Redefining the Roles of Alkali Activators for Porous Carbon

Alkali activation was the common method to prepare commercial porous carbon. In a mixed alkali activation system, the role of individual alkali was generally assumed to be the same as in single alkali activation system, and only low corrosiveness of weak alkali was mostly emphasized. However, the intrinsic roles of individual alkali should be finely understanded and redefined to illuminate the activation pathway from the perspective of internal chemical reactions rather than corrosiveness. Herein, combing the in situ TG-MS analysis, DFT calculation and other characterizations, the activation processes were precisely tracked and the activation pathways were proposed. In the mixed alkali activation system, the strong alkali KOH served as the activation promoter, first decomposing into K2O, which then attacks the C-C bonds, forming active reaction sites defined as pore seeds. The weak alkali K2CO3 acted as the activation pathway modifier, CO32− preferentially etched the pore seeds over K2O due to the lower reaction barrier of CO32− interacting with the pore seeds. Consequently, the rough etching reaction of KOH was replaced and suppressed by the gentler action of CO32− forming more micropores. When the ratio of strong to weak alkali was 1:1, the obtained CK1K2-122 owned the highest microporosity (82.61%) and large specific surface area (1962.18 m2 g-1). It exhibited high specific capacitance of 296.7 F g-1 and excellent cycling stability with 98.3% retention after 10,000 cycles. The supercapacitor demonstrated high energy density of 114.4 Wh kg-1 at power density of 17.5 kW kg-1, with a broad potential window of 3.5 V.