Preparation method and application of nanosheet-like Bi-Bi2O3 electrocatalyst

Abstract

A method for preparing and applying a nanosheet-like Bi-Bi₂O₃ electrocatalyst, belonging to the technical field of electrocatalysis, is disclosed. The method involves dissolving a bismuth salt in a water / methanol solution, adding aluminum / zinc foil, and stirring for 5-10 min to form a black precipitate. After centrifugation, washing, and drying, a uniformly morphological Bi-Bi₂O₃ electrocatalyst is obtained. This catalyst exhibits excellent catalytic activity and stability for the electrocatalytic reduction of CO₂ to formate. Formate, as the core product, shows a Faradaic efficiency exceeding 90% between -1.0 V and -1.2 V, with the highest formate Faradaic efficiency reaching 92.4% at -1.0 V. Furthermore, its catalytic performance showed no significant degradation during a continuous 25-hour stability test. This invention provides a simple, rapid, low-cost, and scalable synthesis method with excellent catalytic activity and stability. It can be used in the membrane-free co-production of formate in the electrocatalytic reduction of CO₂ and its coupled glycerol oxidation, providing a catalytic foundation for the industrial application of CO₂ electroreduction.

Description

Technical Field

[0001] This invention belongs to the field of electrocatalysis, specifically relating to a method for preparing and applying a nanosheet-like electrocatalyst. Background Technology

[0002] Electrocatalytic carbon dioxide (CO2) reduction is a novel CO2 resource recovery technology that has emerged in recent years. Under normal temperature and pressure, CO2 can be converted into high-value chemicals and fuels, such as carbon monoxide, formic acid, methanol, ethylene, ethanol, and acetone, using electrical energy. With the development of renewable energy sources such as wind and solar power leading to decreasing electricity costs, and against the backdrop of research and development of low-cost, high-performance catalysts, electrocatalytic CO2 reduction technology has shown promising industrial application prospects. Previous studies have shown that among the various reduction products, carbon monoxide and formic acid have the highest economic feasibility. This is mainly because multi-carbon products involve multiple electron transfer steps, resulting in complex synthesis processes, diverse products, and difficulties in obtaining high-purity single products, leading to challenges in product separation and extremely high energy costs, thus resulting in relatively low economic value. Formic acid, as a liquid product containing a single carbon atom (C1), has been the subject of extensive catalyst design for the electrocatalytic reduction of CO2 to formic acid. Catalysts primarily utilize single-atom metals such as Bi, Sn, and In, as well as alloys, oxides, hybrids, and carbon composites. However, the synthesis of most of these catalysts involves high-temperature carbonization and hydrothermal processes, resulting in high energy consumption and long material preparation cycles, hindering large-scale industrial applications. Developing electrocatalysts that combine low cost, rapid synthesis, ease of large-scale synthesis with high catalytic activity, high selectivity, and long-term stability is crucial for the industrial application of electrocatalytic CO2 reduction technology. Summary of the Invention

[0003] To achieve the aforementioned objectives and address the problems existing in the prior art, this invention proposes a low-cost, simple, low-energy-consumption, and scalable method for synthesizing nanosheet-like Bi-Bi2O3 electrocatalysts, and applies it to the field of electrochemical CO2 reduction to formate production; meeting the basic needs of industrial development: the Faraday efficiency has reached over 90%, and the current density in a flow-through electrolytic cell reaches 400 mA cm⁻¹. -2 .

[0004] The technical solution adopted in this invention includes the following steps:

[0005] A method for preparing a nanosheet-like Bi-Bi2O3 electrocatalyst includes the following steps:

[0006] Step 1: Using metallic bismuth salt as a precursor, dissolve it in an aqueous solution or methanol solution, while simultaneously adding acid to adjust the pH until the solution becomes clear, indicating that the bismuth salt has completely dissolved. The pH adjustment range is typically between 0.1 and 2; the stronger the acidity of the solution, the more metallic bismuth salt dissolves, and the greater the amount of catalyst that can be prepared subsequently.

