Cobalt oxide nanoparticles on TiO₂ nanorod/FTO as a photoanode with enhanced visible light sensitization

Cobalt oxide nanoparticles were sensitized on hydrothermally grown TiO₂ nanorods on FTO (fluorine-doped tin oxide) by electrochemical deposition, followed by rapid thermal annealing under air and N₂. We investigated the formation of the nanostructure with different electrodeposition times, electrolyte concentrations, and annealing temperatures for improved photoelectrochemical (PEC) properties. A structural investigation showed the formation of a mixture of CoO/Co₃O₄ oxides dependant on annealing temperature and atmosphere. The oxide formation equilibrium shifted from Co₃O₄ to a mixture of CoO/Co₃O₄ and finally to monoxide when temperature is lowered from 700°C to 350°C. Improved PEC properties were shown by the mixture of oxides compared to a system with CoO and Co₃O₄ alone on TiO₂. Electrodeposition time was found to have a linear relationship with the nanoparticle size of cobalt oxide formed on TiO₂. Here we propose a cost effective and simple method to fabricate a hetero-junction system with improved PEC properties.