Enhanced photoelectrochemical activity of vertically aligned ZnO-coated TiO₂ nanotubes

Vertically aligned ZnO-TiO₂ hetero-nanostructures constructed of anatase TiO₂ nanotubes (NTs) and wurtzite ZnO coatings are fabricated by atomic layer deposition of ZnO coatings on electrochemical anodization formed TiO₂ NTs, and their photoelectrochemical activities are studied through photoelectrochemical and electrochemical characterization. Compared with bare TiO₂ NTs, the transient photocurrent increases to over 1.5-fold for the annealed ZnO-coated TiO ₂ NTs under visible illumination. The ZnO-coated TiO₂ NTs also show a longer electron lifetime, a lower charge-transfer resistance and a more negative flat-band potential than the bare TiO₂ NTs, confirming the improved photoelectrochemical activity due to the enhanced charge separation.