New insight into the effect of oxygen vacancies on electrochemical performance of nickel-tin oxide/reduced graphene oxide composite for asymmetric supercapacitor

Limited electrochemical active sites and high electrical resistivity of transition metal oxides deteriorate the electrochemical activities. Oxygen vacancies (OVs) creation in transition metal oxides has been used to expose more electrochemically active sites. NaBH₄ is widely used as an oxygen scavenging agent which creates oxygen vacancies by removing the oxygen atoms bonded with the metal. Herein, Ni[sbnd]Sn oxide/reduced graphene oxide (NSG) composite with abundant OVs was successfully prepared via hydrothermal method. OV-NSG 2 exhibited the highest specific capacitance of ~1800 F g⁻¹ at 2 A g⁻¹ current density. The fabricated asymmetric supercapacitor device consisting of OV-NSG 2 as positive electrode and sonochemically reduced graphene oxide as the negative electrode exhibited the highest energy density of ~41.04 W h kg⁻¹ at a power density of ~1.476 kW kg⁻¹. The retention of energy density was found to be ~60 % when the power density increased to ~2.432 kW kg⁻¹. The device showed ~80 % capacitance retention after 10,000 continuous GCD cycles. Two ASC devices connected in series could power a 1.8 V red LED light for ~1 min.