3D transition metal monatomic catalyst and preparation method and application thereof

Abstract

The invention relates to the technical field of monatomic catalysts, in particular to a 3D transition metal monatomic catalyst and a preparation method and application thereof. The preparation method comprises the following steps: firstly, pretreating an NF skeleton; preparing a mixed solution containing N, N-dimethylformamide, ethanol, water, nickel nitrate nonahydrate and terephthalic acid; vertically placing the NF skeleton in the mixed solution for hydrothermal reaction to obtain a Ni-BDC / NF precursor; performing electrochemical deposition in a three-electrode system; and performing metal deposition in an electrolyte solution containing metal salt and sodium fluoride, and forming the target catalyst by taking the Ni-BDC / NF precursor as a working electrode. The method is suitable for various carriers, the loading of different metals can be regulated and controlled, the controllable synthesis of the monatomic catalyst is realized, and the metal content is accurately controlled by adjusting the electro-deposition time. The catalyst shows excellent activity and stability in an electro-catalytic reaction, and has a wide application prospect.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of single-atom catalysts, in particular to a 3D transition metal single-atom catalyst and a preparation method and application thereof. BACKGROUND

[0002] With the decrease of the size of nanoparticles, the number of exposed surface atoms will increase, and the atomic structure, electronic structure and surface defects will be improved, so adjusting the size of the particles to the atomic level to obtain a single-atom catalyst is a method of maximizing the atomic utilization efficiency and improving the catalytic activity.

[0003] At present, in addition to the common impregnation method, high-temperature pyrolysis method and coprecipitation method, there are also solid-phase reduction method and plasma-enhanced chemical deposition method for the synthesis of single-atom catalysts. For example, the patent document with the publication number CN115722265A discloses a preparation method and application of a transition metal single-atom catalyst, and the specific preparation steps are as follows: first, a mixture containing a transition metal salt, zinc acetate and 2-methylimidazole is reacted for 1-72 hours, followed by centrifugation, washing and drying to obtain a precursor solid powder; then, the obtained precursor powder is heated at 400-1200℃ for 1-4 hours under a protective atmosphere, and then the obtained black powder is subjected to acid treatment, followed by centrifugal washing to neutral and vacuum drying to obtain a transition metal single-atom catalyst solid powder.

[0004] Although the above method can synthesize a series of single-atom catalysts and has made great progress in this field, the preparation method of single atoms is still complex, and the metal single atoms treated at high temperature have the tendency of agglomeration, or form carbides, oxides, etc., greatly reducing the proportion of atomic dispersion sites in the catalyst. At the same time, due to the instability of carbon precursors at high temperature, the chemical composition and structure around the transition metal single atoms are uncontrollable, which brings adverse effects to the exploration of the catalytic mechanism of the catalyst, and restricts the application of single-atom materials. Therefore, it is crucial to select a single-atom catalyst carrier with a suitable structure and to pre-construct single atoms and surrounding chemical structure sites. SUMMARY

[0005] The present application provides a 3D transition metal single-atom catalyst and a preparation method and application thereof, to solve the problems of agglomeration and formation of carbides in the preparation process of existing single-atom catalysts, and to endow the catalyst with a clear chemical environment.

[0006] According to a first aspect of the present application, the present application provides a preparation method of a 3D transition metal single-atom catalyst, comprising the following steps: Step (1), pretreating the NF framework; Step (2), synthesis of Ni-BDC / NF precursor: a mixed solution containing N, N-dimethylformamide, ethanol, water, nickel nitrate and terephthalic acid is configured; the NF skeleton is vertically placed in the mixed solution for hydrothermal reaction to obtain the Ni-BDC / NF precursor; Step (3), preparation of 3D transition metal monatomic catalyst: electrochemical deposition is carried out in a three-electrode system; wherein, a solution containing metal salt and sodium fluoride is used as the electrolyte solution, the Ni-BDC / NF precursor is used as the working electrode, a graphite rod electrode is used as the counter electrode, a saturated calomel electrode is used as the reference electrode, and the metal atoms are deposited on the Ni-BDC / NF by using constant current electrodeposition.

