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Microblock Ionomers: A New Concept in High Temperature, Swelling‐Resistant Membranes for PEM Fuel Cells
Author(s) -
Zhu Z.,
Walsby N. M.,
Colquhoun H. M.,
Thompsett D.,
Petrucco E.
Publication year - 2009
Publication title -
fuel cells
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.485
H-Index - 69
eISSN - 1615-6854
pISSN - 1615-6846
DOI - 10.1002/fuce.200800140
Subject(s) - ionomer , swelling , membrane , nafion , ionic bonding , materials science , polymer , chemical engineering , relative humidity , polymer chemistry , ionic conductivity , proton exchange membrane fuel cell , fabrication , phase (matter) , chemistry , composite material , electrolyte , electrode , ion , electrochemistry , organic chemistry , copolymer , thermodynamics , alternative medicine , pathology , engineering , biochemistry , medicine , physics
A novel series of polyaromatic ionomers with similar equivalent weights but very different sulphonic acid distributions along the ionomer backbone has been designed and prepared. By synthetically organising the sequence‐distribution so that it consists of fully defined ionic segments (containing singlets, doublets or quadruplets of sulphonic acid groups) alternating strictly with equally well‐defined nonionic spacer segments, a new class of polymers which may be described as microblock ionomers has been developed. These materials exhibit very different properties and morphologies from analogous randomly substituted systems. Progressively extending the nonionic spacer length in the repeat unit (maintaining a constant equivalent weight by increasing the degree of sulphonation of the ionic segment) leads to an increasing degree of nanophase separation between hydrophilic and hydrophobic domains in these materials. Membranes cast from ionomers with the more highly phase‐separated morphologies show significantly higher onset temperatures for uncontrolled swelling in water. This new type of ionomer design has enabled the fabrication of swelling‐resistant hydrocarbon membranes, suitable for fuel cell operation, with very much higher ion exchange capacities (>2 meq g –1 ) than those previously reported in the literature. When tested in a fuel cell at high temperature (120 °C) and low relative humidity (35% RH), the best microblock membrane matched the performance of Nafion 112. Moreover, comparative low load cycle testing of membrane ‐electrode assemblies suggests that the durability of the new membranes under conditions of high temperature and low relative humidity is superior to that of conventional perfluorinated materials.