CuS-SnS composite catalyst for preparing formic acid through CO2 electroreduction in wide pH window as well as preparation method and application of CuS-SnS composite catalyst

Abstract

The invention relates to a CuS-SnS composite catalyst for preparing formic acid through CO2 electroreduction in a wide pH window as well as a preparation method and application of the CuS-SnS composite catalyst. The preparation method comprises the following steps: preparing a mixed precursor aqueous solution containing copper salt and tin salt; and under a stirring condition, dropwise adding a sodium sulfide aqueous solution into the mixed precursor aqueous solution for reaction, and carrying out solid-liquid separation and vacuum drying on a reacted sample to obtain the CuS-SnS composite catalyst with rich phase interfaces and crystal defects. Compared with the prior art, an electronic coupling effect is formed between CuS and SnS in the prepared CuS-SnS composite catalyst, the selectivity of generating formic acid through CO2 electroreduction is remarkably improved, and the Faraday efficiency of formic acid is larger than 90% in a wide pH 0-14 window.

Description

Technical Field

[0001] The present invention relates to the field of catalytic material synthesis, and in particular to a copper sulfide-stannous sulfide (CuS-SnS) composite catalyst for producing formic acid through CO2 electroreduction with a wide pH window, and a preparation method and application thereof. Background Art

[0002] Using clean electricity from photovoltaic or wind power to convert carbon dioxide into fuels and high-value chemicals through electrocatalysis is a carbon neutral solution with great application prospects. Among them, formic acid is not only widely used in the pharmaceutical, leather and textile industries, but can also be used as a hydrogen storage carrier for fuel cells. It is one of the most economically viable products of CO2 electrochemical reduction (CO2RR). In recent years, through catalyst engineering, interface microenvironment construction, reactor optimization design and operating conditions optimization, electrocatalytic carbon dioxide reduction technology has made certain progress in current density, selectivity and energy conversion efficiency. However, in widely used neutral / alkaline electrolytes, the reaction process will consume a large amount of CO2 and produce carbonate (bicarbonate) by-products, which brings huge challenges at the equipment level and limits the further development of electrocatalytic carbon dioxide to formic acid.

[0003] At present, some research is devoted to the development of catalysts for CO2 electroreduction. For example, patent CN115233245A mentions copper sulfide-bismuth sulfide heterojunction nanosheet catalysts. Although the catalyst shows high activity for CO2 electroreduction to formic acid under alkaline conditions, it is limited to a specific alkaline environment, and its performance under acidic or neutral conditions has not been reported, and it cannot meet the application requirements of a wide pH window. Another patent CN112028110A introduces nanosheet copper sulfide materials, which mainly focus on the morphology control of copper sulfide and its application in semiconductor and antibacterial fields. It does not involve its performance in the field of CO2 electroreduction, and cannot be used to solve the problem of achieving high-selectivity CO2 reduction to formic acid in a wide pH range.

[0004] In neutral / alkaline electrolyte, CO2 and OH react during CO2 electroreduction. - Formation of CO3 2- / HCO3 2- On the one hand, the single-pass conversion efficiency of CO2 is reduced. On the other hand, the carbonate formed at the electrode interface blocks the channels of the gas diffusion electrode. In addition, the continuous input of CO2 reduces the pH value of the electrolyte, which also leads to poor stability of the catalyst and membrane. In contrast, operating CO2RR in an acidic electrolyte can provide a feasible solution to effectively address the above challenges by bypassing the formation of carbonates. However, high hydrogen ion concentration promotes HER and reduces the efficiency of CO2RR products.

[0005] Therefore, there is an urgent need to design and prepare catalysts that can achieve efficient CO2RR to formic acid at industrial-grade current density and high selectivity in pH-universal electrolytes. Summary of the Invention

[0006] The purpose of the present invention is to overcome the defects of the above-mentioned prior art and provide a CuS-SnS composite catalyst for CO2 electroreduction to formic acid in a wide pH window, as well as its preparation method and application, so as to solve the technical problem of CO2RR producing formic acid in a wide pH window.

