CN110451489B

CN110451489B - Cobalt nitride embedded porous nitrogen-doped graphene material, and preparation method and application thereof

Info

Publication number: CN110451489B
Application number: CN201910729287.4A
Authority: CN
Inventors: 张进涛; 舒欣欣; 马继臻
Original assignee: Shenzhen Research Institute Of Shandong University; Shandong University
Current assignee: Shenzhen Research Institute Of Shandong University; Shandong University
Priority date: 2019-08-08
Filing date: 2019-08-08
Publication date: 2021-03-16
Anticipated expiration: 2039-08-08
Also published as: CN110451489A

Abstract

The disclosure provides a cobalt nitride embedded porous nitrogen-doped graphene material, and a preparation method and application thereof, wherein the cobalt nitride embedded porous nitrogen-doped graphene material comprises nitrogen-doped graphene and Co_5.47N nanoparticles, a cellular structure with worm-like traces on the surface of the nitrogen-doped graphene, Co_5.47The N nanoparticles are embedded at the ends of the pore-like structures of the worm-like traces. The preparation method comprises the following steps: sequentially adding cobalt acetate and tannic acid into the dispersion liquid of the graphene oxide, uniformly mixing to obtain a suspension, separating out solid materials in the suspension, and heating to a temperature of not lower than 600 ℃ in a mixed atmosphere of nitrogen and ammonia gas for pyrolysis. The present disclosure provides materials that exhibit effective multifunctional catalytic activity on ORR, HER, and OER in alkaline solutions.

Description

Cobalt nitride embedded porous nitrogen-doped graphene material, and preparation method and application thereof

Technical Field

The disclosure belongs to the field of electrochemistry, relates to an electrocatalyst, and particularly relates to a cobalt nitride embedded porous nitrogen-doped graphene material, and a preparation method and application thereof.

Background

The statements herein merely provide background information related to the present disclosure and may not necessarily constitute prior art.

The large consumption of traditional fossil fuels leads to serious climate and environmental problems, which have raised concerns for developing clean and efficient electrochemical energy conversion and storage technologies, such as fuel cells, metal air batteries, and water electrolysis devices. The performance of these energy storage and conversion devices is determined by several fundamental electrochemical reactions. For example, rechargeable zinc-air batteries are receiving increasing attention due to their advantages of low cost, environmental friendliness, and high theoretical energy density. The Oxygen Evolution Reaction (OER) and the Oxygen Reduction Reaction (ORR) are two key half-reactions that determine the final performance of a zinc-air cell. In addition, electrolysis of water mainly involves Hydrogen Evolution Reaction (HER) and Oxygen Evolution Reaction (OER), which is a very promising method for obtaining clean hydrogen energy. Due to the multiple electron transfer process and slow kinetics of ORR, OER and HER, highly efficient electrocatalysts are needed to reduce the reaction overpotential and increase the conversion efficiency. To date, significant advances have been made in single-function OER or ORR electrocatalysts. For example, platinum (Pt) and its alloy based catalysts are effective ORR/HER catalysts, while ruthenium (Ru)/iridium (Ir) and its oxides represent the most advanced catalyst materials for OER. However, as far as the present inventors have learned, such noble metal-based catalysts have limited reserves, are costly, have poor stability, and generally cannot be used as multifunctional electrocatalysts for ORR, HER, and OER simultaneously.

Disclosure of Invention

In order to overcome the defects of the prior art, the present disclosure aims to provide a cobalt nitride embedded porous nitrogen-doped graphene material, and a preparation method and an application thereof, wherein the material shows effective multifunctional catalytic activity on ORR, HER and OER in an alkaline solution.

In order to achieve the purpose, the technical scheme of the disclosure is as follows:

in a first aspect, the present disclosure provides a cobalt nitride embedded porous nitrogen-doped graphene material comprising nitrogen-doped graphene and Co_5.47N nanoparticles, a cellular structure with worm-like traces on the surface of the nitrogen-doped graphene, Co_5.47The N nanoparticles are embedded at the ends of the pore-like structures of the worm-like traces.

Co in materials provided by the present disclosure_5.47The N nano-particles are embedded at the tail ends of the pore-shaped structures of the worm-shaped traces, so that the rapid interface electron transfer and ion diffusion of corresponding reactions can be promoted, and meanwhile, the aggregation and crushing of the cobalt nitride nano-particles can be effectively inhibited, so that the material disclosed by the invention has effective multifunctional catalytic activity on ORR, HER and OER in an alkaline solution.

