Preparation method of nitrogen-doped carbon nanosheet@cobalt-nickel-iron transition metal composite material and its application in water electrolysis and hydrogen evolution

Abstract

The present invention provides a method for preparing a nitrogen-doped carbon nanosheet @ cobalt-nickel-iron three-transition metal composite material and its application in water electrolysis and hydrogen evolution. The preparation method of the composite material of the present invention is to mix melamine, cobalt acetate tetrahydrate, and nickel nitrate hexahydrate precursors, form a composite through a hydrothermal reaction, and then carry out a replacement reaction with potassium iron oxalate, and calcine at a high temperature to simultaneously realize iron-cobalt-nickel three-transition metal loading, nitrogen doping, and melamine carbonization into carbon nanosheets, and finally obtain a nitrogen-doped carbon nanosheet @ cobalt-nickel-iron three-transition metal composite material. Compared with the traditional preparation method, the method of the present invention has mild, simple, and rapid reaction conditions, one-step calcination to realize carbon nanosheet synthesis, three-transition metal loading, nitrogen doping, and high yield, and the prepared composite material has excellent electrocatalytic performance for water electrolysis and hydrogen evolution reaction.

Description

Technical Field

[0001] The invention relates to the technical field of hydrogen evolution electrocatalysis, and in particular to a preparation method of a nitrogen-doped carbon nanosheet@cobalt-nickel-iron three-transition metal composite material and its application in hydrogen evolution by electrolysis of water. Background Art

[0002] At present, traditional fossil fuels dominate the energy structure, but their reserves are limited, and their large-scale use will lead to environmental pollution and other problems. Therefore, the development of new energy to replace traditional fossil fuels has become the key to solving energy and environmental problems. Among many new energy sources, hydrogen energy stands out with its high efficiency, cleanliness, and renewable characteristics. Electrocatalytic water decomposition, as a hydrogen production technology, is regarded as a very promising hydrogen production method. This process mainly includes the oxygen evolution reaction (OER) at the anode and the hydrogen evolution reaction (HER) at the cathode, but there are problems of efficiency loss and high overpotential. It is necessary to use efficient electrocatalysts to reduce the overpotential and improve the energy conversion efficiency. Therefore, the importance of electrochemical catalysts in electrocatalytic reactions is becoming increasingly prominent.

[0003] Precious metal-based catalysts such as Pt, Ru and Ir composite materials are widely used in the field of electrocatalysis due to their excellent catalytic performance and stability. In particular, metal Pt, as a HER electrocatalyst, exhibits extremely low starting potentials in both acidic and alkaline electrolytes, but its large-scale application is limited due to its scarcity, high cost and poor durability.

[0004] Compared with precious metals, transition metals have the advantages of low cost and easy access, and are ideal substitutes for precious metals. D-block transition metals have attracted extensive attention due to their unique outer electron structure and the ability to form multiple types of complexes. For example, transition metals such as Co, Ni, and Fe are considered high-quality substitutes for precious metal nanoparticles due to their high abundance and low price.

[0005] Carbon nanomaterials are abundant in reserves, have good electrical conductivity, large specific surface area and are easy to control. They have attracted much attention in the fields of electrocatalysis, environment, energy conversion, etc., and are often used as catalytic carriers, such as activated carbon, graphene, carbon nanofibers and carbon nanotubes. Researchers are constantly developing new carbon nanomaterials, and the carbon nano family is growing and the classification is becoming more and more complicated. Carbon nanocomposites not only have adjustable porous structures and surface chemical properties, but also have many advantages as catalyst carriers, such as metal phase reduction, acid and alkali resistance, high temperature stability and low cost, and have broad application prospects. In the field of electrocatalysis, carbon nanomaterials as carriers can evenly disperse metal particles, enhance conductivity, improve catalyst stability, and synergistically improve catalytic performance. In view of the excellent performance of transition metals and carbon nanomaterials in the field of electrocatalysis, transition metal-modified carbon nanomaterials are expected to show excellent catalytic performance and become a research hotspot. The combination of transition metal-based materials and carbon matrices can improve the stability of metal-based materials, increase the conductivity of carbon-based materials, and exert excellent electrocatalytic performance. In addition, the 4d electrons of transition metals can produce high catalytic effects. Loading transition metals with poor conductivity on highly conductive carbon substrates can not only improve conductivity, but also protect active sites to enhance their catalytic performance. In addition, doping nitrogen atoms in transition metal-carbon-based materials will change the electron spin state of the atoms connected to them, thereby generating new active sites.

