Preparation method of 3DOM ZnO catalyst with different pore diameters and application of 3DOM ZnO catalyst in CO2 electroreduction

Abstract

The invention discloses a preparation method of a 3DOM ZnO catalyst with different pore diameters and application of the 3DOM ZnO catalyst in CO2 electroreduction, a polymethyl methacrylate (PMMA) template with a three-dimensional opal structure is constructed by an emulsion polymerization method, and three-dimensional ordered macroporous zinc oxide (3DOM ZnO) with different pore diameters is successfully prepared by dipping in a Zn (NO3) 2.6 H2O methanol solution (containing a citric acid chelating agent) and calcining. SEM verifies the structural stability of the material, PXRD and BET characterization show the chemical composition and large specific surface area characteristic of the material, and a CO2 adsorption and desorption curve further reveals the regulation and control effect of the pore diameter on the CO2 adsorption capacity. Researches show that the 3DOM material not only solves the problem of specific surface area reduction caused by collapse of a traditional MOF precursor, but also promotes active site exposure and an interface electrochemical process by virtue of mutually communicated pore channels, a high specific surface area and an open structure. The invention provides a new idea of structure-performance collaborative optimization for designing a high-efficiency CO2RR catalyst.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of new materials, and relates to an inorganic catalyst for carbon dioxide capture and conversion into value-added products, in particular to preparation of 3DOM ZnO catalysts with different pore sizes and application thereof in CO2 electroreduction. BACKGROUND

[0002] The world is currently experiencing a great change that has not occurred in a century. With the rapid development of the global economy, human society is heavily dependent on non-renewable fossil fuels including oil, coal and natural gas. The combustion of fossil fuels also leads to excessive emission of CO2 gas, which poses a serious threat to human beings and nature, and human society is facing severe challenges. In order to avoid serious damage to the environment and the economic society and to realize the harmonious coexistence of human beings and nature, it is urgent to reduce the concentration of CO2 in the atmosphere. However, CO2 has a stable chemical structure, and the central carbon atom has a stable hybridization form, so it is difficult to activate CO2 molecules by directly cleaving the C=O double bond. Only under relatively harsh conditions such as high temperature, high pressure or high overpotential, can the catalytic conversion of CO2 molecules be realized. So far, researchers have developed various methods to realize the resource utilization of carbon dioxide, such as biological transformation, organic catalysis, photocatalysis, electrocatalysis and photoelectrochemical conversion. Among them, electrocatalytic conversion of carbon dioxide is considered as a potential way for carbon resource recycling and sustainable fuel production. The selective formation of different reduction products such as HCOOH / HCOO - , CO, HCHO, CH4, C2H4, CH3OH, C2H5OH, etc. is greatly related to the electronic effect of the metal.

[0003] According to research reports, the electrocatalytic CO2 reduction technology always faces challenges such as insufficient active site exposure, low mass transfer efficiency and slow reaction kinetics. Traditional Zn-based catalysts have high selectivity for CO2 reduction to CO, but are limited by small specific surface area and poor structural stability, making it difficult to achieve efficient and durable CO2 conversion. Especially when using MOF precursors, the collapse of the structure will cause a sharp decrease in the specific surface area, which seriously limits the efficiency of CO2 adsorption and the first electron transfer step.

[0004] 3DOM ZnO, as a new type of three-dimensional ordered macroporous ZnO catalyst, has a broad application prospect in the field of electrocatalytic CO2 reduction due to its special structure and excellent electrocatalytic activity. The 3DOM ZnO catalyst has the following characteristics:

[0005] (1) Structural properties: 3DOM ZnO catalysts are synthesized by a template method, which has a unique three-dimensional ordered macroporous structure. This structure increases the active surface area, promotes the penetration of electrolyte, and accelerates ion / proton transfer. The design of this structure helps to improve the mass transfer efficiency and accessibility of active sites in catalytic reactions.

[0006] (3) Active sites: The introduction of oxygen vacancies changes the d-band center of ZnO, enhances the activity of CO2, and provides excellent kinetic conditions for CO generation, playing a key role in accelerating CO2 activation and reducing CO generation energy barriers.

[0007] (4) Environmental friendliness: As a material abundant on Earth, the development of ZnO catalysts is of great significance for upgrading greenhouse gases into valuable fuels and raw materials.

[0008] (5) Other applications: In addition to its application in electrocatalytic CO2 reduction, 3DOM ZnO catalysts are also widely studied for other fields such as lithium-sulfur batteries, photocatalytic hydrogen production, environmental purification, etc.

