The catalytic activity of vanadium pentoxide film modified electrode on the electrochemical oxidation of hydrogen sulfide in alkaline solutions

The presence of vanadium pentoxide (V₂O₅) as a deposited film at the glassy carbon electrode was found to promote the electrochemical oxidation of aqueous sulfide solution. The over potential of sulfide oxidation in alkaline buffer solution (pH 10.28) at this film modified electrode is decreased substantially by 500 mV in comparison to that at the bare glassy carbon electrode (GCE). The proposed mechanism indicated that the primary electron transfer and hence the observed anodic current at the modified electrode was due to the oxidation of the reduced species (V₂O ₄) into VO3- species which precipitated as V₂O₅ at the electrode surface. The electrode process found to be controlled by mass transport conditions and the calculated value of diffusion coefficient for sulfide (6.8 × 10^-9 m² s^-1) was 10-folds greater than that at the GCE. A Tafel-like plot for the data under the present experimental conditions is used to calculate the standard rate constant for sulfide oxidation. The rate constant adopted a value of 6.6 × 10 ^-5 cm s^-1 at high [HS^-], where the electrode process is expected to proceed at a slow rate. The reactivity of the present system was insignificantly affected by the formation of elemental sulfur and other insoluble vanadium species.