High mass loading flower-like MnO 2 on NiCo 2 O 4 deposited graphene/nickel foam as high-performance electrodes for asymmetric supercapacitors.

The implementation of high mass loading MnO 2 on electrochemical electrodes of supercapacitors is currently challenging due to the poor electrical conductivity and elongated electron/ion transport distance. In this paper, a NiCo 2 O 4 /MnO 2 heterostructure was built on the surface of three-dimensional graphene/nickel foam (GNF) by a hydrothermal method. The petal structured NiCo 2 O 4 loaded on graphene played a wonderful role as a supporting framework, which provided more space for the growth of high mass loading MnO 2 microflowers, thereby increasing the utilization rate of the active material MnO 2 . The GNF@NiCo 2 O 4 /MnO 2 composite was used as a positive electrode and achieved a high areal capacitance of 1630.5 mF cm -2 at 2 mA cm -2 in the neutral Na 2 SO 4 solution. The asymmetric supercapacitor assembled with the GNF@NiCo 2 O 4 /MnO 2 positive electrode and activated carbon negative electrode possessed a wide voltage window (2.1 V) and splendid energy density (45.9 Wh kg -1 ), which was attributed to the satisfactory electroactive area, low resistance, quick mass diffusion and ion transport caused by high mass loading MnO 2 .