In a second aspect, the disclosure provides a preparation method of a cobalt nitride embedded porous nitrogen-doped graphene material, which comprises the steps of sequentially adding cobalt acetate and tannic acid into a dispersion liquid of graphene oxide, uniformly mixing to obtain a suspension, separating solid materials in the suspension, and heating to a temperature of not lower than 600 ℃ in a mixed atmosphere of nitrogen and ammonia gas for pyrolysis.

Tannic acid in the present disclosure has a benzene ring structure, and can form pi-pi accumulated electrostatic interaction with graphene oxide, so that tannic acid can be stably combined on graphene oxide, and meanwhile tannic acid has phenolic hydroxyl group which can be combined with Co²⁺Ion chelation forms a stable five-membered chelate ring, which in turn enables Co to be chelated by tannic acid²⁺And dispersing ions to the surface of the graphene oxide. Secondly, it is found through experiments that only cobalt acetate can embed Co on the nitrogen-doped graphene through the method_5.47N, and other cobalt salts, such as cobalt chloride, cobalt nitrate, cobalt sulfate, etc., cannot embed Co into nitrogen-doped graphene_5.47And N is added. Third, the fabrication method of the present disclosure enables the formation of Co_5.47The thermal etching motion of the N nanoparticles on the reduced graphene oxide surface will result in the formation of worm-like pores during nitridation, which will generate more surface defects to enhance the electrocatalytic activity.

In a third aspect, the disclosure provides an application of the cobalt nitride embedded porous nitrogen-doped graphene material in the field of metal-air batteries and/or in electrolytic water.

In a fourth aspect, the present disclosure provides an electrode material comprising the cobalt nitride embedded porous nitrogen-doped graphene material.

In a fifth aspect, the present disclosure provides a zinc-air battery, wherein the cobalt nitride embedded porous nitrogen-doped graphene material is used as an air cathode.

In a sixth aspect, the present disclosure provides an electrocatalyst, wherein the active component is the cobalt nitride embedded porous nitrogen-doped graphene material.

In a seventh aspect, the present disclosure provides a method for electrolyzing water, in which the cobalt nitride is embedded in a porous nitrogen-doped graphene material as an electrocatalyst, and a zinc-air battery is used to decompose water into hydrogen and oxygen.

The beneficial effect of this disclosure does:

preparation method of the present disclosure in layered porous rGO sheetsIn situ synthesis of Co_5.47N nanoparticles, Co_5.47The in situ formation and thermo-kinetic etching of N nanoparticles results in the formation of worm-like channels and pores on the rGO surface. The material prepared by the present disclosure has excellent electrocatalytic activity for ORR, HER and OER, and can be made into rechargeable zinc-air batteries. The prepared zinc-air battery has high open-circuit potential (1.45V) and high power density (120.7 mWcm) at 0.67V^-2) Excellent cycle stability over 330h and good rechargability. In addition, the material disclosed by the invention has a good gas generation rate when being used for electrolyzing water.

Drawings

The accompanying drawings, which are included to provide a further understanding of the disclosure, illustrate embodiments of the disclosure and together with the description serve to explain the disclosure and are not to limit the disclosure.

FIG. 1 is Co prepared according to example 3 of the present disclosure_5.47N @ N-rGO-750, wherein a is a scanning electron microscope and b is a transmission electron microscope;

FIG. 2 shows Co prepared separately in examples 1, 2, 4 of the present disclosure_5.47N@N-rGO-650、Co_5.47N@N-rGO-700、Co_5.47Electron micrograph of N @ N-rGO-800, a is Co_5.47Scanning electron micrograph of N @ N-rGO-650, b is Co_5.47Scanning electron micrograph of N @ N-rGO-650, c is Co_5.47Transmission electron micrograph of N @ N-rGO-650, d is Co_5.47Scanning electron micrograph of N @ N-rGO-700, e is Co_5.47Scanning electron micrograph of N @ N-rGO-700, f is Co_5.47Transmission electron micrograph of N @ N-rGO-700, g is Co_5.47Scanning electron micrograph of N @ N-rGO-800, h is Co_5.47Scanning electron micrograph of N @ N-rGO-800, i is Co_5.47Transmission electron microscope photograph of N @ N-rGO-800;

FIG. 3 shows Co prepared in examples 1 to 4 of the present disclosure_5.47N@N-rGO-650、Co_5.47N@N-rGO-700、Co_5.47N@N-rGO-750、Co_5.47An XRD spectrum of N @ N-rGO-800;

FIG. 4 is Co prepared according to example 5 of the present disclosure_5.47N @ N-rGO-750-2h scanning electron microscope picture;

FIG. 5 is a drawing showingCo prepared in example 6 of this disclosure_5.47N @ N-rGO-750-3h scanning electron microscope picture;

