Structure Sensitivity and Catalyst Restructuring for CO2 Electro-reduction on Copper

Cu is the most promising metal catalyst for CO2 electroreduction (CO2RR) to multi-carbon products, but the structure sensitivity of the reaction and the stability versus restructuring of the catalyst surface under reaction conditions are still controversial. Here, atomic scale simulations of surface energies and reaction pathway kinetics supported by experimental evidence unveil that CO2RR does not take place on perfect planar Cu(111) and Cu(100) surfaces but rather on steps or kinks defects, and that these planar surfaces tend to restructure in reaction conditions to the active stepped surfaces. By combining basin hopping global sampling and grand canonical density functional theory, we show that the extremely low CO coverage on (111) and (100) surfaces, originating from sluggish CO2 conversion and unfavorable CO binding, limits the ability of these surfaces to reduce CO2 to multi-carbon products. Steps and kinks at surfaces, despite the lack of decrease in C-C coupling barriers on these sites, exhibit a significant increase in activity arising from beneficial CO2 activation and higher CO coverage. Notably, the square motifs adjacent to defects, not the defects themselves, are the active sites for CO2RR via synergistic effect. In addition, the strong binding of CO on defective sites acts as a thermodynamic driving force for the restructuring of planar surfaces to active stepped terminations under reactive conditions. We evaluate these mechanisms against experiments of CO2RR on UHV-prepared ultraclean Cu surfaces. Overall, our findings highlight the structural sensitivity in steering CO2RR and elucidate the origin of in situ restructuring of Cu catalysts during the reaction. We furthermore feature that the active sites for CO2RR are created under reaction conditions.