Epitaxial Stabilization of Ultrasmall Cu Nanoparticles With High-Energy {110} Facets on Ti₃C₂ MXene for Efficient CO₂-to-Acetate Electrocatalysis

The electrochemical CO₂ reduction reaction (CO₂RR) to multicarbon (C₂₊) 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 C₂₊ selectivity. In this work, we overcome these challenges by constructing a well-defined Cu/Ti₃C₂ 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/Ti₃C₂ composite catalyst exhibits exceptional performance in the CO₂RR, achieving a total C₂ 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 CO₂ conversion.