Unveiling Nonlinear Platinum Oxidation Dynamics in Proton Exchange Membrane Fuel Cell Catalyst Layers: New Phenomena and Sensitivity Insights

Proton exchange-membrane fuel cells (PEMFCs) are increasingly expected to operate at high-efficiency potentials of 0.75–0.85 V. Under such conditions, rapid electrochemical oxidation of platinum accelerates performance decay, making a clear understanding of Pt oxidation kinetics essential. Whereas log-linear growth of Pt oxides has been well documented at the catalyst level using rotating disk electrode, comparable studies under full membrane electrode assembly (MEA) conditions remain limited. This study systematically probes Pt oxidation on MEAs across 0.75–0.85 V while independently adjusting temperature (25–90°C) and anode/cathode relative humidity (20–100%). A previously unreported two-segment, log-time evolution of Pt oxide coverage is revealed: growth accelerates early, then slows or even reverses as surface oxides undergo Pt–O place exchange and form three-dimensional, reduction-resistant structures. Higher temperature, higher humidity, and higher potential each accelerated Pt oxide growth. The insights advance fundamental understanding of Pt-oxide dynamics in practical PEMFC environments and have great significance for mitigating high-potential decay.