Transition metal nickel monatomic difunctional electrocatalyst as well as preparation method and application thereof

Abstract

The invention relates to a transition metal nickel monatomic difunctional electrocatalyst and a preparation method and application thereof, and belongs to the technical field of carbon dioxide electrolysis. The catalyst takes a transition metal nickel monatomic as an active component, the loading capacity of the active component is 2-5wt.%, a nitrogen-doped carbon material is taken as a carrier, and the microstructure of the carrier is a rhombic dodecahedron with the particle size of 100-200nm. The difunctional electrocatalyst used in the invention has excellent double functions of carbon dioxide electroreduction and sulfur dioxide electrooxidation activity, is applied to the constructed novel carbon dioxide electrolysis system, has lower electric energy consumption and operation cost compared with the traditional electrolysis system, and has huge application potential.

Description

Technical Field

[0001] The present invention relates to a transition metal nickel single-atom bifunctional electrocatalyst, a preparation method thereof, and an application thereof, belonging to the technical field of carbon dioxide electrolysis technology. Background Art

[0002] Among many resource utilization methods, carbon dioxide electrolysis coupled with renewable electricity has received extensive attention due to its mild operating conditions, product diversity and other advantages.

[0003] Traditional carbon dioxide electrolysis consists of two half-reactions: carbon dioxide reduction reaction at the cathode and oxygen evolution at the anode. The thermodynamic potential of the oxygen evolution reaction is as high as 1.23V, and the oxygen evolution reaction is a typical four-electron transfer process, which consumes almost 90% of the electrical energy input. In addition, most commercially available oxygen evolution electrocatalysts are composed of precious metals iridium or ruthenium. The high cost and limited abundance further hinder the commercial application of carbon dioxide electrolysis technology. The oxygen generated at the anode has little utilization value, which will lead to a reduction in the energy efficiency of carbon dioxide electrolysis. Therefore, replacing the oxygen evolution reaction with an anodic oxidation reaction that is more favorable thermodynamically and kinetically is the most effective way to improve the energy efficiency of carbon dioxide electrolysis. The thermodynamic potential of the sulfur dioxide electrooxidation reaction is only 0.16V, and the reaction is a two-electron transfer process, making it a potential anodic oxidation reaction that can replace the oxygen evolution reaction.

[0004] In addition, in most carbon dioxide electrolysis systems, since the catalysts used for the cathode CO2 reduction and the anode oxygen evolution reaction are different, the preparation cost of the catalyst and the system operation cost are relatively high, which is not conducive to commercial application. Most of the known bifunctional electrocatalysts that can be used in the carbon dioxide mixed electrolysis system are mainly made of precious metal materials. Such materials have high costs and limited abundances, which are not conducive to the further development of carbon dioxide electrolysis technology.

[0005] Therefore, the development of low-cost bifunctional electrocatalysts is crucial for the industrial application of carbon dioxide electrolysis technology. Summary of the Invention

[0006] In order to overcome the deficiencies of the prior art, the purpose of the present invention is to provide a transition metal nickel single-atom bifunctional electrocatalyst, a preparation method thereof, and an application thereof. The bifunctional electrocatalyst is a single-atom catalyst centered on transition metal nickel. The bifunctional electrocatalyst can be used to catalyze CO2 reduction and SO2 oxidation simultaneously, effectively reducing the power consumption, and realizing the production of CO at the cathode and H2SO4 at the anode at the same time.

[0007] In order to achieve the above purpose, the technical solution adopted by the present invention is as follows:

[0008] In a first aspect, the present invention provides a transition metal nickel single-atom bifunctional electrocatalyst, wherein the catalyst uses transition metal nickel single atoms as the active component, the loading of the active component is 2-5 wt.%, and a nitrogen-doped carbon material is used as the carrier, and the microscopic morphology of the carrier is a rhombic dodecahedron with a size of 100-200 nm.

