Impact of CeO x Additives on Cathode Catalyst Layer Poisoning

The impact of CeOx crystallite size on CeOx dissolution was investigated. Three CeOx additives were prepared having crystallite sizes of 6, 13, or 25 nm. An ex-situ method was developed to evaluate the chemical stability of these three CeOx samples, as well as one commercially available CeOx. It was determined that surface area, rather than crystallite size, is the best predictor of chemical stability. In-situ membrane electrode assembly (MEA) testing of the four CeOx additives demonstrated that prior to accelerated stress testing (AST), negligible dissolution of the CeOx additives occurs. Following AST cycling, it was found that end of life (EOL) performance was identical regardless of differences in total CeOx dissolution observed from the ex-situ testing. Finally, it was shown that increasing the anode RH during AST cycling leads to significantly higher EOL performance losses which was attributed to increased CeOx dissolution.