Preparation method of metal-doped ZnO catalyst with three-dimensional ordered macroporous structure and application of metal-doped ZnO catalyst in CO2 electroreduction

Abstract

The invention provides a preparation method of a metal-doped ZnO catalyst with a three-dimensional ordered macroporous structure and application of the metal-doped ZnO catalyst in CO2 electroreduction. 3DOM-ZnO (metal-doped three-dimensional ordered macroporous zinc oxide) is synthesized by adopting a method for preparing 3DOM ZnO (600) (three-dimensional ordered macroporous zinc oxide) with the highest CO selectivity by using a PMMA (polymethyl methacrylate) microsphere template with the sacrificial particle size of 600nm. The doping proportion of other metal sources (Ag / Cu / Co / Ni and the like) and the Zn source is regulated and controlled to enable the catalyst to have mutually synergistic metal sites, the electronic structure of the catalyst is changed through doping, and the CO2RR performance is improved. The prepared 3DOM-ZnO catalyst not only has high specific surface area and can provide more active sites, but also induces charge redistribution through a metal synergistic effect, adjusts intermediate adsorption and effectively improves CO2RR performance. Wherein the CO selectivity of the 3DOMAg-ZnO and the CO selectivity of the 3DOM Cu-ZnO can reach 94% and 95.6% at-1 V, and the 3DOMAg-ZnO and the 3DOM Cu-ZnO have good stability within 24 h.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of new materials, and relates to an electrocatalytic material, in particular to preparation of a three-dimensional ordered macroporous structure different metal doped ZnO catalyst and application thereof in CO2 electro-reduction. BACKGROUND

[0002] With the rapid development of industrialization and economy, the over-consumption of fossil fuels leads to a sharp increase in atmospheric carbon dioxide, causing serious environmental problems and energy crisis. Under the driving of renewable electricity, carbon dioxide can be electrocatalytically reduced to chemical raw materials. This indicates a new path for CO2 to be converted into valuable chemical products, for sustainable carbon cycle and energy storage. However, the activity and selectivity of ECO2R are severely limited by the chemical inertness of CO2 and the highly efficient competitive reaction of hydrogen evolution. Therefore, a large number of studies have been carried out in the development of stable electrocatalysts to promote the kinetics of ECO2R, and researchers have been committed to meet the industrial requirements of high reaction rate and high selectivity of CO. In recent years, with the development of advanced characterization techniques and theoretical simulation, the exploration of catalytic mechanism gradually deepens into the electronic structure of the catalyst and its interaction with intermediates, providing a bridge for a deeper understanding of the structure-property relationship. In the past few years, various ECO2R catalysts have emerged, including noble metal catalysts (Ag, Au and Pd), molecular catalysts (metal porphyrins and metal phthalocyanines) and single-atom catalysts (SACs). These catalysts are still far from meeting the actual demand, and efficient catalytic materials and in-depth analysis of the mechanism of the reaction are still a great challenge.

[0003] Transition metal-based catalysts (TMCs) show great potential for further electronic structure modulation due to their d-electron richness, and have been widely used in electrochemical ECO2R. Among these transition metals, zinc is a kind of non-noble metal with low cost and abundance, which has the most practical application potential and can be widely used in ECO2R to CO. In the work of Mirtha A. O. Lourenco et al., a new type of electrocatalyst based on zinc oxide (ZnO) and biochar was proposed for the electrocatalytic reduction of carbon dioxide. They synthesized materials with different weight ratios of ZnO to biochar, i.e. pyrolyzed chitosan (CTO) and pyrolyzed spent coffee (CBC). The results show that the structure of CTO contains pyridine and pyridone-N species, which is a carbon matrix for ZnO particles, and its performance is better than that of CBC. The study of various weight ratios of ZnO to CTO shows that the composite material containing 40.6wt% biochar exhibits the best performance, with a peak value of 85.8% CO selectivity at -1.1V compared with the reversible hydrogen electrode (RHE), and a CO partial current density of 75.6mA·cm -2However, its Faraday efficiency has not yet reached more than 90%, and there is still a lot of room for improvement.

