Enhanced specific capacitance by a new dual redox-active electrolyte in activated carbon-based supercapacitors

Commercial electrochemical capacitors exhibit high power density and long cycle life but suffer from low energy density due to low specific capacitance of activated carbon (<200 F g−1). Redox-enhanced electrochemical capacitors achieve higher specific energy by adding redox-active ingredients to the electrolyte, which provide additional faradaic pseudo-capacitance. Here, high-performance and stable aqueous redox electrochemical capacitors using a new dual-active electrolyte is developed, and the specific capacitance of activated carbon increases to 885 F g−1 after adding 0.05 M FeBr3 with no degradation over 10,000 cycles in a two-electrode cell, which is more than four-fold of the original capacitance of 204 F g−1. In addition, PVA was introduced to the electrolyte and proved to be a useful way to increase the coulombic efficiency. Moreover, this new energy storage system delivers high specific energy of 40 Wh kg−1 in 0.5 M Na2SO4 based on the mass of electrodes.