Method for preparing formate salt by using carbonate electro-reduction and application thereof

Abstract

The application discloses a method for preparing formate by electro-reduction of carbonate and application thereof. The method comprises the following steps: 1) loading a tin-based oxygen-containing compound electrode as a working electrode, an Ag / AgCl electrode or an Hg / HgO electrode as a reference electrode, a platinum electrode as a counter electrode, and a carbonate solution as an electrolyte to assemble a three-electrode system, and loading the electrolyte into a gas diffusion electrochemical reaction cell; 2) introducing oxygen-containing gas into the gas diffusion electrochemical reaction cell, and then sequentially performing local reduction of the tin-based oxygen-containing compound, electro-reduction of the carbonate and regeneration of the tin-based oxygen-containing compound by electrifying, and the above steps are cyclically performed. The method for preparing formate by electro-reduction of carbonate has the advantages of simple operation, simple equipment, reliable principle, low cost, high stability and the like, and is suitable for large-scale industrial application.

Description

Technical Field

[0001] The present invention relates to the technical field of electrocatalysis, and in particular to a method for preparing formate by utilizing carbonate electroreduction and application thereof. Background Art

[0002] With the large-scale use of fossil fuels, the content of carbon dioxide (CO2) in the atmosphere is constantly increasing, causing environmental problems such as global warming and ocean acidification, threatening human survival and ecological stability. Studies have shown that relying solely on nature's own "carbon cycle" can no longer effectively control the increase in CO2 content in the atmosphere. There is an urgent need for an artificial "carbon cycle" to achieve the sustainable development goal of "carbon neutrality". At present, the use of renewable energy to drive the conversion of CO2 into fuel or high-value-added chemicals is becoming an important technical segment of the artificial "carbon cycle" (O'BRIEN CP, et al. CO2electrolyzers[J]. Chemical Reviews, 2024, 124(7): 3648-3693.). However, when using existing methods to reduce CO2, a large amount of CO2 will generate carbonates (CO3 2- It is generally considered to be an electrochemically inert substance), which will seriously affect the carbon and energy conversion efficiency (Vass, A., et al. Anode catalysts in CO2 electrolysis: challenges and untapped opportunities. ACS Catal. 2022, 12(2), 1037-1051.). In addition, the direct reduction of gaseous CO2 systems is often complex in structure and has poor stability, which greatly limits their practical application.

[0003] Therefore, it is of great significance to develop a method for reducing carbonate to formate with simple operation, simple equipment, reliable principle, low cost and high stability. Summary of the Invention

[0004] The object of the present invention is to provide a method for preparing formate by utilizing carbonate electroreduction and its application.

[0005] The technical solution adopted by the present invention is:

[0006] A method for preparing formate by electroreduction of carbonate comprises the following steps:

[0007] 1) Assembling a three-electrode system by using an electrode loaded with a tin-based oxygen-containing compound 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;

[0008] 2) passing an oxygen-containing gas into the gas diffusion electrochemical reaction cell, and then applying electricity to carry out local reduction of the tin-based oxygen-containing compound in the potential range of -0.8V to 0V (relative to the reversible hydrogen electrode RHE), adjusting the potential to carry out electro-reduction of the carbonate in the potential range of -1.0V to -0.8V, and adjusting the potential to carry out regeneration of the tin-based oxygen-containing compound in the potential range of -0.4V to 0.4V, and repeating the above steps.

[0009] Preferably, the tin-based oxygen-containing compound in step 1) is at least one of tin dioxide (SnO2), stannous oxide (SnO), tin hydroxide (Sn(OH)4), and stannous hydroxide (Sn(OH)2).

[0010] Preferably, the electrode loaded with the tin-based oxygen-containing compound in step 1) is a carbon electrode loaded with the tin-based oxygen-containing compound.

[0011] Preferably, the solute in the carbonate solution in step 1) is at least one of potassium carbonate (K2CO3), sodium carbonate (Na2CO3), and lithium carbonate (Li2CO3).

