Start-up and Shut-down phases for Proton Exchange Membrane Fuel Cell stacks are known to damage the Cathode Catalyst Layer inducing an irreversible loss of performance. An original Accelerated Stress Test has been designed to mimic the Start-up phase in real-life system conditions. The impact of cathode potential on the degradation mechanisms of the Pt/C components within the Cathode Catalyst Layer by local electrochemical and physicochemical analyses provided a deep understanding of the cathode evolution. An unexpected cell performance improvement is observed between 1.0 and 1.2 V cathode potential, especially at high current density. A beneficial modification of the properties occurs suggesting that fresh Cathode Catalyst Layer exhibits non-optimized carbon support properties. However, a significant structure subsidence appears when the cathode potential is above 1.4 V. In this condition, modification/compaction of cathode layer due to carbon corrosion alters mass transport and empathizes water flooding through the electrode.
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