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 (FEC2+) of 80.9% with partial current density (jC 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 FEC2+ of 63.8% at jC2+ 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.

Electroreduction of carbon dioxide to multi-electron reduction products using poly(ionic liquid)-based Cu-Pd catalyst.

Electrocatalytic reduction of CO2 (CO2RR) to multi-electron (> 2e-) products provides a green and sustainable route for producing fuels and chemicals. Introducing the second metal element is a feasible strategy for "managing" the key intermediate on Cu-based materials to further improve the CO2RR catalytic performance. In this work, palladium, which promises the generation of CO, was introduced into the poly(ionic liquid)-based copper hybrid (Cu@PIL) to construct a novel Cu-Pd bimetallic electrocatalyst (Cu@PIL@Pd). Remarkably, with a small dosage of palladium (2.0 mol% compared with Cu), a high faradaic efficiency (FE) for C2+ products (68.7%) was achieved at -1.01 V (with respect to the reversible hydrogen electrode (RHE), the same below) with a high partial current density of 178.3 mA cm-2. Meanwhile, high selectivity towards CH4 (FE = 42.5%) and corresponding partial current density of 172.8 mA cm-2 were obtained on the same catalyst at -1.24 V, signifying a significant potential-dependent selectivity. Mechanistic studies reveal that both copper and palladium oxides are reduced to metallic states during the CO2RR. The presence of the adjoint copper phase and the highly dispersed electrostatic layer promote the generation of CO on the palladium components (both the PdO2 phase and the Pd(II) site). Besides, the local CO* was enriched by the significant diffusion resistance of CO in the PIL layer. The spillover of CO* from Pd sites to the adjoint Cu sites, accompanied by the increased local concentration of CO* around Cu sites, accounted for the observed good CO2RR catalytic performance, especially the high C2+ product selectivity.