Preparation method of a rare earth tin-based pyrochlore metal oxide and application thereof in electrocatalytic reduction of carbon dioxide

Abstract

This invention discloses a class of rare-earth tin-based pyrochlore metal oxides, their preparation methods, and applications, belonging to the field of electrocatalyst technology. Addressing the limitations of traditional tin-based catalysts in the intrinsic activity, low current density, and low selectivity of the electrocatalytic reduction of carbon dioxide to formate, this invention provides a class of rare-earth tin-based pyrochlore metal oxides with the general structural formula A₂B₂O₇, where A is selected from a rare-earth metal ion and B is selected from Sn ions. This invention anchors the Sn active component into the rare-earth pyrochlore lattice via a one-step hydrothermal method, utilizing the A-O-Sn electronic synergistic effect between rare-earth elements and Sn to achieve precise control of the electronic structure and coordination environment of the Sn site, optimizing the key intermediate *OCHO, thereby significantly improving selectivity and split current. The preparation method of the rare-earth tin-based pyrochlore metal oxides in this invention is simple to operate, easy to mass-produce, exhibits excellent CO₂ electroreduction performance, and has good prospects for industrial application.

Description

Technical Field

[0001] This invention relates to the field of electrocatalyst technology, specifically to a method for preparing a class of rare earth tin-based pyrochlore metal oxides and their application in the electrocatalytic reduction of carbon dioxide (CO2), particularly suitable for the highly selective production of formate. Background Technology

[0002] With the increasing severity of global climate change and the growing challenges of fossil fuel shortages, electrocatalytic carbon dioxide (CO2) reduction technology driven by renewable electricity not only provides a highly promising technological path for reducing carbon emissions but also opens up new avenues for the efficient conversion of intermittent electrical energy into high-value-added chemicals and fuels. Among the many potential products of electrocatalytic CO2 reduction, formates have attracted considerable attention due to their broad application prospects. In terms of market demand, the global annual demand for formates has reached millions of tons and continues to expand. More importantly, electrocatalytic carbon dioxide to formic acid technology demonstrates significant economic feasibility; this product pathway can achieve the highest profit per mole of electrons and has excellent energy output value (approximately US$0.43 / kWh), making it one of the most commercially promising target products for electrocatalytic carbon reduction. To date, tin (Sn)-based catalysts have been recognized as ideal candidate catalysts for formate production due to their abundant resources, low cost, and environmental friendliness. However, the kinetic bottlenecks caused by their intrinsic properties remain significant. The adsorption strength of Sn on *OCHO is not optimal, resulting in a high reaction energy barrier and limited reaction activity, manifested as low current density and low selectivity, which makes it difficult to meet the needs of industrial applications.

[0003] Therefore, to solve the above problems, it is urgent to start by regulating the electronic structure and coordination environment of Sn-based catalysts, and redesign electrocatalysts through a synergistic optimization strategy to break through this bottleneck. Summary of the Invention

[0004] To address the aforementioned issues, this invention synthesizes a class of rare-earth tin-based pyrochlore metal oxides. This material is anchored within the rare-earth pyrochlore lattice by the Sn active component, utilizing the electronic synergistic effect between rare-earth elements and Sn to achieve precise control over the electronic structure and coordination environment of Sn sites. Furthermore, it features a simple preparation process, low cost, and low energy consumption, demonstrating its potential application value as a highly efficient CO2 reduction electrocatalyst.

[0005] To achieve the above-mentioned objective, the first aspect of the present invention provides:

[0006] A class of rare earth tin-based pyrochlore metal oxides, characterized by having the general structural formula A2B2O7, wherein A is a rare earth metal element and the B site is composed of Sn element.

[0007] In one embodiment, element A is preferably La, Ce, Pr, Nd, or Sm.

[0008] In one embodiment, the rare earth tin-based pyrochlore metal oxide is: La2Sn2O7, Ce2Sn2O7, Pr2Sn2O7, Nd2Sn2O7, or Sm2Sn2O7.

[0009] A second aspect of the present invention provides:

[0010] The above-mentioned rare earth tin-based pyrochlore metal oxides are prepared by methods such as solid-state reaction, sol-gel method, co-precipitation method, combustion method, hydrothermal method or microwave method according to the stoichiometric ratio.

[0011] In one embodiment, it is prepared by a hydrothermal reaction method.

[0012] In one embodiment, the hydrothermal method includes the following steps: 1) mixing potassium stannate trihydrate and the desired rare earth nitrate, adding deionized water and sonicating; 2) then slowly adding potassium hydroxide solution to the solution prepared in step 1); 3) transferring the mixture obtained in 2) to a polytetrafluoroethylene-lined high-pressure reactor for heating, and then naturally cooling to room temperature; (4) separating and washing the product obtained in step 3), drying and grinding to obtain a rare earth tin-based pyrochlore electrocatalyst.

