来源：ACS Publications
The advancement of polymer electrolyte fuel cells (PEFCs) relies on materials capable of enhancing electrochemical performance while maintaining long-term operational stability. Rare earth elements (REEs), characterized by partially filled 4f orbitals, tunable redox chemistry, and oxygen vacancy formation, have emerged as effective modifiers for both polymer electrolyte membranes and electrode catalysts. Their incorporation enables improved proton transport, optimized water management, and modulation of fuel oxidation and oxygen reduction reactions through electronic structure tuning. Despite these advantages, key challenges persist, including inconsistent mechanistic interpretations, limited durability evaluation under realistic conditions, and trade-offs between catalytic enhancement and ionic conductivity. Additional concerns, such as REE migration, structural instability under dynamic operation, and techno-economic limitations, hinder large-scale application. This review provides a critical and integrated assessment of REE incorporation in PEFC systems by linking membrane transport properties with electrocatalytic activity. Integration in this review refers to the common REE chemistries, including Ce3+/Ce4+ redox cycling, oxygen-vacancy engineering, and electronic structure modulation, which simultaneously regulate proton transport, water management, radical scavenging, and electrocatalytic processes across the membrane–electrode assembly. Emphasis is placed on structure–property–performance relationships, vacancy-driven mechanisms, and degradation behavior. This work identifies key contradictions and emerging design strategies by synthesizing recent studies and proposes a unified framework to guide the development of high-performance, durable, and scalable PEFC technologies.