Two biomass material-derived self-doped (N/O) porous carbons from waste coriander and lilac with high specific surface areas and high capacitance for supercapacitors

Waste coriander and lilac were used to prepare two kinds of porous carbon for use in high-performance supercapacitors. The aim was to expand the application and increase the value of waste coriander and lilac, and to explore the difference in activation conditions of the two biomass materials. Specifically, a two-step method using KOH as the activation agent was employed to generate 3D self-doped (N/O) coriander-based porous carbon (CPC) and lilac-based porous carbon (LPC) by adjusting the activation temperature. Interestingly, the activation temperature of 600 °C results in maximum specific capacitances for both CPC and LPC, up to 421 F g−1 and 524 F g−1, respectively, which are higher than most other bamboo-derived porous carbon materials previously reported. Surprisingly, LPC-600 has a specific surface area of up to 2565 m2 g−1 and a very high content of N and O elements, which contributes to the electrode wetting, surface redox reactions and pseudo-capacitance for ion diffusion. The energy density of LPC-600 assembled into a symmetric supercapacitor in 6 M KOH and 1 M Na2SO4 solutions can even reach 18.17 W h kg−1 and 40.97 W h kg−1, respectively. Overall, this study confirms that these waste coriander- and lilac-derived porous carbon materials can not only reduce the wastage of resources but also provide two suitable sources for the preparation of porous carbon for high-performance electrochemical energy storage.