Abstract
Hierarchical structures of transition metal oxides with well-defined compositions are crucial for achieving advanced electrodes for energy storage devices. Herein, we first demonstrate the hierarchically structured MoO3 assembled by twisted nanoribbons with a hybrid composition for improved rate capability and cycle stability of the pseudocapacitor. The hierarchical, flower-like structures of MoO3 assembled by hybrid nanoribbons were induced by the specific interactions of MoO3 interlayers with ionic liquids (ILs), as proven by spectroscopic and electrochemical analyses. Furthermore, the interlayer modification of MoO3 crystallites through IL interaction enabled unique pseudocapacitive behaviors for fast and reversible proton intercalation/extraction that could not be observed by conventional MoO3. In this research, we used control samples to prove our hypothesis that the capacitor performances of MoO3 can be improved by a hierarchical structure and hybrid composition. These structural and compositional features of the hybrids greatly enhanced the rate capability by fast ion diffusion while improving cycle stability due to efficient stress release. More importantly, we observed the dramatic enhancement of ion diffusion coefficients of hybrids for good rate capability, because ion diffusion into the layered structure is very critical for maintaining specific capacitance at the high current density. The facilitated ion diffusion is attributed to the hierarchical nanostructure for a short diffusion length and ion accessibility, the high ion mobility in hybrids, and the interlayer modification of MoO3 by IL coating. Therefore, this research offers new insight into the rational design of advanced electrode materials on the basis of the hierarchical complex structures of transition metal oxides with well-defined hybrid compositions for future applications in energy conversion and storage.