Synthesis of fcc/2H and f cc /4H Copper Nanodisks Towards Carbon Dioxide Reduction

Abstract Two-dimensional Cu nanostructures containing noncanonical face-centered cubic/hexagonal close-packed (fcc/hcp) heterophase boundaries are attractive for CO2 electroreduction but remain difficult to prepare by wet-chemical methods. Here, we report a high-temperature solution reduction route to Cu nanodisks with a thickness of 26.5 ± 2.3 nm and a diameter of 85.6 ± 3.7 nm. Transmission electron microscopy reveals abundant fcc/2H and fcc/4H interfaces on the nanodisk side surfaces, where the 2H and 4H polytypes exhibit AB and ABCB stacking, respectively. In CO2-saturated 0.1 M KHCO3, the nanodisks achieve a methane Faradaic efficiency of 60.4% at −1.25 V vs the reversible hydrogen electrode and outperform fcc Cu nanoparticle and microsheet controls tested at the same catalyst loading. Density functional theory calculations indicate that the free-energy penalty for forming the *CHO intermediate is smaller on the fcc/2H and fcc/4H models than on fcc Cu. These results support a thermodynamic contribution of heterophase interfaces to the observed methane selectivity; the calculations do not establish a reduction in kinetic activation barriers. This solution-phase route therefore provides access to phase-engineered Cu nanodisks and enables structure−property relationships relevant to CO2-to-CH4 electrocatalysis.