CN114855210B - Molten salt method in-situ synthesis carbon-based single-atom nanosheet and preparation method and application thereof - Google Patents

Abstract

The invention discloses a preparation method for in-situ synthesis of carbon-based single-atom nanosheets by a molten salt method, comprising: mixing ferrocene and 2-methylimidazole to obtain a first mixture, and mixing zinc oxide, sodium chloride and chloride Calcium is mixed and ground to obtain the second mixture, and the first mixture and the second mixture are placed in a container; the first mixture is blown into the second mixture by argon, and at the same time, the first mixture and the second mixture in the container are gradiently calcined , after cooling, carbon-based single-atom nanosheets containing sodium chloride/calcium chloride mixed salt were obtained; carbon-based single-atom nanosheets were washed with deionized water, stirred, filtered, and vacuum-dried to obtain carbon-based in-situ synthesis of molten salt method single-atom nanosheets. This method enables one-step access to catalysts with high electrocatalytic _CO2 reduction activity. The present invention also provides the carbon-based single-atom nanosheet prepared by the method, and the application of the carbon-based single-atom nanosheet in electrocatalytic _CO2 reduction.

Description

In-situ synthesis of carbon-based single-atom nanosheets by a molten salt method and its preparation method and application

technical field

The invention relates to the technical field of nanomaterial preparation, in particular to an in-situ synthesis of carbon-based single-atom nanosheets by a molten salt method, a preparation method and application thereof.

Background technique

In recent years, with the rapid development of cities and industries, the concentration of CO ₂ in the atmosphere has risen sharply, destroying the earth's carbon cycle system, and thus causing a series of serious environmental problems, posing challenges to human survival and development. Therefore, mankind urgently needs to find a solution to reduce the concentration of CO ₂ in the atmosphere and avoid further deterioration of the environment. Reducing the concentration of CO ₂ in the atmosphere mainly starts from two aspects. One is to use clean energy such as solar energy and wind energy to supply energy, reduce the use of fossil fuels, and reduce the production and emission of CO ₂ from the source; The existing CO ₂ is captured, separated, and transformed to produce compounds with high added value.

In _CO2 conversion, electrocatalytic reduction of _CO2 to obtain high value-added fuels is one of the most concerned conversion methods. Electrocatalytic reduction of _CO2 is the use of wind energy, hydrogen energy and other renewable energy to provide electric energy to drive electrocatalysts to reduce _CO2 , and finally generate carbon monoxide, methane, formic acid, methanol and _C2 products or even multi-carbon products. In this process, clean energy is used to power and generate electricity, thereby reducing _CO2 emissions at the source, and the process of _CO2 adsorption and activation, electron transfer, protonation, and product desorption occurs on the electrocatalyst driven by electricity. , and eventually converted into fossil fuels with high added value, reducing the concentration of CO ₂ in the atmosphere. Therefore, this method is of great research value and development prospect. However, the C=O bond energy in CO ₂ is large (806kJmol ^-1 ), and higher energy is required to break bonds to form intermediates with CO bonds or CH bonds in the reaction process, and the electrochemical reduction of CO ₂ is a process involving many The process of electron transfer and proton coupling, so the _CO2 conversion efficiency is usually limited, and the selectivity of a single product is not high. Therefore, the development of electrocatalytic _CO2 reduction catalysts with high selectivity, high catalytic activity and good stability is an urgent problem for scientists to overcome.

Carbon-based materials as supports for electrocatalysts are not only cheap and easy to obtain, but also have good chemical stability and electrical conductivity. At the same time, the surface of the carbon skeleton is easy to modify and dope, which is conducive to the improvement and promotion of catalyst performance. In addition, carbon-based materials can be assembled into various sizes and structures, such as zero-dimensional carbon nanodots, one-dimensional carbon nanotubes and nanofibers, two-dimensional carbon nanosheets, three-dimensional carbon foams, etc. Among them, two-dimensional materials have been widely studied by researchers because of their excellent optical, electrical, magnetic and structural properties, and the structure and electronic properties of nanosheets can be adjusted by changing the thickness or doping of nanosheets.

