Photo-Electrochemical Properties of Anodised Titania Nanotube Arrays Annealed in Nitrogen Atmosphere

Self organised aligned titania nanotubes were synthesised by electrochemical anodisation of titanium foil and the effect of annealing in nitrogen atmosphere was investigated. The diameter and length of nanotubes were 90–110 nm and 450–500 nm respectively giving high aspect ratio nanomaterial. Samples annealed in nitrogen atmosphere were found to retain the tubular structure with diameter 80–110 nm. Annealing of nanotubes in nitrogen atmosphere indicated substitution of nitrogen into the TiO2 lattice; however large amounts were still present as physisorbed, chemisorbed and possibly as O—Ti—N structure in TiO2 lattice. The photo-electrochemical properties of titania electrodes were investigated under solar simulated and visible illumination. The effect of methanol as hole acceptor was also investigated. The electrodes annealed in N2 atmosphere demonstrated higher solar photocurrent response than air annealed electrode. The sample annealed for 1 h in N2 resulted in optimum photocurrent response under solar simulated illumination. The photocurrent response obtained with the electrolyte containing methanol was found to be increased by a factor of 2.4 under solar simulated light and 1.3 under visible illumination, however the overall visible photocurrent response was very small compared to the solar simulated response. The additional small peaks at negative potentials may involve excitation from filled defect level.