Operation of a PEM Stack with High Impurity Anode Feeds in a Recycle Mode

A Ballard PEM stack (Nexa power module) was utilized in this work, providing 1200 watts of unregulated DC power at a nominal output voltage of 26 VDC. In deference to normal operational procedures, high levels of inert gases were deliberately added to the anode feed. Fuel exhaust management in the Nexa system was carried out by adding a manual exhaust line into the exterior fuel exhaust purge line. This exhaust management system provided the opportunity to optimize the exhaust flow rate and increase system efficiency in a recycle mode. This type of operation provides a dual use of membranes in the MEAs as both gas purifier and as solid electrolytes. The PEM stack was successfully operated with up to 7.5% nitrogen in the absence of a palladium-based hydrogen separator. In further experiments, a hydrocarbon reformate containing high levels of CO2 and H2O was also used in the Nexa stack after troublesome CO and H2S poisons were removed. Both fuels successfully ran the Nexa stack. Recycle operation may be used to reduce the size and complexity of the fuel processing system at a specified power level.