Harnessing Lewis Acidity and Hydrophilicity of Surface-Engineered MXenes to Stabilize Cu(I) in an Oxidative...

Stabilizing metastable Cu(I) species during electrochemical CO₂ reduction remains a fundamental challenge, as their rapid electroreduction into metallic Cu undermines C-C coupling and long-term selectivity. Here, we overturn this limitation through the interfacial engineering of Cu₂O with hydroxy-terminated Ti₃C₂T_x MXene, creating an adaptive catalyst that sustains Cu(I) redox dynamics under strongly reducing conditions. In situ-grown Cu₂O nanocubes leverage Ti³⁺ Lewis acid sites and surface -OH/F groups to establish a hydrophilic, locally oxidative microenvironment─an unconventional stabilization regime that defies the typical reductive decay of oxide-derived Cu. This interfacial-driven approach delivers a 3-fold increase in activity and a 46% Faradaic efficiency toward C₂ products, while maintaining stability beyond 70 h. Spectro-electrochemical Raman analyses, cyclic voltammetry, and real-time potential of zero charge analyses established that MXene-Cu coupling modulates and elevates local pH to enhance CO₂ solubility, strengthens *CO adsorption, and uniquely stabilizes the rarely explored *C₂H₅O^- intermediate, thereby providing an unexpected mechanistic pathway to selective multicarbon formation. By demonstrating that dynamic redox equilibria, rather than static oxidation states, govern efficient CO₂-to-fuel conversion, this work redefines Cu-based electrocatalysis and establishes a new paradigm for designing resilient electrocatalysts through electronic and chemical environment control.