Single-step anodization for synthesis of hierarchical TiO2 nanotube arrays on foil and wire substrate for enhanced photoelectrochemical water splitting

A hierarchical nanoporous-TiO2 nanotube composite structure consisting of a nanoporous top layer with smooth underlying nanotubes was obtained by a single-step anodization technique. The growth of such composite structure has also been applied to Ti wire substrate for the first time. The photoelectrochemical performance was examined under AM 1.5 simulated solar irradiation in 1 M KOH electrolyte. In general, the hierarchical architecture demonstrated improved photoelectrochemical activity over plain TiO2 nanotubes. Furthermore, the composite structure on a wire substrate was also found to enhance photoelectrochemical activity over a foil substrate. Under optimized conditions, over a 40% increase in hydrogen generation for hierarchical nanotubes over plain nanotubes is observed and over 25% increase in hydrogen generation using a wire substrate over a foil substrate is observed.