Cooperative Interfacial and Electrolyte Engineering in Au@Cu 2 O Core@Shell Nanocatalysts for Efficient CO 2 Reduction to C 2+ Products at Circumneutral pH

ABSTRACT Developing advanced catalytic systems for efficient electrochemical CO 2 reduction ( e ‐CO 2 RR) at industrially relevant current densities under environmentally benign conditions remains challenging. Herein, we report Au@Cu 2 O ( n ) core@shell nanocatalysts with outstanding e ‐CO 2 RR performance at ‐200 mA cm −2 in near‐neutral media, where the Cu 2 O shell thickness is tuned by adjusting Au seed solution volume ( n mL). In 1.0 M KHCO 3 , the thin‐shelled Au@Cu 2 O ( n = 5) nanocatalyst achieves an exceptional Faradaic efficiency (FE C2+ : 50.6 ± 3.3%) and a cathodic energy efficiency (EE C2+ : 29.1 ± 1.3%) for C 2+ products, outperforming its thicker counterparts (e.g., Au@Cu 2 O ( n = 2); FE C2+ : 19.6 ± 2.7%, EE C2+ : 8.9 ± 0.9%) and individual control components. This enhanced performance stems from a strong core@shell electron transfer effect that modulates copper oxidation state (OS Cu ) and preserves the core@shell architecture. Intriguingly, iodide addition triggers divergent, shell‐thickness‐dependent effects. Iodide modulates both structural reconstruction and OS Cu of the Au@Cu 2 O ( n = 2) nanocatalyst, boosting C 2+ product selectivity (S C2+ ) fourfold. Conversely, iodide disrupts the pre‐existing, highly favorable core@shell electronic interactions of the Au@Cu 2 O ( n = 5) nanocatalyst, driving OS Cu away from the favorable regime and thereby suppressing S C2+ . These findings underscore the importance of cooperatively engineering interfacial electronic properties and electrolyte microenvironments for efficient e ‐CO 2 RR at circumneutral pH.