Regulating Spillover Effect in Cu-Ag via Zeolite Frameworks for Efficient CO₂ Electroreduction

Electrochemical CO₂ reduction reaction (CO₂RR) has been regarded as a promising green technology for lowering atmospheric CO₂ level and producing value-added products. For multi-carbon (C₂₊) chemical production, Cu-based electrocatalysts have been developed by various strategies, such as defect engineering, alloying with other metals, and morphological engineering. Among these various strategies, the spillover effect between Cu and Ag has been considered as an effective avenue for modulating CO₂RR selectivity and activities. However, previous works about spillover effect have focused on controlling the Cu/Ag ratio rather than regulating the interface reaction between Cu and Ag.
Herein, we propose a novel strategy to optimize spillover effect on the Cu surface by modulating anion species in zeolite framework-augmented gas diffusion electrode (GDE). In CO₂RR, anions such as Cl, Br, and I can modulate the Cu surface oxidation states and create Cu (0)-Cu (I) mixed sites which facilitate C-C coupling by modifying *CO binding. However, these anions can easily migrate to the anodic side by crossover in anion exchange membrane under high current density conditions. Thus, we augmented AgX (X = Cl, Br, and I)-incorporated zeolite A (AgX-Zeolite A) on Cu electrocatalysts to modulate spillover effect by restricting anion migration. They showed lower hydrogen production and more efficient CO₂RR compared to bare Cu electrocatalysts in 1 M KOH electrolyte conditions. Especially, AgCl-, AgBr-, and AgI-Zeolite A on Cu electrocatalysts exhibited 586.3, 495.8, and 456.4 mA/cm² as maximum partial current densities for C₂₊ products. This trend is in inverse relationship with the electronegative force of anion species. With increasing electronegative force, the Cu (I) sites become more dominant rather than Cu (0)-Cu (I) mixed sites. However, AgCl-, AgBr-, and AgI-Zeolite A on Cu electrocatalysts showed the 0.89, 1.17, and 1.14 as Faradaic efficiency (FE) ratio of ethanol (C₂H₅OH)/ethylene (C₂H₄), respectively. These results verified that anion species stabilized by zeolite framework not only accelerate C₂₊ production but also steer the CO₂RR pathway to specific products via spillover effect. Our work provides an insight of zeolite framework-augmented GDEs for high rate and selective C₂₊ chemical production in CO₂RR.