Multi-cavity carbon nanorod packaged bismuth oxide catalyst as well as preparation method and application thereof

Abstract

The invention discloses a multi-cavity carbon nanorod packaged bismuth oxide catalyst as well as a preparation method and application thereof, and belongs to the technical field of catalyst preparation. The preparation method comprises the following steps: constructing a composite micelle containing metal ions by using a dual-surfactant P123 and sodium oleate, co-assembling the composite micelle with a melamine oligomer generated based on a Schiff base reaction, and carbonizing and reducing to obtain the nitrogen-doped carbon nanorod loaded bismuth oxide nanoparticle catalyst with a chamber structure. The prepared catalyst has excellent catalytic performance and stability when applied to preparation of formic acid through reduction of carbon dioxide under electro-catalysis, the highest Faraday efficiency of formic acid under the potential of-1.3 V vs.RHE is 96%, and the partial current density of formic acid can reach 34.8 mA cm <-2 >. In the catalysis process of 42 h, the Faraday efficiency of formic acid can be kept at 86% or above, and the method has good application prospects.

Description

Technical Field

[0001] The present invention belongs to the field of catalysts, and specifically relates to a method for preparing a multi-chamber carbon nanorod-encapsulated bismuth oxide catalyst, and its application in the electrocatalytic reduction of carbon dioxide (CO2) to produce formic acid. Background Art

[0002] In recent years, global climate change has become increasingly severe. Greenhouse gas emissions, primarily carbon dioxide (CO2), have led to crises such as frequent extreme weather events, ecosystem degradation, and sea level rise, forcing humanity to accelerate its search for low-carbon transition pathways. While the proliferation of renewable energy and the development of carbon capture and storage (CCS) technologies offer some solutions for emissions reduction, they still face bottlenecks such as high costs, significant storage risks, and resource waste. Against this backdrop, carbon dioxide electrochemical reduction (CO2RR) technology, with its ability to convert CO2 into high-value-added fuels and chemicals (such as ethylene, formic acid, and ethanol) while simultaneously coupling with renewable energy to achieve a "negative carbon cycle," has become a cutting-edge approach to addressing the dual challenges of environmental and energy conservation.

[0003] Electrocatalytic CO₂RR (electrocatalytic CO₂RR) holds a central position among numerous CO₂ conversion technologies due to its mild reaction conditions, tunable product selectivity, and inherent compatibility with green power systems. This technology utilizes electrocatalysts to drive the targeted activation and reconfiguration of CO₂ molecules, converting intermittent wind and solar energy into chemical energy for storage. This not only alleviates the challenges of renewable energy consumption but also provides the chemical industry with a carbon source to replace fossil feedstocks, potentially reshaping the "carbon circular economy" industry chain. However, the large-scale application of CO₂RR remains constrained by two key challenges: the development of efficient catalysts and the optimization of reactor systems. At the catalytic level, current research focuses on enhancing the intrinsic activity and selectivity of active sites. Copper-based materials, due to their unique CC coupling capabilities, are a preferred choice for the synthesis of multi-carbon products, but they face challenges such as high overpotentials and poor stability. Single-atom catalysts (SACs) and alloy materials have achieved breakthroughs in improving CO₂ selectivity by precisely manipulating their electronic structures. Molecular catalysts, through biomimetic design, mimic the efficient conversion mechanisms of enzymes. Despite this, issues such as competitive adsorption of intermediates and catalyst surface reconfiguration in complex reaction pathways still require in-depth atomic-level mechanistic insights. Reactor design must balance mass transfer efficiency, product separation, and scalability costs. Traditional H-type electrolyzers are limited by the low solubility of CO2. While newer configurations, such as flow cells and membrane electrode assemblies (MEAs), significantly increase current density through the supply of gaseous CO2, membrane interface corrosion, three-phase interface regulation, and system integration remain bottlenecks in engineering applications.

[0004] In the field of CO2RR, precious metal-based electrocatalysts (such as gold (Au), palladium (Pd), and silver (Ag)) have been widely studied. For example, gold and silver catalysts exhibit excellent catalytic performance in converting CO2 to carbon monoxide. However, the high cost of precious metals limits their promotion in practical applications. In contrast, bismuth (Bi)-based catalysts have gradually become a hot topic in CO2RR research due to their advantages such as low price, good stability, and low toxicity. However, nanometal particles are prone to aggregation and deformation at high temperatures, resulting in a decrease in catalytic efficiency, especially during long-term operation, where electrochemical stability is significantly reduced. Therefore, how to prepare bismuth-based catalysts with good dispersion and small particle size has become a difficult problem in current research.

