A selenium-deficient tin diselenide nanosheet electrocatalyst and a preparation method and application thereof

Abstract

The application discloses a preparation method of a selenium-defect-rich tin diselenide nanosheet electrocatalyst, which comprises the following steps: dissolving selenium dioxide and a metal tin salt, adding a hydrazine hydrate solution, stirring and mixing, and performing a hydrothermal reaction to obtain the selenium-defect-rich tin diselenide nanosheet electrocatalyst. The application further discloses the selenium-defect-rich tin diselenide nanosheet electrocatalyst obtained by the above preparation method and application of the selenium-defect-rich tin diselenide nanosheet electrocatalyst as a working electrode in formic acid electro-synthesis. The catalyst provided by the application realizes high selectivity of HCOOH electro-synthesis in alkaline, neutral and acidic electrolytes, respectively, and the corresponding pH conditions reach an industrial level in terms of HCOOH partial current density, and the catalyst fully exhibits excellent HCOOH electro-synthesis performance in a full pH range.

Description

Technical Field

[0001] This invention relates to the field of electrocatalyst technology, specifically to a tin diselenide nanosheet electrocatalyst rich in selenium defects, its preparation method, and its application. Background Technology

[0002] The electroreduction of carbon dioxide (CO2) into high-value-added carbon-containing chemicals (such as carbon monoxide, formic acid, and methane) using renewable energy sources has yielded various reduction products. Formic acid (HCOOH) is considered one of the most techno-economically viable products and has been widely used in practical applications. To date, several major p-block metal group catalysts, including Sn, In, and Bi, as well as a series of corresponding metal oxides (such as tin oxide and indium oxide), have been reported for the electroreduction of CO2 to synthesize HCOOH. Among these, tin-based materials are widely used for the electroreduction of CO2 to HCOOH due to their low cost and moderate adsorption energy for the *OOCH intermediate in the electrosynthesis of HCOOH. However, currently reported tin-based catalysts have limitations in achieving high selectivity at industrial-grade current densities (>200 mA cm⁻¹). -2 Significant challenges remain in the electrosynthesis of HCOOH.

[0003] Currently, most HCOOH electrosynthesis is carried out in alkaline or neutral electrolytes, inevitably forming carbonate byproducts and reducing CO2 utilization efficiency. Using acidic electrolytes is one effective way to solve these problems. However, due to the competitive hydrogen evolution side reaction and unavoidable proton concentration changes during CO2 electroreduction, achieving sustained and efficient CO2 conversion in acidic electrolytes remains a significant challenge. Therefore, in industrial applications, developing ideal catalysts that function well across the entire pH range is essential. For example, Chinese patent document CN115584522A discloses a method for preparing a three-dimensional porous electrode and its application in the acidic electrocatalytic reduction of CO2 to formic acid. The method involves uniformly mixing a catalyst, polymer, and organic solvent to prepare a composite slurry, uniformly coating the slurry onto carbon cloth using a scraper to obtain an unformed preform, and finally drying it to obtain a three-dimensional porous electrode, enabling the electroreduction of HCOOH under acidic conditions with a pH less than 3.77.

[0004] Due to the slow reaction kinetics in proton formation and transport, the formation of the *OOCH intermediate is often the rate-determining reaction step. Therefore, accelerating proton formation and transfer is an effective method to improve the *OOCH / HCOOH formation rate. Introducing defect structures is considered one of the most direct and effective methods for controlling the electronic and surface structures of metals, and has been extensively studied in recent years. For example, Chinese patent document CN116103680A discloses an oxygen-vacancy-rich bismuth oxycarbonate electrocatalyst and its preparation method. Bismuth salt is dissolved in ethylene glycol and aqueous solution, and an appropriate amount of auxiliary conductive salt is added and then refrigerated to obtain an electrolyte. Bismuth oxycarbonate nanosheets rich in oxygen vacancies are electrochemically deposited on the working electrode using a constant current method. The introduction of oxygen vacancies improves the conductivity of bismuth oxycarbonate, enhances its water-splitting ability, and improves its intrinsic activity in HCOOH synthesis.

