CdSe-MoS2: A Quantum Size-Confined Photocatalyst for Hydrogen Evolution from Water under Visible Light

Under visible light irradiation, CdSe-nanoribbons photocatalyze H-2 evolution from aqueous sodium sulfite/sulfide solution with a quantum efficiency of 9.2% at 440 nm, whereas bulk CdSe is not active for the reaction. Photoelectrochemical measurements show that the activity of nano-CdSe is caused by a raised flatband potential (-0.55 V, NHE) which follows from the increased bandgap (2.7 eV) of this quantum confined material. In the presence of a sulfide ion, the flatband potential is fixed to -0.43 V (NHE), slightly below the sulfide redox potential (-0.48 V, NHE). When the nanoribbons are chemically linked to MoS2 nanoplates that were obtained by exfoliation and ultrasonication of bulk MoS2, the activity increases almost four times, depending on the mass percentage of MoS2. Cyclic voltammetry reveals that the enhancement from the MoS2 nanoplates is due to a reduction of the H-2 evolution overpotential. In contrast, chemical linkage of Pt nanoparticles to the nanoribbons does not affect the photocatalytic activity.