The morphology of nominal single geometric monolayer (MLgeo; 980 μC/cm 2 geo passed, see SI) electrodeposited Cu/FTO films was characterized by scanning electron microscopy energy dispersive X-ray spectroscopy (SEM-EDS; Figure ). Cu particles are evident as higher-contrast (brighter) spots in SEM images, relative to the low-contrast (darker) FTO support (Figure ). An EDS line scan, performed along a 36 μm section incident to five of these brighter particles, corresponds to increased Cu K emission with the location of bright spots along the line scan (Figure ). Cu particles form on the FTO support in a cubic structure with an average face length of 0.37 ± 0.12 μm (average and standard deviation of n = 72 particles; Figure ). Films of electrodeposited Cu/CeO2-δ were also characterized by SEM-EDS (Figure ).