ꢀ Alkaline conditions facilitate the formation of phenoxyl
and benzosemiquinone radicals, i.e. local inhomogeneities in
pH should be avoided when such building blocks are
present. The application of such aromatic building blocks in
alkaline–anion exchange membrane fuel cells holds the risk of
an enhanced susceptibility to HOꢀ and related radicals,
especially when hydroxyl end-groups are present.
20 J. A. Kerres, D. Xing and F. Schonberger, J. Polym. Sci., Part B:
¨
Polym. Phys., 2006, 44(16), 2311.
21 C. Hamiciuc, M. Bruma and M. Kapper, J. Macromol. Sci. A,
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22 P. Xing, G. P. Robertson, M. D. Guiver, S. D. Mikhailenko and
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23 B. Liu, G. P. Robertson, M. D. Guiver, Y.-M. Sun, Y.-L. Liu,
J.-Y. Lai, S. Mikhailenko and S. Kaliaguine, J. Polym. Sci.,
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ꢀ The number of potentially reactive end-groups (especially
of hydroxyl groups and fluorine atoms) should be minimized
(e.g. by endcapping of the polymers with a monofunctional
aromatic monomer).
24 W. L. Harrison, F. Wang, J. B. Mecham, V. A. Bhanu, M. Hill,
Y. S. Kim and J. E. McGrath, J. Polym. Sci., Part A: Polym.
Chem., 2003, 41, 2264.
25 F. Schonberger, M. Hein and J. Kerres, Solid State Ionics, 2007,
¨
178, 547.
26 N. Y. Arnett, W. L. Harrison, A. S. Badami, A. Roy, O. Lane,
F. Cromer, L. Dong and J. E. McGrath, J. Power Sources, 2007,
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27 K. B. Wiles, C. M. de Diego, J. de Abajo and J. E. McGrath,
J. Membr. Sci., 2007, 294, 22.
28 Z. Bai, J. A. Shumaker, T. D. Dang, M. Yoonessi and
M. F. Durstock, Polym. Preprints, 2006, 47(1), 140.
29 Y. S. Kim, M. J. Sumner, W. L. Harrison, J. S. Riffle,
J. E. McGrath and B. S. Pivovar, J. Electrochem. Soc., 2004,
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ꢀ The ether bridge of poly(arylene ether)s has to be
stabilized against HOꢀ radical, acid or base induced cleavage
by appropriate electron-withdrawing substituent in ortho- or
para-position in order to reduce the probability of chain
cleavage during fuel cell operation.32 Any cleaved ether
bridges might activate a cascade of (further) radical induced
reactions (especially in a locally alkaline medium).
30 M. Sankir, Y. S. Kim, B. S. Pivovar and J. E. McGrath, J. Membr.
Sci., 2007, 299, 8.
31 T. L. Norsten, M. D. Guiver, J. Murphy, T. Astill, T. Navessin,
S. Holdcroft, B. L. Frankamp, V. M. Rotello and J. Ding, Adv.
Funct. Mater., 2006, 16, 1814.
Acknowledgements
The authors thank Dr Svetlin Mitov and Dr Stefan Jagiella for
their help and useful discussions.
¨
32 F. Schonberger, A. Chromik and J. Kerres, Polymer, 2009, 50,
2010.
33 Z. Bai, M. F. Durstock and T. D. Dang, J. Membr. Sci., 2006, 281,
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