Preparation method, product and application of copper-based catalyst

Abstract

The invention relates to the technical field of CO2RR electrocatalysts, in particular to a preparation method, a product and application of a copper-based catalyst. The preparation method of the copper-based catalyst comprises the following steps: mixing a Cu salt solution with a ligand solution to obtain a mixed solution; and reacting the mixed solution to obtain the copper-based catalyst, the ligand in the ligand solution is 1, 3, 5-tri (4-carboxyl) benzene. The copper-based catalyst (MOF) is synthesized by taking 1, 3, 5-tri (4-carboxyl phenyl) benzene as a ligand, and the preparation method is simple; the copper-based catalyst prepared by the method is used for electro-catalysis of CO2RR, C2 + selectivity is high, and hydrogen evolution is low.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of CO2RR electrocatalyst, in particular to a preparation method of copper-based catalyst, product and application. BACKGROUND

[0002] In addition to forming simple molecular catalysts, metals and organic matter are widely studied by people, which are porous materials MOF with periodic network structure formed by metal ions or metal clusters and organic ligands through coordination bond. The MOF usually has a large internal surface area and extended nanoscale porosity. It is extremely competitive to synthesize MOF with copper as metal node. Various oxidation forms of copper ions can enrich the coordination mode, and different oxidation state copper ions can coordinate various organic ligands to enrich the structure and topological type of MOF; secondly, copper-based MOF can form strong metal coordination bond, which can maintain the structural integrity in a certain acid-base condition and solvent environment.

[0003] In fact, researchers have developed many copper-based MOFs, such as Cu-BDC (Cu 2+ and terephthalic acid (BDC) ligand) and its series of MOFs, Cu-NDC (Cu 2+ and 2,6-naphthalene dicarboxylic acid (NDC) ligand) and its series of MOFs. At present, the Cu-based MOF in the prior art is only used as a precursor for synthesizing catalyst in the field of electrocatalytic CO2RR, and there is no related report on directly using Cu-based MOF as CO2RR electrocatalyst. SUMMARY

[0004] Based on the above, the present application provides a preparation method of copper-based catalyst, product and application.

[0005] To achieve the above purpose, the present application provides the following solutions:

[0006] One of the technical solutions of the present application is a preparation method of copper-based catalyst, comprising the following steps:

[0007] Mixing the Cu salt solution and the ligand solution to obtain a mixed solution;

[0008] The mixed solution is reacted to obtain the copper-based catalyst;

[0009] The ligand in the ligand solution is 1,3,5-tris (4-carboxyl) benzene.

[0010] The second technical solution of the present application is a copper-based catalyst prepared by the above preparation method.

[0011] The third technical solution of the present application is a working electrode, which is prepared by dropping the copper-based catalyst ink solution on the surface of the electrode material.

[0012] The fourth aspect of the present application is the application of the above-mentioned copper-based catalyst or the working electrode in the electrocatalytic CO2RR.

[0013] The present application has the following technical effects:

[0014] The copper-based catalyst (MOF) synthesized by taking 1,3,5-tri(4-carboxyl phenyl) benzene as a ligand has a simple preparation method; the copper-based catalyst prepared by the method has high C2+ selectivity and low hydrogen evolution when used in electrocatalytic CO2RR. BRIEF DESCRIPTION OF DRAWINGS

[0015] In order to more clearly illustrate the technical solutions of the embodiments of the present application or the prior art, the drawings needed in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application, and other drawings can also be obtained by those skilled in the art without creative labor on the basis of these drawings.

[0016] Figure 1 (a) HKUST-1, (b) HKUST-2, (c) HKUST-1@carbon paper electrode, (d) HKUST-2@carbon paper electrode.

[0017] Figure 2 (a) XRD comparison diagram of HKUST-1 and HKUST-2, (b) Raman comparison diagram of HKUST-1 and HKUST-2.

[0018] Figure 3 XPS spectrum comparison diagram of HKUST-1 and HKUST-2; wherein, (a) C 1s spectrum, (b) Cu 2p spectrum.

[0019] Figure 4 (a) N2 adsorption-desorption isotherm distribution diagram of HKUST-1 and HKUST-2, (b) HKUST-1 pore size distribution diagram, (c) HKUST-2 pore size distribution diagram.

[0020] Figure 5 Electrochemical characterization of HKUST-1 and HKUST-2; wherein, (a) linear voltammetry characteristic curve, (b) electrochemical impedance spectrum, (c)-(d) cyclic voltammetry characteristic curve.

[0021] Figure 6 (a)-(b) electrochemically active surface of HKUST-1 and HKUST-2, (c) electric double layer capacitance of HKUST-1 and HKUST-2.

[0022] Figure 7Performance plots for electrocatalytic CO2RR at different operating potentials for (a) HKUST-1, (b) HKUST-2, (c) C2+ products, H2for HKUST-1 and HKUST-2.

