Temperature Effects on theMolecular Dynamics of Modified Nafion® Membranes Incorporating Ionic Liquids? Cations: A 1H NMRD Study

CARLA MARTINS; LUISA NEVES; I. M. COELHOSO; FABIAN VACA CHAVEZ; JOÃO CRESPO; PEDRO J. SEBASTIÃO

FUEL CELLS

WILEY-V C H VERLAG GMBH

Lugar: Weinheim; Año: 2013 vol. 13 p. 1166 - 1176

1615-6846

Nafion® is the polymer electrolyte membrane most used in fuel cells (PEMFC), however Nafion® presents some limitations due to the water loss with increasing temperature. In this work is presented the study of the molecular dynamics in modified Nafion®/ionic liquids (IL) cations membranes with increasing temperature, by proton NMR relaxometry (1H NMRD). Three Nafion® membranes modified with Phenyltrimethylammonium (TMPA+), 1-n-butyl-3-methylimidazolium (BMIM+) and n-dodecyltrimethylammonium (DTA+) IL cations were considered. This study allowed the evaluation of the effect of the IL cations incorporation in Nafion® membranes and to assess the degree of confinement of the IL cations in the membranes matrix in relation with the water content. Thermogravimetry analysis was also performed to study the water loss with increasing temperature of the Nafion®/IL cations membranes. It was possible to establish a correlation between the water content and the IL cations self-diffusion coefficients. The sequential order of the hydration level obtained for the studied systems was Nafion®/DTA+>Nafion®/BMIM+  Nafion®/H+>Nafion®/ TMPA+, while the water loss follows the sequence Nafion®/ H+>Nafion®/BMIM+∼Nafion®/DTA+>Nafion®/TMPA+. The Nafion®/BMIM+ presented the largest temperature variation of both the self-diffusion coefficient and the hydration conditions. In terms of PEMFCs efficiency, the Nafion®/ DTA+ modified membrane seems to offer the largest and stable hydration conditions with temperature.