First-principles study on proton dissociation properties of fluorocarbon-and hydrocarbon-based membranes in low humidity conditions

Michihisa Koyama, Kazunori Bada, Kenji Sasaki, Hideyuki Tsuboi, Akira Endou, Momoji Kubo, Carlos A. Del Carpio, Ewa Broclawik, Akira Miyamoto

    Research output: Contribution to journalArticlepeer-review

    19 Citations (Scopus)


    We present a theoretical study on the proton dissociation properties of the membranes for polymer electrolyte fuel cells. A density functional theory method is used to study the influence of fluorocarbon and hydrocarbon backbones on proton dissociation, the interaction of water molecules with the sulfonic acid group, and the energy barriers for proton dissociation. Better proton dissociation properties of CH3SO3H compared to CF 3-SO3H are observed from statistical analyses of the optimized structures for both systems. However, the calculated energy barriers for proton dissociation are lower for CF3SO3H than for the CH3SO3H system. At the same time, the interaction of water molecules is stronger for CH3SO3H than for CF 3SO3H. Also, the analysis of the hydrogen-bonding network in both systems shows that the number of hydrogen bonds formed around the sulfonic acid group in CH3SO3H is larger than that in CF3SO3H. Therefore, the decrease of the energy barrier with increasing number of coordinating water molecules, pronounced in the case of CF3SO3H, may lower the barrier, which enhances good proton conductivity of a hydrocarbon-based polymer in low humidity conditions. Thus the hydration ability of a sulfonic acid group is an important factor for realizing better proton dissociation in low humidity conditions.

    Original languageEnglish
    Pages (from-to)17872-17877
    Number of pages6
    JournalJournal of Physical Chemistry B
    Issue number36
    Publication statusPublished - Sept 14 2006

    All Science Journal Classification (ASJC) codes

    • Physical and Theoretical Chemistry
    • Surfaces, Coatings and Films
    • Materials Chemistry


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