From Performance Boost to Degradation Mechanism: How Oxygen‐Enriched Cathode Operation Enhances Durability in PEMFCs

ABSTRACT Oxygen concentration critically governs the oxygen reduction reaction rate in proton exchange membrane fuel cells (PEMFCs), influencing both performance and durability. This study systematically evaluated oxygen concentrations from 21% to 100% using electrochemical measurements, accelerated stress tests, and structural characterization. Results indicate that 45% oxygen provides the optimal performance–durability balance. Increasing oxygen from 21% to 45% significantly improved open‐circuit voltage, power density, and high‐current performance, reduced polarization losses, and lowered total resistance by over 50%, whereas further increases offered diminishing returns. In 150 h durability testing, H _2% –45%O ₂ showed a voltage decay rate of 66.67 µV h ^{− 1} , maximum power loss of 1.76%, total resistance increase of 7.25%, and ECSA loss of 0.68%, all markedly superior to H ₂ –air operation. Microstructural analysis confirmed enhanced gas distribution and reduced catalyst degradation and Pt agglomeration. Moderate oxygen enrichment thus effectively balances performance with durability, offering practical guidance for optimizing PEMFC cathode gas supply.