[0009] In a second aspect, the present invention provides a method for preparing the above-mentioned transition metal nickel single-atom bifunctional electrocatalyst, comprising the following steps:

[0010] (1) Prepare a methanol solution containing zinc nitrate hexahydrate and nickel salt, stir and ultrasonicate to obtain solution A;

[0011] (2) Prepare a methanol solution containing 2-methylimidazole, stir and ultrasonicate to obtain solution B;

[0012] (3) Mix the solution B obtained in step (2) and the solution A obtained in step (1) and stir at room temperature to obtain solution C;

[0013] (4) Let the solution C obtained in step (3) stand under constant temperature conditions;

[0014] (4) Centrifuge, wash, and then dry to obtain a catalyst precursor;

[0015] (5) Under an argon atmosphere, pyrolyze the catalyst precursor obtained in step (4), and after cooling to room temperature, the transition metal nickel single-atom bifunctional electrocatalyst is obtained.

[0016] Further, in the above technical solution, in step (1), the nickel salt is one of nickel nitrate hexahydrate, nickel acetate tetrahydrate, and nickel chloride hexahydrate;

[0017] The molar ratio of zinc nitrate hexahydrate to nickel salt is 1:1 - 1:4;

[0018] The ratio of the volume of methanol to the amount of substance of zinc nitrate hexahydrate is 300 ml:0.01 mol - 300 ml:0.03 mol;

[0019] The stirring time is 5-10 min;

[0020] The ultrasonication time is 10-20 min.

[0021] Further, in the above technical solution, in step (2), the molar ratio of 2-methylimidazole to zinc nitrate hexahydrate is 8:1 - 20:1;

[0022] The ratio of the volume of methanol to the amount of substance of 2-methylimidazole is 100 ml:0.2 mol - 100 ml:0.08 mol;

[0023] The stirring time is 5 - 10 min;

[0024] The ultrasonic time is 10 - 20 min.

[0025] Further, in the above technical solution, in step (3), the stirring time is 20 - 30 min.

[0026] Further, in the above technical solution, in step (4), the temperature of the constant temperature is 30 - 60 °C;

[0027] The standing time is 12 - 48 h.

[0028] Further, in the above technical solution, in step (5), the temperature of the pyrolysis is 900 - 1100 °C, and the pyrolysis time is 60 - 120 min.

[0029] In a third aspect, the present invention provides an application of the above-mentioned transition metal nickel single-atom bifunctional electrocatalyst in a mixed electrolysis system for carbon dioxide reduction and sulfur dioxide oxidation. In the mixed electrolysis system, both the cathode and the anode use gas diffusion electrodes supporting the bifunctional electrocatalyst.

[0030] Further, in the above technical solution, the preparation method of the gas diffusion electrode is: dispersing the bifunctional electrocatalyst in an isopropanol solution containing Nafion to obtain a catalyst slurry, depositing the catalyst slurry on a gas diffusion layer, and drying to obtain a gas diffusion electrode supporting the bifunctional electrocatalyst;

[0031] The mass ratio of the bifunctional electrocatalyst to Nafion is 4:1.

[0032] Further, in the above technical solution, in the mixed electrolysis system, the anolyte is an acidic aqueous sulfite solution with a pH of 0.5 - 2, the catholyte is an aqueous bicarbonate solution, and the diaphragm is a proton exchange membrane.

[0033] Further, in the above technical solution, the deposition method includes one of manual scraping, spraying, and electrostatic spraying.

[0034] Further, in the above technical solution, the anolyte is one of an aqueous potassium sulfite solution and an aqueous sodium sulfite solution, and one of sulfuric acid, hydrochloric acid, and perchloric acid is used to adjust the pH of the anolyte; the catholyte is one of potassium bicarbonate, sodium bicarbonate, and cesium bicarbonate.

[0035] Further, in the above technical solution, the proton exchange membrane includes one of Nafion 115, Nafion 117, Nafion 211, and Nafion 212.

