Novel Direct Methanol Fuel Cell MEA Technology for Electronics Applications

Specific plans to meet the obectives of the programme include the synthesis, characterisation, and fabrication into proton-transport membranes of three new types of ionomers, namely: (i) micro-phase separated aromatic ether-ketone ionomers, including especially semi-crystalline ionomers in which the ionic (sulfonic acid) groups will segregate into the amorphous phase, leaving the crystalline regions to provide mechanical strength, resistance to swelling and good methanol-barrier characteristics. The molecular design of such materials will build on our recent discovery that swelling-resistant ionomers with high proton-exchange capacities can be obtained by concentrating the ionic groups into very short segments of an aromatic polymer chain. (ii) semi-crystalline ionomer-composites comprising blends of high-proton-exchange capacity dopants such as phthalocyanine tetrasulfonic acids with high molar mass poly(ether-ketone) sulfonic acids. It is anticipated that the phthalocyanine component will be excluded from the ordered, crystalline phase, and concentrated in the amorphous, ionic phase, increasing proton conductivity through this phase without loss of the mechanical integrity arising from the non-hydrated crystalline phase. Preliminary evidence from non-crystalline blends suggests that the phthalocyanine component will be irreversibly bound within the ionic regions of the polymer matrix, and will therefore be resistant to extraction by aqueous methanol. (iii) hyperbranched ionomers obtained by copolymerisation of a sulfonatable AB2-type monomer with a non-sulfonatable AB-type monomer, followed by sulfonation of the resulting copolymer to afford an entirely novel type of ionomer in which the ionic groups are concentrated in a highly branched phase. Since hyperbranching can be regarded as an incipient form of cross-linking, hyperbranched materials of this type should show greater resistance to swelling and to methanol crossover when compared to their linear analogues of equivalent ion-exchange capacity. Solvent-systems will be designed for all ionomers synthesised in this project; where necessary making use of acidic and/or strongly hydrogen bonding solvents to take the more solvent-resistant, semi-crystalline ionomers into solution for membrane casting. The objective here is to supply membrane samples (with a minimum area of 300 sq. cm) to the lead partner for ongoing evaluation in DMFC operation, with continuous feedback of results into the membrane design and synthesis programme.