Sustainable Conversion of Pomelo Peel Into Porous Activated Carbon With Hierarchical Nanoarchitectonics for High‐Performance Supercapacitors

ABSTRACT The sustainable valorization of agricultural waste into functional carbon materials offers an environmentally friendly strategy for developing advanced energy‐storage systems. In this study, hierarchically porous activated carbon (PAC) was successfully synthesized from pomelo peel ( Citrus maxima ), an abundant agricultural by‐product, through controlled carbonization followed by NaHCO 3 ‐assisted chemical activation. The synthesized PAC was comprehensively characterized to investigate its structural, morphological, textural, and surface chemical properties. The material exhibited a hierarchically porous carbon framework with partial graphitic ordering, a high specific surface area of 1101 m 2 g −1 , and abundant oxygen‐ and nitrogen‐containing functional groups that facilitate electrolyte accessibility, rapid ion transport, and efficient charge storage. Electrochemical evaluation in both three‐ and two‐electrode configurations using 1 M H 2 SO 4 demonstrated excellent capacitive performance. The symmetric SSM/PAC‖PAC/SSM device delivered a device‐level specific capacitance of 101.5 F g −1 at 1 A g −1 , corresponding to an estimated single‐electrode‐equivalent‐specific capacitance of approximately 406 F g −1 for an ideal symmetric cell. The device further achieved an energy density of 14.1 Wh kg −1 at a power density of 250 W kg −1 , and outstanding cycling stability with 96% capacitance retention after 10,000 charge–discharge cycles. The enhanced electrochemical performance is attributed to the synergistic effects of the hierarchical pore structure, partial graphitic domains, and heteroatom‐enriched surface chemistry generated through the NaHCO 3 activation process. This work demonstrates an efficient and sustainable route for converting pomelo peel into high‐value porous carbon and highlights its potential as a renewable electrode material for next‐generation supercapacitors and biomass‐based energy‐storage technologies.