[0013] In one embodiment, in step (1), the mass of potassium stannate trihydrate is 485~490 mg, the mass of rare earth nitrate is 860~890 mg, and the volume of deionized water is 50~80 mL.

[0014] In one embodiment, the concentration of potassium hydroxide solution in step (2) is 0.1 M to 0.2 M, and the pH of the resulting mixture solution is 12 to 14.

[0015] In one embodiment, the heating temperature of the mixture in step (3) is 180~200°C and the heating time is 22~26h.

[0016] In one embodiment, step (4) involves centrifuging at 7000-9000 rpm for 10 minutes. Then, anhydrous ethanol and deionized water are added for washing 2-3 times, and finally, the mixture is dried in a vacuum drying oven at 60 ℃ for 10-12 hours.

[0017] A third aspect of the invention provides:

[0018] Based on the above-mentioned application of rare earth tin-based pyrochlore metal oxide catalysts in the efficient electrocatalytic reduction of carbon dioxide to produce formate.

[0019] Beneficial effects

[0020] This invention addresses the limitations of traditional Sn-based catalysts in electrocatalytic CO2 reduction reactions due to the single electronic structure of active sites and the deviation of adsorption strength for the key intermediate OCHO from the optimal range. By orderly anchoring the Sn active component within a rare-earth pyrochlore (A₂B₂O₇) lattice, and utilizing the AO-Sn electronic synergy between rare-earth elements (La, Ce, Pr, Nd, Sm) at the A-site and Sn at the B-site, precise control over the electronic structure and coordination environment of the Sn sites is achieved. This strategy effectively optimizes the adsorption energy of the OCHO intermediate, lowers the reaction energy barrier, and thus significantly improves reaction activity while maintaining high selectivity. This invention employs a one-step hydrothermal synthesis method, which is mild, simple to operate, and low-cost, making it suitable for large-scale production. By controlling the types of rare-earth elements, this invention achieves systematic optimization of the electronic structure of Sn sites, providing a new approach for the design of high-performance electrocatalysts. Attached Figure Description

[0021] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. The drawings are provided for reference and illustration only and are not intended to limit the present invention.

[0022] Figure 1 This is a schematic diagram of the crystal structure of the rare earth tin-based pyrochlore metal oxide provided for this invention.

[0023] Figure 2 This is an X-ray diffraction (XRD) curve of the La2Sn2O7 catalyst in Example 1 of the present invention.

[0024] Figure 3 This is a Faraday efficiency distribution diagram of the products at various potentials under the electrocatalytic reduction of carbon dioxide by the La2Sn2O7 catalyst in Example 1 of the present invention.

[0025] Figure 4 The formate fractional currents at various potentials of the La2Sn2O7 catalyst in Example 1 of this invention are shown.

[0026] Figure 5 This is an X-ray diffraction (XRD) curve of the Ce2Sn2O7 catalyst in Example 2 of the present invention.

[0027] Figure 6 This is a Faraday efficiency distribution diagram of the products at various potentials under the electrocatalytic reduction of carbon dioxide by the Ce2Sn2O7 catalyst in Example 2 of the present invention.

[0028] Figure 7 The formate fractional currents at various potentials of the Ce2Sn2O7 catalyst in Example 2 of this invention are shown.

[0029] Figure 8This is an X-ray diffraction (XRD) curve of the Pr2Sn2O7 catalyst in Example 3 of the present invention.

[0030] Figure 9 This is a Faraday efficiency distribution diagram of the products at various potentials under the electrocatalytic reduction of carbon dioxide by the Pr2Sn2O7 catalyst in Example 3 of the present invention.

[0031] Figure 10 The formate fractional currents at various potentials of the Pr2Sn2O7 catalyst in Example 3 of this invention are shown.

[0032] Figure 11 This is an X-ray diffraction (XRD) curve of the Nd2Sn2O7 catalyst in Example 4 of the present invention.

[0033] Figure 12 This is a Faraday efficiency distribution diagram of the products at various potentials under the electrocatalytic reduction of carbon dioxide by the Nd2Sn2O7 catalyst in Example 4 of the present invention.

[0034] Figure 13 The formate fractional currents at various potentials of the Nd2Sn2O7 catalyst in Example 4 of this invention are shown.

[0035] Figure 14 This is an X-ray diffraction (XRD) curve of the Sm2Sn2O7 catalyst in Example 5 of the present invention.

[0036] Figure 15 This is a Faraday efficiency distribution diagram of the products at various potentials under the electrocatalytic reduction of carbon dioxide by the Sm2Sn2O7 catalyst in Example 5 of the present invention.

