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Identical location scanning electron microscopy (IL-SEM) and transmission electron microscopy (IL-TEM) are used to follow the degradation of the cathodic catalytic Pt/C electrode layer in a real proton-exchange membrane fuel cell under operation. During an accelerated stress test, mimicking start-up/shutdown conditions, the IL-SEM analysis reveals the formation and growth of cracks in the electrode layer, which expose the underlying membrane, leading to the creation of isolated islands of the electrode layer that tend to delaminate from the membrane. This is found to correlate with a 2- to 4-fold increase of the cell resistance. Nanoscale IL-TEM imaging shows that the diameter of the primary particles of the carbon support shrinks by on average 20%. Consequently, the Pt particles on the support agglomerate and grow by 63% contributing to an observed 65% loss in the electrochemically active surface area. The corrosion of the structural weak points of the carbon support leads to structural collapse. This collapse of the porous structure and weakening of connective points within the cathodic catalyst layers coincide with increased cell and mass transport resistance, resulting in large performance losses. While similar effects have been indicated before, the IL microscopy analysis provides a deeper understanding of the underlying mechanisms and the connection between morphological changes and fuel cell performance losses.
Strandberg et al. (Thu,) studied this question.