Syntheses And Supercapacitor Electrode Properties Of Cobalt Based Metal Oxides And Nitrogen Doped Graphene Composites

At present,human society is facing increasingly acute challenges in the energy and development,and search for a clean and efficient energy and storage energy materials increasingly become urgent.Supercapacitors have higher current density,shorter charge and discharge times,longer service life,and better environmental protection compared to conventional capacitors and conventional batteries.Therefore,the research and development of supercapacitor materials have aroused great concern of scientific research workers.Among the various metal oxides,the cobalt trioxide and cobalt cobaltate have become the focus of the research because of the cost is more inexpensive,the reserves are richer,the environment is more friendly and the poisoning is more mild.However,poor conductivity,easy to agglomerate,small interface area contact with the electrolyte restrict the metal oxide practical application in the capacitor prospects.Graphene is a two-dimensional honeycomb-shaped carbon material formed by sp2 hybridization of carbon atoms.It has attracted extensive research attention for its excellent strength,larger specific surface area and outstanding conductivity.Graphite has excellent chemical stability and has wide application prospects in mechanics,optics,thermodynamics and electrochemistry.As an example to further explore the nature of graphene to expand its scope of application,the researchers in the graphene surface doping new elements to synthesis new graphene-based materials.The introduction of nitrogen can repair the structural defects on graphene surface,thus increasing the active sites on the surface of graphene and enhancing the storage capacity of graphene.The combination of metal oxides and nitrogen-doped graphene not only can play their respective performance advantages,but also can cuase electron transfer between Co₃O₄ and N-doped graphene,and further enhance the properties of the composite capacitor.So the development of high quality supercapacitor material can be meaningful and valuable.The following are main contents of this paper:1.Co₃O₄ N-doped graphene composites were prepared by microwave-calcination with polyacrylamide?PAM?as the surfactant.The structure,morphology and electrochemical properties of Co₃O₄/NG complex were characterized by XRD,Raman,FTIR,XPS,TEM,ICP and electrochemical examination.The experimental results indiacte that the composites can be calcined at 750 ? for 3 h after heating at 950 W for 15 min.The Co₃O₄ nanoparticles can be uniformly dispersed on the surface of nitrogen-doped graphene,and the specific capacitance can be 1288.2 F g-1 measured at the current density of 1 A g-1.The excellent electrochemical activity of Co₃O₄/ NG complex is mainly due to the synergistic effect between Co₃O₄ nanoparticles and nitrogen-doped graphene.NiCo₂O₄/NG nanocomposites were prepared by hydrothermal-calcination method using hexamethylene tetramine?HMT?and urea?Urea?as the alkali source.The structure,morphology and electrochemical properties of NiCo₂O₄/NG complex were characterized by XRD,TGA,FTIR,Raman,TEM,XPS,ICP and electrochemical workstation.The experimental results show that the product is calcined at 350 ? for 3h after hydrothermal at 180 ? for 24 h,and the NiCo₂O₄ crystals with uniform diameter are deposited on the surface of nitrogen-doped graphene.The specific capacitance of NiCo₂O₄/NG can be 2147.4 F g-1 at the current density of 1 A g-1.The excellent electrochemical activity of NiCo₂O₄/NG complex is in addition to the synergistic effect between NiCo₂O₄ nanotubes and nitrogen-doped graphene,and the NiCo₂O₄ nanotube crystal with three-dimensional mesoporous structure can greatly increase the metal oxidation material and electrolyte contact area,which result a better capacitance performance.The duplex metal-doped Co₃O₄@NiCo₂O₄ N-doped graphene composites were synthesized by hydrothermal-calcination method utilizating HMT as the alkali source and PAM as the surfactant.The structure,morphology and electrochemical properties of Co₃O₄@NiCo₂O₄/NG complex were characterized by ICP,XRD,Raman,FTIR,TEM,XPS and electrochemical tests.The experimental results show that the amount of hexamethylenetetramine and a small amount of polyacrylamide surfactants are favorable to the sandwich-shaped binary metal-NG complex.After heating at 180 ? for 24 h,the product is calcined at 350 ? for 3 h to form a sheet of NiCo₂O₄ crystal surface with Co₃O₄ nanoparticles and mixed with nitrogen-doped graphene to form a sandwich-like space structure.The specific capacitance measured at a current density of 1 A g-1 was 2387.5 F g-1.The excellent performance of the Co₃O₄@NiCo₂O₄/NG complex is due to the special three-dimensional space structure of the sandwich and the further electronic synergistic effect between the metal oxide and the nitrogen-doped graphene.