[0037] Figure 16 The formate fractional currents at various potentials of the Sm2Sn2O7 catalyst in Example 5 of this invention are shown.

[0038] Figure 17 The image shows the X-ray diffraction (XRD) curve of the SnO2 catalyst in Comparative Example 1.

[0039] Figure 18 This is a diagram showing the Faradaic efficiency distribution of the products at various potentials under the electrocatalytic reduction of carbon dioxide using the SnO2 catalyst in Comparative Example 1.

[0040] Figure 19 The formate partial current is shown at various potentials of the SnO2 catalyst in Comparative Example 1.

[0041] Figure 20 This is a comparison of the Faraday efficiency of the simple metal oxide SnO2 catalyst, rare earth tin-based pyrochlore metal oxide Ce2Sn2O7 catalyst, and Nd2Sn2O7 catalyst prepared in Comparative Example 1 for the electrocatalytic reduction of carbon dioxide to formate.

[0042] Figure 21 The figure shows a comparison of the partial currents of the electrocatalytic reduction of formate by carbon dioxide using the simple metal oxide SnO2 catalyst, rare earth tin-based pyrochlore metal oxide Ce2Sn2O7 catalyst, and Nd2Sn2O7 catalyst prepared in Comparative Example 1.

[0043] Figure 22 The values ​​are the Faraday efficiency and partial current of the rare earth tin-based pyrochlore metal oxide Ce2Sn2O7 catalyst and Nd2Sn2O7 catalyst prepared in Comparative Example 1 for the electrocatalytic reduction of formate by carbon dioxide. Detailed Implementation

[0044] To make the objectives, technical solutions, and effects of this invention clearer and more explicit, the following examples provide a more detailed description of the invention. It should be noted that the specific embodiments described herein are merely illustrative and not intended to limit the scope of the invention.

[0045] The intrinsic characteristics of Sn-based catalysts still result in significant kinetic bottlenecks, manifested in low current density and low selectivity, making it difficult to meet the demands of industrial applications. For example... Figure 1 As shown, the rare-earth tin-based pyrochlore metal oxide of this invention anchors the Sn active component within the rare-earth pyrochlore lattice. Utilizing the electronic synergistic effect between rare-earth elements and Sn, it achieves precise control over the electronic structure and coordination environment of the Sn sites. This is expected to solve the inherent problems of Sn-based catalysts in CO2 electrocatalytic reduction and can significantly improve the electrocatalytic performance of CO2 reduction. Furthermore, it features a simple preparation process, low cost, and low energy consumption, demonstrating its potential application value as a highly efficient CO2 reduction electrocatalytic material.

[0046] This invention provides a class of rare earth tin-based pyrochlore metal oxides, characterized in that their general structural formula is A2B2O7, wherein A is a rare earth metal element and the B position is composed of Sn element.

[0047] In one embodiment, element A is preferably La, Ce, Pr, Nd, or Sm.

[0048] In one embodiment, the rare earth tin-based pyrochlore metal oxide is: La2Sn2O7, Ce2Sn2O7, Pr2Sn2O7, Nd2Sn2O7, or Sm2Sn2O7.

[0049] The method for preparing rare earth tin-based pyrochlore metal oxides provided by this invention involves preparing the oxides according to stoichiometric ratios via solid-state reaction, sol-gel method, co-precipitation method, combustion method, hydrothermal method, or microwave method.

[0050] In one embodiment, it is prepared by a hydrothermal reaction method.

[0051] In one embodiment, the hydrothermal method includes the following steps: mixing potassium stannate trihydrate and the desired rare earth nitrate in stoichiometric proportions, adding deionized water and sonicating; then slowly adding 0.1 M to 0.2 M potassium hydroxide solution dropwise to the prepared solution to adjust the pH of the mixture to 12 to 14; transferring the resulting mixture to a polytetrafluoroethylene-lined autoclave and heating at 180 to 200°C for 22 to 26 hours, then naturally cooling to room temperature; washing 2 to 3 times with anhydrous ethanol and deionized water respectively; and finally drying in a vacuum drying oven at 50 to 60°C for 10 to 12 hours.

[0052] The process of preparing an electrode using the catalyst prepared in this invention and evaluating the catalytic performance of the electrode for carbon dioxide reduction is as follows:

[0053] a) Electrode preparation: 10-20 mg of rare earth tin-based pyrochlore metal oxide catalyst and 4-6 mg of carbon black were dispersed in 0.5-1 mL of isopropanol, 0.5-1 mL of deionized water, and an appropriate amount of Nafion (5% by mass) solution to prepare a slurry. The dispersion was then ultrasonically treated for 20-30 minutes. Ink was then uniformly sprayed onto the surface of the carbon paper gas diffusion layer to form the working electrode, which was then dried in a vacuum oven at 50-60 ℃ for 6 h for later use.

