Denticity-Controlled N-Heterocyclic Carbene Stabilization of Copper Nanoparticles Enhances C2 Selectivity in CO2 Electroreduction

Abstract Electrochemical CO2 reduction (CO2RR) to multicarbon products offers a route to green chemical feedstocks. While nanostructured Copper (Cu) catalysts provide a high density of undercoordinated sites that are generally associated with enhanced C–C coupling, their practical application is hindered by rapid structural degradation under operating conditions. In this work, we demonstrate that multidentate N-heterocyclic carbene (NHC) ligands can mitigate these effects by providing enhanced surface stabilization compared to monodentate analogues. We synthesized Cu nanoparticles (CuNPs) functionalized with mono-, bi-, tridentate, and polymeric NHC ligands and evaluated their performance in CO2-saturated 0.5 M KHCO3. We found that increasing NHC denticity systematically improves ambient stability, preserves structural integrity even after cathodic electrolysis, and enhances C2 selectivity. Among the series, tripodal NHC-stabilized Cu nanoparticles achieved a ∼40% Faradaic efficiency (FE) toward C2 products which is a 60-fold increase over oleylamine-capped controls. These catalysts also exhibited a positive shift in C2 onset potential to –1.1 V vs RHE and a partial C2 current density of ∼60 mA/mg at –1.7 V vs RHE. Post-electrocatalytic analysis via FE-SEM and XPS analyses are consistent with reduced catalyst restructuring in the multidentate system. These findings identify multidentate NHC ligation as a promising strategy for designing durable, highly selective nanocatalysts for CO2 conversion.