[0006] Patent document CN 111921551 B records a method for preparing a nitrogen-doped carbon framework material coated with an iron-cobalt-nickel ternary alloy, which uses a ball milling method to obtain an ellagic acid-iron-cobalt-nickel complex, and then adds melamine for co-pyrolysis to obtain a nitrogen-doped carbon nanotube-grafted carbon nanosheet nanoframe, in which iron-cobalt-nickel ternary transition metal alloy nanoparticles are coated. The material has high oxygen reduction and oxygen evolution dual-functional catalytic activity, and can effectively improve the efficiency of electrochemical energy storage and conversion devices such as rechargeable zinc-air batteries, proton exchange membrane fuel cells, and water electrolysis hydrogen production systems. However, the electrocatalytic hydrogen evolution performance of the material was not tested in this document, and its preparation process is relatively complicated. Summary of the invention

[0007] The purpose of the present invention is to provide a preparation method of a nitrogen-doped carbon nanosheet@cobalt-nickel-iron transition metal composite material and its application in electrolysis of water for hydrogen evolution. The preparation method of the present invention has the advantages of simple process, mild conditions and low cost, and the prepared composite material has excellent performance in electrolysis of water for hydrogen evolution.

[0008] The object of the present invention is achieved in that:

[0009] A method for preparing a nitrogen-doped carbon nanosheet@cobalt-nickel-iron transition metal composite material comprises the following steps:

[0010] (1) A methanol solution of cobalt acetate tetrahydrate and nickel nitrate hexahydrate is prepared, melamine is added to the solution, and ultrasonic treatment is performed to obtain a mixed solution; the mixed solution is transferred to an autoclave for heating, and then transferred to a flask for evaporation and drying to obtain a melamine-cobalt nickel complex; wherein the mass ratio of cobalt acetate tetrahydrate to nickel nitrate hexahydrate is 4.2:5.

[0011] (2) dispersing the melamine-cobalt-nickel complex obtained in step (1) in methanol, adding an aqueous solution of potassium iron oxalate, and standing the mixture. The obtained product is centrifuged, washed, and dried to obtain a melamine-cobalt-nickel-iron powder;

[0012] (3) The melamine-cobalt-nickel-iron powder obtained in step (2) is heated to 550° C. and calcined for 3 h under an inert atmosphere, then heated to 700° C. and calcined for 3 h, and finally heated to 900° C. and calcined for 3.5 h to obtain a nitrogen-doped carbon nanosheet@cobalt-nickel-iron transition metal composite material.

[0013] In the step (1), the ultrasonic treatment time is 10 min, the ultrasonic power is 350 W, the temperature is room temperature, the reaction temperature in the autoclave is 130° C., the reaction time is 12 h, the drying temperature is 60° C., and the drying time is 12 h.

[0014] In the step (2), the standing time is 30 minutes, the centrifugal speed is 5000 r / min, the drying temperature is 60° C., and the drying time is 12 hours.

[0015] In the step (3), the inert atmosphere is a nitrogen atmosphere, and the heating rate is 5°C / min.

[0016] The present invention also provides an application method of the obtained nitrogen-doped carbon nanosheet@cobalt-nickel-iron transition metal composite material, which comprises dispersing the nitrogen-doped carbon nanosheet@cobalt-nickel-iron transition metal material into a dispersant to obtain a dispersion liquid, applying the dispersion liquid droplets on the surface of a glassy carbon electrode, and drying the dispersion liquid to be used as a working electrode for hydrogen evolution detection, wherein the dispersant is N'N-dimethylformamide.

