Acid assisted hydrothermal treatment for lignocellulose disruption to prepare achnatherum splendens derived hierarchical porous carbon cathodes in zinc-ion hybrid capacitors

Biomass carbon materials are promising cathodes for zinc ion hybrid capacitors (ZIHCs) due to their admirable cost performance, electrochemical stability, and capacitive behavior. However, traditional biomass carbon preparation methods based on single chemical activation neglect the complex structure of biomass, formed by densely cross-linked cellulose, hemicellulose, and lignin, which hinders the activation process to achieve high specific surface area (SSA) and hierarchical porous structure. Herein, achnatherum splendens (ASS) is firstly employed as a carbon source, and a new strategy of HCl assisted hydrothermal treatment combined with chemical activation is proposed to regulate porous structure and heteroatom adulteration. Acid assisted hydrothermal treatment disintegrates the lignocellulose framework in ASS, facilitating the penetration of chemical activators and enhancing the pore creating and heteroatom doping efficiency. As a result, the prepared biomass carbon exhibits a higher SSA (3000.35 m²·g⁻¹) and richer hierarchical pore structures than those of controlled samples. The superior accessible surface area and charge carrier migration channels provided by regulated porous structure would equilibrate the flux and electric field distributions and provide abundant active sites. Along with the increased electrochemical activity and affinity for electrolyte enabled by N/O heteroatom doping, electrochemical performance would be dramatically improved. The assembled ZIHC achieves an excellent specific capacity (158.6 mAh·g⁻¹), energy density (126.8 Wh·kg⁻¹), and cycling stability (90.9% capacity retention over 15,000 cycles). Ex-situ characterizations, COMSOL simulations, and theoretical calculations are conducted to reveal performance enhancement mechanism. This study provides new insights for the development of advanced porous carbon and high-performance ZIHCs.