Catalyst for electrocatalysis of CO2RR and preparation method thereof

Abstract

The invention relates to the technical field of CO2RR catalysts, in particular to a catalyst for electrocatalysis of CO2RR and a preparation method of the catalyst. The preparation method of the catalyst for electrocatalysis of CO2RR comprises the following steps: step 1, uniformly mixing a Sn salt solution and a Zn salt solution to obtain a mixed solution; sequentially adding an alkali solution A into the mixed solution for reaction 1, and adding an alkali solution B for reaction 2 to obtain a ZnSn (OH) 6 hollow cube; step 2, dispersing the ZnSn (OH) 6 hollow cubes in water to obtain a dispersion liquid; and uniformly mixing the dispersion liquid with a Cu salt solution, carrying out a hydrothermal reaction to obtain a CuxZnSn (OH) 6 hollow cube, and annealing to obtain the catalyst for electrocatalysis of CO2RR. The catalyst prepared by the method has a hollow cubic structure, can provide larger specific surface area and metal sites for reaction, and is more beneficial to electro-catalysis of CO2RR.

Description

Technical Field

[0001] The present invention relates to the technical field of CO2RR catalysts, and in particular to a catalyst for electrocatalytic CO2RR and a preparation method thereof. Background Art

[0002] Copper-based bimetallic catalysts have been extensively studied in the field of electrocatalytic CO₂RR. For example, the Cu-Ag bimetallic catalyst synthesized by Zhang et al. has been able to achieve a Faradaic efficiency of 67.6% for total C₂ products in the electrocatalytic CO₂RR process. Despite this, they still pointed out that the catalyst's high selectivity for C₂ is achieved by re-adsorbing *CO during operation. However, considering that the chemical reaction rate of excessive *CO intermediates is controlled by subsequent processes such as C–C coupling, if the chemical reaction rate of this process is too slow, it may cause catalyst poisoning, thereby affecting the catalyst's activity and durability. Moreover, considering the economic value of precious metals, the development of non-precious metals as alternatives is obviously of great significance. Summary of the Invention

[0003] In view of this, the present invention provides a catalyst for electrocatalytic CO2RR and a preparation method thereof.

[0004] To achieve the above object, the present invention provides the following solutions:

[0005] One of the technical solutions of the present invention is a method for preparing a catalyst for electrocatalytic CO2RR, comprising the following steps:

[0006] Step 1: mixing a Sn salt solution and a Zn salt solution to obtain a mixed solution; adding alkaline solution A to the mixed solution to carry out reaction 1, and adding alkaline solution B to carry out reaction 2 to obtain ZnSn(OH)6 hollow cubes;

[0007] Step 2: Dispersing the ZnSn(OH)6 hollow cubes in water to obtain a dispersion; mixing the dispersion with a Cu salt solution to perform a hydrothermal reaction to obtain Cu x ZnSn(OH)6 hollow cube;

[0008] Step 3, the Cu x The ZnSn(OH)6 hollow cube was annealed to obtain the catalyst (Cu x ZnSnO3).

[0009] The second technical solution of the present invention is a catalyst for electrocatalytic CO2RR prepared according to the above preparation method.

[0010] The third technical solution of the present invention is a working electrode, which is prepared by making the above-mentioned catalyst for electrocatalytic CO2RR into an ink solution and drop-coating it on the surface of the electrode material.

[0011] A fourth technical solution of the present invention is the use of the above-mentioned catalyst for electrocatalytic CO2RR or the above-mentioned working electrode in electrocatalytic CO2RR.

[0012] The present invention discloses the following technical effects:

[0013] The method of the invention is simple to operate, does not require precious metals, has low cost, and is easy to promote and apply industrially.

[0014] The catalyst prepared by the method of the present invention has a hollow cubic structure, which can provide a larger specific surface area and metal sites for reaction, and is more conducive to electrocatalytic CO2RR (the optimal formic acid selectivity reaches 93%, while the hydrogen evolution selectivity is less than 5%). BRIEF DESCRIPTION OF THE DRAWINGS

[0015] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0016] Figure 1 Figure 2 shows the NMR standard curves for quantitative detection of (a) formic acid and (b) ethanol.

[0017] Figure 2 Scanning electron microscope images of (a) hollow ZnSn(OH)6, (b) hollow Cu6ZnSn(OH)6, (c) hollow Cu6ZnSnO3, and EDS mapping images of (d)-(g) hollow Cu6ZnSnO3.

[0018] Figure 3 Scanning electron microscope images of (a) solid ZnSn(OH)6, (b) hollow Cu8ZnSn(OH)6, and (c) hollow Cu8ZnSnO3.

[0019] Figure 4 (a)-(c) solid ZnSnO3, (d)-(f) solid Cu6ZnSnO3, (g)-(i) solid Cu 16 TEM image of ZnSnO3.

[0020] Figure 5(a)-(c) High-resolution transmission electron microscopy images of hollow Cu6ZnSnO3, (d)-(g) energy-dispersive X-ray spectroscopy elemental surface scans of hollow Cu6ZnSnO3 (blue-Cu, green-Zn, yellow-Sn, red-O), (h)-(j) local high-resolution transmission electron microscopy images of hollow Cu6ZnSnO3, (k)-(n) local energy-dispersive X-ray spectroscopy elemental surface scans.

[0021] Figure 6 (a) Hollow Cu x XRD comparison of ZnSnO3, (b) hollow Cu x Cu, Zn and Sn contents of ZnSnO3.

[0022] Figure 7 Hollow ZnSnO3, hollow Cu6ZnSnO3 and hollow Cu 16 Comparative XPS spectra of ZnSnO3; including (a) Zn2p spectrum, (b) Sn 3d spectrum, and (c) O 1s spectrum.

[0023] Figure 8 Hollow ZnSnO3, hollow Cu6ZnSnO3 and hollow Cu 16 XPS spectrum of ZnSnO3; including (a) Cu 2p spectrum, (b) Cu LMM spectrum.

[0024] Figure 9 is (a) ZnSnO3, Cu6ZnSnO3 and Cu 16 N2 adsorption and desorption isotherms of ZnSnO3; (b) ZnSnO3, (c) Cu6ZnSnO3, (d) Cu 16 Pore ​​size distribution diagram of ZnSnO3.

