In order to understand the origin of performance variations in polymer electrolyte membrane fuel cells (PEMFCs), a series of membrane-electrode assemblies (MEAs) with identical electrode layer compositions were prepared using different electrode Curing conditions, their performances were evaluated, and their morphologies determined by scanning electron rnicroscopy (SEM). The polarization curves varied markedly primarily due to differences in morphologies of electrodes, which were dictated by the curing processes. The highest performing MEAs (1.46W cm(-2) peak power density at 3.2 A cm(-2) and 80 degrees C) were prepared using a slow curing process at a lower temperature, whereas those MEAs prepared using a faster curing process performed poorly (0.1948Wcm(-2) peak power density at 440mAcm(-2) and 80 degrees C). The slowly cured MEAs showed uniform electrode catalyst and ionomer distributions, as revealed in SEM images and elemental maps. The relatively faster cured materials exhibited uneven distribution of ionomer with significant catalyst clustering. Collectively, these results indicate that to achieve optimal performance, factors that affect the dynamics of the curing process, such as rate of solvent evaporation, must be carefully controlled to avoid solvent trapping, minimize catalyst coagulation, and promote even distribution of ionomer. (c) 2008 Published by Elsevier B.V.