Ethanol-assisted solvothermal synthesis of porous nanostructured cobalt oxides (CoO/Co3O4) for high-performance supercapacitors

The porous mixed-phase CoO/Co3O4 nanocomposites have been prepared by a facile ethanol-assisted solvothermal approach without a subsequent calcination process and the composites are formed by aggregations of many nanoparticles with an average diameter of 5 ± 2 nm. The porous structures are verified by BET test results with a typical type-IV isotherm curve and a high surface area (∼186.27 m2 g−1). Electrochemical properties are characterized by cyclic voltammetry, galvanostatic charge-discharge measurements and electrochemical impedance spectroscopy. The CoO/Co3O4 electrode exhibits a high capacitance of 451 Fg−1 at a current density of 1 Ag−1, which is higher than that of the pure CoO electrode (203 Fg−1). Interestingly, the CoO/Co3O4 shows a low equivalent series resistance (0.16 Ω) and superior cycle stability (108% retention after 5000 cycles). Moreover, an asymmetric supercapacitor based on this hybrid CoO/Co3O4 and activated carbon can deliver an energy density of 10.52 Wh kg−1 at a power density of 140 W kg−1. These results indicate the CoO/Co3O4 composites will be a promising electrode material for high-performance supercapacitor applications.