Stabilizing High-Valence Copper(I) Sites with Cu–Ni Interfaces Enhances Electroreduction of CO₂ to C₂₊ Products

In this study, the copper-nickel (Cu–Ni) bimetallic electrocatalysts for electrochemical CO₂ reduction reaction(CO₂RR) are fabricated by taking the finely designed poly(ionic liquids) (PIL) containing abundant Salen and imidazolium chelating sites as the surficial layer, wherein Cu–Ni, PIL–Cu and PIL–Ni interaction can be readily regulated by different synthetic scheme. As a proof of concept, Cu@Salen-PIL@Ni(NO₃)₂ and Cu@Salen-PIL(Ni) hybrids differ significantly in the types and distribution of Ni species and Cu species at the surface, thereby delivering distinct Cu–Ni cooperation fashion for the CO₂RR. Remarkably, Cu@Salen-PIL@Ni(NO₃)₂ provides a C2+ faradaic efficiency (FE_C2+) of 80.9% with partial current density (j_C2+) of 262.9 mA cm⁻² at −0.80 V (versus reversible hydrogen electrode, RHE) in 1 m KOH in a flow cell, while Cu@Salen-PIL(Ni) delivers the optimal FE_C2+ of 63.8% at j_C2+ of 146.7 mA cm⁻² at −0.78 V. Mechanistic studies indicates that the presence of Cu–Ni interfaces in Cu@Salen-PIL@Ni(NO₃)₂ accounts for the preserve of high-valence Cu(I) species under CO₂RR conditions. It results in a high activity of both CO₂-to-CO conversion and C–C coupling while inhibition of the competitive HER.