Solar-Driven Photoelectrochemical Water Oxidation over an n-Type Lead-Titanium Oxyfluoride Anode

Mixed anion compounds (e.g., oxynitrides and oxysulfides) are potential candidates as photoanodes for visible-light water oxidation, but most of them suffer from oxidative degradation by photogenerated holes, leading to low stability. Here we show an exceptional example of a stable, mixed anion water-oxidation photoanode that consists of an oxyfluoride Pb2Ti2O5.4F1.2 having a band gap of ca. 2.4 eV. Pb2Ti2O5.4F1.2 particles, which were coated on a transparent conductive glass (FTO) support and were subject to post-deposition of a TiO2 overlayer, generated anodic photocurrent upon band-gap photo-excitation of Pb2Ti2O5.4F1.2 (λ < 520 nm) with a rather negative photocurrent onset potential of ca. –0.6 V vs. NHE, which was independent of the pH of electrolyte solution. Stable photoanodic current was observed even without loading a water oxidation promoter such as CoOx. Nevertheless, loading CoOx onto the TiO2/Pb2Ti2O5.4F1.2/FTO electrode further improved the anodic photoresponse by a factor of 2–3. Under AM1....