Polypyrrole coated bismuth core-shell nanowire with cavity as well as preparation method and application of polypyrrole coated bismuth core-shell nanowire

Abstract

The invention discloses a polypyrrole coated bismuth core-shell nanowire with a cavity as well as a preparation method and application thereof, and relates to the technical field of CO2 electroreduction. The nanowire takes a bismuth formate oxide nanowire as an inner core, and the surface of the nanowire is coated with a polypyrrole shell layer. When the material is applied to CO2 electroreduction, the inner core is reduced into metal bismuth and generates volume shrinkage, and a cavity is formed between the core and the shell to promote substance transmission. The polypyrrole shell layer can maintain the one-dimensional morphology, restricts the reconstruction of the catalyst, and utilizes the hydrophobic and aerophilic characteristics of the polypyrrole shell layer to regulate and control the interface microenvironment and promote proton transport. Compared with an uncoated material, the catalyst has the advantages that the current density is obviously improved, the formic acid Faraday efficiency is continuously higher than 90% in a wide potential range of-0.6 to-1.1 V (vs. RHE), the efficiency is kept above 80% in a test for more than 350 hours, and the catalyst shows excellent stability and application potential.

Description

Technical Field

[0001] This invention relates to the field of CO2 electroreduction technology, and more specifically, to a cavitary polypyrrole-coated bismuth core-shell nanowire, its preparation method, and its application. Background Technology

[0002] The escalating global climate change is primarily rooted in the rapid rise in atmospheric carbon dioxide (CO2) concentrations caused by human activities. Developing efficient carbon neutrality technologies is imperative for achieving sustainable development goals. Against this backdrop, the carbon dioxide electroreduction reaction (CO2ER), as a highly promising conversion pathway, has attracted widespread attention from academia and industry. This technology utilizes electricity generated from renewable energy sources such as solar and wind power to directly convert captured CO2 into high-value-added fuels and chemicals, such as carbon monoxide, formic acid, ethylene, and ethanol, under normal temperature and pressure. This process not only helps achieve negative CO2 emissions or resource utilization but also stores intermittent renewable energy in the form of chemical energy, thus constructing an ideal "artificial carbon cycle." This is of significant strategic importance for ensuring energy security and promoting the low-carbon transformation of the chemical industry.

[0003] Despite the promising prospects of electrochemical CO2ERs, their large-scale practical application still faces numerous severe challenges. First, the dynamic reconstruction of catalysts is one of the core difficulties in current research. Under the influence of reduction potential, the surface structure, chemical valence state, and coordination environment of many high-performance metal-based catalysts (such as copper, tin, and bismuth) do not remain in their initial state but undergo significant and irreversible dynamic evolution. This reconstruction behavior makes it difficult to accurately identify the true active sites, leading to a complex trade-off between catalyst activity, selectivity, and stability. Insufficient understanding of the reconstruction mechanism severely restricts the rational design and development of efficient and stable catalysts. Second, mass transport limitations during the reaction process are another key bottleneck affecting reaction efficiency and selectivity. As a nonpolar molecule, CO2 has very low solubility in aqueous electrolytes, resulting in severe mass transfer limitations, making it difficult to effectively increase the reaction current density, thus affecting the economic feasibility of the entire process. Simultaneously, the complex mass transfer processes involving CO2, protons, hydroxide ions, and products near the reaction interface significantly alter the local pH and reactant concentration, thereby interfering with the reaction pathway and product distribution. Therefore, overcoming the reconstruction and mass transfer problems in the catalytic process is a crucial breakthrough for achieving high-efficiency CO2ER.

[0004] In view of this, the present invention is proposed. Summary of the Invention

[0005] The purpose of this invention is to provide a cavity-structured polypyrrole-coated bismuth core-shell nanowire, its preparation method, and its applications. Its core-shell structure effectively suppresses morphological changes caused by electrochemical reconstruction, and the cavity structure formed during the CO2ER reaction greatly facilitates mass transport in the CO2ER process, thereby achieving efficient and stable CO2ER applications.

