There has been growing recent interest in the development of electrochemical and photoelectrochemical approaches toward effective fixation (reduction) of carbon dioxide. Having in mind a fact that the linear O=C=O molecule is very stable, the CO₂ electroreduction requires large overpotentials. In other words, utilization of renewable energy to convert carbon dioxide and water into fuels would require selective CO₂-reduction catalysts or efficient and robust semiconductors. There is a need to design unique nano-architectures consisting of the CO₂ photocatalyst/semiconductor stabilized with the outer protective layer.

Our study utilizes copper(I) oxide either stabilized with nanostructured titania or ultra-thin films of certain, conducting or redox, polymers (e.g. polyaniline, polypyrrole, PEDOT, poly(4-vinylpyridine)). While in a case of the mixed oxide semiconductor, we have explored formation the p-n heterojunction favoring increase of density of the electron population within the conduction band following deposition of TiO₂ over the electrodeposited large crystals of Cu₂O, in the latter case we tailor light absorption properties and affect the system’s stability. Upon illumination (from the copper(I) oxide side), charge transport to the reaction sites should be enhanced and the overall electric conductivity (at the catalytic interface) increases. Having in mind both hydrophilic and hydrophobic properties of Nafion over-coating, the outer-most ultra-thin film of Nafion, having properties of both robust (protective) layer and wetting (favoring proton mobility) medium, has been applied. Moreover, the outer-most over-layer of Nafion is expected to facilitate attraction of CO₂ (dissolved in the sodium sulfate electrolyte) at the photoelectrochemically active mixed-metal-oxides interfaceSpecial attention has been paid to synthesis, characterization and optimization of the hybrid photocathode, namely the Nafion-protected mixed-oxides (Cu₂O-TiO₂) and polymer modified copper(I) oxide systems (deposited on fluorine-doped tin oxide covered glass, FTO) toward photoelectrochemical reduction of carbon dioxide.