The electrocatalytic reduction of CO₂ to CO and syngas, which underpin multi-million tons scale processes such as olefin synthesis, methanol synthesis and Fischer-Tropsch, is a promising strategy to convert CO₂ into value-added chemicals and to foster the introduction of renewable electricity in the chemical industry. Gold is the most active electrocatalysts capable to produce CO at low overpotentials and with excellent selectivity [1]. Many strategies, such as nanostructuring [2] and grafting with organic ligands, have been proposed to further enhance its performance. However, the fundamental knowledge of how the atomistic structure of the catalyst surface influences reaction rates and selectivity remains a very important missing fundamental insight.

In this work, we experimentally established – for the first time – that atomic steps and undercoordinated sites control the activity of Au for CO₂ reduction [3]. We performed a thorough experimental investigation of gold single crystals having well-defined surface orientations. Low-index single crystals, such as (111), (100) and (110), were compared to a steps-rich (211) surface. The electrochemical reduction of CO₂ to CO was found to exhibit a pronounced structure sensitivity: the CO partial current density registered with the most active catalysts (i.e., (110) and (211)) is ca. 20-fold higher than the one measured with Au (100), see Figure 1.

We further established the dominance of steps by selective poisoning experiments: the reaction was found to be largely suppressed if surface defects, such as atomic steps, were selectively blocked with inert (poisoning) Pb atoms.

The findings obtained with these model electrodes provide important targets for the design and synthesis of more efficient nanostructured catalysts. Furthermore, they offer elements to optimize the theoretical description of the electrochemical interface and reaction kinetics, which in turn may strengthen the prediction accuracy of future screening investigations.

[1]        Z. P. Jovanov, H. A. Hansen, A. S. Varela, P. Malacrida, A. A. Peterson, J. K. Nørskov, I. E. L. Stephens, I. Chorkendorff, J. Catal. 2016, 343, 215–231.

[2]        W. Zhu, Y.-J. Zhang, H. Zhang, H. Lv, Q. Li, R. Michalsky, A. A. Peterson, S. Sun, J. Am. Chem. Soc. 2014, 136, 16132–16135.

[3]        S. Mezzavilla, S. Horch, I. E. L. Stephens, B. Seger, I. Chorkendorff, Angew. Chem. Int. Ed. 2019, 58,3774–3778