Novel high-performance nanocomposite proton exchange membranes based on poly (ether sulfone)

In the present research, proton exchange membranes based on partially sulfonated poly (ether sulfone) (SPES) with various degrees of sulfonation were synthesized. It was found that the increasing of sulfonation degree up to 40% results in the enhancement of water uptake, ion exchange capacity and proton conductivity properties of the prepared membranes to 28.1%, 1.59 meq g(-1), and 0.1455 cm(-1), respectively. Afterwards, nanocomposite membranes based on S-PES (at the predetermined optimum sulfonation degree) containing various loading weights of organically treated montmorillonite (OMMT) were prepared via the solution intercalation technique. X-ray diffraction patterns revealed the exfoliated structure of OMMT in the macromolecular matrices. The S-PES nanocomposite membrane with 3.0 wt% of OMMT content showed the maximum selectivity parameter of about 520,000 S s cm(-3) which is related to the high conductivity of 0.051 S cm-1 and low methanol permeability of 9.8 x 10(-8) cm(2) s(-1). Furthermore, single cell DMFC fuel cell performance test with 4 molar methanol concentration showed a high power density (131 mW cm(-2)) of the nanocomposite membrane at the optimum composition (40% of sulfonation and 3.0 wt% of OMMT loading) compared to the Nafion(R) 117 membrane (114 mW cm(-2)). Manufactured nanocomposite membranes thanks to their high selectivity, ease of preparation and low cost could be suggested as the ideal candidate for the direct methanol fuel cell applications. (C) 2009 Elsevier Ltd. All rights reserved.