Three-dimensional hierarchical NiCo2O4 nanowire@Ni3S2 nanosheet core/shell arrays for flexible asymmetric supercapacitors.

Three-dimensional (3D) hierarchical NiCo2O4@Ni3S2 core/shell arrays on Ni foam were synthesized by a facile, stepwise synthesis approach. The 3D heterogeneous NiCo2O4 nanostructure forms an interconnected web-like scaffold and serves as the core for the Ni3S2 shell. The as-prepared NiCo2O4@Ni3S2 nanowire array (NWA) electrodes exhibited excellent electrochemical performance, such as high specific areal capacitance and excellent cycling stability. The specific areal capacitance of 3.0 F cm(-2) at a current density of 5 mA cm(-2) is among the highest values and the only 6.7% capacitance decay after 10 000 cycles demonstrates the excellent cycling stability. A flexible asymmetric supercapacitor (ASC) was fabricated with activated carbon (AC) as the anode and the obtained NiCo2O4@Ni3S2 NWAs as the cathode. The ASC device exhibited a high energy density of 1.89 mW h cm(-3) at 5.81 W cm(-3) and a high power density of 56.33 W cm(-3) at 0.94 mW h cm(-3). As a result, the hybrid nanoarchitecture opens a new way to design high performance electrodes for electrochemical energy storage applications.