[0004] In addition, zinc metal can be combined with other metals to achieve higher efficiency and selectivity, such as copper (Cu). However, copper is a relatively expensive metal, and it is rarely used for combination when preparing enhanced zinc-based catalysts with the same function. Currently, in addition to research on supercapacitors and photocatalysts, only a few studies on the preparation of zinc-based materials have been reported. In the case of ECO2R, most of them are still at the stage of preparing reduced graphene oxide (rGO)-based catalysts, and expensive metal sources such as Cu, Au, nickel (Ni), Ag, cobalt (Co) porphyrin and iron (Fe) porphyrin materials are used. However, most of the rGO-based electrocatalysts described so far have low operational durability, and the production on an industrial scale is not environmentally and economically feasible, which limits the pace of practical application. If a sustainable and cost-effective catalyst can be prepared from a low-cost source and the selectivity and long-term carbon dioxide electrolysis can be achieved, the industry will make significant progress. SUMMARY

[0005] In view of the shortcomings of the existing ECO2R catalysts, the purpose of the present application is to provide a preparation method of a metal-doped ZnO catalyst with a three-dimensional ordered macroporous structure, which improves the CO2RR performance by doping different metals.

[0006] The technical scheme adopted by the present application is as follows:

[0007] A preparation method of a three-dimensional ordered macroporous structure metal-doped ZnO catalyst (3DOM M-ZnO), specifically comprising the following steps:

[0008] S1. Dissolve Zn(NO3)2·6H2O and another metal (Ag, Cu, Ni, Co, Mg, Al, etc.) nitrate in anhydrous methanol in a certain molar ratio under continuous stirring, add citric acid, stir, and prepare a precursor solution;

[0009] S2. Then immerse 600nm polymethyl methacrylate (PMMA) microspheres in the solution obtained in S1, stir at room temperature, vacuum filter the obtained suspension, dry overnight, and heat treat in a nitrogen atmosphere at 300-600℃, with a temperature rising rate of 1℃ / min -1 After cooling to room temperature, the 3DOM M-ZnO is obtained.

[0010] Further, the metal in S1 is Ag, Cu, Ni, Co, Bi, Mo, Mg or Al.

[0011] Further, the stirring at room temperature in S2 is 3-6h.

[0012] Further, the heat treatment in the nitrogen atmosphere in S2 is heating at 300 DEG C and 600 DEG C for 3h, and the heating rate is 1 DEG C / min -1 .

[0013] Compared with the prior art, the present application has the following beneficial effects:

[0014] 1. The present application introduces different metals on the basis of 3DOM ZnO for the first time by electronic regulation and pore size adjustment, so as to make the catalyst have mutually synergistic metal sites by regulating the doping ratio of metal source and Zn source, and to prepare 3DOM M-ZnO catalyst (M=Co, Ni, Cu, Ag, Al, Mo, etc.) by changing the electronic structure of the catalyst through doping, wherein each element is uniformly distributed, and the three-dimensional ordered macroporous structure is stable.

[0015] 2. The present application prepares 3DOM M-ZnO catalyst with high performance, which not only has high specific surface area to provide more active sites, but also effectively improves the CO2RR performance through metal synergistic effect to induce charge redistribution and adjust intermediate adsorption, wherein the CO selectivity of 3DOM Ag-ZnO and 3DOM Cu-ZnO can reach 94% and 95.6% at-1V, and has good stability within 24h. BRIEF DESCRIPTION OF DRAWINGS

[0016] Figure 1 It is a synthesis process diagram of 3DOM M-ZnO;

[0017] Fig. 2 is a SEM and TEM diagram of the catalyst;

[0018] (a, d) 3DOM Ag-ZnO (1:10), (b, e) 3DOM Cu-ZnO (1:32) and (c, f) 3DOM Al-ZnO (1:50);

[0019] Fig. 3 is an EDS element mapping image of 3DOM Ag-ZnO (1:10) catalyst;

[0020] Fig. 4 is an EDS element mapping image of 3DOM Cu-ZnO (1:32) catalyst;

[0021] Fig. 5 is an EDS element mapping image of 3DOM Al-ZnO (1:50) catalyst;

[0022] Fig. 6 is a PXRD image of different doping ratios;

