Preparation method of novel bismuth-based electrode material for electrocatalytic carbon dioxide reduction

Abstract

The application belongs to the field of new energy materials, and relates to a preparation method and application of a novel bismuth-based electrode material for electrocatalytic carbon dioxide reduction. The novel bismuth-based electrode material is a bismuth oxide carbonate nanosheet electrode, and the electrode contains rich oxygen vacancies. The application discloses a catalytic effect of the bismuth oxide carbonate nanosheet electrode rich in oxygen vacancies on carbon dioxide reduction. The bismuth oxide carbonate nanosheet rich in oxygen vacancies in the application is easy to synthesize with raw materials being easy to obtain and a simple and convenient method. The introduction of oxygen vacancies can significantly improve the selectivity and activity of the bismuth oxide carbonate material in electrocatalytic carbon dioxide reduction and new energy electric energy driven carbon dioxide reduction, and has a good application prospect.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of preparation and application of new energy materials, and particularly relates to preparation of a new bismuth-based electrode material and application of the bismuth-based electrode material in electrocatalytic reduction of carbon dioxide and new energy-driven reduction of carbon dioxide. BACKGROUND

[0002] Utilizing new energy electric energy to drive electrocatalytic reaction realizes efficient conversion of solar energy to chemical energy, and provides an effective and mild method for relieving energy and environmental crisis. Among them, electrocatalytic reduction of carbon dioxide as one of the technical means to realize carbon neutralization has attracted great attention. Formic acid as one of the products of carbon dioxide reduction is considered as one of the most potential products for commercialization due to its high energy density and wide application in fuel cells. In the process of reduction of carbon dioxide to formic acid, the catalysts commonly used and widely studied are represented by Sn, In, Co, Cu and Bi-based catalysts. Among them, bismuth-based electrode materials have attracted widespread attention due to their low cost and environmental friendliness. However, the bismuth-based electrode materials reported so far are often limited by low intrinsic activity, and therefore have problems such as low faradic efficiency and current density in activity evaluation, thereby hindering the development and large-scale application of bismuth-based electrode materials in electrocatalytic reduction of carbon dioxide to formic acid.

[0003] Studies have shown that the presence of Bi-O structure can effectively reduce the overpotential of the reaction and improve the selectivity. Bismuth carbonate has a unique layered structure and rich Bi-O bonds, which provide suitable reaction sites for electrocatalytic reduction of carbon dioxide. However, as a semiconductor, the poor intrinsic conductivity and the few active sites exposed by Bi2O2CO3 seriously hinder its application in electrocatalytic reduction of carbon dioxide. In addition, water as a proton source for the production of formic acid in electrocatalytic reduction of carbon dioxide, its high cracking energy barrier will hinder the generation rate of formic acid. Oxygen vacancy as one of the defects of metal oxide has unique electronic properties and strong oxygen affinity. It can regulate the electronic structure of metal sites and improve the water splitting rate, thereby promoting the generation of formic acid. Therefore, introducing oxygen vacancies into bismuth carbonate is expected to improve the performance of bismuth carbonate in electrocatalytic reduction of carbon dioxide, and realize the application of bismuth carbonate electrode material in carbon dioxide conversion. SUMMARY

[0004] The application aims to provide a preparation method of a novel bismuth-based electrode material for electrocatalytic reduction of carbon dioxide, so as to realize wide application of the material in electrocatalytic reduction of carbon dioxide to formic acid. The prepared bismuth-based electrode material is oxygen vacancy-rich bismuth oxy carbonate nanosheet, the provided preparation method is simple, raw materials are easy to obtain, no additional binder is needed, the cost is low and the method is environment-friendly. The excellent characteristics of the two-dimensional structure enable the bismuth oxy carbonate to contain a large number of active sites, the introduction of oxygen vacancies significantly improves the conductivity of the bismuth oxy carbonate, enhances the water splitting ability and intrinsic activity of the bismuth oxy carbonate in electrocatalytic reduction of carbon dioxide to formic acid, and thus realizes efficient conversion of electrical energy to chemical energy.

[0005] In order to achieve the above-mentioned purpose, the specific technical solutions of the application are as follows:

[0006] A preparation method of an oxygen vacancy-rich bismuth oxy carbonate nanosheet electrode, the method comprises the following steps:

[0007] (1) Bismuth salt is added into a mixed solvent of ethylene glycol and water and stirred vigorously. Then, an appropriate amount of auxiliary conductive salt is added to dissolve, and the obtained solution is refrigerated, so as to obtain an electrolyte used for electrochemical deposition.