[0007] The preparation method of the 3D transition metal monatomic catalyst of the application comprises pretreatment of the NF skeleton, synthesis of the Ni-BDC / NF carrier and electrochemical deposition in a three-electrode system, and the operation steps are clear, without the need for complex equipment or tedious processes. By controlling the time and current density of electrochemical deposition, the loading amount of metal monatomic catalyst can be accurately controlled, and rapid and efficient catalyst preparation can be realized. The NF skeleton is vertically placed in a mixed solution with a specific composition to prepare the Ni-BDC / NF precursor, which can ensure uniform deposition of the Ni-BDC material on the NF skeleton, thereby facilitating subsequent deposition of metal atoms. The electrochemical deposition method can uniformly deposit metal atoms on the Ni-BDC / NF precursor, avoiding the common problem of metal atom aggregation in traditional high-temperature pyrolysis methods. Tests such as XRD and Ac-TEM prove that there are no metal nanoparticles in the catalyst, and the metal exists in the form of monatomic. The addition of sodium fluoride in the electrolyte solution further stabilizes the dispersion state of the metal atoms, preventing them from migrating or aggregating during the deposition process, and ensuring the high performance of the catalyst. The preparation method of the application is not only suitable for a specific metal or carrier, but also can be widely applied to the preparation of monatomic catalysts of various transition metals (such as V, Cr, Mn, Fe, Co, Cu, Zn, etc.). At the same time, by adjusting the carrier material, it can also be extended to other types of carriers, and has wide applicability.

[0008] Further, in the step (2), the volume ratio of N,N-dimethylformamide (DMF), ethanol and water is (10-30):(1-2):1. The mixed solvent system of DMF, ethanol and water can effectively dissolve nickel nitrate nonahydrate and terephthalic acid, ensuring the uniform dispersion of the reactants in the solution. By adjusting the solvent ratio, the reaction conditions can be further optimized to ensure sufficient contact between the reactants, thereby improving the synthesis quality of the Ni-BDC / NF carrier. The appropriate solvent ratio also helps to form high-quality Ni-BDC structures. DMF as the main solvent can provide good solubility and reaction environment, while the addition of ethanol and water can adjust the reaction rate and crystallization process, thereby obtaining more uniform and stable Ni-BDC nanostructures.

[0009] Further, the mass ratio of nickel nitrate nonahydrate, terephthalic acid and N,N-dimethylformamide is (6-8):(7-9):3. Nickel nitrate nonahydrate and terephthalic acid are the key reactants for synthesizing Ni-BDC. By optimizing the above ratio, the stoichiometric ratio between metal ions and organic ligands during the reaction process can be accurately matched, which helps to form high-quality Ni-BDC structures and avoid side reactions or incomplete reactions caused by excess or deficiency.

[0010] Further, in the step (2), the hydrothermal reaction temperature is 120-130℃ and the reaction time is 8-12h. The hydrothermal reaction temperature and time are key factors affecting the synthesis quality of the Ni-BDC / NF carrier. A temperature range of 120-130℃ can ensure efficient reaction while avoiding side reactions or structure damage caused by excessively high temperature. At the same time, a reaction time of 8-12h ensures sufficient reaction, allowing Ni-BDC to grow uniformly on the surface of the nickel foam. Excessive temperature or time may lead to excessive crystal growth, forming larger agglomerates; while lower temperature or shorter time may result in incomplete crystal growth, affecting the performance of the carrier.

[0011] Further, in the step (3), the metal salt includes one or more of vanadium trichloride, chromium nitrate nonahydrate, manganese chloride, iron nitrate nonahydrate, cobalt nitrate hexahydrate, copper nitrate trihydrate and zinc nitrate hexahydrate.