[0054] b) Construction of the flow cell reactor: The counter electrode is a Pt foil, and the reference electrode is Ag / AgCl, used for calibrating the counter electrode potential. An anion exchange membrane is used to connect the working electrode (1 × 2.5 cm²). 2 The actual reaction area is 0.5 × 2 cm. 2 The electrode was separated from the counter electrode. All tests used high-purity CO2 (99.999%), with a flow rate of 20–30 sccm and an electrolyte of 1 M KOH (pH = 14 ± 0.2). All potential values ​​were adjusted to the RHE reference potential according to the formula E(RHE) = E(Ag / AgCl) + 0.059 × pH + 0.198.

[0055] c) Product Detection: Each catalyst was electrolyzed at its corresponding potential for 30 min under a CO2 atmosphere. Gas products were analyzed using online gas chromatography (GC), with argon as the carrier gas. Quantification of gaseous products was performed by obtaining a standard curve using a mixed gas while quantifying hydrogen with a TCD detector, and by quantifying carbon monoxide with an FID detector. A steady-flow bottle was used to filter and dehumidify the gas at the chromatographic front end, and the carbon dioxide flow rate was controlled by a gas flow quality controller. Samples were taken continuously at 10-minute intervals until two consecutive measurements showed consistent product distribution. Data from the final sampling point were then used for catalytic performance evaluation. Electrolytes were collected after the reaction and subsequently quantitatively analyzed by high-performance liquid chromatography (HPLC) for the formate.

[0056] To make the objectives, technical solutions, and effects of this invention clearer and more explicit, the following examples provide a more detailed description of the invention. It should be noted that the specific embodiments described herein are merely illustrative and not intended to limit the scope of the invention.

[0057] Example 1: Preparation of La2Sn2O7 catalyst and evaluation of its electrocatalytic CO2 reduction performance.

[0058] Preparation of La₂Sn₂O₇ catalyst. 489.8 mg of potassium stannate trihydrate and 866 mg of lanthanum nitrate hexahydrate were added to 50 mL of deionized water and sonicated for 10 min. Then, 0.2 M potassium hydroxide solution was slowly added dropwise to the above solution to maintain the pH at approximately 12. The resulting mixture was then transferred to a 100 mL PTFE-lined autoclave and heated at 180°C for 24 h, followed by natural cooling to room temperature. Finally, the mixture was washed 2–3 times with anhydrous ethanol and deionized water at a centrifugation speed of 7000–9000 rpm. The washed material was then transferred to a 60 °C vacuum drying oven and dried for 10–12 h, followed by grinding to obtain the rare-earth tin-based La₂Sn₂O₇ catalyst. Figure 2 The X-ray diffraction (XRD) curves shown indicate that La2Sn2O7 forms a pyrochlore cubic crystal system.

[0059] Construction of the flow cell reactor. A Pt foil was used as the counter electrode, and an Ag / AgCl was used as the reference electrode for calibrating the counter electrode potential. An anion exchange membrane was used to connect the working electrode (1 × 2.5 cm⁻¹). 2 The actual reaction area is 0.5 × 2 cm. 2The electrode was separated from the counter electrode. All tests used high-purity CO2 (99.999%), with a flow rate of 30 sccm and an electrolyte of 1 M KOH (pH=14±0.2). All potential values ​​were adjusted to the RHE reference potential according to the formula E(RHE) = E(Ag / AgCl) + 0.059 × pH + 0.198.

[0060] Performance evaluation of La₂Sn₂O₇ catalyst for CO₂ reduction. La₂Sn₂O₇ was electrolyzed at the appropriate potential for 30 min under a CO₂ atmosphere. Gas products were analyzed using online gas chromatography with argon as the carrier gas. Quantification of gaseous products was performed by obtaining a standard curve using a mixed gas while simultaneously performing quantitative analysis of hydrogen with a TCD detector, and quantitative analysis of carbon monoxide using an FID detector. A steady-flow bottle was used to filter and dehumidify the gas at the chromatographic front end, and the carbon dioxide flow rate was controlled by a gas flow mass controller. Continuous sampling was performed at 10-minute intervals until two consecutive measurements showed consistent product distribution. Data from the final sampling point were then used for catalytic performance evaluation. Electrolytes were collected after the reaction and subsequently quantitatively analyzed by high-performance liquid chromatography (HPLC) for formate. Figure 3 The product distribution of La2Sn2O7 for the electrocatalytic reduction of carbon dioxide at different voltages is shown. La2Sn2O7 exhibits the highest formate selectivity, approximately 53.5%, at -1.0 V (vs. RHE). Figure 4 It demonstrated a formate partial current of 35.9 mA cm⁻¹. -2 . Figure 22 The values ​​are the Faraday efficiency and partial current of the rare earth tin-based pyrochlore metal oxide Ce2Sn2O7 catalyst and Nd2Sn2O7 catalyst prepared in Comparative Example 1 for the electrocatalytic reduction of formate by carbon dioxide.

