One-step synthesis of architectural Ni₃S₂ nanosheet-on-nanorods array for use as high-performance electrodes for supercapacitors

Although a wide variety of three-dimensional porous electrode architectures have been created for supercapacitors to markedly enhance the charge and mass transfer associated with cycling, their low volumetric energy densities limit applications in many energy storage systems. In this work, we report a unique electrode architecture consisting of Ni₃S₂ nanosheet-onto-Ni₃S₂-nanorods grown on nickel foam and prepared using a simple one-step hydrothermal method. When tested as an electrode for a supercapacitor (using a three-electrode configuration), this material exhibited excellent rate capability and cycling stability at high cycling rates. The obtainable capacitance decreased by <42% as the current density was increased from 20 to 240 mA cm^-2, and the capacity retained 89.3% of its initial value after 5000 cycles at a cycling rate of 120 mA cm^-2. Further, an asymmetric supercapacitor consisting of the Ni₃S₂ nanosheet-onto-Ni₃S₂-nanorods electrode and an activated carbon (AC) electrode displayed a volumetric energy density as high as ∼ 1.96 mWh cm^-3, with the potential to bridge the performance gap between thin-film Li batteries and commercial AC//AC supercapacitors. The outstanding electrochemical performance is attributed to the good mechanical adhesion and electrical connection with the substrate, high contact area with the electrolyte and alleviated structural pulverization during the ion insertion/desertion process. It is predicted that the architectural Ni₃S₂-nanosheet-on-nanorods array prepared with this facile method offers great potential promise in large-scale energy storage device applications.