A modified bismuth-based catalyst, a method of preparation and use thereof

Abstract

The application discloses a modified bismuth-based catalyst, a preparation method and application thereof, and belongs to the field of electrochemical reduction of CO2 catalysis. The application realizes in-situ synthesis of bismuth oxide and early construction of a Bi-O-C structure by hybridizing boron-doped carbon black and bismuth oxide. In particular, during the process of electrochemical reduction of carbon dioxide, the bismuth oxide is partially and spontaneously irreversibly restructured into bismuth subcarbonate (Bi2O2CO3), forming bismuth subcarbonate composite bismuth oxide (Bi2O2CO3 / Bi2O3). The existence of the structure significantly improves the application performance of the catalyst in the electrochemical reduction of carbon dioxide, and the catalyst has high formic acid selectivity, high catalytic efficiency, excellent stability and large working current capacity.

Description

Technical Field

[0001] This technology relates to the field of electrochemical CO2 reduction catalysis, specifically to bismuth-based catalysts, preparation methods, and their applications in the electroreduction of carbon dioxide. Background Technology

[0002] Electrochemical carbon dioxide reduction reactions, which convert clean and sustainable energy into electricity, represent a technology with enormous potential, promising to contribute to mitigating the global climate crisis while promoting the recycling of carbon dioxide. This process can efficiently convert carbon dioxide into a variety of beneficial chemicals, particularly formate / formic acid, which is not only a key intermediate in chemical synthesis, leather, pharmaceuticals, and textiles, but also holds significant appeal. Simultaneously, formate / formic acid shows great promise as a hydrogen storage / transport medium and as a relatively safe liquid carrier in direct formic acid fuel cells, possessing considerable potential for the development of hydrogen technology and the advancement of carbon neutrality.

[0003] In the electroreduction of carbon dioxide, the product selectivity varies among different metal active sites. For example, metals such as indium (In), tin (Sn), lead (Pb), bismuth (Bi), and mercury (Hg) exhibit high formic acid selectivity. Zhang Biaobiao et al. (Journal of the American Chemical Society, Vol. 145, pp. 14101-14111, 2023; Title: Indium Cyanamide for Industrial-Grade CO Electroreduction to Formic Acid.) constructed an InNCN catalyst by coordinating linear cyanamide anions with indium, achieving a product selectivity of 500 mA cm⁻¹. −2 The formic acid faradaic efficiency reached 81.4% at the specified current density; Bao Xinhe et al. (Year 59, Volume 59, Pages 4814-4821, Angewandte Chemie International Edition; Title: In Situ Reconstruction of a Hierarchical Sn-Cu / SnO) x (Core / Shell Catalyst for High-Performance CO2 Electroreduction.) Preparation of a SnO-containing... x Sn-Cu / SnO shell x Core-shell structured catalysts, at 243 mA cm⁻¹ −2 The formic acid faradaic efficiency reaches 90% at the current density.

[0004] Against this backdrop, bismuth-based catalysts have attracted widespread attention due to their advantages such as low toxicity, easy availability, and environmental friendliness. Furthermore, their low side reaction hydrogen evolution activity and good affinity for *OCHO, a key intermediate in formic acid formation, enable them to exhibit high selectivity in the electroreduction of carbon dioxide to formate / formic acid. Therefore, corresponding electrocatalysts have been developed for this process. For example, the creation of defects (NTD-Bi) on bismuth oxide nanotubes has shown promising results at 140 mA cm⁻¹. −2 At the specified current density, the formic acid faradaic efficiency reaches 95% (Nature Communications, Vol. 10, p. 2807, 2019; Title: Structural defects on converted bismuth oxide nanotubes enable highly active electrocatalysis of carbon dioxide reduction). However, the complexity and variability of the actual reaction environment, especially for bismuth-based catalysts in the electroreduction of carbon dioxide, lead to dynamic changes in the active sites. Specifically, bismuth-based catalysts may spontaneously undergo irreversible reconstruction, forming basic bismuth carbonate in an aqueous carbonate electrolyte. Studies have confirmed that this basic bismuth carbonate exhibits superior performance in the catalytic process of formic acid production from the electroreduction of carbon dioxide.

[0005] Carbon materials, due to their unique properties such as diverse pore structures, tunable chemical compositions, and easily modifiable surface groups, can effectively form and stabilize highly dispersed active sites when hybridized with bismuth species. This improves electron transfer and modulates electronic structure, thereby adjusting the affinity for reactants / intermediates / products. This hybridization strategy provides a broad avenue for enhancing catalyst performance.

[0006] Furthermore, heteroatom doping is a commonly used strategy in research to improve catalyst performance. For example, doping with boron (B), nitrogen (N), and sulfur (S) has been extensively studied and proven to significantly improve catalyst performance. In particular, boron doping has been shown to enhance the hydrophobicity of catalysts. In the process of carbon dioxide electroreduction, especially in a flow cell, highly hydrophobic catalysts can better contact carbon dioxide, improve the mass transfer rate, and thus enhance the performance of carbon dioxide electroreduction. Summary of the Invention

[0007] To address the shortcomings of existing technologies, the technical problem this invention aims to solve is to provide a method for preparing a modified bismuth-based catalyst. Another technical problem this invention aims to solve is to provide and analyze a modified bismuth-based catalyst product. Finally, the technical problem this invention aims to solve is to provide an application of the modified bismuth-based catalyst in the electroreduction of carbon dioxide. The modified bismuth-based catalyst provided by this invention improves the hydrophobic properties of the catalyst, thereby significantly enhancing its performance in the electroreduction of carbon dioxide.

