Microwave-hydrothermal preparation of a graphene/hierarchy structure MnO2 composite for a supercapacitor

► Graphene/hierarchy structure MnO2 composites were synthesized by microwave-hydrothermal method. ► The hierarchy structure of MnO2 is composed of MnO2 nanospheres and MnO2 sheets. ► GN/MnO2-10% electrode showed a specific capacitance of 244 F/g at 100 mA/g in 1 mol/L Li2SO4. ► Capacity retention of 94.3% was obtained after 500 cycles in a 1 mol/L Li2SO4 solution.