Sn-Decorated Cu for Selective Electrochemical CO₂ to CO Conversion: Precision Architecture beyond Composition Design

Sn-decorated Cu (Cu–Sn) electrodes were proposed as an alternative to Ag- and Au-based electrocatalysts for the selective reduction of CO2 to CO. Here we demonstrate that selectivity does not only depend on catalyst surface composition, but is strongly affected by the electrode morphology. At current densities above 10 mA·cm–2, we find that morphology can control the CO2 reduction pathways to CO and other products, including the competing H2 evolution, on the Cu–Sn surface. An electrode design with dendritic morphological features yields the highest CO partial current density of 11.5 mA·cm–2 at −1.1 V vs RHE, avoiding the significant loss of CO selectivity observed for an electrode with less sharp, rounder morphological features. Efficient CO2 mass transport to the catalyst surface and a high local CO2 concentration, promoted by the dendritic structure, stabilize the Cu-SnO overlayer, suppress the competing H2 evolution reaction, and maintain CO selectivity above 85% over a wide potential range.