Three-dimensionally assembled Graphene/α-MnO 2 nanowire hybrid hydrogels for high performance supercapacitors

Abstract We present a facile hydrothermal method to produce graphene-metal oxide composite that offer synergistic effect of three-dimensional (3D) graphene and electroactive α-MnO2 nanowires to improve high energy storage capability in supercapacitors. The graphene/α-MnO2 nanowire hydrogel is prepared via a simple hydrothermal route, in which graphene and α-MnO2 nanowires are self-assembled into 3D macroporous network structures. An asymmetric supercapacitor device is fabricated by using graphene/α-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 ∼94% capacitance retention after 1000 cycles. The graphene/α-MnO2 nanowires hybrid hydrogels may have great potential in developing energy storage devices with high energy and power densities.