NAMS 2002 Workshop - ICOM 2008

Fuel Cells II – 4
Thursday July 17, 10:30 AM-11:00 AM, Wai’anae
Ion-Exchange Membranes from Side-Chain Sulfonated Poly(arylene ether)s
J. Meier-Haack (Speaker), Leibniz Institute of Polymer Research Dresden, Dresden, Germany -
mhaack@ipfdd.de
K. Schlenstedt, Leibniz Institute of Polymer Research Dresden, Dresden, Germany
W. Butwilowski, Leibniz Institute of Polymer Research Dresden, Dresden, Germany
C. Vogel, Leibniz Institute of Polymer Research Dresden, Dresden, Germany
Polymer electrolyte membranes and in particular cation exchange membranes
are used in a broad field of applications such as low fouling membranes in water
and wastewater treatment, solid polymer electrolytes in electrochemical
processes (e.g. low temperature fuel cells) or as ion-selective membranes in
sensors.
Despite of some drawbacks, today poly(perfluoroalkylsulfonic acid)s such as
Nafion® and similar materials are still the standard membrane materials for
polymer electrolyte fuel cells (PEMFC). The disadvantages of these materials
and the demand for new energy conversion/production systems have initiated
world-wide research activities on the development of alternative membrane
materials for PEMFC. Among the various materials suggested, sulfonated
poly(arylene ether)s are seen as the most promising ones due to their
outstanding chemical and thermal stabilities, high glass transition temperature
(Tg) as well as their good solubility in dipolar aprotic solvents such as N-methyl-2pyrrolidone
(NMP), dimethylsulfoxide (DMSO) or N,N- dimethylacetamide
(DMAc) and film forming properties. However these materials have two main
disadvantages over Nafion-like materials, namely: (1) the hydrolytic instability of
aromatic sulfonic acids [1] and (2) the lower acidity of the sulfonic acid groups,
leading to lower conductivities at comparable ion-exchange capacities.
Vogel et al. reported on a surprisingly high hydrolytic stability of polystyrene
sulfonic acid [1]. First indications of hydrolysis were found only after treatment in
water at 200°C for 24h. On the other hand poly(styrene sulfonic acid) is not
suitable for applications in fuel cells due to its chemical instability arising from the
tertiary carbon in the polymer backbone. These results led us to the idea to
prepare chemically stable poly(arylene ethers) with a pending phenyl ring, which
can be sulfonated selectively, in order to mimic poly(styrene sulfonic acid).
Having the sulfonic acid group in the side chain has further advantages as has
been described in the literature by Lafitte et al. [2 - 4] or Guiver et al. [5].
Recently, we reported on poly(arylene ether)s prepared from bis-(4-
fluorophenyl)-sulfone bis-(4-hydroxyphenyl)- sulfone and phenylhydroquinone [6,
7], which can be selectively sulfonated at the external benzene ring. Secondly, to