Synergistic regulation of carbonyl oxygen active sites and micropores in lignite-derived porous carbon for high-performance supercapacitors

Oxygen-rich porous carbon derived from low-rank lignite offers a cost-effective route to pseudocapacitive materials. Here, we integrate NaCl hard templating, freeze-drying, and KOH activation to construct oxygen-rich lignite-derived porous carbon (OLPC) with abundant micropores and high carbonyl oxygen content. Machine learning feature analysis and density functional theory (DFT) jointly reveal the critical roles of pore structure and carbonyl oxygen species in enhancing capacitive performance. The optimized OLPC-600 exhibits a high specific surface area (2132 m² g⁻¹), a 71 % micropore ratio, and significant carbonyl oxygen content (6.18 % CO). This material achieves a specific capacitance of 357 F g⁻¹ at 0.5 A g⁻¹ and an energy density of 16.2 Wh kg⁻¹ at 275 W kg⁻¹ in a symmetric supercapacitor. The synergy between micropores and carbonyl functionalities accounts for this superior performance. These findings highlight a practical pathway for lignite valorization and provide a cost-effective strategy for designing high-performance carbon-based energy storage materials.