[0005] The stability of CO2RR electrocatalysts is one of the core challenges that limit their large-scale application. Nanoparticles of metal-based catalysts (such as Cu, Ag, Bi, etc.) tend to agglomerate under high potential or long-term operation. For example, copper-based catalysts may increase particle size and reduce active surface area due to surface atomic migration in a reducing environment, resulting in a significant decrease in catalytic activity. Some catalysts may undergo crystal phase changes during the reaction. For example, bismuth oxide (Bi2O3) may be partially reduced to metallic bismuth (Bi 0 ), leading to structural destruction of active sites. Carbon-based supports (such as carbon nanotubes and graphene) are susceptible to oxidation or corrosion at high potentials or in acidic or alkaline electrolytes, causing catalyst shedding or support structural collapse. Reaction intermediates (such as CO and formate) are excessively adsorbed on the catalyst surface, forming a passivation layer that covers the active sites. For example, strong CO adsorption on the Cu catalyst surface hinders further CO2 reduction. Overcoming this bottleneck requires precise catalyst design.

[0006] Research has shown that support materials play a crucial role in improving catalyst performance. Supports not only provide a large surface area for the CO2RR active components but also effectively inhibit their aggregation, thereby improving catalyst stability. Catalyst performance can be further optimized by manipulating the morphology and chemical properties of the support material. Currently, the preparation of supported metal catalysts primarily relies on post-treatment methods, such as pre-loading metal particles onto the support via impregnation. However, catalysts prepared using post-treatment methods are prone to losing the metal active components during the catalytic process, resulting in decreased stability. In recent years, some studies have reported the preparation of highly efficient bismuth-based catalysts using in situ methods. Compared with post-treatment methods, in situ methods can fix the metal on the support, reducing the loss of metal active components during the catalytic process and thus improving catalyst stability. However, in situ methods require precise design of the catalyst structure, and reports on simple in situ catalyst preparation are limited, thus further research is needed. Summary of the Invention

[0007] The present invention aims to provide a metal-modified surfactant as a soft template for preparing a nitrogen-doped carbon-supported bismuth oxide catalyst with a cavity structure by in situ self-assembly. By encapsulating and confining the metal particles in the chamber, the metal particles are prevented from agglomerating and the intrinsic stability of the catalyst is improved.

[0008] To achieve the above objectives, the present invention provides a nitrogen-doped carbon-supported bismuth oxide catalyst with a cavity structure, comprising a nitrogen-doped carbon rod as a carrier and bismuth oxide nanoparticles active centers supported therein.

[0009] Preferably, the nitrogen-doped carbon-supported bismuth oxide catalyst is a carbon rod with a diameter of 2-5 μm and a cavity structure; the particle size of the bismuth oxide nanoparticles in the active center of the gold nanocluster is 5-30 nm; and the bismuth element content is 10-35 wt%.

[0010] The present invention provides a preparation method of a nitrogen-doped carbon-supported metal catalyst with a cavity structure. The method comprises the following steps: using metal-modified P123 as a template, reacting with formaldehyde and 3,5-diaminobenzoic acid to generate an imine through a Schiff base reaction, and subsequently cross-linking with nitrogen source melamine to generate a melamine oligomer to obtain a polymer precursor, and then carbonizing and reducing the polymer to obtain a nitrogen-doped carbon-supported bismuth oxide catalyst.

[0011] A multi-cavity carbon nanorod-encapsulated bismuth oxide catalyst comprises a nitrogen-doped carbon rod carrier and internally loaded bismuth oxide nanoparticle active centers. The catalyst is a carbon nanorod with a diameter of 2-5 μm and a cavity structure; the bismuth oxide nanoparticles have a particle size of 5-30 nm; and the bismuth content in the catalyst is 10-35 wt%.

[0012] Furthermore, the nitrogen-doped carbon rods were prepared by the following method: (a) forming a composite micelle template using P123 and sodium oleate as dual surfactants; (b) cross-linking formaldehyde, 3,5-diaminobenzoic acid and melamine through a Schiff base reaction to generate melamine oligomers, which were co-assembled with the composite micelle template to form a polymer precursor; (c) carbonizing the polymer precursor in an inert atmosphere and then calcining it in a reducing atmosphere to obtain a nitrogen-doped carbon rod support.

[0013] Further, the following steps are included: S1, dissolving P123 and sodium oleate in deionized water, stirring to form a composite micelle solution, and then adding bismuth nitrate pentahydrate and nitric acid to obtain a composite micelle solution containing bismuth ions; S2, dissolving melamine and 3,5-diaminobenzoic acid in deionized water to obtain a mixed solution; S3, mixing the solutions of step S1 and S2, adding formaldehyde solution to carry out Schiff base reaction to generate a polymer precursor; S4. The polymer precursor is centrifuged, washed, dried, and then ground, and then subjected to carbonization and reduction treatments in a tube furnace in sequence to obtain the catalyst.

