(278c) Investigation of PEM Fuel Cell Behavior: Swelling and Viscoelastic Properties of Nafion

Recent work on PEM fuel cells has demonstrated the importance of membrane mechanical properties and swelling behavior on cell performance. Indeed, mechanical properties and swelling should be considered as integral factors when developing new membranes, improving cell design and creating models. The existence of two stable ignited states in autohumidified fuel cells and the cells' responses to dynamic conditions have revealed chemical-mechanical coupling in which the membrane's mechanical properties are changed by its water content which in turn changes cell performance and water production. This work presents several examples of fuel cell behavior for which mechanical properties and swelling are believed to be responsible and discusses the mechanical properties of membranes determined thus far and their relevance to cell performance.

Methods for determining viscoelastic and swelling behavior under fuel cell-like conditions of elevated temperature and humidity are discussed. Constant-strain stress-relaxation and constant-stress creep experiments are performed, as are preliminary tests of Nafion swelling under a confining pressure.