Engineering Surface Amine Modifiers of Ultrasmall Gold Nanoparticles Supported on Reduced Graphene Oxide for Improved Electrochemical CO2 Reduction

Ultrasmall gold (Au) nanoparticles with high mass activity have great potential for practical applications in CO2electroreduction. However, these nanoparticles often suffer from poor product selectivity since their abundant low-coordinated sites are favorable for H2evolution. In this work, a catalyst, reduced graphene oxide supported ultrasmall Au nanoparticles (≈2.4 nm) is developed which delivers high Au-specific mass activities (>100 A g-1) and good Faradaic efficiencies (32-60%) for the CO2-to-CO conversion at moderate overpotentials (450-600 mV). The efficiencies can be improved to 59-75% while retaining the ultrahigh mass activities via a simple amine-modification strategy. In addition, an amine-structure-dependent effect is revealed: linear amines promote the CO formation whereas the branched polyamine greatly depresses it; the increasing alkyl chain length boosts the promotion effect of linear amines. The strong Au-amine interaction and molecular configuration induced amine coverage on the ultrasmall Au NPs may contribute to this effect.