[0023] (a) 3DOM Ag-ZnO with different doping ratios, (b) 3DOM Cu-ZnO with different doping ratios, (c) 3DOM Al-ZnO with different doping ratios, (d) 3DOM Co-ZnO with different doping ratios, (e) 3DOM Ni-ZnO with different doping ratios, (f) 3DOM Bi-ZnO (1:50), (g) 3DOM Mo-ZnO (1:50) PXRD images;

[0024] Figure 7 is the XPS spectra of each metal;

[0025] (a) Ag 3d of 3DOM Ag-ZnO, (b) Cu 2p of 3DOM Cu-ZnO, (c) Al 2p of 3DOM Al-ZnO and (d) XPS survey of three different metal-doped catalysts;

[0026] Figure 8 is the XPS spectra of 3DOM M-ZnO with different doping ratios (a) O 1s, (b) Zn 2p;

[0027] Figure 9 is the LSV curves and (d) Nyquist plots of (a, c) 3DOM Ag-ZnO with different doping ratios and (b, d) 3DOM Cu-ZnO with different doping ratios;

[0028] Figure 10 is the (a) LSV curves, (b) FE(CO), (c) CO partial current density, (d) Nyquist plots, (e) stability test at -1 V of 3DOM M-ZnO with different metal doping;

[0029] Figure 11 is the carbon dioxide adsorption and desorption isotherm. DETAILED DESCRIPTION

[0030] The technical solutions of the present application will be further described in detail below in combination with specific embodiments and the accompanying drawings.

[0031] The main raw material information involved in the following examples is as follows:

[0032] Zinc nitrate hexahydrate (Zn(NO3)2·6H2O) was purchased from Sinopharm Chemical Reagent Co., Ltd.;

[0033] Copper nitrate trihydrate (Cu(NO3)2·3H2O) was purchased from Sinopharm Chemical Reagent Co., Ltd.;

[0034] Aluminum nitrate nonahydrate (Al(NO3)3·9H2O) was purchased from Sinopharm Chemical Reagent Co., Ltd.;

[0035] Silver nitrate (AgNO3) was purchased from Sinopharm Chemical Reagent Co., Ltd.;

[0036] Molybdenum nitrate (Mo(NO3)4) was purchased from National Pharmaceutical Group Chemical Reagent Co., Ltd.

[0037] Bismuth nitrate (Bi(NO3)3) was purchased from National Pharmaceutical Group Chemical Reagent Co., Ltd.

[0038] Citric acid (C6H8O7) was purchased from Wuxi Minfeng Reagent Factory, Jiangsu.

[0039] Methyl methacrylate (C5H8O2) was purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.

[0040] Anhydrous methanol (CH3OH) was purchased from Lianlong Bohua (Tianjin) Pharmaceutical Chemical Co., Ltd.

[0041] Potassium persulfate (K2S2O8) was purchased from Anjieji.

[0042] The instruments involved in the following examples and their model information are as follows:

[0043] Intelligent magnetic stirrer (ZNCL-GS240, Tianjin Xingke Technology Co., Ltd.);

[0044] Centrifuge (H1-16K table type high speed centrifuge, Kechuang instrument);

[0045] Vacuum drying oven (DZF-6030A, Shanghai Yiheng Instrument Co., Ltd.);

[0046] Scanning electron microscope (ZEISS GeminiSEM 500);

[0047] Electrochemical workstation (CHI660E B21491, Shanghai Chenhua Instrument Co., Ltd.);

[0048] Gas chromatograph (GC9790 II, Fuli Instrument);

[0049] Hydrogen generator (SPH-300, Beijing Zhonghui Pu Analysis Technology Institute);

[0050] Full-automatic air source (SPB-3, Beijing Zhonghui Pu Analysis Technology Institute);

[0051] KCl saturated Ag / AgCl reference electrode (R0303, Shanghai Yueci);

[0052] Fourier infrared spectrometer (Thermo Scientific Nicolet iS20, USA).

[0053] In the following examples, Zn(NO3)2·6H2O, C6H8O7, C5H8O2, CH3OH, K2S2O8, etc. are all analytical pure.

