IN-SITU RESISTANCE MEASUREMENTS OF NAFION(R)-117 MEMBRANES IN POLYMERELECTROLYTE FUEL-CELLS

The resistance of the Nafion(R) 117 membrane in H-2/O-2 and H-2/air po lymer electrolyte fuel cells (PEFCs) has been measured in situ using f ast current pulses. The dependence of the membrane resistance on curre nt density, temperature, pressure and flow-field design was investigat ed. It was found that, independent of other variations, the resistance increases with increasing current density. When the current density i n the cell is increased from 0.2 to 0.7 A cm(-2), the membrane resista nce increases by up to 22%. Even on open circuit the resistance at 60 degrees C is 15%-35% higher than that measured ex situ, indicating tha t the membrane is not fully hydrated under the fuel cell operating con ditions. The resistance on open circuit also depends on the design of the flow field. In a design with forced gas convection the resistance at 60 degrees C is substantially higher (210 m Omega cm(2)) than in a design without forced convection (186 m Omega cm(2)).