Graphitic carbon nitride supported single-atom cu catalysts, methods of making and using the same

Abstract

The present application relates to the technical field of nanometer catalyst, in particular to a kind of graphite phase carbon nitride supported single-atom Cu catalyst and its preparation method and application.The catalyst of the present application exposes the active site of active metal to the greatest extent, improves the catalytic activity and selectivity of the catalyst, and reduces the cost of the catalyst;And the loading amount of Cu atom in g-C3N4 can be regulated by changing the addition amount of copper salt, which is a single-atom catalyst with high metal loading.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of nanocatalysts, in particular to a graphite phase carbon nitride loaded monatomic Cu catalyst and a preparation method and application thereof. BACKGROUND

[0002] The rapid development of society cannot be separated from fossil energy. However, the excessive use of fossil fuels leads to the emission of a large amount of carbon dioxide (CO2), which causes a series of climate and environmental problems such as global warming, sea level rise, and ocean acidification. The electrocatalytic reduction of carbon dioxide (CO2RR) driven by intermittent renewable electricity provides a promising technical means to solve this global challenge. The reduction products of CO2RR are as many as 16 or more, including carbon-hydrogen compounds: methane (CH4), ethylene (C2H4), and carbon monoxide (CO), methanol (CH3OH), formic acid (HCOOH), ethanol (C2H5OH), acetic acid (CH3COOH), isopropyl alcohol (n-C3H7OH), and other carbon-oxygen compounds. CH4 is the carbon dioxide reduction product with the highest energy density, and is an important raw material for the manufacture of many chemical products including aromatic hydrocarbons.

[0003] Graphite phase carbon nitride (g-C3N4) can be prepared from inexpensive precursors such as urea, monocyamide, dicyandiamide, tricyanic acid, melamine, and melamine cyanuric acid through a simple heat treatment process, so it is abundant in source and low in cost. In addition, g-C3N4 has good physical and chemical stability and a large specific surface area, which makes it a good choice for catalyst carriers in heterogeneous catalysis. In addition, C in g-C3N4 has a high affinity for oxygen-binding intermediates (*OCH x , O and OH) in the reaction of CO2 reduction to produce deep reduction products such as CH4. Using g-C3N4 as a catalyst carrier and loading specific metal atoms as active sites on its surface can effectively improve the efficiency of electrocatalytic reduction of CO2 and its selectivity for specific reduction products.

[0004] Effective catalytic active sites are the fundamental reason for determining the performance of heterogeneous catalysts. By constructing highly coordinated unsaturated atomic-level dispersed catalytic materials, the atomic utilization efficiency of the catalyst can be improved. Compared with traditional supported metal catalysts, single-atom catalysts (SACs) with atomic-level dispersed metal atoms as active sites have the advantages of adjustable and separable active sites and high utilization rate of active components, making them deeply studied in the field of electrocatalytic CO2 reduction. Single atoms (metal or non-metal) can be stabilized by the crystal lattice or coordination environment of two-dimensional materials in the form of doping or anchoring through strong covalent bonds, but the constrained single atoms or coordination environment still remain coordination unsaturation, which provides high catalytic active sites. The catalytic properties of active sites are essentially caused by strong electronic interactions between confined single atoms and two-dimensional structure hosts, leading to the formation of new electronic states. The metal content of the current single-atom catalyst materials is usually low, because a single metal atom is prone to migration and aggregation driven by its large surface energy, resulting in the loss of catalyst activity, and the increase of metal loading will also increase the force of metal aggregation. In addition, the existing preparation methods of single-atom metal catalysts are complicated and harsh, and the precursors used are expensive, making it difficult to achieve large-scale production. SUMMARY

[0005] In view of the shortcomings and deficiencies of the prior art, the purpose of the present application is to provide a simple preparation method of single-dispersed metal Cu atom catalyst supported on graphite phase carbon nitride carrier and its application in electrocatalytic reduction of carbon dioxide. The catalyst of the present application exposes the active sites of the active metal to the greatest extent, improves the catalytic activity and selectivity of the catalyst, and reduces the cost of the catalyst; and the loading amount of Cu atoms in g-C3N4 can be adjusted by changing the amount of copper salt added, so as to prepare a single-atom catalyst with high metal loading.