At present, the synthesis techniques mainly include exfoliation, chemical deposition, solvothermal, hydrothermal and other methods. As a fast, simple, high-yield, and low-cost synthetic method, the molten salt method is more and more widely used in the preparation of materials. For example, in the Chinese patent literature with the patent number CN111974435A, the method first weighs magnesium citrate, potassium citrate and ammonium oxalate according to a certain proportion and puts them in a corundum boat for pyrolysis under nitrogen conditions. After the reaction, pickling and water washing obtain N-doped Carbon nanosheets, and then immerse N-doped carbon nanosheets in copper nitrate aqueous solution to obtain a precursor by impregnation method, and finally calcine at a low temperature in a hydrogen/nitrogen mixed gas atmosphere to obtain Cu/N-doped carbon nanosheets. Compared with the existing preparation methods, the synthesis temperature of the method is lower, the raw materials are cheap and easy to obtain, and the product has a uniform structure and a uniform appearance. However, the preparation process is relatively complicated. It is first necessary to synthesize N-doped carbon nanosheets and then load active metals on them. The synthesis process can be further simplified by innovative methods.

Contents of the invention

The invention provides a preparation method for in-situ synthesis of carbon-based single-atom nanosheets by a molten salt method, which can obtain a catalyst with high electrocatalytic reduction _CO2 activity in one step.

A preparation method for in-situ synthesis of carbon-based single-atom nanosheets by a molten salt method, comprising:

(1) Mix ferrocene and 2-methylimidazole to obtain the first mixture, mix and grind zinc oxide, sodium chloride and calcium chloride to obtain the second mixture, and place the first mixture and the second mixture in a container middle;

(2) Pass argon into the container, the first mixture is blown into the second mixture by the argon, and at the same time, the first mixture and the second mixture in the container are gradiently calcined, and after cooling, a mixture containing chlorine is obtained. Initial carbon-based single-atom nanosheets of sodium chloride/calcium chloride mixed salt;

(3) washing and stirring the initial carbon-based single-atom nanosheets with deionized water, suction filtration, and vacuum drying to obtain carbon-based single-atom nanosheets synthesized in situ by a molten salt method.

The invention distributes the Fe-N active sites in the carbon-based nano sheet with a large specific surface area through a one-step method, thereby exposing as many Fe-N active sites as possible, thereby enhancing the catalytic activity.

In step (1), the molar ratio of 2-methylimidazole to ferrocene is 60:1-70:1.

In step (1), in order to prevent calcium chloride from absorbing water and deliquescent during the grinding process, first place sodium chloride and zinc oxide in an agate mortar with a molar ratio of 6:1–7:1 to grind evenly, and then add Calcium chloride continues to be ground until it is uniform. Since different ratios of sodium chloride/calcium chloride will affect the eutectic point of the mixed salt, in order to form nanosheets of carbon materials during the pyrolysis process with less loss, the mixed salt needs to achieve a lower Melting temperature, so the molar ratio of sodium chloride to calcium chloride is 7:13–3:2.

In step (1), the distance between the first mixture and the second mixture is 1-2 cm, and the distance is crucial to the formation of Fe-N sites. If the distance is too large, part of the first mixture will be blown to The second mixture has cooled and sank before, resulting in the reduction of Fe-N sites; if the spacing is too small, it is easy to cause ferrocene to accumulate in some areas to form iron particles.

In step (1), the container is a corundum boat or a porcelain boat.

In step (2), the purity of the argon is 95%-99.999%, and the gas flow rate of the argon is 10-20mL/min. The concentration of argon is of great significance to the protection of materials during calcination. The higher the purity of argon, the better the protection of materials during calcination.

In step (2), the parameters of the gradient calcination are: first, the temperature is raised to 300-400°C at a heating rate of 2-5°C/min, and the temperature is raised to 300-400°C at a heating rate of 2-5°C/min. 500-600°C, stay for 0.5-2h, and finally raise the temperature to 700-1000°C at a heating rate of 1-10°C/min, and the calcination time is 0.5-3h.

When 2-methylimidazole reaches the flash point temperature, that is, at 155 ° C, the vaporized 2-methylimidazole is blown onto the second mixture by argon flow, and the nitrogen element in 2-methylimidazole is mixed with zinc oxide. The zinc undergoes a coordination chemical reaction to form a zeolite imidazole framework material (ZIF-8) with a Zn-N bond. When the temperature rises to 300–400°C, the sublimated ferrocene diffuses onto the ZIF-8 carrier and decomposes. After that, it combines with the nitrogen of ZIF-8 to replace Zn to form Fe-N bond.

