Modification of Sulfonated poly(ether sulfone) Proton Exchange Membrane with Reduced Swelling

There is an increasing interest over the past few years in the development of proton exchange membrane fuel cells (PEMFC) due to their potential applications in portable and stationary devices [1-4]. Perfluorinated copolymers such as Nafion® are the most commonly used PEMs owing to their good chemical and physical stability and high proton conductivity. However, the high cost, high methanol crossover rate and difficulty in synthesis and processing limit their extensive commercialization. Therefore, numerous efforts have been dedicated to develop new PEM materials and a great number of polymers have been proposed [5,6]. Among the potential alternatives, sulfonated poly(ether sulfone)s (SPESs) have attracted considerable attention because of their advantages of low cost, easy preparation, controllable composition, good mechanical strength and high chemical and thermal stabilities [7-9]. However, like other sulfonated aromatic main-chain polymers, the SPESs should possess high sulfonation level in order to achieve sufficient proton conductivity. Unfortunately, too high a loading of acidic groups induces excessive swelling which cause early pinhole formation, mechanical failure and fuel crossover during the fuel cell operation. In order to improve the dimensional stability, many approaches such as blending, crosslinking, developing hybrid and/or composite membranes have been reported in the literature and the modified membranes were found to have better dimensional stability than the unmodified ones [10]. Recently, we reported the results on modification of SPES with polyacrylonitrile (PAN) and blending of SPES with polysulfone (PSU) and crosslinking at high temperature [11]. In this article, we discuss our further studies on the properties of modified SPES membranes.