FIG. 6 shows Co prepared in examples 5 and 6 of the present disclosure_5.47N@N-rGO-750-2h、Co_5.47N @ N-rGO-750-3h XRD spectrum;

FIG. 7 shows Co prepared in examples 1 to 4 of the present disclosure_5.47N@N-rGO-650、Co_5.47N@N-rGO-700、Co_5.47N@N-rGO-750、Co_5.47Cyclic Voltammogram (CV) of N @ N-rGO-800;

FIG. 8 shows Co prepared in examples 1 to 4 of the present disclosure_5.47N@N-rGO-650、Co_5.47N@N-rGO-700、Co_5.47N@N-rGO-750、Co_5.47ORR-OER polarization curve of N @ N-rGO-800;

FIG. 9 is Co prepared according to example 3 of the present disclosure_5.47The cyclic charge-discharge curve of the N @ N-rGO-750 catalyst in the liquid zinc-air battery;

FIG. 10 shows Co prepared in examples 1-4 of the present disclosure_5.47N@N-rGO-650、Co_5.47N@N-rGO-700、Co_5.47N@N-rGO-750、Co_5.47HER polarization curves for N @ N-rGO-800 and Pt/C.

Detailed Description

It should be noted that the following detailed description is exemplary and is intended to provide further explanation of the disclosure. Unless defined otherwise, 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 disclosure belongs.

It is noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of example embodiments according to the present disclosure. As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, and it should be understood that when the terms "comprises" and/or "comprising" are used in this specification, they specify the presence of stated features, steps, operations, devices, components, and/or combinations thereof, unless the context clearly indicates otherwise.

In view of the fact that the existing noble metal-based catalyst cannot be used as an ORR, HER and OER multifunctional electrocatalyst at the same time, the present disclosure provides a cobalt nitride embedded porous nitrogen-doped graphene material, and a preparation method and an application thereof.

In an exemplary embodiment of the present disclosure, a cobalt nitride embedded porous nitrogen-doped graphene material is provided, which includes nitrogen-doped graphene and Co_5.47N nanoparticles, a cellular structure with worm-like traces on the surface of the nitrogen-doped graphene, Co_5.47The N nanoparticles are embedded at the ends of the pore-like structures of the worm-like traces.

In one or more embodiments of this embodiment, the graphene is reduced graphene oxide.

In another embodiment of the disclosure, cobalt acetate and tannic acid are sequentially added into a dispersion liquid of graphene oxide and uniformly mixed to obtain a suspension, and after solid materials in the suspension are separated, the suspension is heated to be not lower than 600 ℃ in a mixed atmosphere of nitrogen and ammonia gas for pyrolysis.

Tannic acid in the disclosure has a benzene ring structure and can interact with static electricity accumulated in graphene oxide pi-pi, so that tannic acid can be stably combined on graphene oxide, and meanwhile, two adjacent phenol oxygen molecules in tannic acid are towards Co²⁺The empty d orbit of the ion provides lone pair electrons, thereby forming a stable five-membered chelate ring, and further enabling Co to be chelated by tannic acid²⁺And dispersing ions to the surface of the graphene oxide. Secondly, it is found through experiments that only cobalt acetate can embed Co on the nitrogen-doped graphene through the method_5.47N, and other cobalt salts, such as cobalt chloride, cobalt nitrate, cobalt sulfate, etc., cannot embed Co into nitrogen-doped graphene_5.47And N is added. Third, the fabrication method of the present disclosure enables the formation of Co_5.47Reduction of oxidized stone with N nano particlesThe thermal etching motion on the graphene surface will result in the formation of worm-like pores during nitridation, which will generate more surface defects to enhance the electrocatalytic activity.

The pyrolysis in the present disclosure achieves the simultaneous reduction of GO and in NH₃In situ formation of Co in the presence of_5.47And N nano-particles.

In one or more embodiments of the embodiment, cobalt acetate is added into the graphene oxide dispersion liquid for uniform dispersion, then tannic acid is added and uniformly mixed to obtain a suspension, solid materials in the suspension are separated, washed and dried, and then heated to be not lower than 600 ℃ in a mixed atmosphere of nitrogen and ammonia gas for pyrolysis.

In one or more embodiments of the present disclosure, the graphene oxide, the cobalt acetate, and the tannic acid are added at a ratio of 55-65: 0.001-0.003: 0.7-0.8, mg: mol: g.

in one or more embodiments of this embodiment, the volume ratio of nitrogen to ammonia is 2.5 to 3.5: 1.

In one or more embodiments of this embodiment, the pyrolysis temperature is 650 to 800 ℃. When the pyrolysis temperature is 740-760 ℃, the performance of the prepared material is better.

In one or more embodiments of this embodiment, the pyrolysis temperature is between 0.5 and 5 hours.

