When comparing the 94 h and 500 h tests, it is clear that the
shorter test is insufficient in demonstrating the very large durability
improvement that ceria provides fuel cell membranes. The
decrease in the total emission of fluoride upon incorporation of the
additives for the 500 h test was more than an order of magnitude
larger than the 94 h test showed. Barring localized failures, ceria, of
either formulation, was able to dramatically inhibit membrane
degradation, to the extent that even after 500 h of extreme
degradation conditions, membrane electrode assemblies remain
nearly pristine.