Photochemical Deposition of Pt on CdS for H2 Evolution from Water: Markedly Enhanced Activity by Controlling Pt Reduction Environment

Pt is one of the most effective cocatalysts used in hydrogen evolution photocatalysts in water splitting. However, because Pt is an expensive noble metal, the efficient and optimum use of Pt is of high importance. In this work, the effect of loading conditions for Pt nanoparticles on the surface of CdS as a model photoabsorber was studied to reveal the important parameters for obtaining Pt cocatalyst of high activity. The activities of as-prepared Pt/CdS samples were evaluated in H-2 evolution from photocatalytic water splitting using Na2S and Na2SO3 as sacrificial reagents. It was found that the solution environment during Pt photoreduction played a critical role. Pt/CdS photocatalyst with Pt reduced in NaOH alkaline solution exhibited a markedly higher H-2 evolution activity (similar to 1300 mu mol h(-1)) than samples obtained in acidic or neutral solution (<50 mu mol h(-1)). Further materials characterization revealed H, evolution rate (wool that, in alkaline solution, Pt4+ species in the precursor (H2PtCl6 center dot xH(2)O) can be well reduced to metallic Pt-0, which shows high hydrogen evolution activity. On the other hand, in acidic or neutral solution, Pt4+ species can be only partially reduced to Pt2+ species, which are deposited on the surface of CdS. It is suggested that the promotional effect of alkaline conditions on Pt reduction is attributable to enhanced hydrolysis of PtCl62- to species containing fewer Cl- ions, such as Pt(OH)(5)Cl2- and Pt(OH)(6)(2-), which are then more easily reduced.