Abstract
A tailor-made annealing procedure was developed for Nafion in order to avoid a critical degradation of the mechanical properties associated with a decrease of the ionic conductivity. The formation of layered morphologies, prevalently oriented in the direction parallel to the membrane surface, is responsible of the decay in fuel cell operation conditions. Nafion membranes are annealed at 140 °C over 7 days in the presence of dimethylsulfoxide (DMSO) as a proton-acceptor solvent. The important increase of mechanical stability is related to the formation of a crystalline phase, which acts as a physical cross-linker. The procedure is followed by hydrothermal annealing in liquid water in order to obtain an optimal water uptake at equilibrium (tailor made). To better understand the behavior of these polymers, we use the INCA method (Ionomer n (c) Analysis) and compare with dynamic mechanical analysis (DMA). The stabilized materials are proposed for use in intermediate temperature fuel cells, where the mechanical stabilization by the annealing procedure plays a fundamental role.