ABSTRACT
Electrochemical technologies primarily include three categories, namely batteries, fuel cells, and electrochemical supercapacitors (ES). A significant attention has drawn on the development of ES, primarily due to their high power density, long lifecycle, and bridging function for the power/energy gap between traditional dielectric capacitors and batteries/fuel cells. The major challenges of ES in practical use are low energy density and high production cost. One of the approaches to overcome these challenges is to develop new electrode materials. Hierarchical nanostructures have the potential to be applied as electrode materials. Different from the mechanism of electrostatic double-layer capacitor (EDLC), pseudocapacitors mainly originate from the rapid redox reaction on the electrode surface. The specific capacitance of pseudocapacitors is much higher than that of EDLC, and the transition metal oxides (TMOs) are the main material for pseudocapacitors. Composites prepared by combining two or more TMOs may exhibit better electrochemical performance than a single material due to the synergistic effect of different TMOs.
