N-Heterocyclic Carbene Coordinated Cu Single Atoms on Poly(ionic Liquid) for Selective Electroreduction of CO₂ to CH₄ at High Current Density

Finely adjusting the local environment of Cu single atom (SA) is crucial but challenging for the fabrication of electrocatalysts for the CO₂ reduction reaction (CO₂RR) to produce clean energy methane (CH₄). Herein, poly(ionic liquid)s-stabilized Cu SAs with tunable Br–Cu–C_x configuration were directly synthesized through the self-polymerization of the ionic liquid monomer, a bis-vinylimidazolium salt, in the presence of Cu precursor. Synchrotron X-ray absorption fine structure, soft X-ray absorption, and X-ray photoelectron spectroscopy analyses showed that the Cu SAs were coordinated with N-heterocyclic carbene derived from the imidazole ring. The optimal catalyst Cu@P-2 with moderate Cu loading afforded a high Faradaic efficiency of ∼70% at a high current of −250 mA cm⁻² in the CO₂RR to CH₄, associating with a turnover frequency as high as 1.0 s⁻¹. This outstanding performance is assigned to the high density Cu SAs reaching strong affinity towards *CO intermediates in the case of moderate Cu loading, as revealed by in situ attenuated total reflection surface-enhanced infrared absorption spectroscopy analysis and theoretical calculated free energy profiles of CO₂RR to CH₄.