Electrochemical responses from surface oxides present on HNO3-treated carbons

Carbons of different surface oxide compositions, which were prepared from HNO₃ oxidation of polyacrylonitrile-based carbon fabric followed by heat treatment at different temperatures, were subjected to electrochemical response analysis using a voltammetric method. Temperature programmed desorption was employed to analyze the surface oxide composition. A significant amount of unstable oxides that can be irreversibly removed with reduction using a cathodic potential sweep were found to be present on the oxidized carbons. About 2.6 electrons are required to remove one oxygen atom from the carbon surface, and this may be the first quantitative study ever reported. After the initial cathodic sweep, no irreversible reduction peak response was observed for the subsequent electrochemical measurements. The capacitive performance of the carbons is related to the population of stable CO-desorbing complexes that can be determined with thermal desorption after the cathodic sweep. The present work has shown that carbon capacitance increases from 170 to 190 F/g with an increase of the CO-desorbing oxides from 1.31 to 1.56 mmol/g. This means that each stable CO-desorbing oxide is able to store 0.8 electron charge per volt within the potential window employed, suggesting the effective role of CO-desorbing oxides in improving the capacitance.