Photo(Electro)Chemical Oxidation of Water by the Persulfate Ion Over Aqueous Suspensions of Strontium Titanate SrTiO3 Containing Lanthanum Chromite LaCrO3

The photodecomposition of the S2O2‐ 8 ion to the SO2‐ 4 ion with concomitant oxidation of water to molecular oxygen over n‐type SrTiO3 powders mixed with LaCrO3 (mole fraction x = 0–1), using UV light (λ > 300 nm), is considerably faster than the photochemical (UV) decomposition of S2O2‐ 8 in water or the thermal reaction with or without the powder under the same conditions. The rate of oxygen formation is dependent on the temperature (Eact = 61 kJ/mol), the persulfate concentration in first order and x. At 64°C and constant [S2O2‐ 8] a maximum rate is found at x = 0.25. The rate determining step, i.e. the transfer of an energy‐rich electron from the conduction band to the S2O2‐ 8 ion, is expected to proceed faster in the case of p‐type semiconductors. In view of the reported p‐type conductivity of LaCrO3, which has previously been doped with the charge‐compensating Sr11 ion, our results with the SrTiO3‐x LaCrO3 powders are in agreement with these expectations. The sensitivity of these materials towards visible irradiation is much lower than their UV response (about 1–2%) which has also been found by determining i/V and i/λ characteristics of SrTiO3‐x LaCrO3 single crystals under illumination in a photoelectrochemical cell