Boosting Energy Storage Performance of Co–Mn Oxide Nanostructures by Ultraviolet Radiation in Hybrid Supercapacitors

Cobalt–manganese oxide is a promising electrode material for supercapacitors due to its high theoretical capacity. However, poor electrical conductivity and structural stability limit the energy storage capacity of the Co–Mn oxide material. Herein, an ultraviolet (UV) light radiation strategy is proposed to prepare nitrogen-doped Co–Mn mixed oxide nanoarrays with enhanced electrochemical energy storage for supercapacitors. Co–Mn mixed oxide nanoarrays were first prepared by the hydrothermal method and then irradiated by a UV lamp to induce nitrogen doping. Because of the nanowire array architecture and UV-induced nitrogen doping, the obtained N-doped Co–Mn oxide shows a boosted charge storage performance with specific capacity of 2534 F g–1 (6.28 F cm–2) at 1 mA cm–2 and improved cyclic stability. Even without nitrogen doping, Co–Mn mixed oxide irradiated by UV light still has a high specific capacity of 1940 F g–1 at 1 mA cm–2 and good rate performance (1267 F g–1 at 60 mA cm–2), which is better than that of the Co–Mn mixed oxide sample prepared by conventional resistance furnace heat treatment. Furthermore, a high specific energy of 31.5 W h kg–1 is obtained for the hybrid supercapacitor device assembled by N-doped Co–Mn mixed oxide and N-doped graphene. These remarkable electrochemical performances suggest that the UV radiation method can effectively enhance the electrochemical properties of transition metal oxide materials. This work also provides an alternative to conventional thermal treatment in preparing high-performance electrode materials.