Dissolution and Migration of Platinum in PEMFCs Investigated for Start/Stop Cycling and High Potential Degradation

Dissolution and migration of platinum due to start/stop degradation and increased cathode potentials were studied for commercial membrane electrode assemblies (MEA). The chosen conditions closely mimic real situations in automotive operation. In start/stop tests, we observed a strongly enhanced platinum dissolution due to the dynamic interplay of repeated cell start-up and consecutive normal fuel cell operation, which is related to platinum oxidation (start-up) and reduction (normal operation) cycles. Consequently, the performed test protocols distinguish between dynamic and static load profiles. Electrochemical investigations before and after degradation monitor the loss in cell performance. Since electron microscopy offers the unique possibility to unravel and distinguish degradation due to carbon corrosion and agglomeration or platinum dissolution, a focus was set on this method. For the start/stop MEA pronounced platinum dissolution accompanied by the formation of large platinum precipitations in the membrane was found. Carbon corrosion was also observed, but did not lead to a significantly reduced porosity and loss in platinum dispersion. In contrast, the MEA which was exposed to high constant potentials exhibited severe damage to the 3D cathode structure due to carbon corrosion. However, no pronounced platinum dissolution was observed and only few Pt precipitations were found in the membrane itself.