Characterization of Sulfonylated Poly(styrene) Based Proton Exchange Membranes for Fuel Cells

Abstract

The change from an energy industry based on fossil fuels to an energy industry based on renewable energy sources is a global challenge. For this reason, dynamic storage systems are needed to be developed for fluctuating wind and solar energy. Water electrolysis and fuel cells are important energy converters that offer the possibility of using hydrogen as an energy carrier. Generally, good thermal-oxidative stability and high proton conductivity are expected for membranes in fuel cells [1].As an alternative to perfluorosulfonic acid based membranes, hydro-carbon based proton exchange membranes may reduce stack costs. This assumption motivates us to synthesize and investigate polymer membranes whose proton conductor is cross-linked sulfonated sulfonylated poly(styrene) (ssPS). The advantage of ssPS in contrast to sulfonated polystyrene is the stability of the sulfonic acid group at temperatures around 100°C [2]. Disadvantages of ssPS are the water solubility at high degrees of sulfonation (ion exchange capacity of about 3,5 mmol/g) and poor film formation properties.According to this, the proton conductor must be cross-linked during synthesis and embedded in a nonpolar polymer matrix during the membrane production.Our investigations show that ssPS (non-cross-linked) has a similar thermal-oxidative stability as Nafion® (examined by thermal analysis/oxidative induced temperature (OIT)) [3]. The cross-linking of ssPS with divinylbenzene mixtures leads to a less good thermal-oxidative stability. Furthermore, our results show that the water uptake can be adjusted by varying the amount of cross-linker. In addition, the proton exchange membranes show conductivities in the range of Nafion® 117 at room temperature.The presentation will show the development of a new proton exchange membrane and its characterization. To discuss the membranes quality, the focus is on ion exchange capacity (stability at 90°C), thermal-oxidative stability (differential scanning calorimetry), water uptake and electrical resistance as a function of temperature up to 90°C.This work is supported by the Federal Ministry of Education and Research (BMBF).[1] J.A.Kerres, A.Katzfuß, A.Chromik, V.Atanasov, J. Appl. Polym. Sci. 2014 , 131 , 39889.[2] H.Widdecke, M.Dettmer, W.Reith, Patent DE4425216C2, 2003.[3] G.W.Ehrenstein, G.Riedel, P.Trawiel, Thermal analysis of plastics, Hanser Verlag, 2004.