[0009] The present invention innovatively prepares three-dimensional ordered macroporous (3DOM) ZnO catalysts by a template method, effectively solving the above technical bottlenecks. SUMMARY

[0010] The present invention aims to provide 3DOM ZnO catalysts with different pore sizes as electron donors to achieve efficient electrochemical reduction of CO2.

[0011] To achieve the above purpose, the technical solution adopted by the present invention is as follows:

[0012] A preparation method of different pore size 3DOM ZnO catalysts, comprising the following steps:

[0013] Step 1. Synthesis of different pore size (190nm-1.1μm) PMMA: In N2 atmosphere, first add 15-75mL methyl methacrylate and deionized water and stir for 1h, then add 0.12g-0.44g potassium persulfate, mix and stir for 4h, control the reaction system temperature at 70-90℃ throughout the process, obtain the suspension, cool, centrifuge at 3000-10000r / min for 60-90min, dry at 40-45℃ for 12h or more, collect and reserve;

[0014] Step 2. Preparation of 3DOM ZnO catalysts with different pore sizes (190 nm-1.1 μm): 3.56 g of Zn(NO3)2 6H2O was weighed and dissolved in 5 mL of CH3OH, 2.25 g of citric acid was added as a chelating agent and stirred for 1 h, then PMMA with different pore sizes was immersed in the obtained solution and stirred for 4 h, vacuum filtered, and dried at 20-25℃ for 12 h or more.

[0015] In the present application, the different pore sizes in steps 1 and 2 are 190 nm-1.1 μm.

[0016] Preferably, in step 1, the centrifugal speed is 10000 r / min, and the centrifugal time is 90 min.

[0017] Preferably, in step 1, the drying temperature is 40℃, and the drying time is 12 h.

[0018] Preferably, in step 1, the subsequent test reaction time is set to 2 h.

[0019] Preferably, in step 1, 600 rpm is selected as the optimal speed.

[0020] Preferably, in step 2, the PMMA soaking time is 4 h.

[0021] Preferably, in step 2, the drying temperature is 25℃, and the drying time is 12 h.

[0022] Compared with the prior art, the present application has the following beneficial effects:

[0023] 1. The present application uses emulsion polymerization method to construct a poly(methyl methacrylate) (PMMA) template with three-dimensional opal structure, and through immersion in Zn(NO3)2 6H2O methanol solution (containing citric acid chelating agent) and calcination, three-dimensional ordered macroporous zinc oxide (3DOM ZnO) with different pore sizes (190 nm-1.1 μm) is successfully prepared. SEM confirms the structural stability, PXRD and BET characterization shows the chemical composition and large specific surface area characteristics (220.14 m 2 / g), and CO2 adsorption-desorption curve further reveals the regulation of pore size on CO2 adsorption capacity. Studies have shown that 3DOM materials, with interconnected pore channels, high specific surface area and open structure, not only solve the problem of specific surface area reduction caused by the collapse of traditional MOF precursors, but also promote the exposure of active sites and interfacial electrochemical processes. The present application provides a new idea for the structural-performance synergistic optimization of designing efficient CO2RR catalysts.

[0024] 2. The preparation method of the application realizes optimal CO selection performance by introducing oxygen vacancy defect structures and determining the pore size of the PMMA template. The design of rich oxygen vacancy defects will possibly serve as electron trap sites, and the current-driven electrons will be concentrated to Zn atoms, forming a highly concentrated electron density; the d-band center of ZnO is optimized, the activation energy barrier of CO2 is successfully reduced, and the electrochemical reduction effect is good, and at a low overpotential of-1 V, the 3DOM ZnO catalyst realizes a CO faradic efficiency of 92%, which is much higher than the 56% of the traditional ZnO.

[0025] 3. The 3DOM structure also effectively promotes the penetration of the electrolyte and the transfer of charges, so that the CO partial current density reaches 8.88 mA / cm 2 at-1.2 V, and in a stability test of up to 24 hours, the efficiency is always maintained above 89%, and the 3DOM ZnO catalyst exhibits great application potential and research value in the field of electrocatalytic CO2 reduction.

