Strontium Titanate Photoelectrodes. Efficient Photoassisted Electrolysis of Water at Zero Applied Potential

Irradiation of an n-type semiconductor SrTiO₃ electrode in an electrochemical cell is shown to result in the sustained conversion of H₂O to H₂ and O₂. In 9.5 M NaOH oxidation occurs at the photoelectrode at potentials more positive than ca. -1.3 V vs. a saturated calomel electrode (SCE), and H₂ evolution is observed at the Pt electrode which is not illuminated. Results reported herein show for the first time that the electrolysis of H₂O can be driven photochemically without any external bias. The photoeffect obtains upon irradiation with light of shorter wavelength than 390 nm which corresponds closely to the known absorption edge for the valence band to conduction band transition in SrTiO₃. The photocurrent reaches its maximum value near 330 nm and the response is nearly constant with increasing excitation energy. Quantum efficiency for electron flow is found to be 1.0 ± 0.20 upon irradiation with light of shorter wavelength than 330 nm at applied potentials of ≥1.5 V. Current efficiency is excellent, producing H₂ and O₂ in the correct stoichiometric ratios. Photoelectrode stability has been confirmed by experiments carried out in oxygen-18 labeled H₂O and by the lack of weight loss in the SrTiO₃.