[0008] (2) The electrolyte prepared in (1) is placed into an ice water bath, carbon dioxide is introduced into the electrolyte, a cleaned conductive substrate is used as a working electrode, and a platinum wire is used as a counter electrode. Under the action of a magnetic stirrer, the electrochemical deposition process on the working electrode is completed by using a constant current method.

[0009] (3) The electrode after deposition is repeatedly washed with deionized water and ethanol, and dried, so as to obtain an oxygen vacancy-rich bismuth oxy carbonate nanosheet electrode.

[0010] Preferably, the bismuth salt in the electrolyte includes BiCl3, Bi(NO3)3 and the like, and the auxiliary conductive salt includes NaCl, NaBr, NaI, Na2SO4, KCl, KBr, KI, K2SO4 and the like. The concentration of the bismuth salt is 0.01-0.5 M, and the concentration of the auxiliary conductive salt is 0.01-1 M. More preferably, the concentration of the bismuth salt is 0.02 M, and the concentration of the auxiliary conductive salt is 0.085 M.

[0011] The application uses a mixed solution of water and ethylene glycol as a solvent (including only water, a mixed solution of ethylene glycol and water with different volume ratios, and only ethylene glycol), and the volume ratio of water to ethylene glycol is preferably (0-2):(1-10), and more preferably 1:3. In some specific embodiments of the application, the volume ratio is 0:1, 1:1 or 1:3.

[0012] Preferably, the substrate is carbon paper, gas diffusion electrode, carbon cloth, metal mesh electrode, metal foam electrode, metal foil electrode, etc.

[0013] Preferably, the carbon dioxide needs to be continuously passed into the electrolyte at a flow rate of 2-100 mL / min.

[0014] Preferably, the rotation speed of the magnetic stirrer is 100-1000 rpm.

[0015] Preferably, the deposition current is-10 to-80 mA / cm 2 , and more preferably-40 mA / cm 2 .

[0016] Preferably, the deposition time is 300 s-3600 s, and more preferably 900 s.

[0017] The application provides the application of the prepared Bi2O2CO3 electrode rich in oxygen vacancies in electrocatalytic reduction of carbon dioxide and new energy electric energy driven reduction of carbon dioxide.

[0018] Compared with the prior art, the application has the following beneficial effects:

[0019] (1) The preparation method of the Bi2O2CO3 nanosheet electrode rich in oxygen vacancies is simple, convenient and easy to operate, does not require too many devices, the raw materials are easy to obtain, the price is low, and the method is easy to scale up.

[0020] (2) The Bi2O2CO3 nanosheet electrode rich in oxygen vacancies prepared by the application can realize efficient conversion of carbon dioxide to formic acid, has a low overpotential, a Faraday efficiency close to 100%, an electric energy to chemical energy conversion efficiency close to 60%, can maintain long-term stability, and has wide application value. BRIEF DESCRIPTION OF DRAWINGS

[0021] The accompanying drawings, which form a part of the present application, are used to provide a further understanding of the present application, and the illustrative embodiments thereof and their descriptions serve to explain the present application, and do not constitute improper limitations on the present application. In the drawings:

[0022] Figure 1 The Bi2O2CO3 nanosheet electrode rich in oxygen vacancies prepared for Example 1;

[0023] Figure 2 The (a) scanning electron microscope (SEM) and (b) transmission electron microscope (TEM) of the Bi2O2CO3 nanosheet electrode rich in oxygen vacancies prepared for Example 1;

[0024] Figure 3The electron paramagnetic resonance (EPR) spectrum of the oxygen-vacancy-rich Bi2O2CO3 nanosheet electrode prepared in Example 1 is shown.

[0025] Figure 4 To demonstrate the Faraday efficiency of the electrocatalytic reduction of formic acid by carbon dioxide, (a) commercial Bi2O2CO3 and (b) the oxygen-vacancy-rich Bi2O2CO3 nanosheet electrode prepared in Example 1;

[0026] Figure 5 This is a stability test diagram of the electrocatalytic carbon dioxide reduction performance of the oxygen-vacancy-rich Bi2O2CO3 nanosheet electrode prepared in Example 1.

[0027] Figure 6 The following are the performance of the oxygen-vacancy-rich Bi2O2CO3 nanosheet electrode prepared in Example 1 for new energy-driven carbon dioxide reduction: (a) stability test; (b) energy conversion efficiency from solar energy to chemical energy.

