Heteroatom-enriched multiscale porous carbon from Semen Cassiae for high-energy supercapacitors

We report a heteroatom-enriched multiscale porous carbon (SC-HMPC-4-700) synthesized via a green, single-step KOH activation of Semen Cassiae biomass. This process achieves simultaneous in situ doping with N (2.8 at%), O (10.4 at%), P (1.1 at%), and S (1.2 at%), reaching a total heteroatom content of 15.5 at%. The resulting carbon exhibits an interconnected tri-modal (micro/meso/macro) pore network and a highly developed surface area of 3097.2 m2 g−1. Such an architecture synergistically enhances ion diffusion, electrolyte infiltration, and charge storage kinetics. As an electrode in alkaline medium, SC-HMPC-4-700 delivers an elevated capacitance of 360 F g−1 at 0.5 A g−1 and maintains 292 F g−1 at 20 A g−1, reflecting outstanding high-rate stability supported by both electric double-layer and pseudocapacitive contributions. Fabricated as a symmetric cell using 1-ethyl-3-methylimidazolium tetrafluoroborate-based electrolyte, the as-prepared electrode achieves 280 F g−1, retains 90.7 % capacitance over 10,000 cycling tests, and offers an energy density of 119.1 Wh·kg−1 at 875 W kg−1. These results underscore the promise of Semen Cassiae-derived carbon as a high-energy electrode material, and highlight the critical interplay between heteroatom functionality and the pore hierarchy in advanced energy storage systems.