[0054] Example 1

[0055] 3DOM Ag-ZnO (1 : 10) was prepared by the following method, which comprises the following steps:

[0056] S1. 0.012 mmol of Zn(NO3)2.6H2O and AgNO3 (Zn:Ag = 10:1) were added to 5 ml of anhydrous methanol, 2.25 g of citric acid was added and stirred for 1 h;

[0057] S2. Then 600 nm PMMA (2.0 g) microspheres were immersed in the solution obtained in S1, stirred at room temperature for 4 h, the obtained suspension was vacuum filtered to remove excess solution, dried overnight at room temperature, after drying overnight at room temperature, the sample was heat treated at 300 °C under nitrogen atmosphere for 3 h, with a ramp rate of 1 °C min -1 Subsequently, the sample was heated at 300 °C and 600 °C for 3 h, respectively, with a ramp rate of 1 °C min -1 After gradually cooling to room temperature, a brown powder was collected, and 3DOM Ag-ZnO (1 : 10) was obtained.

[0058] Example 2

[0059] 3DOM Cu-ZnO (1 : 32) was prepared by the following method, which comprises the following steps:

[0060] S1. 0.012 mmol of Zn(NO3)2.6H2O and Cu(NO3)2 (Zn:Cu = 32:1) were added to 5 ml of anhydrous methanol, 2.25 g of citric acid was added and stirred for 1 h;

[0061] S2. Then 600 nm PMMA (2.0 g) microspheres were immersed in the solution obtained in S1, stirred at room temperature for 4 h, the obtained suspension was vacuum filtered to remove excess solution, dried overnight at room temperature, after drying overnight at room temperature, the sample was heat treated at 300 °C under nitrogen atmosphere for 3 h, with a ramp rate of 1 °C min -1 Subsequently, the sample was heated at 300 °C and 600 °C for 3 h, respectively, with a ramp rate of 1 °C min -1 After gradually cooling to room temperature, a brown powder was collected, and 3DOM Cu-ZnO (32:1) was obtained.

[0062] Example 3

[0063] 3DOM Al-ZnO (1 : 50) was prepared by the following method, which comprises the following steps:

[0064] S1. 0.012 mmol of Zn(NO3)2.6H2O and Al(NO3)3 (Zn:Al = 50:1) were added to 5 ml of anhydrous methanol, 2.25 g of citric acid was added and stirred for 1 h;

[0065] S2. Then 600 nm PMMA (2.0 g) microspheres were immersed in the solution obtained from S1, stirred at room temperature for 4 h, the obtained suspension was vacuum filtered to remove the excess solution, dried at room temperature overnight, after drying at room temperature overnight, the sample was heat treated at 300 °C under nitrogen atmosphere for 3 h with a ramp rate of 1 °C min -1 , then the sample was heated at 300 °C and 600 °C for 3 h, respectively, with a ramp rate of 1 °C min -1 After gradually cooling to room temperature, a brown powder was collected, 3DOM Al-ZnO (50:1) was obtained.

[0066] Example 4

[0067] A method for preparing 3DOM Co-ZnO (1:50) specifically includes the following steps:

[0068] S1. 0.012 mmol of Zn(N03)2-6H20 and Co(N03)2(Zn:Co = 50:1) were added to 5 ml of anhydrous methanol, 2.25 g of citric acid was added and stirred for 1 h;

[0069] S2. Then 600 nm PMMA (2.0 g) microspheres were immersed in the solution obtained from S1, stirred at room temperature for 4 h, the obtained suspension was vacuum filtered to remove the excess solution, dried at room temperature overnight, after drying at room temperature overnight, the sample was heat treated at 300 °C under nitrogen atmosphere for 3 h with a ramp rate of 1 °C min -1 , then the sample was heated at 300 °C and 600 °C for 3 h, respectively, with a ramp rate of 1 °C min -1 After gradually cooling to room temperature, a brown powder was collected, 3DOM Co-ZnO (50:1) was obtained.

