Hybrid symmetric supercapacitor assembled by renewable corn silks based porous carbon and redox-active electrolytes

Abstract We have prepared nitrogen doped biomass activated carbon (CSC-1) using the agricultural wastes corn silks as raw materials and ZnCl2 as activating agent (the same weight of corn silks and ZnCl2) carbonized at 800 °C. The activated carbon has high specific surface areas of 1764.8 m2 g−1, large specific capacitance of 358.0 F g−1 at 0.5 A g−1, 67% of the capacitance retention at 20 A g−1, and 99.2% of initiatory specific capacitance after 5000 consecutive cycles. To improve the energy density of the symmetric supercapacitor based on CSC-1 electrodes, we employed the 1 M H2SO4 aqueous solution with alizarin red (AR) and bromoamine acid (ABA) as an advanced electrolyte to fabricate a novel hybrid symmetric cell. Surprisingly, the above device obtains a high specific capacitance of 260.8 F g−1 and a high energy density of 17.8 Wh kg−1, which are markedly higher than those in the conventional electrolyte. The improved energy storage is attributed to Faradaic pseudocapacitance related to the redox-active species of AR and ABA in the H2SO4 electrolyte. Based on the excellent characteristics, the device is expected as a promising candidate to fabricate high performance supercapacitors.