Unlocking the loading limit in single-atom photocatalysts <i>via</i> defect-induced metal trapping

Despite their great promise, the practical use of single-atom catalysts (SACs) is often limited by their unsatisfactory metal loading, primarily due to the limited availability of binding sites on the substrate. Herein, we report a defect-assisted metal trapping strategy to unlock the loading limit by generating highly tunable sulfur vacancies on ZnIn₂S₄ (ZIS) <i>via</i> electrochemical desulfurization, followed by the subsequent photodeposition of Co and Ni single atoms at high loadings (4.8 wt% Co and 6.7 wt% Ni). Such bimetallic SACs (Sv-ZIS-CoNi) exhibit a remarkable hydrogen evolution rate of 51.5 mmol g^-1 h^-1 under visible light due to synergistic interaction between adjacent Co and Ni atoms, outperforming state-of-the-art ZnIn₂S₄-based photocatalysts. Our catalyst retains 98% of its activity after five cycles of continuous operation due to the robust anchoring of single-atom sites at sulfur vacancies. This work provides a facile approach for synthesizing high-loading SACs through defect engineering.