H3PO4 activated carbons as the electrode materials of supercapacitors using an ionic liquid electrolyte

H3PO4-activated carbons were prepared from Chinese fir sawdust, and their pore structure, surface chemistry and morphology were characterized by nitrogen adsorption, SEM and XPS. Their electrochemical performance as electrode materials for supercapacitors using[BMIM] [PF6] as the electrolyte was investigated by cyclic voltammetry, galvanostatic charge/discharge and electrochemical impedance spectroscopy. Results indicate that H3PO4 activation at 800 to 950℃ produces highly developed mesopores with a volume percentage as high as 66% of the total porosity. The carbon prepared at a H3PO4 to sawdust mass ratio of 3:1 has a specific capacitance of 162 F/g and delivers an energy density of 22.5 Wh/kg at 0.5 A/g. The specific capacitance remains at 86% after 5 000 cycles at 5 A/g, suggesting good cycling stability and rate capability. H3PO4 activation is an effective method to prepare activated carbons for use in ionic liquid-based supercapacitors.