Simultaneous Electrocatalytic CO2 Reduction and Enhanced Electrochromic Effect at WO3 Nanostructured Electrodes in Acetonitrile

Serious concerns about climate change make the reutilization of CO2 particularly attractive; one option for reutilization is the electroreduction of CO2 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 WO3 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 CO2 as being the main product in both dry and humid acetonitrile, together with formate in the presence of humidity. Interestingly, purging with CO2 causes not only 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 WO3 electrodes. On the basis of these observations, a mechanism is proposed in which WO3 is not only the electrode material but also a mediator in the CO2 reduction process