[0070] Example 5

[0071] A method for preparing 3DOM Ni-ZnO (1:50) specifically includes the following steps:

[0072] S1. 0.012 mmol of Zn(N03)2-6H20 and Ni(N03)2(Zn:Ni = 50:1) were added to 5 ml of anhydrous methanol, 2.25 g of citric acid was added and stirred for 1 h;

[0073] S2. Then 600 nm PMMA (2.0 g) microspheres were immersed in the solution obtained from S1, stirred at room temperature for 4 h, the obtained suspension was vacuum filtered to remove the excess solution, dried at room temperature overnight, after drying at room temperature overnight, the sample was heat treated at 300 °C under nitrogen atmosphere for 3 h with a ramp rate of 1 °C min -1Subsequently, the sample was heated at 300 °C and 600 °C for 3 h, respectively, with a ramping rate of 1 °C min -1 After gradually cooling to room temperature, the brown powder was collected, and 3DOM Ni-ZnO (50:1) was obtained.

[0074] Example 6

[0075] The preparation method of 3DOM Bi-ZnO (1:50) specifically comprises the following steps:

[0076] S1. 0.012 mmol of Zn(N03)2-6H20 and Bi(N03)3(Zn:Bi = 50:1) were added into 5 ml of anhydrous methanol, 2.25 g of citric acid was added and stirred for 1 h;

[0077] S2. Then 600 nm PMMA (2.0 g) microspheres were immersed in the solution obtained in S1, stirred at room temperature for 4 h, the obtained suspension was vacuum filtered to remove excess solution, and dried at room temperature overnight. After drying at room temperature overnight, the sample was heat treated at 300 °C in a nitrogen atmosphere for 3 h, with a ramping rate of 1 °C min -1 , Subsequently, the sample was heated at 300 °C and 600 °C for 3 h, respectively, with a ramping rate of 1 °C min -1 After gradually cooling to room temperature, the brown powder was collected, and 3DOM Bi-ZnO (50:1) was obtained.

[0078] Example 7

[0079] The preparation method of 3DOM Mo-ZnO (1:50) specifically comprises the following steps:

[0080] S1. 0.012 mmol of Zn(N03)2-6H20 and Mo(N03)4(Zn:Mo = 50:1) were added into 5 ml of anhydrous methanol, 2.25 g of citric acid was added and stirred for 1 h;

[0081] S2. Then 600 nm PMMA (2.0 g) microspheres were immersed in the solution obtained in S1, stirred at room temperature for 4 h, the obtained suspension was vacuum filtered to remove excess solution, and dried at room temperature overnight. After drying at room temperature overnight, the sample was heat treated at 300 °C in a nitrogen atmosphere for 3 h, with a ramping rate of 1 °C min -1 , Subsequently, the sample was heated at 300 °C and 600 °C for 3 h, respectively, with a ramping rate of 1 °C min -1 After gradually cooling to room temperature, the brown powder was collected, and 3DOM Mo-ZnO (50:1) was obtained.

[0082] The CO2RR performance of 3DOM M-ZnO was explored, in which the CO selectivity of 3DOM Ag-ZnO and 3DOM Cu-ZnO can reach 94% and 95.6% at -1 V, and have good stability within 24 h. Product characterization and performance test:

[0083] (1) SEM and TEM of 3DOM M-ZnO

[0084] Figure 2 is the SEM and TEM images of the catalysts (a, d) 3DOM Ag-ZnO (1:10), (b, e) 3DOM Cu-ZnO (1:32) and (c, f) 3DOM Al-ZnO (1:50). 3DOM Ag-ZnO (1:10), 3DOM Cu-ZnO (1:32), 3DOM Al-ZnO (1:50) all show three-dimensional ordered macroporous structure. The partial damage of macroporous wall in the transmission electron microscopy image is due to the ultrasonic dispersion of the sample during the detection process Figure 2d -f). It can still be found from the transmission electron microscopy and scanning electron microscopy images that the sample has uniform pore wall, which provides effective support for the structural stability of the catalyst.

[0085] (2) EDS element mapping of 3DOM M-ZnO

[0086] Figures 3-5 are characterized by EDS element mapping, indicating that the elements Zn, O and M are uniformly distributed in each catalyst.

