Serious concerns about the climate change make particularly attractive the reutilization of CO 2 , being one option the electroreduction of CO in acetonitrile solutions on a range of electrode materials. Among them, transition metal oxides stand out as cost effective alternatives. In this context, the electrocatalytic activity of nanostructured WO 3 electrodes for carbon dioxide reduction in both humid and dry acetonitrile media has been addressed by using electrochemical and spectroelectrochemical measurements. Importantly the cathodic faradaic process starts at potentials as high as-0.16 V vs SHE. Gas chromatography measurements show CO as being the main product in both dry and humid acetonitrile, together with formate in the presence of humidity. Interestingly, purging with CO 2 not only causes the appearance of cathodic faradaic currents, but also an increase in capacitive currents, which are directly associated with an enhanced electrochromic effect. The ICP-MS determination of tungsten upon electrolysis confirms a minor electrodissolution of WO 3 electrode. On the basis of these observations, a mechanism is proposed in which WO 3 is not only the electrode material, but also a mediator in the CO 2 reduction process

One of the main current goals of humanity is the CO 2 conversion into high energy compounds for facilitating both a diminution of the CO 2 atmospheric levels and the development of energy storage strategies. In many studies, TiO 2 has been successfully used as a photocatalyst for CO 2 reduction, but there is still a lack of understanding of its catalytic behavior. In this context, CO 2 reduction has been studied on nanoporous TiO 2 electrodes in acetonitrile media by means of (spectro) electrochemical methods (ATR-IR and UV−vis). Importantly, the onset of the cathodic Faradaic processes related with CO 2 reduction on TiO 2 electrodes is located at −0.81 V versus SHE, which is less negative than that observed for metal electrodes under similar conditions. UV−vis spectroelectrochemical results indicate that the electrocatalytic behavior of TiO 2 is related to the generation of oxygen vacancies and Ti 3+ sites at its surface and promoted by electrolytes with nonintercalating cations in agreement with recent results on WO 3 electrodes. ATR-IR spectroelectrochemical measurements allow for monitoring of the TiO 2 /solution interfacial state as reduction proceeds. Specifically, IR bands for carbon monoxide and carbonyl groups related with carbonate and oxalate are observed. Additionally, a chromatographic analysis shows CO and oxalate as main products. With controlled water addition (0.5 M), methanol and CO were found to be the main products. Based on these results, a mechanism for CO 2 reduction on TiO 2 electrodes is presented in which the regeneration of the TiO 2 surface by oxide electrodissolution/deposition is a critical step.

Transition metal oxides (TMO) have been successfully used as electrocatalytically active materials for CO2 reduction in some studies. Because of the lack of understanding of the catalytic behavior of TMOs, electrochemical methods are used to investigate the CO2 reduction in thin-film nanostructured electrodes. In this context, nanostructured thin films of Fe2O3 and MoO3 in an aprotic medium of acetonitrile have been used to study the CO2 reduction reaction. In addition, a synergistic effect between CO2 and the TMO surface is observed. Faradic cathodic processes not only start at lower potentials than those reported with metal electrodes, but also an increase in capacitive currents is observed, which is directly related to an increase in oxygen vacancies. Finally, the results obtained show CO as a product of the reduction.