Preparation method of pbbio2oh and application thereof in electrocatalytic synthesis of formic acid from carbon dioxide

Abstract

The application relates to the technical field of electrocatalytic carbon dioxide reduction, in particular to a preparation method of PbBiO2OH and application of the PbBiO2OH in electrocatalytic carbon dioxide synthesis of formic acid. The PbBiO2OH is prepared by adopting a method of "directly mixing Bi salt and Pb salt + one-step hydrothermal method", without needing complex pretreatment or post-treatment, and the reaction equipment is simple, and the reaction condition is mild. The PbBiO2OH prepared by the application is regulated through double-metal cooperation and OH intercalation, not only expands the high-selectivity potential range to a wide potential range of 0.85V~‑1.55V (vs. RHE), but also realizes 220-hour high-current density stable operation, and solves the core contradiction that the selectivity and stability of a single-metal Bi-based catalyst cannot be compatible.

Description

Technical Field

[0001] This invention relates to the field of electrocatalytic carbon dioxide reduction technology, and in particular to a method for preparing PbBiO2OH and its application in the electrocatalytic synthesis of formic acid from carbon dioxide. Background Technology

[0002] The information disclosed in the background section of this invention is intended only to enhance the understanding of the overall background of the invention and is not necessarily to be construed as an admission or in any way implying that such information constitutes prior art known to those skilled in the art.

[0003] Utilizing the CO2 reduction reaction (CO2RR) process to convert it into high-value-added products is a reasonable strategy that achieves two goals at once, simultaneously mitigating climate change and the energy crisis.

[0004] The conversion of CO2 to formic acid involves only the transfer of two electrons, making the reaction relatively easy to occur. Formic acid, as an important chemical intermediate, has a wide range of applications in energy, pharmaceuticals, and food processing. However, the electrocatalytic reduction of CO2 faces several challenges, including high overpotential, low conversion rate, poor catalyst stability and low selectivity, unclear catalyst structure, and ambiguous catalytic mechanism, all of which limit its development. Summary of the Invention

[0005] In view of this, the present invention provides a method for preparing PbBiO2OH and its application in the electrocatalytic synthesis of formic acid from carbon dioxide. The present invention prepares PbBiO2OH via a one-step hydrothermal method, which exhibits excellent selectivity and stability for the electrocatalytic reduction of carbon dioxide to formic acid. It demonstrates superior performance, and the preparation method is simple, with low raw material costs and high catalyst yield, making it suitable for industrial applications.

[0006] To achieve the above objectives, the present invention is implemented through the following technical solution: In a first aspect, the present invention provides a method for preparing PbBiO2OH, comprising the following steps: Using acetic acid, ammonia, and water as solvents, bismuth and lead salts were added to the solvents, ultrasonically dispersed, and subjected to hydrothermal reaction. The resulting product was then washed with water, centrifuged, dried, and ground to obtain the PbBiO2OH catalyst.

[0007] This invention uses a "direct mixing of Bi salt and Pb salt + one-step hydrothermal method" to prepare PbBiO2OH, which requires no complicated pretreatment or posttreatment, and the reaction equipment is simple and the reaction conditions are mild.

[0008] Furthermore, the molar ratio of bismuth salt to lead salt is 1.5-2.5:1. The molar ratio of bismuth salt to lead salt has a significant impact on material properties. Experiments have shown that PbBiO2OH prepared with a molar ratio of 1.5-2.5:1 exhibits better performance, displaying the lowest gaseous Faraday efficiency across the entire test potential range. Preferably, the molar ratio of bismuth salt to lead salt is 2:1.

[0009] Furthermore, the bismuth salt is Bi2(NO3)2·5H2O; the lead salt is Pb(NO3)2.

[0010] Furthermore, the volume ratio of acetic acid, ammonia, and water is 1-3:1:5-7. The concentration of ammonia is 25-28%.

[0011] Furthermore, the hydrothermal reaction temperature is 170-190 ℃; the hydrothermal reaction time is 10-14 h. The hydrothermal reaction temperature and time affect the morphology and crystallinity of PbBiO2OH. Strict control of the hydrothermal reaction temperature and time is beneficial for synthesizing PbBiO2OH with good morphology and crystallinity.

[0012] Furthermore, after the hydrothermal reaction is complete, the mixture is cooled, washed with water, centrifuged, and dried.

[0013] Furthermore, the drying temperature is 55-70 ℃.

[0014] In a second aspect, the present invention provides a working electrode comprising PbBiO2OH prepared by the preparation method described in the first aspect.

[0015] Thirdly, the present invention provides a method for preparing a working electrode, comprising the following steps: The PbBiO2OH prepared by the method described in the first aspect, deionized water, ethanol and 5% Nafion solution are mixed, ultrasonicated, drop-coated onto carbon paper, and dried to obtain the working electrode.

