Preparation method and application of a carbon-supported copper-bismuth bimetallic vesicle catalyst

Abstract

The present invention relates to the technical field of catalysts, and discloses a preparation method and application of a carbon-supported copper-bismuth bimetallic vesicle-type catalyst, which includes the following steps: (1) preparing hollow mesoporous carbon spheres HMCS; (2) preparing the copper-bismuth bimetallic vesicle-type catalyst: adding the HMCS prepared in step (1), Cu(NO<subgt;3< / subgt;)<subgt;2< / subgt>·3H<subgt;2< / subgt>O and Bi(NO<subgt;3< / subgt;)<subgt;3< / subgt>·5H<subgt;2< / subgt>O to ethylene glycol in sequence, ultrasonically dispersing them evenly, adding NaBH<subgt;4< / subgt> under magnetic stirring to obtain solution C, centrifuging and washing solution C to collect the precipitate, and drying the precipitate to obtain the copper-bismuth bimetallic vesicle-type catalyst. By virtue of the stable spherical surface and dense distribution environment of the hollow mesoporous carbon spheres, the present invention constructs a bimetallic vesicle-type catalyst by restricting and fixing the growth space of Bi and Cu, and realizes the one-step production of pure formic acid from CO<subgt;2< / subgt> in combination with the solid electrolyte electrolytic cell technology, and a pure formic acid aqueous solution can be obtained without separation.

Description

Technical Field

[0001] The present invention relates to the technical field of catalysts, and particularly relates to a preparation method and application of a carbon-supported copper-bismuth bimetallic vesicle-type catalyst. Background Art

[0002] Carbon dioxide is the final product during the use of fossil fuels and can cause a serious greenhouse effect. Converting carbon dioxide into some valuable fossil fuels is an important problem that urgently needs to be solved globally, and among them, the electrochemical method is one of the most promising methods at present.

[0003] Nanostructure engineering is a very promising strategy for regulating electroreduction CO2 catalysts. In order to improve the utilization efficiency of metals and enhance their intrinsic catalytic activity, efforts have been made to expose more active sites by reducing the size of metal nanoparticles or increasing their dispersion. However, ultrafine nanoparticles with a super-high active area are usually prone to overgrowth and aggregation at high reaction temperatures, and their complex synthesis process makes the manufacturing cost of the catalyst high. At the same time, during long-term operation, the aggregation or deformation of ultrafine particles will reduce the catalytic efficiency, resulting in poor stability of the electrochemical process. Therefore, it is very challenging to prepare ultrafine nanoparticles. For this reason, it is very effective to use suitable substrates such as graphene oxide, carbon nanotubes, metal-organic framework-derived carbon, and metal supports to stabilize ultra-small nanoparticles.

[0004] Carbon materials are abundant in reserves, with a flexible structure and excellent electrochemical stability (Varela AS, Ju W, Strasser P. Molecular nitrogen-carbon catalysts, solid metal organic framework catalysts, and solid metal / nitrogen-doped carbon (MNC) catalysts for the electrochemical CO2 reduction [J]. Advanced Energy Materials, 2018, 8(30).). However, in electrocatalytic reactions, carbon materials have poor conductivity and strong inherent selectivity for gas products, which usually limits their application in the electrocatalytic CO2 reduction reaction (Birdja YY, Pérez-Gallent E, Figueiredo MC, et al. Advances and challenges in understanding the electrocatalytic conversion of carbon dioxide to fuels [J]. Nature Energy, 2019, 4(9):732-745.); (Zhang Z, Dou H, Gao R, et al. Steering carbon hybridization state in carbon-based metal-free catalysts for selective and durable CO2 electroreduction [J]. ACS Catalysis, 2022, 12(24):15218-15229.). On the other hand, defects and bent lattices in the carbon material structure can be modified at the nanoscale with metals by means of doping, strain, etc., to disperse metal atoms to the greatest extent and create new catalytic integration behaviors beyond expectations (Wicks J, Jue ML, Beck VA, et al. 3D-printable fluoropolymer gas diffusion layers for CO2 electroreduction [J]. Adv Mater, 2021, 33(7):e2003855.).Therefore, many studies have been devoted to improving the catalytic performance by regulating the macroscopic or microscopic atomic structure between the metal and the carbon support (Yang HP, Lin Q, Zhang HW, et al. Platinum / nitrogen-doped carbon / carbon cloth: A bifunctional catalyst for the electrochemical reduction and carboxylation of CO2 with excellent efficiency[J]. Chem Commun (Camb), 2018, 54(33): 4108-4111.); (Wang Z, Zhou Y, Liu D, et al. Carbon-confined indium oxides for efficient carbon dioxide reduction in a solid-state electrolyte flow cell[J]. Angew Chem Int Ed Engl, 2022, 61(21): e202200552.). It has been reported that carbon-supported Bi-based components have achieved remarkable results in the selectivity of formic acid products (Wu D, Wang X, Fu X-Z, et al. Ultrasmall Bi nanoparticles confined in carbon nanosheets as highly active and durable catalysts for CO2 electroreduction[J]. Applied Catalysis B: Environmental, 2021, 284.). Ultrasmall Bi nanoparticles have great application potential in the field of electrocatalytic reduction of CO2. Chen et al. (Lee CW, Hong JS, Yang KD, et al. Selective electrochemical production of formate from carbon dioxide with bismuth-based catalysts in an aqueous electrolyte[J]. ACS Catalysis, 2018, 8(2): 931-937.) synthesized amorphous BiO uniformly loaded on carbon black by a simple solvothermal method. x nanoparticles with a particle size of less than 10 nm. Compared with the large-sized BiO synthesized by thermal decomposition x nanoparticles, the BiO generated by the induction of organic solventsx The nanoparticles significantly inhibited the growth of the Bi-O second coordination shell. This structural difference indicates a large structural disorder around the Bi sites, providing more binding sites for the electron transfer and protonation reactions of CO2 radicals. Subsequently, a 0.5 M NaCl solution was used as the electrolyte to simulate the seawater environment for the electrocatalytic reduction of CO2 reaction. The BiO x / C catalyst had an average selectivity for formic acid of 93.4% in the voltage range of -1.77 V to -1.0 V. In addition, Wu et al. (Wu D, Wang X, Fu X-Z, et al. Ultrasmall Bi nanoparticles confined in carbon nanosheets as highly active and durable catalysts for CO2 electroreduction[J]. Applied Catalysis B: Environmental, 2021, 284.) successfully prepared ultrasmall Bi nanoparticles confined in carbon fibers by the method of carbon cloth impregnation and calcination fixation, with a particle size of about 5 nm. The ultrasmall Bi nanoparticles provided abundant active sites for carbon dioxide conversion. At the same time, the Bi nanoparticles were wrapped in carbon nanosheets, tightly and uniformly covering the carbon cloth substrate, improving the electron transfer ability. The synthesized self-supported electrocatalyst showed good electrocatalytic reduction CO2 activity. The optimized Bi-PVP / CC600 catalyst had a Faraday efficiency for formic acid exceeding 81% in the voltage range of -0.72 V to -1.01 V and was able to maintain current stability for nearly 40 hours at a high current density of about -54 mA cm -2 .

