Facet-Selective Deposition of Ultrathin Al₂O₃ on Copper Nanocrystals for Highly Stable CO₂ Electroreduction to Ethylene

Catalysts based on Cu nanocrystals (NCs) for electrochemical CO₂-to-C₂₊ conversion with high activity have been a subject of considerable interest, but poor stability and low selectivity for a single C₂₊ product remain obstacles for realizing sustainable carbon-neutral cycles. Here, we used the facet-selective atomic layer deposition (FS-ALD) technique to selectively cover the (111) surface of Cu NCs with ultrathin Al₂O₃ to increase the exposed facet ratio of (100)/(111), resulting in a faradaic efficiency ratio of C₂H₄/CH₄ for overcoated Cu NCs 22 times higher than that for pure Cu NCs. Peak performance of the overcoated catalyst (Cu NCs/Al₂O₃-10C) reaches a C₂H₄ faradaic efficiency of 60.4 % at a current density of 300 mA cm⁻² in 5 M KOH electrolyte, when using a gas diffusion electrode flow cell. Moreover, the Al₂O₃ overcoating effectively suppresses the dynamic mobility and the aggregation of Cu NCs, which explains the negligible activity loss and selectivity degradations of Cu NCs/Al₂O₃-10C shown in stability tests.