[0016] Furthermore, the volume ratio of PbBiO2OH, deionized water, ethanol, and 5% Nafion solution is 5 mg: 470-490 μL: 470-490 μL: 20-40 μL.

[0017] Furthermore, the ultrasound time is 25-35 minutes.

[0018] Furthermore, the PbBiO2OH loading on the working electrode was 0.8-1.5 mg / cm³. -2 .

[0019] Fourthly, the present invention provides the application of PbBiO2OH prepared by the preparation method described in the first aspect or the working electrode described in the second aspect in the electrocatalytic synthesis of formic acid from carbon dioxide.

[0020] Traditional Bi-based catalysts (such as bismuth oxycarbonate) can only maintain about 85% formic acid selectivity within a narrow potential window, and are prone to structural reconstruction, dissolution, and deactivation at high current densities. The PbBiO2OH provided by this invention achieves deactivation through bimetallic synergy and OH... Intercalation control not only extends the high-selectivity potential range to a wide potential range of 0.85V to -1.55V (vs. RHE), but also achieves 220 hours of stable operation at high current density.

[0021] Compared with the prior art, the present invention has achieved the following beneficial effects: This invention uses non-precious metals Pb and Bi as raw materials, which are abundant and inexpensive, thus reducing raw material costs. The PbBiO2OH prepared by this invention employs a "direct mixing of Bi and Pb salts + one-step hydrothermal method," requiring no complex pretreatment or post-treatment, using simple reaction equipment and mild reaction conditions. Compared with most existing nanomaterial catalyst preparation methods, this invention achieves a more considerable production yield. The PbBiO2OH prepared by this invention achieves a high yield through bimetallic synergy and OH... Intercalation regulation not only extended the potential range of high selectivity to a wide range of 0.85V to -1.55V (vs. RHE), but also achieved stable operation at high current density for 220 hours, solving the core contradiction of "selectivity and stability cannot be achieved simultaneously" in single-metal Bi-based catalysts. Attached Figure Description

[0022] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0023] Figure 1 These are SEM images of the materials prepared in Example 1 of this invention, where (a) is BiPb, (b) is PbBiO2OH, and (c) is Bi3Pb. Figure 2 These are characterization diagrams of the PbBiO2OH catalyst prepared in Example 1 of the present invention, wherein (a) is a TEM image, (b) is an HRTEM image, and (c) is a SAED image; Figure 3 These are XPS spectra of Bi2O2CO3 and PbBiO2OH, where (a) is the total XPS spectrum of Bi2O2CO3 and PbBiO2OH, (b) is the Bi 4f high-resolution XPS spectrum of Bi2O2CO3 and PbBiO2OH, and (c) is the Pb 4f high-resolution XPS spectrum of PbBiO2OH. Figure 4 This is the XRD refinement result of PbBiO2OH; Figure 5 This is a comparison chart of the gaseous product Faradaic efficiencies of catalysts with different Bi / Pb ratios; Figure 6 These are the LSV curves of Bi2O2CO3 and PbBiO2OH under Ar and CO2 conditions; Figure 7 This is a stability graph of the PbBiO2OH catalyst. Detailed Implementation

[0024] It should be noted that the following detailed descriptions are exemplary and intended to provide further illustration of the invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0025] The technical solution of the present invention will be further described below with reference to specific embodiments.

[0026] Example 1 Catalyst for synthesizing PbBiO2OH: 0.4416 g of Pb(NO3)2 and 1.2935 g of Bi(NO3)3·5H2O were dispersed in a mixed solution of 4 mL deionized water, 2 mL acetic acid, and 12 mL ammonia. After ultrasonic dispersion, the mixture was stirred at room temperature for 30 minutes, then transferred to a 50 mL high-pressure reactor and reacted at 180 °C for 12 hours. After cooling, the precipitate was collected by washing with water and centrifugation, dried in a 60 °C oven, and ground to obtain PbBiO2OH catalyst powder, with a final mass of 0.9 g.

[0027] When the molar ratio of Bi salt to Pb salt is 1:1 and 3:1, it is named BiPb and Bi3Pb, respectively. When the molar ratio is 2:1, it is named Bi2Pb, i.e., PbBiO2OH.

[0028] Figure 1 These are SEM images of the materials prepared in Example 1 of this invention, where (a) is BiPb, (b) is PbBiO2OH, and (c) is Bi3Pb. Figure 1 As shown, with the increase of Bi salt, the catalyst morphology exhibits a gradient evolution: from ultrathin defective nanosheets at low Bi content to regular nanosheets with moderate thickness at Bi:Pb=2:1, and finally forming a layered structure with obvious thickness under high Bi content conditions.