[0061] Example 2: Preparation of Ce2Sn2O7 catalyst and evaluation of its electrocatalytic CO2 reduction performance.

[0062] Preparation of Ce₂Sn₂O₇ catalyst. 489.8 mg of potassium stannate trihydrate and 868.4 mg of cerium nitrate hexahydrate were added to 50 mL of deionized water and sonicated for 10 min. Then, 0.2 M potassium hydroxide solution was slowly added dropwise to the above solution to maintain the pH at approximately 12. The resulting mixture was then transferred to a 100 mL PTFE-lined autoclave and heated at 180°C for 24 h, followed by natural cooling to room temperature. Finally, the mixture was washed 2–3 times with anhydrous ethanol and deionized water at a centrifugation speed of 7000–9000 rpm. The washed material was then transferred to a 60 °C vacuum drying oven and dried for 10–12 h, followed by grinding to obtain the rare earth tin-based Ce₂Sn₂O₇ catalyst. Figure 5The X-ray diffraction (XRD) curves shown indicate that Ce2Sn2O7 forms a pyrochlore cubic crystal system.

[0063] Construction of the flow cell reactor. A Pt foil was used as the counter electrode, and an Ag / AgCl was used as the reference electrode for calibrating the counter electrode potential. An anion exchange membrane was used to connect the working electrode (1 × 2.5 cm⁻¹). 2 The actual reaction area is 0.5 × 2 cm. 2 The electrode was separated from the counter electrode. All tests used high-purity CO2 (99.999%), with a flow rate of 30 sccm and an electrolyte of 1 M KOH (pH=14±0.2). All potential values ​​were adjusted to the RHE reference potential according to the formula E(RHE) = E(Ag / AgCl) + 0.059 × pH + 0.198.

[0064] Performance evaluation of Ce₂Sn₂O₇ catalyst for CO₂ reduction. Ce₂Sn₂O₇ was electrolyzed at the appropriate potential for 30 min under a CO₂ atmosphere. Gas products were analyzed using online gas chromatography with argon as the carrier gas. Quantification of gaseous products was performed by obtaining a standard curve using a mixed gas while quantifying hydrogen with a TCD detector, and by quantifying carbon monoxide with an FID detector. A steady-flow bottle was used to filter and dehumidify the gas at the chromatographic front end, and the carbon dioxide flow rate was controlled by a gas flow mass controller. Continuous sampling was performed at 10-minute intervals until two consecutive measurements showed consistent product distribution. Data from the final sampling point were then used for catalytic performance evaluation. Electrolytes were collected after the reaction and subsequently quantitatively analyzed by high-performance liquid chromatography (HPLC). Figure 6 The product distribution of the electrocatalytic reduction of carbon dioxide by Ce₂Sn₂O₇ at different voltages is shown. Figure 6 Ce2Sn2O7 exhibited excellent formate selectivity of approximately 90.4% at -1.2 V (vs. RHE). Figure 7 It demonstrated its industrial-grade formate partial current at 211.9 mA cm⁻¹. -2 .

[0065] Example 3: Preparation of Pr2Sn2O7 catalyst and evaluation of its electrocatalytic CO2 reduction performance.

[0066] Preparation of Pr₂Sn₂O₇ catalyst. 489.8 mg of potassium stannate trihydrate and 870 mg of praseodymium nitrate hexahydrate were added to 50 mL of deionized water and sonicated for 10 min. Then, 0.2 M potassium hydroxide solution was slowly added dropwise to the above solution to maintain the pH at approximately 12. Subsequently, the resulting mixture was transferred to a 100 mL polytetrafluoroethylene-lined autoclave and heated at 180°C for 24 h, then allowed to cool naturally to room temperature. Finally, the mixture was washed 2–3 times with anhydrous ethanol and deionized water at a centrifugation speed of 7000–9000 rpm. The washed material was then transferred to a 60 °C vacuum drying oven and dried for 10–12 h, followed by grinding to obtain the rare earth tin-based Pr₂Sn₂O₇ catalyst. Figure 8 The X-ray diffraction (XRD) curves shown indicate that Pr2Sn2O7 forms a pyrochlore cubic crystal system.

