Hierarchical NiCo2O4@NiMoO4 core-shell hybrid nanowire/nanosheet arrays for high-performance pseudocapacitors

Three-dimensional (3D) hierarchical NiCo2O4@NiMoO4 core-shell nanowire/nanosheet arrays (NWSAs) for high-performance pseudocapacitors are fabricated directly on Ni foam via a two-step approach which involves hydrothermal and calcination processes. The formation of 3D interconnected networks is greatly beneficial for the facile electrolyte penetration and fast electron transport in the hybrid system. The optimized NiCo2O4@NiMoO4 hybrid electrode delivers a much enhanced areal capacitance of 5.80 F cm(-2) at 10 mA cm(-2) with excellent rate capability (83.6% retention for current density increased from 10 to 80 mA cm(-2)) and remarkable cycling stability (81.8% retention over 5000 cycles at a high current density of 50 mA cm(-2)). In addition, an asymmetric supercapacitor (ASC) was assembled by using the optimized NiCo2O4@NiMoO4 NWSAs as a positive electrode and activated carbon as a negative electrode in 2 M KOH electrolyte. The as-fabricated ASC device can achieve a maximum areal capacitance of 1.54 F cm(-2) and a high energy density of 5.64 mW h cm(-3) (21.7 W h kg(-1)). After charging, two ASC devices in series can efficiently power a 5 mm diameter LED and a commercial digital meter. In view of their outstanding electrochemical performance and the cost-effective fabrication process, this unique integrated nanoarchitecture may show great promise as superior pseudocapacitive electrodes for potential applications in energy storage.