TiO₂ nanotubes formed in aqueous media: Relationship between morphology, electrochemical properties and the photoelectrochemical performance for water oxidation

The effect of voltage and electrolyte composition on the formation of TiO₂ nanotube films over its morphology, semiconductor properties and photoelectrochemical performance for water oxidation was studied. TiO ₂ nanotube films were formed by potentiostatic anodization in 0.1 M H₂SO₄/0.05 M HF and 0.1 MH₂SO₄/0.05M NH₄F during 1 h at four different voltages. SEM images showed a more significant chemical attack when NH₄F was employed, evidenced by larger tube diameters and thinner films. The semiconductor properties were altered by the nature of the counter-ion utilized during film growth, obtaining films with a higher density of donor and less positive flat band potential in NH₄F electrolytes. The films formed in NH₄F showed higher photopotentials and photocurrent related to the modification of their morphology and semiconductor properties, attaining a maximum at formation voltage of 15 V.