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 degrees C. The activated carbon has high specific surface areas of 1764.8 m(2) 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.