Origin of Enhanced Overall Water Splitting Efficiency in Aluminum-Doped SrTiO₃ Photocatalyst

With near unity quantum efficiency and operational stability surpassing 250 days in outdoor conditions, aluminum-doped SrTiO₃ (Al:SrTiO₃) with tailored cocatalysts is one of the promising photocatalysts for scalable solar H₂ production. Nevertheless, mechanistic insights behind Al-doping and Rh cocatalyst-induced enhanced overall water splitting (OWS) efficiency are not well elucidated. Herein, detailed charge carrier dynamics from sub-picosecond to milliseconds are unveiled for Al:SrTiO₃ by transient (optical and microwave probe) spectroscopy measurements. The obtained transients are rationalized using a theoretical model considering bimolecular recombination, trapping and detrapping processes. Due to a decrease in an n-type doping density, Al doping of SrTiO₃ significantly prolongs bulk carrier lifetime from 50 ns to 12.5 µs (consistent with the previous report). The crucial electron extraction process by the Rh cocatalyst located on the surface from Al:SrTiO₃ occurs well before the decay of charge carriers. In contrast, µs-long electron extraction time observed in SrTiO₃ is significantly slower than tens of ns bulk carrier lifetime, thus reducing the photocatalytic OWS reaction. Complementary analysis in conjunction with in situ charge carrier dynamics in water interface addresses the mechanistic insight into Al-doping-induced enhancement of OWS activity. Correlating material properties, carrier dynamics and photocatalytic activity is expected to help design next-generation photocatalysts via dopant and/or defects engineering for efficient solar-fuel production.