In situ electrochemical characterization of CuxO-based gas-diffusion electrodes (GDEs) for CO2 electrocatalytic reduction in presence and absence of liquid electrolyte and relationship with C2+ products formation

Copper oxide-based gas-diffusion electrodes (CuxO/GDEs) for CO2 electrocatalytic reduction are investigated in presence and absence of liquid electrolyte (liquid- and gas-phase operations) in terms of (i) catalytic reactivity in compact-design flow cells (with the electrodes located on the two sides of a Nafion membrane) and (ii) in situ electrochemical characterization by electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV) and chronoamperometry (CA). On the same electrocatalyst, the adoption of liquid- or gas-phase operations induces significant changes in the catalytic behaviour with formation of C2+ chemicals observed only in gas-phase. Parallel tests by EIS, complemented by CV and CA measurements, evidence that the catalytic properties of these electrodes, and in turn the selectivity paths, are largely determined by transport limitations rather than only by the intrinsic properties of the electrocatalysts. The EIS technique, used here for the first time to compare liquid- and gas-phase operations, has proved to be a strategic tool, providing insights into the critical factors needed to optimize performance beyond the properties of the electrocatalysts themselves.