CO tolerance of nano-architectured Pt–Mo anode electrocatalysts for PEM fuel cells

PEM fuel cell membrane electrode assemblies with Nafion electrolytes and commercial Pt-based cathodes were tested with Pt0.8Mo0.2 alloy and MoOx@Pt core–shell anode electrocatalysts for CO tolerance and short-term stability to corroborate earlier thin-film RDE results. Polarization curves at 70 °C for the Pt0.8Mo0.2 alloy in H2 with 25–1000 ppm CO showed a significant increase in CO tolerance based on peak power densities in comparison to PtRu electrocatalysts. MoOx@Pt core–shell electrocatalysts, which showed extremely high activity for H2 in 1000 ppm CO during RDE studies, performed relatively poorly in comparison to the Pt0.8Mo0.2 and PtRu alloys for the same total catalyst loading on a per area basis in MEA testing. The discrepancy is attributed to residual stabilizer from the core–shell synthesis impacting catalyst-ionomer interfaces. Nonetheless, the MoOx@Pt electrochemical performance is superior on a per-gram-of-precious-metal basis to the Pt0.8Mo0.2 electrocatalyst for CO concentrations below 100 ppm. Due to cross-membrane Mo migration, the stability of the Mo-containing anode electrocatalysts remains a challenge for developing stable enhanced CO tolerance for low-temperature PEM fuel cells.