[0006] In one aspect, the present application provides a preparation method of graphite phase carbon nitride supported single-atom Cu catalyst, comprising the following steps:

[0007] (1) Preparation of precursor: uniformly mix solid copper divalent ion salt powder and solid molten salt powder; then add powdered g-C3N4 and mix uniformly to obtain a solid precursor;

[0008] (2) Catalyst preparation: heat the solid precursor obtained in step (1) to 400-550°C in a mixed gas atmosphere containing 0-5% hydrogen, and maintain for 3-4h to obtain a catalyst crude product; wash and dry the catalyst crude product with deionized water and / or ethanol to obtain a graphite phase carbon nitride supported single-atom Cu catalyst.

[0009] In some embodiments, the content of Cu element in the graphite phase carbon nitride supported single-atom Cu catalyst is 10-25%.

[0010] In some embodiments, the solid-state copper divalent ion salt is solid-state CuCl2·2H2O.

[0011] In some embodiments, the solid-state molten salt is selected from one or more of KCl, LiCl, NaCl.

[0012] In some embodiments, the solid-state molten salt is KCl and LiCl.

[0013] When there are two or more of the solid-state molten salts, they can be ground into powder separately and then mixed. One or two of the solid-state molten salt powders can be mixed with the solid-state copper divalent ion salt powder first, and then the other solid-state molten salt powder is added. The order is not limited and the purpose is to mix uniformly.

[0014] In some embodiments, the mass ratio of the solid-state copper divalent ion salt, the solid-state molten salt, and g-C3N4 is (0.1-0.3 g):(1-2 g):1 g.

[0015] In some embodiments, when the solid-state molten salt is KCl and LiCl, the mass ratio of KCl and LiCl is (1.2-1.4 g):1 g.

[0016] In some embodiments, the solid-state copper divalent ion salt powder and the solid-state molten salt powder are mixed uniformly by grinding the solid-state copper divalent ion salt and the solid-state molten salt into 40-80 mesh powders separately and then mixing.

[0017] In some embodiments, the mixing is grinding and mixing by adding an appropriate amount of anhydrous ethanol to the solid-state copper divalent ion salt powder and the solid-state molten salt powder, and then drying after mixing.

[0018] The amount of the appropriate amount of anhydrous ethanol is adjusted according to the amount of the powder, and the purpose is to mix the solid-state copper divalent ion salt powder and the solid-state molten salt powder uniformly and facilitate grinding.

[0019] The drying method after mixing is not limited and can be drying by lamp irradiation. Generally, drying by lamp irradiation is used, and the drying time is 10-20 minutes.

[0020] In some embodiments, the temperature is raised at a rate of 3-5°C / min.

[0021] In some embodiments, the washing is alternating washing with deionized water and ethanol, and the drying temperature after washing is 50-70°C, and the drying is performed under vacuum for 8-15 h.

[0022] When alternating washing with deionized water and ethanol is used, solid-liquid separation can be performed by centrifugation, filtration, etc. The centrifugal speed can be 6000-8000 r / min, and the centrifugation time is 1-2 min.

[0023] In some embodiments, the inert mixed gas containing 0-5% hydrogen is an Ar mixed gas containing 0-5% hydrogen.

[0024] In some embodiments, the inert mixed gas containing 0-5% hydrogen is an Ar mixed gas containing 5% hydrogen.

[0025] In some embodiments, the inert mixed gas containing 0-5% hydrogen has a flow rate of 20-30 mL / min.

[0026] In another aspect, the present application provides a graphite phase carbon nitride loaded monatomic Cu catalyst prepared by the preparation method of the present application.

[0027] In another aspect, the present application also provides the graphite phase carbon nitride loaded monatomic Cu catalyst prepared by the preparation method of the present application or the application of the graphite phase carbon nitride loaded monatomic Cu catalyst in the electrocatalytic reduction of carbon dioxide to prepare methane.

[0028] The present application uses graphite phase carbon nitride as a catalyst carrier, KCl / LiCl as a precursor of molten salt ionic liquid, and CuCl2·2H2O as a copper metal source, and pyrolysis is carried out under a reducing atmosphere; at 400-520℃, KCl / LiCl is converted into a molten salt ionic liquid, the dispersion of metal Cu in the reaction process is improved through the ionic liquid, the coordination of metal Cu atoms and nitrogen / carbon on the graphite phase carbon nitride is promoted, the great surface energy of a single metal atom is overcome through coordination chemical bonds, the metal Cu atom is anchored on the surface of the carrier without being aggregated into nanoparticles, and a single-atom catalyst material loaded with atomically dispersed metal is prepared. For Cu, 1 metal Cu atom is fixed by 4 nitrogen atoms to form Cu-N4 or 1 metal Cu atom is fixed by 2 nitrogen atoms and 2 carbon atoms to form a Cu-N2C2 structure; after the above coordination structure is formed, the metal Cu atom and the groups around it form an active center, and the special electronic structure makes it have good catalytic activity and selectivity.

