Abstract
PEMs represent an important part of fuel cell systems and a wide variety of copolymers has already been used as membranes in the process of PEMFC (hydrogenated, aromatics, fluorinated, and aliphatic). Perfluorosulfonic acid (PFSA) membranes have been reported in many surveys because they have been employed in mature PEMFC technologies. A more recent challenge deals with membranes that can maintain high performance at high temperature (> 150 °C) and low relative humidity (< 25-30 %), in which phosphonic acid or nitrogenous heterocycles (e.g. imidazole, benzimidazole or pyrrazole) are tethered to the polymeric backbone of different nature. These functions enable the migration of protons through a diffusion mechanism which involves a proton hoping from one azole site to one another via an “proton-acceptor / proton-donor » interaction. Original partially fluorinated poly(IEVE-alt-CTFE)94%-co-poly(CTFE-alt-GCVE)6% and poly(IEVE-alt-CTFE)82%-co-poly(CTFE-alt-GCVE)18%) terpolymers crosslinkable by addition reaction between a cyclocarbonate and an amine groups. Original crosslinked membranes were processed from a s-PEEK-Na (under –SO3Na form)/ poly(CTFE-alt-IEVE)94%-g-1H-1,2,4-triazole-3-thiol90%-co-poly(CTFE-alt-GCVE)6% terpolymer blend in the presence of primary aliphatic diamines (1,3-propanediamine (DiA) or tetraethylenepentamine (TEPA)). Indeed, crosslinking both improves the membranes’ mechanical properties and reduces their swelling rates (at 90 °C) by total immersion in water. However, their protonic conductivities were unexpectedly low (for membrane 40%-A / 60-B-ret-DiA (n = 1.5), σ = 4.3 mS.cm-1 at 140 °C, HR < 25 %). Crosslinking reduces the mobility of polymeric chains of the resulting membranes, and this limits the reorientation of nitrogenous heterocycles that allow proton transport at high temperatures and low RH thereby inducing a loss of conductivity values. To reduce the swelling and to improve the membrane durability, it is necessary to crosslink future PEMs and/or to reinforce them at the same time. It is impractical to expect that a single type of membrane can meet the requirements of all of the possible automotive, stationary, and portable fuel cell applications. Mechanical properties, oxidative stabilities, and single cell performances of those materials will be investigated in further studies.