Pyrolysis Regulation of Agarose into Hierarchical Porous Carbon for Supercapacitor Applications

Fundamental understanding of the biomass pyrolysis process on a molecular level provides important guidelines for designing advanced porous carbon materials. In this study, the effects of KOH and K2CO3 activators on the thermal decomposition of agarose were elucidated using TG-FTIR-GCMS coupling techniques. The results demonstrate that the presence of KOH/K2CO3 shifts the pyrolysis gaseous products from organic fragments to CO2 and H2O, thereby preserving more C-C bonds in the solid phase and facilitating the subsequent aromatization process. Furthermore, compared to using KOH as the sole activator, the K2CO3/KOH co-activation strategy suppresses the violent evolution of CO2 within the 300–400 °C range, thereby alleviating the structural shock to the material skeleton and ensuring its integrity. Therefore, the HPC-KCO prepared via a synergistic KOH/K2CO3 co-activation and one-step carbonization process exhibits a high specific surface area of 1670 m2 g−1 and successfully retains its interconnected hierarchical porous framework. Benefiting from its well-developed porous structure, HPC-KCO exhibits an impressive specific capacitance of 370 F g−1 when employed in zinc-ion capacitors. Furthermore, the assembled symmetric supercapacitor demonstrates robust stability over a wide temperature range from −60 to 100 °C, delivering a remarkable capacitance of 121 F g−1 even at −60 °C. This work offers a new insight for synthesizing porous structures of biomass-derived carbon.