[0012] Further, in the step (3), the concentration ratio of the metal salt to sodium fluoride is 1: (3-5). Sodium fluoride plays a key role in the electrochemical deposition process. By controlling the concentration ratio of the metal salt to sodium fluoride to be 1: (3-5), the migration and agglomeration of metal atoms during the deposition process can be effectively inhibited. Sodium fluoride can form a stable coordination structure with metal ions, thereby ensuring that the metal atoms are uniformly dispersed in the form of single atoms on the Ni-BDC / NF carrier. The uniformly dispersed metal single atoms can form stronger interactions with the carrier, enhancing the overall stability of the catalyst.

[0013] Further, in the step (3), the current for constant current electrodeposition is 8-12 mA / cm 2 , and the time is 3-8 min; the stirring rate of the three-electrode system is 700-900 r / min. By setting the current density for constant current electrodeposition to be 8-12 mA / cm 2 , the deposition time to be 3-8 minutes, and the stirring rate to be 700-900 r / min, the present application not only optimizes the uniform dispersion of metal single atoms and the stability of the catalyst, but also significantly improves the catalytic performance.

[0014] Further, the step (1) specifically comprises: cleaning the foamed nickel in acetone and water, respectively, then ultrasonic cleaning with hydrochloric acid, and then cleaning with water and anhydrous ethanol, and finally vacuum drying to obtain the NF framework. Through the detailed design of the foamed nickel pretreatment step, not only the cleanliness and high activity of the NF framework are ensured, but also an ideal foundation is provided for the subsequent growth of Ni-BDC and deposition of metal single atoms.

[0015] Preferably, the concentration of hydrochloric acid is 2-6 M; the ultrasonic time is 10-30 min; and the vacuum drying temperature is 50-70°C for 3-12 h. By setting the concentration of hydrochloric acid to be 2-6 M, the ultrasonic time to be 10-30 min, and the vacuum drying temperature to be 50-70°C for 3-12 h, not only the cleaning effect of the foamed nickel is optimized, but also the surface activity of the foamed nickel is significantly improved, providing an ideal foundation for the subsequent preparation of the catalyst.

[0016] According to a second aspect of the present application, the present application provides a 3D transition metal single atom catalyst prepared by the above preparation method.

[0017] Further, in the 3D transition metal single atom catalyst, the loading of the 3D transition metal is 0.2-2 wt%. Within the above loading range, the metal atoms can be uniformly dispersed in the form of single atoms on the Ni-BDC / NF carrier, avoiding the agglomeration of metal atoms, and also enhancing the exposure of active sites, thereby improving the adsorption and activation capacity of the catalyst for reaction intermediates (such as *OH, *O, *OOH), and further improving the catalytic performance.

[0018] Preferably, the 3D transition metal comprises one or more of V, Cr, Mn, Fe, Co, Cu and Zn, more preferably Fe.

[0019] According to a third aspect of the present application, the present application also provides the use of the above-mentioned 3D transition metal single-atom catalyst in an electrocatalytic oxygen evolution reaction.

[0020] Advantages of the present application: The preparation method of the 3D transition metal single-atom catalyst of the present application is not only suitable for a certain carrier, but also has universality for various carriers, and can prepare single-atom catalysts with different metals loaded on different carriers.

[0021] The preparation method of the present application is very simple for metal content regulation, and the metal content on the carrier can be regulated by controlling the time of the electrodeposition process.

[0022] The single-atom catalyst prepared by the preparation method of the present application applied in the electrocatalytic oxygen evolution shows excellent catalytic activity. BRIEF DESCRIPTION OF DRAWINGS

[0023] In order to more clearly illustrate the technical solutions of the present application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments or prior art description. Obviously, the drawings in the following description are some embodiments of the present application, and other drawings can also be obtained by those skilled in the art without creative labor.

[0024] Figure 1 is a synthesis route map of a 3D transition metal single-atom catalyst provided by the present application.