[0012] Preferably, the pH value of the carbonate solution in step 1) is 8 to 14. The local reduction of the tin-based oxygen-containing compound in the potential range of -0.8V to 0V by applying electricity to the carbonate solution can expose a large number of oxygen vacancies on the surface of the tin-based oxygen-containing compound, thereby realizing the adsorption of CO3 2- ions in the carbonate solution.

[0013] Further preferably, the pH value of the carbonate solution in step 1) is 8.3 to 13.

[0014] Preferably, the volume percentage content of oxygen in the oxygen-containing gas in step 2) is 0.001% to 25%.

[0015] Further preferably, the oxygen-containing gas in step 2) is air.

[0016] Preferably, the time for the local reduction of the tin-based oxygen-containing compound in step 2) is 0.001s to 100s.

[0017] Preferably, the time for the electro-reduction of the carbonate in step 2) is 0.001s to 100s.

[0018] Further preferably, the time for the electro-reduction of the carbonate in step 2) is 5s to 40s.

[0019] Preferably, the time for the regeneration of the tin-based oxygen-containing compound in step 2) is 0.001s to 100s.

[0020] Further preferably, the regeneration time of the tin-based oxygen-containing compound in step 2) is 0.001s to 20s.

[0021] Preferably, the number of cycles in step 2) is ≥ 1.

[0022] A method for preparing formate by utilizing carbonate electroreduction as described above is used for preparing formic acid.

[0023] Principle of the invention: The invention adopts the step potential method, firstly, the power is applied in the potential range of -0.8V to 0V to locally reduce the tin-based oxygen-containing compound, so that a large number of oxygen vacancies are exposed on the surface of the tin-based oxygen-containing compound, thereby realizing the reduction of CO3 in the carbonate solution. 2- ions, and then adjust the potential in the potential range of -1.0V to -0.8V to absorb CO3 2- ions are electroreduced to CO and HCOO - ions (tin-based oxygen-containing compounds will also be reduced), and then adjust the potential in the potential range of -0.4V to 0.4V to regenerate the tin-based oxygen-containing compounds, oxidize the deeply reduced tin-based oxygen-containing compounds into stable tin-based oxygen-containing compounds, and promote CO3 2- Ions migrate to the double layer (tin-based oxygen-containing compounds will undergo irreversible structural damage when reduced at negative potential for a long time, and need to be oxidized at positive potential to maintain stability, and CO3 2- The ions are negatively charged, and applying negative reduction potential for a long time will cause CO3 2- The ions are expelled from the double layer by Coulomb repulsion and cannot be adsorbed on the surface of the locally reduced tin-based oxygen-containing compound).

[0024] The beneficial effects of the present invention are as follows: the method for preparing formate by utilizing carbonate electroreduction of the present invention has the advantages of simple operation, simple equipment, reliable principle, low cost, high stability, etc., and is suitable for large-scale industrial application.

[0025] Specifically:

[0026] 1) The method for preparing formate by utilizing carbonate electroreduction of the present invention can 2- It is converted into carbon monoxide (CO) and formic acid (HCOOH) with high economic added value, with extremely high product selectivity and performance stability, and has great value in the fields of carbon emission reduction and renewable energy utilization;

[0027] 2) The method of preparing formate by electroreduction of carbonate of the present invention is low-cost and highly stable, can be used to prepare formic acid, and is suitable for large-scale industrial application;

[0028] 3) The method of preparing formate by carbonate electroreduction of the present invention realizes a closed-loop technology for carbon dioxide capture and reuse. Gaseous carbon dioxide can be directly collected by an alkaline solution without directly participating in a reduction reaction. No special reaction apparatus is required, and the reaction apparatus has a simple structure. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 The surface of SnO2 with different oxygen vacancy contents is affected by CO3 2- The adsorption energy variation trend diagram.

[0030] Figure 2 This is the in situ Raman thermogram of cyclic voltammetry of potassium carbonate solution.

[0031] Figure 3 This is the chronoamperometric in situ Raman thermogram of potassium carbonate solution.

[0032] Figure 4 Schematic diagram of the step potential method in the embodiment.

[0033] Figure 5 Graph showing the electroreduction effect of carbonate in the examples. DETAILED DESCRIPTION

[0034] The present invention will be further explained and illustrated below with reference to specific embodiments.

