Tuning the morphology and size of NiMoO4 nanosheets anchored on NiCo2O4 nanowires: the optimized core-shell hybrid for high energy density asymmetric supercapacitors

Abstract

Core-shell architectures have stimulated growing research interest because of their optimized physical/chemical properties and potential in many energy-related applications. In this work, a facile two-step hydrothermal-annealing method was adopted to synthesize hierarchical core-shell NiCo2O4@NiMoO4 nanoarrays on nickel foam substrate, and by controlling the growth time (2 h, 5 h and 8 h) of NiMoO4 precursor, three different morphologies and sizes of NiMoO4 nanosheets were obtained, and their morphology-dependent electrochemical performance was investigated. The results revealed that NiCo2O4@NiMoO4/NF (5 h) hybrid electrode exhibits a much enhanced specific capacitance of 2806 F g−1 at 5 A g−1, nearly three times than that of pristine single-composition NiCo2O4 electrode (974 F g−1). The superior performance was attributed to the porous hierarchical structure and reasonable morphology and nanosheets thickness, which could lower electrons transfer resistance and alleviate the strain during repeated redox reactions. Furthermore, the assembled NiCo2O4@NiMoO4 (5 h)//Activated carbon asymmetric supercapacitor shows a high energy density of 64.2 Wh kg−1 (750 W kg−1), and good cycling durability of 87.7% specific capacitance retention over 5000 cycles. This work provides a novel morphology-controllable approach for the synthesis of high performance core-shell electrodes for supercapacitors.