Metal oxide top layer as an interfacial promoter on a ZnIn2S4/TiO2 heterostructure photoanode for enhanced photoelectrochemical performance

We designed metal oxide coated ZnIn2S4/TiO2 (ZT) heterostructure photoanodes for enhanced photoelectrochemical performance via hydrothermal and dip-coating methods. The effects of thin metal oxide coating layers, such as TiO2, Al2O3, and SiO2, on the structural, morphological, optical, and photoelectrocatalytic activity of ZT photoanodes were investigated in detail. The metal oxide coating layers significantly enhanced the photoelectrochemical performance of ZT in the following order: SiO2/ZT>Al2O3/ZT>TiO2/ZT>ZT, all at pH 11.5 under simulated one sun illumination. A two-fold boost in the photocurrent density of ZT was recorded after a surface coating of a thin SiO2 layer among the studied metal oxide layers. The charge transfer resistance measured from the electrochemical impedance spectroscopy (EIS) analysis was less for the SiO2/ZT photoanode, indicating enhanced charge separation between the oxide surface layer and electrolyte. The enhanced photoelectrochemical performance due to the thin SiO2 coating was attributed to the improved interface properties that led to the effective charge transfer processes in the vicinity of the electrolyte. (C) 2015 Elsevier B.V. All rights reserved.