[0005] Although significant progress has been made in the study of electroreduction of CO2 to synthesize HCOOH under different electrolyte conditions, achieving industrial-grade current densities (>200 mA cm⁻¹) across the entire pH range remains a challenge. -2 The electrosynthesis of HCOOH still faces problems such as low selectivity. Summary of the Invention

[0006] The purpose of this invention is to provide a method for preparing a tin diselenide nanosheet electrocatalyst rich in selenium defects. The prepared catalyst is rich in selenium defects and exhibits excellent catalytic performance for HCOOH electrosynthesis.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0008] A method for preparing a tin diselenide nanosheet electrocatalyst rich in selenium defects includes the following steps: dissolving selenium dioxide and a tin salt, adding them to a hydrazine hydrate solution, stirring and mixing, and then performing a hydrothermal reaction to obtain a tin diselenide nanosheet electrocatalyst rich in selenium defects.

[0009] The preparation principle of the selenium-defect-rich tin diselenide nanosheet electrocatalyst provided by this invention is as follows: Hydrazine hydrate, a reducing agent, is added to a uniformly dispersed mixed solution of selenium dioxide and metallic tin salt. The strongly reducing hydrazine hydrate molecules degrade the Sn in the solution. 2+ and Se 4+ When reduced to atoms, highly reactive Sn and Se atoms combine to form tin diselenide molecules, accompanied by the formation of selenium defects. The introduction of these selenium defects allows more electrons to transfer from Se sites to Sn sites, effectively accelerating the dissociation of water molecules, increasing the proton transfer rate, and thus accelerating the efficient conversion of CO2 at tin active sites.

[0010] The tin salt is a soluble salt, and preferably, the tin salt is stannous chloride dihydrate.

[0011] The molar ratio of selenium dioxide to metallic tin salt is 1.5–2.5:1. This invention prepares tin diselenide nanosheets with varying purities rich in selenium defects by changing the amount of selenium dioxide used. When the molar concentration of selenium dioxide is too low, the purity of the obtained tin diselenide decreases, and impurity tin phases are present, resulting in no significant improvement in the performance of electroreduction of CO2 to synthesize HCOOH. When the molar concentration of selenium dioxide is too high, selenium impurity phases appear, significantly reducing the performance of HCOOH electrosynthesis.

[0012] Furthermore, selenium dioxide and metallic tin salt were dissolved in water, resulting in a mixed solution with a selenium dioxide mass concentration of 7.4–22.2 g / L. -1 The mass concentration of tin salt is 15.0 g / L. -1 Preferably, the mass concentration of selenium dioxide is 14.8 g / L. -1 .

[0013] In this process, selenium dioxide and metallic tin salt are dissolved in a certain amount of aqueous solution, the reaction temperature is room temperature, and the stirring time is 10–20 min. Preferably, the stirring time is 20 min.

[0014] Furthermore, in the mixed solution after adding hydrazine hydrate, the mass concentration of hydrazine hydrate was 54.8 g / L. -1 .

[0015] In this process, after adding the hydrazine hydrate solution to the mixed solution of selenium dioxide and tin salt, the reaction temperature is at room temperature, and the stirring time is 3–8 minutes. Excessive stirring time will affect the uniformity of the morphology of tin diselenide and the formation of selenium defects, thus affecting the performance of the electrocatalyst. Preferably, the stirring time is 3 minutes.

[0016] The hydrothermal reaction temperature is 160–200 °C. By changing the hydrothermal reaction temperature, tin diselenide nanosheets with different selenium defect contents are prepared. When the hydrothermal reaction temperature is too low, it is difficult to form tin diselenide nanosheets rich in selenium defects; when the hydrothermal reaction temperature is too high, the tin diselenide nanosheets are prone to undergo a crystal phase transformation at high temperatures, thereby reducing the performance of electroreduction of CO2 to prepare HCOOH.

[0017] Preferably, the molar ratio of selenium dioxide to tin salt is 1.5–2:1, and the hydrothermal reaction temperature is 180–200°C. By limiting the above molar ratio and reaction temperature, the purity and content of selenium defects in the prepared tin diselenide nanosheets are more conducive to improving the selectivity of electroreduction of CO2 to prepare HCOOH.

[0018] The present invention also provides a tin diselenide nanosheet electrocatalyst rich in selenium defects obtained according to the above preparation method.

[0019] The catalyst contains abundant selenium defects in tin diselenide nanosheets, and the atomic ratio of selenium to tin in the tin diselenide nanosheet electrocatalyst is 1.8 to 2.0:1.

[0020] The present invention also provides an application of the above-mentioned selenium-defect-rich tin diselenide nanosheet electrocatalyst as a working electrode in the electrosynthesis of formic acid.

[0021] Furthermore, the application of the selenium-defect-rich tin diselenide nanosheet electrocatalyst as a working electrode in the electrosynthesis of formic acid at industrial-grade current densities across the entire pH range.

