Self-Assembly and Transport Limitations in Confined Nafion Films

TitleSelf-Assembly and Transport Limitations in Confined Nafion Films
Publication TypeJournal Article
Year of Publication2013
AuthorsModestino, Miguel A., Devproshad K. Paul, Shudipto Dishari, Stephanie A. Petrina, Frances I. Allen, Michael A. Hickner, Kunal Karan, Rachel A. Segalman, and Adam Z. Weber
Pagination867 - 873
Date Published02/2013

Ion-conducting polymers are important materials for a variety of electrochemical applications. Perfluorinated ionomers, such as Nafion, are the benchmark materials for proton conduction and are widely used in fuel cells and other electrochemical devices including solar-fuel generators, chlor-alkali cells, and redox flow batteries. While the behavior of Nafion in bulk membranes (10 to 100s μm thick) has been studied extensively, understanding its properties under thin-film confinement is limited. Elucidating the behavior of thin Nafion films is particularly important for the optimization of fuel-cell catalyst layers or vapor-operated solar-fuel generators, where a thin film of ionomer is responsible for the transport of ions to and from the active electrocatalytic centers. Using a combination of transport-property measurements and structural characterization, this work demonstrates that confinement of Nafion in thin films induced thickness-dependent proton conductivity and ionic-domain structure. Confining Nafion films to thicknesses below 50 nm on a silicon substrate results in a loss of microphase separation of the hydrophilic and hydrophobic domains, which drastically increases the material’s water uptake while in turn decreasing its ionic conductivity.

Short TitleMacromolecules