Disclosure of charge storage mechanisms in molybdenum oxide nanobelts with enhanced supercapacitive performance induced by oxygen deficiency

Molybdenum oxide (MoO₃), with superior features of multi-electrochemical states, high theoretical capacitance, and low cost, is a desirable supercapacitor electrode material but suffers from low conductivity and insufficient active sites. The MoO₃ capacitance can be largely amplified by introducing oxygen (O) vacancies, but the mechanisms at the atomic scale are still ambiguous. Herein, O vacancies are created at the O2 and O3 sites in the MoO₃ nanobelts by carbonization to maximize the supercapacitance in the MoO_2.39. The supercapacitive storage is mainly ascribed to the proton adsorption at the O1 sites to create Mo–OH, leading to an expansion of the interlayer spacing along the lattice B-axis. Roughly 98% of the initial supercapacitance is retained after 1000 cycles, due to the reversible change in the interlayer spacing. Our results provide an insight into the oxygen deficiency-related mechanisms of the supercapacitive performance at the atomic scale and devise a facile method to enhance the supercapacitance for energy storage and conversion. Graphic abstract: [Figure not available: see fulltext.]