[0035] Example:

[0036] A method for preparing formate by electroreduction of carbonate, comprising the following steps:

[0037] 1) Tin dioxide was dispersed in anhydrous ethanol to prepare a slurry with a mass fraction of 0.63%, and the slurry was then coated on the surface of a carbon paper electrode and dried to prepare a carbon paper electrode loaded with tin dioxide (the loading amount of tin dioxide was 0.004 g / cm 2 ), a tin dioxide-loaded carbon paper electrode was used as a working electrode, a Hg / HgO electrode was used as a reference electrode, a platinum electrode was used as a counter electrode, and a 0.5 mol / L potassium carbonate aqueous solution (pH 12.1, with sufficient Ar gas introduced) was used as an electrolyte to assemble a three-electrode system, and the electrolyte was loaded into a gas diffusion electrochemical reaction cell (capable of controlling the atmosphere);

[0038] 2) Air was continuously introduced into the gas diffusion electrochemical reaction cell, and then the potential was controlled to -0.7 V (relative to the reversible hydrogen electrode RHE) for 30 s (local reduction of tin dioxide to form SnOCO3), and then the potential was adjusted to -1.0 V for 20 s (CO3 2- ions are electroreduced to CO and HCOO -ions), then adjust the potential to 0 V for 10 s (regeneration of tin dioxide), and repeat this cycle. The number of cycles is ≥ 1.

[0039] Test part:

[0040] 1) The surface effects of SnO2 with different oxygen vacancy contents on CO3 obtained by theoretical calculation 2- The adsorption energy change trend diagram is as follows Figure 1 shown.

[0041] Depend on Figure 1 It can be seen that as the oxygen vacancy content on the SnO2 surface increases, its effect on CO3 2- The adsorption capacity is also greatly enhanced.

[0042] 2) The three-electrode system in this embodiment was placed in an in-situ Raman reaction cell for in-situ Raman observation. Cyclic voltammetry was used during the test. The voltage position was from 1.21 V to -0.99 V, and the cycle was 1 cycle. The scan rate was 100 mV / s. The obtained in-situ Raman thermogram was as follows: Figure 2 (The bluer the color in the figure, the weaker the signal, and the redder the color, the stronger the signal).

[0043] Depend on Figure 2 It can be seen that: in potassium carbonate aqueous solution, when the voltage drops to -0.29V, SnO2@634cm -1 The signal begins to weaken, and SnO x -CO3@74 / 99cm -1 The signal increases rapidly until -0.82V and the two signals disappear together, revealing that CO3 2- In alkaline environment, SnO x The adsorption voltage range of the surface.

[0044] 3) The three-electrode system in this embodiment was placed in an in-situ Raman reaction cell for in-situ Raman observation. During the test, the chronoamperometry was used, and the potential was controlled at -0.69 V and -0.74 V for 100 s. The obtained in-situ Raman thermal map is shown in FIG. Figure 3 (a is the in-situ Raman thermogram corresponding to a potential of -0.69 V, and b is the in-situ Raman thermogram corresponding to a potential of -0.74 V; the bluer the color in the figure, the weaker the signal at that location, and the redder the color, the stronger the signal at that location).

[0045] Depend on Figure 3 It can be seen that the potential of -0.69V and -0.74V in potassium carbonate aqueous solution can achieve the effect of tin-based oxide on CO3 2- The adsorption is faster as the potential is lower and slower as the potential is higher. When the potential is -0.69V, CO3 2-The adsorption is completed in about 10 seconds and can last for more than 100 seconds. When the potential is -0.74V, CO3 2- The adsorption was completed around 3s but could only last around 70s, revealing that CO3 2- In alkaline environment, SnO x Surface adsorption characteristics.

[0046] 4) The schematic diagram of the step potential method in this embodiment is as follows Figure 4 shown.

[0047] Depend on Figure 4 It can be seen that the adsorption potential can reduce tin-based oxygen-containing compounds to a suitable oxidation state to complete the CO3 2- adsorption, the reduction potential can make the adsorbed CO3 2- The open circuit potential can oxidize the deeply reduced tin-based oxygen-containing compounds to a stable state and promote the CO3 2- Migrate to the double layer.