[0007] The purpose of the present invention can be achieved by the following technical solutions:

[0008] A first aspect of the present invention provides a method for preparing a CuS-SnS composite catalyst for CO2 electroreduction to formic acid over a wide pH window, comprising the following steps:

[0009] S1, preparing a mixed precursor aqueous solution containing copper salt and tin salt;

[0010] S2. Under stirring conditions, adding a sodium sulfide aqueous solution dropwise to the mixed precursor aqueous solution to react, inducing heterogeneous nucleation of CuS and SnS by establishing a Cu-Sn-S ternary reaction interface, thereby forming a composite catalytic structure with rich phase interfaces and crystal defects;

[0011] S3. The reaction product in S2 is subjected to solid-liquid separation and vacuum drying to obtain a CuS-SnS composite catalyst. An electronic coupling effect is formed between the CuS and SnS phases in the CuS-SnS composite catalyst. The electronic coupling effect is used to improve the selectivity of CO2 to formic acid conversion, and the formic acid Faradaic efficiency is greater than 90% in a wide pH window of 0 to 14.

[0012] Furthermore, in S1, the copper salt is selected from one of copper sulfate, copper chloride, and copper nitrate, and the concentration during preparation is 0.05 to 1 mol / L, preferably copper chloride with a content of 0.1 mol / L;

[0013] The tin salt is selected from one of stannous sulfate, stannous nitrate and stannous chloride, and the concentration thereof is 0.05 to 1 mol / L, preferably stannous chloride with a content of 0.1 mol / L.

[0014] Furthermore, in S1, the concentration of the sodium sulfide water solution is 0.1 to 1 mol / L, preferably 0.2 mol / L;

[0015] The droplet addition rate is 500 to 10,000 μL / min, preferably 4,000 μL / min;

[0016] The stirring time is 1 to 60 minutes, preferably 5 minutes; the rotor speed used during stirring is 100 to 1000 rpm, preferably 500 rpm.

[0017] Furthermore, in S2, a specific method for establishing the Cu-Sn-S ternary reaction interface includes: controlling the temperature of the reaction system between 20°C and 80°C, preferably between 25°C and 35°C, to promote heterogeneous nucleation of CuS and SnS.

[0018] Furthermore, in S3, the vacuum drying condition is 30-80°C, and the drying time is 5-24 hours, preferably 50°C, 12 hours.

[0019] Furthermore, in S3, in the obtained CuS-SnS composite catalyst, the molar ratio of CuS to SnS is 1:0.1 to 1:1, preferably 1:1, to optimize the electronic coupling effect in the composite catalytic structure.

[0020] Furthermore, in S3, the solid-liquid separation process includes performing reduced pressure filtration using a filter membrane with a pore size of 0.1 μm to 0.5 μm.

[0021] The second aspect of the present invention provides a CuS-SnS composite catalyst prepared by the above method, wherein the CuS-SnS composite catalyst particle size is 10 to 50 nm, and an electronic coupling effect is formed between the CuS and SnS phases in the CuS-SnS composite catalyst, thereby improving the selectivity of CO2 to formic acid conversion, so that the CuS-SnS composite catalyst can achieve a formic acid Faradaic efficiency of >90% in the CO2 electroreduction to formic acid production over a wide pH range of 0 to 14.

[0022] The third aspect of the present invention provides an application of the CuS-SnS composite catalyst as described above, wherein the composite catalyst is used as a cathode catalyst in a flow electrolyzer for producing formic acid by CO2 electroreduction with a wide pH window. The flow electrolyzer is a three-electrode electrochemical reaction system comprising a cathode, an anode, a reference electrode, and an ion exchange membrane attached to the anode.

[0023] Furthermore, in the flow electrolyzer, when the composite catalyst is used as a cathode catalyst, the partial current density of CO2 electroreduction to formic acid is 10 to 1000 mA / cm 2 The Faradaic efficiency of formic acid is about 90%, and at 500mA / cm 2 It can operate stably for more than 18 hours at a high current density and maintain the Faradaic efficiency of formic acid above 80%.

[0024] The experimental results show that the CuS-SnS composite catalyst provided by the present invention can achieve 670 mA cm-3 at pH 0.94, pH 7.80 and pH 13.86 in a flow electrolytic cell. -2 、823mA cm -2 and 670mAcm -2 The partial current density of formic acid is between 100 and 800 mA cm -2 The Faradaic efficiency of formic acid is about 90% at a total apparent current density of 500 mA cm -2 The catalyst can operate stably for more than 18 hours at a high current density and maintain a Faradaic efficiency of formic acid above 80%, indicating that the CuS-SnS composite catalyst of the present invention has good stability and is suitable for commercial applications.