[0025] Figure 2 is an XRD map of a series of 3D transition metal single-atom catalysts (M-Ni-BDC / NF, wherein M=(V, Cr, Mn, Fe, Co, Cu, Zn)) provided by the present application.

[0026] Figure 3 is an SEM map of a Fe-Ni-BDC / NF single-atom catalyst provided by the present application, wherein, Figure 3 (a) is one of the SEM maps of the Fe-Ni-BDC / NF single-atom catalyst, Figure 3 (b) is the second SEM map of the Fe-Ni-BDC / NF single-atom catalyst.

[0027] Figure 4 is an EDS element distribution map of the Fe-Ni-BDC / NF single-atom catalyst provided by the present application.

[0028] Figure 5 is an Ac-TEM image of the Fe-Ni-BDC / NF single atom catalyst provided by an embodiment of the present application.

[0029] Figure 6 is a catalytic performance chart of a series of 3D transition metal single atom catalysts (M-Ni-BDC / NF, where M=(V, Cr, Mn, Fe, Co, Cu, Zn)) provided by an embodiment of the present application.

[0030] Figure 7 is a catalytic performance chart of the Fe-Ni-BDC / NF single atom catalyst provided by an embodiment of the present application, wherein, Figure 7 (a) is a catalytic performance chart of the Fe-Ni-BDC / NF single atom catalyst under different electrodeposition times; Figure 7 (b) is the Fe-Ni-BDC / NF single atom catalyst under electrodeposition for 5 min.

[0031] Figure 8 is a catalytic performance comparison chart of the Fe-Ni-BDC / NF single atom catalyst under electrodeposition for 5 min and the catalyst of Comparative Example 1 provided by an embodiment of the present application. DETAILED DESCRIPTION

[0032] In order to make the objectives, technical solutions and advantages of the present application clearer, the technical solutions in the present application will be described clearly and completely below in combination with the drawings in the present application. Obviously, the described embodiments are some of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative labor fall within the scope of protection of the present application.

[0033] Embodiment 1 The present embodiment provides a preparation method of a 3D transition metal single atom catalyst, comprising the following steps: Step (1), pretreatment of the NF skeleton: the NF is cut into a size of 6x2 cm, ultrasonic cleaning in acetone for 30 min, then water washing, followed by ultrasonic cleaning in 3 M hydrochloric acid for 30 min, then deionized water (DI) and anhydrous ethanol cleaning to remove organic matter, ions, oxides and other residues of the NF sample, and finally drying in a vacuum oven at 60℃ for 10 h.

[0034] Step (2), synthesis of Ni-BDC / NF: as Figure 1As shown, 140 mg of nickel nitrate nonahydrate (Ni(NO₃)₂·9H₂O) and 160 mg of terephthalic acid (BDC) were dissolved in a mixture of 60 mL of N,N-dimethylformamide (DMF), 3 mL of ethanol, and 3 mL of deionized water. The mixture was thoroughly mixed and transferred to a 100 mL Teflon-lined autoclave (filling level no greater than 80%). Then, the NFs were placed vertically into the solution and secured with a Teflon rod. The autoclave was sealed and maintained in an oven at 125°C for 10 hours. After cooling to room temperature, the NFs were removed and ultrasonically washed with water and ethanol for at least three times. The washed NFs were then dried in a vacuum oven at 60°C overnight. The product obtained in this step is designated Ni-MOF / NF.

[0035] Step (3), preparation of 3D transition metal single atom catalyst: Figure 1 As shown, electrochemical deposition was carried out in a three-electrode system. A solution containing 0.01 M metal salt and 0.04 M sodium fluoride was used as the electrolyte solution, and the metal salt was VCl3. The Ni-BDC / NF obtained above was used as the working electrode (WE), the graphite rod electrode was used as the counter electrode (CE), and the saturated calomel electrode was used as the reference electrode (RE). The current density was 10 mA / cm 2 The metal atoms were uniformly deposited on the surface of Ni-BDC / NF by constant current electrodeposition for 300 s and the stirring rate of the three-electrode system was 800 r / min. The undeposited metal ions were washed away with deionized water, and then the surface was dried at 60°C in a vacuum drying oven for 10 h to obtain the corresponding metal single atom catalyst, which was denoted as V-Ni-BDC / NF.