[0087] (3) PXRD of 3DOM M-ZnO with different metal doping ratios

[0088] Figure 6 is PXRD images of (a) 3DOM Ag-ZnO with different doping ratios, (b) 3DOM Cu-ZnO with different doping ratios, (c) 3DOM Al-ZnO with different doping ratios, (d) 3DOM Co-ZnO with different doping ratios, (e) 3DOM Ni-ZnO with different doping ratios, (f) 3DOM Bi-ZnO (1 :50), (g) 3DOM Mo-ZnO (1 :50). The structure and chemical valence of the catalysts were evaluated by PXRD and XPS, and the effect of the phase composition of the samples on the catalytic activity was studied. In the PXRD spectrum of the catalyst (Figure 6), each catalyst has characteristic peaks of 3DOM ZnO, retaining the crystal structure of ZnO, but different doped metals exhibit different valences, and the peaks related to the (002) and (101) planes of ZnO move to a higher 2Q angle, indicating that the zinc oxide has a very slight shrinkage due to the doping of the metal. Through in-situ doping, the Ag element in 3DOM Ag-ZnO exists in the form of Ag element, and the characteristic peak area of Ag gradually increases as the ratio increases. In addition, the metal elements in each catalyst exist in the form of oxides Figure 6b -g), and the characteristic peaks are enhanced as the doping metal ratio increases.

[0089] (4) XPS spectra of M and 3DOM M-ZnO

[0090] Figure 7 is the XPS spectra of each metal (a) Ag 3d of 3DOM Ag-ZnO, (b) Cu 2p of 3DOM Cu-ZnO, (c) Al 2p of 3DOM Al-ZnO, and (d) XPS total spectra of three different metal-doped catalysts. The elemental composition and atomic valence in the catalysts were further verified by XPS analysis. As shown in Figure 7a , in 3DOM Ag-ZnO, the XPS spectrum of Ag has binding energies (BEs) of 373.69 and 367.66 eV at the center of Ag + 3d 2 / 3 and Ag 3d 5 / 2 , respectively. The two peaks appearing at 374.93 and 368.02 eV confirm the presence of Ag 0 . It can be observed from the PXRD spectrum that only elemental Ag is detected, and the atomic radius of Ag is smaller than that of Zn and the difference between them is not large, and Ag atoms can partially insert into the host lattice or replace Zn atoms at oxygen vacancies, while the remaining Ag is dispersed on the surface of the catalyst in the form of an element. The partial replacement of Zn atoms by Ag doping causes local charge compensation, and at the same time, modulates the electronic structure of the vicinity, causing changes in the electron cloud density. The XPS spectrum of 3DOM Cu-ZnO shows Cu2p 1 / 2 and Cu 2p 3 / 2two spin-orbit peaks (corresponding to BE 953.35 and 933.34 eV, respectively. Their shake-up satellite peaks are located at 960.37 and 942.97 eV, respectively. This indicates that the copper element exists in the form of Cu 2+ in the catalysts Figure 7b ). In addition, the peak corresponding to Al 2p appears in 3DOM Al-ZnO, indicating that Al 3+ ( Figure 7c ) exists in the catalyst material. The XPS survey spectra of three different metal-doped catalysts are shown in Figure 7d .

[0091] Figure 8 is the XPS spectrum of 3DOM M-ZnO with different doping ratios (a) O 1s, (b) Zn 2p. The content of oxygen vacancies in the synthesized samples was determined by high-resolution O 1s XPS spectrum. The O 1s spectrum of 3DOM ZnO has two prominent peaks at 529.72 and 531.47 eV, corresponding to O atoms in Zn-O and O atoms near oxygen vacancies, respectively. For the three metal-doped catalysts, the abundance of oxygen vacancies leads to an increase in the amount of surface adsorbed oxygen, with a significant high binding energy shift. This further confirms that abundant oxygen vacancies are generated on the 3DOM M-ZnO catalyst due to the charge compensation effect. The XPS spectrum of the original zinc oxide shows Zn 2p 1 / 2 and Zn 2p 3 / 2 peaks of divalent Zn at 1044.22 and 1021.04 eV. In contrast, these peaks of 3DOM M-ZnO are replaced by higher binding energy about 0.2-0.8 eV Figure 8b , meaning that the electron density around the zinc atom is depleted. Metal doping changes the electron cloud density, which can effectively inhibit the evolution of H2. The quantitative analysis results are shown in Tables 1 and 2.

