A carbon fiber paper based electrode of high activity for electro-oxidation of aqueous sulfur dioxide

Abstract

Significant improvements in the activity of a carbon-based electrode for the electro-oxidation of aqueous sulfur dioxide were obtained by introducing surface oxygen functionalities through the anodization of carbon fiber paper (CFP) in sulfuric acid solution. Electrodes of varying surface oxygen content (2.9 atomic% to 25.6 atomic%) and relative proportion of different types of oxygen functional groups were obtained by changing the anodization potential and the concentration of sulfuric acid. The activity of the optimal electrode was quantified by exchange current density and charge transfer resistance, respectively. The exchange current density was about 2.17-times the pristine CFP electrode (17.6 × 10−4μA cm−2 compared to 8.09 × 10−4μA cm−2). The morphological and structural changes in the electrode on anodization were determined using field emission scanning electron microscopy (FESEM), X-ray diffraction (XRD) and Raman analysis. The chemical analysis of the electrode surface, done using X-ray photoelectron spectroscopy (XPS), showed a strong correlation between the electrode’s activity and the ratio of the percentage of hydroxyl groups to the sum of percentages of epoxy and carbonyl groups. The electrode performed well in an accelerated stability test based on cyclic voltammetry for over 1000 cycles.