[0025] Figure 10 Local SEM and EDS mapping of Cu6ZnSnO3 catalyst supported on hydrophobic carbon paper.

[0026] Figure 11 (a)Cu x LSV of ZnSnO3 (x=0, 6, 8, 16); (b) ZnSnO3, (c) Cu6ZnSnO3, (d) Cu8ZnSnO3, (e) Cu 16 CV curves of ZnSnO3 in N2 / CO2 atmosphere; (f) Cu x EIS test graph of ZnSnO3 (x=0, 6, 8, 16).

[0027] Figure 12The electrochemical active surface test diagram is shown in Figure 1. Among them, (a) ZnSnO3, (b) Cu6ZnSnO3, (c) Cu8ZnSnO3, (d) Cu 16 Electrochemically active surface test results of ZnSnO3; (e) double layer capacitance; (f) Tafel slope.

[0028] Figure 13 (a) hollow ZnSnO3, (b) hollow Cu4ZnSnO3, (c) hollow Cu6ZnSnO3, (d) hollow Cu8ZnSnO3, (e) hollow Cu 16 Comparison of electrocatalytic CO2RR performance of (f) damaged ZnSnO3 and hollow CuZnSnO3.

[0029] Figure 14 Comparison diagram of solid / hollow samples Cu6ZnSnO3: (a) solid, (b) hollow.

[0030] Figure 15 (a) Cu6ZnSnO3 cycle stability test, (b) scanning image and EDS mapping of Cu6ZnSnO3 electrode after reaction. DETAILED DESCRIPTION

[0031] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as limiting the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0032] It should be understood that the terms described herein are intended only to describe particular embodiments and are not intended to limit the present invention. In addition, for numerical ranges herein, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. The intermediate value within any stated value or stated range, and each smaller range between any other stated value or intermediate value within the stated range, is also encompassed within the present invention. The upper and lower limits of these smaller ranges may be independently included or excluded within the scope.

[0033] Unless otherwise indicated, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art. Although only preferred methods and materials are described herein, any methods and materials similar or equivalent to those described herein may also be used in the practice or testing of the present invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials associated with the documents. In the event of any conflict with any incorporated document, the contents of this specification shall prevail.

[0034] It will be apparent to those skilled in the art that various modifications and variations may be made to the specific embodiments described herein without departing from the scope or spirit of the invention. Other embodiments will be apparent to those skilled in the art from the description of the invention. The description and examples are intended to be exemplary only.

[0035] The words “include,” “including,” “have,” “contain,” etc. used in this document are open-ended terms, meaning including but not limited to.

[0036] The "room temperature" mentioned in the present invention, unless otherwise specified, refers to 20-30°C.

[0037] Low-coordinated Zn sites can optimize the binding energy of COOH intermediates and have optimal adsorption energy for *COOH, thereby reducing the CO2 activation energy barrier and facilitating the conversion of CO2 to CO. On the other hand, the introduction of Zn can improve the stability of the material. The Cu-Sn bimetallic catalyst exhibits high selectivity for CO. By adjusting the ratio of the two, it was found that the amount of Sn doping has a significant effect on the selectivity of CO and the reaction rate. As the amount of Sn doping increases, the reaction rate shows a downward trend. The morphology and structure of the catalyst are more inclined to various three-dimensional configurations with large specific surface areas, such as shell / core structures and hollow structures, which can greatly enhance the ability of physical adsorption. Based on the above content, the present invention designed and synthesized a trimetallic catalyst based on three metals: Cu, Zn, and Sn. The catalyst is designed as a hollow cube to increase its specific surface area and metal catalytic sites, and the optimal electrocatalytic CO2RR state is achieved by adjusting the internal Cu and Zn contents. Characterization using SEM, TEM, and XRD confirmed the successful synthesis of samples with varying copper doping levels. Experimental determination revealed that the optimal sample, Cu6ZnSnO3, achieved the highest formic acid selectivity of 93% at -1.5V vs. RHE, while hydrogen evolution was reduced to less than 5%. At the same operating voltage, hydrogen evolution was reduced by nearly 10 times compared to the undoped ZnSnO3 sample and by 5 times compared to the solid sample. Furthermore, selectivity remained essentially unchanged after 40 hours of cycling stability testing.

[0038] A first aspect of the present invention provides a method for preparing a catalyst for electrocatalytic CO2RR, comprising the following steps:

[0039] Step 1: mixing a Sn salt solution and a Zn salt solution to obtain a mixed solution; adding alkaline solution A to the mixed solution to carry out reaction 1, and adding alkaline solution B to carry out reaction 2 to obtain ZnSn(OH)6 hollow cubes;

[0040] Step 2: Dispersing the ZnSn(OH)6 hollow cubes in water to obtain a dispersion; mixing the dispersion with a Cu salt solution to perform a hydrothermal reaction to obtain Cux ZnSn(OH)6 hollow cube;

[0041] Step 3, the Cu x The ZnSn(OH)6 hollow cube was annealed to obtain the catalyst (Cu x ZnSnO3).

[0042] In a preferred embodiment of the present invention, in step 1, the solvent of the Sn salt solution is anhydrous ethanol, the Sn salt is SnCl45H2O, and the concentration of the Sn salt solution is 70 mg / mL; the solvent of the Zn salt solution is water, and the Zn salt is ZnCl2; the Zn salt solution also includes sodium citrate; the concentration of the Zn salt in the Zn salt solution is 4.5 mg / mL, and the concentration of sodium citrate is 8.6 mg / mL.

[0043] In the present invention, sodium citrate is used as a complexing agent to form a complex with high-valent metal ions, which is beneficial for the formation of ZnSn(OH)6 hollow cubes and Cu x ZnSn(OH)6 hollow cube CO2RR catalyst plays a decisive role.

[0044] In a preferred embodiment of the present invention, in step 1, the alkaline solution A is a 2M NaOH solution (the solvent is water); and the alkaline solution B is a 0.5M NaOH solution (the solvent is water).

[0045] In a preferred embodiment of the present invention, in step 1, the volume ratio of the Sn salt solution to the Zn salt solution, alkaline solution A and alkaline solution B is 1:6:1:4; the reaction 1 is specifically stirred at room temperature for 1 hour; and the reaction 2 is specifically stirred at room temperature for 15 minutes.

