Electrochemical Synthesis and Characterisation of Titanium Dioxide Thin Films for Solar Energy Applications in Semi-Arid Environments

Dye-sensitised solar cells and photoelectrochemical hydrogen production based on titanium dioxide photoanodes represent promising sustainable energy conversion technologies for Nigeria's semi-arid northern zones that receive among the highest solar irradiance levels in sub-Saharan Africa, yet materials performance data under representative northern Nigerian operating conditions are lacking. This study synthesises titanium dioxide thin films by anodisation of titanium foil substrates and sol-gel dip-coating methods, and evaluates their performance as photoanodes under simulated and natural solar irradiance conditions representative of Kano State, North West Nigeria. Film morphology and crystal structure are characterised by scanning electron microscopy, transmission electron microscopy, and X-ray diffraction. Optical properties are determined by UV-visible diffuse reflectance spectroscopy, and bandgap values are derived from Tauc plots. Photoelectrochemical performance is measured in a three-electrode cell under AM 1.5G solar illumination, recording photocurrent density-voltage curves, electrochemical impedance spectra, and incident photon-to-current efficiency spectra. The effect of nitrogen doping using urea as a nitrogen source on visible light absorption and photocurrent generation is investigated. Electron recombination lifetime is extracted from Bode and Nyquist impedance plots. Natural sunlight performance testing at the Kano site is conducted over fourteen measurement days, and thermal stability under high ambient temperature is evaluated by annealing experiments. Findings establish performance benchmarks for titanium dioxide photoanodes under semi-arid Nigerian conditions, providing design parameters for solar energy application development in the North West geopolitical zone. Keywords: titanium dioxide, thin films, photoelectrochemical, solar energy, Kano