Drastic Layer‐Number‐Dependent Activity Enhancement in Photocatalytic H 2 Evolution over n MoS 2 /CdS ( n ≥ 1) Under Visible Light

Exploiting noble‐metal‐free cocatalysts is of huge interest for photocatalytic water splitting using solar energy. As an efficient cocatalyst in photocatalysis, MoS 2 is shown promise as a low‐cost alternative to Pt for hydrogen evolution. Here we report a systematical study on controlled synthesis of MoS 2 with layer number ranging from ≈1 to 112 and their activities for photocatalytic H 2 evolution over commercial CdS. A drastic increase in photocatalytic H 2 evolution is observed with decreasing MoS 2 layer number. Particularly for the single‐layer (SL) MoS 2 , the SL‐MoS 2 /CdS sample reaches a high H 2 generation rate of ≈2.01 × 10 −3 m h −1 in Na 2 S–Na 2 SO 3 solutions and ≈2.59 × 10 −3 m h −1 in lactic acid solutions, corresponding to an apparent quantum efficiency of 30.2% and 38.4% at 420 nm, respectively. In addition to the more exposed edges and unsaturated active S atoms, valence band–XPS and Mott–Schottky plots analysis indicate that the SL MoS 2 has the more negative conduction band energy level than the H + /H 2 potential, facilitating the hydrogen reduction.