Cation Vacancies in Ti‐Deficient TiO2 Nanosheets Enable Highly Stable Trapping of Pt Single Atoms for Persistent Photocatalytic Hydrogen Evolution

The stabilization of single‐atom catalysts on semiconductor substrates is pivotal for advancing photocatalysis. TiO2, a widely employed photocatalyst, typically stabilizes single atoms at oxygen vacancies - sites that are accessible but prone to agglomeration under illumination. Here, we demonstrate that cation vacancies in Ti‐deficient TiO2nanosheets provide highly stable anchoring sites for Pt single atoms, enabling persistent photocatalytic hydrogen evolution. Ultrathin TiO2 nanosheets with intrinsic Ti4+ vacancies are synthesized via lepidocrocite‐type titanate delamination and Pt single atoms are selectively trapped within these vacancies through a simple immersion process. The resulting Pt‐decorated nanosheets exhibit superior photocatalytic hydrogen evolution performance, outperforming both Pt nanoparticle‐loaded nanosheets and benchmarked Pt single‐atom catalysts on P25. Crucially, Pt atoms anchored at Ti4+ vacancies display remarkable resistance to light‐induced agglomeration, a key limitation of conventional single‐atom photocatalysts. Density functional theory calculations reveal that Pt incorporation into Ti4+ vacancies is highly thermodynamically favorable and optimizes hydrogen adsorption energetics for enhanced catalytic activity. This work highlights the critical role of cation defect engineering in stabilizing single‐atom co‐catalysts and advancing the efficiency and durability of photocatalytic hydrogen evolution.