[0005] The researchers attributed this performance improvement to the effective interfacial charge transfer between carbon and Bi nanoparticles. Although the intrinsic activity of metallic Bi and the carbon-supported catalyst has been improved, due to the relatively low intrinsic conductivity of both Bi and carbon, the binding ability and interaction between the two are still relatively weak, and the understanding of the electron orbital interaction between them is still far from sufficient (Han N, Ding P, He L, et al. Promises of main group metal–based nanostructured materials for electrochemical CO2 reduction to formate[J]. Advanced Energy Materials, 2019, 10(11)). Therefore, developing new regulation strategies to enhance the interaction between Bi and carbon is of great significance for constructing high-performance electrocatalytic CO2 reduction catalysts. Summary of the Invention

[0006] The present invention aims to overcome the shortcomings of existing technologies and provide a method for preparing and applying carbon-supported copper-bismuth bimetallic vesicle catalysts. By leveraging the stable spherical surface and dense distribution of hollow porous carbon spheres, the growth space of Bi and Cu is restricted and fixed, creating a bimetallic vesicle nanoreactor structure. Copper is anchored by defects on the carbon surface, strengthening the bismuth-carbon interaction.

[0007] In order to achieve the above object, the technical solution of the present invention is: a method for preparing a carbon-supported copper-bismuth bimetallic vesicle catalyst, characterized in that it comprises the following steps:

[0008] (1) Preparation of hollow mesoporous carbon spheres:

[0009] Tetraethyl orthosilicate, ammonium hydroxide solution, ethanol, and deionized water were mixed and stirred to obtain solution A. Resorcinol and formaldehyde solution were added to solution A and stirred to obtain solution B. Solution B was centrifuged and washed to collect an orange precipitate. The precipitate was dried to obtain a polymer-coated SiO2 sample, named SiO2@Polymer. SiO2@Polymer was calcined to obtain a black block solid. The black block solid was ground and added to a NaOH solution. After stirring, the precipitate was collected by centrifugation and dried to obtain hollow mesoporous carbon spheres, referred to as HMCS.

[0010] (2) Preparation of copper-bismuth bimetallic vesicle catalyst:

[0011] HMCS, Cu(NO3)2·3H2O and Bi(NO3)3·5H2O prepared in step (1) were added to ethylene glycol in sequence, and after ultrasonic dispersion, NaBH4 was added under magnetic stirring to obtain solution C. Solution C was centrifuged and washed to collect the precipitate. The precipitate was dried to obtain a copper-bismuth bimetallic vesicle catalyst, referred to as Bi-Cu / HMCS.

