Influence of the shell thickness on the degradation of Ru@Pt core-shell catalysts in PEM fuel cells

Polymer electrolyte membrane fuel cells, which are fueled by reformate, are reliant on highly active, CO tolerant Ru@Pt core-shell anode catalysts. As little is known of the degradation behaviour of these catalysts, the herein presented study investigated membrane electrode assemblies (MEAs), which were stressed under fuel cell relevant conditions, via electrochemical and physical methods. Two catalysts with different shell thicknesses (Ru@1 Pt and Ru@2 Pt) were incorporated in the MEAs to investigate how the shell thickness influences the degradation behaviour. While the MEA incorporating Ru@1 Pt as anode catalyst was higher in performance than Ru@2 Pt MEA under reformate conditions in the beginning, it strongly degraded during stress testing to end up with a lower performance than Ru@2 Pt afterwards. Due to cyclic voltammetry experiments, it was evidenced that for both catalysts Ru was leached from the anode and crossed over to the cathode – but to a significantly lower extent for Ru@2 Pt. This was further quantified by advanced corrected (scanning) transmission electron microscopy coupled with energy dispersive spectroscopy detector. Additionally, due to imaging local degradation effects were observed for the anode, while Ru poisoning the Pt catalyst was found to be a global problem in the cathode.