[0008] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows:

[0009] A modified bismuth-based catalyst, wherein the modified bismuth-based catalyst is formed by combining a boron-doped oxidized carbon material with an oxidized bismuth-based catalyst.

[0010] Preferably, the bismuth-based catalyst for oxidation is bismuth oxide, basic bismuth carbonate, or a combination of the two or a generated bismuth oxide, and the carbon material for oxidation is oxidized carbon black, oxidized graphene, oxidized carbon nanotubes, or oxidized carbon fibers.

[0011] Preferably, the molar content of elemental bismuth in the oxidized bismuth-based catalyst is 10% to 30%; the molar ratio of the carbon oxide material to the oxidized bismuth-based catalyst is 1:1 to 10.

[0012] Preferably, the modified bismuth-based catalyst is formed by boron-doped oxidized carbon black and bismuth oxide; boron-doped oxidized carbon black and basic bismuth carbonate; boron-doped oxidized carbon black and a combination of bismuth oxide and basic bismuth carbonate; boron-doped oxidized graphene and bismuth oxide; or boron-doped oxidized carbon nanotubes and bismuth oxide.

[0013] A method for preparing a modified bismuth-based catalyst, comprising the following steps:

[0014] (1) The carbon material is mixed with an aqueous nitric acid solution to obtain an oxidized carbon material;

[0015] (2) The prepared oxidized carbon material is mixed with boric acid to obtain boron-doped oxidized carbon material;

[0016] (3) The oxidized bismuth-based catalyst is mixed with boron-doped oxidized carbon material to obtain the final product.

[0017] The preferred step (3) involves mixing the bismuth-based oxidized catalyst with the boron-doped oxidized carbon material by mixing bismuth nitrate with the boron-doped oxidized carbon material under the action of dimethylimidazole, or by mixing bismuth trioxide with the boron-doped oxidized carbon material to obtain the final product.

[0018] The preferred step (1) is an aqueous solution of nitric acid with a mass fraction of 20-60%. Step (1) requires heating and stirring for oxidation, and the required temperature is 75-85℃. Step (2) involves high-temperature pyrolysis in a nitrogen atmosphere, and the high-temperature pyrolysis temperature is 800-1000℃. Step (3) requires stirring at a temperature of 15-25℃.

[0019] The preferred step (1) refers to an aqueous solution of nitric acid with a mass fraction of 40%; the carbon material is carbon black, and the carbon black type is superconducting K90 or Ketjenblack EC 600 JD superconducting carbon black; the step (1) requires heating and stirring for oxidation, and the required temperature is 80 ℃;

[0020] The conditions for high-temperature pyrolysis in step (2) under nitrogen atmosphere are 1000 °C for 2 h; the mass ratio of the carbon black oxide to boric acid is 2: (1~4);

[0021] The mass ratio of boron-doped carbon black oxide, bismuth nitrate and dimethylimidazole in step (3) is 1:12:(10~16); the stirring time for the two solutions is 48 h; and the stirring temperature is 20 ℃.

[0022] The modified bismuth-based catalyst of the present invention is used as a catalyst in the electroreduction of carbon dioxide.

[0023] When electrocatalytically reducing carbon dioxide to formic acid, a silver chloride electrode is used as the reference electrode and a platinum sheet or iridium oxide as the auxiliary electrode. The carbon dioxide-saturated aqueous electrolyte includes carbon dioxide-saturated KOH solution, NaHCO3 solution, KHCO3 solution, RbHCO3 solution, CsHCO3 solution, Na2CO3 solution, K2CO3 solution, KOH solution, CsOH solution, and LiOH solution.

[0024] Beneficial effects:

[0025] The modified bismuth-based catalyst provided by this invention constructs a special catalyst structure: by hybridizing boron-doped carbon black oxide with bismuth oxide, in-situ synthesis of bismuth oxide and early construction of the Bi−O−C structure are achieved. This early construction of the Bi−O−C structure effectively promotes the irreversible reconstruction of basic bismuth carbonate during the electroreduction of carbon dioxide. Specifically, during the electroreduction of carbon dioxide, bismuth oxide partially and spontaneously irreversibly reconstructs into basic bismuth carbonate (Bi2O2CO3), forming a basic bismuth carbonate composite bismuth oxide (Bi2O2CO3 / Bi2O3). The presence of this structure significantly improves the catalyst's performance in the electroreduction of carbon dioxide. During the in-situ reconstruction of bismuth species into basic bismuth carbonate by boron-doped carbon black oxide during the electroreduction of carbon dioxide, additional Bi−O−C interactions are provided for the formation and stabilization of the abundant Bi−O structure, resulting in the final catalyst: basic bismuth carbonate composite bismuth oxide (Bi2O2CO3 / Bi2O3).

[0026] The modified bismuth-based catalyst of this invention exhibits high formic acid selectivity, high catalytic efficiency, excellent stability, and the ability to operate at high current in the electroreduction of carbon dioxide. At 800 mA cm⁻¹ −2 Even at current densities below 100 mA / cm², it still achieves a formic acid Faradaic efficiency of 95.2%, in a membrane electrolyzer at 100 mA / cm². −2 It can be stably operated for 12 hours at a current density, and the formic acid faradaic efficiency is still greater than 82%.

