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

Abstract

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 (Co₃O₄/MnO₂/GO) was successfully prepared. Briefly, electrochemical deposition and sintering were applied to grow Co₃O₄ nanosheets on nickel foam. Subsequently, MnO₂ nanosheets were deposited on Co₃O₄ nanosheets via the thermal decomposition of a KMnO₄ aqueous solution. Finally, graphene oxide was added to improve the performance of the composite. Particularly, the as-obtained Co₃O₄/MnO₂/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⁻¹ at 1 A g⁻¹ in a three-electrode system. Besides, the electrode showed a promising rate performance of 853 F g⁻¹ at a high current density of 20 A g⁻¹. Moreover, the electrode displayed a relatively high energy density of 97.92 W h kg⁻¹ at a power density of 125 W kg⁻¹ and long cycle life of 93% retention after 5000 cycles at 10 A g⁻¹ in a two-electrode system. Thus, all the electrochemical tests suggest that the Co₃O₄/MnO₂/GO binder-free electrode is a potential candidate for energy storage.