[0025] The technical mechanism of the present invention is:

[0026] The CuS-SnS composite catalyst of the present invention has abundant phase interfaces and crystal defects, and these characteristics play a vital role in the efficient catalytic performance in a wide pH window. The lattice distortion and defect sites present at the phase interfaces provide a large number of active sites for the CO2 reduction reaction. These active sites can interact with the reactants under different pH conditions, promoting the adsorption, activation and subsequent reaction steps of CO2 molecules. On the one hand, the defect sites can effectively stabilize the key intermediates in the CO2 reduction reaction, thereby improving the activity and selectivity of formic acid production; on the other hand, the abundant phase interfaces and defect structures help to accelerate the conversion and desorption of the reaction intermediates, allowing the catalyst surface to continuously carry out the CO2 reduction reaction. For example, there are a large number of unsaturated coordinated atoms at the interface between CuS and SnS. These atoms have strong electronic attraction and can effectively adsorb and polarize CO2 molecules in a wide pH window, reducing the activation energy of the reaction, thereby achieving efficient CO2 reduction to formic acid while maintaining high selectivity.

[0027] CuS-SnS composite catalysts exhibit excellent chemical stability and structural adaptability, enabling them to maintain stable catalytic activity and structural integrity across a wide pH window. In electrolytes of varying pH, the catalyst's chemical composition and structure can adapt to environmental changes, avoiding significant dissolution, oxidation, or other adverse chemical reactions. Both CuS and SnS possess inherently good chemical stability, and their composite further enhances this stability. For example, in acidic environments, the SnS structure effectively resists acid attack, while the presence of CuS inhibits excessive SnS dissolution.

[0028] Compared with the prior art, the present invention has the following beneficial effects:

[0029] The particle size range of the CuS-SnS composite catalyst disclosed in the invention is 10 to 50 nm, and the size is uniform. The present invention also discloses a preparation method of the above-mentioned CuS-SnS composite catalyst and the application of the CuS-SnS composite catalyst in the carbon dioxide electroreduction reaction. Under the action of rich defects and multiphase interfaces, the present invention improves its electron transport ability, and the unsaturated coordination sites formed are beneficial to the activity of CO2RR to produce formic acid. It shows high formic acid selectivity and industrial-grade current density in a wide pH window of 0 to 14, and realizes the single selective electrocatalytic reduction of carbon dioxide to formic acid without the generation of other liquid products (such as methanol, ethanol and propanol, etc.). In a flow electrolyzer, carbon dioxide can be efficiently converted into formic acid based on the CuS-SnS composite catalyst. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 X-ray diffraction patterns of the CuS-SnS composite catalyst prepared in the present invention and its comparative samples CuS and SnS.

[0031] Figure 2 These are scanning electron microscope images of the CuS-SnS composite catalyst prepared in the present invention and its comparative samples CuS and SnS.

[0032] Figure 3 Particle size distribution diagram of the CuS-SnS composite catalyst prepared by the present invention.

[0033] Figure 4 The cathode potential-time curve and formic acid Faraday efficiency-time curve obtained from the constant current stability test of the CuS-SnS composite catalyst prepared in the present invention for catalyzing the carbon dioxide electroreduction reaction in a flow electrolyzer.

[0034] Figure 5 The Faradaic efficiency and partial current density of formic acid in the carbon dioxide electroreduction reaction of the composite catalyst of the present invention under different pH conditions are shown as follows: (a) pH 0.94; (b) pH 7.80; (c) pH 13.86.

[0035] Figure 6 A schematic diagram of the disassembled structure of the flow electrolyzer used for testing the composite catalyst of the present invention. DETAILED DESCRIPTION

[0036] Overall, the present invention relates to a CuS-SnS composite catalyst for the electroreduction of CO2 to formic acid in a wide pH window and a preparation method thereof. The catalyst is prepared by a simple chemical precipitation method and has a unique nanosheet structure with a thickness of 2 to 3 nm and a particle size of 10 to 50 nm. Its innovation lies in inducing heterogeneous nucleation of CuS and SnS by establishing a Cu-Sn-S ternary reaction interface, forming a composite catalytic structure with rich phase interfaces and crystal defects. This structure not only significantly improves the selectivity of CO2 to formic acid conversion, but also achieves efficient catalytic performance in a wide pH window of 0 to 14, with a formic acid Faradaic efficiency of over 90%.