[0026] 4. The raw materials (zinc nitrate hexahydrate, citric acid, methyl methacrylate, potassium persulfate and methanol) adopted by the application are cheap and easy to obtain, the preparation process is simple and time-saving, and the application can be used for small-scale operation in the laboratory and is expected to realize industrial application. BRIEF DESCRIPTION OF DRAWINGS

[0027] Figure 1 is a SEM diagram of PMMA of the products obtained in Examples 1-7;

[0028] Figure 2 is a SEM diagram of 3DOM ZnO and (h) ordinary ZnO of the products obtained in Examples 1-7;

[0029] Figure 3 Figure 3 is a PXRD diagram of 3DOM ZnO and (h) ordinary ZnO of the products obtained in Examples 1-7;

[0030] Figure 4 is (a) nitrogen adsorption-desorption isotherm and (b) pore size distribution diagram of the synthesized sample;

[0031] Figure 5 is a CO2 reduction test diagram; wherein (a) LSV curves of different catalysts in a saturated 0.1M KHCO3 electrolyte with a scanning rate of 20 mV / s, (b) FE(CO) of different catalysts, (c) CO partial current density, (d) Nyquist diagram, (e) stability test at a potential of-1 V;

[0032] Figure 6 Figure 6 is three parallel experiments of 3DOM ZnO (1.1 μm) electrocatalytic carbon dioxide test;

[0033] Figure 7 is (a) CO2 adsorption-desorption isotherm and (b) CO2 logarithmic adsorption-desorption isotherm of the synthesized sample;

[0034] Figure 8 Fourier transform infrared spectrogram (FT-IR) of 600 nm 3DOM ZnO. DETAILED DESCRIPTION

[0035] The technical solutions of the present application are further described in detail below in combination with specific embodiments and drawings. The main raw materials and their manufacturers involved in the following examples are as follows:

[0036] Zinc nitrate hexahydrate (Zn(NO3)2·6H2O) was purchased from Sinopharm Chemical Reagent Co., Ltd.;

[0037] Citric acid (C6H8O7) was purchased from Minfeng Reagent Factory in Wuxi, Jiangsu;

[0038] Methyl methacrylate (C5H8O2) was purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.;

[0039] Methanol (CH3OH) was purchased from Lianlong Bohua (Tianjin) Pharmaceutical Chemical Co., Ltd.;

[0040] Potassium persulfate (K2S2O8) was purchased from Anjieji.

[0041] The instruments and their model information involved in the following examples are as follows:

[0042] Intelligent magnetic stirrer (ZNCL-GS240, Tianjin Xingke Science and Technology Co., Ltd.);

[0043] Centrifuge (H1-16K table type high-speed centrifuge, available from Kechuang Instrument Co., Ltd.);

[0044] Vacuum drying oven (DZF-6030A, Shanghai Yiheng Instrument Co., Ltd.);

[0045] Scanning electron microscope (ZEISS GeminiSEM 500);

[0046] Electrochemical workstation (CHI660E B21491, Shanghai Chenhua Instrument Co., Ltd.);

[0047] Gas chromatograph (GC9790 II, Fuli Instrument Co., Ltd.);

[0048] Hydrogen generator (SPH-300, Beijing Zhonghui Pu Analysis Technology Institute);

[0049] Full-automatic air source (SPB-3, Beijing Zhonghui Pu Analysis Technology Institute);

[0050] KCl-saturated Ag / AgCl reference electrode (R0303, Shanghai Yueci);

[0051] Fourier infrared spectrometer (Thermo Scientific Nicolet iS20, USA).

[0052] In the following examples, Zn(NO3)2·6H2O, C6H8O7, C5H8O2, CH3OH, K2S2O8 are all analytically pure.

[0053] Based on the principle of radical polymerization, the selection of appropriate reaction conditions (such as reaction time, stirring speed, reaction temperature, monomer concentration and initiator concentration) is crucial to the particle morphology and particle size of the formed PMMA microspheres.

[0054] In order to obtain monodisperse PMMA microspheres with high yield and excellent stability, the optimal conditions for the size and morphology of the required microspheres are explored by adjusting the reaction parameters, and the performance of 3DOM ZnO for CO2RR is further improved.

[0055] As shown in Table 1.1, when the reaction time is too short, the polymerization is not sufficient, there is a pungent smell, and there is a stratification phenomenon after standing overnight, and the surface of the PMMA microspheres is uneven; when the reaction time is greater than 1.5h, the particle size increases with the extension of the reaction time, but the PMMA particle size cannot be greatly improved by too long reaction time, therefore we set the reaction time to 2h in the subsequent test.

[0056] Table 1.1 Effect of controlling reaction time as a single variable on PMMA microsphere particle size.

[0057]

[0058] As shown in Table 1.2, when the magnetic speed is too low, MMA and H2O cannot be fully mixed, the liquid surface is stratified in a round-bottom flask, the lower layer is a white suspension, the upper layer is an oily MMA liquid, there is a pungent smell, and there is a stratification phenomenon after standing overnight. With the increase of the speed of the magnetic stirrer, the particle size increases slightly, and since the high speed will make the reaction violent, the reaction solution will produce vortex, and 600rpm is the best.

