Screening Surface Structure-Electrochemical Activity Relationshipsof Copper Electrodes under CO2Electroreduction Conditions

Understanding how crystallographic orientation influences the electrocatalytic performance of metal catalysts can potentially advance the design of catalysts with improved efficiency. Although single crystal electrodes are typically used for such studies, the one-at-a-time preparation procedure limits the range of secondary crystallographic orientations that can be profiled. This work employs scanning electrochemical cell microscopy (SECCM) together with co-located electron backscatter diffraction (EBSD) as a screening technique to investigate how surface crystallographic orientations on polycrystalline copper (Cu) correlate to activity under CO2 electroreduction conditions. SECCM measures spatially resolved voltammetry on polycrystalline copper covering low overpotentials of CO2 conversion to intermediates, thereby screening the different activity from low-index facets where H-2 evolution is dominant to high-index facets where more reaction intermediates are expected. This approach allows the acquisition of 2500 voltammograms on approximately 60 different Cu surface facets identified with EBSD. The results show that the order of activity is (111) < (100) < (110) among the Cu primary orientations. The collection of data over a wide range of secondary orientations leads to the construction of an electrochemical-crystallographic stereographic triangle that provides a broad comprehension of the trends among Cu secondary surface facets rarely studied in the literature, [particularly (941) and (741)], and clearly shows that the electroreduction activity scales with the step and kink density of these surfaces. This work also reveals that the electrochemical stripping of the passive layer that is naturally formed on Cu in air is strongly grain-dependent, and the relative ease of stripping on low-index facets follows the order of (100) > (111) > (110). This allows a procedure to be implemented, whereby the oxide is removed (to an electrochemically undetectable level) prior to the kinetic analyses of electroreduction activity. SECCM screening allows for the most active surfaces to be ranked and prompts in-depth follow-up studies

Automated summary

Understanding how crystallographic orientation affects the electrocatalytic performance of metal catalysts is crucial for improving catalyst efficiency. This study combines scanning electrochemical cell microscopy (SECCM) with electron backscatter diffraction (EBSD) to investigate the correlation between surface crystallographic orientations on polycrystalline copper (Cu) and activity under CO2 electroreduction conditions. The results show that the order of activity is (111) < (100) < (110) among the Cu primary orientations. Furthermore, the study reveals that the ease of electrochemical stripping of the naturally formed passive layer on Cu is grain-dependent, with low-index facets being easier to strip. This research provides a method to rank the most active surfaces for further study.