[0067] Construction of the flow cell reactor. A Pt foil was used as the counter electrode, and an Ag / AgCl was used as the reference electrode for calibrating the counter electrode potential. An anion exchange membrane was used to connect the working electrode (1 × 2.5 cm⁻¹). 2 The actual reaction area is 0.5 × 2 cm. 2 The electrode was separated from the counter electrode. All tests used high-purity CO2 (99.999%), with a flow rate of 30 sccm and an electrolyte of 1 M KOH (pH=14±0.2). All potential values ​​were adjusted to the RHE reference potential according to the formula E(RHE) = E(Ag / AgCl) + 0.059 × pH + 0.198.

[0068] Evaluation of the electrocatalytic CO2 reduction performance of Pr2Sn2O7 catalyst. Pr2Sn2O7 was electrolyzed at the appropriate potential for 30 min under a CO2 atmosphere. Gas products were analyzed using online gas chromatography with argon as the carrier gas. Quantification of gaseous products was performed by obtaining a standard curve using a mixed gas while simultaneously performing quantitative analysis of hydrogen with a TCD detector, and quantitative analysis of carbon monoxide using an FID detector. A steady-flow bottle was used to filter and dehumidify the gas at the chromatographic front end, and the carbon dioxide flow rate was controlled by a gas flow mass controller. Continuous sampling was performed at 10-minute intervals until two consecutive measurements showed consistent product distribution. Data from the final sampling point were then used for catalytic performance evaluation. Electrolytes were collected after the reaction and subsequently quantitatively analyzed by high-performance liquid chromatography (HPLC) for the formate. Figure 9 The product distribution of Pr₂Sn₂O₇ electrocatalyzed carbon dioxide reduction at different voltages. For example... Figure 9 Pr2Sn2O7 showed approximately 54.9% formate selectivity at -0.8 V (vs. RHE). Figure 10 It demonstrated a formate partial current of 51.8 mA cm⁻¹.-2 .

[0069] Example 4: Preparation of Nd2Sn2O7 catalyst and evaluation of its electrocatalytic CO2 reduction performance.

[0070] Preparation of Nd₂Sn₂O₇ catalyst. 489.8 mg of potassium stannate trihydrate and 876.7 mg of niobium nitrate hexahydrate were added to 50 mL of deionized water and sonicated for 10 min. Then, 0.2 M potassium hydroxide solution was slowly added dropwise to the above solution to maintain the pH at approximately 12. The resulting mixture was then transferred to a 100 mL PTFE-lined autoclave and heated at 180°C for 24 h, followed by natural cooling to room temperature. Finally, the mixture was washed 2–3 times with anhydrous ethanol and deionized water at a centrifugation speed of 7000–9000 rpm. The washed material was then transferred to a 60 °C vacuum drying oven and dried for 10–12 h, followed by grinding to obtain the rare earth tin-based Nd₂Sn₂O₇ catalyst. Figure 11 The X-ray diffraction (XRD) curves shown indicate that Nd2Sn2O7 forms a pyrochlore cubic crystal system.

[0071] Construction of the flow cell reactor. A Pt foil was used as the counter electrode, and an Ag / AgCl was used as the reference electrode for calibrating the counter electrode potential. An anion exchange membrane was used to connect the working electrode (1 × 2.5 cm⁻¹). 2 The actual reaction area is 0.5 × 2 cm. 2 The electrode was separated from the counter electrode. All tests used high-purity CO2 (99.999%), with a flow rate of 30 sccm and an electrolyte of 1 M KOH (pH=14±0.2). All potential values ​​were adjusted to the RHE reference potential according to the formula E(RHE) = E(Ag / AgCl) + 0.059 × pH + 0.198.

[0072] Evaluation of the electrocatalytic CO2 reduction performance of Nd₂Sn₂O₇ catalyst. Pr₂Sn₂O₇ was electrolyzed at the appropriate potential for 30 min under a CO₂ atmosphere. Gas products were analyzed using online gas chromatography with argon as the carrier gas. Quantification of gaseous products was performed by obtaining a standard curve using a mixed gas while simultaneously performing quantitative analysis of hydrogen with a TCD detector, and quantitative analysis of carbon monoxide using an FID detector. A steady-flow bottle was used to filter and dehumidify the gas at the chromatographic front end, and the carbon dioxide flow rate was controlled by a gas flow mass controller. Continuous sampling was performed at 10-minute intervals until two consecutive measurements showed consistent product distribution. Data from the final sampling point were then used for catalytic performance evaluation. Electrolytes were collected after the reaction and subsequently quantitatively analyzed by high-performance liquid chromatography (HPLC) for the formate. Figure 12The distribution of its carbon dioxide reduction products was shown. Nd2Sn2O7 exhibited a maximum formate selectivity of approximately 94.1% at -1.0 V (vs. RHE), demonstrating that the regulation of Sn-based pyrochlore by rare earth element Nd achieves excellent electrocatalytic carbon dioxide reduction performance. Figure 13 It demonstrated a formate partial current of 253.2 mA cm⁻¹. -2 .