When the temperature reaches 500–600°C, the melting point of the mixed salt is reached, and the molten salt solution diffuses into the carbonized product to prevent the formation of van der Waals force, thereby further inhibiting the stacking of sp2 ^- coordinated carbon layers along the z-axis to form graphene shape carbon nanosheets, staying at this temperature for a sufficient time can not only ensure that all the products form graphene-like carbon nanosheets, but also form as many Fe-N bonds as possible in the molten salt, because as the temperature rises, the pyridine nitrogen , pyrrole nitrogen will be converted into graphitic nitrogen, thereby losing the ability to coordinate with Fe, and the molten salt solution formed at this temperature can completely wrap the product, reducing the subsequent loss of N and Fe- Reduction of N active sites.

When the temperature reaches 700–1000°C, further carbonization will increase the degree of graphitization.

The stirring in the step (3) is magnetic stirring, and the stirring parameters are: the stirring speed is 300-600rpm, and the stirring time is 2-4h.

Further, the molar ratio of ferrocene, zinc oxide and 2-methylimidazole is 2-3:80-90:150-200, and the molar ratio of sodium chloride to zinc oxide is 6:1-6.5:1 , the molar ratio of sodium chloride to calcium chloride is 2:3–3:2, first the calcination temperature is 350–400°C, the calcination time is 1–2h, then the calcination temperature is 500–600°C, and the calcination time is 1–2h 2h, the final calcination temperature is 800-1000℃, and the calcination time is 2-3h.

Further preferably, the molar ratio of sodium chloride to calcium chloride is 2:3, and the eutectic temperature of the mixed salt is 504°C.

The amount of zinc oxide needs to be higher than that of ferrocene to ensure that there are enough Zn-N sites to exchange with ferrocene, but the amount of zinc oxide should not be too high, otherwise Zn atoms cannot be completely removed during high temperature calcination , the Zn-N structure remains in the material; the amount of ferrocene should not be too high, which will lead to the formation of iron particles instead of single atoms in the calcination process, and too low will reduce the Fe-N active sites and reduce the catalyst activity; the mixed salt The amount also needs to be higher than that of dimethylimidazole to ensure that the molten salt solution can completely wrap the product to make it grow two-dimensionally to form nanosheets. Although the amount of mixed salt is high, it will also form a two-dimensional nanosheet structure, but it will cause unnecessary resource waste and energy consumption.

The preparation principle of the in-situ synthesis of carbon-based single-atom nanosheet catalysts provided by the present invention is as follows: when the temperature of the tube furnace rises to 155° C., the flash point of 2-methylimidazole, 2-methylimidazole is sublimated and As the argon gas flow diffuses to the back end of the corundum boat, the nitrogen element in 2-methylimidazole undergoes a coordination chemical reaction with the zinc in zinc oxide to form a zeolite imidazole framework material (ZIF-8). When the temperature reaches 300-400 °C, the ferrocene sublimated and diffused into the ZIF-8 support begins to decompose and combine with nitrogen in ZIF-8 to form Fe-N bonds. When the temperature reaches 500-600°C, which is higher than the melting point of the mixed salt, the molten salt solution diffuses into the carbonized product to prevent the formation of van der Waals force, thereby further inhibiting the stacking of sp2 ^- coordinated carbon layers along the z-axis to form graphene carbon nanosheets. When the temperature reaches 800-1000°C, the carbonization degree of the product further increases. When the pyrolysis process ended and the temperature dropped to room temperature, the white mixed salt crystals were distributed in the black product, which was due to the precipitation of carbonized products from the mixed salt during the cooling process. Finally, the heat-treated material was washed with deionized water to completely remove the mixed salts, and the carbon-based single-atom nanosheet material was obtained.

The carbon-based single-atom nanosheets synthesized in situ by the molten salt method are prepared by adopting the preparation method of in-situ synthesis of the carbon-based single-atom nanosheets by the molten salt method.

The carbon-based single-atom nanosheets synthesized in situ by the molten salt method have a thickness of 2-5 nm.

The present invention also provides the application of the carbon-based single-atom nanosheet catalyst synthesized in situ by the molten salt method in the electrocatalytic reduction of CO ₂ .

A carbon-based single-atom nanosheet catalyst synthesized in situ by the molten salt method was attached to carbon paper as a working electrode, while Ag/AgCl was used as a reference electrode, and platinum wire was used as a counter electrode to form a three-electrode system for electrocatalytic reduction of CO ₂ .