[0036] Further, in the above technical solution, the concentration of the sulfite aqueous solution is 0.1 - 0.5 M; the concentration of the bicarbonate aqueous solution is 0.2 - 1.0 M.

[0037] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0038] (1) The transition metal nickel single-atom catalyst provided by the present invention has a three-dimensional rhombic dodecahedron morphology. Compared with two-dimensional flakes and one-dimensional nanowire structures, on the one hand, it can avoid the migration and aggregation of metal single atoms, which is conducive to the anchoring and uniform dispersion of single atoms; on the other hand, this three-dimensional structure can provide a larger specific surface area, which is conducive to the exposure of active sites and maximizes the activity expression of the catalyst. The transition metal nickel single atoms provided by the present invention are centered on transition metal nickel. Utilizing the characteristic that metal Ni has a similar outer electron structure to Pt and Pd with SO2OR activity, it is successfully applied to a mixed electrolysis system for carbon dioxide reduction and sulfur dioxide oxidation. Reducing the metal particle size to the atomic level can significantly improve the intrinsic activity of the metal. In addition, single-atom sites can maximize the atomic utilization rate. Therefore, the Ni single-atom catalyst has extremely high SO2OR activity.

[0039] (2) In the preparation method of the transition metal nickel single atoms provided by the present invention, zinc nitrate hexahydrate is used as the zinc salt. During the subsequent in-situ growth of ZIF8, the morphology formed by the coordination of zinc nitrate and dimethylimidazole is a regular rhombic dodecahedron. In addition, during the preparation of the Ni-ZIF8 precursor, by first separately preparing a metal salt methanol solution and a dimethylimidazole methanol solution and then mixing them, it is beneficial to the in-situ growth of Ni-ZIF8 and the formation of the rhombic dodecahedron morphology, and can effectively avoid the formation of nickel clusters and nanoparticles. There is no need for subsequent treatment to remove possible nickel clusters and nanoparticles during the preparation process, thus realizing the uniform loading of nickel single atoms. The present invention can also control the density of active component nickel single atoms by controlling the addition amount of nickel in the precursor, and has good application prospects.

[0040] (3) The transition metal nickel single-atom bifunctional electrocatalyst provided by the present invention not only has better electrocatalytic activity than most transition metal single-atom catalysts, but also has good stability. The present invention uses sulfur dioxide oxidation to replace the anodic oxygen evolution reaction, which can not only effectively remove sulfur dioxide pollutants, but also produce sulfuric acid, an industrial raw material, at the anode. Brief Description of the Drawings

[0041] Figure 1 It is a schematic diagram of the reaction process of the mixed electrolysis system for carbon dioxide reduction and sulfur dioxide oxidation of the present invention;

[0042] Figure 2XRD pattern of the catalyst obtained in Example 2 of the present invention;

[0043] Figure 3 HAADF-STEM image of the catalyst obtained in Example 2 of the present invention;

[0044] Figure 4 HR-TEM image of the catalyst obtained in Example 2 of the present invention;

[0045] Figure 5 N1s XPS spectra of the catalysts obtained in Example 1, Example 2 and Example 3 of the present invention;

[0046] Figure 6 SO2OR activity comparison diagrams of Application Example 1, Application Example 2 and Application Example 3 of the present invention;

[0047] Figure 7 SO2OR activity comparison diagrams of Application Example 2, Application Example 4 and commercial 20% Pt / C of the present invention;

[0048] Figure 8 CO Faraday efficiency comparison diagrams of Application Example 1, Application Example 2 and Application Example 3 of the present invention;

[0049] Figure 9 CO reduction current density comparison diagrams of Application Example 1, Application Example 2 and Application Example 3 of the present invention;

[0050] Figure 10 Electrochemical performance diagrams of Application Example 5 of the present invention tested in a mixed electrolysis system for carbon dioxide reduction and sulfur dioxide oxidation;

[0051] Figure 11 Long-term operation stability of Application Example 5 of the present invention in a mixed electrolysis system for carbon dioxide reduction and sulfur dioxide oxidation. Detailed implementation manners

[0052] The following non-limiting examples can enable those of ordinary skill in the art to more comprehensively understand the present invention, but do not limit the present invention in any way.