[0092] Table 1 Atomic ratio of 3DOM M-ZnO studied by XPS method

[0093] Catalysts M (at. %) Zn (at. %) O (at. %) 3DOM Ag-ZnO (1 :10) 1.82 45.34 52.84 3DOM Cu-ZnO (1 :32) 1.06 47.88 51.06 3DOM Al-ZnO (1 :50) 0.84 47.32 51.84

[0094] Table 2 XPS analysis results of 3DOM Ag-ZnO (1:10) catalyst

[0095] Catalysts Ag 0 / Ag total a (%)]]> 3DOM Ag-ZnO (1 :10) 42.86

[0096] (5) Electro-catalytic CO2RR test of the product of the present application

[0097] Method for preparing working electrode: 1 mg of catalyst and 2 μL of Nafion solution (5 wt%) were dispersed in 100 μL of ethanol (alternatively, isopropanol, methanol, water, etc.) and sonicated for 30 min to form a homogeneous ink. The catalyst ink was drop-casted on L-type glassy carbon in two times and dried in air for more than 30 min as working electrode.

[0098] Electrochemical measurements were performed in a three-electrode system, with a two-compartment electrolyzer (sealed) (H-type electrolyzer) connected to an electrochemical workstation. The cathode and anode compartments were separated by a proton exchange membrane (Nafion N-117), which contained 0.1 M potassium bicarbonate as electrolyte. Ag / AgCl and Pt sheet (1 x 1 cm 2 ) saturated with KCl were used as the reference and counter electrodes, respectively. The electrocatalytic reduction products of carbon dioxide were detected by online gas chromatography (GC) with a thermal conductivity detector (TCD) and a flame ionization detector (FID). Among them, TCD can detect H2, O2, N2 within the limit of 100 ppm, while FID can detect CH4, CO and hydrocarbons from C2 to C6 at the level of 0.1 ppm. E was converted to RHE reference electrode (vs. = E (vs. Ag / AgCl) + 0.197 V + 0.0591 x pH). Carbon dioxide was fed into the electrolyzer at a flow rate of 20 standard cubic centimeters per minute (sccm) controlled by a mass flow meter. The electrochemical response was recorded using an electrochemical workstation.

[0099] Figure 9 is the LSV curves and (d) Nyquist plots of (a, c) 3DOM Ag-ZnO with different doping ratios and (b, d) 3DOM Cu-ZnO with different doping ratios. After successfully obtaining 3DOM M-ZnO materials doped with different metals, the electrocatalytic carbon dioxide reduction performance of the prepared samples was determined using 0.1 M potassium bicarbonate aqueous solution. As shown in (a, b), with the increase of the doping ratio of Ag, the catalyst has a larger current density, while the LSV curves of 3DOM Cu-ZnO can be seen that 3DOM Cu-ZnO (1:32) has the largest current density, which is due to the increase of electron concentration to produce higher electronic conductivity, which is conducive to the transfer of electrons to active sites in the process of carbon dioxide electro-reduction, thereby improving the electrochemical activity. These results are verified by EIS plots (c), which show that 3DOM Cu-ZnO (1:32) has a smaller interfacial charge transfer resistance (RCT). Figure 9a Figure 9b

[0100] ​​Figure 10 is (a) LSV curves, (b) FE(CO), (c) CO partial current density, (d) Nyquist plots, (e) stability test at -1 V of different metal doped 3DOM M-ZnO. Linear sweep voltammetry (LSV) was tested at a scan rate of 20 mV / s. Among several catalysts, 3DOM Ni-ZnO (1:50) and 3DOM Cu-ZnO (1:32) have comparable current density, and 3DOM Ni-ZnO (1:50) has a more positive onset potential. In addition, 3DOM Ag-ZnO (1:10) also shows a higher current density. When the voltage is -1 V, the CO Faraday efficiency of 3DOM Cu-ZnO (1:32), 3DOM Ag-ZnO (1:10) is 95.6% and 94%, which is significantly improved compared with 3DOM ZnO Figure 10b ). The CO selectivity of other metal doped catalyst materials decreases significantly, which is due to the change of electronic density causing the HER reaction activity to increase. As shown in Figure 10c , at -1 V, the CO partial current density of 3DOM Cu-ZnO (1:32), 3DOM Ag-ZnO (1:10) is not much different, which is 6.2, 6.02 mA cm -2 , indicating that 3DOM Cu-ZnO (1:32) has the highest activity among all samples, reaching a maximum of 10.78 mA cm -2 , indicating that it has good CO2RR catalytic activity. Electrochemical impedance spectroscopy (EIS) was used to evaluate the electronic transfer ability Figure 10d . The introduction of different metals narrows the band gap, resulting in high carrier density, causing the catalyst to accelerate the electron transfer process. In order to further evaluate the CO2RR performance of the catalyst, stability test Figure 10e was carried out. At -1 V constant voltage electrolysis for 24 h, the CO current density and FE of 3DOM Cu-ZnO (1:32) and 3DOM Ag-ZnO (1:10) do not decrease significantly, indicating that the material has good stability.