[0059] Table 1.2 Effect of controlling magnetic stirrer speed as a single variable on PMMA microsphere particle size.

[0060]

[0061] Since the reaction temperature of potassium persulfate initiator should not be too high, as shown in Table 1.3, with the increase of the reaction temperature, the particle size slightly decreases.

[0062] Table 1.3 Effect of controlling temperature as a single variable on PMMA microsphere particle size.

[0063]

[0064] To better explore the relationship between the amount of initiator and monomer, the amount of initiator was controlled as a single variable, as shown in Table 1.4, and the amount of MMA was adjusted to 60 ml to observe the change in particle size. With the increase of the amount of initiator, the particle size decreased significantly. Too little amount of initiator would make the suspension too thick, and the speed of the magnetic child would decrease.

[0065] Table 1.4 Effect of controlling the amount of initiator as a single variable on the particle size of PMMA microspheres.

[0066]

[0067] As shown in Table 1.5, the ratio of monomer to water was controlled as 2:16, 3:16, 4:16, 5:16, and 6:16. With the increase of monomer concentration, the particle size increased significantly. When the ratio was 5:16, the PMMA microspheres showed uneven size; and when the ratio increased to 6:16, the reaction was violent, the suspension was too thick, and the speed of the magnetic child decreased.

[0068] Table 1.5 Effect of controlling the monomer concentration as a single variable on the particle size of PMMA microspheres.

[0069]

[0070] In summary, the monomer concentration and the amount of initiator have the greatest impact on the particle size of PMMA.

[0071] 3DOM ZnO catalysts have both three-dimensional ordered macropores and mesopores. In addition, the surface area of the catalyst increases with the increase of the particle size of PMMA microspheres, which enhances the exposure of active sites, resulting in a larger contact area between active substances and CO2 molecules, and improves the catalytic reaction rate. Among them, the surface area of ordinary ZnO is the smallest, only 2.2456 m 2 / g; the surface area of 3DOM ZnO(600nm) catalyst is the largest, reaching 220.1416 m 2 / g, and the surface area of 3DOM ZnO(1.1μm) is significantly reduced to 194.8829 m 2 / g, which is due to the uneven size of PMMA templates, which causes the structure to twist and partially collapse.

[0072] Among several catalysts, the CO Faradaic efficiency of 3DOM ZnO (600 nm) is 90.5% at -1 V, far exceeding the 56% of normal ZnO; the CO partial current density of ZnO, 3DOM ZnO (190 nm), 3DOM ZnO (220 nm), 3DOM ZnO (260 nm), 3DOM ZnO (350 nm), 3DOM ZnO (410 nm), 3DOM ZnO (600 nm) is 1.02, 3.11, 3.22, 3.89, 4.16, 4.63, 5.18 mA cm -2 , respectively, indicating that 3DOM ZnO (600 nm) has the highest activity among all samples, reaching a maximum of 8.88 mA cm -2 at -1.2 V, indicating that it has good CO2RR catalytic activity. The Nyquist plot shows that 3DOM ZnO (600 nm) exhibits the smallest charge transfer resistance among all catalysts, while the resistance of ZnO is the largest. As the pore size of 3DOM ZnO increases, the specific surface area increases, which can effectively reduce the interface energy barrier, promote charge transfer, and improve the intrinsic activity of the catalyst, which means that it promotes the formation of CO2·- intermediate by the first electron transfer step. To further evaluate the CO2RR performance of 3DOM ZnO (600 nm), we conducted a stability test. The current density and FE of CO did not show significant decay after 24 h of constant voltage electrolysis at -1 V, indicating that the material has good stability.

[0073] Example 1

[0074] A method for preparing a 3DOM ZnO catalyst with a pore size of 600 nm, comprising the following steps:

[0075] Step 1. Under N2 atmosphere, first add methyl methacrylate 60 mL and deionized water 240 ml under strong magnetic stirrer for 2 h, then add potassium persulfate 0.16 g to obtain a suspension, continue to stir for 4 h, turn off the reaction, cool and centrifuge at 10000 r / min for 90 min to obtain a precipitate. Dry it in a 40°C oven overnight and collect it for use. The unit of the amount of substance is mol, and the unit of volume is mL.

[0076] Step 2. Weigh 3.56 g of Zn(NO3)2 6H2O and dissolve it in 5 mL of CH3OH, then add 2.25 g of citric acid as a chelating agent and stir for 1 h. Finally, immerse the 600 nm PMMA in the obtained solution and stir for 4 h, vacuum filter and dry overnight at room temperature.

