Bridging knowledge gaps in liquid- and vapor-fed CO2 electrolysis through active electrode area

Abstract

Increased use of gas diffusion electrodes for CO 2 electroreduction widens the experimental phase space that was previously inaccessible using foil electrodes, raising fundamental questions over the impacts of key variables that translate between liquid- and vapor-fed CO 2 electrolysis systems. This work focuses on studying the interplay of current-potential profiles and electrochemically active surface area (ECSA) by implementing a Cu nanoflower catalyst morphology. The results show decreased overpotentials as much as 460 and 174 mV for foil and gas diffusion electrodes, respectively, while maintaining or improving multi-carbon product current density. These overpotential shifts and product activities normalized by ECSA lead to current-potential relationships akin to those of the Tafel description, which are found through a continuum model to be useful for describing the roughness dependence for both liquid- and vapor-fed systems. This analysis establishes a holistic approach for establishing catalyst design criteria to improve materials development for CO 2 electrolysis technologies. • Distinct catalyst morphologies are translated between electrode types • Reaction rate toward CO 2 R and C 2+ products is enhanced at lower overpotentials • Increase in J geo up to ∼735× and ∼10× are observed with foil and GDEs, respectively • Experiments and model show Tafel-like description of roughness and potential shift CO 2 electrolysis coupled with renewable energy sources is an attractive method for producing industrially relevant chemicals while reducing emissions. Recent advancements have focused on evolving the electrode architecture from metal foils to porous gas diffusion electrodes for improving the reaction rate. However, the contributions from surface kinetics and local reaction environment are convoluted and vary when translating from liquid- to vapor-fed systems. Herein, we draw connections between these systems by evaluating identical catalyst structures of varying roughness for both electrode types. Our experimental and modeling approaches provide better understanding of the interplay between electrode structure and reaction environment on the activity and selectivity. We observe nominal changes in the intrinsic activity of Cu with significant overpotential savings corresponding to the roughness factors across electrode types. We achieve a ∼700- and ∼10-fold increase in multi-carbon product formation by designing roughened catalysts for both foil and gas diffusion-type electrodes, respectively. We showcase catalyst surface area as a key descriptor for understanding the interplay between the electrode structure and local reaction environment on activity and selectivity. Both experimental and computational modeling determine heightened reaction rates toward CO 2 R at lower overpotentials, which uncover a clear dependence on electrode roughness.