A molecular dynamics simulation study of hydrated sulfonated poly(ether ether ketone) for application to polymer electrolyte membrane fuel cells: Effect of water content

Sulfonated poly(ether ether ketone) (S-PEEK) with 40% of degree of sulfonation was studied using full atomistic molecular dynamics simulation in order to investigate the nanophase-segregated structures, focusing on the sulfonate group and water phase at various water contents such as 10, 13, and 20 wt %. By analyzing the pair correlation function, it is found that as the water solvation of sulfonate groups proceeds more with increasing water content, the distance between sulfonate groups is increased from 4.4 angstrom (10 wt %) to 4.8 angstrom (13 wt %) to 5.4 angstrom (20 wt %), and the hydronium ions (H3O+) become farther apart from the sulfonate groups. The water coordination number for water and the water diffusion are enhanced with increasing water content because the internal structure of the water phase in S-PEEK approaches that of bulk water. Compared to the Nafion and Dendrion membranes, the S-PEEK membrane shows less internal structure in the water phase and smaller water diffusion, indicating that the S-PEEK has less nanophase segregation than the Nafion and Dendrion membranes. (C) 2009 American Institute of Physics. [DOI: 10.1063/1.3138922]