End group cross-linking of sulfonated polymer electrolyte membranes via click reaction

Abstract

The development of novel polymer electrolyte membranes (PEMs) with high proton conductivity, good mechanical flexibility and less humidity dependence remains an important challenge to the realization of practical PEM fuel cells and other alternative energy applications. For this reason, various researches of hydrocarbon polymer membranes have been investigated as alternative PEM materials due to their excellent mechanical, thermal stability and high proton conductivity. However, their major problem, such as excessive water swelling and weak durability, are unsuitable to satisfy practical operations. Cross-linking is a simple and efficient method to reducing water uptake and also enhancing mechanical properties and dimensional stability. In this study, end group cross-linking via'click' reaction were introduced to highly sulfonated PEMs. Click reaction has the advantages such as short reaction time, a high yield and superior region selectivity. Thus, the method has been used to synthesize a wide variety of linear, branched and cross-linked polymer. Here we have focused on developing new materials that are capable of conducting protons under low RH conditions and show excellent long term stability. This method is one of the effective methods for highly sulfonated PEMs because end group cross-linking improves mechanical and chemical stabilities without loss of acid sites or chemical structure change of the polymer main chain. The click reaction functionalized end group cross-linked membranes are expected to be promising materials for various alternative energy applications.