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Copper (Cu) is a leading catalyst for CO$_2$ electroreduction (CO2RR) to multi-carbon products, though its structure sensitivity and stability remain debated. This study reveals that CO2RR does not occur on perfect Cu(111) and Cu(100) surfaces but rather on defect sites, such as steps and kinks [1,2]. Under reaction conditions, these planar surfaces restructure into more active stepped surfaces [2]. Atomic-scale simulations and experiments demonstrate that CO coverage on pristine surfaces is too low to support efficient CO2RR. In contrast, steps and kink sites enhance CO$_2$ activation and CO coverage, significantly boosting catalytic activity. However, the square motifs near step edges, rather than the undercoordinated atomic sites present at step edges and kink sites themselves, emerge as the primary active sites for C-C coupling [3].
Electrochemical experiments combined with scanning tunneling microscopy measurements show that pristine Cu surfaces mainly produce hydrogen, while stepped surfaces yield hydrocarbons. Surface restructuring under CO2RR reaction conditions, driven by CO adsorption, increases step density and promotes the formation of stepped surfaces with enhanced catalytic performance. These findings emphasize the crucial role of surface defects in CO2RR and the self-activation of Cu surfaces under reaction conditions.
The influence of step density and step orientation on the product distribution in electrochemical CO2RR for UHV- prepared Cu(111) and Cu(100) will be presented. Whereas the defects and step-rich motifs enable CO$_2$ conversion into hydrocarbons, the pre-catalyst’s facet determines the exact product distribution. Hence, this work offers new insights into catalyst design. Future work should investigate these active site structures and develop methods to steer the operando surface restructuring for improved CO2RR efficiency.
- Scholten, F., Nguyen, K. C., Bruce, J. P., Heyde, M., Roldan Cuenya, B., Identifying Structure-Selectivity Correlations in the Electrochemical Reduction of CO$_2$: A Comparison of Well-Ordered Atomically Clean and Chemically Etched Copper Single-Crystal Surfaces. Angew. Chem. Int. Ed. 60, 19169-19175 (2021).
- Nguyen, K. C. et al. The Influence of Mesoscopic Surface Structure on the Electrocatalytic Selectivity of CO$_2$ Reduction with UHV-Prepared Cu(111) Single Crystals. ACS Energy Lett. 9, 644-652 (2024).
- Cheng, D., Nguyen, K. C., Sumaria, V., Wei, Z., Zhang, Z., Gee, W., Li, Y., Morales-Guio, C. G., Heyde, M., Roldan Cuenya, B., Alexandrova, A. N., Sautet, P., Structure Sensitivity and Catalyst Restructuring for CO$_2$ Electro-reduction on Copper. Submitted (2024).
