MnO2 Nanoflowers and Reduced Graphene Oxide 3D Composites for Ultrahigh‐Energy‐Density Asymmetric Supercapacitors

Uniform MnO2 nanoflowers and a reduced graphene oxide (rGO) 3D nanostructure composite are synthesized on Ni foam using a two-step electrodeposition and hydrothermal method. The surface morphology and composition of the 3D nanostructure hybrid are intensively analyzed. MnO2/rGO/Ni is tested using a typical three-electrode system for potential use as a supercapacitor electrode. The hybrid electrode has a high areal specific capacitance. An asymmetric supercapacitor (ASC) device is assembled and characterized using MnO2/rGO/Ni as the positive electrode and rGO/Ni as the negative electrode to further evaluate the electrochemical capability of the hybrids. Electrochemical characterizations indicate that the ASC device can be cycled reversibly between 0V and 2.0V in 1m Na2SO4 aqueous electrolyte. The maximum areal specific capacitance of 760.1 mFcm(-2) (1266.83 Fg(-1)) and the maximum ultrahigh energy density of 150.45 Whkg(-1) are obtained, demonstrating the potential for use as binder-free electrodes in pseudocapacitors.