[0053] Unless otherwise specified, the materials used in the examples of the present invention can be obtained through commercial channels or prepared according to the conventional methods well-known to those skilled in the art.

[0054] Example 1

[0055] The preparation method of the transition metal nickel single-atom bifunctional electrocatalyst of Example 1 includes the following steps:

[0056] (1) 2.98 g of zinc nitrate hexahydrate and 11.632 g of nickel nitrate hexahydrate were successively added to 300 ml of methanol. After stirring for 5 min, it was ultrasonically dispersed for 10 min to obtain a green and clear solution A;

[0057] (2) 16.42 g of dimethylimidazole was dissolved in 100 ml of methanol. After stirring for 10 min, it was ultrasonically dispersed for 15 min to obtain a light yellow and clear solution B;

[0058] (3) Solution A and solution B were mixed and mechanically stirred for 20 min to obtain solution C;

[0059] (4) Solution C was placed in a forced air drying oven and left standing at a constant temperature of 60 °C for 24 h;

[0060] (5) After the reaction was completed, the precipitate was collected by centrifugation and washed with methanol at least 3 times. After the precipitate and the centrifuged supernatant showed no green color, the solid product was dried in a vacuum oven at 60 °C for 12 h to obtain a purple catalyst precursor Ni-ZIF8;

[0061] (6) 500 mg of Ni-ZIF8 was weighed and placed in a tubular furnace. Under an Ar atmosphere, it was heated to 900 °C at a heating rate of 5 °C / min and held for 120 min. After cooling to room temperature, a black solid was obtained, which was the transition metal nickel single-atom bifunctional electrocatalyst, named NiNC-900. The Ni loading was measured to be 3.1 wt.% by ICP-OES.

[0062] Example 2

[0063] The preparation method of the transition metal nickel single-atom bifunctional electrocatalyst of Example 2 includes the following steps:

[0064] (1) 2.98 g of zinc nitrate hexahydrate and 9.508 g of nickel chloride hexahydrate were successively added to 300 ml of methanol. After stirring for 10 min, it was ultrasonically dispersed for 15 min to obtain a green and clear solution A;

[0065] (2) 16.42 g of dimethylimidazole was dissolved in 100 ml of methanol. After stirring for 15 min, it was ultrasonically dispersed for 20 min to obtain a light yellow and clear solution B;

[0066] (3) Solution A and solution B were mixed and mechanically stirred for 30 min to obtain solution C;

[0067] (4) Solution C was placed in a forced air drying oven and left standing at a constant temperature of 40 °C for 48 h;

[0068] (5) After the reaction was completed, the precipitate was collected by centrifugation and washed with methanol at least 3 times. After no green color appeared in both the precipitate and the centrifuged supernatant, the solid product was dried in a vacuum oven at 60 °C for 12 h to obtain the purple catalyst precursor Ni-ZIF8;

[0069] (6) Weigh 500 mg of Ni-ZIF8 and place it in a tubular furnace. Under an Ar atmosphere, it was heated to 1000 °C at a heating rate of 5 °C / min and held for 90 min. After cooling to room temperature, a black solid was obtained, which was the transition metal nickel single-atom bifunctional electrocatalyst, named NiNC-1000. The Ni loading was measured to be 3.9 wt.% by ICP-OES.

