Charge carrier recombination in TiO2 and SrTiO3 single crystals: Impact of CoOx cocatalyst loading

Titanium dioxide (TiO2) and strontium titanate (SrTiO3) are widely used photocatalytic materials in photoelectrochemical (PEC) water-splitting processes. Recent advancements have aimed at improving energy conversion efficiency by loading cobalt oxide (CoOx) cocatalysts onto these materials' surfaces to enhance O-2 evolution and capture photogenerated holes. Charge carrier recombination plays a crucial role in PEC reactions. This investigation explores the impact of CoOx loading on various crystal faces on the charge carrier recombination dynamics in TiO2 and SrTiO3 single crystals using the microwave photoconductivity decay (mu-PCD) technique. The results indicate that CoOx loading increases the charge carrier recombination for both TiO2 and SrTiO3 across all crystal faces, as observed from the decay curves. Additionally, different tendencies of the injected photon density and temperature dependence of the carrier lifetime, derived from mu-PCD curves, reveal that CoOx loading on TiO2 surfaces introduces the new surface recombination center that dominates the charge carrier recombination. In contrast, for SrTiO3, the surface recombination center remains unchanged across all crystal faces. Consequently, these findings suggest that while CoOx loading on SrTiO3 surfaces does not affect the charge carrier dynamics and remains effective for water splitting, it poses a risk of enhancing carrier recombination and reducing efficiency in TiO2.