[0036] Example 2 This embodiment provides a method for preparing a 3D transition metal single atom catalyst, which is different from that of Example 1 in that: in step (3), the metal salt is Cr(NO3)3·9H2O, and the obtained metal single atom catalyst is Cr-Ni-BDC / NF.

[0037] Example 3 This embodiment provides a method for preparing a 3D transition metal single atom catalyst, which is different from Example 1 in that: in step (3), the metal salt is MnCl2, and the obtained metal single atom catalyst is Mn-Ni-BDC / NF.

[0038] Example 4 This embodiment provides a method for preparing a 3D transition metal single atom catalyst, which is different from that of Example 1 in that: in step (3), the metal salt is Fe(NO3)3·9H2O, and the obtained metal single atom catalyst is Fe-Ni-BDC / NF.

[0039] Example 5 The embodiment provides a preparation method of a 3D transition metal monatomic catalyst, which is different from the embodiment 1 in that in the step (3), the metal salt is Co(NO3)3·6H2O, and the obtained metal monatomic catalyst is Co-Ni-BDC / NF.

[0040] Example 6 The embodiment provides a preparation method of a 3D transition metal monatomic catalyst, which is different from the embodiment 1 in that in the step (3), the metal salt is Cu(NO3)3·3H2O, and the obtained metal monatomic catalyst is Cu-Ni-BDC / NF.

[0041] Example 7 The embodiment provides a preparation method of a 3D transition metal monatomic catalyst, which is different from the embodiment 1 in that in the step (3), the metal salt is Zn(NO3)3·6H2O, and the obtained metal monatomic catalyst is Zu-Ni-BDC / NF.

[0042] Comparative Example 1 The comparative example provides a preparation method of a 3D transition metal monatomic catalyst, which is different from the embodiment 1 only in that in the step (3), the sodium fluoride (NaF) is not added in the electrolyte solution.

[0043] Comparative Example 2 The comparative example provides a preparation method of a 3D transition metal monatomic catalyst, which is different from the embodiment 1 only in that in the step (3), the time for the electrochemical deposition in the three-electrode system is different. The electro-deposition time is set to 120 s, 600 s, 1200 s and 1800 s respectively.

[0044] Test Example 1 (1) The NF, Ni-BDC, Ni-BDC-NF, V-Ni-BDC-NF catalyst in the embodiment 1, the Cr-Ni-BDC-NF catalyst in the embodiment 2, the Mn-Ni-BDC-NF catalyst in the embodiment 3, the Fe-Ni-BDC-NF catalyst in the embodiment 4, the Co-Ni-BDC-NF catalyst in the embodiment 5, the Cu-Ni-BDC-NF catalyst in the embodiment 6 and the Zn-Ni-BDC-NF catalyst in the embodiment 7 are subjected to XRD test.

[0045] From Figure 2The XRD patterns of each catalyst can be seen, in addition to the prominent and sharp diffraction peaks of the NF support at 44.6° and 51.8°, all other diffraction peaks belong to Ni-BDC, and no metal characteristic peaks are found in the XRD patterns. The loadings of each transition metal are 0.2-2% by ICP test, as shown in Table 1, indicating that no nanoparticles related to transition metals are formed.

[0046] Table 1

[0047] (2) Take Fe-Ni-BDC / NF as an example to test the catalysts of the embodiments by SEM and EDS.

[0048] Figure 3 of Figure 3 (a) and Figure 3 (b) show the surface morphology of the Fe-Ni-BDC / NF single-atom catalyst, which presents as vertically grown on the NF surface on the ultra-thin 2D nanosheet.

