Superscript text Commercial activated carbon was modified by surface treatment using nitric acid, The modified carbons were characterized by X-ray photoelectron spectroscopy (XPS).The resultant carbon electrode-based electric double-layer capacitors (EDLCs)were assembled with 1 mol/L （NH4）2SO4 as the electrolyte. The influence of introduced functional groups, such as hydroxyl and carbonyl, on the performance of EDLCs was studied by Constant current charge-discharge. These functional groups significantly improved the wettability of AC. As a result, the specific capacitance of the carbon modified with 40wt.%HNO3 achieved a specific capacitance of 223.45 F/g at a current density of 5mA/cm2, which is 100.9% higher than that of original AC.