[0046] The present invention does not impose any particular limitation on the stirring speed in reaction 1 and reaction 2, and any stirring speed commonly used by those skilled in the art may be used.

[0047] In a preferred embodiment of the present invention, in step 2, the Cu salt and the Cu in the ZnSn(OH)6 hollow cube 2+ :Zn 2+ Molar ratio = 4-16:1.

[0048] More preferably, Cu 2+ :Zn 2+ Molar ratio = 4 to 8:1; more preferably, Cu 2+ :Zn 2+ Molar ratio = 5-7:1.

[0049] In a preferred embodiment of the present invention, in step 2, the temperature of the hydrothermal reaction is 180° C. and the time is 5 hours.

[0050] In a preferred embodiment of the present invention, in step 3, the annealing is specifically carried out under an inert atmosphere at 1°C min -1 After the temperature reaches 300℃, the heating is stopped and the furnace is cooled.

[0051] When preparing ZnSn(OH)6 hollow cubes, after reaction 2 is completed, the process further includes separation, washing and drying the obtained precipitate.

[0052] After the hydrothermal reaction is completed, the steps of collecting the precipitate by centrifugation, and washing and drying the precipitate are also included.

[0053] The second aspect of the present invention provides a catalyst for electrocatalytic CO2RR prepared according to the above preparation method.

[0054] A third aspect of the present invention provides a working electrode, which is prepared by making the above-mentioned catalyst for electrocatalytic CO2RR into an ink solution and drop-coating it on the surface of an electrode material;

[0055] In a preferred embodiment of the present invention, the ink solution is prepared by mixing a catalyst for electrocatalytic CO2RR with an ethanol solution and Nafion; and the electrode material is hydrophobic carbon paper.

[0056] The mass volume ratio of catalyst, ethanol solution and Nafion used for electrocatalytic CO2RR was 10 mg:970 μL:20 μL.

[0057] A fourth aspect of the present invention provides a use of the above-mentioned catalyst for electrocatalytic CO2RR or the above-mentioned working electrode in electrocatalytic CO2RR.

[0058] Unless otherwise specified, the technical solutions described in the present invention are all conventional solutions in the field, and the reagents or raw materials used, unless otherwise specified, are purchased from commercial channels or have been disclosed.

[0059] The test method involved in the present invention is as follows:

[0060] 1. Electrochemical experiments

[0061] Electrochemical characterization primarily included linear sweep voltammetry (LSV), cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), electric double-layer capacitance (CDL), Tafel slope, and electrochemically active surface area (ECSA) measurements. Electrochemical measurements were performed using a CHI660E electrochemical workstation (Shanghai) in a three-electrode system, with a platinum wire and an Ag / AgCl electrode serving as the counter and reference electrodes, respectively. A proton exchange membrane was used between the cathode and anode.

[0062] Linear sweep voltammetry involves applying a potential to an electrode that varies linearly at a constant rate over time and recording the resulting current versus potential curve to produce a voltammogram. During the sweep, when the potential reaches the reduction potential of the oxidized species or the oxidation potential of the reduced species on the electrode, the corresponding redox reaction occurs, generating a Faradaic current. By analyzing parameters such as the shape, peak potential, and peak current of the voltammogram curves of working electrodes with different catalyst loadings, the Faradaic current magnitudes of the working electrodes with different catalyst loadings at corresponding voltages can be compared to determine their catalytic performance. Electrochemical measurements were performed using a CHI660E electrochemical workstation (Shanghai) in a three-electrode system, with a platinum wire and an Ag / AgCl electrode serving as the counter and reference electrodes, respectively. A proton exchange membrane was used between the cathode and anode. The electrolyte used was a 0.1 M KHCO solution. Excess nitrogen and carbon dioxide were introduced before testing, and LSV curves were obtained under different atmospheres at a sweep rate of 0.1 V / s. Comparison of the LSV curves under different atmospheres provides a rough estimate of the electrode catalytic activity and its reaction voltage window. At the same time, the changes in LSV of three working electrodes loaded with different catalysts after CO2 was introduced for the same time can be compared.

[0063] Cyclic voltammetry involves controlling the electrode potential at a certain rate and in a certain direction (positive or negative sweep) to form a current-potential curve (iE). The last cycle is usually selected for plotting, as this curve reflects the iE relationship. Analysis of this curve can reveal information about the electrochemical reaction, such as the location of the redox peak, current peak value, and half-width.

[0064] Electrochemical impedance spectroscopy involves applying a small-amplitude AC signal of varying frequencies to an electrochemical system and measuring the change in the voltage-to-current ratio of the AC signal as a function of the sinusoidal frequency ω, or the change in the impedance phase angle Φ as a function of ω. This allows for analysis of electrode process dynamics, double layer behavior, and diffusion, and for studying electrode materials, solid electrolytes, conductive polymers, and corrosion protection mechanisms. Two common electrochemical impedance spectroscopy methods are the Nyquist plot and the Bode plot. The Z' (real part) and Z" (imaginary part) in the Nyquist plot represent the electron transfer resistance (Rct) at the electrode surface. Its value is equivalent to the diameter of the semicircle and can be used to describe the interface characteristics between the electrode and the electrolyte. The Nyquist plot consists of two parts: the semicircular portion at high frequencies corresponds to electron transport-limited processes, while the linear portion at low frequencies corresponds to diffusion-limited processes. Calculating the electron transfer resistance Rct at the electrode surface can explain certain phenomena in experimental processes such as photocatalysis and electrocatalysis.

[0065] The electrochemical active area is an important parameter for characterizing the activity of electrode reactions. It is usually measured by cyclic voltammetry to compare the size of the electrode active area. In fact, the test method of ECSA is the same as the above-mentioned voltammetry cycle, except that the parameters of the cyclic voltammetry experiment, such as scan rate, number of cycles and potential range, need to be adjusted. The ECSA of the material is evaluated by cyclic voltammetry, and the scan rate v is changed in the non-Faraday region. The current density j in the non-Faraday region is linearly related to the scan rate v. According to Cd=j / v, the active area of ​​the material can be obtained to evaluate the active sites of the material. The specific operation is: using a three-electrode system, the working electrode is the electrode prepared in the embodiment, the reference electrode is an Ag / AgCl electrode, the counter electrode is a platinum wire, the electrolyte is a 0.1M KHCO3 solution, and a nitrogen-saturated electrolyte is used to ensure that it is not affected by other substances during the cyclic voltammetry test. First, measure its open circuit voltage and take the value within the range of open circuit voltage ±0.05V. By scanning the CV curve at different scan rates of 50mV / s, 40mV / s, 30mV / s, 20mV / s, and 10mV / s, take the current density at the midpoint as the difference, recorded as j, and make a graph of j and v. The slope is the capacitance of the corresponding electrode. By comparing the capacitance, the ECSA size of the electrode is compared.