[0014] Furthermore, in step S1: the mass ratio of P123 to sodium oleate is (2-5):1; the molar ratio of bismuth nitrate pentahydrate to melamine is 1:(4-8); and the molar ratio of nitric acid to melamine is (2-3):1.

[0015] Furthermore, the temperature of the Schiff base reaction in step S3 is 20-40 °C, and the reaction time is 1-3 h.

[0016] Furthermore, in step S4: the carbonization temperature is 500-700 ° C, and the time is 2-4 h; the reduction treatment is carried out in a hydrogen atmosphere at a temperature of 300-400 ° C, and the time is 3-5 h.

[0017] Application of multi-compartment carbon nanorods encapsulated bismuth oxide catalyst in electrocatalytic carbon dioxide reduction to formic acid.

[0018] Further, the following steps are included: (a) loading the catalyst onto carbon paper as a working electrode; (b) CO2 was introduced into an H-type electrolytic cell, 0.5 M KHCO3 was used as the electrolyte, and a potential of -0.8 V to -1.3 V (vs. RHE) was applied for constant potential electrolysis.

[0019] Furthermore, the catalyst loading is 1 mg cm -2 .

[0020] Furthermore, the catalyst was subjected to constant potential electrolysis at -1.3 V vs. RHE.

[0021] Preferably, the method for preparing the catalyst comprises the following steps: S1, 0.06 g P123 (PEO 20 -PPO 70 -PEO 20 ) and 0.02 g sodium oleate (SO) were dissolved in 20 mL of deionized water and stirred at 500 rpm at 30 °C. Subsequently, 0.485 g of bismuth nitrate pentahydrate and 1 mL of 65% nitric acid were added to obtain a composite micelle solution. S2, adding 0.485 g Bi(NO3)3·5H2O to the composite micelle solution and stirring for 3 h to obtain a composite micelle solution containing metal ions; S3. Dissolve 0.63 g of melamine and 0.152 g of 3,5-diaminobenzoic acid in 49 mL of deionized water to obtain solution B. S4. Mix solutions A and B and stir for 1 h, add 8 mL of formaldehyde solution, and react for 2 h; S5. The reaction solution was centrifuged, washed twice with ethanol, washed once with water and dried to obtain a polymer powder. The polymer powder was then ground and carbonized and reduced in a tube furnace at 500°C.

[0022] Preferably, the molar ratio of each substance is bismuth nitrate pentahydrate: melamine = 1:5; 3,5-aminobenzoic acid: melamine = 1:5; nitric acid: melamine = 14.4:5.

[0023] Preferably, the washing method in step S2 comprises washing with ethanol and deionized water until neutral; the centrifugation condition is 9000-10000 rpm and carried out at room temperature.

[0024] Preferably, the mass ratio of P123 to sodium oleate is 3:1.

[0025] Preferably, the loading amount of bismuth element is 19.6%.

[0026] The present invention provides a nitrogen-doped carbon-supported bismuth oxide nanoparticle catalyst for the following applications: A1. Used for electrocatalytic reduction of carbon dioxide to produce formic acid; Preferably, 4 mg of catalyst powder was weighed and dissolved in 20 μL of Nafion solution and 780 μL of isopropanol. Ultrasonication was performed for 30 min to obtain catalyst ink. 100 μL of catalyst ink was evenly dispersed in a 1 cm -2 The gas diffusion electrode was used as the working electrode with a loading of 1 mg cm -2 , carbon paper as the working electrode, platinum mesh electrode as the counter electrode, and Ag / AgCl reference electrode as the reference electrode. The electrochemical test was carried out in an H-type electrolytic cell containing 60 mL of 0.5M KHCO3 electrolyte. First, high-purity CO2 was passed into the cathode chamber at a rate of 30 sccm for 30 min, and then electrochemical impedance spectroscopy, linear sweep voltammetry, and constant potential electrolysis tests were performed. After the electrolysis was completed, the gas products were analyzed by gas chromatography. Take 100 μL of 100 ppm DMSO solution, use heavy water as the internal standard solution, and mix it with 500 μL of cathode electrolyte. The concentration of HCOO- was analyzed by nuclear magnetic resonance spectroscopy instrument, and the specific content was calculated using the HCOOH standard curve.