[0077] Example 2

[0078] A method of preparing a 3DOM ZnO catalyst having a pore size of 190 nm, comprising the steps of:

[0079] Step 1. Under N2atmosphere, 80 °C, first add methyl methacrylate 30 mL and deionized water 240 ml, stir for 2 h under strong magnetic stirrer, then add potassium persulfate 0.3 g, obtain a suspension, continue to stir for 4 h, stop the reaction, cool down and centrifuge at 10000 r / min for 90 min, obtain a precipitate. Dry it in an oven at 40 °C overnight, collect and reserve. The unit of the amount of substance is mol, and the unit of volume is mL.

[0080] Step 2. Weigh 3.56 g Zn(NO3)2 6H2O, dissolve it in 5 mL CH3OH, then add 2.25 g citric acid as a chelating agent, stir for 1 h, finally immerse the 190 nm PMMA in the obtained solution, stir for 4 h, vacuum filter, and dry overnight at room temperature.

[0081] Example 3

[0082] A method of preparing a 3DOM ZnO catalyst having a pore size of 220 nm, comprising the steps of:

[0083] Step 1. Under N2atmosphere, 70 °C, first add methyl methacrylate 30 mL and deionized water 240 ml, stir for 2 h under strong magnetic stirrer, then add potassium persulfate 0.3 g, obtain a suspension, continue to stir for 4 h, stop the reaction, cool down and centrifuge at 10000 r / min for 90 min, obtain a precipitate. Dry it in an oven at 40 °C overnight, collect and reserve. The unit of the amount of substance is mol, and the unit of volume is mL.

[0084] Step 2. Weigh 3.56 g Zn(NO3)2 6H2O, dissolve it in 5 mL CH3OH, then add 2.25 g citric acid as a chelating agent, stir for 1 h, finally immerse the 220 nm PMMA in the obtained solution, stir for 4 h, vacuum filter, and dry overnight at room temperature.

[0085] Example 4

[0086] A method of preparing a 3DOM ZnO catalyst having a pore size of 260 nm, comprising the steps of:

[0087] Step 1. Methyl methacrylate 60 mL and deionized water 240 mL were stirred for 2 h at 80 °C under N2atmosphere, then potassium persulfate 0.44 g was added to obtain a suspension, which was stirred for another 4 h. The reaction was stopped and the suspension was cooled and centrifuged at 10 000 r / min for 90 min to obtain a precipitate, which was dried in an oven at 40 °C overnight. The material was collected for use. The unit of the amount of substance is mol, and the unit of volume is mL.

[0088] Step 2. 3.56 g of Zn(NO3)2 6H2O was dissolved in 5 mL of CH3OH, and 2.25 g of citric acid was added as a chelating agent and stirred for 1 h. Finally, the PMMA of 260 nm was immersed in the obtained solution and stirred for 4 h, vacuum filtered, and dried at room temperature overnight.

[0089] Example 5

[0090] A method for preparing a 3DOM ZnO catalyst with a pore size of 350 nm, comprising the following steps:

[0091] Step 1. Methyl methacrylate 30 mL and deionized water 240 mL were stirred for 2 h at 80 °C under N2atmosphere, then potassium persulfate 0.16 g was added to obtain a suspension, which was stirred for another 4 h. The reaction was stopped and the suspension was cooled and centrifuged at 10 000 r / min for 90 min to obtain a precipitate, which was dried in an oven at 40 °C overnight. The material was collected for use. The unit of the amount of substance is mol, and the unit of volume is mL.

[0092] Step 2. 3.56 g of Zn(NO3)2 6H2O was dissolved in 5 mL of CH3OH, and 2.25 g of citric acid was added as a chelating agent and stirred for 1 h. Finally, the PMMA of 350 nm was immersed in the obtained solution and stirred for 4 h, vacuum filtered, and dried at room temperature overnight.

[0093] Example 6

[0094] A method for preparing a 3DOM ZnO catalyst with a pore size of 410 nm, comprising the following steps:

[0095] Step 1. Methyl methacrylate 45 mL and deionized water 240 mL were stirred for 2 h at 80 °C under N2atmosphere, then potassium persulfate 0.16 g was added to obtain a suspension, which was stirred for another 4 h. The reaction was stopped and the suspension was cooled and centrifuged at 10 000 r / min for 90 min to obtain a precipitate, which was dried in an oven at 40 °C overnight. The material was collected for use. The unit of the amount of substance is mol, and the unit of volume is mL.

[0096] Step 2. 3.56 g of Zn(NO3)2 6H2O was weighed and dissolved in 5 mL of CH3OH, 2.25 g of citric acid was added as a chelating agent and stirred for 1 h. Finally, the 410 nm PMMA was immersed in the obtained solution and stirred for 4 h, vacuum filtered, and dried at room temperature overnight.

