High-performance asymmetric supercapacitor with ultrahigh energy density based on hierarchical graphene sheets@NiO core-shell nanosheets and 3D drilled graphene sheets hydrogel

In this work, we have successfully developed an advanced asymmetric supercapacitor (ASC) based on hierarchical graphene sheets@NiO (GN@NiO) core-shell nanosheets as positive electrode and 3D drilled graphene sheets (DGNs) hydrogel as negative electrode for the first time. The anode materials were synthesized by an efficient chemical bath deposition method followed by thermal annealing, and the resulting GN@NiO electrode shows an ultrahigh specific capacitance of 1092 F g(-1) at 1 A g(-1). Additionally, the cathode materials were fabricated via a two-step process: chemical reduction at a low temperature and cost-effective cobalt catalyzed gasification strategy. Thanks to the mesoporous hydrogel structure, the porous DGNs electrode displays a specific capacitance up to 268 F g(-1) at 1 A g(-1) and the value is higher than that of major carbon-based materials. The optimized GN@NiO//DGNs ASC device provides a specific capacitance of 122.5 F g(-1) at 0.5 A g(-1) and an maximum energy density of 43.2 Wh kg(-1) and even retains 19.5 Wh kg(-1) at 20,000 W kg(-1), in addition, an excellent cycling stability with 95.5% capacitance retention after 5000 cycles at 6 A g(-1). Our ASC device has great prospect for high energy density storage systems applications and expands the design space for graphene-based materials used in supercapacitors. Keywords: graphene; nickel oxide; porous hydrogel; hierarchical core-shell structure; asymmetric supercapacitor. (C) 2017 Elsevier B.V. All rights reserved.