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Abstract

The unresolved dynamic morphology of copper electrodes during the electrochemical CO 2 reduction (CO 2 RR) impedes deriving structure‐reactivity relationships and controlling the catalytic properties of CO 2 RR electrocatalysts under operating conditions. We demonstrate that electrochemical atomic force microscopy (EC‐AFM) is a powerful tool for the real‐space characterization of catalysts under realistic CO 2 RR conditions. Despite the challenges related to imaging within a highly gas‐evolving potential regime (down to –1.1 V vs. the reversible hydrogen electrode), the evolution of structural features ranging from the micrometer to the atomic‐scale could be resolved during CO 2 RR. Using Cu(100) as model surface, distinct nanoscale surface morphologies and their potential‐dependent transformations from granular to smoothly curved mound‐pit surfaces or structures with rectangular terraces are revealed during CO 2 RR in 0.1 M KHCO 3 . The density of undercoordinated copper sites during CO 2 RR is shown to increase with decreasing potential. In situ atomic scale imaging reveals specific adsorption occurring at distinct cathodic potentials impacting the observed catalyst structure. These results show the complex interrelation of the morphology, structure, defect density, applied potential and electrolyte in copper CO 2 RR catalysts, which are key for understanding and controlling the catalyst selectivity.