The Proximal Protonation Source in Cu−NH_x−C Single Atom Catalysts Selectively Boosts CO₂ to Methane Electroreduction

Abstract

Regulating the coordination environment of active sites has proved powerful for tapping into their catalytic activity and selectivity in homogeneous catalysis, yet the heterogeneous nature of copper single-atom catalysts (SACs) makes it challenging. This work reports a bottom-up approach to construct a SAC (rGO@Cu-N(H_x)-C) by inlaying preformed amine coordinated Cu²⁺ units into reduced graphene oxide (rGO), permitting molecular level revelation on how the proximal N-site functional groups (N-H or N-CH₃) impact on the carbon dioxide reduction reaction (CO₂RR). It is demonstrated that the N-H moiety of rGO@Cu-NH_x-C can serve as an in situ protonation agent to accelerate the CO₂-to-methane reduction kinetics, delivering a methane current density (163 mA/cm²) 2.42-times that with the -CH₃ substituted counterpart rGO@Cu-N-C. Operando spectroscopic studies and theoretical calculations elucidate that the high methane faradaic efficiency (77.1 %) achieved here is enabled by opening up the energetically favorable formyl pathway (*OCHO pathway) against the traditional *CO pathway that normally leads to various CO₂RR products other than methane. Our strategy sets the stage to precisely modulate single-atom catalysts for efficient and selective electrochemical CO₂ reduction.