Nanoconfinement dynamics and crystal plane exposure: Synergistic promotion of simulated solar-driven H2O-to-H2 conversion on host (CdS)-guest (Ti single-atom) nano-photocatalyst

Hexagonal cadmium sulfide (h-CdS) is very prospective in photocatalytic hydrogen production due to its appropriate band structure, and researchers concern so much on the morphological characteristics of nanoparticles (NPs) and nanorods (NRs). Due to different dimensions of two forms of nanostructures, very different nanoconfinement (NF) characteristics are presented, leading to different separation and migration kinetics of photoexcitons, thereby showing different catalytic performance. However, the inherent mechanism is still ambiguous, and this NF effect extensively exists in photocatalytic process, even determining the final catalytic performance. Herein, CdS NPs and CdS NRs here were synthesized and decorated by single-atomic titanium (Ti SAs) to construct two forms of nanoconfined systems with host (CdS)-guest (Ti) (H-G) interaction. Due to the typical three-dimensional (3D) NF dynamics of CdS NPs, the H-G interaction of optimized CdS NPs-Ti nanocatalyst played an isotropic synergistic dynamics on body-to-surface (BTS) photoexcitons migration, dramatically suppressing their recombination behaviors, thereby achieving more considerable improvement of simulated sunlight (SSL)-driven HER photoactivity (14.10 mmol·h−1·g−1, 22.5-fold of CdS NPs, AQY400 nm = 20.44%), and outperforming many non-precious metal and precious metal modified CdS nanocatalysts under same experimental conditions. Surface transient photovoltage (TPV) and first-principle calculations revealed that the appropriate crystal plane exposure and typical 3D NF dynamics of CdS NPs highly benefits to the formation of Ti-S bonding interactions followed by the isotropic H-G synergistic dynamics, possessing more boosted BTS migration kinetics of photoexcitons followed by highly suppressed recombination kinetics, thereby acquiring higher solar-to-hydrogen (STH) conversion efficiency. This study provides a prospective insight for elucidating an observable NF dynamics of photoexcitons.