[0029] The preparation method maximally exposes the active sites of the active metal through simple physical grinding and redox reactions, improves the catalytic activity and selectivity of the catalyst, and reduces the cost of the catalyst; and the loading amount of Cu atoms in g-C3N4 can be regulated by changing the amount of copper salt added, and a single-atom catalyst with a high metal loading amount can be prepared.

[0030] Compared with the prior art, the present application has the following advantages and beneficial effects:

[0031] (1) The carrier used in the present application is graphite phase carbon nitride, which can be prepared from cheap precursors, i.e., urea, and has abundant raw material sources and low cost.

[0032] (2) The synthesis method of the present application is simple and easy to operate, has good repeatability, and can be used for large-scale synthesis of single-atom Cu catalysts, solving the problems of existing single-atom catalyst synthesis methods, i.e., being relatively complicated and harsh in reaction conditions and difficult to realize large-scale production.

[0033] (3) The synthesis method of the present application is carried out under the condition of a small amount of solvent, avoiding pollution to the environment caused by the use of a large amount of solvent; and the time consumption is short, which can greatly shorten the preparation period of the catalyst, and is an environmentally friendly and green synthesis method.

[0034] (4) The catalyst synthesized by the synthesis method of the present application has excellent catalytic performance when applied to the electrocatalytic reduction of carbon dioxide to prepare methane, and has good catalytic activity and single product selectivity.

[0035] (5) When the catalyst of the present application is doped with 25% of Cu element (relative to the mass of carbon nitride, calculated based on the mass of copper salt), the single-atom Cu catalyst can obtain a Faraday efficiency (FE max ) of methane close to 59.6% when used in the reaction of catalytic electro-reduction of carbon dioxide.

[0036] Term Explanation

[0037] Certain embodiments of the present application will now be described in detail. The present application contemplates all alternatives, modifications and equivalents of the described embodiments, which are within the scope and spirit of the present application as defined by the claims. One skilled in the art will recognize many methods and materials as being suitable for use in practicing the present application. The present application is in no way limited to the methods and materials described herein. In the event that one or more of the incorporated literature, patents, and similar materials differs from or contradicts with the present application, including but not limited to defined terms, term application, described techniques, etc., the present application controls.

[0038] It should be further recognized that certain features of the present application, described in detail in a number of independent embodiments, can also be provided in combination in a single embodiment. Conversely, various features of the present application, described in detail in a single embodiment, can also be provided separately or in any appropriate subcombination.

[0039] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. All patents and publications identified are incorporated herein by reference in their entirety.

[0040] The term "room temperature" means ambient temperature, which can be 10-40°C or 15-40°C, or 20-35°C, or 20-30°C.

[0041] The term "%vol" means volume percent.

[0042] The term "wt%" means mass percent.

[0043] In the description of the present specification, the description of the terms "one embodiment", "some embodiments", "an example", "a specific example", or "some examples" and the like means that the specific features, structures, materials or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present application. In the present specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Also, the specific features, structures, materials or characteristics described can be combined in any appropriate manner in any one or more embodiments or examples. In addition, the person skilled in the art can combine and combine the different embodiments or examples described in the present specification and the features of the different embodiments or examples, without contradiction.

[0044] In the following, all the numbers disclosed herein are approximate, whether or not the word "approximately" or "about" is used. The value of each number can vary by 1%, 2%, 5%, 7%, 8%, 10%, 15%, or 20% or more. Whenever a number with a value of N is disclosed, any number with a value of N + / - 1%, N + / - 2%, N + / - 3%, N + / - 5%, N + / - 7%, N + / - 8%, N + / - 10%, N + / - 15%, or N + / - 20% is also explicitly disclosed, where "+" or "-" means plus or minus. BRIEF DESCRIPTION OF DRAWINGS

[0045] Figure 1 XRD (X-ray diffraction) patterns of g-C3N4 / Cu monatomic catalysts obtained in Examples 1, 2, 3, and 4 of the present application and g-C3N4; no crystal phase of metal Cu appears on the XRD spectrum, which to some extent shows that the catalyst obtained in the present application is a Cu monatomic catalyst material.

