Method for preparing bismuth-based electrode through electro-deposition

Abstract

The invention provides a method for preparing a bismuth-based electrode through electro-deposition, and belongs to the technical field of electrochemical carbon dioxide reduction. According to the invention, a simple one-step electrodeposition method is utilized to prepare the bimetallic electrode loaded with bismuth and rare earth elements, that is, a porous carbon material is subjected to appropriate hydrophilic pretreatment and then is cleaned and dried to obtain a hydrophilic electrode substrate, and then the hydrophilic electrode substrate is placed in an aqueous electrodeposition liquid composed of bismuth and rare earth element metal salts and a certain amount of additives; and preparing the bismuth-based bimetallic catalyst electrode by adopting a one-step co-deposition method under a constant voltage condition. When the prepared bismuth-based bimetallic electrode is applied to production of formic acid through electrocatalytic reduction of carbon dioxide, the Faraday efficiency reaches up to 95% or above, and the electrocatalytic activity is remarkably higher than that of a single metal bismuth electrode. The method for preparing the bi-metal bismuth-based electrode through electro-deposition and one-step co-precipitation has the advantages of being easy and convenient to operate, safe, environmentally friendly, easy to industrially amplify and the like, and has wide application prospects in the field of carbon dioxide electrochemical conversion.

Description

Technical Field

[0001] The present invention belongs to the field of electrocatalytic reduction reaction, and relates to a preparation method of a bismuth-based electrode for electrochemically catalytically reducing carbon dioxide. Background Art

[0002] The concentration of carbon dioxide in the atmosphere has reached a record high. Some measures need to be taken to reduce carbon dioxide emissions to address the threat of climate change brought by greenhouse gases. Carbon dioxide conversion technology has attracted much attention because of its potential to reduce greenhouse gas emissions through thermochemical, biological, electrochemical, and photochemical conversion mechanisms. Among them, electrochemical carbon dioxide reduction technology is very promising and can produce high-value products such as fuels and chemicals using clean energy under mild conditions. This technology is expected to reduce China's dependence on fossil fuels in energy and chemical production. Formic acid has a huge market demand in industries such as rubber, leather, pharmaceuticals, and new energy. Therefore, the electrochemical reduction of carbon dioxide into high-value formic acid has become a research hotspot.

[0003] The molecular inertness of carbon dioxide and the slow proton migration make the kinetics of the electrochemically catalytic reduction of carbon dioxide slow. How to promote the reaction kinetics, inhibit the hydrogen evolution side reaction, provide rich catalytic active centers and a catalyst structure with high stability, reduce the energy barrier for the conversion of carbon dioxide into formic acid, and prepare a cathode that can efficiently convert carbon dioxide into formic acid has become the key bottleneck of carbon dioxide electrocatalytic reduction technology. Due to its high oxygen affinity and low *H binding force, bismuth element has a high hydrogen evolution overpotential and is beneficial to the formation of the carbon dioxide reaction intermediate *OCHO, and has received extensive attention in the field of electrocatalytic reduction of carbon dioxide to produce formic acid. However, the single-metal bismuth-based catalyst still needs to be further improved in terms of activity, stability, energy efficiency, and selectivity. Compared with single-metal elements, bimetallic catalysts have changeable electronic structures and spatial arrangements and have a higher ability to adsorb and activate carbon dioxide. Therefore, preparing a cathode loaded with a bimetallic catalyst is expected to improve the overall performance of the electrocatalytic reduction of carbon dioxide to produce formic acid.

