Lattice Carbon-Mediated Ultralow-Barrier C-C Coupling for Selective CO Electroreduction to Ethylene

Understanding the mechanistic pathways of catalytic CO₂ reduction is essential for the rational design of high-performance electrocatalysts. A key challenge in converting CO₂ to multi-carbon (C₂₊) products is the high energy barrier for C─C coupling, which limits both activity and selectivity. Here, using combined density functional theory (DFT) and molecular dynamics simulations, we demonstrate that lattice carbon sites at the edges of MXene (Ti₂C(OH)₂) serve as highly effective adsorption centers for ^*CO intermediates during CO electroreduction. Remarkably, these sites significantly reduce the C─C coupling barrier through a lattice carbon-mediated mechanism (LCMM). Electronic structure analyses, including projected densities of states, Bader charge partitioning, differential charge density, and electron localization function calculations, reveal that the LCMM facilitates substantial electron transfer to adsorbed CO. This electron enrichment weakens the C≡O bond while simultaneously promoting C─C bond formation, overcoming conventional coupling limitations. Our findings provide fundamental insights into C─C bond formation mechanisms and establish new design principles for developing selective C₂ electrocatalysts.