[0017] The present invention is to mix melamine, tetrahydrated cobalt acetate and hexahydrated nickel nitrate, form a melamine-cobalt-nickel complex through a hydrothermal reaction, and then carry out a replacement reaction with potassium iron oxalate, and carry out high-temperature calcination to simultaneously realize the loading of three transition metals of cobalt, nickel and iron, and carbonize the melamine into carbon nanosheets with nitrogen doping, and finally obtain a nitrogen-doped carbon nanosheet@cobalt, nickel and iron three transition metal composite material. After the formation of the melamine-cobalt-nickel complex, cobalt and nickel are used as seeds for subsequent potassium iron oxalate loading on the surface of melamine, so that potassium iron oxalate can be positioned on the surface of melamine to replace cobalt and nickel, and a three-metal alloy is formed to enhance the dispersibility of the transition metal on carbon. At the same time, due to the occurrence of the replacement reaction between cobalt and nickel and potassium iron oxalate, compared with the alloy formed by the one-step reaction of the three metals of cobalt, nickel and iron, the method of the present invention can reduce the size of the transition metal alloy nanoparticles, enhance its specific surface area, and thus enhance the performance of hydrogen evolution by electrolysis of water.

[0018] The preparation method of the present invention is simple, green and environmentally friendly, has low preparation cost, and mild reaction conditions (no strong acid reagent is required, no freeze drying is required). After high-temperature calcination, the three transition metals of iron, cobalt and nickel are loaded, nitrogen doped and melamine are carbonized into carbon nanosheets in one step, and finally a nitrogen-doped carbon nanosheet@cobalt, nickel and iron transition metal composite material is obtained. The melamine-cobalt nickel complex undergoes a replacement reaction with potassium iron oxalate to form a metal alloy. The metal alloy has good dispersibility on the carbon material, the metal alloy has a smaller nanoscale, a larger specific surface area, and is loaded on the surface of the carbon material, which is conducive to the exposure of catalytic active sites, all of which are conducive to enhancing the electrolytic water hydrogen evolution performance of the composite material.

[0019] The nanocomposite material prepared by the method of the present invention has excellent electrocatalytic performance, exhibits lower overpotential and Tafel slope and high capacitance value for hydrogen evolution reaction, and has good stability, thus providing a new option for the study of hydrogen evolution by electrolysis of water. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 It is a schematic diagram of the preparation process of the nitrogen-doped carbon nanosheet@cobalt-nickel-iron transition metal composite material of the present invention.

[0021] Figure 2 1 is a scanning electron microscope image of the nitrogen-doped carbon nanosheet@cobalt-nickel-iron transition metal composite material prepared in Examples 1 to 3 at a scale of 200 nm; wherein (A) is a scanning electron microscope image of the composite material prepared in Example 1, (B) is a scanning electron microscope image of the composite material prepared in Example 2, and (C) is a scanning electron microscope image of the composite material prepared in Example 3.

[0022] Figure 3The figures are transmission electron microscope images of the nitrogen-doped carbon nanosheet@cobalt-nickel-iron transition metal composite materials prepared in Examples 1 to 3; wherein (A) and (D) are transmission electron microscope images of the composite material prepared in Example 1 at a scale of 200 nm and a high-resolution transmission electron microscope image at a scale of 10 nm, respectively; (B) and (E) are transmission electron microscope images of the composite material prepared in Example 2 at a scale of 50 nm and a high-resolution transmission electron microscope image at a scale of 10 nm, respectively; (C) and (F) are transmission electron microscope images of the composite material prepared in Example 3 at a scale of 50 nm and a high-resolution transmission electron microscope image at a scale of 10 nm, respectively.

[0023] Figure 4 The nitrogen-doped carbon nanosheets@cobalt prepared in Example 1 (1) nickel (1) Element mapping diagram of Fe-III transition metal composite materials; wherein, (A) is the mapping diagram of all elements, (B) is the mapping diagram of C elements, (C) is the mapping diagram of N elements, (D) is the mapping diagram of O elements, (E) is the mapping diagram of Co elements, (F) is the mapping diagram of Fe elements, and (G) is the mapping diagram of Ni elements.

[0024] Figure 5 1 is an X-ray diffraction pattern of the nitrogen-doped carbon nanosheet@cobalt-nickel-iron transition metal composite material prepared in Examples 1 to 3.

[0025] Figure 6 The nitrogen-doped carbon nanosheets@cobalt prepared in Example 1 (1) nickel (1) X-ray photoelectron spectrum of Fe-III transition metal composite materials; wherein, (A) is the overall spectrum of the composite material, (B) is the C peak diagram, (C) is the N peak diagram, (D) is the Fe peak diagram, (E) is the Co peak diagram, and (F) is the Ni peak diagram.

