Overall, these results clearly indicate that CO2 itself plays a crucial role in copper degradation, and that no electrochemical current or products of CO2 ER are necessary for copper degradation to occur. The role of CO2 instead of CO2 ER products in the copper degradation process is corroborated by the lack of a correlation with the KHCO3 concentration (Figure , panels a-d). Degradation was fast at less reducing electrochemical potentials, when the driving force for copper plating is smaller, which is consistent with the rapid degradation observed on the separate islets (that should exhibit no plating forces at open-circuit conditions) in the bulk copper sample compared to the part of the sample that was under EWE = 0 V. At more negative electrochemical potentials, only larger particles show corrosion, but at less negative potentials both large and small particles exhibit corrosion.