[0073] Example 5: Preparation of Sm2Sn2O7 catalyst and evaluation of its electrocatalytic CO2 reduction performance.

[0074] Preparation of Sm₂Sn₂O₇ catalyst. 489.8 mg of potassium stannate trihydrate and 888.9 mg of samarium nitrate hexahydrate were dissolved in 50 mL of deionized water and sonicated for 10 min. Then, 0.2 M potassium hydroxide solution was slowly added dropwise to the above solution to maintain the pH at approximately 12. The resulting mixture was then transferred to a 100 mL PTFE-lined autoclave and heated at 180°C for 24 h, followed by natural cooling to room temperature. Finally, the mixture was washed 2–3 times with anhydrous ethanol and deionized water at a centrifugation speed of 7000–9000 rpm. The washed material was then transferred to a 60 °C vacuum drying oven and dried for 10–12 h, followed by grinding to obtain the rare earth tin-based Sm₂Sn₂O₇ catalyst. Figure 14 The X-ray diffraction (XRD) curves shown indicate that Sm2Sn2O7 forms a pyrochlore cubic crystal system.

[0075] Construction of the flow cell reactor. A Pt foil was used as the counter electrode, and an Ag / AgCl was used as the reference electrode for calibrating the counter electrode potential. An anion exchange membrane was used to connect the working electrode (1 × 2.5 cm⁻¹). 2 The actual reaction area is 0.5 × 2 cm. 2 The electrode was separated from the counter electrode. All tests used high-purity CO2 (99.999%), with a flow rate of 30 sccm and an electrolyte of 1 M KOH (pH=14±0.2). All potential values ​​were adjusted to the RHE reference potential according to the formula E(RHE) = E(Ag / AgCl) + 0.059 × pH + 0.198.

[0076] Performance evaluation of Sm₂Sn₂O₇ catalyst for CO₂ reduction. Sm₂Sn₂O₇ was electrolyzed at the appropriate potential for 30 min under a CO₂ atmosphere. Gas products were analyzed using online gas chromatography with argon as the carrier gas. Quantification of gaseous products was performed by obtaining a standard curve using a mixed gas while simultaneously performing quantitative analysis of hydrogen with a TCD detector, and quantitative analysis of carbon monoxide using an FID detector. A steady-flow bottle was used to filter and dehumidify the gas at the chromatographic front end, and the carbon dioxide flow rate was controlled by a gas flow mass controller. Continuous sampling was performed at 10-minute intervals until two consecutive measurements showed consistent product distribution. Data from the final sampling point were then used for catalytic performance evaluation. Electrolytes were collected after the reaction and subsequently quantitatively analyzed by high-performance liquid chromatography (HPLC) for formate. Figure 6 The product distribution of Sm₂Sn₂O₇ electrocatalytic carbon dioxide reduction at different voltages. For example... Figure 15 Sm2Sn2O7 showed approximately 82.3% formate selectivity at -1.0 V (vs. RHE). Figure 16 It demonstrated a formate partial current of 116.9 mA cm⁻¹. -2 .

[0077] Comparative Example 1: Preparation of a simple metal oxide SnO2 catalyst and evaluation of its electrocatalytic CO2 reduction performance.

[0078] Simple metal oxide SnO2 catalyst powder was synthesized via a hydrothermal method. 489.8 mg of potassium stannate trihydrate was dissolved in 50 mL of deionized water and sonicated for 10 min. Next, 0.2 M potassium hydroxide solution was slowly added dropwise to the solution to maintain the pH at approximately 12. The resulting mixture was then transferred to a 100 mL PTFE-lined autoclave and heated at 180°C for 24 h, followed by natural cooling to room temperature. Finally, the mixture was washed 2–3 times with anhydrous ethanol and deionized water at a centrifugation speed of 7000–9000 rpm. The washed material was then transferred to a 60 °C vacuum drying oven and dried for 10–12 h to obtain the desired SnO2 catalyst powder. Figure 17 The X-ray diffraction (XRD) curves shown indicate that SnO2 has formed a rutile crystal system.