[0097] Example 7

[0098] A method for preparing a 3DOM ZnO catalyst with a pore size of 1.1 μm, comprising the following steps:

[0099] Step 1. Under a N2 atmosphere, 75 mL of methyl methacrylate and 240 mL of deionized water were added to a strong magnetic stirrer and stirred for 2 h at 80°C. Then, 0.16 g of potassium persulfate was added to obtain a suspension, and the stirring was continued for 4 h. After the reaction was stopped, the mixture was cooled and centrifuged at 10,000 r / min for 90 min to obtain a precipitate. The precipitate was dried in an oven at 40°C overnight and collected for use. The unit of the amount of substance is mol, and the unit of volume is mL.

[0100] Step 2. 3.56 g of Zn(NO3)2 6H2O was weighed and dissolved in 5 mL of CH3OH, 2.25 g of citric acid was added as a chelating agent and stirred for 1 h. Finally, the 1.1 μm PMMA was immersed in the obtained solution and stirred for 4 h, vacuum filtered, and dried at room temperature overnight.

[0101] The products obtained in Examples 1-7 were tested

[0102] (1) SEM images of PMMA microspheres with different pore sizes

[0103] Fig. 1 is the SEM images of PMMA with different pore sizes, including (a) 190 nm, (b) 220 nm, (c) 260 nm, (d) 350 nm, (e) 410 nm, (f) 600 nm, and (g) 1.1 μm. As shown in Fig. 1, a series of PMMA microspheres with different pore sizes were successfully prepared by the method of the present application. The particle sizes of the PMMA microspheres below 600 nm are uniform, but the particle sizes of the PMMA microspheres above 1.1 μm are not uniform.

[0104] (2) SEM images of 3DOM ZnO with different pore sizes

[0105] Figure 2 are SEM images of (a) 190 nm, (b) 220 nm, (c) 260 nm, (d) 350 nm, (e) 410 nm, (f) 600 nm, (g) 1.1 μm 3DOM ZnO, and (h) common ZnO, respectively. As shown in Figure 2, all catalysts exhibit three-dimensionally ordered macroporous structure, macropores are spherical and connected by walls between each other. With higher specific surface area, it is helpful for gas diffusion to the inner space of the material. This helps CO2 to transport to the active sites quickly. As shown in Figure 2, the structure of 3DOM ZnO (1.1 μm) is distorted and partially collapsed due to the size inhomogeneity of PMMA template. In addition, we observed that common ZnO is nanosheet structure. Figure 2g Figure 2h

[0106] (3) PXRD patterns of 3DOM ZnO with different pore sizes

[0107] Figure 3 are PXRD patterns of (a) 190 nm, (b) 220 nm, (c) 260 nm, (d) 350 nm, (e) 410 nm, (f) 600 nm, (g) 1.1 μm 3DOM ZnO, and (h) common ZnO, respectively. The structure of catalysts was evaluated by PXRD analysis. As shown in Figure 3, the characteristic peaks of catalysts correspond to (110), (002), (101), (102) planes of ZnO, respectively, which proves the successful synthesis of 3DOM ZnO. Figure 3

[0108] (4) Nitrogen adsorption-desorption isotherms and pore size distribution of the synthesized samples

[0109] Figure 4 are (a) nitrogen adsorption-desorption isotherms and (b) pore size distribution of the synthesized samples. From Figure 4, we can see that all ZnO catalysts exhibit typical type IV isotherm and H3 hysteresis loop. The results show that 3DOM ZnO catalysts have both three-dimensionally ordered macropores and mesopores. In addition, the surface area of catalysts increases with the increase of PMMA microspheres size, which enhances the exposure of active sites, resulting in larger contact area between active species and CO2 molecules, and improves the catalytic reaction rate. Among them, the surface area of common ZnO is the smallest, only 2.2456 m 2 / g; the surface area of 3DOM ZnO (600 nm) catalyst is the largest, 220.1416 m 2 / g, and the surface area of 3DOM ZnO (1.1 μm) is significantly reduced, 194.8829 m 2 / g, which is due to the size inhomogeneity of PMMA template, resulting in the distortion of the structure and partial collapse.

[0110] ​​​(5) CO2 electrochemical reduction performance test

[0111] Method for preparing working electrode: 1 mg of catalyst and 2 μL of Nafion solution (5 wt%) were dispersed in 100 μL of ethanol and sonicated for 30 min to form a homogeneous ink. The catalyst ink was drop-cast twice on L-type glassy carbon and dried in air for more than 30 min as working electrode.

