Tailoring the binary metal oxide along with developing new synthetic methods for controlling resultant nanostructures in a predictive way is an essential requirement for achieving the further improved electrochemical performance of pseudocapacitors. Here, through a rational design of the supersaturation-mediated driving force for hydrothermal nucleation and crystal growth, we successfully obtain one-dimensional (1-D) nickel molybdenum oxide (NiMoO4) nanostructures with controlled aspect ratios. The morphology of the 1-D NiMoO4 nanostructures can be tuned from a low to a high aspect ratio (over a range of diameter sizes from 80 to 800 nm). Such a controllable structure provides a platform for understanding the electrochemical relationships in terms of fast relaxation times and improved ion-diffusion coefficients. We show that the 1-D NiMoO4 electrode with a high aspect ratio (HAR) exhibits a much higher specific capacitance of 1335 F g-1 at a current density of 1 A g-1 compared to the other electrodes with a relatively low aspect ratio, which is due to the unique physical and chemical structure being suitable for electrochemical kinetics. We further demonstrate that an asymmetric supercapacitor consisting of the tailored HAR-NiMoO4 electrode can achieve an energy density of 40.7 Wh kg-1 and a power density of 16 kW kg-1.
Keywords: asymmetric supercapacitor; controlled aspect ratio; electrochemical reaction kinetics; energy storage material; nanowire architecture.