Al-doped SrTiO₃ (SrTiO₃:Al) is currently the only known particulate photocatalyst that achieves near-unity apparent quantum efficiency (AQE) for overall water splitting. The underlying mechanism by which Al doping enhances photocatalytic performance has attracted widespread attention, as uncovering how photogenerated charges are efficiently utilized is critical for the rational design of high-performance photocatalysts. Such insights are essential for advancing scalable solar-to-hydrogen conversion technologies. Developing SrTiO₃:Al model photocatalysts with well-defined structures and high activity is therefore fundamental to elucidating the mechanisms behind their exceptional charge separation and surface reaction efficiencies. In this work, we systematically investigate the effects of various synthesis parameters on the photocatalytic performance of SrTiO₃:Al prepared via a flux method. The parameters studied include the temperature, the phase and amount of Al₂O₃ dopant, and the morphology and crystallinity of the SrTiO₃ precursor. The photocatalytic activity of SrTiO₃:Al exhibits a volcano-type dependence on the synthesis temperature, with the highest activity achieved at 1423 K. The crystal structure of the Al₂O₃ dopant also plays a critical role: γ-Al₂O₃ and partially crystalline α-Al₂O₃ (with 80% α-phase) lead to markedly improved performance. The optimal amount of Al₂O₃ added depends strongly on the type of precursor, 1 mol% for hydrothermally synthesized precursors and 1~2 mol% for those prepared via solid-state synthesis. At a fixed Al₂O₃ content of 2 mol%, the properties of the precursor significantly affect the final particle morphology, size distribution, and crystallinity. The best-performing sample exhibits high crystallinity and a narrow particle size distribution centered around 200 nm. Al doping in SrTiO₃:Al not only repairs lattice defects and suppresses excessive grain growth but also promotes the exposure of high-index facets. These findings suggest that multiple synthesis parameters synergistically govern the doping concentration and spatial distribution of Al, ultimately modulating lattice quality, particle structure, and charge separation efficiency—thereby determining the overall water splitting activity of SrTiO₃:Al.

Key words: Al doped SrTiO₃, photocatalytic overall water splitting, flux method, particulate photocatalyst