[0037] The present invention significantly improves the efficiency and selectivity of CO2 electroreduction to formic acid by constructing a CuS-SnS composite material. The electronic coupling effect between CuS and SnS is a key factor in achieving this performance improvement. Specifically, the electronic coupling effect formed between the CuS and SnS phases not only optimizes the electronic structure of the catalyst but also enhances its adsorption and activation ability for CO2 molecules. By controlling the molar ratio of CuS to SnS, the present invention optimizes the electronic coupling effect in the composite catalytic structure, thereby achieving efficient CO2 electroreduction to formic acid over a wide pH window.

[0038] In specific implementation, the preparation method of the CuS-SnS composite catalyst of the present invention comprises the following steps:

[0039] Step 1) preparing a precursor solution of a mixture of Cu salt and Sn salt;

[0040] Step 2) Under stirring, the sodium sulfide aqueous solution is added dropwise to the solution of step 1) using a peristaltic pump. After the reaction, the solution is filtered under reduced pressure and washed to obtain a CuS-SnS composite catalyst;

[0041] Step 3) drying the sample obtained in step 2) in a vacuum drying oven;

[0042] In specific implementation, the copper salt in step 1) can be selected from copper sulfate, copper chloride, copper nitrate, etc., with a concentration of 0.05 to 1 mol / L -1 , wherein the copper salt is preferably copper chloride, and the content is preferably 0.1 mol L -1 Tin salts can be selected from stannous sulfate, stannous nitrate, stannous chloride, etc., with a concentration of 0.05 to 1 mol L -1 , wherein the tin salt is preferably stannous chloride, and the content is preferably 0.1 mol L -1 The volume of deionized water is between 50 and 200 mL, with 100 mL being the most preferred volume.

[0043] In the specific implementation, the concentration of the sodium sulfide aqueous solution in step 2) is 0.1 to 1 mol L -1 , the content is preferably 0.2 mol L-1 The volume of deionized water is 50-200 mL, and the most preferred volume is 100 mL. The peristaltic pump has a dripping speed of 500-10000 μL min -1 , which is preferably 4000 μL min -1 The stirring time is 1 to 60 minutes, preferably 5 minutes, and the rotor speed is 100 to 1000 rpm, preferably 500 rpm.

[0044] In specific implementation, the vacuum drying conditions used in step 3) are 30-80° C. for 5-24 hours, preferably 50° C. for 12 hours.

[0045] The CuS-SnS composite catalyst prepared by the above preparation method will be used for electrochemical carbon dioxide reduction reaction.

[0046] In a specific implementation, the catalyst is used in a flow electrolyzer for carbon dioxide electroreduction, wherein the flow electrolyzer is a three-electrode electrochemical reaction system including a cathode, an anode, and a reference electrode;

[0047] an ion exchange membrane attached to the anode electrode;

[0048] a middle plate having a liquid flow channel attached to the anion exchange membrane;

[0049] A reference electrode placed in the center of the middle plate;

[0050] An anode electrode is attached to the intermediate plate.

[0051] In a specific implementation, the method for carbon dioxide electroreduction includes preparing formic acid by carbon dioxide electroreduction in acidic, neutral and alkaline systems;

[0052] In a specific implementation, the material of the cathode is the carbon material of the CuS-SnS composite catalyst in the above technical solution;

[0053] In specific implementation, the material of the anode includes metal iridium, metal ruthenium, IrO2, RuO2 loaded titanium felt / mesh, NiFeLDH, NiFeO x one or more of the supported carbon materials;

[0054] In a specific implementation, the ion exchange membrane includes one or more of cation exchange membranes such as Nafion 115, Nafion 117, and Nafion N212, anion exchange membranes such as Sustainion X37-50 FA, Sustainion X37-50 RT, Neosepta AMX, Neosepta AHA, and Aemion AP1-HNN8-50-X, and bipolar membranes such as Fumasep FBM-PK and Neosepta BP-1E;

[0055] In a specific implementation, the cathode electrolyte includes but is not limited to one or more solutions of potassium and sodium bicarbonate, carbonate, sulfate, chloride and hydroxide, with a concentration of 0.001 mol L -1 ~Highest solubility;

[0056] In a specific implementation, the anolyte includes one or more solutions of H2SO4, HClO4, H3PO4, KOH and NaOH, with a concentration of 0.001 mol L -1 ~Highest solubility;

