Carbon quantum dot loaded diatomic electrocatalyst and preparation method and application thereof

Abstract

The invention discloses a carbon quantum dot loaded diatom electrocatalyst and a preparation method and application thereof. The preparation method comprises the following steps: dissolving and mixing diethylene triamine pentaacetic acid and salt of metal M1 in water, and performing reflux reaction to obtain a complex solution of the metal M1; adding salt of metal M2 for reflux reaction, filtering after the reaction is finished, and removing a solvent from filtrate to obtain a solid complex of bimetals M1 and M2; drying and calcining to obtain a diatomic electrocatalyst precursor; and carrying out post-treatment and freeze-drying to obtain the diatomic electrocatalyst. The carbon quantum dot loaded bimetallic atom site catalyst is obtained by a preparation strategy of coupling molecular design and quantum dot confinement, and is used for research on deep reduction of carbon dioxide into methane through electro-catalysis. The obtained catalyst has excellent methane production activity on an electro-catalysis carbon dioxide reduction reaction under an alkaline condition and a flow cell configuration, and still has relatively good stability under long-term work.

Description

Technical Field

[0001] The present invention relates to the technical field of carbon dioxide reuse, and particularly relates to a carbon quantum dot-loaded dual-atom electrocatalyst, a preparation method thereof, and an application thereof. Background Art

[0002] Single-metal atom catalysts show great application prospects in green energy devices, small molecule conversion, environmental remediation, etc. However, to meet the application requirements, the overall catalytic performance of single-atom catalysts should be improved by increasing the intrinsic properties and the density of catalytic active sites. To ensure the atomic distribution of metal atoms, the metal loading of traditional single-atom catalysts is usually kept below 5 wt%, which greatly limits the improvement of their catalytic performance.

[0003] Recently, dual-metal atom catalysts with various combinations have been developed to further enhance the catalytic activity of single-atom catalysts through synergistic effects, especially for multi-step catalytic reactions. The close proximity of two adjacent metal atoms to each other can induce strong electronic interactions and regulate the spin state and / or d-band center of the metal atoms, providing the possibility of optimizing the adsorption and dissociation of reactant molecules or intermediates to promote catalytic activity.

[0004] Compared with traditional single-atom catalysts, dual-atom catalysts have higher catalytic activity, stability, and versatility, and can achieve structural controllability by adjusting the interaction between atoms. Dual-atom catalysts with various combinations can further enhance the catalytic activity compared to single-atom catalysts through synergistic effects. Two bonded or adjacent metal atoms can cause strong electronic interactions and regulate the spin state of the metal atoms and / or the d-band center, providing the possibility of optimizing the adsorption and dissociation energy of reactant molecules or intermediates to promote catalytic activity. Through reasonable design and regulation, the ratio, structure, and distribution mode of dual-atom catalysts can be adjusted to the optimal state to achieve better catalytic effects. Therefore, dual-atom catalysts are considered to be the next generation of high-efficiency catalytic materials and have great application potential in future catalytic research. However, at the same time, further in-depth research is also needed to fully utilize their advantages and solve the challenges they face.

[0005] Diatomic catalysts are widely used in fields such as oxygen reduction reaction, hydrogen production by electrolyzing water, carbon dioxide reduction, etc. These reactions are of great significance in energy conversion and environmental protection. For example, CN 103848982 A discloses a liquid bimetallic catalyst, its preparation method and uses. The preparation method is to dissolve metal halides in deionized water, add a certain amount of tert-butanol and chelating agent P, and then stir at a temperature of -10°C - 50°C for 0.1 - 48 h. After the chelating agent is fully chelated, a cobalt cyanate solution of one or several metals M2 is gradually added dropwise; then the precipitate formed by the reaction is separated and washed; then small molecules or monomolecular polyols are added; and then under stirring conditions at 30 - 80°C, vacuum drying is carried out for 0.5 - 100 h, and the water content in the product is measured to be between 0.01% and 1%; finally, under the condition of 30 - 120°C, ultrasonic activation reaction is carried out for 0.5 - 20 h to obtain a uniform liquid bimetallic cyanide catalyst. This catalyst is used for copolymerization of carbon dioxide and propylene oxide to prepare polycarbonate polyol.