[0004] Efficient bismuth-based bimetallic alloy catalysts can be prepared by means of interface engineering, defect engineering, doping engineering, etc. However, the preparation process is complex and cumbersome, and the reaction conditions are harsh, with high energy consumption. To simplify the preparation process of bismuth-based bimetallic catalysts, the invention patent CN 118272839 A describes "a method for electrocatalytic reduction of carbon dioxide to formic acid", which discloses the synthesis of cerium dioxide / bismuth oxycarbonate catalysts by a one-step hydrothermal method. The bismuth-oxygen bond structure retained in bismuth oxycarbonate can stabilize the carbon dioxide radical ion intermediate, thus promoting the efficient synthesis of formate. In a three-electrode H-type electrolytic cell system, when the prepared cerium dioxide / bismuth oxycarbonate bimetallic catalyst is used for the electrocatalytic reduction of carbon dioxide to formic acid, its Faraday efficiency can reach 91%. However, the reaction conditions in the preparation process of the bimetallic catalyst involved in this invention are harsh and need to be carried out at a high temperature above 150 °C. Moreover, the prepared bimetallic catalyst needs to be further prepared into a reduction cathode by a drop-coating method, and the electrode preparation process is relatively complicated, with high energy consumption and long time consumption.

[0005] Electrodeposition is a simple, fast and low-energy-consuming electrode preparation method. The invention patent CN 118326463 A discloses "an organically functionalized bismuth catalyst electrode and its preparation method and application". This invention first prepares an electrodeposition solution with bismuth salt, organic ligand, water-soluble binder and deionized water as raw materials; then, by means of electrodeposition, by adjusting electrodeposition parameters such as the ratio of bismuth salt to organic ligand in the electrodeposition solution, deposition current and deposition time, the bismuth salt and organic ligand in the electrodeposition solution react to form bismuth complexes. At the same time, the bismuth complexes grow in-situ on the electrode, and an organically functionalized bismuth catalyst-based electrode can be obtained. However, the formic acid Faraday efficiency of the single-metal Bi-based catalyst electrode prepared by this invention is less than 90%, and the energy efficiency also needs to be improved. Preparing a cathode loaded with a bimetallic catalyst by electrodeposition will become an efficient and simple method for preparing a carbon dioxide catalytic reduction electrode, but there is no relevant report at present. Summary of the Invention

[0006] The object of the present invention is to provide a simple, efficient and industrially scalable method for preparing a bismuth-based electrode. Considering the deficiencies of a single-metal bismuth electrode, such as low activity, low selectivity and limited energy efficiency, the present invention proposes to prepare a bimetallic catalyst electrode composed of bismuth and rare earth elements such as lanthanum or cerium by electro-deposition one-step coprecipitation method. In the present invention, a one-step co-electrodeposition method is proposed to prepare a bismuth-based bimetallic electrode. By in-situ electrochemical reduction, metal Bi and rare earth elements are simultaneously deposited on the surface of a porous carbon material. Citrate and urea in the electro-deposition solution are used to regulate the crystallization of the electro-reduction process, realizing the co-deposition of multiple metals. The electrode is optimized by regulating the process parameters of the electro-deposition process. When specifically applied, the corresponding electro-deposition solution system needs to be selected in combination with the target metal. Compared with a single bismuth metal electrode, the bismuth-based bimetallic electrode prepared by the present invention has the doping of rare earth elements enriching the electron density around Bi, thereby enhancing the binding energy between the Bi active center and the *OCHO intermediate, and further reducing the energy barrier for the electrochemical reduction of carbon dioxide to formic acid. In addition, the co-electrodeposition doping of rare earth elements and Bi can effectively improve the morphology of the Bi-based catalyst, forming amorphous structures such as needle tips and flakes, significantly improving the ability to adsorb and activate carbon dioxide, and thus improving the catalytic performance. Compared with the existing methods, the method for preparing a bismuth-based bimetallic electrode by electro-deposition one-step coprecipitation method has the advantages of low energy consumption, short time consumption, simple operation and simple process.