[0022] The tin diselenide nanosheet electrocatalyst rich in selenium defects provided by this invention exhibits performance at industrial current densities (>200 mA / cm²). -2 This achieves high selectivity. Specifically, the selectivity for HCOOH in alkaline, neutral, and acidic electrolytes is 94.1%, 81.7%, and 78.1%, respectively, with peak deflection current densities of 800, 568, and 495 mA cm⁻¹, respectively. -2 Its electrocatalytic performance far surpasses that of commercial tin diselenide catalysts.

[0023] The selenium-defect-rich tin diselenide nanosheet electrocatalyst provided by this invention can effectively improve its adsorption and dissociation ability for water molecules, accelerate proton transfer and intermediate formation rate, thereby further enhancing its electrocatalytic activity, which is of great significance for realizing the preparation of HCOOH under industrial conditions.

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] (1) The selenium-defect-rich tin diselenide nanosheet electrocatalyst provided by this invention achieves highly selective CO2 catalytic conversion to HCOOH and has a wide operable pH window (2.0–14.0). It realizes HCOOH electrosynthesis at industrial-grade current densities under different pH environments, providing the possibility for further large-scale industrial applications.

[0026] (2) The tin diselenide nanosheet electrocatalyst rich in selenium defects provided by the present invention effectively regulates the electronic structure of tin diselenide by introducing selenium defects, making the electron density around the tin sites more abundant, effectively accelerating the dissociation of water molecules into more protons, thereby accelerating the formation of intermediate *COOH, and finally accelerating the HCOOH synthesis process. Attached Figure Description

[0027] Figure 1 The image shows a scanning electron microscope (SEM) image of the catalyst prepared in Example 1.

[0028] Figure 2X-ray diffraction (XRD) pattern of the catalyst prepared in Example 1;

[0029] Figure 3 Electron paramagnetic resonance (EPR) images of the catalysts prepared in Examples 1 and 2-3;

[0030] Figure 4 The Faraday efficiency of the catalyst prepared in Example 1 for the electroreduction of CO2 to HCOOH in an application example.

[0031] Figure 5 The Faraday efficiency of the catalysts prepared in Examples 1 and 2-3 for the electroreduction of CO2 to HCOOH in an application example.

[0032] Figure 6 The Faraday efficiency of the catalysts prepared in Examples 1 and 4-5 for the electroreduction of CO2 to HCOOH in the application example at pH=14.0. Detailed Implementation

[0033] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Modifications or equivalent substitutions made by those skilled in the art based on their understanding of the technical solutions of this invention, without departing from the spirit and scope of the invention, should be covered within the protection scope of this invention. The raw materials used in the following specific embodiments are all commercially available.

[0034] Example 1

[0035] (1) Weigh 443.8 mg of selenium dioxide solid particles and 451.3 mg of stannous chloride dihydrate solid particles, dissolve them in 30 mL of deionized water, stir at room temperature for 20 min, and set aside.

[0036] (2) Add 2 mL of 85 wt.% hydrazine hydrate solution to the solution prepared in step (1) and stir for 5 min; transfer the resulting mixed solution to a 50 mL hydrothermal reactor and hydrothermally react at 180 °C for 24 h.

[0037] (3) The initial product obtained in step (2) is centrifuged and washed with water and ethanol more than 3 times. Finally, it is dried in a vacuum oven at 60°C for 12 hours to obtain tin diselenide nanosheet catalyst rich in selenium defects.

[0038] The microstructure of the prepared catalyst was observed by scanning electron microscopy (SEM). The SEM results are as follows: Figure 1As shown, the morphology of the selenium-defect-rich tin diselenide catalyst is a hexagonal sheet structure with a sheet thickness of approximately 50 nm. The X-ray diffraction (XRD) pattern of the selenium-defect-rich tin diselenide prepared in this embodiment is shown below. Figure 2 As shown, the characteristic peaks of tin diselenide crystal phase can be observed, and the electron paramagnetic resonance (EPR) spectrum is as follows. Figure 3 As shown, the presence of selenium defects is clearly visible, indicating the successful preparation of tin diselenide nanosheet electrocatalysts rich in selenium defects.

[0039] Example 2

[0040] Following the preparation process of Example 1, the hydrothermal reaction temperature in step (2) was changed to 160°C to obtain the catalyst of Example 2.

[0041] Example 3

[0042] Following the preparation process of Example 1, the hydrothermal reaction temperature in step (2) was changed to 200°C to obtain the catalyst of Example 3.

