Graphene-supported Cu2O-CoO heterojunctions for high performance supercapacitors

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Transition metal oxides are excellent electrode materials for supercapacitors because of their high theoretical capacitance, good stability, environmental friendliness, and tunable structure. In this study, Cu2O-CoO heterojunction materials loaded on graphene oxide (Cu2O-CoO/GO) are prepared via the precipitation, hydrothermal, and heat treatment processes. Through the adsorption of transition metal ions by the oxygen-containing functional groups of GO, followed by alkali titration as well as hydrothermal reaction of Cu2+ and Co2+ ions, the hydroxides of metals are adsorbed on GO. Meanwhile, the reduced GO completes the self-assembly, and the GO with good spatial structure supports the formation of Cu2O-CoO heterojunction structure. The Cu2O-CoO/GO electrode material combines the high conductivity of GO with the excellent internal conductivity of Cu2O-CoO, and its abundant active sites and specific surface area, thereby ensuring good electrochemical performance. Thus, it enables reversible ion adsorption and desorption, exhibits the pseudocapacitance of copper oxide and cobalt oxide, and has higher capacitance performance than Cu2O/GO and CoO/GO electrodes. The specific capacitance of Cu2O-CoO/GO at 1 A g−1 is 723 F g−1. Cu2O-CoO/GO/ASC exhibits an energy density of 44.1 Wh kg−1 at 794 W kg−1 and capacitance retention rate of 89.3 % after 10,000 cycles. This indicates that the material has significant potential for a wide range of supercapacitor applications.