Anisotropic Facet Doping Amplifies Built‐In Electric Field in Single‐Particle Photocatalysts

Controllable chemical doping is an effective strategy to tailor electronic structure and charge‐carrier dynamics in semiconductors, especially in one‐step‐excitation semiconductor photocatalysts. However, achieving a controllable dopant distribution within a single‐particle photocatalyst without compromising its well‐defined redox facets remains a significant challenge. Here, using a two‐step molten‐salt synthesis as a controlled platform, we reveal facet‐selective Al 3+ incorporation in SrTiO 3 while preserving the desired cuboctahedron morphology with exposed {100}/{111} facets. Increasing the Al 3+ supply within this morphology‐preserving window leads to a pronounced facet‐anisotropic distribution within individual particles, with the Al content along {111} exceeding that along {100} by more than twofold from the surface toward the bulk. This facet‐anisotropic distribution enhances the inter‐facet electrostatic asymmetry associated with the intrinsic built‐in electric field. As a demonstration, 4.0 mol% Al‐doped SrTiO 3 delivers an apparent quantum yield of 81.1% at 335 nm for overall water splitting, producing H 2 and O 2 in a stoichiometric 2:1 ratio with a hydrogen evolution rate of 3364.13 µmol·h −1 . This work establishes facet‐resolved dopant distribution as a spatial design parameter for efficient particulate photocatalysis.