[0101] As shown in Table 3, the selectivity of 3DOM N-ZnO to CO is not as good as that of 3DOM ZnO without N doping, which is due to the destruction of the structure caused by the introduction of N source high temperature calcination, resulting in a large number of reduction of active sites. In addition, the FE(CO) of 3DOM M-ZnO with different metal doping ratios is shown in Table 4.

[0102] Table 3 FE(CO) of 3DOM N-ZnO catalyst.

[0103] Catalysts FE(CO) 3DOM N-ZnO (1 :50) 44％ 3DOM N-ZnO (1 :20) 40％ 3DOM N-ZnO (1 :10) 32％

[0104] Table 43 FE(CO) of DOM M-ZnO catalysts.

[0105]

[0106] Figure 11 is a carbon dioxide adsorption desorption isotherm. The carbon dioxide adsorption desorption isotherms of 3DOM Cu-ZnO (1:32), 3DOM Ag-ZnO (1:10) and 3DOM Al-ZnO (1:10) are similar, and 3DOM Cu-ZnO (1:32) has slightly better carbon dioxide adsorption capacity than the other two, indicating that Cu doping can provide more CO2 capture sites, which is conducive to the adsorption of CO2 molecules by the catalyst to promote the first electron transfer step. The selectivity is improved because the metal dopant can stabilize the oxygen vacancy by accepting electrons in the oxygen vacancy, induce charge redistribution, and adjust the adsorption strength of CO* to the ideal degree, which is conducive to the desorption of CO and improves the catalytic efficiency of CO2RR.

[0107] The above description is only preferred embodiments of the present application, and it should be pointed out that for ordinary skilled in the art, without departing from the principles of the present application, can make a number of improvements and refinements, these improvements and refinements should also be considered as the protection scope of the present application.

Claims

1. A method for preparing a three-dimensionally ordered macroporous metal-doped ZnO catalyst, characterized by comprising the steps of: Specifically comprising the following steps: ​ S1. Dissolve Zn(NO3)2.6H2O and another metal nitrate in anhydrous methanol with continuous stirring at a certain molar ratio, add citric acid and stir to prepare a precursor solution; S2. Then 600 nm of polymethyl methacrylate microspheres were immersed in the solution obtained in S1, stirred at room temperature, the obtained suspension was vacuum filtered, the excess solution was removed, dried overnight, heat treated in a nitrogen atmosphere at 300-600 °C, temperature ramping rate of 1 °C min -1 , and after cooling to room temperature, 3DOM M-ZnO was obtained.

2. The method for preparing a three-dimensional ordered macroporous metal-doped ZnO catalyst according to claim 1, characterized in that: The metal in S1 is Ag, Cu, Ni, Co, Bi, Mo, Mg or Al.

3. The method for preparing a three-dimensionally ordered macroporous metal-doped ZnO catalyst according to claim 1 or 2, characterized in that: The stirring in S2 is at room temperature for 3-6 h.

4. The method of claim 3, wherein the method comprises: The heat treatment in a nitrogen atmosphere in S2 is heating at 300°C and 600°C for 3 h, respectively, with a temperature increase rate of 1°C min -1 .

5. Application of a three-dimensionally ordered macroporous metal-doped ZnO catalyst prepared by the method of claim 1 in CO2 electro-reduction.

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