[0026] Figure 7 Linear sweep voltammetric polarization curves and corresponding Tafel slope diagrams of the nitrogen-doped carbon nanosheet@cobalt-nickel-iron transition metal composite materials prepared in Examples 1 to 3 for the electrolytic water hydrogen evolution reaction; wherein (A) is a linear sweep voltammetric polarization curve diagram, and (B) is a Tafel slope diagram corresponding to (A).

[0027] Figure 8 The cyclic voltammetry curves of the nitrogen-doped carbon nanosheets@cobalt-nickel-iron transition metal composite materials prepared in Examples 1 to 3 for the electrolysis of water for hydrogen evolution reaction at different scan rates (30, 50, 70, 100, 130, 170, 200, 240, 280, 320 mV / s) in 1.0 M KOH and the linear relationship between the corresponding scan rate and the current density difference; wherein, (A) is the nitrogen-doped carbon nanosheets@cobalt-nickel-iron transition metal composite materials prepared in Example 1 (1) nickel(1) Cyclic voltammetry curve of Fe-3 transition metal composite material, (B) is the nitrogen-doped carbon nanosheet @ cobalt prepared in Example 2 (1) nickel (2) Cyclic voltammetry curve of Fe-3 transition metal composite material, (C) is the nitrogen-doped carbon nanosheet @ cobalt prepared in Example 3 (2) nickel (1) Cyclic voltammetry curve of Fe-3 transition metal composite material, (D) is the current density difference Δj (Δj=j a -j c , j a is the anode current, j c Linear fitting plot of cathodic current) and scan rate at a given potential (+0.873 V vs. RHE).

[0028] Fig. 9 The nitrogen-doped carbon nanosheets@cobalt prepared in Example 1 (1) nickel (1) A graph showing the relationship between the current density of the hydrogen evolution reaction and time for the Fe-3 transition metal composite material at a constant potential of -0.377 V. DETAILED DESCRIPTION

[0029] The present invention is further described below in conjunction with the examples. The processes and methods not described in detail in the following examples are conventional methods well known in the art. Unless otherwise specified, the raw materials or reagents used in the examples are commercially available and can be purchased through commercial channels.

[0030] Example 1

[0031] Combination Figure 1 The method for preparing the nitrogen-doped carbon nanosheet@cobalt-nickel-iron transition metal composite material provided in this embodiment comprises the following steps:

[0032] (1) Preparation of melamine-cobalt-nickel complex

[0033] 21 mg of cobalt acetate tetrahydrate and 25 mg of nickel nitrate hexahydrate were added to 60 mL of methanol, and then 2.5 g of melamine was added. The solution was ultrasonicated for 10 min at an ultrasonic power of 350 W, and then transferred to an autoclave (e.g., a Teflon-lined stainless steel autoclave) at room temperature and heated at 130 ° C for 12 hours. After that, the mixture was transferred to a 250 mL round-bottom flask and evaporated to dryness at a drying temperature of 60 ° C and a drying time of 12 hours to obtain a melamine-cobalt nickel complex.

[0034] (2) Preparation of precursor

[0035] The melamine-cobalt-nickel complex obtained in step (1) was dissolved in 20 mL of methanol, and a solution prepared by mixing 20 mL of water and 30 mg of potassium iron oxalate was added. The mixture was allowed to stand for 30 min, and then washed by centrifugation with a methanol solution at a centrifugal speed of 5000 r / min. The mixture was dried at 60° C. for 12 h to obtain melamine-cobalt-nickel-iron powder.

[0036] (3) Preparation of nitrogen-doped carbon nanosheets@cobalt-nickel-iron transition metal composites

[0037] The melamine-cobalt-nickel-iron powder obtained in step (2) was calcined at high temperature in a nitrogen atmosphere. The high temperature calcination was divided into three stages, namely: heating to 550°C, keeping the temperature constant for 3 hours, heating to 700°C, keeping the temperature constant for 3 hours, and heating to 900°C, keeping the temperature constant for 3.5 hours. The heating rate was 5°C / min to obtain a nitrogen-doped carbon nanosheet@cobalt-nickel-iron transition metal composite material. The composite material prepared in this embodiment is recorded as nitrogen-doped carbon nanosheet@cobalt (1) nickel (1) The iron-III transition metal composite material, wherein the subscript notation of cobalt and nickel refers to that the molar ratio of cobalt to nickel in the raw materials (cobalt acetate tetrahydrate and nickel nitrate hexahydrate) is about 1:1, the same below.

