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Sulphonated Poly(ether ether ketone) Proton Exchange Membranes for Fuel Cell Applications

Polymer electrolyte membrane fuel cells (PEMFCs) are promising new power sources for automotive and portable devices. Nafion® is the currently used membrane in PEMFCs. Although these membranes show high proton conductivity and excellent chemical stability, their high cost makes them unpractical for commercial purposes. Sulphonated poly(ether ether ketone) (SPEEK) ionomers were synthesized using chlorosulphonic acid as the sulphonating agent in dichloromethane medium. Homogeneous proton-conducting membranes were developed from the obtained SPEEK by solvent casting method. Membranes were assessed for their suitability in fuel cell applications. The extent of sulphonation was controlled by varying the reaction time, concentration of polymer, and concentration of sulphonating agent. The SPEEK membranes exhibit degree of sulphonation from 10 to 66%, ion exchange capacity from 0.29 to 1.92 meq/g and maximum water and methanol uptake up to 54 and 22%, respectively, at 25°C. The membranes were characterized by FTIR to confirm sulphonation, and DSC and TGA to investigate the thermal stability. The proton conductivities of such membranes were found to be excellent in the order of 10−2 S/cm in the fully hydrated condition at room temperature as measured by impedance spectroscopy. The durability of the membranes was also tested. The study revealed the possibility of a cheaper alternative membrane for use in PEMFC.