Photoconductivity-Lifetime Product Correlates Well with the Photocatalytic Activity of Oxyhalides Bi4TaO8Cl and PbBiO2Cl: An Approach to Boost Their O2 Evolution Rates

Owing to the shallow valence band maximum generated upon hybridization of Bi/Pb 6s and O 2p orbitals, layered oxyhalides of Bi4TaO8Cl and PbBiO2Cl are stable and promising O-2-evolving photocatalysts for Z-scheme water splitting. However, some questions remain regarding how their synthesis parameter influences the charge carrier dynamics and overall photocatalytic process. Here, we show that the product of the transient pseudophotoconductivity maximum (phi Sigma mu(max)) and half-lifetime (tau(1/2)), as evaluated by time-resolved microwave conductivity (TRMC) measurements, correlates well with the O-2 evolution rates of such oxyhalides. Such correlation in Bi4TaO8Cl is rationalized by the increased crystallite size and decreased Cl/Bi atomic ratio with the increasing calcination temperature. On the basis of this, we examined the processing temperature of the rarely studied PbBiO2Cl by TRMC analysis and demonstrate a 3-fold enhancement of its O-2 evolution rate (apparent quantum efficiency of 3%), which is among the best performances of oxyhalides prepared by a solid-state reaction. This study suggests that TRMC evaluation provides a facile means to examine the potential of semiconducting photocatalysts.