[0023] Figure 8 Results for stability test of HKUST-2 for electrocatalytic CO2RR.

[0024] Figure 9 Scanning plots and EDS spectra of HKUST-2 before and after reaction; where (a)-(c) before reaction, (d)-(f) after reaction.

[0025] Figure 10 (a) HKUST-1 in-situ FTIR test results at -1.8 V vs. RHE total spectrum; (b) 1850-1400 cm -1 local analysis plot; (c) 1300-1000 cm -1 local analysis plot.

[0026] Figure 11 (a) HKUST-2 in-situ FTIR test results at -1.8 V vs. RHE total spectrum; (b) 1850-1350 cm -1 local analysis plot; (c) 1300-1000 cm -1 local analysis plot.

[0027] Figure 12 (a) HKUST-2 in-situ FTIR test results at -2.0 V vs. RHE total spectrum; (b) 1900-1100 cm -1 local analysis plot. DETAILED DESCRIPTION

[0028] Various exemplary embodiments of the present application will now be described in detail, without intent to limit the application, which is only limited by the claims. Understanding that these embodiments are given for purposes of illustration and not for purposes of limitation, it is therefore contemplated to include other embodiments that are within the scope of the application.

[0029] It is to be understood that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting. Additionally, for a range of values of a parameter, unless otherwise indicated, each intervening value by each intervening value, as well as any other stated or intervening value in that stated range is encompassed. In addition, any combination of the above ranges, as well as any other stated or intervening value in that stated range, is encompassed. Unless otherwise indicated, the various aspects of the application described herein can be implemented in a computer- readable storage medium for execution by a processor such that the various aspects of the application can be embodied by a machine. The scope of the application is described in the claims below.

[0030] Unless otherwise indicated, all technical and scientific terms used herein have the same meaning as those commonly understood by one of ordinary skill in the art to which this application pertains. Although methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present application, the preferred methods and materials are described. All publications mentioned in this specification are herein incorporated by reference to disclose and describe the methods and / or materials in connection with which the publications are cited. The citation of any reference is not an admission that it is prior art with respect to the present application.

[0031] Many modifications and variations of the present application described in the specification are possible without departing from the scope or spirit of the application. Other implementations of the application will be apparent to those skilled in the art from consideration of the specification and practice of the application disclosed herein. The specification and examples given are exemplary only.

[0032] As used herein, the terms "comprises", "comprising", "includes", "including", "has", "having", "contains", "containing", or variations thereof, are intended to be open-ended terms that mean including, but not limited to.

[0033] HKUST-1 is a MOF with three-dimensional network porous structure, taking copper as metal node, 1,3,5-tri(4-carboxyl) benzene as ligand. The present application mainly synthesizes a MOF with similar structure by changing the ligand of HKUST-1 to 1,3,5-tri(4-carboxyl) benzene, which is named as HKUST-2. The morphology and structure of the two groups of samples are characterized by SEM, XRD, Raman test, etc. The HKUST-2 has larger pore size and specific surface area than HKUST-1, which is beneficial to the adsorption of CO2, and the ligand of HKUST-2 has more phenyl groups, which is more conducive to the chemical adsorption of CO2. The electrochemical test results show that the HKUST-2 is similar to the HKUST-1 but has larger electrochemical active area, which can provide more reaction sites, so that the C2+ selectivity of the HKUST-2 reaches 60% at-1.4V vs. RHE, while the electrocatalytic performance of the HKUST-1 is only 42%.

[0034] The first aspect of the present application provides a preparation method of a copper-based catalyst, comprising the following steps:

[0035] Mixing a Cu salt solution with a ligand solution to obtain a mixed solution;

[0036] Carrying out reaction on the mixed solution to obtain the copper-based catalyst;

[0037] The ligand in the ligand solution is 1,3,5-tri(4-carboxyl) benzene.

[0038] In a preferred embodiment of the present application, the Cu salt solution is prepared by dissolving Cu salt in water; the Cu salt is Cu(NO3)2·3H2O.

[0039] In a preferred embodiment of the present application, the ligand solution is prepared by dissolving ligand in organic solvent; the organic solvent is anhydrous ethanol.

[0040] In a preferred embodiment of the present application, the mass ratio of the Cu salt to the ligand is 1.3:0.7.

[0041] The present application does not particularly limit the concentration of the Cu salt solution and the ligand solution, and the content of the solvent in the Cu salt solution and the ligand solution can be such that the Cu salt and the ligand are fully dissolved and the subsequent reaction can be smoothly carried out.

[0042] In a preferred embodiment of the present application, the mixture further comprises dimethylformamide and tetrahydrofuran; the volume ratio of the dimethylformamide to the tetrahydrofuran is 8:5; the volume fraction of the tetrahydrofuran in the mixture is 35% to 40%.

[0043] In a preferred embodiment of the present application, the temperature of the reaction is 80℃, and the time is 20h.

