Carbon-Supported Platinum Electrocatalysts Probed in a Gas Diffusion Setup with Alkaline Environment: How Particle Size and Mesoscopic Environment Influence the Degradation Mechanism
Shima Alinejad, Jonathan Quinson, Johanna Schröder, Jacob J. K. Kirkensgaard, Matthias Arenz
Abstract
In recent years, extensive research has been performed concerning the stability of fuel cell catalysts in an acidic environment. By comparison, only few studies address the degradation mechanism(s) of fuel cell catalysts in alkaline media. In this work, we investigate the stability of four different types of Pt/C fuel cell catalysts upon applying accelerated degradation tests in a gas diffusion electrode (GDE) setup equipped with an anion exchange membrane. In contrast to previous investigations exposing the catalysts to a 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 the electrochemically active surface area of the Pt/C catalysts via CO stripping measurements with the change in particle size distribution determined by small-angle X-ray scattering measurements, we demonstrate that (i) the degradation mechanism depends on the investigated Pt/C catalyst and might indeed be different from 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.