Electrochemically modified glassy carbon for capacitor electrodes characterization of thick anodic layers by cyclic voltammetry, differential electrochemical mass spectrometry, spectroscopic ellipsometry, X-ray photoelectronspectroscopy, FTIR, and AFM

Glassy carbon (GC) electrodes were activated by electrochemical constant po tential anodization in order to generate high-surface area, high-capacitanc e electrodes. After anodic oxidation in sulfuric acid the electrodes exhibi ted increased capacitance. After subsequent electrochemical reduction of th e activated layer, a further significant increase in capacitance was observ ed. Growth, structure, and surface properties of the activated electrodes w ere monitored by cyclic voltammetry, differential electrochemical mass spec trometry, spectroscopic ellipsometry, X-ray photoelectron spectroscopy (XPS ), and atomic force microscopy (AFM). Two different types of glassy carbon obtained by pyrolysis at 1000 degrees C and at 2200 degrees C were compared . Differential electrochemical mass spectrometry reveals that CO2 is the ma in reaction product during oxidation, while CO2 and Hz are detected during reduction. The values of surface layer capacitance and thickness determined by spectroscopic ellipsometry increase as linear functions of oxidation ti me, rue resulting volumetric capacitance was at least 100 F/cm(3). After ox idation, the presence of functional surface groups was demonstrated by XPS. The relative contributions of the different surface functionalities depend on the pyrolysis temperature of the GC. Reduction lowered the concentratio n of oxygen-containing functional surface groups. The XPS results were qual itatively confirmed by Fourier transform infrared measurements carried out at the same samples. AFM measurements on glassy carbon showed that the film growth both into and out of the substrate, resulted in a raised surface af ter activation. A qualitative model for film growth is presented. (C) 2000 The Electrochemical Society.