The present invention prepares a carbon-based single-atom nanosheet catalyst synthesized in situ by a molten salt method by combining low-temperature gas diffusion, high-temperature calcination carbonization, and molten salt to control product morphology, so that the Fe-N coordination active center is very good The clear coordination structure improves the selectivity of electrocatalytic _CO reduction to CO.

Compared with prior art, the beneficial effect of the present invention is:

(1) A carbon material loaded with iron atoms is obtained by gas diffusion during low-temperature calcination in the process of temperature programming, and then the carbon material changes shape in the molten salt after the temperature rises and is further carbonized. A molten salt method The carbon-based single-atom nanosheet catalyst synthesized in situ has a nanosheet structure and good structural stability; at the same time, the preparation method is simple and efficient, low in cost, high in controllability and good in reproducibility, and is suitable for industrial production.

(2) During the material preparation process, the mixed salt sodium chloride/calcium chloride acts as a sealed reactor in the molten state, and the carbon material formed by calcining at low temperature to form Fe-N bonds will be dissolved in the molten salt for further pyrolysis, which is beneficial to more A large amount of nitrogen is doped onto the carbon, and the longitudinal growth of the carbon material is inhibited due to the force of the molten salt, thereby forming nanosheets with a large specific surface area. Due to the high N doping content and Fe-N coordination active sites, high specific surface area, the catalyst exhibits excellent electrocatalytic performance, and the CO Faradaic efficiency reaches 95 at the potential of -0.5 V (relative to the reversible hydrogen electrode). %.

(3) Since the mixed salt used in this method is easily soluble in water, after the synthesis is completed, the washing process for removing the mixed salt only needs to use deionized water, and the washing process is simple and effective. It solves the problem that the inorganic salt is difficult to be removed quickly and efficiently in the molten salt synthesis method.

(4) The present invention prepares a carbon-based single-atom nanosheet catalyst synthesized in situ by a molten salt method through a combination of low-temperature gas diffusion, high-temperature calcination carbonization, and molten salt control of product morphology, making Fe-N coordination active The centers are well fixed within the two-dimensional carbon nanosheet structure with high specific surface area, and the clear coordination structure improves the selectivity of electrocatalytic _CO reduction to CO.

Description of drawings

Fig. 1 is the SEM figure of a kind of molten salt method in-situ synthesis carbon-based single-atom nanosheet catalyst prepared in embodiment 1;

Fig. 2 is the TEM figure of a kind of molten salt method in-situ synthesis carbon-based single-atom nanosheet catalyst prepared in embodiment 1;

Fig. 3 is the AFM diagram of a kind of molten salt method in-situ synthesis carbon-based single-atom nanosheet catalyst prepared in embodiment 1;

Fig. 4 is the XRD figure of the catalyst that embodiment 1, 2 and comparative example 1 prepare;

Fig. 5 is the electrochemical polarization curve figure of the catalyst prepared by embodiment 1, 2 and comparative example 1 in three-electrode reaction cell, 0.5M potassium bicarbonate electrolyte;

Fig. 6 is a CO Faradaic efficiency diagram of catalysts prepared in Examples 1, 2 and Comparative Example 1 in a three-electrode reaction cell and 0.5M potassium bicarbonate electrolyte.

detailed description

The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments. It should be understood that these examples are only used to illustrate the present invention and are not intended to limit the scope of the present invention. For the experimental methods without specific conditions indicated in the following examples, the conventional conditions or the conditions suggested by the manufacturer are usually followed.

Example 1

A preparation method for in-situ synthesis of carbon-based single-atom nanosheet catalysts by molten salt method:

Step 1: Weigh 60 mg of ferrocene and 1.707 g of 2-methylimidazole on an electronic balance and place them at 1/4 of one end of the corundum boat.

Step 2: Weigh 0.6512g of zinc oxide and 2.922g of sodium chloride on an electronic balance and put them into an agate mortar to grind evenly, then weigh 8.3235g of calcium chloride and put them into it to mix and grind evenly, and put the ground powder into corundum The other end 2/3 of the boat is at a distance of 1 cm from the mixture of ferrocene and 2-methylimidazole.