[0007] The object of the present invention is achieved by the following technical solutions:

[0008] The porous carbon material is soaked in a concentrated nitric acid solution of 50-70 wt% for 12-24 hours, then rinsed clean with pure water, ultrasonically treated in a polar solvent for 10-30 minutes, and then dried at 80-120 °C for 5-12 hours to obtain a hydrophilic electrode substrate; the hydrophilic electrode substrate is placed into an aqueous electro-deposition solution, and with the hydrophilic electrode substrate as the working electrode, a platinum electrode as the counter electrode, and a saturated silver chloride electrode as the reference electrode, a bismuth-based bimetallic catalyst electrode is prepared by one-step co-deposition method under a constant deposition voltage.

[0009] Furthermore, the porous carbon material used is a porous material such as a woven carbon cloth gas diffusion layer material or a carbon fiber composite paper.

[0010] Furthermore, the aqueous electro-deposition solution is a mixed solution composed of a dilute nitric acid solution of 0.05-0.5 mol / L, bismuth nitrate, rare earth element metal salts and additives.

[0011] Even further, the rare earth element in the aqueous electro-deposition solution is a metal salt of rare earth elements such as cerium or lanthanum.

[0012] Even further, the additives in the aqueous electro-deposition solution are citrate, urea, etc.

[0013] Further, the deposition voltage in the above one-step co-deposition method is -0.10 V to -1.20 V (vs Ag / AgCl).

[0014] Further, the deposition time in the above one-step co-deposition method is 300 to 3600 seconds.

[0015] The method for preparing a bismuth-based electrode by electrodeposition proposed by the present invention can flexibly prepare bismuth-based electrodes with different loadings and different catalytic activities according to actual needs by adopting different deposition voltages, deposition times, and compositions of the aqueous electrodeposition solution. By using the one-step co-electrodeposition method to combine rare earth elements and metallic bismuth, the prepared bismuth-based electrode of the bimetallic catalyst has excellent electrocatalytic activity in the process of electrocatalytic reduction of carbon dioxide to formic acid, can improve the energy efficiency of the reaction process, and has good application prospects.

[0016] The method for preparing a bismuth-based electrode by one-step co-electrodeposition described in the present invention has the following effects compared with other technical methods:

[0017] (1) A bimetallic catalyst electrode composed of bismuth and rare earth elements is directly deposited on a porous carbon material by a simple one-step electrodeposition method. This method couples the catalyst preparation and electrode preparation processes, and there is no need to perform operations such as spraying or drop coating to load the catalyst onto the electrode surface, saving time costs and simplifying the experimental process.

[0018] (2) The process of preparing a bismuth-based electrode by electrodeposition provided by the present invention is carried out under room temperature and atmospheric pressure conditions. The process conditions are mild, the preparation process is safe, and the energy consumption is greatly reduced, which is conducive to industrial scale-up applications.

[0019] (3) The prepared bismuth-based bimetallic catalyst electrode has the ability to efficiently electrocatalytically reduce carbon dioxide to formic acid, and the Faraday efficiency of formic acid is as high as over 95%.

[0020] (4) The prepared bismuth-based bimetallic catalyst electrode has extremely good stability and electrocatalytic activity. Description of the Drawings

[0021] Figure 1 For Bi 50 Monometallic electrode and Bi / Ce 50 Faraday efficiency of formic acid of the bimetallic electrode at different potentials;

[0022] Figure 2 For Bi 50 Monometallic electrode and Bi / Ce 50 Yield of formic acid of the bimetallic electrode at different potentials;

[0023] Figure 3For Bi / Ce at a potential of -1.8 V (vs Ag / AgCl) 50 10 h stability test of electrode 10 and Faraday efficiency of formic acid Detailed implementation mode

[0024] To facilitate the understanding of the technical solution of the present invention by those skilled in the art, the technical solution of the present invention will be further specifically described below in conjunction with the accompanying drawings of the specification and embodiments.

[0025] First, the porous material is subjected to hydrophilic pretreatment. That is, the porous material is cut into a suitable size, then soaked in a 65wt% concentrated nitric acid solution for hydrophilic treatment, and then soaked and ultrasonically cleaned with pure water and absolute ethanol respectively to remove the residual organic impurities on its surface; the carbon fiber composite paper after hydrophilic treatment is placed in a glass petri dish and dried at 90 °C to obtain a hydrophilic electrode substrate material.