[0028] Figure 7 The electrocatalytic carbon dioxide reduction performance of the oxygen-vacancy-rich Bi2O2CO3 nanosheet gas diffusion electrode prepared in Example 2 under different bias voltages is shown in the figures: (a) Faraday efficiency of formic acid; (b) current density.

[0029] Figure 8 The oxygen-vacancy-rich Bi₂O₂CO₃ nanosheet gas diffusion electrode prepared in Example 2 was tested at a current density of 200 mA / cm². 2 Stability test chart;

[0030] Figure 9 The results show the Faraday efficiency and current density of the oxygen-vacancy-rich Bi2O2CO3 nanosheet electrode prepared using bismuth nitrate as a precursor in Example 3 under formic acid at a voltage of -1.5V.

[0031] Figure 10 The results show the Faraday efficiency and current density of the oxygen-vacancy-rich Bi2O2CO3 nanosheet electrodes prepared in Example 4 using different potassium salts as auxiliary conductive salts, under a bias voltage of -1.5V in formic acid.

[0032] Figure 11 These are the EPR spectra of Bi2O2CO3 nanosheet electrodes with different oxygen vacancy concentrations prepared in Example 5, (a) with a water to ethylene glycol volume ratio of 0:1; (b) with a water to ethylene glycol volume ratio of 1:1;

[0033] Figure 12are the local current density maps of the electrocatalytic carbon dioxide to formic acid of Bi2O2CO3 nanosheets electrodes with different oxygen vacancy concentrations prepared in Example 5, (a) commercial Bi2O2CO3; (b) Bi2O2CO3 prepared with a volume ratio of water and ethylene glycol of 0:1; (c) Bi2O2CO3 prepared with a volume ratio of water and ethylene glycol of 1:1. DETAILED DESCRIPTION

[0034] In order to better understand the present application, the present application will be further described below in conjunction with specific drawings.

[0035] Example 1

[0036] Take 253 mg of bismuth trichloride and 200 mg of sodium chloride, dissolve in 30 mL of ethylene glycol. Under the action of a magnetic stirrer, stir at a speed of 900 r / min until the solution is clear. Then, 10 mL of deionized water is added to the solution, and after 1 h of continuous stirring, the prepared solution is placed in a refrigerator for 3 h to obtain the electrolyte required for the subsequent electrochemical deposition process. A carbon paper with a size of 1 x 2 cm 2 is placed in deionized water, acetone, and ethanol solvents for ultrasonic treatment for 10 min respectively, and finally the treated substrate is ultrasonically treated in deionized water for 10 min and dried as a substrate for subsequent bismuth oxide carbonate growth. The prepared electrolyte is placed in an ice water bath while carbon dioxide gas is introduced, and the treated carbon paper is immersed in the electrolyte as a working electrode (the immersed area is 1 x 1 cm 2 ), and a platinum wire is used as a counter electrode. A -40 mA cathode current is applied to the working electrode using an electrochemical workstation, and the deposition time is 900 s. After deposition, the working electrode is taken out and repeatedly rinsed with deionized water and ethanol several times and placed in room temperature for drying to obtain a bismuth oxide carbonate electrode rich in oxygen vacancies, Figure 1 and its structural characterization. The scanning electron microscope (SEM) image shows that the prepared electrode is composed of a network structure of vertically interlaced nanosheets ( Figure 2 a), the transmission electron microscope (TEM) image shows that the single nanosheet exhibits single crystal characteristics ( Figure 2 b), and the crystallinity is good. The electron paramagnetic resonance spectrometer (EPR) shows that the prepared bismuth oxide carbonate contains rich oxygen vacancies, and the corresponding atomic concentration is 0.04% ( Figure 3 ).

[0037] The performance evaluation of electrocatalytic carbon dioxide reduction was conducted in an H-type electrolytic cell separated by a proton exchange membrane (Nafion 117). The oxygen-vacancy-rich bismuth oxycarbonate nanosheets prepared above were used as the working electrode, an Ag / AgCl electrode as the reference electrode, and a platinum sheet as the counter electrode. The cathode electrolyte was a CO2-saturated 0.5M KHCO3 aqueous solution. Electrocatalytic carbon dioxide reduction reaction tests were performed by applying a bias voltage ranging from -1.2 to -1.7 V vs Ag / AgCl to the working electrode. Figure 4 As shown, the oxygen-vacancy-rich bismuth oxycarbonate nanosheets prepared at -1.5V exhibit high selectivity for formic acid, with a Faradaic efficiency of 94%, and maintain a Faradaic efficiency exceeding 80% over a wide voltage range of -1.3 to -1.7V. Compared to commercial bismuth oxycarbonate electrodes, the prepared oxygen-vacancy-rich bismuth oxycarbonate electrode demonstrates higher formic acid selectivity, lower overpotential, and higher current density. Furthermore, in a stability test lasting up to 11 hours (… Figure 5 The total current density was maintained at 35 mA / cm². 2 The selectivity remained above 90% throughout, further demonstrating that the electrode prepared by this invention has excellent selectivity, activity, and long-term durability.

