Copper carbon dioxide reduction electrocatalysts studied by in situ soft X-ray spectro-ptychography

Understanding the morphological and chemical structural changes of electrocatalysts under reaction conditions remains a key challenge. Here, we present a detailed study of how individual cubic copper particles change morphology and oxidation state as a function of applied potential during electrochemical carbon dioxide reduction using in situ soft X-ray spectro-ptychography. In comparison with scanning transmission X-ray microscopy, the spatial resolution is improved by a factor of 3 through measuring patterns of diffracted photons via spectro-ptychography. Quantitative chemical mapping by in situ spectro-ptychography demonstrates that as deposited, primarily mixed copper (I) and copper (0) particles are completely reduced to pure copper (0) and lose initial cubic structure to form irregular dendritic-like structures. This initial demonstration of in situ soft X-ray spectro-ptychography sheds insight on the morphological and chemical changes of copper particles in the carbon dioxide reduction regime and paves the way for more detailed in situ studies of electrochemical materials and processes.