[0057] In a specific implementation, the flow electrolyzer further comprises a metal cathode housing with a serpentine flow channel, an intermediate plate made of polyetheretherketone (PEEK) material, and an anode housing with a serpentine flow channel, see Figure 6 ;

[0058] In a specific implementation, the metal cathode housing with the serpentine flow channel, the intermediate plate made of PEEK material and the anode housing with the serpentine flow channel are attached and fixed to form a sealing structure;

[0059] In a specific implementation, a sealing gasket is provided between the cathode housing and the intermediate plate;

[0060] In a specific implementation, the back surface of the cathode electrode is attached to the serpentine flow channel of the cathode shell;

[0061] The cathode shell is provided with a carbon dioxide inlet and a carbon dioxide outlet;

[0062] The middle plate frame is provided with an anolyte inlet, an anolyte outlet, and a reference electrode placement port;

[0063] The back side of the anode electrode is attached to the serpentine flow channel of the cathode housing;

[0064] The anode shell is provided with an anolyte inlet and an anolyte outlet;

[0065] The CO2 gas flow rate is 3 to 100 SCCM;

[0066] The flow rate of the cathode electrolyte is 0.1-100 mL min -1 ;

[0067] The flow rate of the anolyte is 0.1-100 mL min -1 .

[0068] In a specific implementation, the CuS-SnS composite catalyst is mixed with a binder and an alcohol solvent to form ink, which is then compounded with the carbon material.

[0069] In a specific implementation, in the method for preparing a carbon material of a CuS-SnS composite catalyst, the alcohol solvent includes isopropyl alcohol;

[0070] The binder includes one or more of Teflon PTFE 30, Teflon PTFE 6J, Nafion D521, Nafion 115 / 117 membrane solution, and Sustainion XA-9 alkaline ionomer solution;

[0071] The mass volume ratio of the CuS-SnS composite catalyst to the binder is 1 mg: (1-10) μL;

[0072] The carbon material includes carbon paper and / or carbon cloth;

[0073] The compounding includes bonding with an adhesive;

[0074] The loading amount of the CuS-SnS composite catalyst on the carbon material is 1-10 mg cm -2 .

[0075] The present invention will be described in detail below with reference to the accompanying drawings and specific embodiments. Any features such as preparation methods, materials, structures or composition ratios not explicitly described in this technical solution are considered to be common technical features disclosed in the prior art.

[0076] Example 1

[0077] Example 1 of the present invention provides a method for preparing an electrocatalyst, comprising the following steps:

[0078] Step 1: Weigh 2.26 g of stannous chloride dihydrate and 1.71 g of cupric chloride dihydrate and dissolve them in 100 mL of deionized water with ultrasonication to obtain a solution with a concentration of 0.1 mol L -1 The copper chloride and concentration is 0.1 mol L -1 Stannous chloride mixed with brine solution;

[0079] Step 2: Prepare 0.2 mol L -1100 mL of sodium sulfide aqueous solution was stirred at 500 rpm using a peristaltic pump at 4000 μL min -1 Add the sodium sulfide aqueous solution to the solution in step 1 at a rate of 1:1, continue the reaction for 5 minutes, filter under reduced pressure, and wash with deionized water several times to collect the black precipitate;

[0080] Step 3: Dry the black sample obtained in step 2 in a vacuum drying oven at 50° C. overnight to obtain a CuS-SnS composite catalyst.

[0081] The X-ray diffraction patterns and field emission scanning electron microscope images of the obtained CuS-SnS composite catalyst and its single component comparative sample are shown in FIG. Figure 1 、 2 As shown, combined Figure 3 The results showed that the average particle size of the nanoparticles synthesized by this method was 19 nm and the size was uniform.

[0082] Example 2

[0083] This example is a test of the electrochemical performance of the CuS-SnS composite catalyst in an acidic system.

[0084] The catalytic performance of the electrocatalyst prepared in Example 1 of the present invention was tested for the electroreduction reaction of carbon dioxide.