[0038] In the evaluation of the carbon dioxide reduction activity driven by new energy power, a complete electrolytic cell system was constructed using solar-irradiated photovoltaic panels as the power source and a prepared bismuth oxycarbonate electrode as the cathode. For example... Figure 6 As shown, during the 8-hour test, the constructed full electrolytic cell maintained a Faradaic efficiency of over 93% for formic acid, with a current density of 8.8 mA / cm². 2 The energy conversion efficiency from electrical energy to chemical energy is close to 60%, and the energy conversion efficiency from solar energy to chemical energy is 13.3%, which once again proves the unique advantages of the oxygen-vacancy-rich bismuth oxycarbonate nanosheet electrode prepared by this invention.

[0039] Example 2

[0040] By replacing the carbon paper in Example 1 with a gas diffusion electrode and using it as the substrate for electrochemical deposition, oxygen-vacancy-rich bismuth oxycarbonate nanosheets were grown, resulting in an oxygen-vacancy-rich bismuth oxycarbonate nanosheet gas diffusion electrode. The prepared electrode was used as the cathode for carbon dioxide reduction activity testing. The performance evaluation of electrocatalytic carbon dioxide reduction was conducted in a flow electrolyzer separated by anion exchange membranes, using an Ag / AgCl electrode as the reference electrode, nickel foam as the counter electrode, and a CO2-saturated 1M KOH aqueous solution as the cathode electrolyte. A bias voltage range of -1.5 to -2.7 V was applied to the working electrode versus Ag / AgCl to test the electrocatalytic carbon dioxide reduction reaction. Figure 7As shown, the prepared oxygen-vacancy-rich Bi2O2CO3 nanosheets exhibit more than 90% faradaic efficiency for formic acid over a wide voltage range of -1.5 ~ -2.3 V vs Ag / AgCl. Subsequently, in a stability test for 15 h at a current density of 200 mA / cm 2 Figure 8 , the prepared oxygen-vacancy-rich Bi2O2CO3 nanosheet gas diffusion electrode exhibits excellent stability, which indicates that the prepared electrode can be operated normally at an industrial current density.

[0041] Example 3

[0042] Take 400 mg of bismuth nitrate and 300 mg of sodium chloride, dissolve in 40 mL of ethylene glycol. After stirring the solution to clarity under the action of a magnetic stirrer at a speed of 900 r / min, put it in the refrigerator for 3 h to obtain the electrolyte required for the subsequent electrochemical deposition process. The rest of the process is the same as the above-mentioned Example 1, that is, the oxygen-vacancy-rich Bi2O2CO3 nanosheet electrode prepared by taking bismuth nitrate as the precursor can be obtained. As shown in Figure 9 , the prepared electrode has a faradaic efficiency of more than 90% for electrocatalytic reduction of carbon dioxide to formic acid, and a current density of 25 mA / cm 2 , which indicates that the oxygen-vacancy-rich Bi2O2CO3 electrode prepared by taking bismuth nitrate as the precursor has good activity and selectivity in electrocatalytic reduction of carbon dioxide.

[0043] Example 4

[0044] Take 253 mg of bismuth trichloride, dissolve in 40 mL of ethylene glycol. Stir the solution to clarity under the action of a magnetic stirrer at a speed of 900 r / min. Then, add 255 mg of potassium chloride to the solution, stir and put the obtained solution in the refrigerator for refrigeration. The rest of the process is the same as Example 1, that is, the oxygen-vacancy-rich Bi2O2CO3 nanosheet electrode prepared by taking potassium chloride as the auxiliary conductive salt can be obtained. On this basis, replace potassium chloride with potassium bromide, potassium iodide, potassium sulfate, and the Bi2O2CO3 nanosheet electrode prepared by taking different kinds of potassium salt as the auxiliary conductive salt can be obtained. Then, evaluate the electrocatalytic carbon dioxide reduction performance of the prepared series of electrodes. As shown in Figure 10 , the faradaic efficiency of the electrodes obtained by taking different kinds of potassium salt as the precursor is about 90% for formic acid, and the current density is more than 30 mA / cm 2 . Among them, the oxygen-vacancy-rich Bi2O2CO3 nanosheet electrode prepared by taking potassium chloride as the auxiliary conductive salt has a current density of up to 43 mA / cm 2 , which indicates that it has good activity and application prospect in electrocatalytic reduction of carbon dioxide to formic acid.