Step 3: Calcining the corundum boat in an argon atmosphere. The purity of the argon atmosphere is 99.999%, the heating rate is 5°C/min, the low-temperature calcination temperature is 400°C, and the residence time is 1h, the medium-temperature calcination temperature is 600°C, and the residence time is 1h, and the high-temperature calcination temperature is 1000°C, for 2h.

Step 4: Place the heat-treated powder sample in deionized water, the resistivity of deionized water is 18.2MΩ·cm ^-1 , stir it magnetically for 4 hours, filter the stirred suspension, and then use 1M hydrochloric acid solution for more Pickling and suction filtration, and finally washing with deionized water until neutral. The filtered sample was placed in a vacuum drying oven, kept at a temperature of 60° C., and dried for 12 hours to obtain a carbon-based single-atom nanosheet catalyst synthesized in situ by a molten salt method.

It can be seen from Figure 1 that the prepared carbon-based single-atom nanosheet catalyst in situ by the molten salt method has a nanosheet-like microscopic appearance; it can be seen from Figure 2 that the prepared carbon-based single-atom nanosheet The thickness of nanosheets of carbon-based single-atom nanosheet catalysts is about 2–5nm and there are no agglomerated metal particles; it can be further seen from Figure 3 that the prepared nanosheets of carbon-based single-atom nanosheet catalysts synthesized in situ by molten salt method The thickness is 4nm; It can be seen from Figure 4 that the prepared carbon-based single-atom nanosheet catalyst prepared by the molten salt method does not contain metal nanoparticles, and the degree of crystallization of the material is low.

Application example 1

Example 1 Relevant test methods for preparing CO cathode materials as electrocatalytic _CO2 reduction:

Step 1: Weigh 5 mg of the catalyst prepared in Example 1 with an analytical balance, and at the same time take 450 μL of absolute ethanol and 50 μL of 0.5 wt.% Nafion solution, mix the three evenly and put them into a sample bottle for ultrasonication for 2 hours. Magnetic stirring for 10-12h;

Step 2: Cut out a 1×3cm ² carbon paper, weigh 100 μL of the catalyst solution prepared in Step 1 and add it dropwise to the 1×1 cm ² carbon paper, dry it at room temperature or under infrared light, and use it as a working electrode;

Step 3: Use Ag/AgCl as the reference electrode, platinum wire as the counter electrode, form a three-electrode system together with the working electrode and place it in a sealed H-type electrolytic cell, use 0.5M potassium bicarbonate as the electrolyte solution, The test was carried out under , and the production of CO and _H2 was analyzed by gas chromatography.

The current density of the catalyst at different potentials can be seen from Figure 5; the CO Faradaic efficiency of the catalyst at different potentials can be seen from Figure 6, and the highest CO Faradaic efficiency is about 95%.

Example 2

Compared with Example 1, the only difference is that different high-temperature calcination temperatures are used for molten salt treatment. As in the preparation method of Example 1, the calcination temperature in step 1 was changed from 1000° C. to 900° C., and the rest of the steps were kept unchanged to obtain a carbon-based single-atom nanosheet catalyst.

Application example 2

The method steps are the same as in Application Example 1, the difference is that the carbon-based single-atom nanosheet catalyst prepared in Example 2 is used as the cathode material, and the highest Faradaic efficiency of electrocatalytic _CO2 reduction to CO is about 92%.

Comparative example 1

A preparation method for in-situ synthesis of nitrogen-doped carbon nanosheet catalyst by molten salt method:

Step 1: Weigh 1.707g of 2-methylimidazole on an electronic balance and place it at 1/4 of one end of the corundum boat.

Step 2: Weigh 0.6512g of zinc oxide and 2.922g of sodium chloride on an electronic balance and put them into an agate mortar to grind evenly, then weigh 8.3235g of calcium chloride and put them into it to mix and grind evenly, and put the ground powder into corundum The other end 2/3 of the boat is 1 cm away from the mixture of 2-methylimidazole.

Step 3: Calcining the corundum boat in an argon atmosphere. The purity of the argon atmosphere is 99.999%, the heating rate is 5°C/min, the low-temperature calcination temperature is 400°C, and the residence time is 1h, the medium-temperature calcination temperature is 600°C, and the residence time is 1h, and the high-temperature calcination temperature is 1000°C, for 2h.

Step 4: Place the heat-treated powder sample in deionized water, stir it magnetically for 4 hours, and filter the stirred suspension with suction. The filtered sample was placed in a vacuum drying oven, kept at 60° C., and dried for 12 hours to obtain a catalyst for in-situ synthesis of nitrogen-doped carbon nanosheets by molten salt method.

