Size-dependent reactivity of gold-copper bimetallic nanoparticles during CO2 electroreduction

[Display omitted] •Size-controlled gold-copper alloy nanoparticles synthesized using inverse micelle encapsulation (1.4–24nm).•XPS and XAFS show oxidized gold-copper alloy nanoparticles were formed.•Smaller particles have higher activity for CO2 electroreduction in 0.1M KHCO3.•For this system, Faradaic selectivity does not depend strongly on particle size. New catalysts are needed to achieve lower overpotentials and higher faradaic efficiency for desirable products during the electroreduction of CO2. In this study, we explore the size-dependence of monodisperse gold-copper alloy nanoparticles (NPs) synthesized by inverse micelle encapsulation as catalysts for CO2 electroreduction. X-ray spectroscopy revealed that gold-copper alloys were formed and were heavily oxidized in their initial as prepared state. Current density was found to increase significantly for smaller NPs due to the increasing population of strongly binding low coordinated sites on NPs below 5nm. Product analysis showed formation of H2, CO, and CH4, with faradaic selectivity showing a minor dependence on size. The selectivity trends observed are assigned to reaction-induced segregation of gold atoms to the particle surface and altered electronic or geometric properties due to alloying.