Understanding how dopants distribute within oxide nanostructures is essential for controlling surface chemistry and charge transport in functional photocatalysts. Here, we employ aberration‑corrected STEM, high‑resolution EDS mapping, and electron energy loss spectroscopy (EELS) to resolve dopant incorporation and titanium charge states in Al‑doped SrTiO₃ at sub‑nanometre resolution. Elemental mapping reveals a distinct transition from edge‑enriched Al gradients at low doping (0–2 mol%) to the formation of an Al‑rich surface shell at higher loadings (10–20 mol%). Complementary EELS analysis shows a persistent Ti³⁺‑rich surface layer across all samples, while particle interiors remain fully oxidized (Ti⁴⁺). The decoupling of Al distribution and Ti charge state suggests that Al‑rich surface layers, rather than Ti reduction, govern the observed suppression of catalytic performance at high doping. These results demonstrate the power of combined STEM–EDS–EELS analysis to uncover nanoscale structure–function relationships in perovskite photocatalysts.
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