White clover based nitrogen-doped porous carbon for a high energy density supercapacitor electrode

We have employed the biomaterial white clover as a carbon precursor and ZnCl2 as an activating agent to prepare white clover carbons (WCCs). The WCC-2 (mass ratios of white clover and ZnCl2 is 1 : 2) possesses as high as 6.9 wt% nitrogen content and 857 m(2) g(-1) BET surface area. Furthermore, it exhibits 233.1 F g(-1) specific capacitance at a current density of 1.0 A g(-1), even 82.9% capacitance retention at 20 A g(-1) in 2 mol L-1 KOH electrolyte. The specific capacitance could remain at almost about 100.0% when the cycle number is between the 200-5000 cycles. Because of the wide potential window (0-2.0 V) and high specific capacitance, the WCC-2//WCC-2 symmetric capacitor shows an energy density of 30-13.1 W h kg(-1) under the power outputs of 503.5-9991.5 W kg(-1) in 0.5 mol L-1 Na2SO4 electrolyte. The results demonstrate WCC-2 can be a promising candidate for the electrode material of high performance supercapacitors.