Graphene oxide of the present disclosure is prepared from natural graphite flakes by a modified Hummers method.

According to a third embodiment of the disclosure, an application of the cobalt nitride embedded porous nitrogen-doped graphene material in the field of metal-air batteries and/or in electrolytic water is provided.

In a fourth embodiment of the present disclosure, an electrode material is provided, which includes the cobalt nitride embedded porous nitrogen-doped graphene material.

In a fifth embodiment of the present disclosure, a zinc-air battery is provided, in which the cobalt nitride is embedded in a porous nitrogen-doped graphene material as an air cathode catalyst.

In one or more embodiments of the present disclosure, the air cathode is prepared by coating cobalt nitride embedded porous nitrogen-doped graphene material on carbon paper with an adhesive, and drying.

In one or more embodiments of this embodiment, the zinc-air cell is an aqueous zinc-air cell or a solid-state zinc-air cell.

In a sixth embodiment of the present disclosure, an electrocatalyst is provided, wherein the active component is the cobalt nitride embedded porous nitrogen-doped graphene material.

In a seventh embodiment of the present disclosure, a method for electrolyzing water is provided, in which the cobalt nitride is embedded in a porous nitrogen-doped graphene material as an electrocatalyst, and water is decomposed into hydrogen and oxygen by supplying power to an aqueous zinc-air battery.

In one or more embodiments of this embodiment, the battery is a zinc-air battery.

For more convenient experiments, the zinc-air battery provided by the disclosure is adopted when water is decomposed.

In order to make the technical solutions of the present disclosure more clearly understood by those skilled in the art, the technical solutions of the present disclosure will be described in detail below with reference to specific embodiments.

Graphene Oxide (GO) used in the following examples was prepared from natural graphite flakes by a modified Hummers method.

Example 1

40mL of GO dispersion (1.5mg mL)^-1) Sonication for 20 min, then 2mmol (0.4982g) Co (OAc) were added with vigorous stirring₂·4H₂And O. Subsequently, tannic acid (0.75g) was dissolved in 10mL of deionized water and added to the above mixed solution. The resulting suspension was washed with centrifugal water and flash frozen with liquid nitrogen followed by drying for 12 hours. The resulting sample was loaded into a tube furnace and heated at N₂：NH₃The ratio is 3: 1 to 650 ℃ at a heating rate of 10 ℃/min, pyrolyzing for 1 hour to obtain a sample, and recording as Co_5.47N@N-rGO-650。

Example 2

40mL of GO dispersion (1.5mg mL)^-1) Sonicate for 20 minutes and then add under vigorous agitation2mmol (0.4982g) Co (OAc)₂·4H₂And O. Subsequently, tannic acid (0.75g) was dissolved in 10mL of deionized water and added to the above mixed solution. The resulting suspension was washed with centrifugal water and flash frozen with liquid nitrogen followed by drying for 12 hours. The resulting sample was loaded into a tube furnace and heated at N₂：NH₃The ratio is 3: 1 to 700 ℃ at a heating rate of 10 ℃/min, pyrolyzing for 1 hour to obtain a sample, and recording as Co_5.47N@N-rGO-700。

Example 3

40mL of GO dispersion (1.5mg mL)^-1) Sonication for 20 minutes, followed by addition of 0.4982g Co (OAc) with vigorous stirring₂·4H₂And O. Subsequently, tannic acid (0.75g) was dissolved in 10mL of deionized water and added to the above mixed solution. The resulting suspension was washed with centrifugal water and flash frozen with liquid nitrogen followed by drying for 12 hours. The resulting sample was loaded into a tube furnace and heated at N₂：NH₃The ratio is 3: 1 to 750 ℃ at a heating rate of 10 ℃/min, pyrolyzing for 1 hour to obtain a sample, and recording as Co_5.47N@N-rGO-750。

Example 4

40mL of GO dispersion (1.5mg mL)^-1) Sonication for 20 min, then 2mmol (0.4982g) Co (OAc) were added with vigorous stirring₂·4H₂And O. Subsequently, tannic acid (0.75g) was dissolved in 10mL of deionized water and added to the above mixed solution. The resulting suspension was washed with centrifugal water and flash frozen with liquid nitrogen followed by drying for 12 hours. The resulting sample was loaded into a tube furnace and heated at N₂：NH₃The ratio is 3: 1 to 800 ℃ at a heating rate of 10 ℃/min, pyrolyzing for 1 hour to obtain a sample, and recording as Co_5.47N@N-rGO-800。

