High-performance electrode material for electric double-layer capacitor based on hydrothermal pre-treatment of lignin by ZnCl2

Hierarchical porous carbons (HPCs) were prepared through a simple and friendly method. ZnCl2 was used as an activating agent as well as a catalyst during lignin hydrothermal pre-treatment. The HPCs show a honeycomb structure with abundant micropores and the specific surface area (SSA) of HPCs is in the range of 1097–2955 m2 g−1. The effects of KOH/hydrochar weight ratio and activation temperature on the pore structure and electric double layer capacitor (EDLC) performance of the HPCs were investigated in detail. Compared to hydrothermal carbonization without ZnCl2, the HPCs prepared from hydrothermal pre-treatment with ZnCl2 possess high SSA and specific capacitance (Cs). The sample of 0.5-HPC-600-5 exhibits a high Cs of 384 F g−1 at 40 mA g−1 with 6 M KOH in a two-electrode system as well as excellent cycling stability with 96.96% initial Cs after 10,000 cycles at 2 A g−1. These exciting results show that hydrothermal pre-treatment is an effective route for the preparation of porous carbon with high electrochemical performance from lignin.