The impact of membrane constraint on PEM fuel cell water management

A nonequilibrium force-balance model for water transport within a Nafion-type polymer electrolyte membrane (PEM) fuel cell is developed. The model combines earlier work of Choi , which describes the Schroeder paradox in terms of a capillary pressure jump, with a pressure-based description of water transport, including the partitioning of external pressure between the polymer backbone and the liquid water. The model shows that mechanical compression of the membrane leads to a more uniform distribution of water through the thickness of the membrane, compressing the wetter and more plastic cathode side more than the drier anode side. The model predicts that mechanical compression will decrease membrane water content by 5-30% and decrease back-diffusion of water within the membrane by up to 20%. (C) 2007 The Electrochemical Society.