Photo(Electro)Chemical Oxidation of Water by the Persulfate Ion Over Aqueous Suspensions of Strontium Titanate SrTiO 3 Containing Lanthanum Chromite LaCrO 3

The photodecomposition of the S 2 O 2‐ 8 ion to the SO 2‐ 4 ion with concomitant oxidation of water to molecular oxygen over n‐type SrTiO 3 powders mixed with LaCrO 3 (mole fraction x = 0–1), using UV light (λ > 300 nm), is considerably faster than the photochemical (UV) decomposition of S 2 O 2‐ 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 ( E act = 61 kJ/mol), the persulfate concentration in first order and x . At 64°C and constant [S 2 O 2‐ 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 S 2 O 2‐ 8 ion, is expected to proceed faster in the case of p‐type semiconductors. In view of the reported p‐type conductivity of LaCrO 3 , which has previously been doped with the charge‐compensating Sr 11 ion, our results with the SrTiO 3 ‐ x LaCrO 3 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 SrTiO 3 ‐ x LaCrO 3 single crystals under illumination in a photoelectrochemical cell.