Sn4+ doping combined with hydrogen treatment for CdS/TiO2 photoelectrodes: An efficient strategy to improve quantum dots loading and charge transport for high photoelectrochemical performance

Abstract

We demonstrate that Sn4+ doping and hydrogen treatment can be used as effective strategies to fundamentally improve the loading of CdS quantum-dots per-unit-area and the charge transport of TiO2 nanorods. By tuning doping concentration, the Sn4+ doped TiO2 nanorods which are prepared by one-pot hydrothermal method enhance light absorption, decrease electron transport resistance, then improve photon-to-charge conversion owing to the generation of doping energy level and mixed-cation composition of SnxTi1-xO2. Moreover, after hydrogen treatment at various temperatures, many oxygen vacancies and hydroxyl groups are formed on the surface of SnxTi1-xO2 nanorods, which have broadened light absorption to visible region and facilitated charge separation and transport, thus improving the photoelectrochemical properties. Remarkably, the surface active center density of TiO2 nanorods increases arising from Sn4+ doping and hydrogen treatment, which is beneficial to sensitize more uniform and dense CdS quantum-dots. Additionally, the Sn4+ doped and hydrogen treated CdS/TiO2 photoelectrodes show the maximum photocurrent density of 7.72 mA cm−2 at 0 V versus Ag/AgCl, which is 15.8 and 2.3 times higher than that of conventional TiO2 and CdS/TiO2 photoelectrodes, respectively, due to the enhanced optical absorption, increased heterojunction areas and superior charge transport properties, demonstrating their promising potential in various solar-energy driven applications.