High Performance Composite Electrodes Consisting of Graphene and Cobalt Carbonate for Supercapacitors

Considerable efforts are still ongoing to identify ideal electrode materials for supercapacitors (SCs) which can deliver both high capacitances and excellent cyclic stability. Metal compounds, such as oxides and hydroxides, have been used as the pseudocapacitance materials; however, very few studies on metal carbonate-based compounds have been reported so far. In this study, cobalt carbonate hydroxide nanowire/graphene aerogel and cobalt carbonate microcube/graphene aerogel composites (CCH/GA and CC/GA) are in-situ synthesized as the SC electrodes via a one-step hydrothermal method without further treatment. Optimized process conditions are established and the enhancing effects of graphene on capacitance are identified. The CCH/GA composite electrodes show a remarkable specific capacitance of 1134 F/g at a current density of 1 A/g, which is among the highest capacities reported for all cobalt compounds/graphene composites. The electrode also shows exceptional rate performance and cyclic stability. A high capacity of 731 F/g is also achieved for the optimized CC/GA electrodes under the same testing condition, which has not been reported previously. These nanostructures can make promising electrodes for high performance SCs not only because of the excellent pseudocapacitive properties of the cobalt carbonate-based compounds stemming from the reversible redox reactions of cobalt cations upon cycles, but also because of the synergy arising from the 3D porous and conductive graphene matrix along with cost effectiveness and ease of the synthesis process.