Efficient Fabrication of Hierarchical Porous Carbon Fibers with Tunable Mesopores from Discarded Aramid for Supercapacitors

Template-free synthesis of advanced supercapacitor carbon with tunable interpenetrating micromesoporous structures remains a formidable challenge. Herein, porous carbon fibers with tunable mesopores were fabricated that were derived from discarded aramid fibers by H3PO4-assisted KOH activation without a template. The structural design of porous carbon fibers was achieved by utilizing the dehydration condensation reaction of H3PO4 with the amide groups in the aramid chain segments, which developed primary pores of porous carbon fibers and further facilitated K+ etching and embedding during subsequent KOH activation. The derived porous carbon fibers exhibited extremely tremendous specific surface area, abundant tunable mesopores, and N/O enriched surface. Benefiting from the synergy of the unique hierarchical porous structure and surface characteristics, the optimized porous carbon fiber provided an extremely high specific capacitance of 434.8 F g–1 at 0.2 A g–1 in a 6 M KOH electrolyte and excellent rate performance. Furthermore, in a 1 M Na2SO4 electrolyte, the assembled symmetric aqueous supercapacitor device displayed an ultrahigh energy density of 25.26 Wh kg–1 at a corresponding power density of 450 W kg–1, as well as remarkable cycling stability.