[0044] In some specific embodiments of the present application, the reaction further comprises the steps of collecting the precipitate and washing and drying the precipitate after the reaction is completed.

[0045] The second aspect of the present application provides a copper-based catalyst prepared according to the above preparation method.

[0046] The third aspect of the present application provides a working electrode prepared by dropping an ink solution of the above copper-based catalyst on the surface of an electrode material.

[0047] In a preferred embodiment of the present application, the ink solution is prepared by mixing a catalyst for electrocatalytic CO2RR with an ethanol solution and Nafion; the electrode material is hydrophobic carbon paper.

[0048] The fourth aspect of the present application provides the use of the above copper-based catalyst or the above working electrode in electrocatalytic CO2RR.

[0049] The technical solutions of the present application, if not particularly specified, are conventional solutions in the art, and the reagents or raw materials used, if not particularly specified, are purchased from commercial channels or are already disclosed.

[0050] The test methods involved in the present application are shown as follows:

[0051] 1. Electrochemical experiment

[0052] The electrochemical characterization mainly includes six characterization means of linear sweep voltammetry (LSV), cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), double-layer capacitance (CDL), tafel slope and electrochemical active surface (ECSA) test. The electrochemical measurements are performed in a three-electrode system using a CHI660E electrochemical workstation (Shanghai) with a platinum wire and Ag / AgCl electrode as the counter and reference electrodes, respectively. A proton exchange membrane is used between the cathode and anode.

[0053] Linear sweep voltammetry is to record the relationship between current and potential generated by the linear change of potential on the electrode with constant rate over time to obtain the voltammogram. During the scanning process, when the potential reaches the reduction potential of the oxidized substance or the oxidation potential of the reduced substance on the electrode, the corresponding redox reaction will occur to generate Faraday current. By analyzing the shape, peak potential, peak current and other parameters of the voltammogram of the working electrode with different catalyst loadings, the Faraday current of each working electrode with different catalyst loadings at the corresponding voltage can be compared to determine the catalytic performance. The specific operation is as follows: the electrochemical measurements are performed in a three-electrode system using a CHI660E electrochemical workstation (Shanghai) with a platinum wire and Ag / AgCl electrode as the counter and reference electrodes, respectively. A proton exchange membrane is used between the cathode and anode. The electrolyte used is 0.1M KHCO3 solution. Before testing, excess N2 and CO2 are introduced into it to obtain LSV curves under different atmospheres, and the scan rate is 0.1V / s. By comparing the LSV curves under different atmospheres, the catalytic activity of the electrode and its reaction voltage window can be roughly judged. At the same time, the change of LSV of three working electrodes with different catalyst loadings after introducing CO2 for the same time can be compared.

[0054] Cyclic voltammetry is to control the electrode potential at a certain rate along a certain direction (positive or negative scan) to form a current-potential curve (i-E) by setting the potential range, scan number and scan direction. In the experiment, the last curve is usually selected for plotting, which reflects the i-E relationship. By analyzing this curve, information about the electrochemical reaction can be obtained, such as the position of the oxidation-reduction peak, the current peak value and the half-width, etc.

[0055] Electrochemical impedance is to apply a small amplitude AC signal with different frequencies to the electrochemical system, measure the ratio of AC signal voltage and current with the change of sine wave frequency ω, or the phase angle Φ of impedance with the change of ω. Further analysis of electrode process dynamics, double layer and diffusion, etc. Study the mechanism of electrode materials, solid electrolyte, conductive polymer and corrosion protection. The commonly used electrochemical impedance spectroscopy has two kinds, Nyquist plot and Bode plot, Z'(real part) and Z"(imaginary part) in Nyquist plot show the electron transfer resistance (Rct) on the electrode surface, which is the same as the diameter of the semicircle part, and can be used to describe the characteristics of the interface between the electrode and the electrolyte. Nyquist plot consists of two parts, the semicircle part in the high frequency region corresponds to the electron transfer limited process, and the linear part in the low frequency region corresponds to the diffusion limited process. By calculating the electron transfer resistance Rct on the electrode surface, some phenomena in the process of photocatalysis, electrocatalysis, etc. Can be explained.

[0056] The electrochemical active area is an important parameter to characterize the activity of electrode reaction, which is usually compared by testing the capacitance of the electrode by cyclic voltammetry. In fact, the test method of ECSA is the same as the above-mentioned cyclic voltammetry, but the parameters of cyclic voltammetry experiment need to be adjusted, such as scan rate, cycle number and potential range. The ECSA of the material is evaluated by cyclic voltammetry, and the scan rate v is changed in the non-faradic region. The current density j in the non-faradic 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 site of the material. The specific operation is as follows: a three-electrode system is used, the working electrode is the electrode prepared in the example, the reference electrode is Ag / AgCl electrode, the counter electrode is platinum wire, and the electrolyte is 0.1M KHCO3 solution. The electrolyte is saturated with nitrogen to ensure that it is not affected by other substances during the test of cyclic voltammetry. First, measure the open circuit voltage, and take the value in the range of ±0.05V of the open circuit voltage. Then, scan the CV curve at different scan rates of 50mV / s, 40mV / s, 30mV / s, 20mV / s and 10mV / s, and take the current density at the midpoint as the difference, denoted as j. Plot j vs. v, the slope is the capacitance of the corresponding electrode, and the ECSA of the electrode is compared by comparing the capacitance.