[0112] Electrochemical measurements were performed in a three-electrode system, in which a two-compartment electrolyzer (sealed) (H-type electrolyzer) was 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 products of the electrocatalytic reduction of carbon dioxide were detected by online gas chromatography (GC) with a thermal conductivity detector (TCD) and a flame ionization detector (FID). The TCD can detect H2, O2, N2 within the limit of 100 ppm, while the FID can detect CH4, CO, and C2 to C6 hydrocarbons at the level of 0.1 ppm. The 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 flowmeter. The electrochemical response was recorded using the electrochemical workstation.

[0113] 0.1 M KHCO3 aqueous solution was used as electrolyte.

[0114] Figure 5 is a CO2 reduction test graph, where (a) LSV curves of different catalysts in saturated 0.1 M KHCO3 electrolyte, scan rate 20 mV / s, (b) FE(CO) of different catalysts, (c) CO partial current density, (d) Nyquist plot, (e) stability test at -1 V potential. The electrocatalytic carbon dioxide reduction performance of ordinary ZnO and 3DOM ZnO with different pore sizes was studied in the H-type cell. Linear sweep voltammetry (LSV) was tested in CO2 saturated 0.1 M potassium bicarbonate electrolyte solution, with a scan rate of 20 mV / s. As shown in Figure 5a , among several catalysts, 3DOM ZnO (600 nm) has the highest current density and more positive onset potential. When the voltage is -1 V, the CO faradic efficiency of 3DOM ZnO (600 nm) is 90.5%, far exceeding that of ordinary ZnO (56% Figure 5b ). As shown in Figure 5cThe CO partial current densities of ZnO, 3DOM ZnO (190 nm), 3DOM ZnO (220 nm), 3DOM ZnO (260 nm), 3DOM ZnO (350 nm), 3DOM ZnO (410 nm), and 3DOM ZnO (600 nm) were 1.02, 3.11, 3.22, 3.89, 4.16, 4.63, and 5.18 mA cm-2, respectively, at -1 V, as shown in Fig. 2b. -2 The 3DOM ZnO (600 nm) had the highest activity among all samples, reaching a maximum of 8.88 mA cm-2 at -1.2 V, as shown in Fig. 2c, indicating that it had good CO2RR catalytic activity. -2 The electronic transfer ability of the catalysts was evaluated using electrochemical impedance spectroscopy (EIS) ( Figure 5d ). The Nyquist plot showed that the 3DOM ZnO (600 nm) exhibited the smallest charge transfer resistance among all catalysts, while the ZnO had the largest resistance. As the pore size of the 3DOM ZnO increased, the specific surface area increased, which effectively reduced the interface energy barrier, promoted charge transfer, and improved the intrinsic activity of the catalyst, which meant that it promoted the formation of CO2·- intermediates from adsorbed carbon dioxide molecules through the first electron transfer step. To further evaluate the CO2RR performance of the 3DOM ZnO (600 nm), we conducted a stability test ( Figure 5e ). The current density and FE of CO did not significantly decrease after 24 h of constant voltage electrolysis at -1 V, indicating that the material had good stability.

[0115] Figure 6 Three parallel experiments of 1.1 μm 3DOM ZnO electrocatalytic carbon dioxide testing. As shown in the figure, the selectivity of 3DOM ZnO (1.1 μm) to CO can reach 92%, but due to the existence of structural distortion and uneven pore size distribution, the stability of the catalyst material is not good. Therefore, in multiple tests, the results fluctuate greatly, making it difficult to ensure its reliability as a stable catalyst, and it does not meet the actual application requirements.

[0116] Fig. 7 is (a) the CO2 adsorption-desorption isotherm of the synthesized sample and (b) the CO2 logarithmic adsorption-desorption isotherm. We collected the carbon dioxide adsorption-desorption isotherms of 3DOM ZnO (190), 3DOM ZnO (600), and 3DOM ZnO (1.1 μm) at 293.150 K, and observed that the shapes of the isotherms of the three catalysts were very similar. The catalysts had large pore structures, and the absorption amounts at 1 bar were 198.86, 209.51, and 260.25 cm 3 g-1 It is worth noting that the adsorption amount of 3DOM ZnO(600) is the highest after 0.1 mbar, and 3DOM ZnO(190) is the smallest. 3DOM ZnO(1.1 μm) still moves upward at higher pressure due to the decrease in total pore volume, but the increment after 0.9 bar is significantly reduced, which is due to the uneven internal pore size distribution, making the total pore volume smaller than 3DOM ZnO(600). It is shown that 3DOM ZnO(600) has the best CO2 adsorption capacity, further indicating that large pore size and surface area can provide more CO2 capture sites, which is conducive to the adsorption of CO2 molecules on the catalyst to promote the first electron transfer step.

