Study on two-step and low-temperature wet activation of residual carbon derived from coal gasification fine slag and its electrochemical performance for supercapacitor

Abstract Supercapacitors are promising electrochemical energy storage devices because of their high power density, fast charge–discharge rate, and long cycle life. The development of low-cost and high-performance carbon electrode materials is crucial for improving their practical application. Herein, residual carbon (RC) from coal gasification fine slags (CGFSs) was used as a carbon precursor to prepare low-cost carbon electrode materials (RCHK-X) through HNO₃ pre-activation followed by KOH activation. HNO₃ treatment introduced abundant oxygen-containing functional groups, while subsequent KOH activation further enhanced the surface functionality and specific surface area, removed part of the nitrogen-containing species introduced during acid treatment, and generated more defects and electrochemically active sites. The optimized RCHK-3 sample exhibited a specific surface area of 775 m² g⁻¹ and a low contact angle of 35.0°, suggesting favorable ion accessibility and surface wettability. When used as a supercapacitor electrode, RCHK-3 delivered a specific capacitance of 155 F g⁻¹ at 0.5 A g⁻¹ and maintained 99.03% of its capacitance after 10,000 cycles. This work demonstrates an effective strategy for converting CGFS-derived residual carbon into value-added electrode materials and provides guidance for designing porous carbon materials for high-performance supercapacitors.