[0027] Compared with the prior art, the present invention has the following beneficial effects: The present invention utilizes spherical micelles formed by P123 and SO as pore-forming agents, and modifies bismuth ions onto the micelles. Subsequently, they are co-assembled with melamine oligomers generated by a Schiff base reaction. A nitrogen-doped carbon-supported bismuth oxide nanoparticle catalyst is obtained by carbonization reduction. P123 and sodium oleate not only serve as pore-forming agents but also act as metal ion stabilizers. After carbonization, a catalyst with a cavity structure is formed. Thanks to the restriction of the cavity structure on the bismuth oxide nanoparticles, the catalyst will not be deactivated during long-term use. The present invention directly loads the metal particles onto the carrier through an in-situ method, which greatly improves its stability compared to the existing impregnation method for loading metals.

[0028] The nitrogen-doped carbon-supported bismuth oxide nanoparticle catalyst Bi / N@C prepared by the present invention situ -500 has excellent catalytic performance and stability in H-type electrolytic cells. It can be tested for a long time without deactivation. In the electrocatalytic carbon dioxide reduction reaction to formic acid, the catalyst loading is 1 mg cm -2 In a three-electrode H-type electrolytic cell, the partial current density of formic acid can reach up to 34.8 mA cm -2 The maximum Faradaic efficiency of formic acid is 96%, and the selectivity of formic acid can be maintained above 86% after 42 hours of continuous operation.

[0029] The synthesis method of the present invention is simple, and the dispersion of the loaded bismuth oxide nanoparticles is extremely high. The loss rate of loaded bismuth in the catalyst sample is extremely low, with a loading rate of 19%. It has excellent catalytic performance in the application of electrocatalytic carbon dioxide reduction to formic acid and has good industrial prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 TEM images of catalysts prepared in Examples 1-2, 4-5, and 8-10 of the present invention; Figure 2 This is the SEM energy spectrum of the catalyst prepared in Example 1-2 of the present invention; Figure 3 The nitrogen adsorption-desorption curve, XRD pattern, Raman spectrum, and XPS pattern of the catalyst prepared in Example 1-2 of the present invention are shown; Figure 4 The present invention prepared catalyst performance diagrams for Examples 1-3, including LSV curves, FE distribution, partial current density, Tafel slope, and electrochemical impedance; Figure 5 The present invention is a stability test of the catalyst prepared in Example 1-2; DETAILED DESCRIPTION

[0031] The present invention will be further described below with reference to specific examples, but the present invention is not limited thereto in any way. Example 1

[0032] 0.06 g P123 (PEO 20 -PPO 70 -PEO 20 ) and 0.02 g sodium oleate (SO) were dissolved in 19 mL deionized water and stirred at 500 rpm at 30 ° C. Subsequently, 0.485 g bismuth nitrate pentahydrate and 1 mL 65% nitric acid were added and stirred for 3 h to obtain solution A. 0.63 g melamine and 0.152 g 3,5-diaminobenzoic acid were dissolved in 49 mL deionized water to obtain solution B. Solutions A and B were mixed and stirred for 1 h, 8 mL formaldehyde solution was added, and the reaction was carried out for 2 h. After the reaction was completed, the solid product was separated by centrifugation at 10,000 rpm at room temperature, and the solid product was repeatedly washed with deionized water and anhydrous ethanol until neutral, and then dried in an oven at 80 ° C overnight to obtain a rod-shaped polymer precursor. .Will Carbonization at 500 °C in a nitrogen atmosphere and then reduction at 350 °C in a hydrogen atmosphere for 4 h gave , collected for later use, and transmission electron microscopy showed that the size of bismuth oxide nanoparticles was 5-20 nm ( Figure 1 In a), the dispersion is very good. And the metal particles are loaded inside the chamber ( Figure 1 b) The appearance of the obtained catalyst is as follows Figure 2 As shown in a, it can be seen It is a rod-like structure, and SEM Mapping also shows that the catalyst is loaded inside the carrier ( Figure 2 In b), the actual loading of bismuth is 31.28%. XRD shows that the main component of the catalyst is bismuth oxide ( Figure 3 c), and there is a small amount of metallic bismuth, which can also be proved by XPS coexist( Figure 3 In middle f), Raman spectroscopy shows a high degree of defects ( Figure 3 (d) Nitrogen adsorption and desorption tests show that there are a large number of mesopores in the support ( Figure 3 In middle a), the main pore sizes are concentrated around 5 and 25 nm, and the specific surface area is 115 m 2 g -1 . Example 2

