Synergistic effect of green trace K2CO3 and CO2 activation of zhundong coal for high-performance supercapacitors

Porous activated carbons prepared by green trace K2CO3-assisted CO2, H2O, and CO2/H2O activated high-alkali Zhundong coal are being employed as supercapacitor electrode materials. Effects of trace K2CO3 (2 wt% of carbon precursor) and gas composition on physicochemical structure, the morphology and supercapacitor properties of the active carbon are investigated in detail. The results are showing that activated carbon from trace K2CO3-assisted CO2 activation exhibited excellent performance, indicating that CO2 and K2CO3 have synergistic effect in the activation process. It is mainly due to the higher O content in CO2/N2 atmosphere and promotion by K of O transfer from CO2 to the carbon matrix, which produces more active sites. Trace K2CO3-assisted CO2 activated carbon forms a forked hierarchical pore structure, more oxygen-containing functional groups, increases surface free energy of porous carbon, more potassium-containing group structures, and excellent graphitization of amorphous carbon compared with the other carbons. Its corresponding electrode and symmetrical supercapacitor achieve specific capacitance of 277.7 and 114.5 F g−1, respectively. The energy density is 10.54 Wh kg−1 at 209.98 W kg−1 and the material retained 95.89% after 10 000 cycles. A novel method of green trace K2CO3-assisted CO2 activation of high-alkali Zhundong coal is proposed for high-performance supercapacitors.