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In this work, we investigate
the stability of four different types of Pt/C fuel cell catalysts upon applying
accelerated degradation tests (ADTs) in a gas diffusion electrode (GDE) setup
equipped with an anion exchange membrane (AEM). In contrast to previous
investigations exposing the catalysts to liquid electrolyte, the GDE setup
provides a realistic three-phase boundary of the reactant gas, catalyst and
ionomer which enables reactant transport rates close to real fuel cells.
Therefore, the GDE setup mimics the degradation of the catalyst under more
realistic reaction conditions as compared to conventional electrochemical
cells. Combining the determination of the loss in electrochemically active
surface area (ECSA) of the Pt/C catalysts via CO stripping measurements with
the change in particle size distribution determined by small-angle X-ray
scattering (SAXS) measurements, we demonstrate that i) the degradation
mechanism depends on the investigated Pt/C catalyst and might indeed be
different to the one observed in conventional electrochemical cells, ii) degradation
is increased in an oxygen gas atmosphere (as compared to an inert atmosphere),
and iii) the observed degradation mechanism depends on the mesoscopic
environment of the active phase. The measurements indicate an increased
particle growth if small and large particles are immobilized next to each other
on the same carbon support flakes as compared to a simple mix of two catalysts
with small and large particles, respectively.