[0027] The present invention also provides a method for preparing a modified bismuth-based catalyst. Through this method, boron doping significantly improves the hydrophobicity and conductivity of the composite catalyst, enhances the mass transfer rate, accelerates electron transfer, and suppresses side reactions of the hydrogen evolution reaction. Attached Figure Description

[0028] Figure 1 A schematic diagram of Bi@BOC synthesis;

[0029] Figure 2 Bi@BOC and the control sample Bi@OC, BiO x XRD pattern;

[0030] Figure 3 Bi@BOC and the control sample Bi@OC, BiO x Nitrogen adsorption-desorption curves and pore size distribution diagrams;

[0031] Figure 4 (a) SEM image of sample Bi@BOC, (b) SEM image of sample Bi@OC, (c) SEM image of sample BiO x SEM image;

[0032] Figure 5(a) Samples Bi@BOC, Bi@OC, BiO x Bi- and standard sample Bi2O3 L 3 (b) Near-edge X-ray absorption spectra of samples Bi@BOC, Bi@OC, and BiO x Bi- and standard sample Bi2O3 L 3 Edge X-ray absorption extends the edge absorption spectrum;

[0033] Figure 6 (a) Contact angle test of sample Bi@BOC, (b) Contact angle test of sample Bi@OC;

[0034] Figure 7 For Bi@BOC in a flow cell configuration, at 800 mA cm⁻¹ −2 After a carbon dioxide electroreduction reaction was carried out at a current density of 0.5 h, the electrolyte... 1 H NMR spectrum;

[0035] Figure 8 The Faraday efficiency of each product of Bi@BOC at different current densities is given.

[0036] Figure 9 Figure 1 shows the stability performance test results of Bi@BOC in a membrane reactor.

[0037] Figure 10 In-situ XAFS image of Bi@BOC during the carbon dioxide electroreduction process;

[0038] Figure 11 The in-situ ATR-SEIRAS spectrum of Bi@BOC during the carbon dioxide electroreduction process;

[0039] Figure 12 The XRD pattern of the working electrode coated with Bi@BOC after the fresh electrode undergoes an electroreduction reaction with carbon dioxide.

[0040] Figure 13 (a) High-resolution Bi 4f XPS spectra before and after the reaction with Bi@BOC catalyst coated on the working electrode, (b) High-resolution O 1s XPS spectra before and after the reaction with Bi@BOC catalyst coated on the working electrode, (c) High-resolution C 1s XPS spectra before and after the reaction with Bi@BOC catalyst coated on the working electrode.

[0041] Figure 14 A performance comparison chart of Bi@BOC and other reported catalysts for the electroreduction of carbon dioxide to formic acid. Detailed Implementation

[0042] To facilitate the explanation of the technical solution of this application, some concepts involved in this application will be explained first below.

[0043] Example 1

[0044] Carbon black (2.1 mmol) and an aqueous nitric acid solution (40 wt%, 50 mL) were mixed in a 100 mL flask and stirred in a water bath at 80 °C for 24 h. The solid was then separated by filtration, washed with deionized water, and dried in an oven at 70 °C to obtain carbon black oxide. Carbon black oxide (0.2 g) and boric acid (0.1 g) were mixed in a mortar and thoroughly ground to obtain a relatively homogeneous powder. The mixture was transferred to a porcelain boat and placed in a tube furnace. Pyrolysis was performed at 1000 °C for 2 h under a nitrogen atmosphere to obtain boron-doped carbon black oxide.

[0045] Bismuth nitrate (3 mmol) was dissolved in 50 mL of methanol and sonicated for 30 min to obtain solution A. Dimethylimidazole (17.3 mmol) was dissolved in 60 mL of N,N-dimethylformamide and sonicated to obtain solution B. Solutions A and B were mixed and stirred for 10 min, and then boron-doped carbon black (0.1 g) was added. The mixture was stirred at room temperature for 48 h. Subsequently, the solid was separated by centrifugation, washed with methanol, and dried in an oven at 70 °C to obtain the final sample, denoted as Bi@BOC.

[0046] Example 2

[0047] Carbon black (2.1 mmol) and an aqueous nitric acid solution (40 wt%, 50 mL) were mixed in a 100 mL flask and stirred in a water bath at 80 °C for 24 h. The solid was then separated by filtration, washed with deionized water, and dried in an oven at 70 °C to obtain carbon black oxide. Carbon black oxide (0.2 g) and boric acid (0.2 g) were mixed in a mortar and thoroughly ground to obtain a relatively homogeneous powder. The mixture was transferred to a porcelain boat and placed in a tube furnace. Pyrolysis was performed at 1000 °C for 2 h under a nitrogen atmosphere to obtain boron-doped carbon black oxide.

[0048] Bismuth nitrate (3 mmol) was dissolved in 50 mL of methanol and sonicated for 30 min to obtain solution A. Dimethylimidazole (17.3 mmol) was dissolved in 60 mL of N,N-dimethylformamide and sonicated to obtain solution B. Solutions A and B were mixed and stirred for 10 min, and then boron-doped carbon black (0.1 g) was added. The mixture was stirred at room temperature for 48 h. Subsequently, the solid was separated by centrifugation, washed with methanol, and dried in an oven at 70 °C to obtain the final sample, denoted as Bi@BOC-1.

