Novel graphene/polyaniline/MnO_x 3D-hydrogels obtained by controlled morphology of MnO_x in the graphene/polyaniline matrix for high performance binder-free supercapacitor electrodes

A novel three dimensional ternary composite graphene-based hydrogel was prepared using a simple hydrothermal reaction. The graphene/polyaniline/MnO_x hydrogel named as PGM-HCl, obtained by the controlled morphology of MnO_x by preparing it in an acidic environment using hydrochloric acid (HCl), offered an extremely high specific capacitance of 955 F g^-1 at a current density of 1 A g^-1 and a capacitance retention of 89% after 1000 cycles and 69.1% after 5000 cycles at 20 A g^-1. The synergistic effects created by the pseudocapacitance of PANI, MnO_x and the electrochemical double layer capacitance of graphene highly improved the overall electrochemical performance of these hydrogels compared to the performances of the individual constituents. The electrode prepared from this material gave an extremely high specific energy density of 61.2 W h kg^-1 even at a high power density of 4.5 kW kg^-1. The composite had the superior advantage of being used directly for binder free supercapacitor electrodes and made use of low cost raw materials making it a very promising candidate for cost effective, large scale and high energy applications. A hydrogel PGM was also prepared in the absence of HCl using a purely hydrothermal reaction under the same reaction conditions, for comparison. Thus, this study opens the exciting untapped potential in engineering and synthesizing such composites with existing low cost materials for high performance energy storage devices like supercapacitors.