Electrolysis of water at SrTiO3 photoelectrodes: Distinguishing between the statistical and stochastic formalisms for electron-transfer processes in fuel-forming photoelectrochemical systems

Conventional photoelectrochemical and photovoltaic theory predicts a light intensity threshold for sustaining the net electrolysis of water using semiconductor electrodes, but a stochastic charge-transfer formalism for photoelectrolysis reactions does not predict such threshold behavior. This work examines the theoretical and experimental aspects of light-assisted water electrolysis using n-type SrTiO₃/H₂O interfaces. A theoretical framework, based upon simple chemical kinetic considerations, has been formulated to describe the behavior of such photoelectrosynthetic cells. Experiments conducted on the n-SrTiO₃/5.0 M NaOH(aq)/Pt photoelectrosynthetic cell have revealed a threshold in the short-circuit electrolysis current at 5 × 10^-5 W/cm² of 325-nm illumination. Additional theory and experiments have provided insight into relationships between two-electrode regenerative photoelectrochemical cells, two-electrode photoelectrosynthetic cells, and three-electrode potentiostatic cells. These experiments and theory indicate that a conventional chemical kinetic treatment of interfacial electron-transfer rates appears to be sufficient to describe the photoelectrochemical behavior of SrTiO₃ and TiO₂/aqueous junctions.