Electronic Structure and Photoelectrochemical Properties of an Ir-Doped SrTiO 3 Photocatalyst

The effect of iridium valence in Ir:SrTiO 3 on the electronic structure and the photocatalytic activity in a water splitting reaction was studied. Epitaxial thin film photoelectrodes were grown with controlled Ir valence and used to measure the electrochemical efficiency of Ir:SrTiO 3 . The positions of the in-gap Ir impurity levels were determined by optical and X-ray photoelectron spectroscopies. Comparison with ab initio calculations was used to assign the observed electronic states to either Ir 4+ or Ir 3+ dopants in SrTiO 3 . The measurements show that Ir 3+:SrTiO 3 forms a single midgap impurity state that is strongly localized, completely quenching the photoelectrochemical response. An anodic photoresponse was seen in Ir 4+:SrTiO 3 under visible-light illumination up to a wavelength of 600 nm (hν = 2.0 eV). Ir 4+:SrTiO 3 contains an in-gap state close to the top of the SrTiO 3 valence band. The performance of Ir 4+:SrTiO 3 in electrochemical reactions is compared with cathodic Rh 3+:SrTiO 3, clearly illustrating the importance of strong dopant d-electron hybridization with the oxygen 2p valence band of SrTiO 3 for improving the energy conversion efficiency in SrTiO 3 -based photocatalysts.