[0007] Step 2: Add aluminum foil, zinc foil, or other metals more reactive than bismuth to the above solution. Based on the displacement reaction between bismuth ions and the metal, bismuth is displaced from the solution and forms a black precipitate at the bottom. The synthesis process can be completed in just 5–30 minutes. Stirring can be used to enhance ion mass transfer and reaction, and it is also beneficial for synthesizing smaller nanosheet catalysts.

[0008] Step 3: The above-mentioned black precipitate was collected by centrifugation and then dried in an oven to obtain the final nanosheet-like Bi-Bi2O3 electrocatalyst. Characterization of the catalyst showed that the Bi-Bi2O3 catalyst has a nanosheet-like structure with a size between 500 nm and 2 μm and a nanosheet thickness of 1–10 nm. Its crystal structure consists of Bi and Bi2O3.

[0009] An application of a nanosheet-like Bi-Bi₂O₃ electrocatalyst was described. The obtained material was prepared as a catalyst ink and drop-coated onto carbon fiber paper as the working electrode. Ag / AgCl was used as the reference electrode, and a foil mesh as the counter electrode. 0.1M KHCO₃ was used as the electrolyte. CV activation was performed in an H-type electrolytic cell within a voltage range of -0.6 to -1.8 V (vs. Ag / AgCl) for 10–20 min, completing the activation of Bi-Bi₂O₃. This activated Bi-Bi₂O₃ and allowed it to be directly used for the electrocatalytic reduction of carbon dioxide to formic acid and its coupled oxidation with glycerol to produce formate without a membrane. Polarization curves were then measured under a CO₂ atmosphere, showing a significant increase in current density compared to those under a nitrogen atmosphere. Potentiostatic measurements were subsequently performed using an electrochemical workstation, and the products were analyzed using gas chromatography.

[0010] The aluminum foil used needs to be pretreated to remove the oxide film on the surface. At the same time, the aluminum foil can also be replaced with zinc foil and other metals that are more reactive than bismuth.

[0011] This electrocatalyst exhibits excellent catalytic activity for the electrocatalytic reduction of CO2 to formic acid. Formic acid, as the core product, demonstrates a Faradaic efficiency exceeding 90% between -1.0V and -1.2V, with the highest formic acid Faradaic efficiency reaching 92.4% at -1.0V. Furthermore, the electrocatalyst exhibits excellent stability, showing no significant degradation in catalytic performance during a continuous 25-hour stability test.

[0012] The advantages of this invention are: This method utilizes the redox properties of metals to rapidly prepare a Bi-Bi₂O₃ catalyst with a uniform nanosheet structure at room temperature and pressure. The synthesis method is simple and rapid, requires no high temperature or high pressure, has mild reaction conditions, low cost, and is suitable for large-scale preparation. Simultaneously, this catalyst exhibits excellent catalytic activity and stability for the electrocatalytic reduction of CO₂ to formate. Formate, as the core product, shows a Faradaic efficiency exceeding 90% between -1.0V and -1.2V, with the highest formate Faradaic efficiency reaching 92.4% at -1.0V. Furthermore, this electrocatalyst also exhibits excellent stability; its catalytic performance showed no significant decline during a continuous 25-hour stability test. Considering the limitations of CO₂ solubility and diffusion kinetics in an H-type electrolytic cell, the catalyst was drop-coated onto a gas diffusion electrode, and its electrochemical performance was tested in a flow-through electrolytic cell using 1M KOH as the electrolyte. The results showed that the Bi-Bi₂O₃ catalyst can achieve an efficiency of 400 mA cm⁻¹. -2 With a current density of -0.92V and requiring only a cathode potential of -0.92V, this catalytic activity is superior to most currently reported catalysts, including those containing noble metals and single atoms, and it is expected to be used for industrial electrocatalysis of CO2.