[0012] Furthermore, in step (1), the volume ratio of tetraethyl orthosilicate, ammonium hydroxide solution, ethanol and deionized water is 3-4:3:70:10, the concentration of ammonium hydroxide is 5 wt.%, the mass volume ratio of resorcinol and formaldehyde solution is 400 mg:0.5-1 mL, the concentration of formaldehyde solution is 37 wt.%, the mass volume ratio of resorcinol and tetraethyl orthosilicate is 400 mg:3-4 mL.

[0013] Furthermore, in step (1), resorcinol and formaldehyde solution were added to solution A, and the mixture was stirred at 1000 rpm for 24 h to obtain solution B. Solution B was centrifuged at 9000 rpm, and the precipitate was washed once with water and ethanol respectively, and the orange precipitate was collected. The precipitate was dried at 60°C for 12 h to obtain a SiO2 sample coated with a polymer.

[0014] Further, in step (1), SiO2@Polymer was calcined in a tubular furnace under a nitrogen atmosphere at a temperature of 700°C for 5 hours at a heating rate of 2°C min -1 .

[0015] Further; in step (1), the black block solid is ground and added to a NaOH solution, stirred at 60°C for 10 hours, and then centrifuged at 19000 rpm to collect the precipitate, and dried at 80°C for 12 hours to obtain hollow mesoporous carbon spheres, wherein the concentration of the NaOH solution is 1 mol / L, and the volume ratio of the NaOH solution to resorcinol is 5:8.

[0016] Furthermore, the mass volume ratio of HMCS, Cu(NO3)2·3H2O, Bi(NO3)3·5H2O, NaBH4 and ethylene glycol in step (2) is 20mg:60mg:500mg:100mg:20mL.

[0017] Further, step (2) adding HMCS prepared in step (1) to ethylene glycol, ultrasonically dispersing the mixture uniformly and adding Cu(NO3)2·3H2O, ultrasonically dispersing the mixture uniformly and adding Bi(NO3)3·5H2O, ultrasonically dispersing the mixture uniformly and adding NaBH4 in two batches under magnetic stirring at 1000rpm, and stirring for 1h to obtain solution C.

[0018] Furthermore, in step (2), solution C is centrifuged at 10,000 rpm, washed three times with water and three times with ethanol during the centrifugation process, the precipitate is collected, and the precipitate is dried at 60°C for 12h to obtain a copper-bismuth bimetallic vesicle catalyst.

[0019] Another technical solution of the present invention is: a carbon-supported copper-bismuth bimetallic vesicle catalyst, characterized in that it is prepared by the preparation method of the carbon-supported copper-bismuth bimetallic vesicle catalyst according to any one of claims 1-8.

[0020] The present invention also provides the use of a carbon-supported copper-bismuth bimetallic vesicle catalyst in the production of pure formic acid by electroreduction of carbon dioxide.

[0021] Advantages of the present invention: The present invention selects hollow mesoporous carbon spheres as metal dispersants and stable carriers, effectively restricting the growth space of metals in solutions with alkaline and polar properties, and synthesizing a hierarchical porous nanovesicle electrocatalyst Bi-Cu / HMCS modified with a carbon-copper-bismuth heterojunction through a one-step reduction method. The Bi-Cu / HMCS bimetallic electrocatalyst has a uniform hollow nanovesicle structure. The BiCu nanoclusters are fixed at carbon defects by using the hierarchical pore structure on their surfaces, and the repair of sp 2 hybridization in the graphite carbon structure is promoted through the interaction between the metal and the carbon carrier, which not only increases the attachment density of metal active sites but also greatly improves the CO2 adsorption capacity of the bimetallic nanovesicles. The Bi-Cu / HMCS catalyst electrode is a CO2 reduction electrocatalyst with both catalytic activity, selectivity, and stability. In an H-type electrolytic cell, the Bi-Cu / HMCS electrode achieves a 100% selectivity for formic acid at a low voltage of -0.6V, and its catalytic activity and stability can last for more than 60 hours. In addition, in a solid electrolyte cell, the electrode can efficiently produce a pure formic acid solution with a concentration of 0.6M within 7.5 hours. Description of the Drawings

[0022] Figure 1 is a schematic diagram of the synthesis route of the Bi-Cu / HMCS catalyst of the present invention;

[0023] Figure 2 are the XRD patterns of Bi-Cu / HMCS, Bi / HMCS, BiO x , HMCS (a), SEM images of Bi-Cu / HMCS (b and c), TEM image of Bi-Cu / HMCS (d), high-resolution TEM images of the particles on the surface of the Bi-Cu / HMCS vesicles (e and f);

[0024] Figure 3 are the selected area electron diffraction patterns of BiCu nanoclusters (a) and the carbon surface (b) on Bi-Cu / HMCS;

[0025] Figure 4 are the SEM images of the Bi / HMCS (a), Cu / HMCS (b), and BiOx (c) catalysts, and the TEM images of the Bi / HMCS (d), Cu / HMCS (e), and BiOx (f) catalysts;

[0026] Figure 5 are the N2 isothermal adsorption and desorption curves (a), pore size distribution diagrams (b), Raman spectra (c), and CO2 adsorption isotherms (d) of the HMCS, Bi / HMCS, and Bi-Cu / HMCS catalysts;

