Advanced solid-state asymmetric supercapacitors based on 3D graphene/MnO2 and graphene/polypyrrole hybrid architectures

A three-dimensional graphene wrapped nickel foam (Ni/GF) architecture has been prepared by a facile yet effective and scalable interfacial reduction method. Inspired by the porous and conductive network structures of Ni/GF, we have deposited manganese dioxide (MnO2) and polypyrrole (PPy) nanostructures on the Ni/GF substrates and successfully fabricated a flexible solid-state asymmetric supercapacitor assembled with Ni/GF/MnO2 as the positive electrode and Ni/GF/PPy as the negative electrode in a gel electrolyte. Benefiting from the high capacitance and fast ion transport properties of our hierarchically porous electrodes, the optimized asymmetric supercapacitor exhibits an excellent stability in a high-voltage region of 1.8 V and remarkable cycling stability with only 9.8% decrease of capacitance after 10 000 cycles. Moreover, the device can deliver a high energy density of 1.23 mW h cm (3), which is substantially enhanced compared to most of the reported solid-state supercapacitors. The impressive results presented here may pave the way for promising applications in future energy storage systems.