Well-dispersed Au nanoparticles prepared via magnetron sputtering on TiO2 nanotubes with unprecedentedly high activity for water splitting

Abstract

We report on the fine tuning of sputtered gold nanoparticles (Au NPs) with optimized diameters (7–25 nm) and distribution on the high surface area titania nanotube arrays (TNTs). The uniform coverage of Au NPs both outside and inside the nanotube arrays was possible by adjusting the sputtering current, as confirmed via scanning electron microscopy imaging and X-ray diffraction analysis. Decorating the TNTs with Au NPs extended their optical activity to the visible region of the light spectrum. This red shift was attributed to the localized surface plasmon resonance (LSPR) of Au NPs as verified computationally and experimentally. The Au–TiO2 composites demonstrated 86% increase in the photocurrent compared to the bare TNTs upon their use as photoanodes for water splitting. The photoactivity was found to depend on the size of the sputtered Au NPs. The photocurrent transient measurements under light on/off conditions revealed the photostability of the Au–TiO2 nanocomposites. The Mott–Schottky analysis showed a negative shift in the flat band position of the Au–TiO2 electrodes with increased donor density compared to the bare TNTs. Moreover, the Au–TiO2 showed lower space charge capacitance and longer life time of charge carriers.