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 H₂, using the noble‐metal‐free MoS₂, has attracted huge interest from researchers. However, tuning the number of MoS₂ layers precisely while obtaining small lateral sizes to surge the H₂‐evolution rate is a tremendous challenge. Here, a bottom‐up strategy is designed for the in situ growth of ultrasmall lateral‐sized MoS₂ with tunable layers on CdS nanorods (CN) by controlling the decomposition temperature and concentration of substrate seed (NH₄)₂MoS₄. Here, the bilayer MoS₂ and CN coupling (2L–MoS₂/CN) exhibits the optimum photocatalytic activity. Compared to thicker MoS₂, the 2L–MoS₂ has sufficient reduction capacity to drive photocatalytic H₂ evolution and the ultrasmall lateral size provides more active sites. Meanwhile, the indirect bandgap, in contrast to the direct bandgap of the monolayer MoS₂, suppresses the carrier recombination transferred to 2L–MoS₂. Under the synergistic effect of both, 2L–MoS₂/CN has fast surface chemical reactions, resulting in the photocatalytic H₂‐evolution rate of up to 41.86 mmol g⁻¹ h⁻¹. A novel strategy is provided here for tuning the MoS₂ layers to achieve efficient H₂ evolution.