Electrode structure within PEFCs, including the Pt-ionomer interface, is created while making electrodes from catalyst inks based on ionomer dispersed in solvent. The relationship between final electrode structure and processing conditions is poorly understood. We have varied the solvent used in cathode catalyst inks, and then subjected the resulting MEAs to hydrogen-air performance and durability testing. Specifically, cathodes cast from inks based on inonomer dispersions in water-propanol-isopropanol (W/P cathode) initially perform better than cathodes cast from glycerol-based dispersions (Gly cathode), but are far less durable. After 10,000 potential cycles from 0.60 V to 1.0 V in N2, the performance on air of the W/P cathode falls significantly below that of the Gly cathode. NMR and neutron scattering measurements of ionomer dispersions, as well as AFM and TEM data from cast ionomer films, offer insight into how the effect of solvent choice on the ionomer structure may impact durability.