(486f) Functionalized Inorganic Particle-Doped Composite Proton Exchange Membranes for Enhancement in Fuel-Rejecting and Proton-Conducting Property

Organic-inorganic hybrid proton exchange membranes have gained tremendous attention for use in direct methanol fuel cells due to their combined advantages originated from both the inorganic and organic components. A large variety of polymers have been blended with various inorganic particles by either physical blending or sol-gel process to generate inorganic phase in polymer matrix. The addition of carefully selected inorganic components leads to inhibited methanol crossover and improved stability. The inorganic dopants are usually functionalized to improve the organic-inorganic interfacial compatibility and to introduce additional pathways for proton transfer at the interface, thus increasing proton conductivity of the resultant hybrid membranes. Inorganic dopants such as titania and silica were applied widely for the ease of availability and functionalization. In our previous work various functional groups including phosphonic acid groups, sulfonic acid groups, carboxylic acid groups, amine groups and amino acid groups by means of chelation absorption of these functional groups onto titania. In this study, two kinds of phosphorylated silica submicrospheres are synthesized and incorporated into sulfonated poly(ether ether ketone) (SPEEK) to fabricate hybrid membranes. Phosphorylation is carried out by the reaction of phosphorus oxychloride and the epoxy groups on the silica surface introduced by glycidyl-silane (SiP-I) or poly(glycidyl methacrylate) (SiP-II). The length of the chains and the amount of phosphoric acid groups grafted on the silica surface are tuned by the above two different phosphorylation methods. The dispersion of SiP-II, anti-swelling and methanol resistant property of the SPEEK/SiP-II hybrid membranes are enhanced. And the proton conductivity is increased by doping with both kinds of phosphorylated silica particles, while, interestingly, the SPEEK/SiP-I hybrid membranes with less amounts of phosphoric acid groups show unexpectedly much higher proton conductivity than the SPEEK/SiP-II hybrid one at the same doping content. A proton conductivity of 0.335 S cm^-1 at 60 ^oC and 100%RH is obtained. The result is tentatively discussed in terms of effective proton-conducting groups/sites instead of the absolute amount of acidic groups.