[0066] The Tafel slope is an important parameter used in the field of electrochemistry to describe the kinetics of electrode reactions. It reflects the logarithmic relationship between electrode potential and current density and plays a key role in studying electrode reaction rates and evaluating electrocatalyst performance. The Tafel slope represents the slope of the linear relationship between overpotential (η) and logarithmic current density (logj) in an electrode reaction. Its mathematical expression is η = a + blogj, where b is the Tafel slope, and its unit is (mV dec) -1). a is the intercept, which depends on factors such as the starting conditions of the electrode reaction. This equation, known as the Tafel equation, quantitatively describes the relationship between the electrode reaction rate (measured by current density j) and the overpotential. In an ideal electrochemical system, the Tafel slope can be obtained by linearly fitting the experimentally measured overpotential and the corresponding LSV.

[0067] Chronoamperometry (It) is a method of applying a constant potential to obtain a current-time curve within a set time, which is recorded as an It curve. Chronoamperometry is widely used in many fields. It can be used to study the kinetic behavior of electrochemical reactions, activity evaluation of electrochemical catalysts, process optimization of electrochemical synthesis, etc. In addition, chronoamperometry can also be applied to the design and analysis of electrochemical sensors, as well as research in the field of electrochemical energy storage and conversion. The present invention uses chronoamperometry to select a voltage in a suitable potential range and evaluate the catalyst performance by measuring the Faraday efficiency of the product. The specific operation is: using the same reaction cell (H-type reaction cell), but replacing the closed kettle reaction in which CO2 bubbling is performed before the reaction, a continuous CO2 flow is used during the performance test to ensure that the gas phase product can be analyzed online. 32 mL of 0.1 M KHCO₃ solution was injected into each end of the H cell as the electrolyte. After the reaction cell was assembled, CO₂ was bubbled through the reactor for 20 minutes to fill it with CO₂. The catalytic performance of the catalyst at different voltages was tested. The test lasted 2 hours, with an online monitoring every 20 minutes. After the reaction was complete, the catholyte was collected for quantification of the liquid phase product. The above steps were repeated for performance testing at the next voltage.

[0068] 2. Quantitative Experiment of Electrocatalytic CO2RR Products

[0069] In the electrocatalytic CO2RR process, the chronoamperometry method was used, and the gas phase product analysis was also carried out online using a high performance gas chromatograph GC7920. The liquid product quantification was carried out by collecting the electrolyte after the reaction and using 1 Quantitative analysis was performed by H NMR nuclear magnetic resonance hydrogen spectrum. According to relevant literature, the possible related liquid phase products are mainly formic acid and ethanol. By preparing DMSO, sodium formate, and CH3CH2OH standard solutions with known amounts of substances for NMR testing, the NMR data were used to draw standard curves for quantitative formate and ethanol, as shown in the following figure: Figure 1 shown.

[0070] 3. Electrochemical in situ infrared experiment

[0071] In situ Fourier transform infrared spectroscopy (in situ FTIR) is an instrument widely used in infrared spectroscopy analysis. It uses the Fourier transform principle to convert infrared light signals into a spectrum, providing information on the chemical composition and molecular structure of the sample. By performing infrared testing, the presence of organic functional groups in the material can be characterized to verify the successful synthesis of the catalyst and to compare the differences between them. Electrochemical in situ diffuse reflectance infrared spectroscopy is a characterization method that combines infrared spectroscopy with electrochemical methods. By performing in situ characterization of species at the electrode-electrolyte interface under electrochemical reaction conditions, the electrochemical reaction mechanism, intermediate products on the electrode surface, and adsorbed species can be studied.

[0072] Using a Thermo Fisher Scientific Nicoleti S50 Fourier transform infrared spectrometer in conjunction with a Shanghai Chenhua electrochemical workstation, data were collected to investigate the evolution of intermediates during the reaction and analyze the formation mechanism of C2+ products. Due to the limitations of the reaction environment, a 0.1 M KHCO3 solution pretreated with CO2 was used as the electrolyte. A glassy carbon electrode drop-coated with an ink solution prepared from electrocatalyst powders was used as the working electrode for in situ electrochemical infrared testing. Data were subsequently analyzed and processed using appropriate software.

[0073] The technical solutions provided by the present invention are described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0074] Example 1: Preparation of ZnSn(OH)6 Hollow Cubes (abbreviated as: Hollow ZnSn(OH)6)

[0075] Step 1, prepare solution A: add 0.7 g SnCl45H2O to 10 mL of anhydrous ethanol and stir magnetically until dissolved. The solution is now transparent and keeps stirring until ready for use.

[0076] Prepare Solution B: Add 0.27 g ZnCl2 and 0.516 g sodium citrate to 60 mL deionized water and stir magnetically until dissolved. The solution is now transparent and continues stirring until ready to use.

[0077] In step 2, slowly add solution B to solution A. A white precipitate will gradually appear and disperse in the mixture. After solution B is completely added, stir the mixture for a period of time to ensure thorough mixing. Then, slowly add 10 mL of 2 M NaOH solution dropwise to the mixture. Stir for 1 hour, then add 40 mL of 0.5 M NaOH solution. After stirring for 15 minutes, separate the precipitate, wash with water and ethanol until neutral, and dry in a vacuum at 60°C for 12 hours. The resulting sample is recorded as ZnSn(OH)6 hollow cubes.

[0078] Example 2: Preparation of ZnSn(OH)6 Solid Cubes (Solid ZnSn(OH)6)

[0079] Step 1 is the same as step 1 in Example 1.

