Epitaxial Stabilization of Ultrasmall Cu Nanoparticles With High‐Energy {110} Facets on Ti ₃ C ₂ MXene for Efficient CO ₂ ‐to‐Acetate Electrocatalysis

ABSTRACT The electrochemical CO 2 reduction reaction (CO 2 RR) to multicarbon (C 2+ ) products offers a promising route for sustainable carbon cycling and renewable energy storage. Copper (Cu)‐based nanocatalysts are indispensable for enabling C‐C coupling; however, conventional synthesis methods struggle to consistently produce and stabilize ultrasmall Cu(0) nanoparticles, which are prone to oxidation and aggregation, and fail to preserve their high‐energy facets critical for C 2+ selectivity. In this work, we overcome these challenges by constructing a well‐defined Cu/Ti 3 C 2 heterointerface that leverages a lattice matching mechanism. This approach not only stabilizes ultrasmall Cu(0) nanoparticles under ambient conditions but also promotes the preferential exposure and stabilization of high‐energy (110) facets. The resulting Cu/Ti 3 C 2 composite catalyst exhibits exceptional performance in the CO 2 RR, achieving a total C 2 Faradaic efficiency of 72.5%, with acetate alone reaching 42.5% at an industrially relevant current density of 235 mA·cm −2 . Combined spectroscopic and computational studies reveal that the electronic metal‐support interaction and epitaxial growth are key to stabilizing the active structure, while the exposed Cu(110) facets lower the kinetic barriers for the critical C‐C coupling step toward acetate. This study underscores the vital importance of precise interfacial and crystallographic control in developing efficient and stable electrocatalysts for CO 2 conversion.