COMPETITIVE PHOTOANODIC OXIDATION OF HALIDE-IONS AND WATER AT A TIO2 THIN-FILM ELECTRODE - AN IN-SITU PHOTOCALORIMETRIC AND ANALYTICAL STUDY

Photocalorimetry was used to determine the current efficiency of the p hotoanodic oxidation of halide ions (0.2 M Cl-, Br- and I-) competing with that of water at a polycrystalline TiO2 (rutile) thin film electr ode for a range of pH values. For Cl- and Br- the results were checked by chemical analysis (spectrophotometry, polarography) of oxidation p roducts present in the electrolyte solution. Photocurrent efficiencies determined photocalorimetrically and analytically for the formation o f halogens (Cl-2 and Br-2 + Br-3(-)) in acid solution were in satisfac tory agreement. Observations made at pH 9 suggest the formation of ClO - and BrO- on the time scale of the experiments. The photocurrent effi ciency for oxidation of the halide ions at a given pH was found to inc rease in the order Cl-, Br-, I- and to decrease, for each species, wit h increasing pH. This corroborates the trends reported by other worker s from rotating ring disk electrode studies using rutile single-crysta l electrodes.