Highly Efficient Electrocatalytic CO₂ Reduction to C₂₊ Products on a Poly(ionic liquid)-Based Cu⁰–Cu^I Tandem Catalyst

Electroreduction of CO₂ on a polymer-modified Cu-based catalyst has shown high multi-electron reduction (>2 e⁻) selectivity, however, most of the corresponding current densities are still too small to support industrial applications. In this work, we designed a poly(ionic liquid) (PIL)-based Cu⁰–Cu^I tandem catalyst for the production of C₂₊ products with both high reaction rate and high selectivity. Remarkably, a high C₂₊ faradaic efficiency (FE (Formula presented.)) of 76.1 % with a high partial current density of 304.2 mA cm⁻² is obtained. Mechanistic studies reveal the numbers and highly dispersed Cu⁰-PIL-Cu^I interfaces are vital for such reactivity. Specifically, Cu nanoparticles derived Cu⁰-PIL interfaces account for high current density and a moderate C₂₊ selectivity, whereas Cu^I species derived PIL-Cu^I interfaces exhibit high activity for C−C coupling with the local enriched *CO intermediate. Furthermore, the presence of the PIL layer promotes the C₂₊ selectivity by lowering the barrier of C−C coupling.