[0045] Example 5​

[0046] The electrochemical deposition process was completed by changing the volume of water and ethylene glycol in the electrolyte in Example 1 above to 0 mL, 40 mL (volume ratio of water to ethylene glycol is 0:1) and 20 mL, 20 mL (volume ratio of water to ethylene glycol is 1:1) respectively, that is, bismuth subcarbonate nanosheet electrodes with different oxygen vacancy concentrations (0.03% and 0.06% respectively) were obtained. Figure 11 Compared with the commercial bismuth subcarbonate electrode, the prepared bismuth subcarbonate electrodes with different concentrations all exhibited higher formic acid current density (J). Figure 12

[0047] As can be seen from the above examples, the bismuth subcarbonate electrodes with different oxygen vacancy concentrations prepared by the simple electrochemical deposition method of the present application realize efficient electrocatalytic reduction of carbon dioxide and carbon dioxide reduction driven by new energy electric energy.

[0048] The above only describes the preferred embodiments of the present application and is not intended to limit the present application, and any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.​

Claims

1. A method for preparing an oxygen-vacancy-rich bismuth oxy carbonate electrocatalyst, characterized in that, The method is based on an electrochemical deposition method, comprising the following steps: (1) a certain amount of bismuth salt is added to a mixed solvent of water and ethylene glycol and stirred to dissolve, wherein the volume ratio of water to ethylene glycol is (0-2):(1-10), then an appropriate amount of auxiliary conductive salt is added and stirred to dissolve, and the solution is refrigerated to obtain an electrolyte used for electrochemical deposition; (2) the electrolyte prepared in (1) is placed in an ice water bath, and carbon dioxide is introduced into the electrolyte, a cleaned conductive substrate is used as a working electrode, a platinum wire is used as a counter electrode, and the electrochemical deposition process on the working electrode is completed by using a constant current method under stirring; (3) the electrode after deposition is repeatedly rinsed with deionized water and ethanol, and dried to obtain a bismuth subcarbonate nanosheet electrode rich in oxygen vacancies.

2. The method of synthesis of an electrocatalyst according to claim 1, characterized in that, The bismuth salt in the electrolyte includes BiCl3 or Bi(NO3)3, and the concentration of the bismuth salt is 0.01-0.5 M.

3. The method of synthesis of an electrocatalyst according to claim 1, wherein, The auxiliary conductive salt in the electrolyte includes NaCl, NaBr, NaI, Na2SO4, KCl, KBr, KI or K2SO4, and the concentration of the auxiliary conductive salt is 0.01-1 M.

4. The method of synthesis of an electrocatalyst according to claim 1, wherein, By changing the volume ratio of water to ethylene glycol in the electrolyte, bismuth subcarbonate nanosheets with different oxygen vacancy concentrations can be obtained.

5. The method of synthesis of an electrocatalyst according to claim 1, wherein, The conductive substrate includes carbon paper, a gas diffusion electrode, carbon cloth, a metal mesh electrode, a metal foam electrode or a metal foil electrode.

6. The method of synthesis of an electrocatalyst according to claim 1, wherein, In the electrochemical deposition process, carbon dioxide needs to be continuously introduced into the electrolyte at a flow rate of 2-100 mL / min.

7. The method of synthesis of an electrocatalyst according to claim 1, wherein, In the electrochemical deposition process, the electrolyte needs to be continuously stirred at a speed of 100-1000 rpm.

8. The method of synthesis of an electrocatalyst according to claim 1, wherein, In the electrochemical deposition process, the deposition current is -10 to -80 mA / cm 2 .

9. The method of synthesis of an electrocatalyst according to claim 1, wherein, In the electrochemical deposition process, the deposition time is 300 s-3600 s.

10. A bismuth subcarbonate nanosheet electrode rich in oxygen vacancies prepared by the synthesis method of any one of claims 1-8.

11. The use of a bismuth subcarbonate nanosheet electrode rich in oxygen vacancies prepared by the synthesis method of any one of claims 1-8 in electrocatalytic carbon dioxide reduction and new energy electric power driven carbon dioxide reduction.

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