[0079] Construction of the flow cell reactor. A Pt foil was used as the counter electrode, and an Ag / AgCl was used as the reference electrode for calibrating the counter electrode potential. An anion exchange membrane was used to connect the working electrode (1 × 2.5 cm⁻¹). 2 The actual reaction area is 0.5 × 2 cm. 2The electrode was separated from the counter electrode. All tests used high-purity CO2 (99.999%), with a flow rate of 30 sccm and an electrolyte of 1 M KOH (pH=14±0.2). All potential values ​​were adjusted to the RHE reference potential according to the formula E(RHE) = E(Ag / AgCl) + 0.059 × pH + 0.198.

[0080] Performance evaluation of Sm₂Sn₂O₇ catalyst for CO₂ reduction. Sm₂Sn₂O₇ was electrolyzed at the appropriate potential for 30 min under a CO₂ atmosphere. Gas products were analyzed using online gas chromatography with argon as the carrier gas. Quantification of gaseous products was performed by obtaining a standard curve using a mixed gas while simultaneously performing quantitative analysis of hydrogen with a TCD detector, and quantitative analysis of carbon monoxide using an FID detector. A steady-flow bottle was used to filter and dehumidify the gas at the chromatographic front end, and the carbon dioxide flow rate was controlled by a gas flow mass controller. Continuous sampling was performed at 10-minute intervals until two consecutive measurements showed consistent product distribution. Data from the final sampling point were then used for catalytic performance evaluation. Electrolytes were collected after the reaction and subsequently quantitatively analyzed by high-performance liquid chromatography (HPLC) for formate. Figure 18 The product distribution of SnO2 electrocatalyzed carbon dioxide reduction at different voltages is shown in the figure. SnO2 exhibits approximately 88.1% formate selectivity at -1.0 V (vs. RHE). Figure 19 It demonstrated a formate partial current of 53.1 mA cm⁻¹. -2 .

[0081] Figure 20 and Figure 21 The graph shows a comparison of the Faradaic efficiency and formate fractional current for the electrocatalytic reduction of carbon dioxide to formate by the simple metal oxide SnO2 catalyst and the rare earth tin-based pyrochlore metal oxides Ce2Sn2O7 and Nd2Sn2O7 catalysts prepared in Comparative Example 1. It can be seen that the rare earth tin-based pyrochlore metal oxides Ce2Sn2O7 and Nd2Sn2O7 catalysts exhibit higher Faradaic efficiencies (SnO2: 88.1%; Ce2Sn2O7: 90.4%; Nd2Sn2O7: 94.1%) and higher current densities (SnO2: 53.1 mA cm⁻¹) compared to the simple metal oxide SnO2 catalyst. -2 Ce2Sn2O7: 211.9 mA cm -2 Nd2Sn2O7: 253.2 mA cm -2 This indicates that rare earth tin-based pyrochlore metal oxides Ce2Sn2O7 and Nd2Sn2O7 catalysts have higher electrocatalytic carbon dioxide reduction activity compared with simple metal oxide SnO2 catalysts, demonstrating the superiority of the rare earth tin-based pyrochlore structure.

[0082] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements can be made without departing from the principle of the present invention, and these improvements should also be considered within the scope of protection of the present invention.

Claims

1. A class of rare earth tin-based pyrochlore metal oxides, characterized in that, Its general structural formula is A2B2O7, where A is a rare earth metal element and the B position is composed of Sn element.

2. The rare earth tin-based pyrochlore metal oxide according to claim 1, characterized in that, Element A includes La, Ce, Pr, Nd, or Sm.

3. The rare earth tin-based pyrochlore metal oxide according to claim 1, characterized in that, The formulas for rare earth tin-based pyrochlore metal oxides are: La2Sn2O7, Ce2Sn2O7, Pr2Sn2O7, Nd2Sn2O7, and Sm2Sn2O7.

4. The method for preparing the rare earth tin-based pyrochlore metal oxide according to any one of claims 1 to 3, characterized in that, It is prepared according to the stoichiometric ratio by solid-phase reaction method, sol-gel method, co-precipitation method, combustion method, hydrothermal method or microwave method.

5. The method for preparing rare earth tin-based pyrochlore metal oxide according to claim 4, characterized in that, The preparation steps of the hydrothermal method include: dissolving the nitrate of the A-site element and the potassium stannate of the B-site element in deionized water according to the stoichiometric ratio, adding potassium hydroxide to adjust the pH to 12-14; transferring the mixture to a polytetrafluoroethylene-lined autoclave for heating, then naturally cooling to room temperature, and finally washing and grinding.

6. The method for preparing rare earth tin-based pyrochlore metal oxide according to any one of claims 5, characterized in that, The mixture is heated at 180~200°C for 22~26 hours.

7. The application of the rare earth tin-based pyrochlore metal oxide according to any one of claims 1 to 3 in electrocatalytic carbon dioxide reduction.

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