Influence of substrate morphology on the growth and properties of TiO2 nanotubes in HBF4-based electrolyte

Abstract The present work demonstrates how the growth and photoelectrochemical (PEC) properties of anodic TiO 2 nanotubes (NTs) are influenced by Ti substrates in the new HBF 4 containing electrolyte. Three different Ti substrates, the rough abraded Ti foil, the smooth electropolished Ti and the two-step Ti plate (i.e. the Ti substrate with ordered dimples left by removing the TiO 2 NTs formed in the first-step anodization), are employed for the preparation of TiO 2 NTs. It is revealed that the Ti substrate morphology can largely influence the formation of TiO 2 NTs, particularly in the initial tube generation stage. The two-step Ti substrate has ordered hexagonally distributed dimples which play the role of template for the formation of new TiO 2 NTs. As a result, the TiO 2 NTs grown via a two-step anodization approach have highly ordered structure and extremely smooth sidewalls, hence possess the best PEC performance among the three kinds of substrates.