IL-TEM investigations on the degradation mechanism of Pt/C electrocatalysts with different carbon supports

Utilizing our recently developed method of identical location transmission electron microscopy (IL-TEM) in combination with electrochemical surface area determination, the degradation behavior of different carbon supported Pt catalysts for polymer electrolyte membrane fuel cells (PEMFCs) is investigated. Two different Pt based catalysts supported on a low surface area (LSA) carbon are compared to a Pt catalyst with standard high surface area (HSA) carbon support. One of the LSA carbon supports is of conventional type, while the other is modified by a transition metal. Relative to the standard, both catalysts with LSA carbon support exhibit improved degradation behavior in terms of loss in active surface area upon accelerated stress tests. The catalyst with transition metal modified carbon support thereby exhibits by far superior improvements. The characterization of the bare carbon supports indicates that the observed differences between both catalysts with LSA carbon support are not related to the resistance of the support to complete oxidation to carbon dioxide. Instead, the IL-TEM results reveal that the improved properties of the catalyst with transition metal modified support are due to a stabilization of the Pt particles attached to the support. Particle detachment thus can be drastically reduced and the degradation is limited to a migration and coalescence or sintering mechanism.