Graphene/VO2 hybrid material for high performance electrochemical capacitor
Abstract Vanadium oxides have attracted significant attention for electrochemical capacitor because of their extensive multifunctional properties. In the present work, graphene/VO2 (RG/VO2) hybrid materials with different RG amounts are prepared in a mixture of ammonium vanadate, formic acid and graphite oxide (GO) nanosheets by one-step simultaneous hydrothermal reduction technology. The hydrothermal treatment makes the reduction of GO into RG and the formation of VO2 particles with starfruit morphology. The starfruit-like VO2 particles are uniformly embedded in the hole constructed by RG nanosheets, which makes the electrode–electrolyte contact better. A high specific capacitance of 225 F g−1 has been achieved for RG(1.0)/VO2 electrode with RG content of 26 wt% in 0.5 mol L−1 K2SO4 electrolyte. An asymmetrical electrochemical capacitor is assembled by using RG(1.0)/VO2 as positive electrode and RG as negative electrode, and it can be reversibly charged–discharged at a cell voltage of 1.7 V in 0.5 mol L−1 K2SO4 electrolyte. The asymmetrical capacitor can deliver an energy density of 22.8 Wh kg−1 at a power density of 425 W kg−1, much higher than those of the symmetrical electrochemical capacitor based on the RG and RG(1.0)/VO2 electrodes. Moreover, the asymmetrical capacitor preserves 81% of its initial capacitance over 1000 cycles at a current density of 5 A g−1.