Fuel cells
Proton conduction: So far, most research efforts to develop proton conductive membranes for fuel cells have focused on systems relying on hydrogen bonded water as the conduction media. However, their maximum use temperature is intrinsically limited to approximately the boiling point of water. The operation of PEMFC’s at temperatures above 100ºC would increase efficiency and reduce cost by decreasing the required platinum loading in the membrane electrode assemblies and simplifying the overall heat and water management of the system. An attractive alternative approach proposes the use of amphoteric nitrogen containing heterocycles as the proton conducting species.
The proton conductivity of membranes using heterocyclic motifs, both as dopants or as pendant groups, does not depend significantly on relative humidity (R.H.) and could enable the use of PEMFC’s without external humidification at temperatures well above 100ºC.
Our goal is to develop proton conducting materials using self-assembled block copolymer architectures and nano-confined geometries to generate multifunctional membranes, able to transport protons within hydrated and anhydrous polymer matrices. These new materials will be instrumental in understanding the basic principles governing long-range proton transport and will help design membranes exhibiting high conductivity over a wide range of temperature and relative humidity.
A few examples of the materials synthesized in the lab, along with their proton conductivities as a function of temperature are shown below.
Proton conductivity of Tz1PEI and Siloxane copolymers as a function of reduced temperature T/Tg
Granados-Focil, S., Conway, J.R.*, Meng, Y.#, Smith, L., Triazole functionalized sol-gel
membranes, effect of crosslink density and heterocycle content on water free proton
conduction and membrane mechanical properties. Journal of Macromolecular Science, part
A, polymer chemistry, 2010, 47, 1197. Link
Litt, M.; Granados-Focil, S.; Kang, J., Rigid Rod Polyelectrolytes with Frozen-In Free Volume: High Conductivity at Low RH. In Fuel Cell Chemistry and Operation, American Chemical Society: 2010; Vol. 1040, pp 49-63. Link
Akbey, U., Granados-Focil, S., Coughlin E.B., Graf, R., Spiess, H.W., 1H Solid-State NMR
Investigation of Structure and Dynamics of Anhydrous Proton Conducting Triazole-
Functionalized Siloxane Polymers. J.Phys. Chem. B., 2009, 113, 9151-9160. Link
Litt, Morton H., Granados-Focil, Sergio, Liquid Crystal (polyphenylene sulfonic acids), U.S. Pat # 7375,176, 2008, 45 pp.
Granados-Focil, S., Woudenberg, R.C., Yavuzcetin, O., Tuominen, M.T., Coughlin, E.B., Water-
free proton conducting polysiloxanes: A study on the effect of heterocycle structure.
Macromolecules, 2007, 40, 8708-8713. Link