[0070] Example 3

[0071] The preparation method of the transition metal nickel single-atom bifunctional electrocatalyst of Example 3 includes the following steps:

[0072] (1) Add 2.98 g of zinc nitrate hexahydrate and 9.954 g of nickel acetate tetrahydrate to 300 ml of methanol in sequence. After stirring for 8 min, ultrasonically disperse for 20 min to obtain a green and clear solution A;

[0073] (2) Dissolve 16.42 g of dimethylimidazole in 100 ml of methanol, stir for 8 min and then ultrasonically disperse for 15 min to obtain a light yellow and clear solution B;

[0074] (3) Mix solution A and solution B and mechanically stir for 25 min to obtain solution C;

[0075] (4) Place solution C in a forced-air drying oven and let it stand at 30 °C for 30 h;

[0076] (5) After the reaction was completed, the precipitate was collected by centrifugation and washed with methanol at least 3 times. After no green color appeared in both the precipitate and the centrifuged supernatant, the solid product was dried in a vacuum oven at 60 °C for 12 h to obtain the purple catalyst precursor Ni-ZIF8;

[0077] (6) Weigh 500 mg of Ni-ZIF8 and place it in a tubular furnace. Under an Ar atmosphere, it was heated to 1100 °C at a heating rate of 5 °C / min and held for 120 min. After cooling to room temperature, a black solid was obtained, which was the transition metal nickel single-atom bifunctional electrocatalyst, named NiNC-1100. The Ni loading was measured to be 4.0 wt.% by ICP-OES.

[0078] Comparative Example 1

[0079] Comparative Example 1 is a transition metal Fe single-atom catalyst, and its preparation method is as follows:

[0080] (1) Add 2.98 g of zinc nitrate hexahydrate and 0.404 g of iron(III) nitrate nonahydrate to 300 ml of methanol in sequence. After stirring for 5 min, ultrasonically disperse for 10 min to obtain a light yellow solution A;

[0081] (2) Dissolve 16.42 g of 2-methylimidazole in 100 ml of methanol. After stirring for 10 min, ultrasonically disperse for 15 min to obtain a light yellow clear solution B;

[0082] (3) Mix solution A and solution B and mechanically stir for 20 min to obtain solution C;

[0083] (4) Place solution C in a forced air drying oven and let it stand at a constant temperature of 60 °C for 24 h;

[0084] (5) After the reaction is completed, collect the precipitate by centrifugation and wash the precipitate with methanol at least 3 times. Dry the solid product in a vacuum oven at 60 °C for 12 h to obtain a nearly white catalyst precursor Fe-ZIF8;

[0085] (6) Weigh 500 mg of Fe-ZIF8 and place it in a tubular furnace. Under an Ar atmosphere, heat it to 1000 °C at a heating rate of 5 °C / min and hold for 120 min. After cooling to room temperature, a black solid is obtained, which is the transition metal Fe single-atom catalyst, named FeNC-1000.

[0086] Application Example 1

[0087] Add 10 mg of the NiNC-900 electrocatalyst prepared in Example 1 and 0.05 g of 5% Nafion to 3 ml of isopropanol. After ultrasonically dispersing for 60 min, a catalyst slurry is obtained; The catalyst slurry is deposited on the gas diffusion layer by the method of manual brushing, dried and the catalyst loading is determined by weighing to be 1.0 mg cm -2 .

[0088] Test the CO2RR and SO2OR activities of NiNC-900 in a traditional three-electrode system respectively. During the test of CO2RR activity, use NiNC-900-GDE as the working electrode, Ag / AgCl electrode as the reference electrode, and platinum sheet as the counter electrode. The electrolyte is 0.5 M aqueous potassium bicarbonate solution. Test the product selectivity and catalytic activity in the range from -0.4 V to -1.2 V. During the test of SO2OR activity, use NiNC-900-GDE as the working electrode, saturated calomel electrode as the reference electrode, and platinum sheet as the counter electrode. The electrolyte is 0.5 M aqueous potassium sulfite solution, adjusted to pH = 1 with sulfuric acid, and test the linear sweep curve from 0.4 V to 1.4 V.