Example 5

40mL of GO dispersion (1.5mg mL)^-1) Sonication for 20 min, then 2mmol (0.4982g) Co (OAc) were added with vigorous stirring₂·4H₂And O. Subsequently, tannic acid (0.75g) was dissolved in 10mL of deionized water and added to the above mixed solution. The resulting suspension was washed with centrifugal water and flash frozen with liquid nitrogen followed by drying for 12 hours.The resulting sample was loaded into a tube furnace and heated at N₂：NH₃The ratio is 3: 1 to 750 ℃ at a heating rate of 10 ℃/min, pyrolyzing for 2 hours to obtain a sample, and recording as Co_5.47N@N-rGO-750-2h。

Example 6

40mL of GO dispersion (1.5mg mL)^-1) Sonication for 20 min, then 2mmol (0.4982g) Co (OAc) were added with vigorous stirring₂·4H₂And O. Subsequently, tannic acid (0.75g) was dissolved in 10mL of deionized water and added to the above mixed solution. The resulting suspension was washed with centrifugal water and flash frozen with liquid nitrogen followed by drying for 12 hours. The resulting sample was loaded into a tube furnace and heated at N₂：NH₃The ratio is 3: 1 to 750 ℃ at a heating rate of 10 ℃/min, and pyrolyzing for 3 hours to obtain a sample, which is recorded as Co_5.47N@N-rGO-750-3h。

Example 7

40mL of GO dispersion (1.5mg mL)^-1) Sonication for 20 min, then 2mmol (0.4982g) Co (OAc) were added with vigorous stirring₂·4H₂And O. The resulting suspension was washed with centrifugal water and flash frozen with liquid nitrogen followed by drying for 12 hours. The resulting sample was loaded into a tube furnace and heated at N₂：NH₃The ratio is 3: 1 to 750 ℃ at a heating rate of 10 ℃/min, and pyrolyzing for 1 hour to obtain a sample, which is marked as Co @ N-rGO-750.

Example 8

40mL of GO dispersion (1.5mg mL)^-1) Sonication for 20 min, then 2mmol (0.4759g) of CoCl were added with vigorous stirring₂·6H₂And O. Subsequently, tannic acid (0.75g) was dissolved in 10mL of deionized water and added to the above mixed solution. The reaction could not proceed.

Example 9

40mL of GO dispersion (1.5mg mL)^-1) Sonicate for 20 minutes, then add 2mmolCo (NO) with vigorous stirring₃)₂·6H₂O (0.5821 g). Subsequently, tannic acid (0.75g) was dissolved in 10mL of deionized water and added to the above mixed solution. The reaction could not proceed.

Example 10

40mL of GO dispersion (1.5mg mL)^-1) Sonicate for 20 minutes, then add 2mmolCoSO with vigorous stirring₄·7H₂O (0.5622 g). Subsequently, tannic acid (0.75g) was dissolved in 10mL of deionized water and added to the above mixed solution. The reaction could not proceed.

Characterization of the sample materials prepared in the above examples

Structural characterization

Scanning Electron Microscopy (SEM) was performed by Gemini-SEM-300, Carl Zeiss Microcopy GmbH, and Transmission Electron Microscopy (TEM) was performed on JEOL 2100 PLUS. X-ray diffraction (XRD) was performed by using an X' Pert3 powder X-ray diffractometer. High Resolution Transmission Electron Microscopy (HRTEM) was performed on the FEI-TF20 scientific compass. X-ray photoelectron spectroscopy (XPS) was performed with an electron spectrometer (ESCALAB 250). Raman spectroscopy was performed on a LabRAM HR800 with an excitation laser at 532 nm. N was measured at 77K using a BJ Builder Kubo-X1000 instrument₂Adsorption isotherms.

Electrochemical characterization

Electrochemical testing was performed by using a CHI 760E electrochemical workstation (CH Instrument, Shanghai) with a three-electrode system. A glassy carbon rotating disk electrode (RRDE) coated with the prepared catalyst was used as a working electrode, while an Ag/AgCl electrode and a graphite rod (or Pt sheet) were used as a reference electrode and a counter electrode, respectively. All potentials were measured relative to the Ag/AgCl electrode and calibrated to the reversible hydrogen electrode according to the following equation: e_RHE＝E_Ag/AgCl+0.197+0.0591 × pH. To prepare a catalyst sample solution, 5mg of each example prepared sample was blended with 50 μ L of an ethanol solution (750 μ L of water +250 μ L of absolute ethanol) in 1mL of ethanol solution (5 wt%) under sonication to obtain a homogeneous catalyst sample solution. Then, 12 μ L of the catalyst sample was dropped onto the glassy carbon electrode surface and dried at room temperature. For comparison, Pt/C (20 wt%, ETEK) electrodes were prepared using the same procedure. Cyclic voltammetry measurement at N₂Or O₂Saturated 0.1M KOH electrolyte at-1.0V to 0.2V (vs. Ag/AgCl) at 10mV s^-1Is performed at the scanning rate of (1). LSV curve passage of Oxygen Reduction Reaction (ORR)Using RDE at O₂Saturated 0.1M KOH with 5mV s^-1At a catalyst loading of 0.24mg cm^-2. Oxygen Evolution Reaction (OER) and Hydrogen Evolution Reaction (HER) measurements were respectively at O₂、N₂Saturated 1.0M KOH at 5mV s^-1At a catalyst loading of 0.5mg cm^-2. The carbon paper used had an area of (1X 1 cm).