[0057] Tafel slope is an important parameter in the field of electrochemistry for describing the kinetics of electrode reaction, which reflects the logarithmic relationship between electrode potential and current density. It plays a key role in studying electrode reaction rate and evaluating electrocatalyst performance. Tafel slope represents the slope of the linear relationship between overpotential (η) and logarithmic current density (logj) in the electrode reaction, and its mathematical expression is η=a+blogj, where b is the Tafel slope, with the unit of (mV dec -1) a is the intercept, which is related to the initial conditions of the electrode reaction, etc. This formula is called the Tafel equation, which 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 linear fitting of the overpotential and the corresponding LSV determined by experiment.

[0058] Chronoamperometry (I-t) is a method of applying a constant potential to a current-time curve at a set time, denoted as I-t curve. Chronoamperometry is widely used in many fields. It can be used to study the kinetic behavior of electrochemical reactions, the activity evaluation of electrochemical catalysts, the process optimization of electrochemical synthesis, etc. In addition, chronoamperometry can also be applied to the design and analysis of electrochemical sensors, as well as the research in the field of electrochemical energy storage and conversion. The present application uses chronoamperometry to evaluate the performance of the catalyst by measuring the product Faraday efficiency at a suitable potential interval. The specific operation is as follows: the same reaction cell (H-type reaction cell) is used, but instead of the closed kettle reaction before the reaction, a continuous CO2 flow is used to ensure that the gas phase product can be analyzed online during the performance test. 32 mL of 0.1 M KHCO3 solution is injected into both ends of the H cell to serve as the electrolyte, and the reactor is filled with CO2 after bubbling for 20 min after the reaction cell is equipped. Different voltages are set to test the catalytic performance of the catalyst at different voltages, and the test time is 2 h, with online detection every 20 min. After the reaction is completed, the cathode electrolyte is collected for quantitative analysis of the liquid phase product. Repeat the above operation to test the performance of the catalyst at the next voltage.

[0059] 2. Quantitative experiment of electrocatalytic CO2RR products

[0060] In the process of electrocatalytic CO2RR, chronoamperometry is used, and gas phase product analysis is also performed online detection using high-efficiency gas chromatography GC7920. Liquid product quantification is performed by collecting the electrolyte after the reaction and using 1 H NMR nuclear magnetic resonance hydrogen spectrum for quantitative analysis. According to the related literature, the possible related liquid products are mainly formic acid and ethanol. By preparing DMSO, sodium formate, and CH3CH2OH standard solutions with known amounts of substances for nuclear magnetic testing, the nuclear magnetic data are plotted to obtain the standard curves for quantifying formate and ethanol as shown in Figure 1

[0061] 3. In-situ electrochemical infrared experiment

[0062] ​Fourier transform in situ infrared spectroscopy (FTIR) is a widely used instrument for infrared spectroscopy analysis. It uses the Fourier transform principle to convert infrared light signals into frequency spectra and provides information on the chemical composition and molecular structure of the sample. By conducting infrared tests, it is possible to characterize the presence of organic functional groups in materials to verify the successful synthesis of catalysts and compare them with each other. Electrochemical in situ diffuse reflectance infrared spectroscopy is a characterization method that combines infrared spectroscopy techniques with electrochemical methods. By in situ characterization of species on the electrode-electrolyte interface under electrochemical reaction conditions, it is possible to study electrochemical reaction mechanisms, electrode surface intermediate products, and adsorbed species.

[0063] By using the Thermo Nicolet iS50 Fourier transform infrared spectrometer in combination with the Shanghai Chenhua electrochemical workstation, the changes in intermediates during the reaction process were studied and the formation mechanism of C2+ products was analyzed. In the actual operation process, due to the limitation of the reaction environment, a 0.1M KHCO3 solution pretreated with CO2 was used as the electrolyte, and an ink solution prepared from the electrocatalyst powder was used to drop coat the glassy carbon electrode as the working electrode for electrochemical in situ infrared testing. Subsequently, the corresponding software was used for data analysis and processing.

[0064] The technical solutions provided by the present application will be described in detail below in combination with examples, but they should not be understood as limiting the scope of protection of the present application.

[0065] Example 1: Preparation of HKUST-1 catalyst

[0066] Step 1, prepare solution A: weigh 2.6g Cu(NO3)2·3H2O and stir to dissolve in 30mL deionized water to obtain solution A.