[0027] Figure 6is the XPS survey spectrum of the catalyst (a), the high-resolution XPS spectrum of the Bi 4f orbital (b), the high-resolution XPS spectrum of the Cu 2p orbital (c), and the high-resolution XPS spectrum of the C 1s orbital (d);

[0028] Figure 7 are the linear cyclic voltammograms of the BiOx (a), Bi / HMCS (b), and Cu-Bi / HMCS (c) catalysts tested in 0.1 M KHCO3 at different scan rates in the voltage range of -0.30 to -0.38 V vs. Ag / AgCl, and the slope is the double-layer capacitance (d);

[0029] Figure 8 are the electrochemical performances of the catalyst in an H-type electrolytic cell: the electrochemical impedance diagram (a) at -0.6 V, the LSV curve (b), the partial current density of formic acid (c), the Faraday efficiency of formic acid (d), the total product Faraday efficiency of Bi-Cu / HMCS (e), and the current stability in the H-type electrolytic cell (f);

[0030] Figure 9 is the total product Faraday efficiency of the catalyst in an H-type electrolytic cell;

[0031] Figure 10 is a schematic diagram of a solid electrolyte electrolytic cell for the reduction of CO2 (CO2RR) to produce pure formic acid solution;

[0032] Figure 11 are the CO2RR performances of Cu-Bi / HMCS in a solid electrolyte electrolytic cell: the polarization curve (a), the FE and current density of HCOOH at different full voltages (b), the 1H liquid-phase NMR spectrum of the HCOOH product (c), and the stability test (d) of continuously producing pure formic acid solution under a constant current condition of 100 mA cm -2 and the corresponding formic acid concentration curve (e) detected by HPLC every 2.5 hours. Detailed implementation manners

[0033] The present invention will be further described below in conjunction with specific embodiments, but the present invention is not limited by the embodiments.

[0034] Unless otherwise specified, the reagents, equipment, and methods used in the following examples are all common methods or can be obtained from commercial channels.

[0035] Example 1:

[0036] A preparation method of a carbon-supported copper-bismuth bimetallic vesicle-type catalyst includes the following steps:

[0037] (1) Preparation of hollow mesoporous carbon spheres:

[0038] 70 mL of ethanol and 10 mL of deionized water were added to a 200 mL beaker, and then 3.46 mL of tetraethyl orthosilicate (TEOS) and 3 mL of 5 wt.% ammonium hydroxide were added to the beaker and stirred at 800 rpm at room temperature for 15 minutes to obtain a uniformly dispersed milky white solution. Then, 400 mg of resorcinol and 0.56 mL of 37 wt.% formaldehyde solution were added to the milky white solution and stirred at 1000 rpm for 24 hours to obtain an orange turbid solution. The orange turbid solution was centrifuged at 9000 rpm, and the precipitate was washed once with water and ethanol respectively. The orange precipitate was collected and dried in a constant temperature drying oven at 60 ° C for 12 hours to obtain a SiO2 sample coated with a polymer, named SiO2@Polymer. The SiO2@Polymer was placed in a quartz boat and calcined in a nitrogen atmosphere in a tube furnace at a calcination temperature of 700 ° C for 5 hours with a heating rate of 2 ° C min -1 After the tube furnace cooled, the calcined black block solid was collected, finely ground in a mortar, placed in a beaker containing 250 mL of 1 M NaOH solution, and stirred at 60°C for 10 hours to remove SiO2. The solution was then centrifuged at 19,000 rpm to collect the precipitate, which was then dried in a vacuum drying oven at 80°C for 12 hours to obtain hollow mesoporous carbon spheres (HMCS).

[0039] (2) Preparation of copper-bismuth bimetallic vesicle catalyst:

[0040] 20 mg of HMCS prepared in step (1) was dispersed in 20 mL of ethylene glycol by ultrasound at an ultrasonic frequency of 50 kHz for 30 min. 60 mg of Cu(NO3)2·3H2O was then added to the ethylene glycol solution and ultrasound was continued for 30 min. 500 mg of Bi(NO3)3·5H2O was then added and ultrasound was continued for 30 min. After a uniform solution was formed, the beaker containing the solution was moved to a magnetic stirrer. 100 mg of NaBH4 was added in two batches under magnetic stirring at 1000 rpm and stirred for 1 hour. The precipitate was then collected by high-speed centrifugation at a speed of 10,000 rpm. During the centrifugation process, the precipitate was washed with water three times and with ethanol three times. The collected precipitate was dried in a vacuum oven at 60°C for 12 hours to obtain a copper-bismuth bimetallic vesicle catalyst, referred to as Bi-Cu / HMCS.

[0041] Comparative Example 1:

[0042] The preparation method of the Bi / HMCS catalyst is different from that of Example 1 in that no Cu(NO3)2·3H2O is added during the preparation process, and a copper-free Bi / HMCS catalyst is prepared.

