Effect of Al Doping on the Photoelectrochemical OER Performance of Anisotropic SrTiO₃ Crystals

Perovskite oxide photoanodes are attractive for alkaline water oxidation but are commonly limited by interfacial recombination and sluggish charge transfer. Here we enhance anisotropic SrTiO3 (STO) photoelectrodes via Al doping and identify an optimal composition at 4% Al. In 0.1 M NaOH (pH 13) under simulated AM 1.5G illumination, 4% Al:STO exhibits the highest transient/steady photocurrent and the best LSV performance among all samples, together with a markedly reduced interfacial impedance, indicating accelerated charge extraction and transfer. High-resolution XPS confirms Al incorporation and reveals suppressed Ti3+-related defect states with modified oxygen-associated surface species, consistent with mitigated trap-assisted recombination. Band-structure analysis shows a negative shift in flat-band potential and slight band-gap narrowing after Al doping, providing more favorable carrier energetics. Steady-state and time-resolved photoluminescence further demonstrate strong PL quenching and prolonged carrier lifetime for 4% Al:STO. ECSA analysis suggests increased electrochemically accessible surface sites at the optimal doping level. Overall, moderate Al doping synergistically tunes defects, band energetics, and interfacial kinetics to improve STO photoanodes for solar water splitting.