Huge efforts have been done in the last years on electrochemical and photoelectrochemical reduction of CO ₂ to offer a sustainable route to recycle CO ₂ . A promising route is to electrochemically reduce CO ₂ into CO which, by combination with hydrogen, can be used as a feedstock to different added-value products or fuels. Herein, perpendicular oriented TiO ₂ nanotubes (NTs) on the electrode plate were grown by anodic oxidation of titanium substrate and then decorated by a low loading of silver nanoparticles deposited by sputtering (i.e. Ag/TiO ₂ NTs). Due to their quasi one-dimensional arrangement, TiO ₂ NTs are able to provide higher surface area for Ag adhesion and superior electron transport properties than other Ti substrates (e.g. Ti foil and TiO ₂ nanoparticles), as confirmed by electrochemical (CV, EIS, electrochemical active surface area) and chemical/morphological analysis (FESEM, TEM, EDS). These characteristics together with the role of the TiO ₂ NTs to enhance the stability of CO ₂ ^·- intermediate formed due to titania redox couple (Ti ^IV /Ti ^III ) lead to an improvement of the CO production in the Ag/TiO ₂ NTs electrodes. Particular attention has been devoted to reduce the loading of noble metal in the electrode(14.5 %w/%w) and to increase the catalysts active surface area in order to decrease the required overpotential.

The CO2 that comes from the use of fossil fuels accounts for about 65% of the global greenhouse gases emissions, and it plays a critical role in global climate changes. Among the different strategies that have been considered to address the storage and reutilization of CO2, the transformation of CO2 into chemicals or fuels with a high added-value has been considered a winning approach. This transformation is able to reduce the carbon emissions and induce a “fuel switching” that exploits renewable energy sources. The aim of this brief review is to gather and critically analyse the main efforts that have been made and achievements that have been reached in the electrochemical reduction of CO2 for the production of CO. The main focus is on the prospective of exploiting the intrinsic nature of the electrolysis process, in which CO2 reduction and H2 evolution reactions can be combined, into a competitive approach, to produce syngas. Several well-stablished processes already exist for the generation of fuels and fine-chemicals from H2/CO mixtures of different ratios. Hence, the different kinds of electrocatalysts and electrochemical reactors that have been used for the CO and H2 evolution reactions have been analysed, as well as the main factors that influence the performance of the system from the thermodynamic, kinetic and mass transport points of view.