Drastic Layer-Number-Dependent Activity Enhancement in Photocatalytic H2 Evolution over nMoS2/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, MoS2 is shown promise as a low-cost alternative to Pt for hydrogen evolution. Here we report a systematical study on controlled synthesis of MoS2 with layer number ranging from approximate to 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 MoS2 layer number. Particularly for the single-layer (SL) MoS2, the SL-MoS2/CdS sample reaches a high H-2 generation rate of approximate to 2.01 x 10(-3)m h(-1) in Na2S-Na2SO3 solutions and approximate to 2.59 x 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 MoS2 has the more negative conduction band energy level than the H+/H-2 potential, facilitating the hydrogen reduction.