Interplay of Charge Trapping, Charge Separation, and Chemical Reactivity in Photocatalytic ZnSe‐Based Semiconductor–Metal Hybrid Nanoparticles

Sustainable energy conversion technologies demand efficient, stable, and environmentally compatible photocatalysts. Here, we report heavy-metal-free ZnSe/ZnS─Au hybrid nanoparticles (HNPs) with controlled shell architecture and tunable Au-domain properties. These HNPs are designed to overcome intrinsic limitations of ZnSe-based nanomaterials, including surface oxidation, rapid electron trapping, inefficient charge extraction, and limited chemical reactivity. By correlating photocatalytic performance with structural analysis and ultrafast transient absorption spectroscopy, we reveal how the synergistic effect of shell characteristics and metal-domain properties governs photocatalytic functionality. The ZnS shell (partial, thin, or thick) determines the interplay between surface passivation and charge separation, with complete and thicker shells effectively suppressing surface traps but limiting electron transfer. The Au domains, ranging from single-atom catalysts (SACs) to crystalline tips, further modulate charge separation and chemical reactivity, with larger domains enhancing electron extraction at the expense of reactivity. Optimal photocatalytic performance is achieved with a thin shell decorated with sub-nanometric clusters, enabling efficient charge separation while maintaining substantial surface passivation and high chemical reactivity. This work establishes design principles for heavy-metal-free HNPs, showing that parallel tuning of shell and metal-domain characteristics allows precise control over photocatalytic functionality, paving the way for high-performance photocatalysts in sustainable energy applications.