Beyond C-C Cleavage: CO Detoxification as a Key Step in Ethanol Electrooxidation Revealed by In Situ SERS.

Direct ethanol fuel cells (DEFCs) relying on the complete C1 oxidation pathway face two linked barriers at the anode: the difficulty of C-C bond cleavage and *CO intermediate poisoning. While Pt-based alloys address the former, they are plagued by *CO-induced deactivation, and the mechanism of *CO clearance in alkaline electrolytes has remained elusive. Herein, we demonstrate that effective *CO detoxification plays a critical role in governing the selectivity toward the complete C1 pathway. Using a ternary Ag@Pt7Pd3 core-shell catalyst, we achieve a mass activity of 17.66 A mgPGM-1 with 90.5% retention after 5000 cycles. Through in situ electrochemical surface-enhanced Raman spectroscopy complemented by electronic structure analyses and theoretical calculations, we uncover a dual-mechanism detoxification pathway: Ag modulates the d-band center of Pt/Pd to enhance CO adsorption and activation, while adjacent Pd sites promote *OH formation, which subsequently executes nucleophilic attack on the activated *CO. This cooperative process efficiently removes *CO at low overpotentials, unlocking the C1 pathway and enabling sustained high performance. Our findings highlight the central role of *CO detoxification in steering reaction selectivity and enhancing device performance, thereby completing the key missing piece for enabling efficient DEFCs through the C1 pathway.