[0006] Some studies have found that some diatomic catalysts such as Fe-Ni, Co-Ni, etc. have shown excellent catalytic performance in the field of hydrogen production by electrolyzing water. At the same time, diatomic catalysts such as Cu-Pd, Ag-Pd, etc. have also made remarkable progress in the research of electrocatalytic reduction of carbon dioxide to prepare chemicals. The electrochemical carbon dioxide reduction reaction driven by renewable energy provides a promising way to produce valuable chemical raw materials. Among the products of the electrocatalytic carbon dioxide reduction reaction, methane is a good energy carrier with a maximum combustion heat of 56 kJ·g -1 . In order to achieve high selectivity for methane, *CO-CO coupling at multiple sites should be avoided. Single-site catalysts are ideal candidates for carbon dioxide methanation due to their site isolation characteristics. An effective strategy for synthesizing diatomic catalysts is not only to avoid the aggregation of metal atoms, but also to precisely control the formation of diatomic sites.

[0007] Diatomic catalysts formed in a graphite carbon framework are usually prepared by pyrolyzing metal-organic frameworks with two metal ions at a high temperature above 800°C, as demonstrated by the reported Fe-Co, Fe-Ni, and Cu-Zn diatomic catalysts. Another commonly used process is the heat treatment of two small-molecule metal ion precursors in an inert atmosphere. During this period, the precursors are covalently converted into a carbon substrate implanted with metal ions. However, due to the lack of molecular design level, the two metal atoms usually tend to be randomly distributed in the resulting carbon framework. On the other hand, high-temperature pyrolysis also leads to thermal migration, inducing random distribution and aggregation of metal atoms, resulting in relatively poor diatomic catalyst configurations and low metal loadings. However, the diatomic catalysts reported in the existing literature are usually used for electrocatalytic reduction of carbon dioxide to carbon monoxide, and the deep reduction of carbon dioxide at a single site is difficult, and the reaction mechanism is complex.

[0008] Therefore, there is an urgent need to develop a general and simple method to synthesize catalysts with dense and precise dual-atom configurations and apply them to the study of electrocatalytic deep reduction of carbon dioxide to methane to reveal the reaction mechanism of carbon dioxide methanation and propose appropriate design strategies for single-site catalysts. Summary of the Invention

[0009] Aiming at the problems of great difficulty in the deep reduction of electrocatalytic carbon dioxide at a single site and a complex reaction mechanism, the present invention provides a preparation method of a dual-atom electrocatalyst supported by carbon quantum dots. A dual-metal atom site catalyst supported by carbon quantum dots is obtained by a preparation strategy coupling molecular design and quantum dot confinement and is used in the study of electrocatalytic deep reduction of carbon dioxide to methane. The obtained catalyst has excellent methane production activity for the electrocatalytic carbon dioxide reduction reaction under alkaline conditions and in a flow cell configuration, and still has good stability under long-term operation.

[0010] To achieve the above object, the technical solution adopted by the present invention is:

[0011] A preparation method of a dual-atom electrocatalyst supported by carbon quantum dots, comprising the steps of:

[0012] Step 1, dissolve and mix diethylenetriaminepentaacetic acid and a salt of metal M1 in water, and reflux to obtain a complex solution of metal M1;

[0013] Step 2, add a salt of metal M2 to the solution in Step 1 and reflux. After the reaction is completed, filter, and remove the solvent from the filtrate to obtain a solid complex of dual metals M1 and M2;

[0014] Step 3, dry the solid complex in Step 2 and then calcine to obtain a dual-atom electrocatalyst precursor;

[0015] Step 4, dissolve the dual-atom electrocatalyst precursor in Step 3 in water, centrifuge, filter, dialyze, wash after freeze-drying the supernatant, then dry, dissolve in water and then freeze-dry to obtain the dual-atom electrocatalyst.

