Oxygen Vacancies-enriched MoO3-x Nanobelts for Asymmetric Supercapacitors with Excellent Room/Low Temperature Performance†

Oxygen vacancies-enriched MoO3-x nanobelts with oxygen vacancies up to 20% (equals to MoO2.4) were synthesized by one-step hydrothermal method and demonstrated fast reaction kinetics. An asymmetric supercapacitor was assembled with active carbon (AC) as anode and the as-prepared MoO3-x nanobelts as cathode. A new aqueous electrolyte of H2SO4/ethylene glycol (EG) was investigated and found to work properly at low temperatures, even at -25 oC. MoO3-x nanobelts electrode possesses excellent specific capacitance and rate capacity (1230 F·g-1 and 1220 F·g-1 at 5 A·g-1 and 50 A·g-1, respectively) and cycle performance (100% after 38000 cycles). Its energy and powder densities reached 111 Wh·kg-1 and 803 W·kg-1 or 50 Wh·kg-1 and 27321 W·kg-1 and kept 80 Wh·kg-1 and 794 W·kg-1 or 17 Wh·kg-1 and 23565 W·kg-1 at -25oC. It is hypothesized that the coexistence of oxygen vacancies and low valence Mo ions enhanced both mass and charge transport kinetics as well as catalyzed the redox reactions.