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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–CuI tandem catalyst for the production of C2+ products with both high reaction rate and high selectivity. Remarkably, a high C2+ faradaic efficiency (FEC2+) 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‐CuI interfaces are vital for such reactivity. Specifically, Cu nanoparticles derived Cu0‐PIL interfaces account for high current density and a moderate C2+ selectivity, whereas CuI species derived PIL‐CuI 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. [ABSTRACT FROM AUTHOR]