Oxygen vacancy-enriched MoO3−x nanobelts for asymmetric supercapacitors with excellent room/low temperature performance

Abstract

Oxygen vacancy-enriched MoO_3−x nanobelts with oxygen vacancies up to 20% (equal to MoO_2.4) were synthesized and demonstrated fast reaction kinetics. An asymmetric supercapacitor was assembled with active carbon (AC) as the anode and the as-prepared MoO_3−x nanobelts as the cathode. A new aqueous electrolyte of H₂SO₄/ethylene glycol (EG) was investigated and found to work appropriately at low temperatures, even at −25 °C. The MoO_3−x nanobelts electrode possesses excellent specific capacitance, 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 38 000 cycles). Its energy and power densities reached 111 W h kg⁻¹ and 803 W kg⁻¹ or 50 W h kg⁻¹ and 27 321 W kg⁻¹ and maintained 80 W h kg⁻¹ and 794 W kg⁻¹ or 17 W h kg⁻¹ and 23 565 W kg⁻¹ at −25 °C. It is hypothesized that the coexistence of oxygen vacancies and low valence Mo ions enhanced both mass and charge transport kinetics and catalyzed the redox reactions.