[0026] Then, an aqueous electrodeposition solution is prepared. Take 50 mL of dilute nitric acid (0.1 mol L -1 ), add 0.1~2 mmol of bismuth nitrate pentahydrate, 0.05~2 mmol of cerium nitrate hexahydrate, 0.25 mol~1 mol of urea, and 0.25 mol~1 mol of sodium citrate dihydrate, and stir magnetically until it is clear. The aqueous electrodeposition solution used for the single bismuth metal electrode is the same as the above-mentioned steps except that it does not contain cerium nitrate hexahydrate.

[0027] Finally, the hydrophilic electrode substrate material is placed into the above-prepared aqueous electrodeposition solution, and a bismuth-based bimetallic electrode is prepared by a one-step coprecipitation method. The specific process is as follows: the electrode substrate material obtained after hydrophilic pretreatment is clamped with a platinum sheet electrode clip, the platinum sheet electrode is used as the anode counter electrode, and the saturated calomel electrode is used as the reference electrode, and it is immersed in the electrolytic cell of the aqueous electrodeposition solution. Under the condition of magnetic stirring, electrodeposition is carried out for 300 s~3600 s respectively in a constant voltage working mode of -0.1~-1.2 v (vs Ag / AgCl) to obtain bismuth-based electrodes with different catalyst loadings and catalytic activities. After washing with pure water, it is naturally dried at room temperature for 24 h to obtain a bismuth-based electrode loaded with single metal bismuth or bimetal.

[0028] Example 1 Preparation of single metal bismuth electrode

[0029] In this example, the pretreated electrode substrate is inserted into the prepared electroplating solution as the cathode working electrode, the platinum sheet electrode is used as the anode counter electrode, and the saturated calomel electrode is used as the reference electrode. Under the condition of magnetic stirring, a working electrode with different catalyst loadings and catalytic activities is obtained by a simple one-step electrodeposition method, and the performance of the electrodes prepared under different deposition time conditions for the electrochemical conversion of CO2 to formic acid is compared and analyzed. The specific preparation and performance characterization of the electrode are as follows:

[0030] S1. Hydrophilic pretreatment of the electrode substrate: The original carbon paper is soaked in a 65 wt% concentrated nitric acid solution for 12 hours for hydrophilic treatment. After soaking, the carbon paper is washed clean with pure water, and then soaked and ultrasonically cleaned in pure water and absolute ethanol for 30 min respectively to remove the residual organic impurities on its surface. Finally, the treated carbon paper is placed in a glass petri dish and put into an oven, and dried at 90 °C for 12 hours.

[0031] S2. Preparation of the single Bi aqueous electrodeposition solution: At room temperature, 50 mL of dilute nitric acid (0.1 mol L -1 ) is added with 0.1 mmol of bismuth nitrate pentahydrate, 0.25 mmol of urea, and 0.25 mol of trisodium citrate dihydrate, and magnetically stirred until it is clear.

[0032] S3. Preparation of the single metal Bi electrode by electrodeposition: The 1×1 cm 2 hydrophilic pretreated carbon paper is clamped with a platinum sheet electrode clip as the cathode working electrode; a platinum sheet electrode is used as the anode counter electrode, and a saturated silver chloride electrode is used as the reference electrode. Under magnetic stirring conditions, electrodeposition is carried out at a cathode potential of -0.1~-1.2 V (vs Ag / AgCl). The deposition times are 300 s, 600 s, 1200 s, 1800 s, 3000 s, and 3600 s respectively to obtain working electrodes with different catalyst loadings and catalytic activities. After washing with pure water, it is naturally dried at room temperature for 24 h.

