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_{C 2+}) 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.