Three-dimensionally assembled Graphene/α-MnO2 nanowire hybrid hydrogels for high performance supercapacitors

We present a facile hydrothermal method to produce graphene-metal oxide composite that offer synergistic effect of three-dimensional (3D) graphene and electroactive alpha-MnO2 nanowires to improve high energy storage capability in supercapacitors. The graphene/alpha-MnO2 nanowire hydrogel is prepared via a simple hydrothermal route, in which graphene and alpha-MnO2 nanowires are self-assembled into 3D macroporous network structures. An asymmetric supercapacitor device is fabricated by using graphene/alpha-MnO2 nanowire hydrogel as positive electrode and 3D graphene hydrogel as negative electrode in an aqueous Na2SO4 electrolyte. The asymmetric cell can be cycled in the wide voltage range of 0-2 V and exhibit a gravimetric energy density of 38 Wh kg(-1) with a maximum power density of 258 kW kg(-1). In addition, it shows a good cycle stability with similar to 94% capacitance retention after 1000 cycles. The graphene/alpha-MnO2 nanowires hybrid hydrogels may have great potential in developing energy storage devices with high energy and power densities. (C) 2017 Elsevier Ltd. All rights reserved.