[0006] This invention is implemented as follows: In a first aspect, the present invention provides a polypyrrole-coated bismuth core-shell nanowire with a cavity, the nanowire comprising a metallic bismuth core and a polypyrrole coating layer covering the surface of the metallic bismuth core, wherein a cavity exists between the core and the shell.

[0007] In an optional embodiment, the diameter of the bismuth core is 10-30 nm, the thickness of the polypyrrole coating is 5-30 nm, and the radial thickness of the cavity is 5-20 nm.

[0008] Secondly, the present invention provides a method for preparing bismuth core-shell nanowires with cavities coated with polypyrrole, comprising the following steps: Bismuth nitrate pentahydrate was mixed evenly with N,N-dimethylformamide, and after solvothermal reaction, it was separated, washed and dried to obtain bismuth oxy formate nanowires. The bismuth oxyformate nanowires were added to a mixed solution of pyrrole and potassium persulfate, and after an oxidative polymerization reaction, polypyrrole-coated bismuth oxyformate core-shell nanowires were obtained. The polypyrrole-coated bismuth oxyformate core-shell nanowires were used as electrode materials and electrochemically activated at the CO2 electroreduction reaction potential to obtain the core-shell structured electrode material with cavities.

[0009] In an optional embodiment, the ratio of bismuth nitrate pentahydrate to N,N-dimethylformamide is 1 g:(10 - 200) mL.

[0010] In an optional embodiment, the solvothermal reaction temperature is 100-180°C and the reaction time is 12-48 h.

[0011] In an optional embodiment, the ratio of pyrrole, potassium persulfate and bismuth oxyformate nanowires is 33.5 mg: 5.4 mg: (10-100) mg.

[0012] In an optional embodiment, the oxidative polymerization reaction includes the following steps: adding the bismuth oxyformate nanowires to the mixed solution of pyrrole and potassium persulfate, shaking vigorously for 5-10 minutes, and then letting it stand for 2-3 hours.

[0013] In an optional embodiment, the CO2 electroreduction includes applying a reduction potential to the polypyrrole-coated bismuth-based core-shell nanowires in a CO2-saturated potassium bicarbonate solution.

[0014] In an optional embodiment, the reduction potential relative to the reversible hydrogen electrode is greater than 0.5V and the duration is greater than 1h.

[0015] Thirdly, the present invention provides an application of cavitary polypyrrole-coated bismuth core-shell nanowires in CO2 electroreduction.

[0016] The present invention has the following beneficial effects: This invention first prepares bismuth oxyformate nanowires via a solvothermal method, and then coats their surface with a layer of polypyrrole. In a CO2 electroreduction reaction, these polypyrrole-coated bismuth oxyformate nanowires are reduced under the influence of a reduction potential to form polypyrrole-coated bismuth nanowires. During this process, the polypyrrole shell effectively restricts catalyst reconstruction, maintaining the one-dimensional nanowire morphology of the catalyst. In the CO2 electroreduction reaction, the bismuth oxyformate core is reduced to metallic bismuth, and elements such as carbon, hydrogen, and oxygen are lost, causing the nanowire volume to shrink, thus forming a cavity within the core-shell structure. This ingenious catalyst design effectively avoids the morphology evolution problem caused by catalyst reconstruction in CO2ERs. Simultaneously, the presence of the core-shell structure and the cavity effectively solves the mass transfer problem in the catalytic reaction, thereby achieving efficient and stable CO2ER applications. Compared with materials without polypyrrole coating, its current density is significantly increased. 0.6 to Over a wide potential range of 1.1 V (relative to the reversible hydrogen electrode), the formic acid faradaic efficiency consistently remains above 90%. Furthermore, in continuous testing exceeding 350 hours, the formic acid faradaic efficiency still maintains above 80%, demonstrating exceptional stability and potential for large-scale industrial applications. Attached Figure Description

