Hybrid cobalt-manganese oxides prepared by ordered steps with a ternary nanosheet structure and its high performance as a binder-free electrode for energy storage.

Binder-free electrodes for supercapacitors have attracted much attention as no additive is required in their preparation processes. Herein, a hybrid metal oxide composed of graphene oxide (CoO/MnO/GO) was successfully prepared. Briefly, electrochemical deposition and sintering were applied to grow CoO nanosheets on nickel foam. Subsequently, MnO nanosheets were deposited on CoO nanosheets via the thermal decomposition of a KMnO aqueous solution. Finally, graphene oxide was added to improve the performance of the composite. Particularly, the as-obtained CoO/MnO/GO sample grown on nickel foam possessed a ternary nanosheet structure, and when applied as a binder-free electrode in a supercapacitor, it exhibited an excellent electrochemical performance. Firstly, the electrode exhibited an ultrahigh capacitance value of 2928 F g at 1 A g in a three-electrode system. Besides, the electrode showed a promising rate performance of 853 F g at a high current density of 20 A g. Moreover, the electrode displayed a relatively high energy density of 97.92 W h kg at a power density of 125 W kg and long cycle life of 93% retention after 5000 cycles at 10 A g in a two-electrode system. Thus, all the electrochemical tests suggest that the CoO/MnO/GO binder-free electrode is a potential candidate for energy storage.