NAMS 2002 Workshop - ICOM 2008

Fuel Cells I – 1
Monday July 14, 2:15 PM-3:00 PM, Honolulu/Kahuku
Polyoxadiazole Nanocomposite Fuel Cell membranes operating above
100°C
D. Gomes, GKSS Research Centre Geesthacht GmbH, Germany
S. Nunes (Speaker), GKSS Research Centre Geesthacht GmbH, Germany, nunes@gkss.de
Among the high temperature polymer electrolyte membranes that have been
developed so far, phosphoric acid doped polybenzimidazole [1] , which contains
amphoteric nitrogen groups, is certainly the most investigated system with high
proton conductivity. Here, for the first time the use of a fluorinated polyoxadiazole
doped with phosphoric acid as a proton-conducting membrane is reported for fuel
cell operation at temperatures above 100 °C and low humidities. An advantage of
polyoxadiazoles in comparison to the polybenzimidazoles is the lower reaction
temperature (and time) required for synthesis [2] . The fluorinated polymer is very
stable even in mixtures of sulfuric acid and oleum (20-65 % SO3) [3] .
Protonated polyoxadiazole membranes with a doping level much lower than that
usually applied for polybenzimidazole (0.34 mol of phosphoric acid per
polyoxadiazole unit, 11.6 wt.% H3PO4) had proton conductivity at 120°C and
RH=100% in the order of magnitude of 10 -2 S cm -1 . When experiments are
conducted at low external humidity (relative humidity of 1%), still a high value of
proton conductivity (6 x 10 -3 S cm -1 ) was obtained at 150°C. Higher phosphoric
acid doping levels were possible with the incorporation of sulfonated silica
containing oligomeric fluorinated oxadiazole segments [4] . The functionalized
silica has thermal stability up to 160 °C. With the addition of functionalized silica
not only doping level but also water uptake increased. For the nanocomposite
membranes prepared with the functionalized silica, higher proton conductivity in
all range of temperatures up to 120°C and RH=100% (in the order of magnitude
of 10 -3 S cm -1 ) was observed when compared to the plain membrane (in the
order of magnitude of 10 -5 S cm -1 ).
[1] Q. Li, R. He, J.O. Jensen, d N.J. Bjerrum, Chem. Mater., 15 (2003) 4896-4915.
[2] D. Gomes, C. Borges, J.C. Pinto, Polymer, 45 (2004) 4997-5004.
[3]D. Gomes, S.P. Nunes, Journal of Membrane Science, in press
(http://dx.doi.org/10.1016/j.memsci.2007.11.041).