[0016] To control the distance between the two metal atoms and avoid agglomeration, in the present invention, diethylenetriaminepentaacetic acid is used as a metal chelating agent. This chelating agent can coordinate with two metal atoms on a dimer to obtain a dimer complex containing dual metals. This is due to its longer chain and more carboxyl groups and N atoms in diethylenetriaminepentaacetic acid, and this structure can ensure that the two metal centers in the precursor are at a fixed distance. Subsequently, low-temperature carbonization converts the organic precursor into carbon quantum dots, in which carbon dot confinement is coupled with rich dopants / functional groups, excluding the agglomeration of dual-metal atom sites. In this case, it is easy to obtain highly metal-loaded carbon quantum dots with uniform and dense dual-metal atom sites.

[0017] Compared with other bimetallic atom electrocatalysts, the catalyst in the present invention adopts a molecular design and a carbon dot confinement strategy, and can precisely construct a high density of dual atomic sites in carbon quantum dots. In this method, the precursor metal is pre-coordinated, which can reduce the aggregation of metal sites. In addition, the carbon quantum dots act as "carbon islands" to prevent the migration of bimetallic sites across the "islands" to achieve dynamic stability.

[0018] The metal M1 includes any one of Cu, Fe, Co, Ni, Mn, Zn, and Mo;

[0019] The metal M2 includes any one of Cu, Fe, Co, Ni, Mn, Zn, and Mo;

[0020] The M1 and M2 are the same or different.

[0021] Preferably, at least one of the metal M1 or M2 is Cu. In the electrocatalytic reduction of carbon dioxide, most electrocatalysts lack the ability to stabilize important intermediates (such as *CHO and *COOH), which makes copper (Cu)-based electrocatalysts more active. It has been found that higher selectivity for carbon dioxide methanation can be achieved on single copper sites.

[0022] The molar ratio of the diethylenetriaminepentaacetic acid, the salt of the metal M1, and the salt of the metal M2 is 10:1 to 5:1 to 5. When the metal content is too low, due to the too small number of active sites, the competitive hydrogen evolution reaction is likely to be aggravated, which is not conducive to the progress of the carbon dioxide reduction reaction. Therefore, the metal content should be increased as much as possible, but it should not exceed the limit complexed by the diethylenetriaminepentaacetic acid, because when the content is too high, metal clusters or particles are likely to be formed, which is not conducive to obtaining single atomic sites. The preferred molar ratio is 10:5:5.

[0023] The molar ratio of the salt of the metal M1 and the salt of the metal M2 is 1:0.5 - 2. Preferably, the molar ratio of the salt of the metal M1 and the salt of the metal M2 is 1:1, and the catalyst with the two metal atomic sites coordinated and complexed in equal proportion has a more excellent catalytic effect.

[0024] In step 1, the reaction temperature is 80 - 100 °C, and the reaction time is 2 - 6 h;

[0025] In step 2, the reaction temperature is 80 - 100 °C, and the reaction time is 2 - 6 h.

[0026] Appropriately increasing the temperature can accelerate the chelation of the metal precursor and the diethylenetriaminepentaacetic acid. The solvent used is deionized water. If the temperature is too high, the water evaporates too fast, which is not conducive to the chelation process. Preferably, the reflux time is 4 h, because an appropriate reflux time can ensure that the added metal salt is fully chelated.

[0027] In step 4, the calcination atmosphere is an inert gas, and the heating rate is 1-8 °C / min -1 , the calcination temperature is 200-300 °C, and the calcination time is 1-5 h. Preferably, the heating rate is 5 °C, the calcination temperature is 250 °C, and the calcination time is 2 h. If the calcination temperature is too low, the pyrolysis will be insufficient, while if the temperature is too high, it may lead to the aggregation of metal sites and the loss of single sites; maintaining a sufficient calcination time ensures the full pyrolysis of the precursor.

[0028] The salts of metal M1 and metal M2 are both soluble salts, including one or more of metal nitrates, chlorides, sulfates, and their hydrates.