[0048] 5) The three-electrode system in this embodiment was connected to a gas chromatograph for real-time gas product detection, the gas flow rate was controlled to 25 mL / min, and the electrolyte was extracted after the reaction and ions in the solution were detected using high performance liquid chromatography. The electroreduction effect of carbonate obtained was shown in the figure below. Figure 5 (a is the test result of gaseous products of electro-reduction under air atmosphere, b is the test result of gaseous products of electro-reduction under argon atmosphere, and c is the test result of liquid products under two atmosphere environments).

[0049] Depend on Figure 5 It can be seen that:

[0050] a) In air atmosphere, tin-based oxygen-containing compounds can achieve spontaneous oxidation and then reduction to adsorb CO3 2- , to achieve the CO3 in the solution 2- Continuous adsorption and reduction of ions to produce CO and HCOO - , and has high selectivity, and no H2 is produced in the reaction;

[0051] b) Under argon atmosphere, tin-based oxygen-containing compounds can only achieve CO3 in the early stage of the reaction. 2- Adsorption and reduction of CO and HCOO - However, since there is no oxygen in the reaction system, tin-based oxygen-containing compounds cannot spontaneously oxidize, and thus cannot continuously achieve the CO3 2- Adsorption and reduction of CO and HCOO - , resulting in the late product being only H2;

[0052] In summary, the present invention can realize the continuous catalysis of CO3 by tin-based oxygen-containing compounds based on the step potential method and atmosphere control. 2-Reduction produces CO and HCOO - , suitable for large-scale industrial applications.

[0053] The above embodiments are preferred implementation modes of the present invention, but the implementation modes of the present invention are not limited to the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications that do not deviate from the spirit and principles of the present invention should be considered as equivalent replacement methods and are included in the scope of protection of the present invention.

Claims

1. A method for preparing formate by electroreduction of carbonate, characterized in that: The following steps are involved: 1) Assemble a three-electrode system by using an electrode loaded with a tin-based oxygen-containing compound 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 load the electrolyte into a gas diffusion electrochemical reaction cell; 2) introducing an oxygen-containing gas into a gas diffusion electrochemical reaction cell, then applying power in a potential range of -0.8V to 0V to partially reduce the tin-based oxygen-containing compound, then adjusting the potential in a potential range of -1.0V to -0.8V to electro-reducing the carbonate, and then adjusting the potential in a potential range of -0.4V to 0.4V to regenerate the tin-based oxygen-containing compound, and repeating this cycle; In step 1), the tin-based oxygen-containing compound is tin dioxide.

2. The method for preparing formate by utilizing carbonate electroreduction according to claim 1, characterized in that: Step 1) The solute in the carbonate solution is at least one of potassium carbonate, sodium carbonate, and lithium carbonate.

3. The method for preparing formate by utilizing carbonate electroreduction according to claim 1, characterized in that: Step 1) The pH value of the carbonate solution is 8-14.

4. The method for preparing formate by utilizing carbonate electroreduction according to claim 1, wherein: In step 2), the volume percentage of oxygen in the oxygen-containing gas is 0.001% to 25%.

5. The method for preparing formate by utilizing carbonate electroreduction according to claim 1 or 4, characterized in that: In step 2), the local reduction time of the tin-based oxygen-containing compound is 0.001s to 100s.

6. The method for preparing formate by utilizing carbonate electroreduction according to claim 1 or 4, characterized in that: Step 2) The time for the electroreduction of the carbonate is 0.001s to 100s.

7. The method for preparing formate by utilizing carbonate electroreduction according to claim 1 or 4, characterized in that: In step 2), the regeneration time of the tin-based oxygen-containing compound is 0.001s to 100s.

8. The method for preparing formate by utilizing carbonate electroreduction according to claim 1 or 4, characterized in that: Step 2) The number of cycles is ≥ 1.

9. Use of the method for preparing formate by utilizing carbonate electroreduction as claimed in any one of claims 1 to 8 for preparing formic acid.

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