[0085] 35 mg of CuS-SnS composite catalyst was ultrasonically mixed with 175 μL of Sustainion XA-9 alkaline ionomer solution and 15 mL of isopropanol at room temperature. The mixture was then sprayed onto a 3.5 cm × 4.5 cm carbon paper gas diffusion layer using a spray gun. After drying, a 1 cm × 2 cm carbon paper was cut out as the working electrode, IrO2-loaded titanium felt was used as the counter electrode, a silver / silver chloride electrode was used as the reference electrode, and a Nafion 115 cation exchange membrane was used as the ion exchange medium. The reaction mixture was stirred at 0.05 mol L -1 of sulfuric acid and 0.5 mol L -1 Potassium sulfate mixed solution was used as cathode electrolyte, 0.1 mol L -1 The sulfuric acid solution was used as the anolyte. The carbon dioxide flow rate was maintained at 50 SCCM and the electrolyte flow rate was maintained at 2 mL min during the reduction process. -1 The reaction was carried out using a constant current method with a current density ranging from 100 to 800 mA cm -2 The gas phase products of the reaction were detected by gas chromatography, and the liquid phase products were detected by ion chromatography. The coulomb amount corresponding to the product concentration was calculated, and the catalytic selectivity, activity and other data were obtained based on the total coulomb amount recorded by the electrochemical workstation.

[0086] See also Figure 5 a, Figure 5a is the Faraday efficiency-time curve obtained by the constant current stability test of the CuS-SnS composite catalyst prepared in the present invention for catalyzing the carbon dioxide electroreduction reaction in an acidic flow electrolyzer.

[0087] Example 3

[0088] This example is a test of the electrochemical performance of the CuS-SnS composite catalyst in a neutral system.

[0089] The catalytic performance of the electrocatalyst prepared in Example 1 of the present invention was tested for the electroreduction reaction of carbon dioxide.

[0090] 35 mg of CuS-SnS composite catalyst was ultrasonically mixed with 175 μL of Sustainion XA-9 alkaline ionomer solution and 15 mL of isopropanol at room temperature. The mixture was then sprayed onto a 3.5 cm × 4.5 cm carbon paper gas diffusion layer using a spray gun. After drying, a 1 cm × 2 cm carbon paper was cut out as the working electrode, an IrO2-loaded titanium felt was used as the counter electrode, a silver / silver chloride electrode was used as the reference electrode, and a Fumasep FBM-PK bipolar membrane was used as the ion exchange medium. The reaction mixture was stirred at 1 mol L -1 The potassium bicarbonate solution was used as the cathode electrolyte, 0.1 mol L -1 The sulfuric acid solution was used as the anolyte. The carbon dioxide flow rate was maintained at 50 SCCM and the electrolyte flow rate was maintained at 2 mL min during the reduction process. -1 The reaction was carried out using a constant current method with a current density range of 100–1000 mA cm -2 The gas phase products of the reaction were detected by gas chromatography, and the liquid phase products were detected by ion chromatography. The coulomb amount corresponding to the product concentration was calculated, and the catalytic selectivity, activity and other data were obtained based on the total coulomb amount recorded by the electrochemical workstation.

[0091] See also Figure 5 b, Figure 5 b is the Faraday efficiency-time curve obtained by the constant current stability test of the CuS-SnS composite catalyst prepared in the present invention catalyzing the carbon dioxide electroreduction reaction in a neutral flow electrolyzer.

[0092] Example 4

[0093] This example tests the electrochemical performance of the CuS-SnS composite catalyst in an alkaline system.

[0094] The catalytic performance of the electrocatalyst prepared in Example 1 of the present invention was tested for the electroreduction reaction of carbon dioxide.

[0095] 35 mg of CuS-SnS composite catalyst was ultrasonically mixed with 175 μL of Sustainion XA-9 alkaline ionomer solution and 15 mL of isopropanol at room temperature. The mixture was then sprayed onto a 3.5 cm × 4.5 cm carbon paper gas diffusion layer using a spray gun. After drying, a 1 cm × 2 cm carbon paper was cut out as the working electrode, an IrO2-loaded titanium felt was used as the counter electrode, a silver / silver chloride electrode was used as the reference electrode, and a Sustainion X37-50 FA anion exchange membrane was used as the ion exchange medium. The reaction mixture was stirred at 1 mol L -1 The potassium hydroxide solution was used as the cathode electrolyte, 1 mol L -1 The potassium hydroxide solution was used as the anolyte. The carbon dioxide flow rate was maintained at 50 SCCM and the electrolyte flow rate was maintained at 2 mL min during the reduction process. -1 The reaction was carried out using a constant current method with a current density ranging from 100 to 800 mA cm -2 The gas phase products of the reaction were detected by gas chromatography, and the liquid phase products were detected by ion chromatography. The coulomb amount corresponding to the product concentration was calculated, and the catalytic selectivity, activity and other data were obtained based on the total coulomb amount recorded by the electrochemical workstation.

