Incorporation of heteropoly acid, tungstophosphoric acid within MCM-41 via impregnation and direct synthesis methods for the fabrication of composite membrane of DMFC

Abstract

A heteropoly acid, tungstophosphoric acid (here-in-after TPA) with super acid strength was successfully encaged by two different methods, impregnation and direct synthesis. XRD and FT-IR analyses indicate that significant amount of TPA enraged by impregnation method should have been washed out upon washing treatment for TPA-MCM-41 powder. Due to significant loss of TPA upon washing, TPA was directly synthesized within MCM-41 pore channels using sodium tungstate dehydrate, disodium hydrogenphosphate dodecahydrate and hydrochloric acid. Compared to impregnation method, TPA was more effectively encaged and XRD analyses clearly show that reasonable amount of TPA in TPA-MCM-41 remains even after washing. A uniform distribution of directly synthesized TPA within MCM-41 pore channel was also confirmed by TEM images. In second part of this study, various TPA-encaged MCM-41 powders were used to fabricate composite membranes. For comparison, composite membranes fabricated with calcined MCM-41 and raw TPA, Nafion (R) 115 and casting Nafion (R) membrane were also prepared. The results show that TPA-MCM-41 by direct synthesis method and TPA have enhanced proton conductivity of composite membrane. And MEA fabricated with the composite membrane showing the highest proton selectivity shows better cell performance than others. (C) 2008 Elsevier B.V. All rights reserved.