[0013] More importantly, its high current density and high Faradaic efficiency enable it to co-produce a product—formate—with the anode in the coupling of electro-oxidation with small molecule alcohols such as glycerol, and it can be industrialized in membrane-free devices. This will provide a new low-cost route for the development of electrocatalytic CO2 reduction technology, with broad prospects.

[0014] The synthesis method of this invention is simple, rapid, low-cost, and scalable, and has excellent catalytic activity and good stability. It can be used in the membraneless co-production of formate in electrocatalytic CO2 reduction and its coupled glycerol oxidation, laying a catalytic foundation for the industrial application of CO2 electroreduction. Attached Figure Description

[0015] Figure 1 This is a scanning electron microscope (SEM) image of the Bi-Bi2O3 electrocatalyst.

[0016] Figure 2 This is the XRD pattern of the Bi-Bi2O3 electrocatalyst.

[0017] Figure 3 This is the polarization curve of electrocatalyzed CO2 in Example 2.

[0018] Figure 4 This refers to the Faraday efficiency at different potentials in Example 2.

[0019] Figure 5 This is the polarization curve of electrocatalytic CO2 in the flow cell in Example 2. Detailed Implementation

[0020] The present invention will be further described below with reference to the embodiments.

[0021] Example 1: Preparation of Electrocatalyst

[0022] A method for preparing a nanosheet-like Bi-Bi2O3 electrocatalyst includes the following steps:

[0023] Step 1: Using metallic bismuth salt as a precursor, dissolve it in deionized water while adding acid to adjust the pH until the solution becomes clear, indicating that all the bismuth salt has dissolved. The pH adjustment range is typically between 0.1 and 2. The stronger the acidity of the solution, the more metallic bismuth salt dissolves, resulting in a larger amount of catalyst that can be prepared subsequently. Here, we use a bismuth salt solution concentration of 0.1 mol / L.

[0024] Step 2: Add aluminum foil to the above solution. Based on the displacement reaction between bismuth ions and the metal, bismuth is displaced from the solution and forms a black precipitate at the bottom after 20 minutes. Stirring can be used to enhance ion mass transfer and reaction during the process, and it is also beneficial for synthesizing smaller nanosheet catalysts.

[0025] Step 3: Collect the above-mentioned black precipitate by centrifugation, and then dry it in an oven to obtain the final nanosheet-like Bi-Bi2O3 electrocatalyst. The catalyst is then characterized. Figure 1 The image shows a scanning electron microscope (SEM) image of the Bi-Bi2O3 electrocatalyst. The results indicate that the Bi-Bi2O3 catalyst has a nanosheet structure with a size between 500 nm and 2 μm and a nanosheet thickness between 1 and 10 nm. Figure 2 This is the XRD pattern of the Bi-Bi2O3 electrocatalyst, whose crystal structure consists of Bi and Bi2O3.

[0026] Example 2

[0027] The electrocatalyst prepared in Example 1 was a powder. Nafion solution was used as a binder to drop-coat it onto carbon paper. Specifically, 10 mg of catalyst powder was weighed and added to an ethanol solution containing 20 wt% Nafion. The mixture was sonicated for 30 min to obtain a uniform catalyst ink. This ink was then drop-coated onto carbon fiber paper for use as the working electrode, Ag / AgCl as the reference electrode, and a foil mesh as the counter electrode. The electrolyte was 0.1 M KHCO3 (pH = 6.8). Electrochemical performance was tested using a Shanghai Chenhua CHI 760E workstation in an H-type electrolytic cell. Before the electrochemical tests, argon gas was first introduced into the cathode chamber (flow rate 20 mL / min). -1 To remove impurities from the electrolyte, the solution is bubbled with CO2 for 30 minutes (flow rate 20 mL / min). -1After at least 30 minutes, once the electrolyte is saturated with CO2, cyclic voltammetry (CV) is performed to activate the catalyst. The voltage range is -0.6 to -1.8 V (vs. Ag / AgCl), and the scan time is 10-20 minutes. Following activation, linear voltammetry (LSV) is performed with a voltage range of -0.6 to -2.0 V (vs. Ag / AgCl) and a scan rate of 20 mV / s. -1 Compared to the polarization curve under argon conditions, the current density increased significantly after introducing CO2, and the initial potential was only 0.3V (vs. RHE) (results are shown in the figure). Figure 3 (As shown).

