Precise Tuning of Bilayer Ultrasmall MoS2 Featuring Inhibition of Carrier Recombination and Fast Surface Chemistry for Green H2 Evolution

Abstract Achieving water splitting to produce green H 2 , using the noble‐metal‐free MoS 2 , has attracted huge interest from researchers. However, tuning the number of MoS 2 layers precisely while obtaining small lateral sizes to surge the H 2 ‐evolution rate is a tremendous challenge. Here, a bottom‐up strategy is designed for the in situ growth of ultrasmall lateral‐sized MoS 2 with tunable layers on CdS nanorods (CN) by controlling the decomposition temperature and concentration of substrate seed (NH 4 ) 2 MoS 4 . Here, the bilayer MoS 2 and CN coupling (2L–MoS 2 /CN) exhibits the optimum photocatalytic activity. Compared to thicker MoS 2 , the 2L–MoS 2 has sufficient reduction capacity to drive photocatalytic H 2 evolution and the ultrasmall lateral size provides more active sites. Meanwhile, the indirect bandgap, in contrast to the direct bandgap of the monolayer MoS 2 , suppresses the carrier recombination transferred to 2L–MoS 2 . Under the synergistic effect of both, 2L–MoS 2 /CN has fast surface chemical reactions, resulting in the photocatalytic H 2 ‐evolution rate of up to 41.86 mmol g −1 h −1 . A novel strategy is provided here for tuning the MoS 2 layers to achieve efficient H 2 evolution.