Correlation between impedance spectroscopy and bubble-induced mass transport in the electrochemical reduction of carbon dioxide

Abstract

In the electrochemical conversion of carbon dioxide, high currents need to be employed to obtain large production rates, thus implying that mass transport of reactants and products is of crucial importance. This aspect can be investigated by employing a model that depicts the local environment for the reduction reactions. Simultaneously, electrochemical impedance spectroscopy, despite being a versatile technique, has rarely been adopted for studying the mass transport features during the carbon dioxide (CO2) electroreduction. In this work, this aspect is deeply analyzed by correlating the results of impedance spectroscopy characterization with those obtained by a bubble-induced mass transport modeling under controlled diffusion conditions on a gold rotating disk electrode. The effects of potential and rotation rate on the local environment are also clarified. In particular, it has been found that CO2 depletion occurs at high kinetics when the rotation is absent, giving rise to an increment of the competing hydrogen evolution reaction. This feature reflects in an enlargement of the diffusion resistance, which overcomes the charge transport one.