Dual-Activation Engineering with Molten Salt and KOH: Transforming Waste Fine Coke into Ultrahigh Capacitive Carbon for Supercapacitors

Fine coke is a kind of solid waste produced when high-quality carbon sources, such as needle coke, are used as lithium anode materials. There is a huge challenge in the industry to effectively use waste fine coke. In this study, using waste fine coke as the precursor, we fabricated capacitive carbon electrodes with outstanding electrochemical properties through an optimized KOH dosage in a KCl/NaCl molten salt system. The activation mechanism relies on temperature-dependent competition between molten salt and KOH. At lower temperatures, molten salt plays a dominant role in etching mesopores through mild chemical corrosion. While at elevated temperatures, KOH becomes the primary contributor to micropore formation via intensive alkali activation. This dual-activation strategy enables the synthesis of capacitive carbon for supercapacitors with an ultrahigh specific surface area (1171.24 m 2 g –1 ) and a hierarchical pore structure, ensuring both ion accessibility and charge storage. In a three-electrode system with a 6 M KOH electrolyte, it demonstrated a specific capacitance of 310.5 F g –1 at 0.5 A g –1, with 82.4% capacitance retention at a high current density of 10 A g –1 . What’s more, the assembled symmetric supercapacitor maintained 184 F g –1 at 10 A g –1, attributed to synergistic contributions from electric double-layer capacitance (EDLC, 91.9%) and pseudocapacitance (PC, 8.1%). This work pioneers high-value waste fine coke utilization. Simultaneously, it demonstrates that the synergistic competition between activator KOH and NaCl–KCl molten salt constitutes a green and effective strategy for preparing capacitive carbon materials.