Gas pressure was maintained in the

Gas pressure was maintained in the cell by placing spring loaded pressure relief valves (Swagelok) at the outlets. Tees were placed in the outlet lines with relative humidity sensors in the dead legs of the tees. The water content of the outlet streams was measured with humidity sensors (Honeywell HIH 3610), and the temperature at the humidity sensors was measured with a thermocouple in the gas line. At a flow rate of 10 cm3/ min the humidity sensor responded to changes in the humidity at the anode and cathode in < 2 s. We report here results using an MEA consisting of a Nafion 115 membrane pressed between 2 E-tek electrodes (these consist of a carbon cloth coated on one side with a Pt/C catalyst). The catalyst weight loading at each electrode was 0.4 mg-Pt/cm2. Each electrode was brushed with solubilized Nafion solution to a loading of ∼ 4 mg-Nafion/cm2 before placing the membrane between them (Raistrick, 1989). The assembly was hotpressed at130 ◦C and 10 MPa. Copper foils were pressed against the graphite plates and copper wires were attached to connect them to the external load resistor