High mass loading flower-like MnO₂ on NiCo₂O₄ deposited graphene/nickel foam as high-performance electrodes for asymmetric supercapacitors

Abstract

The implementation of high mass loading MnO₂ on electrochemical electrodes of supercapacitors is currently challenging due to the poor electrical conductivity and elongated electron/ion transport distance. In this paper, a NiCo₂O₄/MnO₂ heterostructure was built on the surface of three-dimensional graphene/nickel foam (GNF) by a hydrothermal method. The petal structured NiCo₂O₄ loaded on graphene played a wonderful role as a supporting framework, which provided more space for the growth of high mass loading MnO₂ microflowers, thereby increasing the utilization rate of the active material MnO₂. The GNF@NiCo₂O₄/MnO₂ 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 Na₂SO₄ solution. The asymmetric supercapacitor assembled with the GNF@NiCo₂O₄/MnO₂ 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 MnO₂.