Dendritic Au/TiO₂ nanorod arrays for visible-light driven photoelectrochemical water splitting

This paper describes the synthesis of TiO₂ branched nanorod arrays (TiO₂ BNRs) with plasmonic Au nanoparticles attached on the surface. Such Au/TiO₂ BNR composites exhibit high photocatalytic activity in photoelectrochemical (PEC) water splitting. The unique structure of Au/TiO₂ BNRs shows enhanced activity with a photocurrent of 0.125 mA cm^-2 under visible light (≥420 nm) and 2.32 ± 0.1 mA cm^-2 under AM 1.5 G illumination (100 mW cm^-2). The obtained photocurrent is comparable to the highest value ever reported. Furthermore, the Au/TiO₂ BNRs achieve the highest efficiency of ∼1.27% at a low bias of 0.50 V vs. RHE, indicating elevated charge separation and transportation efficiencies. The high PEC performance is mainly due to the plasmonic effect of Au nanoparticles, which enhances the visible light absorption, together with the large surface area, efficient charge separation and high carrier mobility of the TiO₂ BNRs. The carrier density of Au/TiO₂ BNRs is nearly 6 times higher than the pristine TiO₂ BNRs as calculated by the Mott-Schottky plot. Based on the analysis by UV-Vis spectroscopy, electrochemical impedance spectroscopy, and photoluminescence, a mechanism was proposed to explain the high activity of Au/TiO₂ BNRs in PEC water splitting. The capability of synthesizing highly visible light active Au/TiO₂ BNR based photocatalysts is useful for solar conversion applications, such as PEC water splitting, dye-sensitized solar cells and photovoltaic devices.