Synthesis of oxygen vacancy-engineered Fe2O3 nanospheres on three-dimensional reduced graphene oxide for ultra-energy density performance of asymmetric supercapacitors

The synthesis of oxygen vacancy (VO) -engineered Fe2O3 (Fe2O3-x) nanospheres on three-dimensional reduced graphene oxide (3D rGO/Fe2O3-x) is proposed via a gentle and high-efficiency hydrothermal approach under reducing conditions for a high-performance asymmetric supercapacitors. The smooth and rounded 3D rGO/Fe2O3-x hydrogel appears to be intact, which possesses extremely light weight and excellent strength. The micromorphology of 3D rGO/Fe2O3-x presents a 3D interconnected macroporous network structure, and the Fe2O3-x nanospheres are distributed on the surface of 3D rGO. The specific capacity of the 3D rGO/Fe2O3-x is up to 273.2 mAh/g. An asymmetric supercapacitor 3D rGO/Fe2O3-x||3D rGO exhibits an ultrahigh energy density of 114 Wh/kg at a power density of 140 W/kg. Over 20000 cycles, the capacitance retention fading and the coulombic efficiency are 6.18% and ∼100%, respectively. Outstanding supercapacitor performances of the 3D rGO/Fe2O3-x||3D rGO are attributed to the formation of the VOs in Fe2O3 crystal structure and the distribution of Fe2O3-x nanospheres on the 3D rGO. The 3D rGO/Fe2O3-x displays great potential for utilization as high-performance supercapacitors.