[0080] In step 2, solution B is slowly added to solution A. A white precipitate is observed to gradually form and disperse in the mixture. After solution B is completely added, the mixture is stirred for a period of time to ensure thorough mixing. Then, 10 mL of 2M NaOH solution is slowly added dropwise to the mixture. Stirring is continued for 1 hour. The precipitate is separated and washed with water and ethanol until neutral. The precipitate is then dried under vacuum at 60°C for 12 hours. The resulting sample is designated as a ZnSn(OH)6 solid cube.

[0081] Example 3: Cu x ZnSn(OH)6 hollow cube (abbreviated as: hollow Cu x Preparation of ZnSn(OH)6

[0082] Step 1, first prepare liquid C: ultrasonically disperse 0.143g of ZnSn(OH)6 hollow cubes in deionized water as much as possible, and stir to prevent it from settling (the amount of water used should be enough to evenly disperse the ZnSn(OH)6 hollow cubes).

[0083] Prepare solution D: Dissolve 1.023 g of CuCl2·2H2O in water to form a blue solution (the amount of water used should be sufficient to fully dissolve the CuCl2·2H2O).

[0084] Step 2: Add liquid D to liquid A to make the metal ion molar ratio of Cu 2+ :Zn 2+ =4:1. The resulting mixed solution was then transferred to a 100 mL stainless steel autoclave and hydrothermally treated at 180°C for 5 h. After cooling, the blue precipitate was collected by centrifugation, washed with ethanol and distilled water, and dried under vacuum at 60°C for 12 h. This yielded a sample of Cu₄ZnSn(OH)₆ hollow cubes.

[0085] The Cu superscript 4 in Cu4ZnSn(OH)6 represents the ratio of copper input, not the element ratio of the actual hollow cube. For specific element content, see Figure 6 (b). For comparison, Cu 2+ / Zn 2+ =6:1, 8:1, 16:1, that is, adding 1.534g, 2.046g, 4.092g of CuCl2·2H2O to obtain Cu x The hollow ZnSn(OH)6 cubes are marked as Cu6ZnSn(OH)6, Cu8ZnSn(OH)6, Cu16 ZnSn(OH)6.

[0086] Example 4: Cu x ZnSn(OH)6 solid cube (abbreviated as: solid Cu x Preparation of ZnSn(OH)6

[0087] The only difference from Example 3 is that the ZnSn(OH)6 hollow cubes in step 1 are replaced by equimolar ZnSn(OH)6 solid cubes.

[0088] Example 5: Cu x ZnSnO3 hollow cubic electrocatalyst (abbreviated as: hollow Cu x Preparation of ZnSnO3

[0089] The Cu prepared in Example 3 x ZnSn(OH)6 hollow cubes were heated in a tube furnace at 1℃min -1 After annealing at 300℃ in an Ar atmosphere, the heating was stopped and the furnace was cooled to obtain a gray-green sample, which was the electrocatalyst. x ZnSn(OH)6 are Cu4ZnSn(OH)6, Cu6ZnSn(OH)6, Cu8ZnSn(OH)6, Cu 16 The electrocatalysts prepared by ZnSn(OH)6 were labeled Cu4ZnSnO3, Cu6ZnSnO3, Cu8ZnSnO3, Cu 16 ZnSnO3.

[0090] With Cu x The preparation method of ZnSnO3 hollow cubic electrocatalyst is the same as that of ZnSn(OH)6 hollow cube, ZnSn(OH)6 solid cube, Cu x ZnSn(OH)6 solid cubes replace Cu x The hollow ZnSn(OH)6 cubes were annealed in the same manner in a tube furnace, and the catalysts obtained were marked as hollow ZnSnO3, solid ZnSnO3, solid Cu x ZnSn(OH)6.

[0091] Example 6: Preparation of working electrode

[0092] 10 mg of the electrocatalyst powder prepared in Example 5 was weighed to prepare 1 mL of ink solution containing 970 μL of anhydrous ethanol and 20 μL of Nafion (D520CS). The solution was ultrasonically treated for half an hour in an ice-water bath. Meanwhile, the hydrophobic carbon paper was cut into 2*0.5 cm 2Then, evenly apply 10 μL of the ink solution on the carbon paper and dry overnight to obtain the working electrode. Prepare more than three such electrodes at the same time for future use.

[0093] The samples prepared in the examples were tested, and the results were as follows:

[0094] 1. Structure and morphology of catalyst

[0095] Among the samples, Cu6ZnSnO3 was the best sample based on the electrocatalytic CO2RR performance. Therefore, the results were discussed mainly based on the sample Cu6ZnSnO3, and the other samples were used as comparison samples.

[0096] By comparison Figure 2 In (a)-(c), it can be seen that in the process of synthesizing Cu6ZnSnO3, the precursor ZnSn(OH)6 is a cube of about 2μm ( Figure 2 In (a), the outer surface is a relatively smooth sheet stack. Figure 2 (b) Cu was incorporated by ion exchange 2+ After that, the size of Cu6ZnSn(OH)6 cubes remains unchanged but the surface changes from lamellar stacking to rough granular stacking. Figure 2 Middle (c) is a scanning electron microscope image of hollow Cu6ZnSnO3, which is obtained by calcining hollow Cu6ZnSn(OH)6 under argon environment. Due to the low heating rate and low annealing temperature, there is no significant change in morphology compared with hollow Cu6ZnSn(OH)6. Figure 2 (d)-(g) are EDS mapping images of hollow Cu6ZnSnO3, and it is observed that Cu, Zn, Sn, and O elements are evenly distributed on the surface of regular cubes.

[0097] As a comparison of the hollow samples, the solid precursor ZnSn(OH)6 Figure 3 As shown in (a), no obvious changes can be seen in the hollow precursor ZnSn(OH)6 under the scanning electron microscope, and subsequent transmission electron microscopy analysis is required. In addition, the scanning electron microscope can also be used to compare hollow samples with different copper contents, that is, the hollow Cu8ZnSn(OH)6 and hollow Cu8ZnSnO3 obtained when Cu:Zn is 8:1. Figure 3 As shown in (b) and (c), it can be seen that there is no obvious change in the morphology, except that the cubic structure may collapse as the copper content increases, which was confirmed in the subsequent transmission electron microscopy results of Cu:Zn=16:1.