[0046] Figure 2 SEM (scanning electron microscope) images of g-C3N4 / Cu monatomic catalysts obtained in Examples 1, 2, 3, and 4 of the present application; Figure 2 (a) is the SEM image of Example 1, i.e. CN-Cu-1, Figure 2 (b) is the SEM image of Example 2, i.e. CN-Cu-2, Figure 2 (c) is the SEM image of Example 3, i.e. CN-Cu-3, Figure 2(d) is the SEM image of CN-Cu-4 of Example 4;

[0047] Figure 3 TEM (Transmission Electron Microscope) images of g-C3N4 / Cu monatomic catalysts obtained from Examples 1, 2, 3, 4 of the present application; Figure 3 (a) is the TEM image of CN-Cu-1 of Example 1, Figure 3 (b) is the TEM image of CN-Cu-2 of Example 2, Figure 3 (c) is the TEM image of CN-Cu-3 of Example 3, Figure 3 (d) is the TEM image of CN-Cu-4 of Example 4;

[0048] Figure 4 Statistical diagram of Faraday efficiency of methane production of g-C3N4 / Cu monatomic catalysts obtained from Examples 1, 2, 3, 4 of the present application and copper powder (CAS No.: 7440-50-8, specification: 99.9%, manufacturer: Aladdin Reagent Co., Ltd.) as a control sample under different current densities. The performance of the catalysts was tested using a flow-type electrolytic cell, with a carbon paper gas diffusion electrode coated with the catalyst as the cathode, an iridium dioxide-coated titanium mesh as the anode, and an anion exchange membrane FAB-PK-130 used to separate the two electrodes. The applied potential was relative to the potential of Ag / AgCl; 1M KOH was used as the electrolyte, and CO2 was passed into the reactor at a flow rate of 50 mL / min -1 . In the performance test of this series of samples, the g-C3N4 / Cu monatomic catalyst obtained from Example 3 was able to obtain the highest Faraday efficiency (FE 2 ) of 59.6% for methane in the products obtained by the reduction of carbon dioxide catalyzed by this series of catalyst materials under a current density of 350 mA / cm max , which was much higher than the methane Faraday efficiency value (FE = 4.4%) measured under the same test conditions for commercially purchased copper powder.

[0049] Figure 5 E-t curve diagrams of g-C3N4 / Cu monatomic catalysts obtained from Examples 1, 2, 3, 4 of the present application tested by chronoamperometry; Figure 5 (a) is the E-t curve of CN-Cu-1 of Example 1, Figure 5 (b) is the E-t curve of CN-Cu-2 of Example 2, Figure 5 (c) is the E-t curve of CN-Cu-3 of Example 3, Figure 5 (d) is the E-t curve of CN-Cu-4 of Example 4, Figure 5(e) E-t curve of copper powder purchased for commercial route. The E-t curve is obtained by measuring the relationship between cathode potential E and time t during electrolysis by giving different fixed current. As the current increases from 100 mA to 400 mA, the cathode potential E (relative to Ag / AgCl electrode) also decreases. DETAILED DESCRIPTION

[0050] In order to make the objectives, technical solutions and advantages of the present application clearer, the present application will be further described in detail below with reference to examples. The specific examples described herein are only used to explain the present application and do not constitute any limitation on the present application. In addition, in the following description, the description of well-known structures and technologies is omitted to avoid unnecessary confusion of the concept of the present disclosure. Such structures and technologies are also described in many publications.

[0051] The reagents used in the present application can be purchased from the market or can be prepared by the method described in the present application.

[0052] Example 1

[0053] (1) Preparation of precursor: 0.581 g of KCl powder (particle size XX), 0.150 g of CuCl2·2H2O powder (particle size XX) and 0.474 g of LiCl powder (particle size XX) were taken respectively, mixed, ground, and ground into a uniform reddish-brown mixture, then about 2 mL of anhydrous ethanol was added, and after a little mixing, a slurry-like mixture was obtained. It was placed under an oven lamp for 10 min, and then cooled to room temperature; 1 g of powder-like g-C3N4 was then added to the mixture, which was then ground and mixed uniformly to obtain a solid precursor with a uniform light yellow color.

