Nitric acid modification of activated carbon electrodes for improvement of electrochemical capacitance

Nitric acid oxidation of activated carbon fabric in combination with calcination in N-2 at different temperatures was conducted to explore the influence of surface carbon-oxygen complexes on the performance of electrochemical capacitors fabricated with the carbon fabric. The performance of the capacitors was tested in 1 M H2SO4 within a potential range of -0.6 and 0.6 V. The specific capacitance of the carbon was found to increase upon oxidation. Surface complex analysis using temperature programmed desorption showed that the double-layer capacitance was enhanced due to the presence of CO-desorbing complexes while CO2-desorbing complexes exhibited a negative effect. The micropore resistance for ion migration was low for these carbons. The electrical connection resistance between the fabric and the backing plate as well as that between the carbon fibers accounted for the major proportion of the overall resistance and was shown to increase due to oxidation. A capacitance increase of more than 40% has been achieved, without increasing IR drop, by nitric acid oxidation followed by 450degreesC calcination that was shown to remove the majority of the CO2-desorbing complexes while retaining the CO-desorbing complexes. (C) 2002 The Electrochemical Society.