[0067] Prepare solution B: weigh 0.68g 1,3,5-tris(4-carboxyl)benzene and stir to dissolve in 30mL anhydrous ethanol to obtain solution B.

[0068] Step 2, slowly add solution A to solution B while stirring, and then add 30mL DMF to improve the solubility of the organic matter. Transfer to a polytetrafluoroethylene high-pressure reaction kettle, and react in an 80°C oven for 20h. After the reaction is completed, collect the obtained sky blue precipitate, wash it repeatedly with deionized water and ethanol for 5 times, and then dry it in a vacuum at 60°C for 12h to obtain the HKUST-1 catalyst.

[0069] Example 2: Preparation of HKUST-2 catalyst

[0070] Step 1, prepare solution C: weigh 1.3g Cu(NO3)2·3H2O and stir to dissolve in 30mL deionized water to obtain solution C.

[0071] Prepare solution D: weigh 0.7 g of 1,3,5-tris(4-carboxyphenyl)benzene and dissolve it in 30 mL of anhydrous ethanol with stirring to obtain solution D.

[0072] Step 2: While stirring, slowly add Solution C to Solution D. After complete addition, add a mixture of DMF and tetrahydrofuran (DMF:THF) to increase the solubility of the organic matter in the mixture (the volume ratio of DMF to THF is 8:5, and the volume fraction of THF in the mixture is 38.5%). Transfer to a polytetrafluoroethylene autoclave and oven-dry for 20 hours at 80°C. Collect the resulting sky-blue precipitate, wash it five times with deionized water and ethanol, and then dry it under vacuum at 60°C for 12 hours to obtain the HKUST-2 catalyst.

[0073] Application Example 1: Electrode Preparation

[0074] Weigh 10 mg of catalyst powder to make 1 mL of ink solution, which contains 970 μL of anhydrous ethanol and 20 μL of Nafion (D520CS). Ultrasonic treatment of the solution was performed for half an hour in an ice water bath. Meanwhile, the hydrophobic carbon paper was cut into 2*0.5 cm 2 Then 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.

[0075] The catalyst prepared in the example was characterized and its performance tested, and the results are as follows:

[0076] 1. Figure 1 This is the scanning electron microscope image of samples HKUST-1 and HKUST-2. Figure 1 In (a), HKUST-1 shows an uneven block shape, but there are round holes on the surface of the sample. This phenomenon is also reflected in HKUST-2 ( Figure 1 In (b), the presence of such pores generates capillary forces that facilitate the adsorption of gases or intermediates, increasing their residence time and thus improving their electrocatalytic CO2RR performance. Figure 1 (c) and (d) are carbon paper electrodes loaded with HKUST-1 and HKUST-2, respectively.

[0077] To further determine the difference between the two groups of catalysts, X-ray diffraction experiments and Raman tests were performed on both groups. The results are shown in Figure 2 .like Figure 2 As shown in (a), the XRD diffraction peaks of HKUST-1 are numerous and dense, which may be due to the emergence of polymorphism during sample synthesis. When performing XRD testing on this sample, multiple crystal diffraction peaks will be superimposed, and compared with a single crystal, multiple peaks will appear and the phenomenon of dense diffraction peaks will appear. Another possibility is that the sample particle size is too large and non-uniform. This phenomenon is Figure 1The XRD patterns of HKUST-1 and HKUST-2 are shown in FIG. 2. It can be seen that the XRD pattern of HKUST-1 is relatively clear, while the XRD pattern of HKUST-2 is relatively unclear. This is because the particle size of the sample is not uniform, and small particle samples can produce more diffraction peaks, making the pattern show more and dense peaks. Because the crystal face orientation of small particle samples is more random, more types of crystal faces can be irradiated by X-rays. In contrast, the XRD pattern of HKUST-2 can see more obvious characteristic peaks, which may be because the overall HKUST-2 is relatively uniform.

[0078] In addition, Raman can better observe the relatively special bonds contained in the catalyst. For example, the Raman spectrum of the catalyst can be used to observe the C=C stretching vibration of the benzene ring in the ligand. Figure 2 As shown in (b) of FIG. 3, first, it can be seen that the Raman spectra of HKUST-1 and HKUST-2 are not much different, because the bonding form of the two is basically the same, and the only difference is the number of benzene rings of the ligand. The number of benzene rings of the ligand (1,3,5-tri(4-carboxyphenyl) benzene) of HKUST-2 is more, so the C=C stretching vibration thereof at 1600 cm -1 is stronger than that of HKUST-1, and the corresponding C-H bending vibration peak at 1340 cm -1 is also higher. Because the Raman activity of copper element is not strong, the peak type is small, so the small peak at 405 cm -1 may be a Cu-O bond. The weak and wide peak at 1430 cm -1 comes from C-C stretching vibration, and 1000 cm -1 may come from C-O bond.