[0043] Comparative Example 2:

[0044] The preparation method of the Cu / HMCS catalyst is different from that of Example 1 in that Bi(NO3)3·5H2O is not added during the preparation process, and a bismuth-free Cu / HMCS catalyst is prepared.

[0045] Comparative Example 3:

[0046] BiO x The preparation method of the catalyst is different from that of Example 1 in that Cu(NO3)2·3H2O and HMCS are not added during the preparation process, and a copper-free BiO x catalyst is prepared.

[0047] I. Morphology and Chemical Composition Analysis of the Catalyst

[0048] The strategy for synthesizing the Bi-Cu / HMCS nanovesicle catalyst is as Figure 1 shown. Briefly, hollow mesoporous carbon spheres (HMCS) were prepared by the soft template method. Due to the long-term washing effect of NaOH, it was dispersed in the ethylene glycol solution to be alkaline, inhibiting the rapid hydrolysis of the bismuth nitrate precursor. The enriched nanosphere shell environment in the solution contributed to the unitized dispersion of Bi 3+ and Cu 2+ metal ions. Under the reduction of NaBH4, Cu-doped bismuth hydroxide nitrate was formed in the alkaline solution and was successfully embedded in the inner and outer porous surfaces of the carbon sphere shell by the strong centrifugal force during stirring, obtaining the Bi-Cu / HMCS catalyst.

[0049] The chemical components in Bi-Cu / HMCS were determined by X-ray diffraction pattern (XRD) test. As Figure 2 shown in -a, it was found that the characteristic peaks of the XRD curve of HMCS at 25° and 44° angles corresponded to the (002) and (100) crystal planes of carbon respectively, proving that the internal SiO2 spherical particles had been completely removed. In addition to showing the characteristic peaks of carbon, the XRD curve of the Bi-Cu / HMCS catalyst could correspond to the PDF card 28-0654 of bismuth hydroxide nitrate [Bi6O6(OH)2](NO3)4·2H2O for the remaining characteristic peak positions. The characteristic peak of Cu was difficult to distinguish in the XRD pattern due to its low content or amorphous state and would be specifically analyzed in the subsequent X-ray photoelectron spectroscopy (XPS). Figure 2Scanning electron microscope images (SEM) at different magnifications in -b and 6-2-c show that the Bi-Cu / HMCS catalyst exhibits an ultrathin nanovesicle structure with uniformly distributed spherical vesicles approximately 250 nm in diameter; a rough carbon shell with a thickness of 6 nm forms the surface of the vesicles, showing a hierarchical porous structure and the attachment of metal nanoclusters. Additionally, each nanovesicle surface has an open macropore approximately 50 nm in diameter, facilitating the internal adsorption of CO2 and the shuttling of protons inside and outside. As Figure 2 shown in -d, the transmission electron microscope image (TEM) of the whole nanovesicle proves that the Cu-doped bismuth alkaline nitrate nanoclusters are successfully dispersed and anchored on the surface of the nanovesicles, without the appearance of large bulk structures such as BiO x in the catalyst ( Figure 4 -c and Figure 4 -f). Lattice spacings belonging to bismuth alkaline nitrate nanoclusters were collected in the high-resolution TEM image (HRTEM) of the surface Bi-Cu clusters, such as 0.281 nm and 0.319 nm, which are slightly larger than the standard lattice spacings in their PDF cards. This is because Cu atoms also exist in the cluster crystals, widening their surface lattice, which is consistent with the Figure 3 results of the bright annular spots belonging to polycrystals shown in the selected area electron diffraction pattern (SAED) of -a polycrystal. Magnifying the vesicle surface, the corresponding high-resolution TEM image shows that there are metal lattices with a diameter less than 5 nm embedded in the curved lattice of carbon on its surface. Measuring the lattice spacing of the metal is 0.245 nm, which can correspond to the (111) crystal plane of CuO. In particular, the SEAD image of the nanovesicle surface shows both the annular halo of carbon and the bright spots of the CuO lattice, as Figure 3 shown in -b, indicating that some CuO microcrystals are partially embedded in the curved lattice of carbon, which is consistent with its HRTEM image.