[0049] Figure 4 The EDS element distribution map shows the uniform distribution of Fe, Ni and O elements.

[0050] (3) Take Fe-Ni-BDC / NF as an example to test the catalysts of the embodiments by Ac-TEM.

[0051] Ac-TEM is further used to test whether the catalysts contain nanoclusters or particles, as shown in Figure 5 In the ordered arrangement of atomic arrays, brighter spots randomly appear, which may be surface-loaded Fe atoms.

[0052] Test Example 2 Test the oxygen evolution performance of the catalyst in an alkaline solution (pH = 14) (1) Test the OER performance of different transition metal single-atom catalysts.

[0053] The catalysts obtained in Examples 1-7 are used as working electrodes, a graphite rod is used as a counter electrode and Ag / AgCl is used as a reference electrode. 1 M potassium hydroxide (KOH) solution is used as an electrolyte, and the OER performance of the material is tested in the Linear Sweep Voltammetry mode of the CHI760E electrochemical workstation.

[0054] Through polarization curve analysis, it can be determined that the catalysts of the present application exhibit excellent OER performance under alkaline conditions. Figure 6The OER performance of the catalysts prepared in Examples 1-7 and the Ni-BDC / NF support is shown, wherein the Fe-Ni-BDC / NF has the optimal OER performance, which reaches a current density of 10 mA / cm 2 of 285.4 mV, which is reduced by 239 mV compared to the Ni-MOF / NF potential. Using different transition metals to modify the Ni-MOF, all of which reach the optimal OER performance after 5 min of electrodeposition. The reason why the Fe-Ni-BDC / NF has the optimal electrocatalytic performance is found by calculation using density functional theory (DFT): Fe is significantly stronger than Ni in the adsorption of *OH, *O and *OOH intermediates, with the most moderate adsorption strength, and the Ni site in Ni(OH)2 is too weak for the adsorption of *O and *OOH, resulting in poor OER performance. The overpotential of the transition metal single-atom catalyst to reach a current of 10 mA / cm 2 is shown in Table 2.

[0055] Table 2 OER performance of different transition metal single-atom catalysts

[0056] (2) Test the OER performance of catalysts with the same transition metal but different deposition times.

[0057] The catalysts obtained in the examples are used as the working electrode, a graphite rod is used as the counter electrode and Ag / AgCl is used as the reference electrode. A 1 M potassium hydroxide (KOH) solution is used as the electrolyte, and the OER performance of the material is tested in the Linear Sweep Voltammetry mode of a CHI760E electrochemical workstation.

[0058] Taking the Fe-Ni-BDC / NF as an example, the OER performance of catalysts electrodeposited for 120 s, 300 s, 600 s, 1200 s and 1800 s is tested. Figure 7 (a) is a catalytic performance diagram of the Fe-Ni-BDC / NF single-atom catalyst under different electrodeposition times, and it can be seen that the sample electrodeposited for 5 min exhibits the optimal point catalytic performance. At a current density of 300 mA cm -2 , the overpotential is 285.4 mV, which is reduced by 239 mV compared to the Ni-MOF / NF potential; Figure 7 (b) is the Fe-Ni-BDC / NF single-atom catalyst electrodeposited for 5 min, which exhibits a huge performance advantage in stability compared to catalysts deposited with other metals. At a current density of 100 mA cm -2 , the stability of the catalyst is checked by chronoamperometry. After 12 h of continuous testing, the OER at a current density of 300 mA cm-2 At this time, the overpotential is only increased by 9 mV. Figure 7 The analysis of polarization curves found that the sample of 5 min electrodepositing exhibits the best electrocatalytic performance and very good stability, which may be due to the low amount of metal atoms deposited in the sample of 2 min electrodepositing, resulting in insufficient performance, and the long deposition time will lead to the aggregation of metal atoms to form nanoclusters or particles, resulting in poor OER performance.