[0043] Example 4

[0044] Following the preparation process of Example 1, the mass of selenium dioxide solid particles in step (1) was changed to 332.8 mg to obtain the catalyst of Example 4.

[0045] Example 5

[0046] Following the preparation process of Example 1, the mass of selenium dioxide solid particles in step (1) was changed to 554.7 mg to obtain the catalyst of Example 5.

[0047] Application example: Electrosynthesis of HCOOH at industrial-grade current densities across the entire pH range

[0048] First, the 10 mg catalyst prepared above was dispersed in 1000 μL of an ethanol / Nafion dispersion with a volume ratio of 9:1. Then, 100 μL of the dispersion was sprayed onto a 0.5*0.5 cm thick surface. 2 After being naturally dried on the gas diffusion electrode, it was placed as the working electrode in a three-electrode flow cell measuring device. This device consists of two compartments separated by anion exchange membranes. A 1.0M KOH solution was used as the alkaline electrolyte, a 1.0M KHCO3 solution as the neutral electrolyte, and a 0.5M mixed solution of K₂SO₄ and H₂SO₄ as the acidic electrolyte. The counter electrode for the alkaline and neutral electrolytes was nickel foam, the counter electrode for the acidic electrolyte was a platinum sheet, and the reference electrode was a silver / silver chloride electrode.

[0049] Cyclic voltammetry (CV) activation: A Shanghai Chenhua CHI 760E electrochemical workstation was used with a CV program. The test range was 0 to -1.4 V vs. RHE, and the scan rate was 50 mV / s. -1 After 40 cyclic scans, the electrode reaches a stable state.

[0050] Linear Scan Voltammetry (LSV) Test: After CV activation, switch the program to LSV, with a test range of 0 to -1.4V vs. RHE, and a scan rate of 5 mV / s. -1 .

[0051] Faraday efficiency (FE) test: Switch the program to constant current voltage-time test. During the constant current test, use gas chromatography to determine the concentration of the gaseous product and calculate the FE of the product. Online quantification is performed using gas chromatography (GC, Fuli 9790II). 1 The FE of liquid products was analyzed using an H nuclear magnetic resonance spectrometer, employing the internal standard method, i.e., using dimethyl sulfoxide as the standard for determination.

[0052] The result is as follows Figure 4 As shown, the selenium-defect-rich tin diselenide nanosheet electrocatalyst prepared in Example 1 exhibited excellent HCOOH electrosynthesis performance across the entire pH range, achieving selectivity of 94.1%, 81.7%, and 78.1% for HCOOH in alkaline, neutral, and acidic electrolytes, respectively, with corresponding HCOOH partial current densities of 800, 568, and 495 mA cm⁻¹. -2 It has reached the industrial-grade level.

[0053] The HCOOH Faradaic efficiencies of the electrocatalysts prepared in Examples 1 and 2-3 were compared under different pH conditions at a voltage of -0.8V vs. RHE. The results are as follows: Figure 5 As shown, the selenium-defect-rich tin diselenide nanosheet electrocatalyst prepared in Example 1 exhibits significantly better HCOOH electrosynthesis performance across the entire pH range than that of Examples 2 and 3.

[0054] The electrocatalysts prepared in Examples 1 and 4-5 were compared in terms of their HCOOH electrosynthesis performance at pH 14.0. The results are as follows: Figure 6 As shown, the electrosynthesis selectivity of the selenium-defect-rich tin diselenide nanosheet electrocatalyst HCOOH prepared in Example 1 is much higher than that in Examples 4 and 5.

Claims

1. The application of a selenium-defect-rich tin diselenide nanosheet electrocatalyst as a working electrode in the electrosynthesis of formic acid, characterized in that, The preparation method of the selenium-defect-rich tin diselenide nanosheet electrocatalyst includes the following steps: dissolving selenium dioxide and metallic tin salt, adding hydrazine hydrate solution, stirring and mixing, and obtaining the selenium-defect-rich tin diselenide nanosheet electrocatalyst through hydrothermal reaction; Among them, the application of the selenium-defect-rich tin diselenide nanosheet electrocatalyst as a working electrode in the electrosynthesis of formic acid at industrial-grade current densities across the entire pH range.

2. The application according to claim 1, characterized in that, The molar ratio of selenium dioxide to metallic tin salt is 1.5~2.5:

1.

3. The application according to claim 1, characterized in that, The hydrothermal reaction temperature is 160~200 ℃.

4. The application according to claim 1, characterized in that, The molar ratio of selenium dioxide to metallic tin salt is 1.5~2:1, and the hydrothermal reaction temperature is 180~200 ℃.

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