[0029] In step 4, the centrifugation speed is 1000-12000 rpm, and the centrifugation time is 10-30 min; in order to fully remove the particles in the carbon quantum dots, the centrifugation speed and time should be extended as much as possible.

[0030] The pore size of the filter membrane used for filtration is 0.01-0.02 mm;

[0031] The dialysis bag used for dialysis is 500-2000 Da, and the dialysis time is 24-72 h. Preferably, it is 600 Da and the dialysis time is 48 h. The metal salt particles have an appropriate size, and the preferred conditions are to remove the undissolved metal salts and uncomplexed metal chelating agents.

[0032] The present invention also provides a carbon quantum dot-supported dual-atom electrocatalyst prepared by the described preparation method.

[0033] The present invention also provides the application of the carbon quantum dot-supported dual-atom electrocatalyst as a working electrode in the electrocatalytic carbon dioxide reaction.

[0034] Preferably, in the electrocatalytic carbon dioxide reaction, a three-electrode system is adopted. Specifically, an Ag / AgCl electrode is used as the reference electrode, a nickel foam is used as the counter electrode, a carbon paper electrode covered with the carbon quantum dot-supported dual-atom electrocatalyst provided by the present invention is used as the working electrode, and a potassium hydroxide solution is used as the electrolyte.

[0035] The metal coordination structure of the carbon quantum dot-supported dual-atom electrocatalyst in the present invention can be represented as MN 2 O 2 , compared with the traditional CuN 4 configuration, the CuN 2 O 2 configuration can stabilize the intermediate and promote the further hydrogenation of *CO to *CHO, thus realizing the electrocatalytic reduction of carbon dioxide to methane. By switching the adjacent metal single-atom sites, the electronic structure of the CuN 2 O 2 configuration can be effectively improved, effectively inhibiting hydrogen evolution and regulating the selectivity and current density of methane.

[0036] Compared with the prior art, the present invention has the following beneficial effects:

[0037] In the present invention, diethylenetriaminepentaacetic acid is used as a metal chelating agent to construct a bimetallic atom electrocatalyst, realizing the regulation of the electronic structure of metal sites on carbon quantum dots. The carbon quantum dots, as "carbon islands", can prevent the migration of bimetallic sites across the "islands" to achieve dynamic stability. The catalyst has both high electrocatalytic activity and good stability in the electrocatalytic reduction of carbon dioxide to methane in an alkaline electrolyte, providing the possibility for the further development and utilization of industrial electrochemical methane production from carbon dioxide. Description of the Drawings

[0038] Figure 1 Transmission electron microscopy (TEM) image of the catalyst DTPA-CuCu-CDs prepared in Example 1.

[0039] Figure 2 High-magnification transmission electron microscopy (TEM) image of the catalyst DTPA-CuCu-CDs prepared in Example 1.

[0040] Figure 3 FT-EXAFS diagram of the catalyst DTPA-CuCu-CDs prepared in Example 1.

[0041] Figure 4 Performance diagram of the catalysts prepared in the examples and comparative examples for the electrocatalytic reduction of carbon dioxide to methane in the application example.

[0042] Figure 5 For the catalyst DTPA-CuCu-CDs prepared in Example 1 at 150 mA cm -2 Stability test diagram for the electrocatalytic reduction of carbon dioxide to methane. Detailed Description of the Invention

[0043] In order to make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention. Those skilled in the art, on the basis of understanding the technical solutions of the present invention, make modifications or equivalent replacements without departing from the spirit and scope of the technical solutions of the present invention, which should all be covered within the protection scope of the present invention.

[0044] The raw materials used in the following detailed description are all purchased from the market.

