(215d) Measurement of the Performance of a 47 Cell PEM Stack with Impurities in the Anode Feed Stream

A 47-cell Ballard® Nexa? PEM stack was used to investigate the distribution of crossover gasses and feed impurities within the anode side of the stack as a steady-state is approached. Separate voltage taps were applied to each MEA in the stack to measure the time-dependent potential and concentration of impurities. Safe operation of the PEM stack requires no more than .01% total inert gas under normal operating conditions; however, by leaving the exhaust valve partially open instead of allowing the system to periodically purge the exhaust line as it was designed, feeds of up to 10% inert gas were safely used in this study. By releasing exhaust gas at a constant rate while drawing a constant current from the stack, a steady-state voltage drop was observed after changing the anode feed from ultra-pure to one diluted with an inert gas such as helium or nitrogen. The change in exhaust gas composition was calculated using gas chromatography, while the potential difference across each MEA was measured to determine the distribution of impurities. The aforementioned technique is useful for performing cell diagnostics and understanding gas distribution within the stack feed manifold and on the catalyst surface of each MEA.