New insights of the imprint at the catalyst-layer/ microporous-layer interface in PEMFC after heavy duty operation of commercial vehicles

Structural degradation and property decay of membrane electrode assemblies (MEAs) are primary causes for the stack performance and lifetime degradation. This study particularly investigates the structural damage and properties evolution of the catalyst-layer/microporous-layer (CL/MPL) interface in the MEA by conducting realvehicle heavy-duty operational durability test and interfacial structure characterization. This research presents the first report and revelation of the causes and effects of CL/MPL interface imprints, and provides targeted advice for relieving MEA interfacial degradation. Results indicate that excessive assembly stress and stress variation during operation of stack causing the detachment of MPL materials at the region below the bipolar plate ridges is the essential cause of the imprints. The average surface contact angles of the aged CLs generally increase and the imprinted region exhibit stronger hydrophobicity than non-imprinted region due to the attachment of MPL materials. While the opposite is observed in MPL. Carbon corrosion induce structural degradation of the CL/MPL interface, leading to significant loss of carbon support and hydrophobic agent. The surface of aged CL become rougher and the pore size become more larger compared to the fresh CL. The formation of the interface imprint makes the contact between CL and MPL at the imprint region tighter, which reduces the interface resistance and inhibits the increase in ohmic polarization.