Hetero‐Interface Maximized UiO‐66‐NH 2 /CeO 2−x Free Radical Scavenging Additives for Long‐Term Operation of Proton Exchange Membrane Fuel Cells

The long‐term durability of proton exchange membrane fuel cells (PEMFCs) remains a critical hurdle for their widespread commercialization, largely because of chemical degradation of the membrane electrode assembly (MEA) by unintentionally generated free radicals during operation. Defective ceria (CeO 2−x ) nanoparticles have emerged as promising radical‐scavenging additives through reversible Ce 3+ /Ce 4+ redox cycling. However, their radical scavenging efficiency is limited by the sluggish regeneration of surface Ce 3+ species, which are the active species for radical scavenging, leading to a gradual loss of their initial scavenging capability during long‐term cell operation. Here, we report a strategy to accelerate Ce 3+ regeneration kinetics by maximizing heterointerface‐derived interactions through simple seed‐mediated growth of defective ceria on the surface of a metal‐organic framework (MOF). In particular, UiO‐66‐NH 2 undergoes partial amorphization and dissolution during the CeO 2−x nanoparticle growth, which enables intimate interfacial contact and enhanced electronic coupling with CeO 2−x . The resulting UiO‐66‐NH 2 /CeO 2−x heterostructure exhibits improved redox cycling and higher Ce 3+ retention under oxidative conditions than commercial ceria nanoparticles. Moreover, when incorporated into the cathode catalyst layer of the MEA, the UiO‐66‐NH 2 /CeO 2−x significantly suppressed the performance degradation, enabling stable single‐cell operation for over 500 h under an accelerated durability test.