[0029] Figure 2 These are characterization images of the PbBiO2OH catalyst prepared in Example 1 of this invention, where (a) is a TEM image, (b) is an HRTEM image, and (c) is a SAED image. Figure 2As shown, the TEM image clearly shows that the PbBiO2OH sample exhibits a two-dimensional nanosheet morphology, and its geometric characteristics are in good agreement with the SEM observation results. Figure 2 a). For example Figure 2 As shown, transmission electron microscopy (TEM) clearly reveals that the PbBiO2OH sample has a typical two-dimensional nanosheet structure, which is consistent with the observation results of scanning electron microscopy (SEM). Figure 2 a). Based on this, the crystal microstructure was characterized in detail using high-resolution transmission electron microscopy (HRTEM). Figure 2 (b) The results showed that the (101) and (110) crystal plane fringes, matching the PbBiO2Cl standard phase (JCPDS No. 39-0802), were clearly distinguishable in the sample, with corresponding lattice spacings of 0.373 nm and 0.276 nm, respectively. Comparing these values ​​with the standard PbBiO2Cl crystal plane parameters ((101) plane 0.382 nm, (110) plane 0.281 nm), it was found that the prepared PbBiO2OH sample exhibited significant lattice shrinkage. To further verify this structural feature, selected area electron diffraction (SAED) tests were performed on the sample. Figure 2 c), the diffraction signals of the (101), (110) and (200) crystal planes belonging to the PbBiO2Cl phase can be clearly identified in the diffraction ring, and the measured values ​​of the interplanar spacing are all less than the standard values. This variation is highly consistent with the HRTEM lattice fringe measurement results, which fully confirms that the sample has the structural characteristics of lattice compression.

[0030] Figure 3 These are XPS spectra of Bi₂O₂CO₃ and PbBiO₂OH, where (a) is the overall XPS spectrum of Bi₂O₂CO₃ and PbBiO₂OH, (b) is the Bi₄f high-resolution XPS spectrum of Bi₂O₂CO₃ and PbBiO₂OH, and (c) is the Pb₄f high-resolution XPS spectrum of PbBiO₂OH. Among them, [the following is a partial translation of the original text, which is incomplete and requires further context]. Figure 3 The full spectrum of a shows that Pb, Bi, and O, three characteristic elements, can be clearly detected in the PbBiO2OH sample, confirming its chemical composition. The fine spectrum of Bi 4f (…) Figure 3 b) Further analysis revealed that PbBiO2OH exhibits a pair of typical characteristic peaks at positions 158.9 eV and 164.2 eV, which are attributed to Bi, respectively. 3+ Bi 4f 7 / 2 with Bi 4f 5 / 2The orbitals indicate that Bi exists in the system in the +3 valence state. Compared with the pure Bi₂O₂CO₃ sample, the binding energy of Bi in PbBiO₂OH shifts towards lower binding energies. This is likely due to the electronegativity difference between Pb (electronegativity 1.8) and Bi (electronegativity 2.0), which promotes electron transfer from Pb to Bi. Furthermore, as... Figure 3 As shown in c, the high-resolution energy spectrum of Pb 4f exhibits a pair of characteristic peaks at 138.2 eV and 142.9 eV, which correspond to Pb, respectively. 2+ Pb 4f 7 / 2 and Pb 4f 5 / 2 The orbital indicates that Pb exists in the structure in the form of +2 valence.

[0031] Figure 4 This is the XRD refinement result of PbBiO2OH. Rietveld refinement is a common method for verifying the reliability of crystal structure analysis. For elementally substituted or doped crystal materials, structure refinement based on isomorphic models can simultaneously obtain the crystallographic parameters of the doped system and complete multiphase quantitative analysis. For example... Figure 4 As shown, this invention uses this method to analyze XRD patterns, performs full-spectrum fitting with FullProf software, selects PbBiO2Cl (JCPDS No. 39-0802) with space group I4 / mmm as the initial model, and obtains key structural parameters such as lattice parameters, atomic occupancy and temperature factor through iterative optimization. The initial PbBiO2Cl model is then corrected and finally determined to be the PbBiO2OH crystal structure.

[0032] Example 2 This embodiment provides a method for preparing a working electrode: Take 5 mg of PbBiO2OH catalyst, 485 μL of deionized water, 485 μL of ethanol, and 30 μL of 5% Nafion solution, mix them, and sonicate for 30 min to obtain catalyst ink. Take 1×1 cm -2 One sheet of YLS 30T carbon paper was coated with 200 μL of ink evenly on its front side and then baked dry to obtain a catalyst loading of 1 mg / cm³. -2 The working electrode.