[0050] II. Composition and Valence State Analysis of the Catalyst

[0051] Through a series of tests on the pore structure and surface defects of the catalyst, the relationship between the metal and the hierarchical pore structure in the nanovesicles was studied. As Figure 5 shown in -a, according to the nitrogen adsorption-desorption test curve combined with the BET (Brunauer-Emmett-Teller) algorithm, the specific surface areas of various catalysts were obtained. The detailed results are shown in Table 1. The specific surface areas of HMCS, Bi / HMCS, and Bi-Cu / HMCS are 538.9 m 2 g -1 , 214.2 m 2 g -1 , and 129.3 m 2 g -1 respectively. As the active sites increase and are fixed, the specific surface area of the catalyst shows a downward trend.Figure 5 -b is the corresponding pore size distribution diagram, from which it can be observed that the pore size of the catalyst is mainly mesoporous. Compared with HMCS, the mesoporous and microporous areas of Bi / HMCS both decrease, indicating that both the micropores and mesopores on the vesicle surface are conducive to the attachment of Bi-based species. After further introducing Cu into the vesicles of Bi-Cu / HMCS, the microporous area decreases rapidly, while the mesoporous area does not change much compared with that of Bi / HMCS, indicating that Cu is mainly inserted into the microporous layer of the nanovesicles. All catalysts show characteristic peaks of the D band and G band of carbon in the Raman spectrum ( Figure 5 -c), located at 1380 cm -1 and 1590 cm -1 wavelengths, respectively. The D band peak is generated by the stretching motion of all sp 2 pairs of atoms in the carbon ring or long chain; while the D band peak is induced by the disorder and defects in the carbon structure. Generally, we use the ratio of the D peak to the G peak to measure the degree of defect or disorder of the carbon material. The intensity ratios (I D / I G ) of the D band and G band of the HMCS, Bi / HMCS and Bi-Cu / HMCS catalysts are 1.02, 0.98 and 0.83 respectively, indicating that the degree of graphite defect is gradually decreasing. It can be inferred that the electron transfer between the metal and the carbon skeleton contributes to the restoration of sp 2 hybridization in the graphite carbon structure. In addition, the CO2 adsorption curve ( Figure 5 -d) proves that the CO2 adsorption capacities of the catalysts from small to large are HMCS < Bi / HMCS < Bi-Cu / HMCS, which is exactly the opposite of the size of their pore specific surface areas, indicating that covering the surface of the hollow nanovesicles with sufficient active sites is the key to increasing the CO2 adsorption capacity and activation ability.

[0052] Table 1 BET specific surface area and pore size distribution of catalysts

[0053]

[0054] The surface valence state and electronic properties were investigated by X-ray photoelectron spectroscopy (XPS). As Figure 6 shown in -a, the XPS survey spectrum confirms that Bi-Cu / HMCS contains four elements: C, O, Cu, and Bi. Table 2 lists the specific element contents in the catalysts. The Bi contents in the Bi / HMCS and Bi-Cu / HMCS catalysts are 4.55 at.% and 6.21 at.%, respectively, indicating that the addition of Cu may help the nanovesicles to anchor more Bi active sites. The high-resolution XPS spectrum of the Bi 4f orbital shows ( Figure 6 -b) that the characteristic peaks at the binding energies of 165.1 eV and 159.8 eV correspond to Bi 4f 5 / 2and Bi 4f 7 / 2 Track, confirm Bi 3+ The valence state is dominant in Bi-Cu / HMCS catalyst. Since the alkaline environment of the nanocapsules effectively limits the reduction and hydrolysis rate of Bi-based precursors, no Bi 0 The characteristic peak of Cu 2p is shown in the high-resolution XPS spectrum ( Figure 6 -c), the characteristic peaks at the binding energies of 935.8eV and 955.4eV belong to Cu 2+ , and the characteristic peaks at 933.8eV and 953.6eV belong to Cu 0 or Cu + . It is worth noting that we found that the peak binding energies of Bi 4f and Cu 2p orbitals of Bi-Cu / HMCS catalysts shifted to higher positions compared with Bi / HMCS and Cu / HMCS catalysts, indicating that there are staggered electron clouds between Cu and Bi and there is a strong metal interaction. Similarly, compared with HMCS catalyst, the peak binding energy of Bi / HMCS catalyst also showed an upward trend, verifying the strong binding effect between metal and nanovesicles. In addition, the high-resolution XPS spectrum of C1s orbital of Bi-Cu / HMCS ( Figure 6 -d) Characteristic peaks corresponding to C=C bonds, C-OH bonds, CO bonds, O-C=O bonds, and π–π* bonds appeared at binding energies of 284.7, 286.2, 287.8, 289.3, and 291.2 eV, respectively. Furthermore, only the Cu-containing Bi-Cu / HMCS and Cu / HMCS catalysts exhibited a π–π* transition peak at 291.2 eV, further indicating a close electronic interaction between the Cu atoms and the carbon framework of the nanocapsules. This interaction, consistent with Raman spectroscopy analysis, promotes more electron transfer, thereby improving the electron transport rate of the electrocatalytic CO2 reaction.

[0055] Table 2 XPS test results of catalyst element content

[0056]

[0057]

