Surface Modification and Performance of Activated Carbon Electrode Material

A commercial activated carbon was modified by surface treatment using three chemicals, nitric acid, hydrogen peroxide, and ammonia, respectively. The modified carbons were characterized by N₂ adsorption-desorption isotherms and FTIR spectroscopy. The resultant carbon electrode-based electric double-layer capacitors (EDLCs) were assembled with 6 mol·L⁻¹ KOH as the electrolyte. The influence of surface modification on the performance of EDLCs was studied by galvanostatic charge-discharge, cyclic voltammetry, and alternating current impedance. The surface modification resulted in no big decrease in specific surface area and little decrease in average pore size, and introduced functional groups, such as hydroxyl, carbonyl, and amidogen, on the carbon surface. These functional groups significantly improved the wettability and reduced the resistance of the activated carbon. As a result, the specific capacitance of the carbon modified with 65% HNO₃ reached 250 F·g⁻¹, 72.4% higher than that of original carbon. The leakage current of testing EDLCs decreased unexpectedly to 3-18 μA, only 0.8%-4.9% that of the original carbon electrode-based EDLC (371 μA).