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 N-2. 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 degrees C to 350 degrees 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.