[0089] Application Example 2

[0090] 10 mg of the NiNC-1000 electrocatalyst prepared in Example 2 and 0.05 g of 5% Nafion were added to 3 ml of isopropanol. After ultrasonic dispersion for 60 min, a catalyst slurry was obtained. The catalyst slurry was deposited on the gas diffusion layer by electrostatic spraying, dried, and the catalyst loading was determined to be 1.0 mg cm -2 。

[0091] The CO2RR and SO2OR activities of NiNC-1000 were respectively tested in a traditional three-electrode system. During the test of CO2RR activity, NiNC-1000-GDE was used as the working electrode, Ag / AgCl electrode as the reference electrode, and a platinum sheet as the counter electrode. The electrolyte was 0.5 M aqueous potassium bicarbonate solution. The product selectivity and catalytic activity in the range from -0.4 V to -1.2 V were tested. During the test of SO2OR activity, NiN C-1000-GDE was used as the working electrode, saturated calomel electrode as the reference electrode, and a platinum sheet as the counter electrode. The electrolyte was 0.5 M aqueous potassium sulfite solution, adjusted to pH = 1 with sulfuric acid, and the linear sweep curve from 0.4 V to 1.4 V was tested.

[0092] Application Example 3

[0093] 10 mg of the NiNC-1100 electrocatalyst prepared in Example 3 and 0.05 g of 5% Nafion were added to 3 ml of isopropanol. After ultrasonic dispersion for 60 min, a catalyst slurry was obtained. The catalyst slurry was deposited on the gas diffusion layer by electrostatic spraying, dried, and the catalyst loading was determined to be 1.0 mg cm -2 。

[0094] The CO2RR and SO2OR activities of NiNC-1100 were respectively tested in a traditional three-electrode system. During the test of CO2RR activity, NiNC-1100-GDE was used as the working electrode, Ag / AgCl electrode as the reference electrode, and a platinum sheet as the counter electrode. The electrolyte was 0.5 M aqueous potassium bicarbonate solution. The product selectivity and catalytic activity in the range from -0.4 V to -1.2 V were tested. During the test of SO2OR activity, Ni NC-1100-GDE was used as the working electrode, saturated calomel electrode as the reference electrode, and a platinum sheet as the counter electrode. The electrolyte was 0.5 M aqueous potassium sulfite solution, adjusted to pH 1 with sulfuric acid, and the linear sweep curve from 0.4 V to 1.4 V was tested.

[0095] Application Example 4

[0096] 10 mg of the FeNC-1000 catalyst prepared in Comparative Example 1 and 0.05 g of 5% Nafion were added to 3 ml of isopropanol, and after ultrasonic dispersion for 60 min, a catalyst slurry was obtained; the catalyst slurry was deposited on the gas diffusion layer by electrostatic spraying, dried, and the catalyst loading was determined to be 1.0 mg cm -2 .

[0097] The SO2OR activity of FeNC-1000 was tested in a traditional three-electrode system, with FeNC-1000 as the working electrode, a saturated calomel electrode as the reference electrode, a platinum sheet as the counter electrode, and 0.5 M aqueous potassium sulfite solution as the electrolyte, adjusted to pH = 1 with sulfuric acid, and a linear sweep curve from 0.4 V to 1.4 V was tested.

[0098] Application Example 5

[0099] 10 mg of the NiNC-1000 electrocatalyst prepared in Example 2 and 0.05 g of 5% Nafion were added to 3 ml of isopropanol, and after ultrasonic dispersion for 60 min, a catalyst slurry was obtained; the catalyst slurry was deposited on the gas diffusion layer by electrostatic spraying, dried, and the catalyst loading was determined to be 1.0 mg cm -2 .

