Time-resolved spectroscopy insights into charge transfer dynamics in quantum dot-based photocatalytic hydrogen evolution.

Solar-driven photocatalytic hydrogen evolution reaction (HER) represents a pivotal strategy for addressing the global energy crisis and achieving carbon neutrality. Colloidal semiconductor quantum dots (QDs) have emerged at the forefront of this field, owing to their size-tunable band structures, efficient charge separation, and versatile surface chemistry. This review focuses on the application of time-resolved spectroscopy, particularly femtosecond transient absorption (fs-TA) and time-resolved photoluminescence (TRPL), to elucidate the ultrafast charge transfer dynamics in QDs and their composite systems. By examining surface/interface engineering, heterojunction fabrication, cocatalyst functionalization, and molecular catalyst integration, we systematically summarize how ultrafast techniques serve as a quantitative "ruler" to resolve charge separation, migration, trapping, and interfacial transfer kinetics. Furthermore, we establish the fundamental structure-activity relationships governing macroscopic photocatalytic performance. Finally, future directions are proposed, including in situ/operando dynamic characterization, multiscale theoretical simulations, and rational system integration for practical applications.