Study of the Constrained Expansion of Nafion within the Hardware of a PEMFC

A study is presented of the expansion of Nafion under compression inside a fuel cell. Under compression between the flow field plates, Nafion elongates and protrudes inside the channels due to a plastic deformation. The thickness of protruded membrane is larger than the uncompressed one, and does not change appreciably by water absorption. On the other hand, the height of the protrusion increases by water absorption, slightly more when the membrane is compressed in its dry form than if it is compressed in fully humidified, expanded, form. Bumps in the protruded membrane are observed that probably reflect changes in the Nafion microstructure. Single cell characterization shows that the assembly with pre-expanded membranes gives rise to about 7% improvement in the maximum power density, attained at 1.6 A.cm(-2) under standard testing conditions. Such improvement is fully attributed to a decrease in the internal resistance. The pre-expanded Nafion, therefore, should be used when high current density demands are foreseen, whereas for low current density, dry membrane assembly may perform like the pre-expanded.