Fig. 3

Silver–copper model catalyst surface with different copper coverages. Scanning electron microscopic images of Ag-Cu surfaces achieved at Cu2+ concentrations of 0.5 ppm (a), 1.5 ppm (b) and 2.5 ppm (c). d Faradaic efficiencies of Ag-Cu surfaces with different Cu coverages for CO2 electrolysis at −1.10 VRHE. The error bars represent the standard deviation from at least three independent measurements