Research On Preparation And Electrochemical Performance Of Co₃O₄/graphene Composites

Supercapacitor is an energy storage device between the traditional capacitor and battery,which attracting great research interests due to high power density and friendly to the environment.However,the lower energy density limits development in supercapacitor.While the electrode material is the core of the supercapacitor,so preparing a comprehensive electrode is an important way to improve the performance of supercapacitor.In recent years,graphene has become a potential material for the great charge transport performance and is used widely as electrode material.Transition metal oxide is one of the most promising electrode material for supercapacitor because of its high theoretical specific capacitance and has also been extensively researched.Therefore,this project is mainly hybridizing transition metal oxides with graphene by a simple hydrothermal method,the synergistic effect of these two materials reveals the huge potential in the performance of supercapacitor.Finally,we optimized the micro-nano structure of the transition metal oxides by using a simple strategy,and explored the relationship between the structure of the material and the electrochemical performance to make the transition metal oxides play the biggest potential as the electrode material.The research contents of this paper are as follows:1.The preparation of Co3O4 nanoflakes/N-doped graphene(NG)and their electrochemical performance.Co3O4 nanoflakes/N-doped graphene(NG)has been synthesized through a facile two-step synthesis route.The phase composition and morphology of the products were characterized by X-ray diffraction(XRD),scanning electron microscopy(SEM)and energy dispersive X-ray spectrometer(EDS).The composites of Co3O4 nanoflakes/N-doped graphene and the Co3O4 nanoflakes were tested by using a three-electrode test system and the results of electrochemical performance were compared.It is found that introduction of NG has effects on the morphology of Co3O4 and leads to a well distribution of Co3O4 nanoflakes.The specific capacitance values of Co3O4 nanoflakes/N-doped graphene is 2.5 times than Co3O4 nanoflakes.The composite presents an enhanced supercapacitor performance than the pristine Co3O4 nanoflakes,mainly due to the strong synergistic effect of the NG and Co3O4.2.Layer-dependent growth of two-dimensional Co3O4 nanostructure arrays on graphene for high performance supercapacitors.Firstly,graphene was in suit synthesized on the 3D Ni foam by chemical vapor deposition method(Ni@grpahene),then the Ni@grpahene was further served as substrate for the subsequent deposition of Co3O4 nanoflakes.Furthermore,the layer number of graphene is adjusted from bilayer to multilayer to investigate the effects of graphene layers on the growth of Co3O4 nanoflake arrays.It is found that the thickness of Co3O4 nanoflakes can be tuned from 70 nm to 13 nm with the increase of the layer number of the graphene sheets due to the different surface diffusion coefficient of Co3O4 nanoparticles.Finally,the electrochemical properties of Co3O4 nanoflake composites with different thickness were researched.The results of electrochemical measurements demonstrate that the hybrid electrode with the thinner nanoflakes presents higher specific capacitance because of the full utilization of the electroactive Co3O4.Particularly,the Co3O4/graphene/Ni hybrid electrode with 13 nm-thick nanoflake delivers a high specific capacitance of 1.75 cm-2 at a current density 1 mA cm-2.Additionally,a capacitance increase of 12.2%of the initial capacitance is observed after 5000 cycles at a current density of 10 mA cm-2.