Cooperative Interfacial and Electrolyte Engineering in Au@Cu2O Core@Shell Nanocatalysts for Efficient CO2 Reduction to C2+ Products at Circumneutral pH.

Developing advanced catalytic systems for efficient electrochemical CO2 reduction (e-CO2RR) at industrially relevant current densities under environmentally benign conditions remains challenging. Herein, we report Au@Cu2O (n) core@shell nanocatalysts with outstanding e-CO2RR performance at -200 mA cm-2 in near-neutral media, where the Cu2O shell thickness is tuned by adjusting Au seed solution volume (n mL). In 1.0 M KHCO3, the thin-shelled Au@Cu2O (n = 5) nanocatalyst achieves an exceptional Faradaic efficiency (FEC2+: 50.6 ± 3.3%) and a cathodic energy efficiency (EEC2+: 29.1 ± 1.3%) for C2+ products, outperforming its thicker counterparts (e.g., Au@Cu2O (n = 2); FEC2+: 19.6 ± 2.7%, EEC2+: 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 (OSCu) and preserves the core@shell architecture. Intriguingly, iodide addition triggers divergent, shell-thickness-dependent effects. Iodide modulates both structural reconstruction and OSCu of the Au@Cu2O (n = 2) nanocatalyst, boosting C2+ product selectivity (SC2+) fourfold. Conversely, iodide disrupts the pre-existing, highly favorable core@shell electronic interactions of the Au@Cu2O (n = 5) nanocatalyst, driving OSCu away from the favorable regime and thereby suppressing SC2+. These findings underscore the importance of cooperatively engineering interfacial electronic properties and electrolyte microenvironments for efficient e-CO2RR at circumneutral pH.