[0096] See also Figure 5 c, Figure 5 c is the Faraday efficiency-time curve obtained by the constant current stability test of the CuS-SnS composite catalyst prepared in the present invention for catalyzing the carbon dioxide electroreduction reaction in an alkaline flow electrolyzer.

[0097] Example 5

[0098] The stability of the CuS-SnS composite catalyst was tested in a flow electrolyzer.

[0099] 35 mg of CuS-SnS composite catalyst was ultrasonically mixed with 175 μL of Sustainion XA-9 alkaline ionomer solution and 15 mL of isopropanol at room temperature. The mixture was then sprayed onto a 3.5 cm × 4.5 cm carbon paper gas diffusion layer using a spray gun. After drying, a 1 cm × 2 cm carbon paper was cut out as the working electrode, IrO2-loaded titanium felt was used as the counter electrode, a silver / silver chloride electrode was used as the reference electrode, and a Fumasep FBM-PK bipolar membrane was used as the ion exchange medium. The reaction mixture was stirred at 0.5 mol L -1 The potassium bicarbonate solution was used as the cathode electrolyte, 0.1 mol L -1 The sulfuric acid solution was used as the anolyte. The carbon dioxide flow rate was maintained at 50 SCCM and the electrolyte flow rate was maintained at 2 mL min during the reduction process. -1 The reaction was carried out using a constant current method with a current density of 500 mA cm -2The liquid phase products of the reaction were detected by ion chromatography, and the coulomb amount corresponding to the product concentration was calculated. The stability data of formic acid generation by CO2RR were obtained based on the total coulomb amount recorded by the electrochemical workstation.

[0100] See also Figure 4 , Figure 4 The cathode potential-time curve and Faraday efficiency-time curve of the composite catalyst prepared by the present invention were obtained by the constant current stability test of the carbon dioxide electroreduction reaction in the flow electrolyzer. The results showed that the composite catalyst had a high stability at 500 mA cm -2 The system can operate stably for more than 18 hours at a total apparent current density of 1.5 wt %. The Faradaic efficiency of formic acid is maintained above 80%.

[0101] It can be seen that the catalyst of the present invention has rich phase interfaces and crystal defects, and these characteristics significantly improve its electrocatalytic performance. The lattice distortion and defect sites at the phase interface provide efficient active sites for the CO2 reduction reaction, promoting the stability and conversion of the reaction intermediates. In addition, by optimizing the reaction conditions (such as reaction temperature, stirring speed, addition rate, etc.), the morphology and size of the catalyst can be accurately controlled, thereby further improving its catalytic activity and stability. The experimental results show that the catalyst of the present invention exhibits excellent electrocatalytic performance under the conditions of pH 0.94, pH 7.80 and pH 13.86, and the partial current density of formic acid reaches 670mA / cm 2 、823mA / cm 2 and 670mA / cm 2 , and in the range of 100~800mA / cm 2 At a total apparent current density of , the Faradaic efficiency of formic acid remains around 90%.

[0102] The catalyst of the present invention exhibits excellent stability in a wide pH window. Its unique electronic structure and abundant defect sites enable it to maintain efficient CO2 reduction activity under acidic, neutral and alkaline conditions. In addition, by optimizing the preparation process, the present invention achieves a high specific surface area and excellent conductivity of the catalyst, thereby significantly improving its stability and durability at high current density. Experiments show that the catalyst of the present invention has a high specific surface area and excellent conductivity at 500mA / cm 2 The catalyst can operate stably for over 18 hours at a high current density, with the Faradaic efficiency of formic acid remaining above 80%. This performance is attributed to the electronic coupling effect and structural stability of the catalyst, which enables it to maintain efficient CO2 reduction capabilities during long-term operation.

[0103] The above is a detailed introduction to a CuS-SnS composite catalyst for use in a wide pH window and high current density, its preparation method, application, and a flow electrolyzer for preparing formic acid by electroreduction of carbon dioxide provided by the present invention. Specific examples are used herein to illustrate the principles and implementation methods of the present invention. The description of the above embodiments is only used to help understand the method of the present invention and its core ideas, including the best mode, and also enables any technician in this field to practice the present invention, including the manufacture and use of any device or system, and the implementation of any combined method. It should be pointed out that for ordinary technicians in this technical field, without departing from the principles of the present invention, the present invention can also be improved and modified in several ways, and these improvements and modifications also fall within the scope of protection of the claims of the present invention.

