Bromine generation on various photoanodes: -Fe2O3, Fe2TiO5, WO3 and TiO2

The competitive photoelectrochemical reactions bromide vs. water (photo)oxidation in an acidic medium (pH = 1.7) were studied on four semiconducting oxides viz. hematite (alpha-Fe2O3), pseudobrookite (Fe2TiO5), tungsten trioxide (WO3) and titanium dioxide (TiO2). The experiments were carried out with thin film electrodes on conductive substrates (FTO/glass) in a vigorously stirred batch reactor under AM1.5 irradiation. Electrical bias was applied to the electrodes, exclusively promoting valence band processes leading to oxidative pathways. The initial Faradaic efficiency (FE0) for bromine generation was determined by chemical analysis (UV-Vis absorbance) of the electrolytes. The semiconducting materials used as photoanodes showed a similar ability to oxidize bromide to bromine. For 0.02 M sodium bromide, a Faradaic efficiency of 100% was obtained for alpha-Fe2O3, WO3 and TiO2, while the highest value for pseudobrookite was 90%. From further analysis, as to competition kinetics, the ratio of the rate constants of water oxidation and bromide oxidation, vH2O / kox, was estimated. alpha-Fe2O3 was the most successful compound among the studied semiconductors.