[0045] Example 1

[0046] (1) Add 10 mmol of diethylenetriaminepentaacetic acid (DTPA) metal chelating agent and 5 mmol of CuCl2 2H 2 After 2H 2 O is dissolved in ultrapure water, it is then refluxed at 90 °C for 4 hours to obtain a single-metal Cu complex, denoted as CuM-DTPA;

[0047] (2) Add 5 mmol of CuCl 2 2H 2 O to the above solution and reflux for another 4 h at the same temperature, cool to room temperature, filter, and then remove the solvent by rotary evaporation to obtain a solid complex of bimetal, denoted as CuCu-DTPA;

[0048] (3) After CuCu-DTPA is dried under vacuum at 60 °C for 5 h, it is heat-treated at 250 °C for 2 h under an argon atmosphere at a heating rate of 5 °C / min to obtain the precursor of the carbon quantum dot-supported dual Cu atom electrocatalyst. -1

[0049] (4) Subsequently, the obtained precursor is dissolved in 100 mL of ultrapure water to form a suspension, ultrasonically treated at room temperature for 30 min, and then the suspension is centrifuged at 12000 rpm for 15 min to collect the brown supernatant.

[0050] (5) The brown supernatant is filtered through a filter (0.22 mm), and then filtered again using a microporous membrane with a pore size of 0.015 mm to obtain a transparent liquid. The obtained transparent liquid is dialyzed using an MD34 (600 Da) dialysis bag for 48 h. The dialyzed solution is freeze-dried, and the obtained powder is washed three times with ethanol. Subsequently, after drying under vacuum at 60 °C for 2 h, the obtained solid is dissolved in a certain amount of water again and subjected to another freeze-drying to finally obtain a carbon quantum dot-supported dual Cu atom electrocatalyst, denoted as DTPA-CuCu nanoparticles.

[0051] The size distribution of the prepared catalyst was observed by transmission electron microscopy (TEM), and the TEM results are as Figure 1 shown, and the HRTEM images are as Figure 2 shown. As can be seen from Figure 1-2 , well-dispersed dots with an average size of about 3 - 5 nm are shown, separated from each other and without lattice fringes, indicating the successful synthesis of amorphous carbon quantum dots by pyrolysis. This isolated single carbon quantum dot structure may help prevent the migration of individual metal atoms from their severe agglomeration. In addition, no obvious metal nanoparticles were observed, indicating the atomic dispersion of metal atoms.

[0052] The FT-EXAFS spectra of the carbon quantum dot-supported dual-atom electrocatalyst prepared in this example are as Figure 3 shown. As can be seen from the extended X-ray absorption fine structure spectra of the Cu K-edge in Figure 3 , only single Cu atoms attributable to Cu-N / O coordination appear, approximately​ The peak at showed no obvious metal-metal peak, indicating the absence of crystalline Cu-based nanoparticles in the sample and further suggesting the atomic dispersion of metal atoms. The above results indicate the synthesis of an atomically dispersed electrocatalyst loaded with carbon quantum dots.

[0053] From Figure 4 The electrocatalytic carbon dioxide reduction performance showed that DTPA-CuCu had the highest methane selectivity at 250 mA cm -2 . From Figure 5 The stability test of electrocatalytic carbon dioxide reduction showed that at 150 mA cm -2 , there was no obvious potential change and decrease in methane selectivity of DTPA-CuCu within 8 h, indicating the excellent stability of the atomically dispersed electrocatalyst loaded with carbon quantum dots for carbon dioxide reduction.

[0054] Example 2

[0055] According to the process of Example 1, the copper salt in step (2) was replaced with a zinc salt to obtain a dual-atom electrocatalyst loaded with carbon quantum dots and Cu and Zn, denoted as DTPA-CuZn.

[0056] Example 3

[0057] According to the process of Example 1, the copper salt in step (2) was replaced with a cobalt salt to obtain a dual-atom electrocatalyst loaded with carbon quantum dots and Cu and Co, denoted as DTPA-CuCo.

[0058] Example 4

[0059] According to the process of Example 1, the copper salt in step (2) was replaced with a nickel salt to obtain a dual-atom electrocatalyst loaded with carbon quantum dots and Cu and Ni, denoted as DTPA-CuNi.

[0060] Example 5

[0061] According to the process of Example 1, the amount of copper salt in step (2) was changed from 5 mmol to 2.5 mmol of copper salt to obtain an electrocatalyst with the coexistence of Cu and Cu atomic pairs and Cu single atoms loaded on carbon quantum dots, denoted as DTPA-CuCu 0.5 .

