Strong R&D progress and increased demand for hydrogen powered fuel-cell cars, is shifting Polymer Electrolyte Fuel Cells (PEFCs) to lower Platinum electrocatalyst loading and to Platinum-cobalt (Pt-Co) alloys that have demonstrated double the kinetic activity improvement [1]. Implementation of these catalysts can lower catalyst cost to $7/kW (from $18/kW of standard Pt/C catalyst), surpassing the automotive requirement target of $10/kW and expediting commercialization [2]. Key challenge in integrating Pt-Co alloy catalyst as well as other Pt-Metal alloyed catalysts into the electrode assembly of PEFC has been durability and stability in the highly acidic environment. Co-alloy dissolution, leaching, surface oxide over layer formation upon heating, hollowing and particle facet loss have been demonstrated for Pt-Metal alloys via short and long lifetime tests and imaging techniques [3]. Amplifying this detrimental impact is the contamination of the membrane and the ionomer thin-film in the catalyst layer distressing conductivity, water uptake, and even gas transport [4]. In this talk, the direct impact of co-alloy and cation contamination in thin ionomer films of thickness < 200 nm is investigated in an effort to illuminate the direct effect of cations on structure and performance. Different levels of neutralization and leaching is mimicked by varying cation concentration and different counter ion types (Co²⁺, Ni²⁺, Na⁺, Cs⁺), which can elucidate impact of strength of ionic crosslinking and interactions on the polymer film’s nano-structure and water uptake behavior, characterized by grazing-incidence X-ray scattering and ellipsometry, respectively. Significant impact of confinement on structure and property will also be explored as a function of ionomer thickness to understand the performance of ionomer thin-films employed in the electrode assembly.

Acknowledgement

This work made use of facilities at the Joint Center for Artificial Photosynthesis at Lawrence Berkeley National Laboratory. This work was funded in part by the National Science Foundation Graduate Fellowship and the Office of Science, Office of Basic Energy Sciences, of the U.S. Department of Energy (under Contract No. DE-AC02-05CH11231).

References

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[3] E. Antolini et al. J. Power Sources, vol. 160, pp. 957–968, 2006.

[4] J. H. Dumont et al. ECS Trans., vol. 80, no. 8, pp. 861–867, 2017.