Fuel Cell Ion-Exchange Membranes: The Inter-Relationship of Composition, Structure, and Function

The polymeric ion-exchange membrane plays a critical role in hydrogen/air, direct methanol, and alkaline fuel cells and thus must meet an array of requirements.  Some requirements are of a general nature, e.g., the need for highly conductive and durable membranes of low cost, while others are specific to the fuel cell type, e.g., the need for very thin membranes in a hydrogen/air fuel cell that operates at low humidity in order to promote the back diffusion of water from the cathode to the anode.  Both short- and long-term fuel cell operation/performance can be improved by optimizing on the membrane materials(s) and morphology.  To perform such an optimization, one must understand the inter-dependence of membrane composition, structure, and function.  For fuel cells, this understanding has arisen primarily from years of progress (both successes and failures) in membrane development and testing. This tutorial will review past and recent research activities dealing with new polymeric materials (e.g., hydrocarbon and perfluorinated ionomers), the manipulation of membrane morphology (e.g., blends, nanocomposites, and block copolymers), and the properties and performance of the resulting membranes in various fuel cell systems.