[0062] Example 6

[0063] According to the process of Example 1, the amount of copper salt in step (2) was changed from 5 mmol to 2.5 mmol of zinc salt to obtain an electrocatalyst with Cu single atoms and Cu and Zn atomic pairs loaded on carbon quantum dots, denoted as DTPA-CuZn 0.5 .

[0064] Example 7

[0065] According to the process of Example 1, the copper salt in step (1) was replaced with a zinc salt to obtain a dual-atom electrocatalyst with carbon quantum dots loaded with Zn and Cu, denoted as DTPA-ZnCu.

[0066] Comparative Example 1

[0067] According to the process of Example 1, the metal chelating agent in step (1) was replaced with ethylenediaminetetraacetic acid (EDTA), and step (2) was not applied, to obtain a single-atom electrocatalyst with carbon quantum dots loaded with single metal Cu, denoted as EDTA-Cu-CDs.

[0068] Comparative Example 2

[0069] According to the process of Example 1, the amount of copper salt in step (2) was changed from 5 mmol to 0 mmol of copper salt, to obtain an electrocatalyst with carbon quantum dots loaded with single Cu atoms, denoted as DTPA-Cu.

[0070] Application Example

[0071] (1) Using a three-electrode system, the carbon paper electrodes covered with the catalysts prepared in the examples and comparative examples were used as the working electrode, the counter electrode was nickel foam, the reference electrode was a saturated Ag / AgCl electrode, and the electrolyte was 1.0 M KOH;

[0072] (2) Carbon dioxide reduction performance test: Using a Shanghai Chenhua CHI 760E electrochemical workstation, nitrogen was introduced into the electrolyte for 30 min before the test. The constant current program was adopted, and the test range was 50 mA cm -2 ~300 mA, and a gas chromatograph was used to record the products and calculate the Faraday efficiency of the products.

[0073] Table 1 Electrocatalytic carbon dioxide reduction performance of quantum dot-loaded dual-atom electrocatalysts at a current density of 250 mA

[0074]

[0075]

[0076] Table 2 Electrocatalytic carbon dioxide reduction performance of the dual-atom electrocatalyst DTPA-CuCu-CDs prepared in Example 1 at different current densities

[0077]

[0078] The DTPA-CuCu catalyst provided in this application example and DTPA-CuNi, DTPA-CuZn, DTPA-CuCo, DTPA-Cu, DTPA-CuCu in the comparative examples 0.5 , DTPA-CuZn0.5 , the results of the electrocatalytic carbon dioxide reduction performance of DTPA-ZnCu and EDTA-Cu in 1.0 M KOH solution are as Figure 4 shown in Table 1.

[0079] For comparison, in Comparative Example 1, ethylenediaminetetraacetic acid with only unit-site chelating ability was used as a ligand to synthesize a single-atom electrocatalyst EDTA-Cu with carbon quantum dots loaded with single-metal Cu. From Figure 4 it can be seen that in the alkaline electrolyte, the DTPA-CuCu catalyst has the highest methane Faradaic efficiency of 73.7%. Among them, the effect of DTPA-CuCu is significantly better than that of DTPA-CuZn-CDs, DTPA-CuCo, DTPA-CuNi, and EDTA-Cu catalysts.

[0080] The results show that the EDTA-Cu-CDs catalyst with a single copper site has the worst electrocatalytic carbon dioxide reduction performance, and the methane Faradaic efficiency is only 22.5%. When another adjacent metal site Co, Ni, Zn, and Cu is applied to change the electronic structure of Cu, the performance is significantly improved, and the methane Faradaic efficiency exceeds 50%.

