Energy funneling and charge separation in CdS modified with dual cocatalysts for enhanced H2 generation

Anchoring molecular cocatalysts on semiconductors has been recognized as a general strategy to boost the charge separation efficiency required for efficient photocatalysis. However, the effect of molecular cocatalysts on energy funneling (i.e., directional energy transfer) inside semiconductor photocatalysts has not been demonstrated yet. Here we prepared CdS nanorods with both thin and thick rods and anchored the conjugated molecules 2-mercaptobenzimidazole (MBI) and cobalt molecular catalysts (MCoA) sequentially onto the surface of nanorods. Transient absorption measurements revealed that MBI molecules facilitated energy funneling from thin to thick rods by the electronic coupling between thin and thick nanorods, which is essentially a light-harvesting antenna approach to enhance the charge generation efficiency in the reaction center (here the thick rods). Moreover, MBI and MCoA molecules selectively extracted photogenerated holes and electrons of CdS nanorods rapidly, leading to efficient charge separation. Consequently, CdS/MBI/MCoA displayed 15 times enhanced photocatalytic H2 evolution (1.65 mL) than pure CdS (0.11 mL) over 3 h of illumination. The amount of H2 evolution reached 60 mL over 48 h of illumination with a high turnover number of 26294 and an apparent quantum efficiency of 71% at 420 nm. This study demonstrates a novel design principle for next-generation photocatalysts.