Assembly of zinc-air cell

By mixing the prepared catalyst ink (5mg ml)^-1) An air electrode was prepared by coating Polytetrafluoroethylene (PTFE) as a binder on carbon paper and drying at 80 ℃ for 2 hours with a catalyst loading of 0.75mg cm^-2。

Aqueous zinc-air battery: the electrochemical cell contains liquid electrolyte, which is 6M potassium hydroxide and 0.2M zinc acetate, and the air electrode and the zinc sheet are respectively used as a cathode and an anode.

Solid state zinc-air battery: 6.3g KOH and 0.20g ZnO were mixed in 9mL water, and the resulting solution was named solution A, 0.15g N, N' -Methylenebisacrylamide (MBA) was added to 0.95mL acrylic acid to prepare solution B, then solution A and solution B were slowly mixed together and kept stirring for 5 minutes, and then 120. mu.LK was added₂S₂O₈To initiate polymerization to obtain polyacrylic acid (PAA) gel-like solid electrolyte. And assembling the prepared air electrode, the zinc foil and a piece of polymer electrolyte into a sandwich structure, and sealing by using an acrylic adhesive tape.

Characterization results

The morphology and structure of all samples were observed by SEM and TEM. As shown in FIG. 1a, Co_5.47SEM image of N @ N-rGO-750 shows a two-dimensional rGO sheet, Co, with many pores_5.47N nanoparticles are uniformly dispersed thereon. Magnified SEM images show that the nanoparticles are uniformly dispersed on the surface of rGO and many worm-like pores can be seen on the surface. In particular, magnified TEM images show worm-like traces on the surface of rGO sheets forming nanoparticles at the end of the traces (fig. 1 b). Co_5.47The thermal etch motion of N nanoparticles on rGO surface will lead to worm formation during nitridationLike pores, which will generate more surface defects to enhance the electrocatalytic activity. At the same pyrolysis temperature, Co_5.47The particle size of N @ N-rGO-750 is far smaller than that of Co @ N-rGO-750 prepared without TA. These results indicate that TA not only regulates the size of the cobalt-containing compounds, but also ensures complete phase conversion to Co during pyrolysis_5.47N。Co_5.47The presence of graphitic layers outside the N nanoparticles indicates Co_5.47The close interaction between N and N-doped graphitic carbon substrates and also improves the mechanical stability of the catalyst. Comparing samples obtained at different pyrolysis temperatures, many wrinkles and few pores were observed on the rGO surface at 650 ℃ (fig. 2a-c), similar to that of bare rGO. As the pyrolysis temperature was increased to 700 ℃, the particle size on the rGO surface became larger and some worm-like channels were observed due to thermal etching of the nanoparticles (fig. 2 d-f). At a temperature of 750 ℃, it is clear that the structure of the worm-like channels can be clearly observed (fig. 1a and 1 b). However, when the temperature reached 800 ℃, rGO sheets with large pores and sintered particles were formed (fig. 2 g-i). The results show that the nanoparticles move together to aggregate at high temperatures while the rGO sheet will be etched due to thermal decomposition of carbon in the presence of the metal catalyst. It was further demonstrated that rGO sheets gradually etched and disappeared as the annealing time increased from 2 hours to 3 hours (fig. 4 and 5). At longer calcination times, Co having larger sizes is formed due to thermal aggregation_5.47N nanoparticles (fig. 5).

Powder XRD analysis was performed to characterize the Co prepared_5.47Crystal structure of N @ N-rGO. As shown in FIG. 3, the diffraction peaks at 43.7,50.8 and 74.9 correspond to Co_5.47The (111), (200) and (220) planes of N, confirming Co_5.47Formation of N the broad diffraction peak at 26 ° is considered to be the (002) graphitic plane of N-rGO. As mentioned above, Co_5.47The crystal structure of the N phase is that some N atoms are deleted in octahedral gaps of Co metal crystal lattices and corresponding vacant sites are formed, so that not only is the Co ensured_5.47The metallic nature of N, but also enhances more active sites through the creation of nitrogen vacancies. When the calcining temperature is increased from 650 ℃ to 800 ℃, the diffraction peak intensity of the graphite carbon is gradually reduced,this is because rGO sheets are gradually etched away as the temperature increases.