[0038] Example 2

[0039] Compared with Example 1, the masses of cobalt acetate tetrahydrate and nickel nitrate hexahydrate used in step (1) of this example are 21 mg and 50 mg respectively, and the rest are the same as those of Example 1 and will not be described in detail. The composite material prepared in this example is denoted as nitrogen-doped carbon nanosheets@cobalt (1) nickel (2) Iron-III transition metal composites.

[0040] Example 3

[0041] Compared with Example 1, the masses of cobalt acetate tetrahydrate and nickel nitrate hexahydrate used in step (1) of this example are 42 mg and 25 mg respectively, and the rest are the same as those of Example 1 and will not be described again. The composite material prepared in this example is denoted as nitrogen-doped carbon nanosheet@cobalt (2) nickel (1) Iron-III transition metal composites.

[0042] The composite materials prepared in Examples 1 to 3 were characterized by their structures. Figure 2~Figure 6 shown.

[0043] Figure 2The scanning electron microscope images of the nitrogen-doped carbon nanosheets@cobalt-nickel-iron three-transition metal composite materials prepared in Examples 1 to 3 are shown. The microstructure of the nitrogen-doped carbon nanosheets@cobalt-nickel-iron three-transition metal composite materials at a scale of 200 nm can be clearly observed through the scanning electron microscope images. The morphology of the carbon nanosheets is visible, the surface is relatively rough, and the metal nanoparticles are loaded on the carbon nanosheets. The scanning electron microscope images can confirm that the nitrogen-doped carbon nanosheets@cobalt-nickel-iron three-transition metal composite materials are successfully synthesized.

[0044] Figure 3 The transmission electron microscope images of the nitrogen-doped carbon nanosheet@cobalt-nickel-iron transition metal composite materials prepared in Examples 1 to 3 are shown. Figure 3 It can be seen that the metal nanoparticles are loaded onto the carbon nanosheets, and the lattice fringes are clearly visible, confirming the successful loading of the metal nanoparticles and the successful synthesis of the nitrogen-doped carbon nanosheet@cobalt-nickel-iron transition metal composite material.

[0045] Figure 4 The nitrogen-doped carbon nanosheets@cobalt prepared in Example 1 (1) nickel (1) Elemental mapping image of Fe-3 transition metal composites. Figure 4 It can be seen that the nitrogen-doped carbon nanosheets@cobalt prepared in Example 1 (1) nickel (1) The Fe-3 transition metal composite material is composed of C, N, O, Fe, Co and Ni elements, and each element is evenly distributed.

[0046] Figure 5 is the X-ray diffraction pattern of the nitrogen-doped carbon nanosheet@cobalt-nickel-iron transition metal composite material prepared in Examples 1 to 3. Figure 5 It can be seen that the composite materials in Examples 1 to 3 exhibit similar characteristic peaks, 2θ=22.31° and 27.41° correspond to the (110) and (200) crystal planes of Co (PDF#74-1229). 2θ=30.11° corresponds to Fe 3 The (101) crystal plane of N (PDF#76-0091), 2θ=44.49° and 51.84° correspond to the (111) and (200) crystal planes of Ni (PDF#87-0712), 2θ=25.09° corresponds to the (111) and (200) crystal planes of Ni (PDF#87-0712). 3 Fe (100) crystal plane (PDF#88-1715). Therefore, it can be proved that Fe, Co, and Ni are successfully loaded onto nitrogen-doped carbon nanosheets.

[0047] Figure 6 The nitrogen-doped carbon nanosheets@cobalt prepared in Example 1 (1) nickel (1) X-ray photoelectron spectrum of Fe-3 transition metal composites. Figure 6(B) shows that C is divided into three peaks: CC, O=C=O and CO; (C) shows the two peaks of doped N, pyridinic N and pyrrolic N; (D) shows the peaks of Fe, the peaks at 713.3 eV and 725.2 eV correspond to Fe-Nx, the peak at a binding energy of 710.8 eV corresponds to Fe 2p3 / 2, the peak at a binding energy of 717.38 eV corresponds to Fe 2p3 / 2, and the peak at 719.8 eV is a satellite peak; (E) shows the peaks of Co, the peaks at 780.8 eV and 786.6 eV correspond to Co 3+ morphology, 796.2 eV corresponds to Co 2p1 / 2; (F) shows the Ni peak, which is mainly divided into three forms: Ni 2p3 / 2 (856.3 eV), Ni 2p1 / 2 (873.3 eV) and satellite peak (862.5 eV).

