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1 2015

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Synthesis and characterization of anion-exchange membranes with various functional groups

Perez-Prior M. T., Garcia-Garcia T., Varez A., Levenfeld B.

Archives of Materials Science and Engineering

2015

Vol. 72, nr 1

16--25

Purpose: In the current study anion-exchange membranes comprised of different functional groups were prepared to be used as electrolyte in fuel cells. Design/methodology/approach: Polysulfone was firstly chloromethylated followed by nucleophilic substitution reaction with the corresponding N-compound, trimethylamine and 1-methylbenzimidazole to obtain the resulting quaternary ammonium and benzimidazolium functionalized membranes, respectively. The membranes thus prepared as well as the starting polymers were characterized by 1H-NMR and FTIR analysis. Findings: The thermal stability of the membranes was lower than the original polymers. However, both membranes exhibited high thermal stability for typical fuel cell operation temperatures below 100°C. The capacity of these materials to absorb water was more favored when benzimidazolium groups were inserted to the polymer instead of quaternary ammonium ones. The ionic conductivity of the membranes in dilute aqueous solution of potassium hydroxide was studied by means of impedance spectroscopy. The results show a clear correlation between the membrane’s electrochemical behaviour with the electrolyte solution embedded in the membrane. In addition, the nature of the functional group modifies the membrane ionic conductivity. So, the membrane ionic conductivity was more than twice as high when the quaternary ammonium groups were replaced by the benzimidazolium ones. Research limitations/implications: The nature of the functional group as well as the number of exchangeable groups plays an important role on the ionic transport through the membrane. Therefore, the membrane ionic conductivity could be significantly improved by modifying the chemical structure of the polymer. Originality/value: The current study describes the main properties of benzimidazolium functionalized membranes. The electrochemical characteristics of this material as well as the thermal stability have been compared to the most commonly used comprising quaternary ammonium groups.