A high-performance asymmetric supercapacitor based on Co(OH)2/graphene and activated carbon electrodes

A high-performance asymmetric supercapacitor has been fabricated using graphene supported Co(OH)2 nanosheet (Co(OH)2/GNS) as the positive electrode and carbon fiber paper supported activated carbon (AC/CFP) as the negative electrode in KOH aqueous electrolyte, respectively. The asymmetric supercapacitor exhibits a significantly improved capacitive performance in comparison with that of the symmetric supercapacitors fabricated with Co(OH)2/GNS or AC/CFP as the electrodes. The improvement is attributed a high conductivity and reversibility of electrode materials, leading to the large specific capacitance and broadened potential window, resulting in a high energy density (19.3 Wh kg− 1 at a power density of 187.5 W kg− 1), excellent power density (3000 W kg− 1 at an energy density of 16.7 Wh kg− 1) and long-term cycling stability (after 20000 cycles, initial capacitance remains well). These encouraging results make these low-cost and eco-friendly materials promising for applications in asymmetric supercapacitors with high energy density, power delivery and cycling stability.