(697e) Hybrid Proton-Conducting Membranes Doping with Various Functionalized Titania for Direct Methanol Fuel Cells
Organic-inorganic hybrid proton-conducting membranes have gained tremendous attention in the field of direct methanol fuel cells (DMFCs). The hybrid membranes combine the intrinsic physical and chemical properties of both inorganic and organic components. A variety of polymers have been doped with various functionalized inorganic particles or inorganic phase to achieve high proton conductivity, low methanol crossover, good mechanical and chemical properties. The tuning of the fuctionalized groups on the inorganic fillers, which could provide additional pathways for proton transfer, is a key issue in fabricating hybrid membranes. Chelation grafting of functional groups onto titania allows facile and fine modifications of the inorganic surface. Titania submicrospheres grafted with phosphonic acid groups (-PO3H2), sulfonic acid groups (-SO3H), carboxylic acid groups (-CO2H), amino groups (-NH2) and amino acid groups (-CO2H, -NH2) were respectively incorporated into chitosan (CS) or sulfonated poly(ether ether ketone) (SPEEK) membrane matrix to fabricate hybrid membranes with improved proton conductivity. The conductivities at room temperature and 100% RH of the chitosan/phosphonic acid-modified titania membrane, the SPEEK/sulfonic acid-modified titania membrane, the SPEEK/carboxylic acid-modified titania membrane and the SPEEK/amino acid-modified titania membrane were 0.011, 0.053, 0.071 and 0.066 S cm-1, respectively, with 15 wt% of fillers. Besides, due to the different proton acceptor/donor capability of functional groups, the hybrid membrane embedded with amino-functionalized titania exhibited higher values at elevated temperature of 60 oC compared with carboxylic-functionalized titania. And the hybrid membrane embedded with amino acid-functionalized titania displayed a superior proton-conducting ability with the proton conductivity of 0.258 S cm-1 at 60 oC. In addition, SPEEK/carboxylic acid-functionalized titania and SPEEK/amino acid-functionalized titania membrane hybrid membranes were also fabricated via in situ sol-gel method and their proton conductivities were 0.063 and 0.047 S cm-1, respectively, nearly three times higher than the control membranes. In conclusion, all the hybrid membranes exhibited enhanced proton conductivity, low methanol crossover, better mechanical and chemical properties, and are promising candidates for DMFCs.