[0049] Example 3

[0050] Carbon black (2.1 mmol) and an aqueous nitric acid solution (40 wt%, 50 mL) were mixed in a 100 mL flask and stirred in a water bath at 80 °C for 24 h. The solid was then separated by filtration, washed with deionized water, and dried in an oven at 70 °C to obtain carbon black oxide. Carbon black oxide (0.2 g) and boric acid (0.4 g) were mixed in a mortar and thoroughly ground to obtain a relatively homogeneous powder. The mixture was transferred to a porcelain boat and placed in a tube furnace. Pyrolysis was performed at 1000 °C for 2 h under a nitrogen atmosphere to obtain boron-doped carbon black oxide.

[0051] Bismuth nitrate (3 mmol) was dissolved in 50 mL of methanol and sonicated for 30 min to obtain solution A. Dimethylimidazole (17.3 mmol) was dissolved in 60 mL of N,N-dimethylformamide and sonicated to obtain solution B. Solutions A and B were mixed and stirred for 10 min, and then boron-doped carbon black (0.1 g) was added. The mixture was stirred at room temperature for 48 h. Subsequently, the solid was separated by centrifugation, washed with methanol, and dried in an oven at 70 °C to obtain the final sample, denoted as Bi@BOC-0.5.

[0052] Example 4

[0053] Carbon black (2.1 mmol) and an aqueous nitric acid solution (40 wt%, 50 mL) were mixed in a 100 mL flask and stirred in a water bath at 80 °C for 24 h. The solid was then separated by filtration, washed with deionized water, and dried in an oven at 70 °C to obtain carbon black oxide. Carbon black oxide (0.2 g) and boric acid (0.1 g) were mixed in a mortar and thoroughly ground to obtain a relatively homogeneous powder. The mixture was transferred to a porcelain boat and placed in a tube furnace. Pyrolysis was performed at 1000 °C for 2 h under a nitrogen atmosphere to obtain boron-doped carbon black oxide.

[0054] Basic bismuth carbonate (3 mmol) was dissolved in 60 mL of N,N-dimethylformamide and sonicated, followed by the addition of boron-doped carbon black oxide (0.1 g). The mixture was stirred at room temperature for 48 h. Subsequently, the solid was separated by centrifugation, washed with methanol, and dried in an oven at 70 °C to obtain the final sample, denoted as Bi2O2CO3@BOC.

[0055] Example 5

[0056] Carbon black (2.1 mmol) and an aqueous nitric acid solution (40 wt%, 50 mL) were mixed in a 100 mL flask and stirred in a water bath at 80 °C for 24 h. The solid was then separated by filtration, washed with deionized water, and dried in an oven at 70 °C to obtain carbon black oxide. Carbon black oxide (0.2 g) and boric acid (0.1 g) were mixed in a mortar and thoroughly ground to obtain a relatively homogeneous powder. The mixture was transferred to a porcelain boat and placed in a tube furnace. Pyrolysis was performed at 1000 °C for 2 h under a nitrogen atmosphere to obtain boron-doped carbon black oxide.

[0057] Basic bismuth carbonate (1.5 mmol) and bismuth trioxide (1.5 mmol) were dissolved in 60 mL of N,N-dimethylformamide and sonicated, followed by the addition of boron-doped carbon black oxide (0.1 g). The mixture was stirred at room temperature for 48 h. Subsequently, the solid was separated by centrifugation, washed with methanol, and dried in an oven at 70 °C to obtain the final sample, denoted as Bi2O3-Bi2O2CO3@BOC.

[0058] Example 6

[0059] Graphene (2.1 mmol) and an aqueous nitric acid solution (40 wt%, 50 mL) were mixed in a 100 mL flask and stirred in a water bath at 80 °C for 24 h. The solid was then separated by filtration, washed with deionized water, and dried in an oven at 70 °C to obtain graphene oxide. Graphene oxide (0.2 g) and boric acid (0.1 g) were mixed in a mortar and thoroughly ground to obtain a relatively homogeneous powder. The mixture was transferred to a porcelain boat and placed in a tube furnace. Pyrolysis was performed at 1000 °C for 2 h under a nitrogen atmosphere to obtain boron-doped graphene oxide.

[0060] Bismuth nitrate (3 mmol) was dissolved in 50 mL of methanol and sonicated for 30 min to obtain solution A. Dimethylimidazole (17.3 mmol) was dissolved in 60 mL of N,N-dimethylformamide and sonicated to obtain solution B. Solutions A and B were mixed and stirred for 10 min, and then boron-doped graphene oxide (0.1 g) was added. The mixture was stirred at room temperature for 48 h. Subsequently, the solid was separated by centrifugation, washed with methanol, and dried in an oven at 70 °C to obtain the final sample, denoted as Bi@BOC-Graphene.

[0061] Example 7

[0062] Multi-walled carbon nanotubes (2.1 mmol) and an aqueous nitric acid solution (40 wt%, 50 mL) were mixed in a 100 mL flask and stirred in a water bath at 80 °C for 24 h. The solid was then separated by filtration, washed with deionized water, and dried in an oven at 70 °C to obtain carbon oxide nanotubes. Carbon oxide nanotubes (0.2 g) and boric acid (0.1 g) were mixed in a mortar and thoroughly ground to obtain a relatively homogeneous powder. The mixture was transferred to a porcelain boat and placed in a tube furnace. Pyrolysis was performed at 1000 °C for 2 h under a nitrogen atmosphere to obtain boron-doped carbon oxide nanotubes.

