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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]

Poly(ionic liquid)-metal (PIL-metal) hybrids were developed as a platform for facilely constructing tandem catalysts to reach highly efficient electrocatalytic reduction of CO 2 (CO 2 RR). By introducing extra metal with distinct CO 2 RR response to Cu-PIL hybrids, Cu@PIL@Ag and Cu@PIL@Bi were obtained. Remarkably, Cu@PIL@Ag exhibits an excellent C 2+ Faradaic efficiency (FE C2+) of 83.2% with a high partial current density (j C2+) of 416.1 mA cm–2 in 3 M KOH and an even higher j C2+ (708.9 mA cm–2) in 1 M KOH, while Cu@PIL@Bi possesses high FE C1 (> 60%) and low FE C2+ (< 5%) in a wide potential range. Mechanistic studies demonstrate the output of such a tandem system, either synergistic or maladjusted, depends on not only CO 2 RR response of Ag and Bi but also specific Cu-Ag and Cu-Bi interactions. Besides, the PIL layer could adjust the reactivity by promoting the dispersion and availability of active sites and enriching the local key intermediates. [Display omitted] • A facile and universal PIL-based electrocatalyst platform was provided for studying the tandem CO 2 RR strategy. • Cu@PIL@Ag exhibits an excellent C 2+ selectivity of 83.2% with a high partial current density of 416.1 mA cm–2 in 3 M KOH. • The CO 2 RR performance depends on response of introduced metal, the Cu-metal interactions, and the characteristics of PIL. [ABSTRACT FROM AUTHOR]

[Display omitted] • Copper@poly ionic liquid (Cu@PIL) hybrid is prepared via in-situ polymerization method. • Multi-electron CO 2 reduction (> 2e–) with industrial current density (≥300 mA cm−2) is realized on this novel Cu@PIL system. • The outer layer of PIL enriches local CO 2 concentration by adsorption CO 2 molecules with cationic fragment. • The structurally induced interfacial electric field at Cu@PIL interface stabilizes polarized intermediates, wherein the anions at the inner PIL layer regulate the current density and product selectivity by different electron donation ability. Ionic liquid-based electrocatalytic CO 2 reduction faces the challenge of achieving high selectivity toward value-added C 2+ products at high reaction rate (≥ 100 mA cm−2). Herein, novel copper@poly(ionic liquid) (Cu@PIL) hybrids demonstrate multi-electron reduction (> 2e–) with current densities ≥ 300 mA cm−2. Remarkably, Cu@PIL with F– anion exhibits high C 2+ faradaic efficiency of 58 % with a high partial current density of 174 mA cm−2. Further, a highest C 2+ partial current density of 233 mA cm−2 was also achieved. Experimental combined theoretical investigations reveal that the "individual" ionic pairs in the outer PIL layer enrich local CO 2 concentration, thereby promoting the CO 2 supply. Besides, an interfacial electric field is induced by the unbonded imidazolium moieties at Cu-PIL interface, which stabilize intermediates. Anions, differing in the electron-donating number to the imidazolium moieties, influence both the enrichment of CO 2 and the stabilization of intermediates, thus regulating current density and product selectivity. [ABSTRACT FROM AUTHOR]