[0048] The electrocatalytic performance of the composite materials prepared in the above three embodiments for hydrogen evolution reaction in water electrolysis was tested below.

[0049] The nitrogen-doped carbon nanosheet@cobalt-nickel-iron transition metal composite materials prepared in Examples 1 to 3 were applied to the electrocatalysis of hydrogen evolution reaction in hydrogen production by electrohydrolysis, and the electrocatalytic performance of three composite materials with different cobalt-nickel raw material ratios was compared, and the specific steps were as follows:

[0050] 1) A three-electrode test system (Autolab 302N electrochemical workstation) was used, with a standard hydrogen electrode as the reference electrode, a platinum wire as the counter electrode, a glassy carbon electrode modified with the prepared composite material as the working electrode, and a 1 mol / L potassium hydroxide solution.

[0051] 2) Disperse 2 mg of the prepared composite material in 1 mL of N'N-dimethylformamide solution (to a concentration of 2 mg / mL) to form a dispersion, and apply 5 µL of the dispersion droplet on the surface of the glassy carbon electrode, and dry it under an infrared lamp (150 W) to form a working electrode.

[0052] 3) Place the three electrodes in an electrolytic cell, immerse them in potassium hydroxide solution, select the electrochemical method, set the parameters, and conduct electrochemical testing of the hydrogen evolution reaction.

[0053] Test results see Figure 7-9 ,Depend on Figure 7 and Figure 8 It can be seen that compared with the composite materials prepared in Examples 2 and 3, the composite material prepared in Example 1 has higher electrocatalytic performance for hydrogen evolution reaction, which is manifested by lower overpotential (10 mA cm -2Under the current density, the overpotential of the material in Example 1 for HER is 385mV, the overpotential in Example 2 is 410mV, and the overpotential in Example 3 is 400mV), a smaller Tafel slope (the Tafel slopes corresponding to Examples 1 to 3 are 106mV / dec, 131mV / dec, and 127mV / dec, respectively) and a higher capacitance value (the capacitance values ​​corresponding to Examples 1 to 3 are: 0.3756 mF / cm 2 , 0.1252mF / cm 2 , 0.3471 mF / cm 2 ).

[0054] Fig. 9 It is shown that the current value of the composite material prepared in Example 1 of the present invention catalyzing the hydrogen evolution reaction only decays by 8.4% after 24 hours, and has good stability.

[0055] Comparative Example 1

[0056] A method for preparing a nitrogen-doped carbon nanosheet@cobalt-nickel-iron transition metal composite material comprises the following steps:

[0057] (1) Take 21 mg of cobalt acetate tetrahydrate and 25 mg of nickel nitrate hexahydrate and dissolve them in 60 mL of methanol solution. Add 2.5 g of melamine to the above solution, add a solution mixed with 20 mL of water and 30 mg of potassium iron oxalate, and ultrasonically treat for 10 min at an ultrasonic power of 350 W. Then transfer to an autoclave (e.g., a Teflon-lined stainless steel autoclave) at room temperature and heat at 130°C for 12 hours. Then, transfer the mixture to a 250 mL round-bottom flask and evaporate to dryness at a drying temperature of 60°C for 12 hours to obtain a melamine-cobalt-nickel-iron complex.

[0058] (2) The melamine-cobalt-nickel-iron composite obtained in step (1) was washed by centrifugation with a methanol solution at a centrifugal speed of 5000 r / min, and dried at 60°C for 12 h to obtain a melamine-cobalt-nickel-iron powder, which was then calcined at high temperature in a nitrogen atmosphere. The high-temperature calcination was divided into three stages, namely: heating to 550°C, keeping the temperature constant for 3 h, heating to 700°C, keeping the temperature constant for 3 h, and heating to 900°C, keeping the temperature constant for 3.5 h. The heating rate was 5°C / min to obtain a nitrogen-doped carbon nanosheet@cobalt-nickel-iron transition metal composite material.