[0063] Bismuth nitrate (3 mmol) was dissolved in 50 mL of methanol and sonicated for 30 min to obtain solution A. Dimethylimidazole (17.3 mmol) was dissolved in 60 mL of N,N-dimethylformamide and sonicated to obtain solution B. Solutions A and B were mixed and stirred for 10 min, and then boron-doped carbon oxide nanotubes (0.1 g) were added. The mixture was stirred at room temperature for 48 h. Subsequently, the solid was separated by centrifugation, washed with methanol, and dried in an oven at 70 °C to obtain the final sample, denoted as Bi@BOC-MWNT.

[0064] Comparative Example 1

[0065] Carbon black (0.5073 g, 2.1 mmol) and an aqueous nitric acid solution (40 wt%, 50 mL) were mixed in a 100 mL flask and stirred in a water bath at 80 °C for 24 h. The solid was then separated by filtration, washed with deionized water, and dried in an oven at 70 °C to obtain carbon black oxide.

[0066] Bismuth nitrate (3 mmol) was dissolved in 50 mL of methanol and sonicated for 30 min to obtain solution A. Dimethylimidazole (17.3 mmol) was dissolved in 60 mL of N,N-dimethylformamide and sonicated to obtain solution B. Solutions A and B were mixed and stirred for 10 min, and then carbon black (0.1 g) was added. The mixture was stirred at room temperature for 48 h. Subsequently, the solid was separated by centrifugation, washed with methanol, and dried in an oven at 70 °C to obtain the final sample, denoted as Bi@OC.

[0067] Comparative Example 2

[0068] Bismuth nitrate (3 mmol) was dissolved in 50 mL of methanol and sonicated for 30 min to obtain solution A. Dimethylimidazole (17.3 mmol) was dissolved in 60 mL of N,N-dimethylformamide and sonicated to obtain solution B. Solutions A and B were mixed and stirred for 10 min. The mixture was stirred at room temperature for 48 h. Subsequently, the solid was separated by centrifugation, washed with methanol, and dried in an oven at 70 °C to obtain the final sample, denoted as BiO. x .

[0069] Test Example 1

[0070] The sample display flowchart of Example 1 is as follows: Figure 1 As shown:

[0071] Figure 1 This is a simplified diagram of the sample synthesis in Example 1, illustrating the process of hybridization of boron-doped carbon black oxide and bismuth oxide.

[0072] Test Example 2

[0073] The samples from Examples 1-3 and the comparative examples were subjected to structural characterization and related performance tests, and the results are as follows: Figure 1-4 As shown:

[0074] Figure 2 The XRD patterns of the sample from Example 1 and the samples from Comparative Examples 1 and 2 are shown. The three samples show a diffraction peak at 27.98°, which corresponds to the (221) crystal plane of Bi2O3, proving the existence of the Bi2O3 structure.

[0075] Figure 3 The nitrogen adsorption-desorption curves and pore size distribution diagrams for the sample of Example 1 and Comparative Examples 1 and 2 show that the nitrogen adsorption isotherm of the synthesized sample is type I+IV. It exhibits relatively small, rapid absorption at low pressure, corresponding to the presence of micropores, and flat and high absorption at high pressure, reflecting the presence of abundant mesopores and macropores. Correspondingly, Example Bi@BOC has the largest surface area (201 m²). 2 g −1 The surface area and pore volume are 0.13 cm³. 3 g −2 ).

[0076] Figure 4 These are SEM images of the sample from Example 1 and the comparative sample. Figure 4 (a) SEM image of sample Bi@BOC, (b) SEM image of sample Bi@OC, (c) SEM image of sample BiO x The SEM image shows the sample as composed of primary particles with a size of tens of nanometers. Loose packing is observed on these carbon-based hybrid materials, while in comparative example 2 BiO xA slightly denser accumulation was found on it.

[0077] Figure 5 The images show the XAFS diagrams of the sample from Example 1, the comparative sample, and the Bi2O3 standard. Specifically... Figure 5 (a) Samples Bi@BOC, Bi@OC, BiO x Bi- and standard sample Bi2O3 L 3 (b) Near-edge X-ray absorption spectra of samples Bi@BOC, Bi@OC, and BiO x Bi- and standard sample Bi2O3 L 3 Edge X-ray absorption extends edge absorption spectrum. Figure 5 XAFS can be used to analyze the valence state of metallic Bi and the coordination environment surrounding it. In the figure, the three samples exhibit Bi-... L 3 Edge X-ray absorption near-edge structure (XANES) spectra indicate that the oxidation state of the bismuth species is close to +3. Bi- L 3 The edge shows a distinct peak at R=2.18 Å, which is attributed to the Bi−O scattering path.

[0078] exist Figure 6 In this study, we compared the contact angles of the samples from Example 1 and Comparative Example 1. Specifically, Figure 6 (a) Contact angle test of sample Bi@BOC, (b) Contact angle test of sample Bi@OC. Notably, after boron doping, the contact angle of Example 1 significantly increased from the initial 26° to approximately 67°. This change clearly demonstrates that the hydrophobicity of Bi@BOC in Example 1 is significantly enhanced compared to Bi@OC in Comparative Example 1.

