Proton exchange membrane fuel cells (PEMFCs) operating at elevated temperatures (>100 °C) hold promise for simplified water-thermal management compared to conventional 60–85 °C systems. However, the complex interplay of activation polarization, oxygen partial pressure and mass transfer at high temperatures remains unresolved, limiting their practical deployment. Herein, we decode a temperature-dependent trade-off. It governs PEMFCs performance across a wide temperature range (60–100 °C) through operando polarization decomposition, limit current method and a validated multiphysics coupling model, revealing that while rising temperatures reduce the intrinsic total mass transfer resistance (Rtotal) and activation overpotential, these benefits are negated by oxygen partial pressure drop due to accelerated water vaporization-induced gas dilution. To address this bottleneck, we propose an oxygen-enriched air control strategy that dynamically adjusts cathode gas composition, achieving 36 % increase in peak power and 90 mV improvement in voltage (@1.6 A/cm2) at 100 °C. Quantification via game-theoretic analysis shows 67 % performance gain from oxygen compensation and 33 % from activation polarization and Rtotal mitigation. Moreover, there is no sign of accelerated durability degradation compared to air under oxygen-enriched air conditions. This work decouples temperature-dependent polarization mechanisms and provides a transformative pathway for next-generation high-temperature PEMFCs systems.
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