[0100] In Figure 1 the electrolytic cell shown, carbon dioxide electrolysis tests were carried out, where both the cathode and anode used Ni NC-1000-GDE as the electrodes, the middle diaphragm was Nafion211, the electrolyte of the cathode was 0.25 M aqueous sodium bicarbonate solution, the electrolyte of the anode was 0.25 M aqueous sodium sulfite solution, adjusted to pH 0.5 with perchloric acid, and carbon dioxide electrolysis tests were carried out by energization, and the gas products at the cathode were detected online by gas chromatography.

[0101] Conclusion:

[0102] Figure 2 It can be seen that no diffraction peaks of Ni NPs appeared in the NiNC-1000 electrocatalyst obtained in Example 2, proving the existence of Ni single atoms.

[0103] Figure 3 It can be seen that many independently dispersed bright spots appeared in the NiNC-1000 electrocatalyst obtained in Example 2 in HAADF-STEM, indicating that Ni is anchored on the nitrogen-doped carbon support in the form of single atoms.

[0104] Figure 4 It can be seen that the microscopic morphology of the NiNC-1000 electrocatalyst obtained in Example 2 is a rhombic dodecahedron, with a size between 100-200 nm.

[0105] Figure 5 It can be seen that the nitrogen in the catalysts obtained from Example 1, Example 2 and Example 3 can be deconvoluted into five forms: pyridine nitrogen, metal nitrogen, pyrrole nitrogen, graphitic nitrogen and nitrogen oxide. The presence of metal nitrogen also indicates that there are Ni single-atom sites in the three catalysts and the single-atom Ni binds to N to form Ni-N sites.

[0106] Figure 6 It can be seen that the SO2OR performance of the Ni-N-C electrocatalysts in Application Example 1, Application Example 2 and Application Example 3 is significantly better than that of the commercial 20% Pt / C catalyst. Taking NiNC-1000 as an example, at 100 mA cm -2 it only requires 0.8 V, while the commercial 20% Pt / C requires 1.05 V. This indicates that the Ni single-atom electrocatalyst has excellent SO2 electro-oxidation activity.

[0107] Figure 7 It can be seen that the FeNC-1000 catalyst in Application Example 4 hardly has SO2OR activity, while the NiNC-1000 and commercial 20% Pt / C in Application Example 2 have obvious SO2OR activity, especially the NiNC-1000 catalyst. For example, at 1.0 V (vs. RHE), the current density of NiNC-1000 is as high as 182 mA cm -2 , that of 20% Pt / C is 88 mA cm -2 , and that of FeNC-1000 is only 6 mA cm -2 , proving that only the transition metal single-atom catalyst with Ni as the central metal has excellent SO2OR activity.

[0108] Figure 8 and Figure 9 It can be seen that the NiNC-1000 electrocatalyst in Application Example 2 has the best CO2RR activity and product selectivity. In the potential window range from -0.4 V to -1.2 V, NiNC-1000 has the highest CO Faraday efficiency and CO partial current density. At -1.2 V, the partial current density of CO is as high as 62 mA cm -2 , far exceeding most of the transition metal single-atom catalysts, proving that the Ni single-atom electrocatalyst has excellent CO2 electro-reduction activity.

[0109] Figure 10It can be seen that when the NiNC-1000 electrocatalyst of Application Example 5 is used as a bifunctional electrocatalyst, it can simultaneously catalyze the electrooxidation of SO2 and the electroreduction of CO2. The voltage at the same current in this new CO2 electrolysis system (CO2RR / / SO2OR) is significantly lower than that in the traditional CO2 electrolysis system (CO2RR / / OER), and the power consumption is reduced by about 50%. This proves that the Ni single-atom electrocatalyst can be used as a bifunctional electrocatalyst.

[0110] Figure 11 It can be seen that the NiNC-1000 electrocatalyst of Application Example 5 can stably operate for nearly 200 h in the new CO2 electrolysis system. The Faraday efficiency of CO remains above 90% and the current density hardly decays, proving that the bifunctional electrocatalyst has good long-term stability.

