(510d) Addressing Transport Losses in Low-Pt and Pt-Free PEM Fuel Cell Cathodes (Invited)

Reducing platinum loading is crucial to realizing broad commercialization of PEM fuel cell powered electric vehicles. Significant efforts are devoted to developing new catalyst materials and architectures that increase the specific or mass activity for the oxygen reduction reaction (ORR). One approach is to reduce the Pt loading by utilizing PtCo or PtNi dealloyed catalysts that yield increased activity. However, the efficacy and durability of these catalysts can be severely hindered by local microstructural transport losses resulting from thin films of the polymer electrolyte (i.e., ionomer) binder and high surface area carbon supports. These local losses become increasingly punitive as the Pt loading is reduced and the local reactant flux at catalyst is increased, yielding greater local reactant depletion. These losses can be further amplified by catalyst degradation, such as the leaching of the transition metal that further inhibits oxygen transport and proton conduction. Alternatively, the use of Pt can be eliminated by using platinum group metal-free (PGM-free) catalysts that could reduce the cost of electrodes by one to two orders of magnitude. Despite recent large increases in ORR activity, the volumetric activity of PGM-free cathodes is still much lower than the Pt counter-part, thus requiring significantly thicker electrodes (e.g., more than ten times thicker). Thus, these electrodes suffer from large oxygen and proton transport losses that are exacerbated by severe liquid water flooding of these electrodes. This presentation will highlight on-going work in our group aimed at reducing the impact of transport losses on the performance of low-Pt and PGM-free cathodes. This work includes in-situ diagnostics, image-based micro-structural modeling, and electrode structure development.