[0058] 3. Analysis of Catalyst Electrocatalytic CO2 Performance

[0059] The electrocatalytic CO2 conversion performance of the catalyst was tested in an H-type electrolytic cell using a CO2-saturated 0.1M KHCO3 electrolyte. First, the double-layer capacitance (C dl ), to infer and C dlThe size of the electrochemical specific surface area is in a proportional relationship. The double-layer capacitance obtained from the slope of the linear fitting line of the current difference at the median voltage and the scanning rate is as Figure 7 shown. We found that the double-layer capacitance of Bi / HMCS is 255 μF cm 2 , which is 5.6 times that of the BiO x bulk catalyst (45 μF cm 2 ). This indicates that the dispersion and fixation effect of the nanovesicles on the metal nanoparticles greatly improves the utilization rate of the metal active sites and the electrochemical active specific surface area. On the other hand, the double-layer capacitance of Bi-Cu / HMCS is 572 μF cm 2 , almost twice that of Bi / HMCS. This is due to the fact that Cu enhances the binding ability between the surface of HMCS and Bi, and the increase in active sites leads to a further improvement in the electrochemical active specific surface area. To evaluate the interfacial resistance characteristics, electrochemical impedance spectroscopy (EIS) was tested in the frequency range from 500 Hz to 1 Hz, as Figure 8 -a shows. In the high-frequency range, the diameter of the semicircle is proportional to the charge transfer resistance, that is, the larger the radius, the higher the electrochemical impedance. By comparison, Bi-Cu / HMCS has the smallest semicircle, so it has the lowest resistance and the highest charge transfer efficiency. These outstanding electrochemical properties will act on the catalytic performance of the Bi-Cu / HMCS catalyst in the electrocatalytic reduction of CO2 reaction.

[0060] The electrocatalytic CO2 reduction performance of the catalyst was first tested in a gastight H-type electrolytic cell. In the linear sweep voltammetry (LSV) curve, the current density of Bi-Cu / HMCS shows a rapid upward trend with the increase of the negative potential. Its partial current density for formic acid in the reaction ( Figure 8 -c) is also higher than that of other catalysts, indicating that Bi-Cu / HMCS has the most efficient catalytic activity. Comparing the formic acid selectivity of various catalysts, the selectivity of the BiO x catalyst for formic acid does not exceed 85% and the reaction potential is relatively high, at -0.8 V; while the selectivity of the Bi / HMCS catalyst for formic acid has a nearly 10% increase, and the highest selectivity for formic acid is 91.4% at a voltage of -0.6 V; in the Bi-Cu / HMCS catalyst, the Faraday efficiency of formic acid has a significant increase in each voltage segment. The Faraday efficiency of formic acid is greater than 90% in the voltage segment from -0.5 V to -1.0 V, and even reaches 100% at -0.6 V. In addition, in the 60-hour CO2 electroreduction stability experiment, the final Faraday efficiency of formic acid can still be maintained above 90%, and the decrease in the current density of the catalyst is almost negligible, showing excellent electrocatalytic activity stability. Figure 8 -e and Figure 9It is the overall Faraday efficiency diagram of all products of the catalyst. It can be found that the Cu / HMCS catalyst can also produce formic acid, indicating that Cu may not only be able to regulate the binding ability of Bi and carbon but also enhance the reaction efficiency of the formic acid pathway. On the other hand, the hollow mesoporous carbon spheres HMCS without metal loading are dominated by H2 products in the catalytic reaction. When Bi metal is loaded, the hydrogen evolution reaction is inhibited to a certain extent; when Bi-Cu clusters are loaded, the hydrogen evolution reaction at low voltages is inhibited to the greatest extent, indicating that the presence of Cu is also beneficial to inhibiting the hydrogen evolution reaction. Therefore, compared with BiO x and Bi / HCMS, the unique hollow vesicle structure and dual active sites of the Bi-Cu / HMCS bimetallic catalyst significantly improve its selectivity and durability for formic acid products.

[0061] Neutral or alkaline electrolytes such as KHCO3 and KOH used in traditional electrochemical test systems for H-type electrolytic cells and flow-type electrolytic cells are designed to inhibit the hydrogen evolution reaction but highlight the problem of purifying liquid products from the mixed solution. Currently, the rise of solid electrolyte electrolytic cells effectively simplifies the purification process of liquid products and can directly produce pure formic acid products. As Figure 10 shown, the solid electrolyte device consists of two membrane electrodes and three metal templates, including two channel plates for gas and liquid flow and a thin plate filled with solid electrolyte (SEE) in the middle. When electrons start to circulate in the electrolytic cell, humidified CO2 undergoes a reduction reaction on the catalyst surface through the gas diffusion layer, and the generated HCOO - is quickly transported to the anion exchange membrane (AEM) and combines with the H + carried by the solid electrolyte, and finally the generated HCOOH is carried away from the solid electrolyte surface by the circulating deionized water for collection. Similarly, the consumed H + ions in the solid electrolyte can be replenished by the water oxygen evolution reaction (OER) occurring on the IrO2 / Ti mesh. The linear sweep voltammetry curve ( Figure 11 -a) shows the catalytic activity of Bi-Cu / HMCS in the solid electrolyte device. As the full cell voltage increases, the current density of the Bi-Cu / HMCS electrode rapidly climbs to the industrially applicable current density. Using a solid electrolyte electrolytic cell such as Figure 10 , the electrocatalytic CO2 performance of the Bi-Cu / HMCS electrode at various voltages is measured. As shown in Figure 11 -b, it is found that it can maintain a selectivity for formic acid above 80% in the voltage range of 2.3V to 2.6V. At a voltage of 2.5V, the Faraday efficiency of formic acid reaches the highest, 91.3%, and the current density at this time is 143mAcm -2 . To meet the requirements of commercial applications, the catalyst is at 100mA cm -2Long-term constant current stability tests were carried out at a current density of []. However, we found that the catalyst maintained a stable cell voltage within 18 hours. However, due to the decrease in the ion exchange capacity of the solid electrolyte, the concentration of the pure formic acid solution produced in the device was limited to about 0.2 M. Therefore, in order to obtain high-quality formic acid products, we tried to continuously update the solid electrolyte to maintain the efficient operation of the formic acid synthesis process on the solid electrolyte. The solid electrolyte was replaced every 2.5 hours of reaction. In this way, our solid electrolyte device could produce more than 0.6 M of pure formic acid products within 7.5 hours of efficient operation, indicating that the Bi-Cu / HMCS catalyst is an excellent electrocatalyst capable of realizing the electrocatalytic reduction of CO2 to high-quality formic acid products.

