AUTHOR=Knauth Philippe , Di Vona Maria Luisa 

TITLE=Hydration and Proton Conductivity of Ionomers: The Model Case of Sulfonated Aromatic Polymers

JOURNAL=Frontiers in Energy Research

VOLUME=2

YEAR=2014

URL=https://www.frontiersin.org/journals/energy-research/articles/10.3389/fenrg.2014.00050

DOI=10.3389/fenrg.2014.00050

ISSN=2296-598X

ABSTRACT=<p>The hydration of proton-conducting ionomers is described in terms of a simplified model, where only osmotic and elastic contributions to the Gibbs free energy of hydration are considered. Although only two physically meaningful parameters are used – the deformation parameter, inversely proportional to the elastic modulus of the ionomer, and the free volume parameter – simulated hydration isotherms are in good agreement with the experiment. The proton mobility <italic>u</italic> inside the electrolyte solution of the ionomer is calculated from the proton conductivity determined at various hydration numbers. Its variation with the proton concentration <italic>c</italic> reveals the percolation threshold of hydrated nanometric channels and the tortuosity of the membrane. Above the percolation threshold, a power law <italic>u</italic> ~ <italic>c</italic><sup>−3</sup> is observed, in agreement with the “universal” law for 3-dimensional percolation. The proton conductivity σ shows at 100°C a maximum of 0.2 S/cm at a hydration number ~90. The σ = <italic>f(c)</italic> plot allows to predict, which hydration conditions are necessary for a desired area specific resistance.</p>