Balancing Surface Passivation and Charge Extraction in InP/ZnSe Core/Shell Quantum Dots for Photocatalytic Hydrogen Evolution

Abstract Indium phosphide quantum dots (InP QDs) are promising low-toxicity photocatalysts; however, their hydrogen (H2) evolution performance is often limited by surface defects and inefficient charge-carrier utilization. Herein, green-emitting InP/ZnSe core/shell QDs with systematically varied ZnSe shell thicknesses at the monolayer (ML) level were synthesized to elucidate how shell growth regulates the structural, photophysical, and photocatalytic properties of InP-based QDs. Among all samples, InP/ZnSe-1.7, corresponding to a 1.7 ML ZnSe shell coating, exhibited the highest H2 evolution rate of 699 μmol h–1 g–1, which apparent quantum yields ranging from 1.9% to 4.6% across the UV-to-visible region. Time-resolved photoluminescence, benzoquinone-assisted quenching analysis, and in-situ transient absorption spectroscopy collectively revealed that the enhanced photocatalytic activity does not arise solely from improved electron extraction, but rather from a favorable balance among surface passivation, suppressed recombination, and efficient carrier utilization. These findings highlight shell-thickness engineering as a key strategy for optimizing InP-based QDs for solar fuel production.