[0079] XPS can be used to detect the surface state and valence of elements of the sample, Figure 3 and the XPS test results of the two groups of samples are shown in FIG. 4. Figure 3 As shown in (a) of FIG. 4, the C1s of the two groups of samples is basically unchanged, indicating that the electronic properties do not change significantly before and after changing the ligand. Figure 3 (b) of FIG. 4 shows the electron change of Cu 2p orbit of HKUST-1 and HKUST-2. It can be seen that Cu2p3 / 2 has a significant right shift (from 934.88 eV to 934.28 eV), and the overall binding energy is lower. This indicates that the electron cloud density of copper is higher after changing the ligand, and the valence is reduced from more +2 to +1 (or 0). Such a change in valence is more conducive to electrocatalytic CO2RR.

[0080] 2. N2 adsorption-desorption isotherm and pore size distribution

[0081] Based on HKUST-1, HKUST-2 is designed and synthesized to utilize the spatial stereo configuration of MOF to improve the specific surface area and porous structure of the catalyst to improve physical adsorption, and to enhance the chemical adsorption capacity by changing the ligand. Therefore, N2 adsorption-desorption isotherm test is used to characterize the adsorption-desorption capacity and to calculate the change of specific surface area.

[0082] Figure 4 The N2 adsorption-desorption isotherm distribution and pore size distribution of HKUST-1 and HKUST-2 are shown in FIG. 2. As shown in FIG. 2(a), the N2 adsorption-desorption isotherms of HKUST-1 and HKUST-2 both exhibit obvious hysteresis loops, indicating that both materials belong to type IV isotherm. The appearance of the hysteresis loop indicates that there are mesopores in the interior, which is prone to capillary phenomenon, which is consistent with the observed material morphology. Figure 4 Figure 1 As shown in FIG. 2(b) and (c), the pore size distributions of the two are shown, and the average pore sizes are calculated to be 2.3509 nm and 4.506 nm, respectively, both of which are within the definition of mesopores, further supporting the reason for the formation of the hysteresis loop. Figure 4

[0083] The specific surface area results of HKUST-1 and HKUST-2 under N2 adsorption and desorption calculated by the BET curve are shown in Table 1. It is found that the specific surface area of HKUST-2 obtained after changing the ligand of HKUST-1 is increased.

[0084] Table 1

[0085]

[0086] 3. Electrochemical characterization of the electrocatalyst

[0087] Electrochemical tests are used to compare the electrochemical performance of the two catalysts for subsequent electrocatalytic CO2RR. The tests include LSV, CV, EIS, etc. Figure 5 FIG. 3(a) is the LSV curve of the two, and there is no big difference in the operating voltage range. The electrochemical impedance results are also shown in FIG. 3(b). It is worth noting that the CV graphs of the two differ under different atmospheres (FIG. 3(c) and (d)). First, both of them show reactivity to CO2. Second, the reduction voltage of copper in HKUST-2 under CO2 atmosphere moves more obviously, which indicates that the copper inside HKUST-2 is more active under the influence of CO2, which is consistent with the XPS results analyzed above. HKUST-2 may be more beneficial to electrocatalytic CO2RR. Figure 5 Figure 5 Further, the electrochemical active surface of HKUST-1 and HKUST-2 is measured by an electrochemical workstation (FIG. 3(a) and (b)), and the double-layer capacitance of the two is calculated (FIG. 3(c)), and it is found that HKUST-2 has a more excellent electrochemical active surface and a more outstanding double-layer capacitance. This means that the catalyst can have more electrochemical reaction active area and active sites when used in the process of electrocatalytic CO2RR.

[0088] Further, the electrochemical active surface of HKUST-1 and HKUST-2 is measured by an electrochemical workstation (FIG. 3(a) and (b)), and the double-layer capacitance of the two is calculated (FIG. 3(c)), and it is found that HKUST-2 has a more excellent electrochemical active surface and a more outstanding double-layer capacitance. This means that the catalyst can have more electrochemical reaction active area and active sites when used in the process of electrocatalytic CO2RR. Figure 6 Figure 6 ​​​​​

[0089] 4. Analysis of electrocatalytic CO2 reduction performance and stability

[0090] Based on the above experimental characterization, the electrocatalytic CO2RR performance of the two has obvious differences, and overall the electrocatalytic CO2RR performance of HKUST-2 is better than that of HKUST-1 at the corresponding operating voltage. The specific results are shown in Figure 7 . Figure 7 Figure (a) shows the electrocatalytic CO2RR performance test results of HKUST-1 in the range of -1.2V to 1.6V vs. RHE. As the operating potential increases, the current density increases accordingly and liquid product C2H5OH gradually appears, the overall hydrogen decreases first and then increases, HCOOH gradually decreases, and CH4 gradually increases. HKUST-2 also shows similar results, the difference is that the selectivity of CO is compressed, and the hydrogen evolution reaction is also inhibited, thereby increasing the selectivity of C2+(shown in Figure (b)). Moreover, the current density of HKUST-2 is not much different from that of HKUST-1, which is consistent with the previous LSV test results. Figure 7 Figure 7 Figure (c) shows the comparison of C2+ products and H2 faradic efficiency of the two catalysts at the corresponding potential. HKUST-2 has the highest C2+ selectivity of 60% at -1.4V vs. RHE, while HKUST-1 also reaches the highest (42%), and the degree of hydrogen evolution of the two is overall slowly weakened and then increased.

