Optimizing the mesopore ratio of lignin-derived hierarchical porous carbon via etching and exfoliation towards high-performance supercapacitors

The trade-off between specific capacitance and rate performance in hierarchical porous carbons (HPC) hinders their widespread use in supercapacitors. Herein, we report a cost-effective synthesis of HPC with a high specific surface area of 2192 m 2 /g, and interconnected micro-mesopores using industrial lignin via in situ etching and gas exfoliation carbonization process. Investigation shows that when the specific surface area is similar, the mesopore-to-micropore volume ratio (R) is critical for balancing specific capacitance and rate performance. Higher micropore volume (low R) enhances capacitance by providing abundant active sites but impedes ion diffusion and degrading rate performance. Conversely, dominant mesopore volume (high R) facilitates rapid ion transport yet reduces adsorption capacity due to limited active sites. Notably, our optimized HPC with R of 0.62 achieves a remarkable specific capacitance of 354F/g at 0.5 A/g and retains 271F/g (76.6 % retention) at 20 A/g. The symmetric supercapacitor demonstrates outstanding energy-power characteristics (11.9 Wh/kg at 302 W/kg) and long-term cycling stability (97.4 % retention after 10,000 cycles). This work provides a strategy for designing advanced carbon electrode materials and a sustainable pathway for biomass utilization.