CoO nanoparticles deposited on 3D macroporous ozonized RGO networks for high rate capability and ultralong cyclability of pseudocapacitors

The integration of pseudocapacitive metal oxides with reduced graphene oxide (RGO) is considered an innovative chemical strategy to resolve both bottlenecks of pseudocapacitor and electrical double-layer capacitor for high performance supercapacitors. Herein, we report a facile synthesis method of highly porous three-dimensional (3D) CoO/RGO nanocomposite via ozone treatment, ice templating, and thermal annealing. The ozonized RGO surface provides a favorable interaction with cobalt precursor for a stable and uniform deposition of well-defined CoO nanoparticles. The morphology, structure, and chemistry of the resulting CoO/RGO nanocomposites are comprehensively characterized by spectroscopic methods. The CoO/RGO nanocomposites show fast and reversible pseudocapacitance due to a large accessible area, rapid ion transport, and low charge transfer resistance arising from 3D internetworked macroporosity. Thus, the nanocomposites achieve high specific capacitance up to 239.4 F g^-1 (volumetric capacitance = 12.04 F cm^-3), excellent rate capability of 79.1%, and ultralong cyclic stabilities (of 93.2% at 10 A g^-1 even up to 10,000 cycles) in 6 M KOH electrolyte. This simple synthesis method offers a promising solution for the design of high performance hybrid energy storage materials consisting of high capacity metal oxides and conductive graphene networks.