Surface X‐Ray Diffraction Study of Ag‐Decorated Cu(100) Under Electrochemical Reduction of CO ₂

Modifying copper‐based catalysts for the electrochemical reduction of CO 2 by silver has attracted much interest as it allows to steer the catalytic selectivity toward multicarbon products. This study investigates the potential‐dependent interface structure of a silver‐decorated Cu(100) electrode under CO 2 reduction conditions by in situ surface X‐ray diffraction. The results show that the electrode surface structure dynamically changes near the onset of the catalytic reaction. Specifically, we find an outward relaxation of the Cu surface layer, which is attributed to formation of CO intermediates, and a complex potential‐dependent change in the interfacial order. Furthermore, these changes are very reversible in fast potentiodynamic experiments, but only partly reversible after long‐term CO 2 reduction.