[0098] To further confirm that solid cubic samples can be obtained without using NaOH etching, the use of transmission electron microscopy is necessary. Figure 4The transmission electron microscope image of the solid sample shows that all samples are black and opaque. This is because the thickness of the solid sample is relatively large, which exceeds the penetration ability of the electron beam. Figure 4 As can be seen from (a) and (b), solid ZnSnO3 can present a regular cubic configuration. Figure 4 (c) shows the morphological details of the edge of solid ZnSnO3, combined with Figure 3 In (a), it can be seen that these step-like shadows are the shadows produced by the layered stacking on the sample surface during transmission. Figure 4 (d)-(f) are solid Cu6ZnSnO3, which also has a relatively regular cubic configuration. However, compared with the solid ZnSnO3 without copper doping, the cube corners of the solid Cu6ZnSnO3 sample are more rounded, which is explained by the fact that some Zn 2+ Cu 2+ The substitution process will damage the regular solid ZnSnO3, and the corners have more exposed sites and are therefore more easily replaced. Figure 4 In (f), it can be observed that the surface of the solid Cu6ZnSnO3 cube has shown a stacking of small particles, which is very different from the surface of the solid ZnSnO3 cube without copper doping. Figure 4 (g)-(i) are samples doped with a large amount of copper. x From the transmission electron microscopy image of ZnSnO3 (x=16), it can be observed that the overall morphology can no longer maintain a cubic configuration, which is consistent with the above analysis.

[0099] Similarly, high-resolution transmission electron microscopy was used to verify the successful contraction of the hollow cube and characterize the distribution of each element in the cube, such as Figure 5 This is the high-resolution transmission electron microscopy image of hollow Cu6ZnSnO3 and its EDS mapping. It is observed that when the Cu doping amount is moderate, the stable hollow structure can still be maintained ( Figure 5 (a)-(c)), and the elements on the surface of the cube are evenly distributed ( Figure 5 (d)-(g)), Figure 5 (h)-(n) show the edge of the hollow cube after local magnification. It is observed that the cube is composed of many particles and the elements are evenly distributed, which is consistent with the prediction.

[0100] Figure 6 (a) is the sample with different copper feed ratio (Cu x Comparison of X-ray diffraction patterns of ZnSnO3 (x=0, 6, 8, 16). 2+When replaced (i.e. ZnSnO3), the X-ray diffraction pattern has no obvious diffraction peaks, only two relatively wide and low diffuse scattering peaks (located at about 33° and 57°), which is a typical feature of amorphous materials. After adding copper elements for ion exchange, new diffraction peaks appear, and as the proportion of copper elements in the feed increases, the diffraction peaks in the displayed spectrum become sharper. By comparing with the standard PDF card, it is identified as CuO and SnO2. This can be explained by Cu 2+ The introduction of Cu makes the amorphous state of ZnSnO3 transform into a crystalline state (the peak becomes obvious), and with the 2+ The peaks of CuO and SnO2 become obvious, but no peaks of ZnO or other forms of zinc are observed. This may be because Zn exists in the amorphous form of ZnSnO3, and the Zn content decreases accordingly after Cu substitution.

[0101] exist Figure 6 (b) shows the Cu x The final content of each metal element in the ZnSnO3 hollow cube is that Sn remains basically unchanged, while Cu increases with the increase of the added amount, while Zn decreases accordingly. This is because the hydrothermal ion exchange method is used in the experiment, and the Zn and Sn in the precursor ZnSn(OH)6 are respectively Zn 2+ 、Sn(OH)6 2- exists in the form of Cu 2+ Will give priority to replacing Zn 2+ Another influencing factor is the solubility product (K sp ), used to describe the solubility of a substance. Generally speaking, the smaller the value, the more difficult it is to dissolve. In an alkaline environment, the solubility product constants of the three metal elements are: K sp,Cu(OH)2 =2.2×10 -20 , K sp,Zn(OH)2 =1.2×10 -17 , K sp,[Sn(OH)6] 2- =1.0×10 -56 , so Cu 2+ Easier to replace Zn 2+ Difficult to replace Sn 4+ .also, Figure 6 (b) When the feed ratio reaches 8:1, Cu 2+ It has basically reached the maximum amount that can be replaced, and when it reaches 16:1, the cubic shape can no longer be maintained.

[0102] XPS spectra were used to understand the valence changes of each element and the surface chemical composition of ZnSnO3 before and after copper was added. 16Three groups of ZnSnO3 (Cu:Zn=16:1) samples are representative. Figure 7 (a) shows the Zn 2p XPS spectra of the three groups of samples. First, as the copper doping amount increases, the characteristic peak of Zn 2p becomes spiky (Cu6ZnSnO3) or even disappears (Cu 16 ZnSnO3), this phenomenon is similar to the previous Figure 6 The conclusion of (b) is the same. Comparing ZnSnO3 and Cu6ZnSnO3, Zn 2p 3 / 2 From 1021.38eV to 1023.98eV, Zn 2p 1 / 2 It shifted from 1044.38eV to 1046.98eV. This shows that the introduction of copper makes Zn 2+ The electron density decreases.

[0103] Figure 7 (b) shows the changes of Sn 3d at different copper doping levels. The Sn 3d spectrum of ZnSnO3 has three main peaks, which are located at 498.68eV, 494.98eV, and 486.58eV respectively; the Sn 3d spectrum of Cu6ZnSnO3 has four main peaks, which are located at 497.68eV, 495.38eV, 489.28eV, and 486.98eV respectively; 16 The Sn 3d spectrum of ZnSnO3 has two main peaks at 494.98eV and 486.58eV. In contrast, the Sn 3d peak of Cu6ZnSnO3, the best copper-doped sample, is broader and shifts toward higher binding energy while maintaining a hollow cubic configuration.

[0104] The O1s of the three groups of samples also have significant differences, at 531.28eV, 533.16eV, and 530.28eV, respectively. The O1s of Cu6ZnSnO3, the best sample, shifts 1.9eV toward higher binding energy, indicating that the electron cloud density around the oxygen atoms decreases and the degree of metal oxidation increases, making the inner electrons (O 1s) of the oxygen atoms more strongly bound to the nucleus, increasing the binding energy, and shifting the XPS peak toward higher energy (e.g., Figure 7 (as shown in (c)).

