| Direct methanol fuel cell (DMFC) has attracted considerable attention as an alternative to the present power sources due to its high efficiency, high power density, low emissions and easy fuel storage and transportation et al. Polyperfluorosulfonic acid ionomer Nafion? has been intensively used in DMFC. However, at present, two"high"drawbacks, high methanol crossover and high cost, limit its wide applications in DMFC. A novel high performance proton exchange membrane with reduced methanol crossover is the target for DMFC membrane.Recognizing the coupling nature of proton, water and methanol transport, we analogized the desired proton exchange membrane (PEM) to a proton preferential proton-methanol separation membrane. Therefore, theories and experiences from the field of membrane separation, especially those from pervaporation were borrowed to this work to develop the methanol-rejective proton exchange membrane.A novel acid-base polyelectrolyte blend membrane for DMFC was prepared by blending a cationic polyelectrolyte, chitosan (CS), with an anionic polyelectrolyte, acrylic acid-2-acrylamido-2-methylpropane sulfonic acid copolymer (P(AA-AMPS)) with lots of–COOH and–SO3H groups. The ionic cross-linked interpenetrating polymer network (IPN) was formed between the two polyelectrolyte polymers. The dual function of P(AA-AMPS) as both an ionic crosslinker and a proton conductor led to not only a notable reduction in methanol permeability but also an increase in proton conductivity. The CS/P(AA-AMPS) membrane with a P(AA-AMPS) content of 41 wt.% exhibited a methanol permeability (P) of 2.41×10-7cm2/s, which was fifteen times lower than that of the Nafion?117 membrane, whereas its proton conductivity (σ) was comparatively high (3.59×10-2S/cm). In terms of the overall selectivity index (β=σ/P), the membrane showed a remarkably highest selectivity of 15.0×104 S s/cm3, which was eight times higher than that of the Nafion?117 membrane.A novel type of acid-based blending DMFC membrane was developed via incorporation of three kinds of organophosphorus acids (OPAs), amino trimethylene phosphonic acid (ATMP), ethylene diamine tetra(methylene phosphonic acid) (EDTMP) and hexamethylene diamine tetra(methy lenephosphonic acid) (HDTMP), into alcohol barrier materials (polyvinyl alcohol/chitosan, PVA/CS) to simultaneously acquire high proton conductivity and low methanol crossover. The as-prepared OPA-doped PVA/CS membranes exhibited remarkably enhanced proton conducting ability, 2-4 times higher than the pristine PVA/CS membrane, comparable with that of Nafion?117 membrane (5.04×10-2 S/cm). The highest proton conductivities of 3.58×10-2, 3.51×10-2 and 2.61×10-2 S/cm for ATMP-, EDTMP- and HDTMP-doped membranes, respectively, were all achieved at highest OPA doping content at room temperature. Regarding the methanol permeation behavior, the EDTMP-doped PVA/CS membrane with an acid content of 13.9 wt.% showed the lowest methanol permeability of 2.32×10-7 cm2/s which was 16 times lower than that of Nafion?117 membrane. In terms of the overall selectivity index (β=σ/P), ATMP-, EDTMP- and HDTMP-doped PVA/CS membranes also presented enhanced selectivity. In addition, the thermal stability and oxidative durability were both significantly improved by the incorporation of OPAs in comparison with pristine PVA/CS membranes.
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