[0017] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0018] Figure 1 A comparison of the CO2ER performance curves of the polypyrrole-coated bismuth formate nanowires prepared in Example 1 and the bismuth formate nanowires prepared in Comparative Example 1. Figure 2Comparison of CO2ER formate Faraday efficiency between polypyrrole-coated bismuth formate nanowires prepared in Example 1 and bismuth formate nanowires prepared in Comparative Example 1. Figure 3 CO2ER stability data for the polypyrrole-coated bismuth oxyformate nanowires prepared in Example 1; Figure 4 Comparison of X-ray diffraction patterns of polypyrrole-coated bismuth formate nanowires prepared in Example 1 and those prepared in Comparative Example 1 before and after CO2ER: Figure 5 Comparison of scanning electron microscope images of polypyrrole-coated bismuth oxyformate nanowires prepared in Example 1 before and after CO2ER; Figure 6 Comparison of scanning electron microscope images of bismuth oxy formate nanowires prepared in Comparative Example 1 before and after CO2ER. Figure 7 Comparison of transmission electron microscopy images of polypyrrole-coated bismuth oxyformate nanowires prepared in Example 1 before and after CO2ER; Figure 8 The contact angles of the polypyrrole-coated bismuth formate nanowires prepared in Example 1 and the bismuth formate nanowires prepared in Comparative Example 1 are compared after CO2ER reconstruction. Figure 9 The in-situ Raman data of the polypyrrole-coated bismuth formate nanowires prepared in Example 1 and the bismuth formate nanowires prepared in Comparative Example 1 are compared after reconstruction by CO2ER. Detailed Implementation

[0019] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0020] The following provides a detailed description of a cavity-coated bismuth core-shell nanowire, its preparation method, and its applications.

[0021] In a first aspect, the present invention provides a polypyrrole-coated bismuth core-shell nanowire with a cavity, the nanowire comprising a metallic bismuth core and a polypyrrole coating layer covering the surface of the metallic bismuth core, wherein a cavity exists between the core and the shell.

[0022] The inventors discovered that in the CO2 electroreduction reaction, the core of bismuth oxyformate nanowires is reduced to metallic bismuth, resulting in the loss of elements such as carbon, hydrogen, and oxygen, causing the nanowire volume to shrink. At this point, the polypyrrole coating on the core surface effectively restricts catalyst reconstruction, thus maintaining the one-dimensional nanowire morphology of the material, and forming a cavity between the core and shell. Combining the hydrophobic and gas-philic properties of the polypyrrole shell, this catalyst can effectively regulate the acidic microenvironment at the reaction interface, promoting proton transport. This ingenious catalyst design effectively avoids the morphology evolution problem caused by catalyst reconstruction in CO2ERs, while the core-shell structure and cavity effectively solve the mass transfer problem in the catalytic reaction, thereby achieving efficient and stable CO2ER applications.

[0023] In an optional embodiment, the diameter of the bismuth core is 10-30 nm, the thickness of the polypyrrole coating is 5-30 nm, and the radial thickness of the cavity is 5-20 nm.

[0024] It should be noted that radial thickness refers to the distance from the outer surface of the bismuth core to the inner surface of the polypyrrole layer.

[0025] Secondly, the present invention provides a method for preparing bismuth core-shell nanowires with cavities coated with polypyrrole, comprising the following steps: S1. Preparation of bismuth oxyformate nanowires: Bismuth nitrate pentahydrate and N,N-dimethylformamide were mixed evenly, and after solvothermal reaction, they were separated, washed and dried to obtain bismuth oxyformate nanowires.

[0026] The ratio of bismuth nitrate pentahydrate to N,N-dimethylformamide is 1 g:(10-200) mL, and the mixing of bismuth nitrate pentahydrate and N,N-dimethylformamide is performed by ultrasonic mixing, wherein the ultrasonic mixing temperature is 20-35℃, the frequency is 100-400W, and the time is 10-60 minutes.

[0027] In an optional embodiment, the solvothermal reaction temperature is 100-180°C and the reaction time is 12-48 h.

[0028] S2. The bismuth oxyformate nanowires are added to a mixed solution of pyrrole and potassium persulfate. After oxidative polymerization, polypyrrole-coated bismuth oxyformate core-shell nanowires are obtained.

