Figure 1. Morphological characterization of plasma-treated Cu foil electrodes.

SEM images of Cu foils treated with O₂ plasma for (a–c) 20 W 2 min; (d–g) 100 W 2 min; and (h–j) 100 W 10 min. (a,b,d,e,h,i) The morphology of the as-prepared foils. (c,f,j) The morphology after the CO₂RR reaction. (g) The sample plasma treated with O₂ at 100 W for 2 min after an additional H₂ plasma treatment at 100 W for 10 min. Scale bars, (a) 10 μm; (b,c,e–g,i,j) 500 nm; (d,h) 20 μm.