[0033] S4. Performance test of electrocatalytic reduction of carbon dioxide: The H-type electrolytic cell is used to evaluate the performance of the single metal Bi electrode for electrocatalytic reduction of carbon dioxide. Among them, NF117 produced by DuPont Company is used as the diaphragm of the cathode chamber and the anode chamber in the H-type electrolytic cell. The electrode prepared in the present invention is used as the working electrode, the saturated silver chloride electrode is used as the reference electrode, and the platinum sheet electrode is used as the counter electrode. The cathode electrolyte is 40 mL of 0.1 M KHCO3 solution saturated with carbon dioxide, and the anode electrolyte is 40 mL of 0.1 M KHCO3 solution. During the CO2 electrochemical reduction process, a mass flow controller is used to continuously introduce carbon dioxide into the cathode electrolyte at a flow rate of 20 mL min -1 to carry out the formic acid production experiment for 60 min at a reduction voltage of -1.0 V~-2.0 V (vs Ag / AgCl). After the reaction, the electrolyte is taken to detect the formic acid concentration, and the formic acid yield and Faraday efficiency are calculated.

[0034] Example 2 Preparation of the Bi / Ce bimetallic electrode

[0035] In this embodiment, a pretreated electrode substrate is inserted as a cathode working electrode into the configured electroplating solution, a platinum sheet electrode is used as an anode counter electrode, and a saturated silver chloride electrode is used as a reference electrode. Under magnetic stirring conditions, a simple one-step electrodeposition method is used to obtain working electrodes with different catalyst loadings and catalytic activities, and the performance of the electrodes prepared under different deposition time conditions for electrocatalytic reduction of carbon dioxide to formic acid is compared and analyzed.

[0036] S1. Hydrophilic pretreatment of the electrode substrate: The original raw carbon paper is soaked in a 65 wt% concentrated nitric acid solution for 12 hours for hydrophilic treatment. After soaking, the carbon paper is washed clean with pure water, and then soaked and ultrasonically cleaned in pure water and absolute ethanol for 30 min respectively to remove the residual organic impurities on its surface. Finally, the treated carbon paper is placed in a glass petri dish and dried in an oven at 90 °C.

[0037] S2. Preparation of Bi / Ce aqueous electrodeposition solution: At room temperature, 50 mL of dilute nitric acid (0.1 mol L -1 ) is added with 0.1 mmol of bismuth nitrate pentahydrate, 0.1 mmol of cerium nitrate hexahydrate, 0.25 mmol of urea, and 0.25 mol of sodium citrate dihydrate, and magnetically stirred until clear.

[0038] S3. Preparation of bimetallic Bi / Ce electrode by electrodeposition method: The 1×1 cm 2 hydrophilic pretreated carbon paper is clamped with a platinum sheet electrode clip as the cathode working electrode; a platinum sheet electrode is used as the anode counter electrode, and a saturated silver chloride electrode is used as the reference electrode. Under magnetic stirring conditions, electrodeposition is carried out at a cathode potential of -0.1~-1.2 V (vs Ag / AgCl). The deposition times are 300 s, 600 s, 1200 s, 1800 s, 3000 s, and 3600 s respectively to obtain working electrodes with different catalyst loadings and catalytic activities. After washing with pure water, it is naturally dried at room temperature for 24 h.

[0039] S4. Electrochemical CO2 reduction performance test: An H-type electrolytic cell is used to evaluate the electrocatalytic CO2 reduction performance of the bimetallic Bi / Ce electrode material. In the H-type electrolytic cell, NF117 produced by DuPont Company is used as the diaphragm for the cathode chamber and the anode chamber. The electrode prepared by the present invention is used as the working electrode, a saturated silver chloride electrode is used as the reference electrode, and a platinum sheet electrode is used as the counter electrode. The cathode electrolyte is 40 mL of 0.1 M KHCO3 solution saturated with CO2, and the anode electrolyte is 40 mL of 0.1 M KHCO3 solution. During the electrochemical reduction of CO2, a mass flow controller is used at 20 mL min -1The flow rate of CO2 was continuously introduced into the catholyte. The formic acid production experiments were carried out for 60 min at reduction voltages of -1.0 V to -2.0 V (vs Ag / AgCl). After the reaction, the electrolyte was taken to detect the formic acid concentration, and the formic acid yield and Faraday efficiency were calculated. Subsequently, the stability tests were carried out for 1 to 10 h at a potential of -1.8 V (vs Ag / AgCl). After the reaction, the electrolyte was taken to detect the formic acid concentration, and the formic acid Faraday efficiency was calculated.