[0029] The ratio of pyrrole, potassium persulfate and bismuth oxyformate nanowires is 33.5 mg: 5.4 mg: (10-100) mg.

[0030] In an optional embodiment, the oxidative polymerization reaction includes the following steps: adding the bismuth oxyformate nanowires to the mixed solution of pyrrole and potassium persulfate, shaking vigorously for 5-10 minutes, and then letting it stand for 2-3 hours.

[0031] S3. Using the polypyrrole-coated bismuth oxyformate core-shell nanowires as electrode materials, electrochemical activation is performed at the CO2 electroreduction reaction potential to obtain the core-shell structured electrode material with cavities.

[0032] In an optional embodiment, the CO2 electroreduction includes: applying a reduction potential to the polypyrrole-coated bismuth-based core-shell nanowires in a CO2-saturated potassium bicarbonate solution, preferably, the concentration of the potassium bicarbonate solution is 0.5 mol / L.

[0033] In an optional embodiment, the reduction potential relative to the reversible hydrogen electrode is greater than 0.5V and the duration is greater than 1h.

[0034] It should be noted that all potentials in this application are relative to the reversible hydrogen electrode.

[0035] Thirdly, the present invention provides an application of cavitary polypyrrole-coated bismuth core-shell nanowires in CO2 electroreduction.

[0036] The features and performance of the present invention will be further described in detail below with reference to embodiments.

[0037] Example 1 This embodiment provides a method for preparing bismuth core-shell nanowires with cavities coated with polypyrrole, which includes the following steps: S1. Preparation of bismuth oxyformate nanowires: 1 g of bismuth nitrate pentahydrate was dissolved in 70 mL of N,N-dimethylformamide and ultrasonically dispersed. The mixture was then placed in a reaction vessel and solvated at 120°C for 24 h. The sample was then centrifuged at 8000 rpm and washed with ethanol. This centrifugation and washing process was repeated three times. Finally, the sample was dried in a 60°C oven to obtain bismuth oxyformate nanowires. S2. Preparation of polypyrrole-coated bismuth oxyformate nanowires: 25 mg of bismuth oxyformate nanowires were added to 10 mL of a mixed solution containing 33.5 mg of pyrrole and 5.4 mg of potassium persulfate. After shaking vigorously for 5 minutes, the solution was allowed to stand for 2 hours to obtain polypyrrole-coated bismuth oxyformate core-shell nanowires. S3. Preparation of cavitary polypyrrole-coated bismuth core-shell nanowires: Polypyrrole-coated bismuth formate core-shell nanowires were directly applied to a CO2 ER. The catalyst powder was adhered to carbon paper as a working electrode using a 5wt% perfluorosulfonic acid solution. A voltage greater than 0.5 V was applied in a CO2-saturated 0.5 mol / L potassium bicarbonate electrolyte for 1 h to obtain cavitary polypyrrole-coated bismuth core-shell nanowires.

[0038] Comparative Example 1 This comparative example provides a method for preparing bismuth oxyformate nanowires, including the following steps: 1 g of bismuth nitrate pentahydrate was dissolved in 70 mL of N,N-dimethylformamide and ultrasonically dispersed. The mixture was then placed in a reaction vessel and solvated at 120 °C for 24 h. The sample was then centrifuged at 8000 rpm and washed with ethanol. The centrifugation and washing process was repeated three times. Finally, the sample was dried in a 60 °C oven to obtain bismuth oxyformate nanowires.

[0039] Experimental Example 1 The hollow polypyrrole-coated bismuth core-shell nanowires prepared in Example 1 and the bismuth oxyformate nanowires prepared in Comparative Example 1 were characterized and tested.

[0040] (1) Characterization of CO2 electroreduction performance and stability: The nanowires of Example 1 and Comparative Example 1 were subjected to CO2ER catalytic reaction, and the results are as follows: Figure 1 , 2 As shown in Figure 3.