[0091] After determining that HKUST-2 has better electrocatalytic CO2RR performance, it is tested for cyclic stability to ensure that the catalyst does not deactivate after a long time of work, Figure 8 , which is the test result. During the 40h cyclic test process, the current shows periodic fluctuations, because the electrolyte cannot be updated in real time during the test, and the electrolyte needs to be replaced manually at regular intervals (4h / time) to ensure a relatively uniform electrocatalytic environment. The current slowly increases in each cycle, which is due to the consumption of water in the electrolysis process, causing the ion concentration in the system to be too high. On the other hand, the overall C2+ product selectivity of HKUST-2 is relatively stable during this cyclic test, which ensures that it can be used for a long time in the field of CO2RR.

[0092] The working electrode used for cycling was characterized for morphology to compare the changes before and after the material, Figure 9 Figures (a)-(c) are the electrode surface before testing, and Figures (d)-(f) are the electrode surface after 40h of testing Figure 9 , it is found that the catalyst surface becomes cleaner, the fine particles that originally existed disappear, and only larger-sized catalysts are left. This may be due to the fact that the fine particles fell off during the electrocatalytic CO2RR process or reacted under the action of negative voltage and were restructured. ​

[0093] 5. Research on the mechanism of electrocatalytic CO2

[0094] In-situ drifts FTIR was used to monitor and record the changes of intermediates at the working electrode interface of HKUST-1 and HKUST-2 during the electrocatalytic CO2RR process. Figure 10 This is the response of HKUST-1 to CO2RR at an operating voltage of -1.8V vs. RHE. Figure 10 In (a), we can see that there is an obvious inverted peak during the reaction, located at 3300 cm -1 Broad peak around 1640cm -1 The broad peak at 2350cm-1 is considered to be the water consumption peak (corresponding to the stretching vibration absorption peak and bending vibration absorption peak of the OH bond of water; and the peak at 2350cm-1 is considered to be the water consumption peak). -1 The inverted peak is the CO2 antisymmetric stretching vibration peak. Considering the 1850-1400cm -1 The spectral peaks in the region are complex and can be obtained by local amplification. Figure 10 In (b), a large number of positive and negative peaks are shown, which are the intermediates produced in the electrocatalytic CO2RR process of HKUST-1. There is a certain kinetic equilibrium in this process. -1 *COOH antisymmetric stretching vibration, 1618 cm -1 A weak inverted peak appeared at 1650 cm, which may be the stretching vibration of C=C. -1 The peak at 1700 cm also confirms the disappearance of the C=C-containing intermediate. -1 is the consumption peak of *CO. A certain number of positive peaks also appeared in the process, such as 1460cm -1 It is the symmetrical stretching vibration of *COOH, 1473cm -1 It belongs to *CH2O, and 1510cm -1 The characteristic peak shift also belongs to *OCCOH. Figure 10 The peak shift region of carbonate is mainly in the middle (c), such as the peak at 1124 cm -1 The inverted peak is the consumption peak of multidentate carbonate, and the peak at 1160 cm -1 The inverted peak is the consumption of *CHO intermediate.

[0095] On this basis, by testing the in situ drifts FTIR of HKUST-2 at the same potential, we can compare the differences in the reaction paths between the two. Figure 11 In (a), we can see the test results of the overall HKUST-2 at -1.8V vs. RHE, and the consumption of water removal (3300cm-1 and 1640 cm -1 The most obvious difference is the CO2 feature peak at 2350 cm -1 The most obvious difference is the CO2 feature peak at 2350 cm -1 The most obvious difference is the CO2 feature peak at 2350 cm -1 The most obvious difference is the CO2 feature peak at 2350 cm -1 The most obvious difference is the CO2 feature peak at 2350 cm -1 The most obvious difference is the CO2 feature peak at 2350 cm -1 The most obvious difference is the CO2 feature peak at 2350 cm -1 The most obvious difference is the CO2 feature peak at 2350 cm Figure 11 The most obvious difference is the CO2 feature peak at 2350 cm Figure 10 The most obvious difference is the CO2 feature peak at 2350 cm -1 The most obvious difference is the CO2 feature peak at 2350 cm -1 The most obvious difference is the CO2 feature peak at 2350 cm -1 The most obvious difference is the CO2 feature peak at 2350 cm -1 The most obvious difference is the CO2 feature peak at 2350 cm -1 The most obvious difference is the CO2 feature peak at 2350 cm The most obvious difference is the CO2 feature peak at 2350 cm