[0054] (2) Preparation of catalyst: 0.750 g of the precursor was heated to 500°C at a rate of 5°C / min in a 20 mL / min 5% vol H2+95% vol argon reduction gas atmosphere and maintained for 3 h, and then naturally cooled to room temperature. The obtained solid was washed with deionized water and ethanol for 3 times respectively, then centrifuged at 8000 r / min, and dried under reduced pressure to obtain a solid, which was ground into a fine powder to obtain a Cu monatomic catalyst with a metal salt loading ratio, which is called CN-Cu-1. The Cu element content in the catalyst CN-Cu-1 was obtained by testing with a thermogravimetric analyzer, which was 11.0%. The catalyst obtained a faradaic efficiency of 55.0% for methane in the reduction products when it was used to catalyze the reduction of carbon dioxide at a current density of 300 mA / cm 2 .

[0055] Example 2

[0056] In a mortar, 0.774 g of KCl and 0.200 g of CuCl2·2H2O were ground for about 5 minutes and mixed well; then 0.632 g of LiCl was ground for about 5 minutes. The above solid powders were mixed and ground to a uniform reddish-brown mixture, and then about 2 mL of anhydrous ethanol was added to obtain a slurry-like mixture. It was placed under an incandescent lamp for 10 min, and then cooled to room temperature; 1 g of powdered g-C3N4 was added to the mixture, which was then mixed and ground well to obtain a solid precursor with a uniform light yellow color. 0.750 g of the precursor was placed in a porcelain boat, which was placed in a tube furnace and heated to 500 °C at a rate of 5 °C / min under a reducing gas atmosphere of about 20 mL / min of 5% H2+95% Ar and maintained for 3 h, and then naturally cooled to room temperature. The obtained solid was washed with deionized water and ethanol three times, respectively, and centrifuged at 8000 r / min, and then dried in vacuum. The obtained solid was ground well to a fine powder to obtain a Cu monatomic catalyst with a metal salt loading ratio, which was named CN-Cu-2. The content of Cu element in the catalyst CN-Cu-2 was 16.9% by testing with a thermogravimetric analyzer. The catalyst CN-Cu-2 catalyzed the reduction of carbon dioxide at a current density of 300 mA / cm2, and the Faraday efficiency of methane in the reduction products was 57.6%. 2

[0057] Example 3

[0058] In a mortar, 0.968 g of KCl and 0.250 g of CuCl2·2H2O were ground for about 5 minutes and mixed well; then 0.790 g of LiCl was ground for about 5 minutes. The above solid powders were mixed and ground to a uniform reddish-brown mixture, and then about 2 mL of anhydrous ethanol was added to obtain a slurry-like mixture. It was placed under an incandescent lamp for 10 min, and then cooled to room temperature; 1 g of powdered g-C3N4 was added to the mixture, which was then mixed and ground well to obtain a solid precursor with a uniform light yellow color. 0.750 g of the precursor was placed in a porcelain boat, which was placed in a tube furnace and heated to 500 °C at a rate of 5 °C / min under a reducing gas atmosphere of about 25 mL / min of 5% H2+95% Ar and maintained for 3 h, and then naturally cooled to room temperature. The obtained solid was washed with deionized water and ethanol three times, respectively, and centrifuged at 8000 r / min, and then dried in vacuum. The obtained solid was ground well to a fine powder to obtain a Cu monatomic catalyst with a metal salt loading ratio, which was named CN-Cu-3. The content of Cu element in the catalyst CN-Cu-3 was 21.4% by testing with a thermogravimetric analyzer. The catalyst CN-Cu-3 catalyzed the reduction of carbon dioxide at a current density of 350 mA / cm2, and the Faraday efficiency of methane in the reduction products was 62.3%. 2 ​The Faraday efficiency of methane in the reduction products is 59.6% when the catalyst is used to reduce carbon dioxide at a current density of 350 mA / cm

[0059] Example 4

[0060] In a mortar, 0.968 g of KCl and 0.250 g of CuCl2-2H2O were ground for about 5 minutes, respectively, and mixed well; and 0.790 g of LiCl was ground for about 5 minutes. The above solid powders were mixed and ground to a uniform reddish-brown mixture, and then about 2 mL of anhydrous ethanol was added to obtain a slurry-like mixture after slight mixing. It was placed under an oven lamp for 10 min, and then cooled to room temperature; 1 g of powdered g-C3N4 was added to the mixture, which was then mixed and ground well to obtain a solid precursor with a uniform light yellow color. 0.750 g of the precursor was placed in a porcelain boat, which was placed in a tube furnace and heated to 520°C at a rate of 5°C / min in a 5% H2+95% Ar reducing gas atmosphere at a flow rate of about 25 mL / min and maintained for 3 h, and then naturally cooled to room temperature. The obtained solid was washed with deionized water and ethanol three times, respectively, and centrifuged at 8000 r / min, and after vacuum drying, the obtained solid was ground well into a fine powder to obtain a Cu monatomic catalyst with a metal salt loading ratio, which is called CN-Cu-4. The content of Cu element in the catalyst CN-Cu-4 was 22.7% by testing with a thermogravimetric analyzer. The Faraday efficiency of methane in the reduction products was 56.4% when the catalyst was used to reduce carbon dioxide at a current density of 350 mA / cm 2 The Faraday efficiency of methane in the reduction products was 56.4% when the catalyst was used to reduce carbon dioxide at a current density of 350 mA / cm