[0059] The composite material prepared in Comparative Example 1 was applied to the electrolysis of water for hydrogen evolution reaction according to the aforementioned method, and its Tafel slope was 156 mV dec. -1 , at 10mA cm -2 The overpotential at the current density is 460mV and the capacitance is 0.1136mF / cm 2The Tafel slope of the composite material catalyzing the hydrogen evolution reaction of water electrolysis in Example 1 is 106 mV dec -1 , at 10mA cm -2 The overpotential at the current density is 385mV and the capacitance is 0.3756mF / cm 2 It can be seen that compared with Comparative Example 1, Example 1 of the present application has a lower overpotential, a smaller Tafel slope and a higher capacitance value.

[0060] Compared with Comparative Example 1, after the melamine-cobalt-nickel complex is formed, cobalt-nickel acts as a seed for subsequent potassium iron oxalate loading on the surface of melamine, so that potassium iron oxalate can be positioned on the surface of melamine to replace cobalt-nickel, and a tri-metal alloy is formed, thereby enhancing the dispersion of transition metals on carbon. At the same time, due to the occurrence of the replacement reaction between cobalt-nickel and potassium iron oxalate, compared with the one-step reaction of the three metals to form an alloy in Comparative Example 1, Example 1 can reduce the size of the transition metal alloy nanoparticles, enhance its specific surface area, and thereby enhance the performance of hydrogen evolution by electrolysis of water.

Claims

1. A method for preparing a nitrogen-doped carbon nanosheet@cobalt-nickel-iron transition metal composite material, characterized in that: The steps include: (1) preparing a methanol solution of cobalt acetate tetrahydrate and nickel nitrate hexahydrate, adding melamine to the solution, and subjecting the solution to ultrasonic treatment to obtain a mixed solution; transferring the mixed solution to an autoclave for heating, and then transferring the mixed solution to a flask for evaporation and drying to obtain a melamine-cobalt nickel complex; wherein the mass ratio of cobalt acetate tetrahydrate to nickel nitrate hexahydrate is 4.2:5; (2) dispersing the melamine-cobalt-nickel complex obtained in step (1) in methanol, adding an aqueous solution of potassium iron oxalate, and standing the mixture. The obtained product is centrifuged, washed, and dried to obtain a melamine-cobalt-nickel-iron powder; (3) The melamine-cobalt-nickel-iron powder obtained in step (2) is heated to 550° C. under an inert atmosphere for 3 h, then heated to 700° C. for 3 h, and finally heated to 900° C. for 3.5 h to obtain a nitrogen-doped carbon nanosheet@cobalt-nickel-iron transition metal composite material.

2. The method for preparing the nitrogen-doped carbon nanosheet@cobalt-nickel-iron transition metal composite material according to claim 1, characterized in that: In the step (1), the ultrasonic treatment time is 10 minutes, the autoclave is heated at 130° C. for 12 hours, the drying temperature is 60° C., and the drying time is 12 hours.

3. The method for preparing the nitrogen-doped carbon nanosheet@cobalt-nickel-iron transition metal composite material according to claim 1, characterized in that: In the step (2), the standing time is 30 minutes, the drying temperature is 60° C., and the drying time is 12 hours.

4. The method for preparing the nitrogen-doped carbon nanosheet@cobalt-nickel-iron transition metal composite material according to claim 1, characterized in that: In the step (3), the inert atmosphere is a nitrogen atmosphere, and the heating rate is 5°C / min.

5. Use of the nitrogen-doped carbon nanosheet@cobalt-nickel-iron transition metal composite material prepared by the method according to any one of claims 1 to 4 as a catalyst in hydrogen evolution reaction by electrolysis of water.

6. The use according to claim 5, characterized in that: The application method is as follows: dispersing the nitrogen-doped carbon nanosheet@cobalt-nickel-iron transition metal composite material into a dispersant to obtain a dispersion liquid, applying the dispersion liquid droplets on the surface of a glassy carbon electrode, and drying to obtain a working electrode.

7. The use according to claim 6, characterized in that: The dispersant is N'N-dimethylformamide.

8. The use according to claim 6, characterized in that: In the hydrogen evolution reaction by water electrolysis, the standard hydrogen electrode is used as the reference electrode and the platinum wire is used as the counter electrode.

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