High-resolution operando CO2 analysis of oxygen-dependent carbon corrosion in PEMFC cathodes

Carbon corrosion is a critical degradation mechanism in proton exchange membrane fuel cells (PEMFCs) and proceeds not only during startup/shutdown but also under normal operation. However, its underlying mechanisms, particularly the influence of oxygen, remain insufficiently understood. Oxygen-dependent carbon corrosion in a PEMFC cathode was investigated by high-resolution operando analysis of CO 2 in the cathode exhaust using a non-dispersive infrared analyzer with 0.01 ppm resolution. A 1 cm 2 single cell was employed to reduce in-plane nonuniformities in gas composition and liquid-water distribution. Cathode oxygen partial pressure and relative humidity (RH) were systematically varied. Steady-state and transient corrosion were assessed under constant IR-free potentials and a 0.5–0.9 V IR-free potential step, respectively. As oxygen partial pressure increased, the steady-state corrosion rate at 0.5 V increased, whereas the transient corrosion amount decreased. Higher relative humidity enhanced transient corrosion, whereas no clear RH dependence was identified for steady-state corrosion. These contrasting dependencies suggest that steady-state corrosion reflects the reaction environment under the specified conditions, whereas transient corrosion is strongly influenced by Pt and carbon surface states established before the potential step. These findings advance the mechanistic understanding of oxygen-dependent carbon corrosion and support more realistic PEMFC durability evaluation and degradation-mitigation strategies.