Boosted Photocatalytic Water Oxidation over BaTaO₂N Produced from Perovskite Oxides Based on Photoinduced Charge Carriers

Photocatalytic water splitting utilizing visible-light-active materials holds promise for a greener and more facile way to generate H2 and O2. Herein, we analyze the strong potential of BaTaO2N for oxygen generation via water splitting based on a fundamental understanding of the behavior of photoinduced charge carriers. We found that the photoexcited electrons in BaTaO2N undergo trapping at trap states 0.4 eV below the conduction band minimum. This electron trapping occurs following significant electron–hole recombination within 200 ps after excitation. We also identified the important role of oxygen evolution cocatalysts not only for effectively enhancing charge-carrier separation but also for reducing the trap-state energy level from 0.4 to 0.1 eV. Overall, the combination of sluggish charge-carrier recombination and effective and rapid hole transfer to CoOx resulted in an almost 100-fold increase in the population of accumulated long-lived electrons in defect-rich BaTaO2N. This observation is consistent with the high O2 evolution rate exhibited by this material. These findings open up new directions and strategies to capitalize on the properties of BaTaO2N and further allow the development of highly effective oxynitride-based materials for water splitting.