[0040] Analysis of reaction products: Through comparative analysis, at the same potential, the FE of the bimetallic Bi / Ce electrode HCOOH was higher than that of the monometallic Bi electrode. In the constant potential mode of -1.8 V (vs Ag / AgCl), the preferably prepared bimetallic Bi / Ce 50 electrode in the electrochemical reduction of CO2 maintained a stable current density of 29 mA cm -2 nearby, and the FE HCOOH reached the highest value (95.6%) (as shown in the appendix Figure 1 ). At a potential of -2.0 V (vs Ag / AgCl), the formic acid yield was as high as 579 μmol h -1 (as shown in the appendix Figure 2 ). The stability experiment showed that the Bi / Ce 50 electrode could carry out continuous operation experiments for 10 h in a 0.5 M KHCO3 saturated CO2 electrolyte, and the FE HCOOH did not decrease significantly during the process, indicating that the electrode prepared by the present invention still had good catalytic activity after 10 h of reaction (as shown in the appendix Figure 3 ).

Claims

1. A method for preparing a Bi-based electrode by electrodeposition, characterized in that: The porous carbon material is soaked in a 50-70% concentrated nitric acid solution for 12-24 hours and then rinsed with pure water, and then soaked in pure water and anhydrous ethanol and ultrasonically cleaned for 30 minutes respectively, and then dried at 80-120°C for 5-12 hours to obtain a hydrophilic electrode substrate; the hydrophilic electrode substrate is placed in an aqueous electrodeposition solution, with the hydrophilic electrode substrate as the working electrode, the platinum electrode as the counter electrode, and the saturated silver chloride electrode as the reference electrode, and a bismuth-based bimetallic catalyst electrode is prepared by a one-step co-deposition method at a constant deposition voltage.

2. A method for preparing a bismuth-based electrode by electrodeposition as claimed in claim 1, characterized in that: The porous carbon material is a porous material such as a woven carbon cloth gas diffusion layer material, a carbon fiber composite paper, etc.

3. A method for preparing a bismuth-based electrode by electrodeposition as claimed in claim 1, characterized in that: The aqueous electrodeposition solution is a mixed solution consisting of a 0.05-0.5 mol / L dilute nitric acid solution, bismuth nitrate, a doped rare earth metal salt and an additive.

4. A method for preparing a bismuth-based electrode by electrodeposition as claimed in claim 3, characterized in that: The rare earth element doped metal salt in the aqueous electrodeposition solution is a metal salt of a rare earth element such as cerium or lanthanum.

5. A method for preparing a bismuth-based electrode by electrodeposition as claimed in claim 3, characterized in that: Additives in aqueous electrodeposition solution are citrate, urea, etc.

6. A method for preparing a bismuth-based electrode by electrodeposition as claimed in claim 3, characterized in that: The molar ratio of bismuth to other doped rare earth elements in the aqueous electrodeposition solution is controlled at 1-6:

1.

7. A method for preparing a bismuth-based electrode by electrodeposition as claimed in claim 1, characterized in that: The deposition voltage in the one-step co-deposition method is -0.10 V to -1.20 V.

8. A method for preparing a bismuth-based electrode by electrodeposition as claimed in claim 1, characterized in that: The deposition time in the one-step co-deposition method is 300 to 3600 seconds.

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