[0041] according to Figure 1 The results show that, at the same potential, the polypyrrole-coated bismuth oxyformate nanowires prepared in Example 1 have a higher current density, demonstrating that their CO2ER activity is significantly higher than that of the catalyst prepared in Comparative Example 1. Figure 2 The results show that the polypyrrole-coated bismuth oxyformate nanowires prepared in Example 1 exhibit significantly higher formic acid conversion Faradaic efficiency. 0.6 to Within a potential range of 1.1 V, its formic acid conversion Faradaic efficiency is higher than 90% (91.9%, 92.7%, 97.9%, 94.6%, 94.8%, 90.6%), demonstrating its excellent CO2ER selectivity. According to Figure 3 The results show that the nanowires of Example 1 exhibited almost constant current density during continuous CO2ER catalytic reactions lasting more than 350 h, and the formic acid conversion Faraday efficiency remained above 80%, demonstrating their excellent CO2ER catalytic stability.

[0042] (2) Characterization of catalyst morphology and structure before and after CO2ER: The nanowires of Example 1 and Comparative Example 1 were subjected to X-ray diffraction patterns, scanning electron microscopy, and transmission electron microscopy before and after CO2ER, respectively. The results are as follows: Figure 4-7 As shown.

[0043] according to Figure 4 The results show that, Figure 4 a represents the crystal structure of the pre-catalyst for CO2ER. It can be seen that both correspond well to the standard card of bismuth oxyformate (card number: 35-0939), proving that the coating of polypyrrole does not affect the crystal structure of bismuth oxyformate nanowires. Figure 4 b shows the crystal structure of the catalyst after CO2ER. It can be seen that after CO2ER, the crystal structures of both catalysts match well with the standard card of metallic bismuth (card number: 85-1329), proving that both catalysts are reconstituted into metallic bismuth in situ after CO2ER reaction.

[0044] according to Figure 5 and 6 The results show that, before CO2ER, the polypyrrole-coated bismuth oxyformate nanowires prepared in Example 1 exhibited a distinct one-dimensional nanowire morphology. Figure 5 a), and this one-dimensional nanowire morphology can be preserved after CO2ER ( Figure 5 b). However, for the bismuth oxyformate nanowires prepared in Comparative Example 1, due to the lack of a polypyrrole coating layer, their initially obvious one-dimensional nanowire morphology ( Figure 6 a) After being processed by CO2ER, it is completely transformed into a two-dimensional nanosheet structure. Figure 6 (b) Such morphological changes can easily lead to a decrease in catalyst performance and make it difficult to determine the true active sites of the catalyst. Therefore, the polypyrrole-coated bismuth formate nanowires with a core-shell structure prepared in Example 1 can effectively avoid morphological evolution of the catalyst in CO2ER under the protection of the polypyrrole shell, maintain the high performance of the active sites, and make the catalyst have high activity and high stability.

[0045] according to Figure 7 The results show that, from Figure 7 As shown in Figure a, the approximately 20 nm diameter bismuth oxyformate nanowires are clearly coated with a layer of polypyrrole, with the bismuth oxyformate core tightly connected to the pyrrole shell. The polypyrrole shell layer is approximately 12 nm thick. After CO2ER reconstruction, the polypyrrole shell layer remains unchanged, while the bismuth oxyformate core is reduced to metallic bismuth. The loss of carbon, hydrogen, and oxygen elements within the core causes the nanowire to shrink, forming a cavity within the core-shell structure. The radial thickness of this cavity is approximately 8 nm. This cavity structure effectively promotes mass transport during the reaction process, providing favorable conditions for the efficient execution of CO2ER.

[0046] (3) Characterization of mass transport properties: Contact angle tests were conducted on the nanowires prepared in Example 1 and Comparative Example 1. The results are shown in the figure. Figure 8 and Figure 9 .

