posted on 2020-01-03, 20:11authored byAman Uddin, Lisa Dunsmore, Hanguang Zhang, Leiming Hu, Gang Wu, Shawn Litster
Low cost and high-performing
platinum group metal-free (PGM-free)
cathodes have the potential to transform the economics of polymer
electrolyte fuel cell (PEFC) commercialization. Significant advancements
have been made recently in terms of PGM-free catalyst activity and
stability. However, before PGM-free catalysts become viable in PEFCs,
several technical challenges must be addressed including cathode’s
fabrication, ionomer integration, and transport losses. Here, we present
an integrated optimization of cathode performance that was achieved
by simultaneously optimizing the catalyst morphology and electrode
structure for high power density. The chemically doped metal–organic
framework derived Fe–N–C catalyst we used allows precise
tuning of the particle size over a wide range, enabling this unique
study. Our results demonstrate the careful interplay between the catalyst
primary particle size and the polymer electrolyte ionomer integration.
The primary particles must be sufficiently large to permit uniform
ionomer thin films throughout the surrounding pores, but not so large
as to impact intraparticle transport to the active sites. The content
of ionomer must be carefully balanced between sufficient loading for
the complete catalyst coverage and adequate proton conductivity, while
not being excessive and inducing large oxygen transport losses and
liquid water flooding. With the optimal 100 nm size catalyst and ionomer
loading, we achieved a high power density of 410 mW/cm2 at a rated voltage and a peak power density of 610 mW/cm2 in an automotive-relevant operating condition.