PEMFC Degradation Assessed by Effluent Analysis from Designed Experiments

Experimental design has been applied to study PEMFC performance and durability as a function of operating conditions. Two levels of relative humidity, clamping pressure and back pressure have been systematically applied to an ON/OFF load cycle. Effluent analysis of fluoride and sulfate has been performed to correlate the emission rates to the durability observed. Background effluent levels for fuel cell test rigs were also assessed. Fluoride emission rates increases with time. The rates are higher for the experiments with back pressure, but they do not correlate well with voltage losses. High initial emission rates of sulfur are observed. After flushing with humidified inert gas, the emission rates decline but are sustained at high rates compared to fluoride. Sulfate emission rates are higher for experiments with high humidification levels. The total mass of sulfur released is higher than expected from the ionomer equivalent weight.