Identical Grain Atomic Force Microscopy Elucidates Facet-Dependent Restructuring of Copper for CO₂ Electroreduction

Studies on the catalyst restructuring during the electrochemical CO₂ reduction reaction (eCO₂RR) are limited and mostly focused on Cu (001) or (111) single crystals as model systems. A comprehensive overview of the dynamic restructuring of different Cu facets is lacking. Here, we first reveal the facet-dependent restructuring of polycrystalline Cu electrodes through electron backscatter diffraction (EBSD) and identical grain atomic force microscopy (AFM). This combined analysis provides new insights into the evolution of crystal domains (EBSD) and surface topography (AFM) at varying conditions (e.g., applied potential and oxidative-reductive pulses). The statistic slope distribution function was applied to study the restructuring asymmetry on five Cu facets (i.e., planar vs. atom stepped). We find that planar Cu (001) shows a square-shaped morphology after eCO₂RR with 4-fold asymmetry restructuring behavior, while triangular features dominate on Cu (111), evidenced by surface changes with 3-fold asymmetry. 2-fold restructuring is observed for Cu (114), (212), and (124) with atom steps, resulting in forming elongated structures. Therefore, the surface restructuring is dominated by the asymmetry of its facet lattice structure (i.e., planar vs. atom-stepped). This work underscores the potential of combining techniques to elucidate the relationship between surface restructuring and crystal facets on different length scales.