Energy storage is vital for the development of numerous fields
including portable electronic devices, medical devices, transport
vehicles, and stationary energy resources [1,2]. The two major
charge storage systems that impact the growth of electrical energy
storage field are batteries and supercapacitors. Compared to lithium
ion batteries, supercapacitors offer unique advantages of high
power density and exceptional cycle life [3,4]. The current main
electrode materials for supercapacitors include carbon-based
materials, conductive polymer and metal oxides [5,6]. However,
the main bottleneck that hinders the practical applications of supercapacitors
is their low energy density. To solve this problem,
maximizing the specific capacitance and/or the cell voltage can
achieve the increase in energy density [7]. One of the promising
approaches for the improvement of energy density is to develop
transition metal oxides or hydroxides as electrode materials, which
can exhibit typical pseudocapacitive behavior. Because that their
fast and reversible surface Faradaic redox reaction, transition metal
oxides or hydroxides can significantly enhance their specific