[0033] 0.06 g of P123 and 0.02 g of sodium oleate were dissolved in 19 mL of deionized water, and 1 mL of 65% nitric acid was added. The mixture was stirred at 30°C for 3 h to obtain Solution A. 0.63 g of melamine and 0.152 g of 3,5-diaminobenzoic acid were dissolved in 50 mL of deionized water to obtain Solution B. Solutions A and B were mixed and stirred for 1 h, and 8 mL of formaldehyde solution was added and reacted for 2 h. After the reaction, the solid product was separated by centrifugation at 10,000 rpm at room temperature. The solid product was repeatedly washed with deionized water and anhydrous ethanol until neutral, and then dried in an 80°C oven overnight to obtain a spherical polymer. This polymer was carbonized at 500°C under a nitrogen atmosphere to obtain N@C. 0.1 g of N@C was added to 40 mL of ethylene glycol and stirred for 30 min. 0.485 g of bismuth nitrate pentahydrate was added and stirred for 2 h, followed by the addition of 10 mL of 0.5 M NaBH₄ solution and stirring for 1 h. The solid product was separated by centrifugation at 10000 rpm at room temperature, and then washed repeatedly with deionized water and anhydrous ethanol until neutral to obtain Bi / N@C im , collected for later use. The obtained catalyst Bi / N@C im The appearance of Figure 2 As shown in c, it can be seen that Bi / N@C im It is an agglomerated block structure. SEM mapping shows that the metal particles are mainly loaded on the outside of the carrier ( Figure 2 d), XRD shows Bi / N@C im The main component is elemental bismuth ( Figure 3 In the middle (c), it can be seen from the transmission electron microscope that Bi / N@C im The metal particle size is above 30 nm ( Figure 1 In Figure c), the actual bismuth loading is 29.58%. Raman spectroscopy shows a low degree of defects ( Figure 3 (d) Nitrogen adsorption and desorption tests show that there are a small amount of mesopores in the support ( Figure 3 In middle a), the main pore size is concentrated around 5 nm, and the specific surface area is 28 m 2 g -1 . Example 3

[0034] In a fume hood, dissolve 1g of Bi(NO₃)₃·5H₂O in 10mL of dilute nitric acid and stir until a clear solution is obtained. Add PVP and continue stirring for 30 minutes. Transfer the solution to an evaporating dish and dry it in an 80°C oven for 24 hours to obtain a loose, yellow precursor powder. Grind the dried powder into a fine powder using a mortar and pestle. Place the precursor powder in a quartz boat with a thickness of no more than 5mm. Heat the mixture in a tube furnace, ventilating air, at a rate of 5°C / min to 500°C and hold for 3 hours. After calcination, cool the mixture naturally to room temperature, wash with ethanol to remove impurities, centrifuge, and dry at 60°C for 2 hours. Grind the mixture again to ensure uniform dispersion of the particles and collect them for later use. Example 4

[0035] 0.06 g P123 (PEO 20 -PPO 70 -PEO 20 ) and 0.02 g sodium oleate (SO) were dissolved in 19 mL deionized water and stirred at 500 rpm at 30 ° C. Subsequently, 0.485 g bismuth nitrate pentahydrate and 1 mL 65% nitric acid were added and stirred for 3 h to obtain solution A. 0.63 g melamine and 0.152 g 3,5-diaminobenzoic acid were dissolved in 49 mL deionized water to obtain solution B. Solutions A and B were mixed and stirred for 1 h, 8 mL formaldehyde solution was added, and the reaction was continued for 2 h. After the reaction was completed, the solid product was separated by centrifugation at 10000 rpm at room temperature, and the solid product was repeatedly washed with deionized water and anhydrous ethanol until neutral, and then dried in an 80 ° C oven overnight to obtain a rod-shaped polymer precursor Bi / N@C situ1 . Bi / N@C situ1 The Bi / N@C was carbonized at 600 °C in a nitrogen atmosphere and then reduced at 350 °C in a hydrogen atmosphere for 4 h to obtain situ1 -600, collected for later use. Transmission electron microscopy shows that the size of bismuth oxide nanoparticles is more than 30 nm ( Figure 1 (g), the dispersion is average, and the actual bismuth loading is 28.7%. Example 5

[0036] 0.06 g P123 (PEO 20 -PPO 70 -PEO 20) and 0.02 g sodium oleate (SO) were dissolved in 19 mL deionized water and stirred at 500 rpm at 30 ° C. Subsequently, 0.485 g bismuth nitrate pentahydrate and 1 mL 65% nitric acid were added and stirred for 3 h to obtain solution A. 0.63 g melamine and 0.152 g 3,5-diaminobenzoic acid were dissolved in 49 mL deionized water to obtain solution B. Solutions A and B were mixed and stirred for 1 h, 8 mL formaldehyde solution was added, and the reaction was continued for 2 h. After the reaction was completed, the solid product was separated by centrifugation at 10000 rpm at room temperature, and the solid product was repeatedly washed with deionized water and anhydrous ethanol until neutral, and then dried in an 80 ° C oven overnight to obtain a rod-shaped polymer precursor Bi / N@C situ1 . Bi / N@C situ1 Bi / N@C was obtained by carbonization at 700 °C in a nitrogen atmosphere and then reduction at 350 °C for 4 h in a hydrogen atmosphere. situ1 -700, collected for later use. Transmission electron microscopy shows that the size of bismuth oxide nanoparticles is above 100 nm and the dispersion is poor ( Figure 1 In h), the actual loading amount of bismuth is 19.6%. Example 6