[0062] The above-described embodiments are only preferred solutions of the present invention and do not impose any form of limitation on the present invention. There are other variations and modifications without exceeding the technical solutions described in the claims.

Claims

1. Application of a carbon-supported copper-bismuth bimetallic vesicle catalyst in the electroreduction of carbon dioxide to pure formic acid, The preparation method of the carbon-supported copper-bismuth bimetallic vesicle catalyst includes the following steps: (1) Preparation of hollow mesoporous carbon spheres: Mix tetraethyl orthosilicate, ammonium hydroxide solution, ethanol, and deionized water and stir evenly to obtain solution A. Add resorcinol and formaldehyde solution to solution A and stir evenly to obtain solution B. Centrifuge and wash solution B to collect the orange precipitate. After drying the precipitate, obtain the SiO2 sample coated with polymer, named SiO2@Polymer. Calcinate SiO2@Polymer to obtain a black block solid. Grind the black block solid and add it to NaOH solution, stir and then centrifuge to collect the precipitate. After drying, obtain hollow mesoporous carbon spheres, abbreviated as HMCS; (2) Preparation of copper-bismuth bimetallic vesicle catalyst: Add the HMCS prepared in step (1), Cu(NO3)2·3H2O, and Bi(NO3)3·5H2O to ethylene glycol in sequence. After ultrasonic dispersion, add NaBH4 under magnetic stirring to obtain solution C. Centrifuge and wash solution C to collect the precipitate. After drying the precipitate, obtain the copper-bismuth bimetallic vesicle catalyst, abbreviated as Bi-Cu / HMCS.

2. The application according to claim 1, wherein: In step (1), the volume ratio of tetraethyl orthosilicate, ammonium hydroxide solution, ethanol to deionized water is 3-4:3:70:10, the concentration of ammonium hydroxide is 5 wt.%, the mass-volume ratio of resorcinol to formaldehyde solution is 400mg:0.5-1mL, the concentration of formaldehyde solution is 37 wt.%, and the mass-volume ratio of resorcinol to tetraethyl orthosilicate is 400mg:3-4mL.

3. The application according to claim 1, wherein: In step (1), add resorcinol and formaldehyde solution to solution A, stir at 1000 rpm for 24 h to obtain solution B. Centrifuge solution B at 9000 rpm, wash the precipitate with water and ethanol once respectively, collect the orange precipitate, and dry the precipitate at 60 °C for 12 h to obtain the SiO2 sample coated with polymer.

4. The application according to claim 1, characterized in that: In step (1), SiO2@Polymer is calcined in a tube furnace under a nitrogen atmosphere at a calcination temperature of 700 °C for 5 h with a heating rate of 2 °C min -1 .

5. The application according to claim 2, characterized in that: In step (1), grind the black block solid and add it to NaOH solution, stir at 60 °C for 10 h and then centrifuge at 19000 rpm to collect the precipitate, dry at 80 °C for 12 h to obtain hollow mesoporous carbon spheres. The concentration of the NaOH solution is 1 mol / L, and the volume ratio of the NaOH solution to resorcinol is 5:

8.

6. The application according to claim 1, wherein: In step (2), the mass-volume ratio of HMCS, Cu(NO3)2·3H2O, Bi(NO3)3·5H2O, NaBH4 to ethylene glycol is 20mg:60mg:500mg:100mg:20mL.

7. The application according to claim 6, wherein: In step (2), add the HMCS prepared in step (1) to ethylene glycol, after ultrasonic dispersion, add Cu(NO3)2·3H2O, after ultrasonic dispersion, add Bi(NO3)3·5H2O, after ultrasonic dispersion, add NaBH4 in two batches under magnetic stirring at 1000 rpm, and stir for 1 h to obtain solution C.

8. The application according to claim 1, wherein: In step (2), solution C was centrifuged at 10,000 rpm, and during centrifugation, it was washed three times with water and three times with ethanol. The precipitate was collected and dried at 60 °C for 12 h to obtain the copper-bismuth bimetallic vesicle-type catalyst.

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