Effect of urea loading on the anodic synthesis of titania nanotube arrays photoanode to enhance photoelectrochemical performance

The development of efficient photoanode to improve the photoelectrochemical performance under UV light was investigated. The nitrogen-doped titania nanotube array was prepared by one step anodic oxidation of titanium foil in a solution of electrolyte-containing urea as nitrogen precursor at 50 V for 2h. During the process, the urea was added to the electrolyte solution with different concentrations, 0.1%, 0.2%, and 0.4% based on the weight of electrolyte that containing 25% water, 0.5% ammonium fluoride, and glycerol. The synthesis was followed by annealing at 500°C for 3h under 60ml/min of N₂ gas to induce the crystalline phase. SEM analysis showed that titania nanotube was successfully synthesized with average diameter is 72 - 153 nm. Refer to XRD analysis titania nanotube mostly have anatase phase with the crystallite size of 27-37 nm depending on loading of urea. Bandgap energy was determined by UV-DRS analysis and showed that nitrogen-doped titania nanotube arrays have smaller bandgap energy. The photoelectrochemical responses of titania nanotube before and after nitrogen doping were examined by linear sweep voltammetry method. Photocurrent density measurements showed better activity on nitrogen-doped titania nanotube. Nitrogen-doped titania nanotube caused the flatband potential shifted to a negative value and the smaller space charge layer, resulting in the higher photocurrent density and photoconversion efficiency.