Effect of Ketone and Sulfone Functional Group Contents on Water Absorption and Oxidative Stability of Poly(Ether Sulfone Ketone) Proton Exchange Membranes

Proton exchange membrane fuel cells (PEMFCs) as efficient and low-emission devices are the subject of many research activities for generating electrical energy during the past three decades. Sulfonated aromatic hydrocarbons and among them poly (arylene ethers) emerged as promising candidates for substitution of perfluorosulfonic acid membranes. The polymer backbone of poly(arylene ethers) may contain different functional groups including ether, sulfone, ketone, phosphazine, etc.[۱, ۲]. It has been proven that there is a close relationship between the structure and properties of these aromatic hydrocarbon polymers and their performance as a proton exchange membrane (PEM).[۳, ۴] In this study sulfonated poly(ether sulfone ketone) containing both sulfone and ketone functional groups were synthesized. By changing the dihalide monomer in condensation polymerization, sulfonated polymers with different contents of sulfone or ketone groups in different ion-exchange capacities and also different IECs were prepared (Figure ۱). The effect of sulfone/ketone group contents on the membrane properties like water absorption and oxidative stability of membranes was studied. The results showed that sulfonated polymers with higher contents of sulfone functional groups represented much higher water absorption which could be the result of the more flexible nature of sulfone connections, in comparison to rigid ketone groups that caused higher free volume. Moreover, oxidative stability of membranes containing lower contents of sulfone groups was better than membranes with more sulfone connections which could be because of their higher free volume and higher water uptake which could promote the diffusion of radicals and faster degradation of membranes (Table ۱).

Keywords:

proton exchange mmebranes , sulfone/ketone content , oxidative stability , water absorption