Preparation And Property Studies Of Graphene-based Supercapacitor Electrode Materials

As a new type of energy storage device,supercapacitor has important application value and huge market potential in many fields,such as communication,transportation,electronics and national defense.Graphene is the best potential electrode material for double-layer supercapacitors due to its excellent conductivity,unique two-dimensional structure and excellent physicochemical properties.Now,the electrochemical properties of graphene materials prepared by different oxidation-reduction methods are significantly different.Moreover,the specific capacitance of single graphene electrode material is low and can not meet the requirements of high energy density of supercapacitors.Thereby,improving the capacitance of graphene electrode is very important and urgency.In this stydy,we tried to synthesis graphene materials with certain capacitive properties by changing the hydrothermal reduction.Then,pseudocapacitive oxide were loaded on the graphene surface and inter layers to improve their specific capacitance requirements of the electrode material.In this paper,the properties of combined electrode materials were also examined.1.The acid reduction and electrochemical properties of graphene oxide?GO?GO was prepared by improved Hummers method and the hydrothermal reduction was performed at 180°C under acidic condition?pH=5?.Reduced GO?RGO?with different reduction degrees were prepared by changing the hydrothermal reaction time.The results showed that RGO product with different reduction degree can be obtained by controlling the hydrothermal reaction time.In the electrochemical test,the specific capacitance of RGO electrode increased first and then decreased with the increase of the hydrothermal reaction time.When the hydrothermal reaction time was lengthened to 6h,the RGO electrode showed the best capacitance performance,and its specific capacitance reached 251 F/g at the current density of 1 A/g,which was 225%higher than that of the GO electrode.After 500 charge and discharge cycles,the specific capacitance retention rate of RGO-6 electrode reached 92%,showing excellent cyclic stability.2.Synthesis and electrochemical properties of NiO/RGO compositesNiO and NiO/RGO composites were prepared by two-step method?hydrothermal reduction-calcining?.It was observed that NiO shows a cluster flower-like morphology,while in NiO/RGO composites,NiO loaded on the surface and inter layer of RGO uniformly with a unique single layer morphology,and the effect of compound was obvious.In the electrochemical property test,the specific capacitance of NiO and NiO/RGO electrodes reached 417 F/g and 620 F/g when the current density was 1 A/g,respectively.Compared with pure NiO material,NiO/RGO composites has better electrochemical properties.After 500 charge and discharge cycles,the specific capacitance retention rate of NiO/RGO electrode reaches 86%,which has excellent cyclic stability.3.Synthesis and electrochemical properties of Zn O/RGO compositesZnO and ZnO/RGO composites were prepared by simple and efficient solvent heating method.It was observed that ZnO has particle morphology.In the composites,the effect of uniform dispersion can be obtained for the aggregated ZnO particles in the RGO matrix.The electrochemical test found that ZnO/RGO electrode could display double-layer and pseudo-capacitor energy storage modes in Na₂SO₄ and KOH electrolyte,respectively.At the current density of 0.2 A/g,the ZnO/RGO electrode exhibited specific capacitance of 100.8 F/g in Na₂SO₄ electrolyte and 53.5 F/g in KOH electrolyte,respectively.Its dual-layer energy storage capacity was higher than that of pseudocapacitor.Moreover,the impedance will be reduced by ZnO and the water electrolyte with the addition of RGO,and greatly improves the conductivity of semiconductor ZnO.We confirm that RGO is an effective electrode composite material.