[0059] As Figure 8 The catalyst sample of Comparative Example 1 without adding NaF exhibits a large performance lag in the OER reaction, and the possible reason is that Fe is not successfully loaded in the electrodepositing process, which is also confirmed in the ICP test, and no Fe is detected in the ICP test.

[0060] Therefore, the universal preparation method of the 3D transition metal monatomic catalyst of the present application loads the transition metal monatomic catalyst on the surface of Ni-BDC / NF by the electrodepositing method, prevents the migration and aggregation of metal ions, and has the advantages of simple preparation method, excellent OER activity and selectivity of the prepared transition metal monatomic catalyst, and especially Fe-Ni-BDC / NF.

[0061] Finally, it should be noted that: the above examples are only used to illustrate the technical solutions of the present application, but not to limit them; although the present application has been described in detail with reference to the foregoing examples, those skilled in the art should understand that: it can still modify the technical solutions recorded in the foregoing examples, or make equivalent replacement for part of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present application.

Claims

1. A method for preparing a 3D transition metal single atom catalyst, characterized in that: The steps include: Step (1), pre-processing NF skeleton; Step (2), synthesis of Ni-BDC / NF precursor: preparing a mixed solution containing N,N-dimethylformamide, ethanol, water, nickel nitrate nonahydrate and terephthalic acid; placing the NF skeleton vertically in the mixed solution for hydrothermal reaction to obtain a Ni-BDC / NF precursor; Step (3), preparation of 3D transition metal single atom catalyst: electrochemical deposition is performed in a three-electrode system; wherein, a solution containing metal salt and sodium fluoride is used as the electrolyte solution, the Ni-BDC / NF precursor is used as the working electrode, the graphite rod electrode is used as the counter electrode, and the saturated calomel electrode is used as the reference electrode, and the metal atoms are deposited on the Ni-BDC / NF by constant current electrodeposition.

2. The preparation method according to claim 1, characterized in that In the step (2), the volume ratio of N,N-dimethylformamide:ethanol:water is (10-30):(1-2):1; And / or, the mass ratio of nickel nitrate nonahydrate, terephthalic acid and N,N-dimethylformamide is (6-8):(7-9):

3.

3. The preparation method according to claim 1, characterized in that In the step (2), the temperature of the hydrothermal reaction is 120-130° C., and the time is 8-12 hours.

4. The preparation method according to claim 1, characterized in that In the step (3), the metal salt includes one or more of vanadium trichloride, chromium nitrate nonahydrate, manganese chloride, iron nitrate nonahydrate, cobalt nitrate hexahydrate, copper nitrate trihydrate and zinc nitrate hexahydrate.

5. The preparation method according to claim 1, characterized in that In the step (3), the concentration ratio of the metal salt to the sodium fluoride is 1:(3-5).

6. The preparation method according to claim 1, characterized in that In step (3), the current of the constant current electrodeposition is 8-12 mA / cm 2 , time is 3-8min; the stirring rate of the three-electrode system is 700-900 r / min.

7. The preparation method according to claim 1, characterized in that The step (1) specifically comprises: washing the nickel foam in acetone and water, then ultrasonically washing it with hydrochloric acid, then washing it with water and anhydrous ethanol, and finally vacuum drying it to obtain a NF skeleton; Preferably, the hydrochloric acid concentration is 2-6 M; the ultrasonication time is 10-30 min; and the vacuum drying temperature is 50-70° C. and the time is 3-12 h.

8. A 3D transition metal single atom catalyst, characterized in that The invention is prepared by the preparation method according to any one of claims 1 to 7.

9. The 3D transition metal single atom catalyst according to claim 8, characterized in that In the 3D transition metal single atom catalyst, the loading amount of the 3D transition metal is 0.2-2 wt%; Preferably, the 3D transition metal includes one or more of V, Cr, Mn, Fe, Co, Cu and Zn, more preferably Fe.

10. Use of the 3D transition metal single atom catalyst according to claim 8 or 9 in an electrocatalytic oxygen evolution reaction.

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