Cerium Migration during PEM Fuel Cell Assembly and Operation

In PEM fuel cells, cerium migration is influenced by proton flux,as well as gradients in electric potential, ion concentration, andwater content. These factors were investigated in ex situexperiments and in operating fuel cells. Potential-inducedmigration was measured ex situ in hydrated window cells. CeriumcontainingMEAs were also fabricated and tested under ASTs.MEA disassembly and subsequent XRF analysis were used toobserve rapid cerium migration within the MEA. During MEA hotpressing, humidification, and low RH operation at OCV, ionicdiffusion causes uniform migration from the membrane into thecatalyst layers. During high RH operation at OCV, in-plane ceriumgradients arise due to variations in water content. These gradientsmay diminish the scavenging efficacy of cerium by reducing itsproximity to generated radicals.