[0117] (8) Fourier transform infrared spectra of 600 nm 3DOM ZnO

[0118] As shown in Figure 8 , Fourier transform infrared spectra (FT-IR) measurements were used to investigate the reaction intermediates on the catalyst surface and explain the origin of CO selectivity. Experiments were performed on 3DOM ZnO in 0.1 M KHCO3 solution saturated with CO2 at a potential of -0.8 to -1.2 V. A sharp rising peak appeared near 1420 cm -1 , which is due to the rapid consumption of protons leading to the accumulation of CO3 2- on the catalyst surface and the shift of HCO 3- to CO3 2- . A reverse peak centered on CO2 appeared in the range of 2331-2360 cm -1 , which is due to the gradual formation of a lower potential due to the consumption of CO2 in the electrolyte. A clear CO absorption band can be observed on 3DOM ZnO, and 1890 cm -1 corresponds to bridging CO (CO B ).

[0119] The present application synthesizes PMMA templates with different pore sizes and applies them to the preparation of catalysts for CO2 electrocatalytic reduction, and introduces oxygen vacancy defect structures to prepare the optimal CO selective catalyst. The catalyst can improve the utilization rate of holes and energy transfer efficiency, thereby promoting the efficient generation of active intermediates, greatly improving the performance of CO2 catalytic reduction, and achieving the protection of environmental pollution.

[0120] The above has exemplarily described the present application, and it should be noted that any simple modification, modification or other equivalent replacement that does not deviate from the core of the present application can fall within the protection scope of the present application without creative labor of those skilled in the art.

Claims

1. A method for preparing different pore size 3DOM ZnO catalysts, characterized in that, The method comprises the following steps: Step 1. Synthesis of PMMA with different pore sizes: under a N2 atmosphere, 15-75 mL of methyl methacrylate is first stirred with deionized water for 1 h, then 0.12 g-0.44 g of potassium persulfate is added, and the mixture is stirred for 4 h, the reaction system temperature is controlled at 70-90 DEG C throughout the process, a suspension is obtained, and the suspension is cooled, centrifuged at 3000-10000 r / min for 60-90 min, and dried at 40-45 DEG C for 12 h or more, and then collected for use; Step 2. Preparation of 3DOM ZnO catalysts with different pore sizes: 3.56 g of Zn(NO3)2 6H2O is weighed and dissolved in 5 mL of CH3OH, 2.25 g of citric acid is added as a chelating agent and stirred for 1 h, and then the PMMA with different pore sizes is immersed in the obtained solution and stirred for 4 h, vacuum filtered, and dried at 20-25 DEG C for 12 h or more.

2. The method for preparing different pore size 3DOM ZnO catalyst according to claim 1, characterized in that: The different pore sizes in steps 1 and 2 are 190 nm-1.1 μm.

3. The method for preparing different pore size 3DOM ZnO catalyst according to claim 1, characterized in that: In step 1, the centrifugal speed is 10000 r / min, and the centrifugal time is 90 min.

4. The method for preparing different pore size 3DOM ZnO catalyst according to claim 1, characterized in that: In step 1, the drying temperature is 40 DEG C, and the drying time is 12 h.

5. The method for preparing different pore size 3DOM ZnO catalyst according to claim 1, characterized in that: The subsequent test reaction time is set to 2 h.

6. The method for preparing a 3DOM ZnO catalyst with different pore sizes according to claim 1, characterized in that: In step 1, a speed of 600 rpm is selected.

7. The method for preparing a 3DOM ZnO catalyst with different pore sizes according to claim 1, characterized in that: In step 2, the PMMA soaking time is 4 h.

8. The method for preparing different pore size 3DOM ZnO catalyst according to claim 1, characterized in that: In step 2, the drying temperature is 25 DEG C, and the drying time is 12 h.

9. Use of the catalyst prepared according to the method of claim 1 or 8 in electrocatalytic reduction of CO2.

10. The use according to claim 9, characterized in that: The method for using the 3DOM ZnO material as a catalyst to electrocatalytically reduce CO2 is as follows: 1 mg of catalyst and 2 μL of Nafion solution (5 wt%) are dispersed in 100 μL of ethanol, and ultrasonic treatment is performed for 30 min to form a homogeneous ink; the catalyst ink is drop-coated on an L-shaped glass substrate in two times, and is naturally dried in air for 30 min or more to obtain a working electrode; the working electrode, a reference electrode and a counter electrode are placed in an electrolyte for electrolysis, the overpotential is-0.8 V to-1.2 V, and the electrolyte is a 0.1 M KHCO3 solution.

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