[0047] according to Figure 8 and Figure 9 The results show that, after CO2ER, the catalyst prepared in Example 1 exhibits significant hydrophobicity. Figure 8 a), while the catalyst prepared in Comparative Example 1 exhibits significant hydrophilicity ( Figure 8 (b) This difference stems from the excellent hydrophobic properties of the polypyrrole shell. CO2, as a nonpolar molecule, has extremely low solubility in aqueous electrolytes, leading to severe mass transfer limitations. The hydrophobic and gas-loving polypyrrole shell, however, can efficiently capture CO2 molecules, accelerating the CO2ER reaction kinetics. Furthermore, in-situ Raman data show that as the reaction potential increases, the surface CO3 on the catalyst prepared in Example 1 increases. 2 Gradually decrease, HCO 3 Gradually increasing ( Figure 9 a) indicates that it can regulate an acidic microenvironment, promote efficient proton transport, and further facilitate CO2ER. The catalyst prepared in Comparative Example 1, however, does not possess this characteristic; its catalyst surface shows CO3... 2 and HCO 3 The content does not change with increasing reaction potential. Figure 9 b). These data indicate that the cavity-coated polypyrrole core-shell nanowires prepared in Example 1 can significantly improve mass transport in the CO2ER process, thereby enabling the catalyst to have a higher current density and higher reactivity.

[0048] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A cavitary polypyrrole-coated bismuth core-shell nanowire, characterized in that, The nanowire comprises a bismuth core and a polypyrrole coating layer covering the surface of the bismuth core, wherein there is a cavity between the core and the shell.

2. The cavitary polypyrrole-coated bismuth core-shell nanowire according to claim 1, characterized in that, The diameter of the bismuth core is 10-30 nm, the thickness of the polypyrrole coating is 5-30 nm, and the radial thickness of the cavity is 5-20 nm.

3. A method for preparing cavitary polypyrrole-coated bismuth core-shell nanowires as described in claim 1 or 2, characterized in that, Includes the following steps: Bismuth nitrate pentahydrate was mixed evenly with N,N-dimethylformamide, and after solvothermal reaction, it was separated, washed and dried to obtain bismuth oxy formate nanowires. The bismuth oxyformate nanowires were added to a mixed solution of pyrrole and potassium persulfate, and after an oxidative polymerization reaction, polypyrrole-coated bismuth oxyformate core-shell nanowires were obtained. The polypyrrole-coated bismuth oxyformate core-shell nanowires were used as electrode materials and electrochemically activated at the CO2 electroreduction reaction potential to obtain the core-shell structured electrode material with cavities.

4. The method for preparing a cavity-coated bismuth core-shell nanowire of polypyrrole according to claim 3, characterized in that, The ratio of the amount of bismuth nitrate pentahydrate to the amount of N,N-dimethylformamide is 1 g:(10-200) mL.

5. The method for preparing a cavity-coated bismuth core-shell nanowire of polypyrrole according to claim 3, characterized in that, The solvothermal reaction temperature is 100-180℃, and the reaction time is 12-48 h.

6. The method for preparing a cavity-coated bismuth core-shell nanowire of polypyrrole according to claim 3, characterized in that, The ratio of pyrrole, potassium persulfate and bismuth oxyformate nanowires is 33.5 mg: 5.4 mg: (10-100) mg.

7. The method for preparing a cavity-coated bismuth core-shell nanowire of polypyrrole according to claim 3, characterized in that, The oxidative polymerization reaction includes the following steps: adding the bismuth oxyformate nanowires to the mixed solution of pyrrole and potassium persulfate, shaking vigorously for 5-10 minutes, and then letting it stand for 2-3 hours.

8. The method for preparing a cavity-coated bismuth core-shell nanowire of polypyrrole according to claim 3, characterized in that, The CO2 electroreduction includes applying a reduction potential to the polypyrrole-coated bismuth-based core-shell nanowires in a CO2-saturated potassium bicarbonate solution.

9. The method for preparing a cavity-coated bismuth core-shell nanowire of polypyrrole according to claim 8, characterized in that, The reduction potential relative to the reversible hydrogen electrode is greater than 0.5V and lasts for more than 1 hour.

10. The application of a cavity-coated bismuth core-shell nanowire as described in claim 1 in CO2 electroreduction.

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