[0037] 0.06 g P123 (PEO 20 -PPO 70 -PEO 20 ) and 0.02 g sodium oleate (SO) were dissolved in 19 mL deionized water and stirred at 500 rpm at 30 ° C. Subsequently, 0.726 g bismuth nitrate pentahydrate and 1 mL 65% nitric acid were added and stirred for 3 h to obtain solution A. 0.63 g melamine and 0.152 g 3,5-diaminobenzoic acid were dissolved in 49 mL deionized water to obtain solution B. Solutions A and B were mixed and stirred for 1 h, 8 mL formaldehyde solution was added, and the reaction was continued for 2 h. After the reaction was completed, the solid product was separated by centrifugation at 10000 rpm at room temperature, and the solid product was repeatedly washed with deionized water and anhydrous ethanol until neutral, and then dried in an 80 ° C oven overnight to obtain a rod-shaped polymer precursor Bi / N@C situ1.5 . Bi / N@C situ1.5 Carbonization at 500 °C in a nitrogen atmosphere and then reduction at 350 °C in a hydrogen atmosphere for 4 h gave Bi / N@C situ1 The actual bismuth loading was 34.56%. Example 7

[0038] 0.06 g P123 (PEO 20 -PPO 70 -PEO 20) and 0.02 g sodium oleate (SO) were dissolved in 19 mL deionized water and stirred at 500 rpm at 30 ° C. Subsequently, 0.97 g bismuth nitrate pentahydrate and 1 mL 65% nitric acid were added and stirred for 3 h to obtain solution A. 0.63 g melamine and 0.152 g 3,5-diaminobenzoic acid were dissolved in 49 mL deionized water to obtain solution B. Solutions A and B were mixed and stirred for 1 h, 8 mL formaldehyde solution was added, and the reaction was carried out for 2 h. After the reaction was completed, the solid product was separated by centrifugation at 10000 rpm at room temperature, and the solid product was repeatedly washed with deionized water and anhydrous ethanol until neutral, and then dried in an 80 ° C oven overnight to obtain a rod-shaped polymer precursor Bi / N@C situ2 . Bi / N@C situ2 Carbonization at 500 °C in a nitrogen atmosphere and then reduction at 350 °C in a hydrogen atmosphere for 4 h gave Bi / N@C situ2 The actual bismuth loading was 38.56%. Example 8

[0039] Without adding P123, the other experimental conditions were the same as those in Example 1 to synthesize nitrogen-doped carbon-supported bismuth oxide nanoparticle catalyst CN-1. From TEM, it can be seen that although the sample maintains a rod-like structure ( Figure 1 However, the expected cavity structure was not formed, and the bismuth nanoparticle size exceeded 50 nm. This phenomenon indicates that P123 plays two roles in the synthesis process: first, it constructs the spherical micelle template through hydrophobic interactions with oleic acid; second, it controls the size of the nanoparticles by stabilizing the metal ions. Example 9

[0040] Without adding sodium oleate, the other experimental conditions were the same as those in Example 1 to synthesize nitrogen-doped carbon-supported bismuth oxide nanoparticle catalyst CN-2. TEM results show that CN-2 exhibits a pure rod-like structure without metal ( Figure 1 This result further confirms the two key roles of SO in the material formation process: one is to participate in the formation of spherical micelles, and the other is to 3+ The coordination effect realizes the effective loading of metal ions. Example 10

[0041] Nitrogen-doped carbon-supported bismuth oxide nanoparticle catalyst CN-3 was synthesized without adding nitric acid and under the same experimental conditions as in Example 1. TEM showed that the sample did not form a similar situ1 Instead of hollow rod-like structures, mesoporous carbon nanospheres with dispersed metal particles were obtained, with particle sizes of approximately 10-20 nm ( Figure 1This result reveals the key role of nitric acid in regulating the polymer morphology. Example 11

