Defect‐Suppressed Molecular Passivation Film Endure the Trade‐Off: Scalable Co‐Passivation for Copper That Withstands Harsh Alkaline Attack

The persistent corrosion of copper in aggressive environments remains a fundamental limitation, challenges related to interfacial integrity, durability, and practical processability have not to be fully addressed. Here, we propose a synergistic passivation strategy with 1‐dodecanethiol (DT) and 2‐mercaptobenzimidazole (MBI) into a low‐defect, ultrathin passivation film on copper. The molecularly engineered passivation film affords a four‐order‐of‐magnitude improvement in corrosion current suppression. Notably, the Cu‐DT‐MBI preserves this four‐order‐of‐magnitude protection even after 24‐h immersion in 1 M NaOH and maintains effective corrosion resistance for more than 13 days. A combination of in situ spectroscopy and cross‐sectional electron microscopy reveals a uniform and continuous passivation film with a thickness of 1.03 nm. The enhanced protection is attributed to the functional complementarity between DT and MBI: DT contributes a hydrophobic alkyl‐chain barrier, while MBI preferentially coordinates with under‐coordinated Cu sites and improves interfacial continuity. DFT calculations further indicate that the passivated surface weakens O 2 and Cl − adsorption, thereby suppressing oxidation and corrosion. Furthermore, a roll‐to‐roll manufacturing process was demonstrated to produce passivated Cu foils that retain excellent conductivity while withstanding harsh alkaline attack. This work provides a foundational framework for designing ultra‐stable molecular interfaces via synergistic passivation.