[0105] Figure 8 It is about hollow ZnSnO3, hollow Cu6ZnSnO3 and hollow Cu 16 Cu 2p and Cu LMM spectra of ZnSnO3 to determine the electron distribution of copper. Figure 8 (a) is the Cu 2p spectrum of the three groups of samples. ZnSnO3 does not contain Cu, so there is no corresponding characteristic peak in the spectrum. Cu6ZnSnO3 and Cu 16Compared with ZnSnO3, the difference is quite large. As the copper feed amount increases (6:1 to 16:1), the overall peak position moves significantly toward the low binding energy direction.

[0106] 2. N2 adsorption-desorption isotherm and pore size distribution

[0107] In order to further understand the pore size characteristics and specific surface area of ​​the catalyst, the present invention conducted N2 adsorption and desorption isothermal experiments. 16 Three groups of ZnSnO3 samples were compared in the experiment. Figure 9 This is the test result. Figure 9 (a) is the nitrogen adsorption-desorption isotherm of the three groups of samples. The analysis shows that the hollow ZnSnO3 belongs to the type I adsorption curve, indicating that the material is mainly microporous structure, while the hollow Cu6ZnSnO3 and hollow Cu 16 ZnSnO3 exhibits type II adsorption, and the material is mainly macroporous. This conclusion is reflected in the pore size test results of each sample ( Figure 9 This was verified in (b)-(d)).

[0108] Table 1 is hollow ZnSnO3, hollow Cu6ZnSnO3, hollow Cu 16 Specific surface area comparison of ZnSnO3, Cu 2+ Replacement of Zn 2+ The specific surface area increases significantly after Cu 2+ The introduction of Cu changed the material arrangement from the original layered dense stacking to fine particle dense stacking, greatly increasing the porosity of the sample. 2+ Time (Cu 16 ZnSnO3), the material structure is damaged and the specific surface area decreases.

[0109] Table 1 Hollow ZnSnO3, hollow Cu6ZnSnO3, hollow Cu 16 Specific surface area of ​​ZnSnO3

[0110]

[0111] 3. Electrochemical characterization of catalysts

[0112] Electrochemical tests were used to characterize the electrochemical activity of the catalysts. Figure 10 The SEM and EDS mapping images of the hydrophobic carbon paper-supported hollow Cu6ZnSnO3 catalyst show uniformly distributed cubic structures attached to the surface of the hydrophobic carbon paper, representing the hollow Cu6ZnSnO3 catalyst awaiting electrochemical characterization. Electrodes with other catalysts were prepared using the same method.

[0113] Electrochemical characterization was performed using the prepared working electrode. Figure 11 and Figure 12 shown. Figure 11 (a) shows the linear voltammetric sweep curves of the working electrodes with different catalysts from 0.3V to -1.8V vs. RHE, which are used to determine the current density at the operating voltage. It can be seen that the overall current density of the copper-doped samples is superior to that of the pure ZnSnO3 catalyst within this operating voltage range.

[0114] Figure 11 (b)-(e) correspond to the cyclic voltammetry characteristic curves of the working electrodes of each catalyst, respectively. Comparing the conditions of each sample under nitrogen and CO2 gas atmospheres, it is found that the reduction potential can be reached at a lower voltage under CO2 atmosphere. This indicates that it is reactive towards CO2. Figure 11 The middle (f) is the impedance test results of each catalyst. The data shows that as the copper content increases, the impedance decreases, which reduces the energy loss during the reaction.

[0115] In addition, electrochemical characterization also includes electrochemically active surface testing and Tafel slope. Figure 12 (a)-(d) are the ECSA test results of different copper doping amounts, based on which the double layer capacitance of the electrode is calculated ( Figure 12 (e) reflects the charge storage capacity and charge transfer characteristics between the electrode surface and the electrolyte solution. The optimal sample, hollow Cu6ZnSnO3, exhibited the highest double-layer capacitance, indicating a higher specific surface area, good conductivity, and suitable surface chemistry, providing more active sites and a larger double-layer capacitance. Figure 12 Figure (f) shows the Tafel slopes of the aforementioned samples. Hollow Cu6ZnSnO3 exhibits the lowest slope, indicating that the easier it is to drive the reaction at the same potential, the higher the catalytic activity. This provides the electrochemical basis for subsequent chronoamperometric testing of the samples' electrocatalytic CO2RR.

[0116] 4. Performance evaluation of electrocatalytic CO2 reduction

[0117] Based on the above electrochemical experimental results, it is assumed that the best sample is hollow Cu6ZnSnO3. This statement has been confirmed in the formal electrocatalytic CO2RR. In this part of the experiment, all the synthesized samples of the examples were subjected to electrocatalytic CO2RR performance tests for comparison. Including: 1. Horizontal comparison: hollow cubic catalysts with different copper doping amounts (ZnSnO3, Cu4ZnSnO3, Cu6ZnSnO3, Cu8ZnSnO3, Cu 16Comparative experiment on electrocatalytic CO2RR of solid and hollow cubes of the hollow best sample (the test results show that it is sample Cu6ZnSnO3) . 2. Longitudinal comparison: comparison of the electrocatalytic CO2RR performance of solid and hollow cubes of the hollow best sample (the test results show that it is sample Cu6ZnSnO3).

[0118] First, the results of the horizontal experiment are as follows Figure 13 As shown, Figure 13 The electrocatalytic CO2RR performance of hollow cubes with different copper doping amounts is demonstrated. First, all samples maintain only formic acid selectivity for CO2 reduction. The hollow ZnSnO3 sample used as a basic comparison sample has a more serious HER during the electrocatalytic CO2RR process, with the highest formic acid selectivity (FE) at a voltage of -1.4 V vs. RHE. HCOOH =58%) and hydrogen now accounts for about the other 37% ( Figure 13 As shown in (a)). With the replacement of the doped Cu 2+ The selectivity of formic acid showed a trend of increasing first and then decreasing, while the degree of hydrogen evolution showed a trend of decreasing first and then increasing ( Figure 13 (a)-(e)). The best formic acid selectivity occurs when the hollow cubic Cu6ZnSnO3 catalyst is used for electrocatalytic CO2RR, where the formic acid selectivity is as high as 93% and hydrogen evolution is suppressed to less than 5% ( Figure 13 (as shown in (c)).

