Electroreduction of carbon dioxide to simple organic fuels and chemicals is a topic of growing scientific and technological interest. The reaction provides means for both reducing emissions of CO₂ into atmosphere and storing renewable energy. The presentation will address low-temperature CO₂-conversion processes based on electrocatalytic and photoelectrochemical approaches. Among important issues are choice of the catalytic or semiconducting materials, their morphology and operating conditions including temperature, solvent, electrolyte, pH etc. There is a need to improve the reaction dynamics and selectivity toward specific products. In practical electrolysis cells, the CO₂-reduction (at cathode) is accompanied by water oxidation (at anode or photoanode).

Given the fact that the CO₂ molecule is very stable, its electroreduction processes are characterized by large overpotentials. It is often postulated that, during electroreduction, the rate limiting step is the protonation of the adsorbed CO product to form the CHO adsorbate. In this respect, the proton availability and its mobility at the photo(electro)chemical interface has to be addressed. On the other hand, competition between such parallel processes as hydrogen evolution and carbon dioxide reduction has also to be considered.

Recently, mixed oxide systems stabilized through Zr-O-W bonds have been demonstrated to be very attractive acid catalysts exhibiting high catalytic activities and good stabilities in many demanding industrial reactions. The mixed WO₃/ZrO₂ systems are characterized by fast charge (electron, proton) propagation during the system’s redox transitions. By dispersing metallic Cu electrocatalytic nanoparticles over, under or within, such active WO₃/ZrO₂ matrices, the electrocatalytic activities of the respective systems toward the reduction of carbon dioxide have been significantly enhanced even at decreased loadings in acid media. The enhancement effects should be attributed to features of the mixed metal oxide support such as porosity and high population of hydroxyl groups (due to presence of ZrO₂), high Broensted acidity of sites formed on mixed WO₃/ZrO₂, fast electron transfers coupled to unimpeded proton displacements (e.g. in H_xWO₃), as well as strong metal-support interactions between nanosized metals (Cu) and the metal (W,Zr) oxo species.

Application of the hybrid system composed of both above-mentioned oxides resulted in high current densities originating from electroreduction of carbon dioxide mostly to methanol (CH₃OH) as demonstrated upon identification of final products.