Dramatic Change in the Step Edges of the Cu(100) Electrocatalyst upon Exposure to CO: Operando Observations by Electrochemical STM and Explanation Using Quantum Mechanical Calculations

Systematic structure–activity correlations in the electrochemical surface science of CO₂ reduction (CO₂R) are typically anchored on low Miller-index (hkl) surfaces with characterization directed at the dominant well-defined basal planes. The present investigation focused on the visualization of the step edges of unreconstructed Cu(100), with and without CO dissolved in 0.1 M KOH, at the early onset-potential region of CO₂R. Operando electrochemical scanning tunneling microscopy revealed that the step-edge direction changed dramatically upon the adsorption–desorption of CO at potentials of −1.0 to −0.8 V. Quantum mechanical calculations corroborated the favorable transformation of the step-edge direction from ⟨110⟩ to ⟨001⟩ as the pristine surface was decorated by CO.