Synergistic Regulation of Shallow Energy Level‐Mediated Carrier Dynamics and Deep Defect Passivation for Enhanced Photocatalytic Hydrogen Evolution Over Zn _0.3 Cd _0.7 S/ZnS Quantum Dots

Aiming at the core bottlenecks of severe carrier recombination and disordered migration in quantum dot (QD) photocatalysis, this study proposes a synergistic strategy of “shallow‐level defect‐mediated carrier temporary storage and heterojunction built‐in electric field‐directed transport” to boost the photocatalytic hydrogen evolution (PHE) performance of ZnCdS QDs (ZCS QDs). Employing 20‐fold excess sulfur, S 2 − replaces organic ligands to establish surface shallow‐level defects (0.26 eV from the conduction band bottom), whose weak electron binding enables temporary carrier storage and suppresses nonradiative recombination. Leveraging these these S 2 − sites, a 20% coverage ZnS partial shell is grown in situ to form a ZCS@ZnS heterojunction. The bandgap difference (ZCS: 2.56 eV; ZnS: 3.6 eV) induces a built‐in electric field, disrupting isotropic carrier migration and driving shallow‐level‐stored electrons to ZnS surface active sites for H 2 evolution. The optimized Zn 0.3 Cd 0.7 S/20%ZnS (SR) exhibits a PHE rate of 51.65 mmol·g −1 ·h −1 (25 times higher than pristine Zn 0.3 Cd 0.7 S) with approximately 80% retention after 5 cycles. This work addresses the “storage‐directed migration” tradeoff of carriers via defect level regulation and interface electric field design, providing a universal approach to optimize the photocatalytic performance of chalcogenide semiconductor QDs.