[0079] Test Example 3

[0080] The samples from Examples 1-3 and the comparative example were subjected to carbon dioxide electroreduction reaction, and the reaction equations are as follows:

[0081] cathode:

[0082]

[0083] anode:

[0084] Electrochemical carbon dioxide reduction was performed on a CHI760E electrochemical workstation (Shanghai Chenhua, China). A flow cell configuration was used, consisting of a working electrode, a carbon paper substrate uniformly coated with catalyst (1 cm × 3 cm), an Ag / AgCl reference electrode in 1 M KOH, and a platinum counter electrode (1 cm × 3 cm). The cathode and anode chambers had a volume of 100 mL and were separated by an anion exchange membrane (AEM, PiperION-A20-HCO3). The working electrode, counter electrode, and anion exchange membrane all had an area of ​​1 cm². −2 .

[0085] The working electrode (cathode) was prepared as follows: Catalyst ink was prepared by ultrasonically mixing catalyst (3 mg) with Nafion solution (5% w / v, 0.03 mL) and isopropanol (0.3 mL) for 30 minutes. Then, 0.33 mL of the ink was coated onto carbon paper, with a coating area of ​​1 × 3 cm. 2 The catalyst loading was 1 mg cm⁻¹ −2 The electrode was dried at 40 °C to obtain the working electrode.

[0086] In both the cathode and anode chambers, 50 mL of 1 M potassium bicarbonate (KHCO3) was added as the electrolyte. Before the electrolysis experiment, high-purity carbon dioxide (99.9999%, 70 mL min) was added. −1 The sample was continuously passed through a flow cell for 5 minutes to remove air from the system. Electrolysis was then performed using a constant current method. The current density (J) was normalized to the geometric area of ​​the working electrode.

[0087] By using the equation E(V) vs. RHE) =E (V vs. Ag / AgCl) + 0.1989 V + 0.0592 × pH, rescale the potential applied to the Ag / AgCl reference electrode to the reversible hydrogen electrode (RHE). Calculate the Faraday efficiency (FE) of the product using the following formula:

[0088]

[0089] in z It is the number of electrons transferred in the target product (formate). z = 2); n It is the actual number of moles of the target product, in mol; F is the Faraday constant, 96485 C × mol. −1 Q is the electrolysis power, C.

[0090] Formate ( j formate The partial current density is calculated using the following formula:

[0091]

[0092] in j total S is the total current density, and S is the reaction area (S = 1 cm²). −2 ).

[0093] Stability testing was conducted in a membrane reactor (MEA). The long-term stability of carbon dioxide electroreduction to formate was evaluated in a flow electrolyzer of a dual-electrode membrane electrode assembly (MEA) separated by anion exchange membranes (AEM, PiperION-A20-HCO3). The cathode electrode was a YLS-30T GDL electrode (2×2 cm). 2 ) Loading 1 mg cm −2 The catalyst was prepared, and the anode electrode was an iridium oxide mesh (2 × 2 cm). 2 A gas stream of carbon dioxide filled with water vapor (20 mL / min) is supplied to the cathode side. −1 The anolyte electrolyte was added at a rate of 5 mL / min. −1 The rate is achieved by circulating 1 M KHCO3. The CO2RR in the MEA system is conducted through a constant current test. In this device, the cathode is filled with a gas stream of carbon dioxide and water vapor, which isolates the influence of the cathode electrolyte and eliminates the influence of gas mass transfer resistance. This makes it a promising device for improving stability and scaling up for industrial application.

[0094] Figure 7 This discloses the Bi@BOC in Example 1 in a flow cell configuration at 800 mA cm⁻¹ −2 After a carbon dioxide electroreduction reaction was carried out at a current density of 0.5 h, the electrolyte... 1 1H nuclear magnetic resonance (NMR) spectrum. This spectrum not only confirmed the formation of formic acid, but also provided a quantitative analysis of its content.

[0095] Table 1: Summary of CO2 electroreduction current density, voltage, and formate Faraday efficiency of the catalyst

[0096]

[0097] One indicator for evaluating the performance of carbon dioxide electroreduction is maintaining a high product Faradaic efficiency at the highest possible current. Table 1 shows the current density, voltage, and formate Faradaic efficiency of the catalyst during carbon dioxide electroreduction, demonstrating that Example 1 Bi@BOC exhibits superior activity in the carbon dioxide electroreduction process, with better performance in current density, voltage, and formate Faradaic efficiency than the comparative example. By comparing Example 1 Bi@BOC with Comparative Example 2 Bi@OC, we find that the introduction of element B significantly improves the catalyst's ability to produce formic acid, even below 600 mA cm⁻¹. −2 The performance of the two catalysts is not significantly different at current densities, but when the current density is greater than 600 mA cm⁻¹, the performance difference becomes more pronounced. −2 Boron-doped samples exhibit better stability at 800 mA cm⁻¹ due to their high hydrophobicity. −2 Even at the specified current density, a formic acid Faradaic efficiency of 95.2% can still be achieved. Furthermore, comparing Example 1 Bi@BOC with Examples 2 Bi@BOC-1 and 3 Bi@BOC-2, it can be seen that the Faradaic efficiency of Examples 2 and 3 is significantly reduced at the corresponding current densities. This indicates that excessive B doping is detrimental to formate formation and negatively impacts catalyst performance. In particular, Comparative Example 1 Bi@OC significantly outperforms Comparative Example 2 BiO in performance. x This is thanks to the addition of carbon black and bismuth oxide hybrids, which greatly improves the overall performance of the catalyst.

