Multiscale X-ray scattering elucidates activation and deactivation of oxide-derived copper electrocatalysts for CO₂ reduction

Electrochemical reduction of carbon dioxide (CO₂) into sustainable fuels and base chemicals requires precise control over and understanding of activity, selectivity and stability descriptors of the electrocatalyst under operation. Identification of the active phase under working conditions, but also deactivation factors after prolonged operation, are of the utmost importance to further improve electrocatalysts for electrochemical CO₂ conversion. Here, we present a multiscale in situ investigation of activation and deactivation pathways of oxide-derived copper electrocatalysts under CO₂ reduction conditions. Using well-defined Cu₂O octahedra and cubes, in situ X-ray scattering experiments track morphological changes at small scattering angles and phase transformations at wide angles, with millisecond to second time resolution and ensemble-scale statistics. We find that undercoordinated active sites promote CO₂ reduction products directly after Cu₂O to Cu activation, whereas less active planar surface sites evolve over time. These multiscale insights highlight the dynamic and intimate relationship between electrocatalyst structure, surface-adsorbed molecules, and catalytic performance, and our in situ X-ray scattering methodology serves as an additional tool to elucidate the factors that govern electrocatalyst (de)stabilization.