[0081] The influence of the proportion of metal M2 on the electrocatalytic carbon dioxide reduction performance was studied. When the content of Cu in metal M2 is 0, since the DTPA-Cu and the EDTA-Cu electrocatalyst in Comparative Example 1 have the same loading of Cu single atoms, they have similar methane activities. When increasing the proportion of Cu in metal M2, there are partial Cu-Cu atom pairs in DTPA-CuCu 0.5 , so the methane selectivity is significantly improved to 57.4%. The influence of the addition order of metal M1 and metal M2 on the electrocatalytic carbon dioxide reduction performance was studied. When metal M1 is replaced with zinc salt, the methane selectivity of DTPA-ZnCu is 64.7%, which is comparable to that of DTPA-CuZn (63.1%), indicating that the addition order of metal salts does not affect the final electrocatalytic carbon dioxide reduction performance.

[0082] Table 2 shows the electrocatalytic carbon dioxide reduction performance of the dual-atom electrocatalyst DTPA-CuCu prepared in Example 1 at different current densities. It can be seen that at a larger current density, the methane selectivity of the catalyst is higher and the yield is also higher.

Claims

1. A method for preparing a carbon quantum dot-supported diatomic electrocatalyst, characterized in that: Includes steps: Step 1, dissolving and mixing diethylenetriaminepentaacetic acid and a salt of metal M1 in water, and subjecting the mixture to a reflux reaction to obtain a complex solution of metal M1; Step 2, adding a salt of metal M2 to the solution of step 1 for reflux reaction, filtering after the reaction is completed, and removing the solvent from the filtrate to obtain a solid complex of bimetallic M1 and M2; Step 3, drying the solid complex of step 2 and then calcining it to obtain a diatomic electrocatalyst precursor; Step 4, dissolving the diatomic electrocatalyst precursor of step 3 in water, filtering, dialyzing, freeze-drying and washing the centrifuged supernatant, and then drying, dissolving in water and freeze-drying to obtain the diatomic electrocatalyst.

2. The method for preparing a carbon quantum dot-supported diatomic electrocatalyst according to claim 1, characterized in that: The metal M1 includes any one of Cu, Fe, Co, Ni, Mn, Zn and Mo; The metal M2 includes any one of Cu, Fe, Co, Ni, Mn, Zn and Mo; The M1 and M2 are the same or different.

3. The method for preparing a carbon quantum dot-supported diatomic electrocatalyst according to claim 1, characterized in that: The molar ratio of the diethylenetriaminepentaacetic acid, the salt of the metal M1 and the salt of the metal M2 is 10:1-5:1-5.

4. The method for preparing a carbon quantum dot-supported diatomic electrocatalyst according to claim 1, characterized in that: The molar ratio of the salt of the metal M1 to the salt of the metal M2 is 1:0.5-2.

5. The method for preparing the carbon quantum dot-supported diatomic electrocatalyst according to claim 1, characterized in that: In step 1, the reaction temperature is 80-100°C and the reaction time is 2-6h; In step 2, the reaction temperature is 80-100° C. and the reaction time is 2-6 h.

6. The method for preparing a carbon quantum dot-supported diatomic electrocatalyst according to claim 1, characterized in that: In step 4, the calcination atmosphere is an inert gas, and the heating rate is 1-8°C min -1 The calcination temperature is 200-300°C, and the calcination time is 1-5h.

7. The method for preparing a carbon quantum dot-supported diatomic electrocatalyst according to claim 1, characterized in that: The salt of the metal M1 and the salt of the metal M2 are both soluble salts, including one or more of metal nitrates, chlorides, sulfates, and hydrates thereof.

8. The method for preparing a carbon quantum dot-supported diatomic electrocatalyst according to claim 1, characterized in that: In step 4, the centrifugal speed is 1000-12000 rpm, and the centrifugal time is 10-30 min; The pore size of the filter membrane used for filtration is 0.01-0.02 mm; The dialysis bags used for dialysis are 500-2000Da, and the dialysis time is 24-72h.

9. A carbon quantum dot-supported diatomic electrocatalyst prepared according to the preparation method according to any one of claims 1 to 8.

10. Use of the carbon quantum dot-supported diatomic electrocatalyst according to claim 9 as a working electrode in an electrocatalytic carbon dioxide reaction.

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