[0033] Performance testing (1) Product Faraday efficiency test In a three-electrode H-type electrolytic cell, a platinum sheet was used as the counter electrode, Ag / AgCl as the reference electrode, and 0.5M KHCO3 as the electrolyte. The Faradaic efficiency of the catalyst products was tested using a chronopotentiometric method, and the products were analyzed at different potentials. All gaseous products were detected by gas chromatography, and liquid products were analyzed using liquid chromatography. The specific formula for calculating the Faradaic efficiency is as follows:

[0034] in, This refers to the CO2 flow rate, z refers to the amount of charge transferred to produce a specific gaseous product (z=2 for H2 and CO), and F is the Faraday constant (96485 C·mol⁻¹). -1 P0 is the atmospheric pressure of the surrounding environment (101.325 Pa), V is the volume of a specific gas detected by the gas phase, i is the total current measured by the electrochemical workstation, and R is the gas constant (8.314 J mol). - 1 K -1 T0 is the temperature during the test (298.15K).

[0035]

[0036] Where V is the volume of the catholyte, and C is the HCOO measured by NMR. - The concentration of is , z is the number of electrons transferred to produce a specific liquid product (z=2 for HCOOH), and F is the Faraday constant (96485 C·mol⁻¹). -1 Q represents the total amount of charge consumed during the electrolysis process.

[0037] The specific results are as follows: Figure 5 This is a comparison chart of the Faradaic efficiencies of gaseous products for catalysts with different Bi / Pb ratios. (See attached chart.) Figure 5 As shown, when the initial feed ratio of Bi:Pb is 2:1 (PbBiO2OH), the overall Faraday efficiency is the best. In particular, in the wide potential range of -0.85V to -1.55V, the Faraday efficiency of the gas is always below 10%, showing excellent performance.

[0038] (2) Electrocatalytic activity test of the product Figure 6 These are the LSV curves of Bi₂O₂CO₃ and PbBiO₂OH under Ar and CO₂ conditions. In a three-electrode H-type electrolytic cell, using a platinum sheet as the counter electrode, Ag / AgCl as the reference electrode, and 0.5 M KHCO₃ as the electrolyte, the comparison between PbBiO₂OH and undoped pure bismuth oxycarbonate is shown. Figure 6 As shown, when a certain voltage is applied, the current density in the CO2 atmosphere is always greater than that in the Ar atmosphere, indicating that the material has a certain electrocatalytic CO2 reduction capability. Furthermore, in a carbon dioxide atmosphere, compared to Bi2O2CO3 (pure bismuth oxycarbonate), PbBiO2OH exhibits a lower onset potential and a higher current density, suggesting that the incorporation of Pb enhances the material's electrocatalytic CO2 reduction performance.

[0039] (3) Stability test of catalyst Figure 7 This is a stability graph of the PbBiO2OH catalyst. The stability of PbBiO2OH was tested in a MEA membrane electrode assembly using commercially available titanium fiber paper coated with oxydioxide as the counter electrode and 1M KOH as the electrolyte. Figure 7 As shown, at 300mA·cm -2 The material operates stably for more than 180 hours at a current density, and the formic acid Faraday efficiency remains above 90%, demonstrating the material's excellent structural stability and its potential for industrial applications.

[0040] 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 method for preparing PbBiO2OH, characterized in that, Includes the following steps: Using acetic acid, ammonia, and water as solvents, bismuth and lead salts were added to the solvents, ultrasonically dispersed, and subjected to hydrothermal reaction. The resulting product was then washed with water, centrifuged, dried, and ground to obtain the PbBiO2OH catalyst.

2. The preparation method according to claim 1, characterized in that, The molar ratio of bismuth salt to lead salt is 1.5-2.5:

1.

3. The preparation method according to claim 2, characterized in that, The bismuth salt is Bi2(NO3)2·5H2O; the lead salt is Pb(NO3)2.

4. The preparation method according to claim 1, characterized in that, The volume ratio of acetic acid, ammonia, and water is 1-3:1:5-7.

5. The preparation method according to claim 1, characterized in that, The hydrothermal reaction temperature is 170-190 ℃; the hydrothermal reaction time is 10-14 h.

6. A working electrode, characterized in that, The working electrode comprises PbBiO2OH prepared by the preparation method of claim 1.

7. A method for preparing a working electrode, characterized in that, The working electrode is obtained by mixing PbBiO2OH, deionized water, ethanol and 5% Nafion solution prepared by the preparation method described in claim 1, sonicating, drop-coating onto carbon paper, and baking dry.

8. The preparation method according to claim 7, characterized in that, The volume ratio of PbBiO2OH, deionized water, ethanol, and 5% Nafion solution is 5 mg: 470-490 μL: 470-490 μL: 20-40 μL.

9. The preparation method according to claim 7, characterized in that, Ultrasonic time 25-35 min; PbBiO2OH loading on working electrode 0.8-1.5 mg / cm2 -2 .

10. The application of the PbBiO2OH prepared by the preparation method according to claim 1 or the working electrode according to claim 6 in the electrocatalytic synthesis of formic acid from carbon dioxide.

Images