Low water swelling and high methanol resistant proton exchange membrane fabricated by cross-linking of multilayered polyelectrolyte complexes

Multilayered polyelectrolyte complexes (PECs) modified proton exchange membranes are successfully prepared from alternating deposition of oppositely charged polyelectrolyte chitosan (CS) and sulfonated poly (aryl ether ketone) bearing carboxyl groups (SPAEK-C) on the surface of Nafion®117 via the layer-by-layer (LBL) method. The cross-linked PEC-coated Nafion® membranes (c-PEC-coated Nafion® membranes) are prepared from heat-induced cross-linking between CS and SPAEK-C via formation of amide bonds. Fourier transform infrared spectroscopy (FT-IR) verifies that cross-linking between ammonium groups of CS and carboxyl groups of SPAEK-C occurs by the formation of amide bonds. The morphology of the membranes is studied in detail by SEM. The c-PEC-coated Nafion® membranes exhibit low water uptake (23.5%, 80 °C), water swelling (14.0%, 80 °C) and methanol permeability (2.7 × 10−7 cm2 s−1). Proton conductivity of the c-PEC-coated Nafion® membranes increase at elevated temperature, reaching the value of 0.131 S cm−1 at 80 °C. These results show that cross-linking of layered CS/SPAEK-C films can effectively reduce water uptake, water swelling and methanol permeability while improve the dimensional stability and maintain high proton conductivity.