Electrode and cell design for CO 2 reduction: A viewpoint

The electrocatalytic reduction of carbon dioxide (CO 2 RR) is a crucial technology to develop the decarbonisation strategy for carbon circularity and producing solar fuels substituting fossil fuels. This viewpoint discusses the role of the electrode and reactor design as the main factor in determining the performance of CO 2 RR, at least under reaction conditions relevant to industrial scalability, evidencing the need to overturn the current strategic vision focused more on improving the characteristics of the electrocatalytic materials. Many parameters characterising the performances (such as Faradaic efficiency, carbon selectivity and potential onset, besides the current density) are strongly influenced and typically dominated (under relevant conditions) by the effective population of adspecies on the electrode surface, which is, in turn, related to mass control and transport resistances, local pH changes, multiphase boundaries, wettability and other aspects. Even the preliminary screening of the catalysts could be incorrect, not operating under representative conditions, and thus without properly choosing the electrode and reactor. Advanced electrode/reactor designs, e.g., based on gas-diffusion electrodes (GDEs) that avoid having a liquid electrolyte (zero-gap design), are necessary to improve CO 2 RR scalability to industrial applications. Even in situ catalyst nanoparticle reconstruction may depend on these aspects. Electrochemical characterization methods like electrochemical impedance spectroscopy (EIS) are the right approach to study electrocatalytic reactions, providing crucial indications on the effective controlling elements that determine the electrocatalyst/electrode performances.