electrons transferred refers to the number of electrons required for the conversion of carbonate to formate, which is 2 here; the formate concentration is in mg / L; the volume is in mL; the Faraday constant is 96485 C / mol; the charge amount is in C; and the formate molar mass is 45 g / mol.

[0047] The charge amount was collected by an electrochemical workstation, and the formate concentration was collected by ion chromatography, and the detection method referred to the national standard GB / T 35665-2017.

[0048] Table 1 The detection results are shown in Table 1, and the following conclusions can be obtained from the test results: (1) the method for realizing electrochemical reduction of carbonates to formate by using bismuth-based material catalysis through pulse potential can make the Faraday efficiency of carbonates converted to formate reach 24.15%; (2) the time of pulse potential has a significant influence on the reaction results, too short will lead to insufficient adsorption and reduction process of carbonate ions on the electrode, and too long will promote the occurrence of side reactions, thereby reducing the efficiency; (3) the selection of adsorption and reduction potential is related to the cyclic voltammetry test, and selecting the potential near the oxidation peak and the reduction peak of the electrode material is beneficial to the adsorption and reduction of carbonate, and too negative or too positive may lead to the intensification of side reactions; (4) the improvement of the concentration of carbonate will promote the reduction performance of carbonate.

Claims

1. A method for electrochemically reducing carbonate to formate using a bismuth-based material, characterized in that: The following steps are involved: (1) Assembling a three-electrode system by a working electrode, a reference electrode, a counter electrode, and an electrolyte, wherein the working electrode is an electrode loaded with a bismuth-based material, and the electrolyte is a carbonate aqueous solution; (2) Applying a potential of -0.8 to 0.4 V to the working electrode to achieve carbonate adsorption, and then adjusting the potential to -2.0 to -1.2 V to achieve carbonate reduction; (3) Treat step (2) as a loop and repeat it in this way.

2. The method for electrochemical reduction of carbonate to formate catalyzed by bismuth-based materials according to claim 1, characterized in that: In step (1), the bismuth-based material includes at least one of metallic bismuth, bismuth oxide, bismuth sulfide, bismuth acetate and bismuth oxycarbonate.

3. The method for electrochemical reduction of carbonate to formate catalyzed by bismuth-based materials according to claim 2, characterized in that: The bismuth-based material is bismuth oxycarbonate.

4. The method of claim 1, wherein the bismuth-based material catalyzes the electrochemical reduction of carbonate to formate. In step (1), the solute in the carbonate aqueous solution is at least one of potassium carbonate, sodium carbonate and lithium carbonate.

5. The method for electrochemical reduction of carbonate to formate catalyzed by bismuth-based materials according to claim 1, characterized in that: In step (1), the concentration of the carbonate aqueous solution is 0.01~7 mol / L.

6. The method of claim 1, wherein the bismuth-based material catalyzes the electrochemical reduction of carbonate to formate. In step (1), the pH of the carbonate aqueous solution is 8-14.

7. The method of claim 1, wherein the bismuth-based material catalyzes the electrochemical reduction of carbonate to formate. In step (2), a potential of -0.8 V is first applied to the working electrode to achieve adsorption of carbonate by the working electrode, and then the potential is adjusted to -1.2 V to achieve reduction of carbonate.

8. The method of claim 1, wherein the bismuth-based material catalyzes the electrochemical reduction of carbonate to formate. In step (2), the time for applying a potential of -0.8 to 0.4 V to the working electrode is 0.1 to 50 s, and the time for applying a potential of -2.0 to -1.2 V to the working electrode is 0.1 to 50 s.

9. The method of claim 1, wherein the bismuth-based material catalyzes the electrochemical reduction of carbonate to formate. In step (1), the substrate of the working electrode is at least one of carbon paper, carbon fiber cloth, glassy carbon, FTO glass, metal foil, PVDF membrane and non-woven fabric; the reference electrode is a Hg / HgO or Ag / AgCl electrode, and the counter electrode is a platinum electrode or a graphite rod.

10. Use of the method according to any one of claims 1 to 9 for catalyzing the electrochemical reduction of carbonate to formate in the preparation of formate.

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