Abstract
Sulfide ions were oxidized at graphite electrodes from chloride brines directly into elemental sulfur, which was identified using X-ray photoelectron spectroscopy. This oxidation occurs at potentials where the Pourbaix diagrams predict that elemental sulfur is unstable. Hence the stability of the resulting elemental sulfur is attributed to kinetic rather than thermodynamic considerations. At the beginning, the process is controlled by both charge transfer at the interface and mass transfer within the electrolyte. Electrochemical and impedance measurements revealed that the resulting elemental sulfur passivates the electrode surface and gradually decreases the rate of the process. This is exhibited in exponential decay of the current and an increase of the polarization resistance of the interface with time of electrolysis. The latter shows an inflection which suggests a change in the resistivity of the sulfur film on the electrode surface. (C) 2003 The Electrochemical Society.