Assessment of the Degradation Mechanisms of Cu Electrodes during the CO2 Reduction Reaction

Catalyst degradation and productselectivity changes are two ofthe key challenges in the electrochemical reduction of CO2 on copper electrodes. Yet, these aspects are often overlooked. Here,we combine in situ X-ray spectroscopy, insitu electron microscopy, and ex situ characterizationtechniques to follow the long-term evolution of the catalyst morphology,electronic structure, surface composition, activity, and product selectivityof Cu nanosized crystals during the CO2 reduction reaction.We found no changes in the electronic structure of the electrode undercathodic potentiostatic control over time, nor was there any build-upof contaminants. In contrast, the electrode morphology is modifiedby prolonged CO2 electroreduction, which transforms theinitially faceted Cu particles into a rough/rounded structure. Inconjunction with these morphological changes, the current increasesand the selectivity changes from value-added hydrocarbons to lessvaluable side reaction products, i.e., hydrogen andCO. Hence, our results suggest that the stabilization of a facetedCu morphology is pivotal for ensuring optimal long-term performancein the selective reduction of CO2 into hydrocarbons andoxygenated products.