[0042] The catalyst samples obtained in Example 1, Example 2, and Example 3 were subjected to electrocatalytic carbon dioxide reduction catalytic performance tests. The test results are shown in the figure. In a wide potential window (-0.8 V ~ -1.3 V vs. RHE), Bi / N@C situ1 -500 and Bi / N@C im The Faradaic efficiency of formic acid is over 90% (a, b, and c in Figure 4), showing excellent selectivity. situ1 The partial current density of formic acid at -1.3 V for -500 reached 34.8 mA cm -2 (e in Figure 4), this value is higher than that of Bi2O3 catalyst (14.9 mA cm -2 ) by 2.3 times. Comparative experiments show that the highest FE of the pure Bi2O3 catalyst is only 59% (Figure 4d), significantly lower than that of the nitrogen-doped supported catalyst. This data clearly demonstrates the synergistic effect of the nitrogen-doped carbon support and the confined structure. Nitrogen doping enhances the electronic conductivity of the support, while the unique cavity structure effectively suppresses metal particle agglomeration, significantly improving the catalyst's activity and stability.

[0043] Tafel curve analysis results ( Figure 4 f) shows that Bi / N@C situ1 The Tafel slope at -500 is 236 mV dec -1 , this value indicates that the rate-determining step (RDS) of the reaction is more likely to be related to the adsorption and activation process of CO2 molecules on the catalyst surface rather than the electron transfer process. This finding is consistent with the research results on bismuth-based catalysts in the existing literature, that is, the CO2 adsorption process is usually the kinetic bottleneck of the CO2 reduction reaction (CO2RR). Compared with other catalysts, Bi / N@C situ1 -500 exhibits a large Tafel slope, indicating that its reaction kinetics are relatively slow. Electrochemical impedance spectroscopy (EIS) analysis further evaluated the electron transfer ability of the catalyst. The Nyquist plot shows that Bi / N@C situ1 The charge transfer resistance (Rct) of -500 is 7.6 Ω, the lowest value among all bismuth-based catalysts (Figure 4g). This result confirms that the loading treatment can effectively reduce the resistance of the catalyst. The lower charge transfer resistance is conducive to promoting the adsorbed CO2 molecules to form key intermediates in the first electron transfer step. The electrochemical active surface area (ECSA) and active site density of the catalyst were evaluated by measuring the double layer capacitance (Cdl).situ1 -500、Bi / N@C im and Bi2O3 have Cdl values of 0.51, 0.67, and 0.58 mF cm, respectively. -2 (Fig. 4h), indicating that the three catalysts have similar electrochemical active areas.

[0044] To evaluate the long-term stability of the catalyst, a 42-h long-term test was conducted in an H-type electrolytic cell ( Figure 5 The results show that Bi / N@C situ1 -500 exhibits excellent stability, maintaining a Faradaic efficiency (FE) of 86.5% and a stable current density throughout the test period, which is superior to most carbon-supported catalysts reported so far. im After 12 hours of operation, the performance decreased significantly, and both the current density and FE decreased significantly ( Figure 5 The catalyst on the electrode was characterized by TEM and XRD. From TEM, it can be seen that although a certain degree of aggregation of metal particles was observed after long-term testing ( Figure 5 However, no significant leaching of metal species from the carbon nanorods was observed, which further confirmed the good confinement effect of the cavity structure. XRD analysis showed that the main phase of the metal species after the stability test was still Bi2O3 ( Figure 5 (d) Example 12

[0045] The catalyst samples obtained in Examples 4 to 7 were tested for their electrocatalytic performance in carbon dioxide reduction. The test conditions were all constant potential electrolysis at 1.0 V vs. RHE for 1 h, and the contents of CO and H2 were determined by gas chromatography, and HCOO was determined by H NMR. - Table 1 shows the performance differences of catalysts prepared under different conditions.

[0046] Table 1 Performance differences of catalysts prepared under different conditions

[0047] Table 1 shows that carbonization temperature significantly influences catalyst performance. Formic acid selectivity decreases with increasing carbonization temperature. This is due to the melting of metallic bismuth as the temperature rises, which is then swept away in the flowing atmosphere and lost. Furthermore, the agglomeration of metal particles caused by the temperature increase also contributes to the performance degradation. Increasing the metal content leads to an increase in the bismuth content of the support, but does not improve formic acid selectivity. This suggests that excessive metal content increases the risk of metal agglomeration, which is detrimental to improving formic acid selectivity.

