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 Al³⁺ incorporation in SrTiO₃ while preserving the desired cuboctahedron morphology with exposed {100}/{111} facets. Increasing the Al³⁺ 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 SrTiO₃ delivers an apparent quantum yield of 81.1% at 335 nm for overall water splitting, producing H₂ and O₂ 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.