[0111] The above embodiments are only preferred embodiments of the present invention and do not limit the implementation manners. The protection scope of the present invention should be subject to the scope defined by the claims. Based on the above description, other different forms of changes or modifications can be made. The obvious changes or modifications derived therefrom are still within the protection scope of the present invention.

Claims

1. A transition metal nickel single-atom bifunctional electrocatalyst, characterized in that, The catalyst uses single-atom transition metal nickel as the active component and nitrogen-doped carbon material as the carrier. The loading of the active component is 2-5 wt.%, the microscopic morphology of the carrier is a rhombic dodecahedron, and the particle size of the rhombic dodecahedron is 100-200 nm.

2. The preparation method of the transition metal nickel single-atom bifunctional electrocatalyst according to claim 1, characterized in that It includes the following steps: (1) Prepare a methanol solution containing zinc nitrate hexahydrate and nickel salt, stir and sonicate to obtain solution A; (2) Prepare a methanol solution containing dimethylimidazole, stir and sonicate to obtain solution B; (3) Mix solution B obtained in step (2) and solution A obtained in step (1) and mechanically stir at room temperature to obtain solution C; (4) Let solution C obtained in step (3) stand under constant temperature conditions; (4) Centrifuge, wash, and then dry to obtain a catalyst precursor; (5) Under an argon atmosphere, pyrolyze the catalyst precursor obtained in step (4), and the transition metal nickel single-atom bifunctional electrocatalyst is obtained after cooling to room temperature.

3. The preparation method according to claim 2, characterized in that, In step (1), the nickel salt is one of nickel nitrate hexahydrate, nickel acetate tetrahydrate, and nickel chloride hexahydrate; The molar ratio of zinc nitrate hexahydrate to nickel salt is 1:1 - 1:4; The ratio of the volume of methanol to the amount of substance of zinc nitrate hexahydrate is 300 ml:0.01 mol - 300 ml:0.03 mol; The stirring time is 5 - 10 min; The sonication time is 10 - 20 min.

4. The preparation method according to claim 2, characterized in that, In step (2), the molar ratio of dimethylimidazole to zinc nitrate hexahydrate is 8:1 - 20:1; The ratio of the volume of methanol to the amount of substance of dimethylimidazole is 100 ml:0.2 mol - 100 ml:0.08 mol; The stirring time is 5 - 10 min; The sonication time is 10 - 20 min.

5. The preparation method according to claim 2, wherein In step (3), the stirring time is 20 - 30 min.

6. The preparation method according to claim 2, wherein In step (4), the constant temperature is 30 - 60 °C; The standing time is 12 - 48 h.

7. The preparation method according to claim 2, characterized in that In step (5), the pyrolysis temperature is 900 - 1100 °C, and the pyrolysis time is 60 - 120 min.

8. Use of the transition metal nickel single-atom bifunctional electrocatalyst described in claim 1 or the transition metal nickel single-atom bifunctional electrocatalyst prepared by the preparation method described in any one of claims 1-7 in a mixed electrolysis system for carbon dioxide reduction and sulfur dioxide oxidation, characterized in that, In the mixed electrolysis system, both the cathode and the anode use gas diffusion electrodes supporting the bifunctional electrocatalyst.

9. The application according to claim 8, characterized in that The preparation method of the gas diffusion electrode is: disperse the bifunctional electrocatalyst in an isopropanol solution containing Nafion to obtain a catalyst slurry, deposit the catalyst slurry on the gas diffusion layer, and dry to obtain a gas diffusion electrode supporting the bifunctional electrocatalyst; The mass ratio of the bifunctional electrocatalyst to Nafion is 4:

1.

10. The application according to claim 8, wherein In the mixed electrolysis system, the anolyte is an acidic sulfite aqueous solution with a pH of 0.5 - 2, the catholyte is a bicarbonate aqueous solution, and the diaphragm is a proton exchange membrane.

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