Metal oxide photoanodes for water splitting.

Solar hydrogen production through photocatalytically assisted water splitting has attracted a great deal of attention since its first discovery almost 30 years ago. The publication of investigations into the use of TiO₂ photoanodes has continued apace since and a critical review of current trends is reported herein. Recent advances in the understanding of the behaviour of nanoparticulate TiO₂ films is summarized along with a balanced report into the utility and nature of titania films doped with non-metallic elements and ordered, nanostructured films such as those consisting of nanotubes. Both of these are areas that have generated a not insignificant degree of activity. One goal of doping TiO₂ has been to extend the photoresponse of the material to visible light. A similar goal has seen a resurgence in interest in Fe₂O₃ photoanodes. Herein, the influence of dopants on the photocurrent density observed at Fe₂O₃ photoanodes and, in this regard, the role of silicon has attracted much attention, and a little debate. Finally, we look beyond the binary oxides. Photoanodes made from new materials such as mixed metal oxides, perovskite structured semiconductors, metal (oxy)nitrides or composite electrodes offer the potential to either tailor the optical band gap or tune the conduction or valence band energetics. Recent work in this area is detailed here.