The steps of the method are as in Application Example 1, the difference is that a nitrogen-doped carbon nanosheet catalyst prepared in Comparative Example 1 by in-situ synthesis of nitrogen-doped carbon nanosheets is used as the cathode material, and the highest Faradaic efficiency of electrocatalytic _CO reduction to CO is about 90%.

It should be noted that the specific implementation methods described above have described the technical solutions and application results of the present invention in detail. Readers should understand that the above embodiments are only the most preferred embodiments and are not intended to limit the present invention. Modifications or equivalent replacements made within the scope of the core theory of the present invention shall fall within the scope of protection of the present invention.

Claims (9)

1. a preparation method for in-situ synthesis of carbon-based single-atom nanosheets by molten salt method, characterized in that, comprising: (1) Mix ferrocene and 2-methylimidazole to obtain the first mixture, mix and grind zinc oxide, sodium chloride and calcium chloride to obtain the second mixture, and place the first mixture and the second mixture in a container middle; (2) Pass argon into the container, the first mixture is blown into the second mixture by the argon, and at the same time, the first mixture and the second mixture in the container are gradiently calcined, and after cooling, a mixture containing chlorine is obtained. Initial carbon-based single-atom nanosheets of sodium chloride/calcium chloride mixed salt; (3) washing and stirring the initial carbon-based single-atom nanosheets with deionized water, suction filtration, and vacuum drying to obtain in-situ synthesis of carbon-based single-atom nanosheets by molten salt method; The parameters of the gradient calcination are: first, the temperature is raised to 300-400°C at a heating rate of 2-5°C/min, and the temperature is raised for 0.5-2h, and then the temperature is raised to 500-600°C at a heating rate of 2-5°C/min. 0.5-2h, and finally raise the temperature to 700-1000℃ at a heating rate of 1-10℃/min, and the calcination time is 0.5-3h. 2. the preparation method of in-situ synthesis of carbon-based single-atom nanosheets by molten salt method according to claim 1, is characterized in that, the mol ratio of described 2-methylimidazole and ferrocene is 60:1-70: 1. 3. the preparation method of in-situ synthesis of carbon-based single-atom nanosheets by molten salt method according to claim 1, characterized in that, first the sodium chloride and the zinc oxide are 6:1-7 according to the molar ratio :1 to grind evenly, then add the calcium chloride and continue to grind until uniform, the mol ratio of the sodium chloride to the calcium chloride is 7:13-3:2. 4. The method for in-situ synthesis of carbon-based single-atom nanosheets by molten salt method according to claim 1, characterized in that the distance between the first mixture and the second mixture is 1-2 cm. 5. the preparation method of in-situ synthesis of carbon-based single-atom nanosheets by molten salt method according to claim 1, characterized in that, the purity of the argon is 95%-99.999%, and the gas flow rate of the argon is 10 –20mL/min. 6. the preparation method of in-situ synthesis of carbon-based single-atom nanosheets by molten salt method according to claim 1, characterized in that, the stirring described in step (3) is magnetic stirring, and the stirring parameters are: the stirring speed is 300- 600rpm, stirring time is 2–4h. 7. A preparation method for in-situ synthesis of carbon-based single-atom nanosheets by molten salt method according to any one of claims 1-6 to obtain in-situ synthesis of carbon-based single-atom nanosheets by molten salt method. 8. The in-situ synthesis of carbon-based single-atom nanosheets by molten salt method prepared by the preparation method of in-situ synthesis of carbon-based single-atom nanosheets by molten salt method according to claim 7, characterized in that, the original In situ synthesis of carbon-based single-atom nanosheets with a thickness of 2–5 nm. 9. According to claim 7 or 8, the in-situ synthesis of carbon-based single-atom nanosheets by molten salt method prepared by the preparation method of molten salt method in-situ synthesis of carbon-based single-atom nanosheets is used in electrocatalytic reduction of _CO2 ,Specific steps are as follows: A carbon-based single-atom nanosheet catalyst synthesized in situ by the molten salt method was attached to carbon paper as a working electrode, while Ag/AgCl was used as a reference electrode, and platinum wire was used as a counter electrode to form a three-electrode system for electrocatalytic _CO2 reduction.

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