Operation of a PEM stack with high impurity anode feeds in a recycle mode

A Ballard PEM stack (Nexa™ power module) was used, providing 1200 w 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 MEA as both gas purifier and as solid electrolytes. The PEM stack was successfully operated with ≤ 7.5% nitrogen in the absence of a Pd-based hydrogen separator. A hydrocarbon reformate containing high levels of CO₂ and H₂O was also used in the Nexa stack after CO and H₂S poisons were removed. Because small amount of poisonous CO comes into the fuel cell system, the overall stack voltage dropped gradually. A concentration gradient of CO existed inside the fuel gas distribution channel. The front fuel cells in the stack were more likely to receive the poisons causing temporary catalyst deactivation. This is an abstract of a paper presented at the AIChE Annual Meeting (Austin, TX 11/7-12/2004).