A model system for photoreduction of CO₂ to CO using visible light has been extensively studied, using a catalyst for which the CO₂/CO reaction is electrochemically reversible. The hybrid system comprises metal oxide nanoparticles functionalised with the enzyme carbon monoxide dehydrogenase (CODH), and sensitised to visible light using a ruthenium bipyridyl photosensitiser. An anatase/rutile TiO₂ mixture (Evonik Degussa P25) was selected as the most suitable semiconductor, and CO production rates and stability were examined as a function of each component (photosensitiser, enzyme and TiO₂). Tolerance to O₂ and effects of different electron donors were also investigated, together with strategies to control enzyme binding at the surface of TiO₂ in order to enhance overall activity.