To study Co_5.47ORR catalytic Activity of N @ N-rGO sample at N₂And O₂Cyclic Voltammetry (CV) tests were performed in saturated 0.1M KOH solution. As shown in FIG. 7, at N₂No reduction peak was observed in the saturated electrolyte. In contrast, when the electrolyte is coated with O₂Upon saturation, a distinct reduction peak occurs near 0.94V, due to the reduction of oxygen. The oxygen reduction peak observed shifts to a more positive potential as the pyrolysis temperature is increased from 650 ℃ to 750 ℃, but the activity decreases slightly when the temperature is further increased to 800 ℃. Notably, Co_5.47The oxygen reduction potential of the N @ N-rGO-750 electrode is better than that of a commercial Pt/C catalyst (Pt/XC-7220 wt%), which indicates that the ORR electrocatalytic activity is more excellent.

The total polarization curves of ORR and OER are shown in FIG. 8, Co_5.47N @ N-rGO-750 has optimal bifunctional catalytic activity, and delta E is 0.77V (delta E is E)_OER-E_ORRIn which E_OERIs 10mA cm^-2Potential at a current density of E_ORRHalf-wave potential). However, Co_5.47N@N-rGO-650，Co_5.47N@N-rGO-700,Co_5.47Δ E for N @ N-rGO-800 and Pt/C were 0.88,0.83,0.91 and 0.97V, respectively. Thus, Co_5.47N @ N-rGO-750 has more excellent application potential of the bifunctional catalytic zinc air battery.

Considering its ORR and OER bifunctional activities, as Co_5.47N @ N-rGO-750 catalyst is an air electrode catalyst, an aqueous rechargeable zinc-air battery is assembled by using 6M potassium hydroxide and 0.2M zinc acetate as electrolytes, the cycle charge and discharge performance of the zinc-air battery is shown in figure 9, and Co can be found_5.47The N @ N-rGO-750 electrode can be cycled continuously for 2000 cycles over 330 hours and only slight potential changes are observed, indicating Co_5.47The N @ N-rGO-750 electrode has good cycling stability.

The present disclosure uses Co_5.47The N @ N-rGO-750 electrocatalyst was used as an air cathode to further assemble a solid zinc-air cell with zinc foil as the anode. In order to adapt to the development trend of portable flexible devices,a solid zinc-air battery was assembled using a polyacrylic acid (PAA) gel electrolyte. Tested, Co_5.47The charge-discharge voltage difference of the N @ N-rGO-750 electrode is less than that of Pt/C-RuO₂Electrodes, description of Co_5.47The efficiency of the N @ N-rGO-750 electrocatalyst is higher. In addition, with Pt/C-RuO₂(24.7mW cm^-2) In contrast, Co_5.47The power density of N @ N-rGO-750 is higher and is 54.6mW cm^-2. It is noted that the discharge current density was 10mA cm^-2Specific capacity of 518mAh g_zn ^-1(normalized by mass of zinc consumed) slightly greater than Pt/C-RuO2(506mAh g)_zn ^-1) The specific capacity of (A) shows that the discharge rate performance is excellent. Co_5.47Flexibility and stability test of N @ N-rGO-750 at a current density of 1mA cm^-2The process was also evaluated, and Co could be found_5.47The charge-discharge voltage of the N @ N-rGO-750 electrode is hardly attenuated, which indicates that the solid zinc-air battery has good flexible application potential. Co_5.47The N @ N-rGO-750 air cathode has long-term cycling stability and reversibility, and no obvious potential attenuation is seen for more than 40h, which indicates that the air cathode has good reversibility. Furthermore, Co_5.47N @ N-rGO-750 can still keep 56% of voltage efficiency in 240 th charge-discharge cycle, and further shows that the stability is better.

Co_5.47The HER catalytic activities of the N @ N-rGO catalyst and commercial Pt/C are shown in FIG. 10. Co_5.47The N @ N-rGO-750 electrode shows quite good HER electrocatalytic activity, has a more positive initial potential (-0.1V vs. RHE), and has a current density of 10mA cm^-2The corresponding over potential is only 0.19V, which is better than Co_5.47N@N-rGO-650(0.26V)，Co_5.47@N-rGO-700(0.22V)，Co_5.47N @ N-rGO-800 (0.23V). These results show that Co_5.47The N @ N-rGO-750 electrode has excellent ORR, OER and HER multifunctional electrocatalytic activity.