[0028] After the LSV test was completed, product selectivity was tested, i.e., potentiostatic tests were performed at different potentials, and quantitative analysis of the gaseous products was carried out using gas chromatography. Automatic injection was performed every 10 minutes, and four measurements were taken at each potential. Formate, as the core product, exhibited a Faradaic efficiency exceeding 90% between -1.0V and -1.2V, with the highest formate Faradaic efficiency reaching 92.4% at -1.0V (results are shown in the figure). Figure 4 (As shown). Stability testing was performed using a constant potential method, with the electrolyte replaced every 5 hours. During a continuous 25-hour test, the current density showed no significant decay, maintaining good stability.

[0029] To further explore the industrial feasibility of this catalyst, a flow-through electrolyzer was introduced to test the polarization curves (e.g., Figure 5 As shown, the catalyst ink was directly drop-coated onto the gas diffusion electrode, with nickel foam used as the counter electrode at the anode. The voltage setting range was -0.6 to -1.6 V, and the scan rate was 20 mV / s. -1 With iR compensation set to 85%, the polarization curve results are as follows: Figure 5 As shown, the Bi-Bi2O3 catalyst exhibits excellent catalytic activity, achieving 400 mA cm⁻¹ catalytic activity with only -0.92 V. -2 The current density meets the requirements for industrial-scale applications.

Claims

1. A method for preparing a nanosheet-like Bi-Bi2O3 electrocatalyst, characterized in that: The preparation method includes the following steps: (1) Dissolve metallic bismuth salt in water or methanol, and simultaneously add acid to adjust the pH to 0.1-2, so that the bismuth salt is completely dissolved, obtaining a clear bismuth salt solution; the concentration range of the bismuth salt solution is 0.01-0.5 mol / L. (2) Add a metal foil that is more reactive than bismuth to the bismuth salt solution, stir the reaction for 5-30 min, and use the redox reaction of the galvanic cell to reduce bismuth and quickly obtain a black precipitate. (3) The above black precipitate was collected by centrifugation and then dried in an oven to obtain nanosheet Bi-Bi2O3 electrocatalyst; The metal foil that is more reactive than bismuth is aluminum foil or zinc foil; The Bi-Bi2O3 electrocatalyst has a nanosheet structure with a size between 500 nm and 2 μm and a nanosheet thickness of 1-10 nm. Its crystal structure is Bi and Bi2O3.

2. The application of a nanosheet-like Bi-Bi2O3 electrocatalyst, characterized in that: The Bi-Bi2O3 electrocatalyst of claim 1 is formulated into a catalyst ink and drop-coated onto carbon fiber paper for use in the electrocatalytic reduction of carbon dioxide to formic acid and its coupled oxidation of glycerol to produce formate salts without a membrane.

3. The application of the nanosheet-like Bi-Bi2O3 electrocatalyst according to claim 2, characterized in that: The Bi-Bi2O3 electrocatalyst of claim 1 was formulated into a catalyst ink and drop-coated onto carbon fiber paper as the working electrode, Ag / AgCl as the reference electrode, and foil as the counter electrode. CV activation was performed in an H-type electrolytic cell with a voltage range of -0.6 to -1.8 V and a scanning time of 10-20 min. After activation of Bi-Bi2O3, it was directly used for the electrocatalytic reduction of carbon dioxide to formic acid and the membraneless co-production of formate salts by coupled oxidation of glycerol.

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