Flexible asymmetric supercapacitors based upon Co₉S₈ nanorod//Co₃O₄@RuO₂ nanosheet arrays on carbon cloth

We have successfully fabricated flexible asymmetric supercapacitors (ASCs) based on acicular Co₉S₈ nanorod arrays as positive materials and Co₃O₄@RuO₂ nanosheet arrays as negative materials on woven carbon fabrics. Co₉S₈ nanorod arrays were synthesized by a hydrothermal sulfuration treatment of acicular Co₃O₄ nanorod arrays, while the RuO₂ was directly deposited on the Co₃O₄ nanorod arrays. Carbon cloth was selected as both the substrate and the current collector for its good conductivity, high flexibility, good physical strength, and lightweight architecture. Both aqueous KOH solutions and polyvinyl alcohol (PVA)/KOH were employed as electrolyte for electrochemical measurements. The as-fabricated ASCs can be cycled reversibly in the range of 0-1.6 V and exhibit superior electrochemical performance with an energy density of 1.21 mWh/cm³ at a power density of 13.29 W/cm³ in aqueous electrolyte and an energy density of 1.44 mWh/cm³ at the power density of 0.89 W/cm³ in solid-state electrolyte, which are almost 10-fold higher than those reported in early ASC work. Moreover, they present excellent cycling performance at multirate currents and large currents after thousands of cycles. The high-performance nanostructured ASCs have significant potential applications in portable electronics and electrical vehicles.