Hierarchically Architectured Nanoporous Biocarbons Prepared via Dual Chemical Activation for Applicability in CO2 Capture and Supercapacitors

Porous carbons are at the forefront of several applications, and their efficiency mainly depends on their overall porosity and surface area, with particular emphasis on the amount of microporous and mesoporous contents. In our current research, we present a facile technique of dual activation to fabricate hierarchically architectured nanoporous biocarbons (HNBCs) via an innovative synthetic interplay of KOH and ZnCl₂ as chemical activating agents. Using KOH activation, it was possible to develop HNBC with a specific surface area of 3070 m² g^–1 and a nearly equal proportion of micropores (53%) and mesopores (47%). The chemical treatment of this material with ZnCl₂ led to the expansion of micropores into mesopores, the ratio of which can be tuned by varying the amount of ZnCl₂ used. While this treatment significantly affected the content of micro- and mesopores, there was a negligible effect on the overall surface area, which proves that there is no compromise in overall porosity. When tested as a CO₂ adsorbent, the material HNBC-5K-Zn1, synthesized using 1 g of ZnCl₂, adsorbed 4.36 and 38.12 mmol of CO₂ at 0 °C and 1 and 30 bar, respectively. For HNBC-5K-Zn1, a reasonably high specific capacitance of 247.6 F g^–1 at a current density of 0.5 A g^–1 was observed, which can be retained to 155 F g^–1 even at a higher current density of 10 A g^–1. This material also exhibited a specific capacitance of 166.71 F g^–1 at 0.5 A g^–1 in a two-electrode system and further demonstrated reasonable energy and power densities of 33.342 Wh/kg and 666.63 W/kg (0.5 A g^–1), respectively. In addition, the prepared material is highly stable even after 5000 cycles, with no significant loss of specific capacitance. The hierarchical porosity with the combination of micro- and mesopores obtained through the dual activation approach is responsible for this excellent performance.