[0119] Furthermore, as the copper incorporation level continued to increase, the catalyst could no longer maintain a stable hollow cubic structure and broke. This sample was named CuZnSnO3 Breakage. The electrocatalytic CO2RR results of this sample are shown in Figure 13 In (f), the C2 product appears, which is the result of the introduction of a large amount of copper. However, this greatly increases the degree of hydrogen evolution, reduces the selectivity of the reaction, and fails to utilize the large specific surface area and multiple reactive sites of the originally designed hollow cubic structure.

[0120] After determining the optimal copper incorporation amount of the hollow sample, it is necessary to longitudinally compare the effects of solid / hollow structures on the electrocatalytic CO2RR. Figure 14 This is a comparison of solid and hollow Cu6ZnSnO3 catalysts. Compared to the solid Cu6ZnSnO3 catalyst, the hollow Cu6ZnSnO3 catalyst exhibits a lower current density at the same potential due to the lower material density of the hollow structure. However, the hollow sample exhibits higher formic acid selectivity, demonstrating that the large pores, high surface area, and multiple active sites provided by the hollow structure can significantly enhance the efficiency of electrocatalytic CO2RR.

[0121] 5. Stability evaluation of electrocatalysts

[0122] The cyclic stability of the catalyst is also an important indicator for considering the performance of the catalyst. In order to explore the cyclic stability of the hollow Cu6ZnSnO3 sample, the stability test was carried out by using the chronoamperometry method with a 4-hour cycle to replace the electrolyte without replacing the working electrode. The electrolyte after each cycle was collected and tested. 1 The yield of the product formic acid was quantitatively analyzed by H NMR. Figure 15 As shown in (a). Figure 15 As shown in (a), the working electrode coated with the catalyst Cu6ZnSnO3 can maintain a stable current and the selectivity of formic acid remains basically unchanged during the 40h cycle, which proves that the catalyst has strong stability. At the same time, the morphology of the working electrode after 40h of reaction was characterized ( Figure 15 (b)), compared with the working electrode before the reaction ( Figure 10 ) found that there was no significant change in the morphology, which further proved that the catalyst Cu6ZnSnO3 can be used stably in the electrocatalytic CO2RR process and achieve long-term catalytic effect.

[0123] In summary, the present invention synthesizes solid / hollow cubic catalysts Cu with different copper incorporation amounts. x ZnSnO3 is used for electrocatalytic CO2RR. By comparing samples with different copper doping amounts, it was found that the hollow Cu6ZnSnO3 sample had the best formic acid selectivity (reaching 93%), at which time the hydrogen evolution selectivity was less than 5%. However, as the copper ratio in the sample increased, the formic acid selectivity decreased, and when too much copper was added, the hollow cube could no longer be maintained stable. On the other hand, by comparing the solid and hollow samples of the best sample Cu6ZnSnO3, it was found that the hollow sample was indeed as hypothesized in the experiment: the hollow cube could provide a larger specific surface area and metal sites for the reaction, which was more conducive to electrocatalytic CO2RR.

[0124] The embodiments described above are merely descriptions of preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Without departing from the spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by persons skilled in the art should fall within the scope of protection defined by the claims of the present invention.

Claims

1. A method for preparing a catalyst for electrocatalytic CO2RR, characterized in that: The following steps are involved: Step 1: mixing a Sn salt solution and a Zn salt solution to obtain a mixed solution; adding alkaline solution A to the mixed solution to carry out reaction 1, and adding alkaline solution B to carry out reaction 2 to obtain ZnSn(OH)6 hollow cubes; Step 2: Dispersing the ZnSn(OH)6 hollow cubes in water to obtain a dispersion; mixing the dispersion with a Cu salt solution to perform a hydrothermal reaction to obtain Cu x ZnSn(OH)6 hollow cube; Step 3, the Cu x The ZnSn(OH)6 hollow cubes are annealed to obtain the catalyst for electrocatalytic CO2RR.

2. The method for preparing a catalyst for electrocatalytic CO2RR according to claim 1, characterized in that: In step 1, the solvent of the Sn salt solution is anhydrous ethanol, the Sn salt is SnCl45H2O, and the concentration of the Sn salt solution is 70 mg / mL; the solvent of the Zn salt solution is water, and the Zn salt is ZnCl2; the Zn salt solution also includes sodium citrate; the concentration of the Zn salt in the Zn salt solution is 4.5 mg / mL, and the concentration of sodium citrate is 8.6 mg / mL.

3. The method for preparing a catalyst for electrocatalytic CO2RR according to claim 1, characterized in that: In step 1, the alkaline solution A is a 2M NaOH solution; the alkaline solution B is a 0.5M NaOH solution.

4. The method for preparing a catalyst for electrocatalytic CO2RR according to claim 1, characterized in that: In step 1, the volume ratio of the Sn salt solution to the Zn salt solution, the alkaline solution A and the alkaline solution B is 1:6:1:4; the reaction 1 is specifically stirred at room temperature for 1 hour; the reaction 2 is specifically stirred at room temperature for 15 minutes.

5. The method for preparing a catalyst for electrocatalytic CO2RR according to claim 1, characterized in that: In step 2, the Cu salt reacts with the Cu in the ZnSn(OH)6 hollow cube. 2+ :Zn 2+ The molar ratio is 4 to 16:1; the temperature of the hydrothermal reaction is 180° C., and the time is 5 hours.

6. The method for preparing a catalyst for electrocatalytic CO2RR according to claim 1, characterized in that: In step 3, the annealing is carried out under an inert atmosphere at 1°C min -1 After the temperature reaches 300℃, the heating is stopped and the furnace is cooled.

7. A catalyst for electrocatalytic CO2RR prepared according to the preparation method according to any one of claims 1 to 6.

8. A working electrode, characterized in that The catalyst for electrocatalytic CO2RR according to claim 7 is prepared by making an ink solution and drop-coating the solution on the surface of the electrode material.

9. The working electrode according to claim 8, characterized in that The ink solution is prepared by mixing a catalyst for electrocatalytic CO2RR with an ethanol solution and Nafion; and the electrode material is hydrophobic carbon paper.

10. Use of the catalyst for electrocatalytic CO2RR according to claim 7 or the working electrode according to claim 8 or 9 in electrocatalytic CO2RR.

Images