Photo-electro-reduction of CO₂ is continuously gaining a considerable interest in view of possible production of carbon-based energy carriers. Given the periodic availability of solar light, of primary importance is to orient the CO₂ conversion versus formation of easily storable fuels such as, e.g. methanol or ethanol. Thus, it is important to diversify the CO₂ reduction products not only by the applied potential but by careful optimisation of the working system. A default approach, consists in using p-type semiconductors as a main component of the CO₂-reduction cathodes. However, the intrinsic drawback of p-type semiconductor photo-cathodes lies in low electron density in the CB and, as generally observed, the lack of catalytic properties towards CO₂ reduction. Thus, in an attempt to increase the conduction band electron population, we will present herein a build-up hybrid photo-electrodes including p-type - n-type semiconductors junctions. An additional advantage of creating such p-type – n-type semiconductor heterojunction is protection of the p-type component against photocorrosion induced by largely negative potentials that offers, at the same time, the possibility to enlarge the choice of employed p-type semiconductors to relatively unstable ones. The requirements for the n-type semiconductors are fulfilled by several metal oxides such as TiO₂ or SrTiO₃, or KTaO₃. Apart the role of heterojunction in CO₂ activation, we will also point out a particular aspect of using a model system involving Au NPs of different sizes deposited on a TiO₂/Ti substrate by examining the electro-reduction of carbon monoxide. This reaction appears as being the crucial, kinetically difficult, step in the electro-reduction of CO₂ to alcohols and hydrocarbons. Recognition and understanding of an individual process might already give a picture of a whole system.