[0098] Figure 8 The optimal sample example 1, Bi@BOC, demonstrates the Faradaic efficiency of each product at different current densities. It can be seen that the efficiency is within the range of 300-800 mA cm⁻¹. −2 Example 1 exhibits high Faraday efficiency for formic acid across a wide voltage range.

[0099] Figure 9 The optimal sample example 1, Bi@BOC, was demonstrated to exhibit stability performance in an anion exchange membrane electrolyzer (MEA) at 100 mA cm⁻¹. −2 After continuous electrolysis for 12 hours, the voltage remained at around -3.5 V, and the Faraday efficiency of formic acid was still higher than 82%.

[0100] Test Example 4

[0101] The sample from Example 1 was subjected to in-situ real-time structural characterization of the carbon dioxide electroreduction reaction.

[0102] Figure 10This paper demonstrates the analysis of Bi@BOC in the carbon dioxide electroreduction process of Example 1 using in-situ X-ray absorption spectroscopy (XAFS). Extensive research indicates that catalyst reconstruction in carbon dioxide is highly complex, and in-situ spectroscopy allows for in-depth analysis of the catalyst. XAFS was used to measure the catalytic conversion of carbon dioxide to formate by Bi@BOC, with an applied voltage range of 0 V to −1 V. vs. RHE. Bi- was collected at different potentials. L 3 Edge XANES spectrum. The figure shows the change in applied potential from open circuit (OCP) to 0 V. vs. During RHE, Bi- L 3 The absorption edge at the edge transfers to a lower energy, reflecting a decrease in the oxidation state.

[0103] When the potential relative to RHE shifts negatively from 0 V to −0.2 V vs. During RHE, Bi- L 3 The edge moves towards higher energies. This indicates that the low-valence bismuth species formed is consumed and restored to its original state during the carbon dioxide electroreduction. As the potential further increases to −1.0 V... vs. RHE, Bi- L 3 The edges shift towards lower energies due to the partial reduction of Bi species at very negative potentials. At the end of the in-situ XAFS test, Bi- L 3 The edge Bi@BOC (spectrum collected 5 minutes after the applied potential switched to the open circuit state) rapidly recovered to the open circuit state, indicating that the hybridization of boron-doped carbon black with bismuth oxide contributes to the catalyst's carbon dioxide activity and stability, as well as the reversibility of the Bi species.

[0104] Figure 11 In-situ ATR-SEIRAS spectra of the Bi@BOC sample from Example 1 were acquired to monitor the structural changes of the catalyst and the formation of reaction intermediates during carbon dioxide electroreduction. During the carbon dioxide electroreduction process, with increasing voltage, the catalytic structure at 1236 cm⁻¹... −1 The appearance of a negative peak can be attributed to HCO3. − Consumption of HCO3 − It is favorable for the formation of basic bismuth carbonate, and at 1100 cm⁻¹ −1 and 1509 cm −1 The peak values ​​at these locations correspond to CO3. 2−This is crucial for the irreversible reconstruction of bismuth species into basic bismuth carbonate, thus further confirming the formation of basic bismuth carbonate. Notably, at a distance of 2107 cm from the intermediate *CO... −1 No corresponding peak was observed at this point, indicating that Bi@BOC has a high CO energy barrier and is therefore not prone to generating the byproduct CO.

[0105] Test Example 5

[0106] In the electroreduction of carbon dioxide, Nafion catalysts are loaded onto carbon paper as working electrodes, and the catalysts typically undergo structural reconstruction after a potential is applied. To gain a deeper understanding of this process, the working electrode with the catalyst coated (Example 1) was characterized by XRD and XPS before and after the reaction.

[0107] Figure 12 A comparison of the XRD patterns of the fresh electrode and the electrode after the reaction showed that the latter exhibited a distinct peak corresponding to basic bismuth carbonate. This indicates that Bi@BOC underwent irreversible structural evolution and generated basic bismuth carbonate as an active site during the carbon dioxide electroreduction process.

[0108] Figure 13 XPS spectra of the fresh electrode and the electrode after the reaction are shown. Specifically... Figure 13 (a) High-resolution Bi 4f XPS spectra before and after the reaction with Bi@BOC catalyst coated on the working electrode; (b) High-resolution O 1s XPS spectra before and after the reaction with Bi@BOC catalyst coated on the working electrode; (c) High-resolution C 1s XPS spectra before and after the reaction with Bi@BOC catalyst coated on the working electrode. In the Bi 4f XPS spectra, a peak of basic bismuth carbonate appears; while in the O 1s XPS spectra, the Bi−O signal relatively increases; in addition, a C=O signal also appears in the C 1s XPS spectra. These changes all indicate the formation of basic bismuth carbonate.

[0109] Test Example 6

[0110] Table 2 compares the performance of Example 1 and previously reported catalysts in the electroreduction of carbon dioxide to formic acid in potassium bicarbonate (KHCO3) electrolyte.

[0111]

[0112] *Voltage refers to the voltage that has undergone iR compensation.

[0113] Figure 14 The performance comparison table of Example 1 and related reported catalysts in the electroreduction of carbon dioxide to formic acid is presented in the form of a figure, which demonstrates that Example 1 has excellent performance in the electroreduction of carbon dioxide.

[0114] The existing literature sources for catalysts are as follows:

[0115] ①Catalyst Bi-DC; Source: ACS Catalysis 2024; Title: Beyond Leverage in Activity and Stability toward CO2 Electroreduction to Formate over a Bismuth Catalyst.