[0061] The method of the present application has been described by preferred embodiments, and the related personnel can obviously make changes or appropriate changes and combinations to the methods and applications described herein within the content, spirit and scope of the present application to realize and apply the present technology. Those skilled in the art can refer to the content herein to make appropriate improvements to the process parameters. It is particularly pointed out that all similar substitutions and changes are obvious to those skilled in the art, and they are considered to be included in the present application.

Claims

1. A method for preparing a graphite-phase carbon nitride-supported single-atom Cu catalyst, characterized in that: The following steps are involved: (1) Precursor preparation: solid copper divalent ion salt powder and solid molten salt powder are mixed evenly; then powdered g-C3N4 is added and mixed evenly to obtain a solid precursor; (2) Catalyst preparation: The solid precursor obtained in step (1) is heated to 400-550°C in a reducing gas atmosphere and maintained for 3-4 hours to obtain a crude catalyst; the crude catalyst is washed with water and / or ethanol and then dried to obtain the catalyst; the reducing gas atmosphere is composed of 0-5% vol hydrogen and the balance is an inert gas; The content of Cu element in the graphite phase carbon nitride supported single atom Cu catalyst is 10 wt% to 25 wt%; The solid molten salt is KCl and LiCl; The mass ratio of KCl and LiCl is (1.2-1.4):1; The mass ratio of the solid copper divalent ion salt, solid molten salt and g-C3N4 is (0.1~0.3): (1~2):

1.

2. The method for preparing the graphite-phase carbon nitride-supported single-atom Cu catalyst according to claim 1, wherein: The solid copper divalent ion salt is solid CuCl2·2H2O.

3. The method for preparing the graphite-phase carbon nitride-supported single-atom Cu catalyst according to claim 1, wherein: The solid copper divalent ion salt powder and the solid molten salt powder are uniformly mixed by first grinding the solid copper divalent ion salt and the solid molten salt into 40-80 mesh powders respectively and then mixing them.

4. The method for preparing the graphite-phase carbon nitride-supported single-atom Cu catalyst according to claim 1, wherein: The solid copper divalent ion salt powder and the solid molten salt powder are uniformly mixed by adding an appropriate amount of anhydrous ethanol to the solid copper divalent ion salt powder and the solid molten salt powder, grinding and mixing, and drying after mixing.

5. The method for preparing the graphite-phase carbon nitride-supported single-atom Cu catalyst according to claim 1, characterized in that: The temperature is increased at a rate of 3-5°C / min.

6. The method for preparing the graphite-phase carbon nitride-supported single-atom Cu catalyst according to claim 1, characterized in that: The washing is performed by alternating washing with water and ethanol; and / or The drying temperature in step (2) is 50-70°C; and / or The drying in step (2) is performed under vacuum conditions for 8 to 15 hours.

7. The method for preparing the graphite-phase carbon nitride-supported single-atom Cu catalyst according to claim 1, characterized in that: The inert gas in the reducing gas atmosphere is argon.

8. The method for preparing the graphite-phase carbon nitride-supported single-atom Cu catalyst according to claim 1, characterized in that: The reducing gas atmosphere is a mixed gas containing 5% vol hydrogen and the balance argon.

9. The method for preparing the graphite-phase carbon nitride-supported single-atom Cu catalyst according to claim 1, characterized in that: The flow rate of the gas in the reducing gas atmosphere is 20-30 mL / min.

10. A graphite-phase carbon nitride-supported single-atom Cu catalyst, characterized in that: The compound is prepared by the preparation method according to any one of claims 1 to 9.

11. Use of the graphite-phase carbon nitride-supported single-atom Cu catalyst prepared by the preparation method according to any one of claims 1 to 9 or the graphite-phase carbon nitride-supported single-atom Cu catalyst according to claim 10 in the electrocatalytic reduction of carbon dioxide to produce methane.

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