Conclusion

The present disclosure has developed a green and simple process to synthesize cobalt nitride nanoparticles in situ on rGO sheets with tannic acid as the dispersant and chelating agent. Co_5.47In situ formation of N nanoparticles and thermo-kinetic etching results in wormlike formation on rGO surfaceA channel and a bore. Benefit from Co_5.47Intrinsic high conductivity of N nanoparticles and synergistic advantage of nitrogen atom doped graphene, Co_5.47N @ N-rGO-750 has excellent electrocatalytic activity for ORR, HER and OER, allowing the assembly of rechargeable zinc air cells and integrated water splitting devices. In particular, Co is used_5.47N @ N-rGO-750 rechargeable zinc air as an air cathode shows excellent cycling stability over 330 h. The solid state zinc-air cell also showed good rechargeable performance (about 40 h). In addition, a water-splitting device driven by a zinc-air battery showed good gas generation rate by using the prepared electrocatalyst.

The above description is only a preferred embodiment of the present disclosure and is not intended to limit the present disclosure, and various modifications and changes may be made to the present disclosure by those skilled in the art. Any modification, equivalent replacement, improvement and the like made within the spirit and principle of the present disclosure should be included in the protection scope of the present disclosure.

Claims

1. A cobalt nitride embedded porous nitrogen-doped graphene material is characterized by comprising nitrogen-doped graphene and Co_5.47N nanoparticles, a cellular structure with worm-like traces on the surface of the nitrogen-doped graphene, Co_5.47The N nanoparticles are embedded at the ends of the pore-like structures of the worm-like traces.

2. The cobalt nitride embedded porous nitrogen-doped graphene material of claim 1, wherein the graphene is reduced graphene oxide.

3. The method for preparing a cobalt nitride embedded porous nitrogen-doped graphene material as claimed in claim 1, wherein cobalt acetate and tannic acid are sequentially added to the dispersion liquid of graphene oxide and uniformly mixed to obtain a suspension, and after solid materials in the suspension are separated, the suspension is heated to a temperature of not lower than 600 ℃ in a mixed atmosphere of nitrogen and ammonia gas for pyrolysis.

4. The method for preparing the cobalt nitride embedded porous nitrogen-doped graphene material as claimed in claim 3, wherein the cobalt acetate is added into the graphene oxide dispersion liquid for uniform dispersion, then the tannic acid is added for uniform mixing to obtain a suspension, solid materials in the suspension are separated, washed and dried, and then heated to not less than 600 ℃ in a mixed atmosphere of nitrogen and ammonia gas for pyrolysis.

5. The method for preparing the cobalt nitride embedded porous nitrogen-doped graphene material as claimed in claim 4, wherein the addition ratio of the graphene oxide, the cobalt acetate and the tannic acid is 55-65: 0.001-0.003: 0.7-0.8, mg: mol: g.

6. the method for preparing the cobalt nitride embedded porous nitrogen-doped graphene material according to claim 5, wherein the volume ratio of nitrogen to ammonia is 2.5-3.5: 1.

7. The method for preparing the cobalt nitride embedded porous nitrogen-doped graphene material according to claim 5, wherein the pyrolysis temperature is 650-800 ℃.

8. The method for preparing the cobalt nitride embedded porous nitrogen-doped graphene material according to claim 7, wherein the pyrolysis temperature is 740-760 ℃.

9. The method for preparing the cobalt nitride embedded porous nitrogen-doped graphene material according to claim 7, wherein the pyrolysis time is 0.5-5 h.

10. Use of the cobalt nitride embedded porous nitrogen-doped graphene material of claim 1 or 2 in the field of metal-air batteries and/or in electrolysis of water.

11. An electrode material comprising the cobalt nitride embedded porous nitrogen-doped graphene material of claim 1 or 2.

12. A zinc-air battery, characterized in that the cobalt nitride-embedded porous nitrogen-doped graphene material of claim 1 or 2 is used as an air cathode.

13. The zinc-air battery of claim 12, wherein the air cathode is prepared by coating cobalt nitride embedded porous nitrogen-doped graphene material on carbon paper with an adhesive and drying.

14. The zinc-air cell of claim 12, wherein said zinc-air cell is a liquid zinc-air cell or a solid zinc-air cell.

15. An electrocatalyst, characterized in that the active component is the cobalt nitride embedded porous nitrogen-doped graphene material according to claim 1 or 2.

16. A method of electrolyzing water, characterized in that the cobalt nitride embedded porous nitrogen-doped graphene material of claim 1 or 2 is used as an electrocatalyst, and a battery is used to decompose water into hydrogen and oxygen.

17. The method of electrolyzing water as recited in claim 16 wherein said cell is a zinc air cell.