Porous carbon derived from Terminalia catappa leaves for energy storage application

Abstract

Three dimensional hierarchical porous carbon was prepared from dry almond leaves (Terminalia catappa) by a two step process. Initially, the leaves were pyrolysed at different temperatures from 700 °C to 1100 °C with an interval of 100 °C and named C-700 to C-1100. An optimised C-1000 carbon sample showed a surface area of 491.3 m² g⁻¹ and a specific capacitance of 212 F g⁻¹ at 2 mA cm⁻². To study the fine tuning of the porous structure and to improve the surface area, the C-1000 sample was activated at different mass ratios of C-1000 and KOH. Among these, the AC-2 sample (C-1000 : KOH = 1 : 2) exhibited hierarchical micro, meso and macro porous structure with a specific surface area of 988.7 m² g⁻¹. It showed a specific capacitance of 394 F g⁻¹, high energy density of 54.7 W h kg⁻¹ and power density of 400 W kg⁻¹ at 2 mA cm⁻² with an excellent cycling stability of 98% over 5000 CV cycles. The AC-2//AC-2 symmetric device delivered a specific capacitance of 33.32 F g⁻¹ at 3 mA cm⁻², cycling stability of 93% after 5000 CV cycles and excellent mechanical flexibility with 98% capacitance retention after 180° bending indicating its prospect for portable electronics application. The results of this study imply a great potential of Terminalia catappa leaf derived porous carbon for efficient and sustainable energy storage devices.