Nitrogen-rich green leaves of papaya and Coccinia grandis as precursors of activated carbon and their electrochemical properties

Activated carbon (AC) was synthesized from papaya and Coccinia grandis leaves (PL-AC and CL-AC, respectively) which are nitrogen-rich precursors and their electrochemical properties were investigated. The synthesis process included carbonization at 400 °C, impurity removal by H 2 SO 4 cleaning, and post activation by NaOH at 720 °C. Surpassing the conventional bamboo-derived AC (B-AC), PL- and CL-ACs show relatively high surface areas of 2664 and 2576 m 2 g −1 , respectively. Moreover, the nitrogen contents in the PL- and CL-ACs were approximately 2.3 and 1.8 at%, respectively. Furthermore, the electrochemical properties of the synthesized PL- and CL-ACs were investigated using both aqueous and organic electrolytes. The specific capacitances of the PL- and CL-ACs were 98.47 and 89.91 F g −1 , respectively, in Na 2 SO 4 electrolyte. Especially, compared to the B-AC, the PL-AC shows a dramatic decrease in series resistances ( R S ) from 1.33 to 0.53 Ω and charge transfer resistances ( R CT ) from 25.83 to 9.00 Ω. The decrease of R S and R CT is attributed to the existence of nitrogen in the PL-AC, resulting in a higher conductivity of electrode material and an enhancement of the charge transfer between electrode material and electrolyte. The large surface area of the PL- and CL-ACs was successfully achieved without detriment to the electrical conductivity. These results suggest that nitrogen-rich PL and CL are potential precursors for the synthesis of nitrogen-doped AC in a one-step process, which can be used as an alternative electrode material for electrochemical capacitors and can potentially be applied for large-scale industrial production with low cost. Activated nitrogen-rich green leaves of papaya and Coccinia grandis show high surface area without the detriment of the electric conductivity.