[0096] The most obvious difference is the CO2 feature peak at 2350 cm Figure 11 The most obvious difference is the CO2 feature peak at 2350 cm -1 The most obvious difference is the CO2 feature peak at 2350 cm -1 The most obvious difference is the CO2 feature peak at 2350 cm The most obvious difference is the CO2 feature peak at 2350 cm

[0097] The most obvious difference is the CO2 feature peak at 2350 cm Figure 12 The most obvious difference is the CO2 feature peak at 2350 cm Figure 11 The most obvious difference is the CO2 feature peak at 2350 cm Figure 12 The most obvious difference is the CO2 feature peak at 2350 cm -1 The most obvious difference is the CO2 feature peak at 2350 cm -1 The most obvious difference is the CO2 feature peak at 2350 cm -1 The most obvious difference is the CO2 feature peak at 2350 cmThe characteristic peak of CO at 1400 cm -1 COOH at 1341 cm -1 The small peak at 1500 cm -1 may be an α, β-unsaturated aldehyde, ketone, etc. conjugated carbonyl compound, 1560 cm -1 is the anti-symmetrical stretching vibration characteristic peak of COOH.

[0098] The micro-morphology of HKUST-1 and HKUST-2 was characterized by SEM and Mapping, and it was found that both of them presented irregular three-dimensional structure and porous surface, rich in Cu and C elements. It was determined by XRD that HKUST-1 presented polycrystalline ligand exchange HKUST-2 crystal form became relatively uniform, and the Raman test results showed that the catalyst existed C=C, Cu-O and other characteristic bonds. The BET test results showed that HKUST-2 had larger specific surface area and pore size than HKUST-1, and had mesoporous structure. It was determined by electrochemical characterization that under the premise of similar LSV, the double-layer capacitance value of HKUDT-2 was larger, which could provide more reaction active area for electrocatalytic CO2RR. In the electrocatalytic CO2RR performance test according to this, HKUST-2 also performed better: at-1.4V vs.RHE, the C2+ selectivity of HKUST-2 reached 60%, which was greatly improved compared with before ligand optimization, and reduced its hydrogen evolution. Therefore, the strategy of introducing MOF to construct large specific surface area and porous structure to enhance physical adsorption, and then adjusting the ligand to improve chemical adsorption, has been effectively applied in the design of electrocatalytic CO2RR catalyst, which also provides a new design idea for the subsequent development and synthesis of catalyst, and makes the copper-based catalyst have a wider application prospect.

[0099] Example 3

[0100] The difference between Example 3 and Example 2 is that 0.7g 1,3,5-tris(4-carboxyl)benzene is replaced by 0.7g H3BTC (1,3,5-benzene tricarboxylic acid).

[0101] The catalyst prepared in Example 3 was tested in the same way as the catalyst prepared in Example 2, and the results showed that at-1.4V vs.RHE, the C2+ selectivity of the catalyst prepared in Example 3 was only 44%.

[0102] The above-described examples only describe the preferred modes of the present application, and do not limit the scope of the present application. Without departing from the design spirit of the present application, various modifications and improvements to the technical solutions of the present application made by those skilled in the art shall fall within the protection scope determined by the claims of the present application.

Claims

1. A method for preparing a copper-based catalyst, characterized by, The method comprises the following steps: mixing a Cu salt solution with a ligand solution to obtain a mixed solution; reacting the mixed solution to obtain the copper-based catalyst; the ligand in the ligand solution is 1,3,5-tris(4-carboxyl) benzene.

2. The method of making a copper-based catalyst according to claim 1, wherein, The Cu salt solution is prepared by dissolving a Cu salt in water; the Cu salt is Cu(NO3)2·3H2O.

3. The method of making a copper-based catalyst of claim 1, wherein, The ligand solution is prepared by dissolving a ligand in an organic solvent; the organic solvent is anhydrous ethanol.

4. The method of making a copper-based catalyst according to claim 2, wherein, The mass ratio of the Cu salt to the ligand is (1-1.5):(0.5-1).

5. The method of making a copper-based catalyst of claim 1, wherein, The mixed solution further comprises dimethylformamide and tetrahydrofuran; the volume ratio of the dimethylformamide to the tetrahydrofuran is 8:5; the volume fraction of the tetrahydrofuran in the mixed solution is 35%-40%.

6. The method of making a copper-based catalyst of claim 1, wherein, The reaction temperature is 80℃ and the reaction time is 20h.

7. The copper-based catalyst prepared by the preparation method in any one of claims 1-6.

8. A working electrode characterized by, The copper-based catalyst in claim 7 is prepared into an ink solution and dropped on the surface of an electrode material.

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

10. The copper-based catalyst in claim 7, or the working electrode in claim 8 or 9, in the application of electrocatalytic CO2RR.

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