Synergistic effect of electron-transfer mediator and interfacial catalytic active-site for the enhanced H2-evolution performance: A case study of CdS-Au photocatalyst

For noble metal cocatalyst-modified photocatalysts with a high H2-evolution performance, both of the rapid electron transfer (or electron capture) from semiconductor to cocatalyst and the following interfacial catalysis for H2 production on the cocatalyst surface are highly required. Compared with Pt-loaded photocatalyst, Au-modified sample usually shows an obviously lower H2-evolution activity due to its inefficient H2-production rate on the Au cocatalyst surface. In this study, the SCN− ions as the catalytic active sites are selectively adsorbed on the Au surface of CdS/Au photocatalysts (CdS/Au-SCN), with the aim of promoting the interfacial H2-evolution reaction on Au cocatalyst and improving the photocatalytic water-splitting efficiency of CdS/Au system. The CdS/Au-SCN photocatalysts were synthesized via a two-step process including the initial photoinduced deposition of Au nanoparticles on CdS surface and the following selective adsorption of SCN− on the Au surface by an impregnation method. It was found that the resultant CdS/Au-SCN photocatalysts exhibited obviously improved photocatalytic H2-evolution activity compared with the CdS, CdS/Au and CdS/SCN photocatalysts. Especially, the CdS/Au-SCN(0.5 mM) achieved the highest photocatalytic activity (109.60 μmol h−1) with an apparent quantum efficiency (QE) of 11.25%, which was clearly higher than that of CdS and CdS/Au by a factor of 2.3 and 1.5 times, respectively. The enhanced H2-evolution performance of CdS/Au-SCN can be attributed to the excellent synergistic effect of Au and SCN−, namely, the Au nanoparticle functions as an effective electron-transfer mediator for the steady capture and rapid transportation of photogenerated electrons from CdS surface, while the adsorbed SCN− serves as the interfacial catalytic active-site to effectively adsorb H+ ions from solution and promote the rapid H2-evolution reaction. The present synergistic mechanism of electron-transfer mediator and interfacial catalytic active-sites may provide some new insights for the design of highly efficient photocatalytic materials.