[0048] In summary, the nitrogen-doped carbon-supported bismuth oxide nanoparticles Bi / N@C prepared in the present invention situ1 -500, with a rod-like micromorphology and a single grain diameter of approximately 2-4 µm. The cavity structure of this catalyst contains bismuth oxide nanoparticles with good dispersion, and the cluster size ranges from 5-20 nm, as determined by transmission electron microscopy (TEM). This invention utilizes a novel and improved soft template method to in situ synthesize multi-cavity carbon-supported metal catalysts. The surfactant's dispersing effect on the metal precursor results in a highly dispersed carbonized metal, and the surfactant also acts as a pore-forming agent. Melamine, a high-nitrogen carbon source, serves as the carrier's framework, and electron transfer occurs between the N species and bismuth, enhancing catalyst performance. The carbonized cavities confine the metal particles, effectively preventing migration and agglomeration of the bismuth oxide nanoparticles during the reaction, thereby improving catalyst stability. The catalyst prepared by the present invention has a selectivity of up to 96% for formic acid in the electrocatalytic carbon dioxide reduction reaction to produce formic acid, and has a very long service life. Its performance far exceeds that of similar catalysts. A performance comparison with similar catalysts is shown in Table 2 (the Faradaic efficiency in the table refers to the Faradaic efficiency after stability testing), and it has good application prospects.

[0049] Table 2 Comparison of the stability of carbon-supported catalysts

[0050] Anyone skilled in the art will be able to utilize the above-disclosed technical content to make many possible changes and modifications to the technical solution of the present invention, or to modify it into equivalent embodiments with equivalent changes, without departing from the scope of the technical solution of the present invention. Therefore, any simple modifications, equivalent changes, and modifications made to the above embodiments based on the technical essence of the present invention that do not depart from the content of the technical solution of the present invention shall still fall within the scope of protection of the technical solution of the present invention.

Claims

1. A multi-chamber carbon nanorod encapsulated bismuth oxide catalyst, characterized in that: The catalyst comprises a nitrogen-doped carbon rod support and an internally loaded bismuth oxide nanoparticle active center. The catalyst is a carbon nanorod with a diameter of 2-5 μm and a cavity structure. The particle size of the bismuth oxide nanoparticles is 5-30 nm. The bismuth element content in the catalyst is 10-35 wt%.

2. The multi-chamber carbon nanorod-encapsulated bismuth oxide catalyst according to claim 1, characterized in that: The nitrogen-doped carbon rods were prepared by the following method: (a) forming a composite micelle template using P123 and sodium oleate as dual surfactants; (b) cross-linking formaldehyde, 3,5-diaminobenzoic acid, and melamine via a Schiff base reaction to generate melamine oligomers, which were then co-assembled with the composite micelle template to form a polymer precursor; and (c) carbonizing the polymer precursor in an inert atmosphere and subsequently calcining it in a reducing atmosphere to obtain a nitrogen-doped carbon rod support.

3. A method for preparing the multi-chamber carbon nanorod-encapsulated bismuth oxide catalyst according to claim 1, characterized in that: The following steps are involved: S1, dissolving P123 and sodium oleate in deionized water, stirring to form a composite micelle solution, and then adding bismuth nitrate pentahydrate and nitric acid to obtain a composite micelle solution containing bismuth ions; S2, dissolving melamine and 3,5-diaminobenzoic acid in deionized water to obtain a mixed solution; S3, mixing the solutions of step S1 and S2, adding formaldehyde solution to carry out Schiff base reaction to generate a polymer precursor; S4. The polymer precursor is centrifuged, washed, dried, and then ground, and then subjected to carbonization and reduction treatments in a tube furnace in sequence to obtain the catalyst.

4. The preparation method according to claim 3, characterized in that In step S1, the mass ratio of P123 to sodium oleate is (2-5):1; the molar ratio of bismuth nitrate pentahydrate to melamine is 1:(4-8); and the molar ratio of nitric acid to melamine is (2-3):

1.

5. The preparation method according to claim 3, characterized in that The temperature of the Schiff base reaction in step S3 is 20-40 ° C, and the reaction time is 1-3 h.

6. The preparation method according to claim 3, characterized in that In step S4: the carbonization temperature is 500-700 ° C, and the time is 2-4 h; the reduction treatment is carried out in a hydrogen atmosphere at a temperature of 300-400 ° C, and the time is 3-5 h.

7. Use of the multi-chamber carbon nanorod-encapsulated bismuth oxide catalyst according to claim 1 or 2 in electrocatalytic carbon dioxide reduction to formic acid.

8. The use according to claim 7, characterized in that The following steps are involved: (a) loading the catalyst onto carbon paper as a working electrode; (b) CO2 was introduced into an H-type electrolytic cell, 0.5 M KHCO3 was used as the electrolyte, and a potential of -0.8 V to -1.3 V (vs. RHE) was applied for constant potential electrolysis.

9. The use according to claim 8, characterized in that The catalyst loading was 1 mg cm -2 .

10. The use according to claim 8, characterized in that The catalyst was subjected to potentiostatic electrolysis at -1.3 V vs. RHE.

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