[0116] ② Catalyst InNCN; Source: 2023 Journal of the American Chemical Society; Title: Indium Cyanamide for Industrial-Grade CO2 Electroreduction to Formic Acid.

[0117] ③ Catalyst NTD-Bi; Source: Nature Communications, 2019; Title: Structural defects on converted bismuth oxide nanotubes capable of highly active electrocatalysis of carbon dioxide reduction.

[0118] ④Catalyst Bi@Sn; Source: Advanced Science, 2020; Title: Bi@Sn Core–Shell Structure with Compressive Strain Boosts the Electroreduction of CO2 into Formic Acid.

[0119] ⑤ Catalyst ZnIn2S4; Source: Nature Communications, 2021; Title: Stabilizing indium sulfide for CO2 electroreduction to formate at high rate by zinc incorporation.

[0120] ⑥ Catalyst L-In; Source: Small, 2022; Title: Transient Solid-State Laser Activation of Indium for High-Performance Reduction of CO2 to Formate.

[0121] ⑦ Catalyst Ni-In2O3@C NFs; Source: ACS Catalysis 2021; Title: In SituCarbon Encapsulation Confined Nickel-Doped Indium Oxide Nanocrystals for Boosting CO2 Electroreduction to the Industrial Level.

[0122] ⑧ Catalyst Sn 2.7 Cu / SnO2; Source: Angewandte Chemie International Edition, 2020; Title: In Situ Reconstruction of a Hierarchical Sn-Cu / SnO2 x Core / ShellCatalyst for High-Performance CO2Electroreduction.

[0123] ⑨ Catalyst Sn3O4; Source: Nano Energy 2020; Title: Tuning Sn3O4 for CO2 reduction to formate with ultra-high current density.

Claims

1. A modified bismuth-based catalyst characterized in that, The modified bismuth-based catalyst is formed by boron-doped oxidized carbon material and oxidized bismuth-based catalyst; The oxidized carbon material is oxidized carbon black, oxidized graphene, oxidized carbon nanotube or oxidized carbon fiber; the oxidized bismuth-based catalyst is bismuth trioxide, bismuth subcarbonate or a combination of the two; The molar content of bismuth in the oxidized bismuth-based catalyst is 10% to 30%; the molar ratio of the oxidized carbon material to the oxidized bismuth-based catalyst is 1:1 to 10.

2. The modified bismuth-based catalyst of claim 1, wherein: The modified bismuth-based catalyst is formed by boron-doped oxidized carbon black and bismuth trioxide; boron-doped oxidized carbon black and bismuth subcarbonate; boron-doped oxidized carbon black and a combination of bismuth trioxide and bismuth subcarbonate; boron-doped oxidized graphene and bismuth trioxide; boron-doped oxidized carbon nanotube and bismuth trioxide.

3. A process for the preparation of a modified bismuth-based catalyst according to claim 1 or 2, characterized in that, The steps are as follows: (1) mixing carbon material and nitric acid aqueous solution to obtain oxidized carbon material; (2) mixing the prepared oxidized carbon material and boric acid to obtain boron-doped oxidized carbon material; (3) mixing the oxidized bismuth-based catalyst and boron-doped oxidized carbon material to obtain the final product.

4. The production method according to claim 3, characterized by, In step (3), the mixing of the oxidized bismuth-based catalyst and boron-doped oxidized carbon material is mixing bismuth nitrate with boron-doped oxidized carbon material under the action of dimethyl imidazole or mixing bismuth trioxide with boron-doped oxidized carbon material to obtain the final product.

5. The preparation method according to claim 3, characterized in that, In step (1), the nitric acid aqueous solution is a solution with a mass fraction of 20% to 60% nitric acid; step (1) requires heating and stirring for oxidation, and the required temperature is 75 to 85°C; step (2) is pyrolysis in a nitrogen atmosphere, and the pyrolysis temperature is 800 to 1000°C; step (3) requires a stirring temperature of 15 to 25°C.

6. The preparation method of claim 3, wherein In step (1), the nitric acid aqueous solution refers to a solution with a mass fraction of 40% nitric acid; the carbon material is carbon black, and the type of carbon black is superconducting K90 or Ketjenblack EC 600 JD superconducting carbon black; step (1) requires heating and stirring for oxidation, and the required temperature is 80°C; Step (2) is pyrolysis in a nitrogen atmosphere at a temperature of 1000°C for 2 hours; the mass ratio of the oxidized carbon black to boric acid is 2: (1 to 4); In step (3), the mass ratio of boron-doped oxidized carbon black, bismuth nitrate and dimethyl imidazole is 1:12: (10 to 16); the stirring time of the two solutions is 48 hours; the stirring temperature is 20°C.

7. Use of the modified bismuth-based catalyst according to any one of claims 1-2 and of the modified bismuth-based catalyst prepared according to any one of claims 3-6, characterized in that, The modified bismuth-based catalyst is used as a catalyst in the electroreduction of carbon dioxide.

8. Use according to claim 7, characterized in that, In the electrocatalytic reduction of carbon dioxide to generate formic acid, a silver chloride silver electrode is used as a reference electrode, and a platinum sheet or iridium oxide is used as an auxiliary electrode; the carbon dioxide-saturated aqueous electrolyte includes carbon dioxide-saturated KOH solution, NaHCO3 solution, KHCO3 solution, RbHCO3 solution, CsHCO3 solution, Na2CO3 solution, K2CO3 solution, KOH solution, CsOH solution, and LiOH solution.

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