[0104] The scope of patent protection for the present invention is defined by the claims and may include other embodiments that can be thought of by those skilled in the art. If these other embodiments have structural elements that are not different from the literal wording of the claims, or if they include equivalent structural elements that are not substantially different from the literal wording of the claims, then these other embodiments should also be included in the scope of the claims.

Claims

1. A method for preparing a CuS-SnS composite catalyst for CO2 electroreduction to formic acid with a wide pH window, characterized in that: The following steps are involved: S1, preparing a mixed precursor aqueous solution containing copper salt and tin salt; S2. Under stirring conditions, adding a sodium sulfide aqueous solution dropwise to the mixed precursor aqueous solution to react, inducing heterogeneous nucleation of CuS and SnS by establishing a Cu-Sn-S ternary reaction interface, thereby forming a composite catalytic structure with rich phase interfaces and crystal defects; S3. The sample obtained in S2 is subjected to solid-liquid separation and vacuum drying to obtain a CuS-SnS composite catalyst with rich phase interfaces and crystal defects. The electronic coupling effect formed between the CuS and SnS phases is used to improve the selectivity of CO2 electroreduction to formic acid, and the formic acid Faradaic efficiency is greater than 90% in a wide pH window of 0 to 14.

2. The method for preparing a CuS-SnS composite catalyst for CO2 electroreduction to formic acid with a wide pH window according to claim 1, characterized in that: In S1, the copper salt is selected from copper sulfate, copper chloride, and copper nitrate, and the concentration during preparation is 0.05 to 1 mol / L; The tin salt is selected from one of stannous sulfate, stannous nitrate and stannous chloride, and the concentration during preparation is 0.05-1 mol / L.

3. The method for preparing a CuS-SnS composite catalyst for CO2 electroreduction to formic acid with a wide pH window according to claim 1, characterized in that: In S1, the concentration of the sodium sulfide water solution is 0.1 to 1 mol / L; The drop rate is 500-10000 μL / min; The stirring time is 1 to 60 minutes; The rotor speed used during stirring is 100 to 1000 rpm.

4. The method for preparing a CuS-SnS composite catalyst for CO2 electroreduction to formic acid with a wide pH window according to claim 1, characterized in that: In S2, the specific method of establishing the Cu-Sn-S ternary reaction interface includes: controlling the temperature of the reaction system between 20°C and 80°C to promote the heterogeneous nucleation of CuS and SnS.

5. The method for preparing a CuS-SnS composite catalyst for CO2 electroreduction to formic acid with a wide pH window according to claim 1, characterized in that: In S3, the vacuum drying condition is 30-80° C., and the drying time is 5-24 hours.

6. The method for preparing a CuS-SnS composite catalyst for CO2 electroreduction to formic acid with a wide pH window according to claim 1, characterized in that: In S3, in the obtained CuS-SnS composite catalyst, the molar ratio of CuS to SnS is 1:0.1 to 1:

1.

7. A CuS-SnS composite catalyst prepared by the method according to any one of claims 1 to 6.

8. The CuS-SnS composite catalyst according to claim 7, characterized in that The particle size of the CuS-SnS composite catalyst is 10 to 50 nm. An electronic coupling effect is formed between CuS and SnS in the CuS-SnS composite catalyst, thereby improving the selectivity of CO2 conversion to formic acid. In addition, in a wide pH window of 0 to 14, the formic acid Faradaic efficiency is greater than 90%.

9. Use of the CuS-SnS composite catalyst as claimed in claim 7, characterized in that: The composite catalyst is used as a cathode catalyst in a flow electrolyzer for producing formic acid through CO2 electroreduction with a wide pH window. The flow electrolyzer is a three-electrode electrochemical reaction system comprising a cathode, an anode, a reference electrode, and an ion exchange membrane attached to the anode.

10. The use of a CuS-SnS composite catalyst according to claim 9, characterized in that: In the flow electrolyzer, when the composite catalyst is used as the cathode catalyst, the partial current density of CO2 electroreduction to formic acid is 10 to 1000 mA / cm 2 , and at 500mA / cm 2 It can operate stably for more than 18 hours at a total apparent current density of , and maintain the Faradaic efficiency of formic acid above 80%.

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