Electrolyte degradation and degradation mitigation in polymer electrolyte fuel cells

Components of polymer electrolyte fuel cell (PEFC) membrane electrode assemblies (MEAs) deteriorate during long-term operation. One of the most serious issues is the deterioration of perfluorinated ionomer membrane used as the solid electrolyte. It has been shown that reactive oxygen species (ROS) such as HO· and HO2· radicals produced at the anode and cathode of the fuel cell as well as within the electrolyte membrane are responsible for the degradation reactions. The formation of hydrogen peroxide (H2O2, a source of these free radicals) during fuel cell operation has been confirmed and degradation by-products have been detected in product water.;Three approaches can be used to minimize the effect of ROS in a PEFC: (i) the use of free radical scavengers; (ii) the use of dispersed peroxide decomposition catalysts within the electrolyte, and (iii) the use of dispersed peroxide decomposition catalysts within the electrodes. The present study is aimed at validating these approaches by: (1) incorporating hydrogen peroxide decomposition catalysts (MnO2; WO3) in the electrodes; and (2) incorporating radical scavengers (CeO2; MnO2; metal nanoparticles) in the electrolyte. The efficacy of the hydrogen peroxide decomposition catalysts is evaluated in terms of: (1) their ability to mitigate the generation of H2O2; and (2) their ability to lower the rate of electrolyte membrane degradation. The former is estimated through rotating ring disk electrode (RRDE) experiments by estimating the percentage of H2O2 detected at the ring electrode during the oxygen reduction reaction. The latter is estimated through MEA studies, wherein the amount of fluoride ions released by the membrane is estimated after a specific operating period in an accelerated test. The efficacy of the radical scavengers incorporated within the electrolyte was evaluated through accelerated durability testing of MEAs.;The first approach (peroxide decomposition within electrodes) yielded a 30-50% reduction in electrolyte membrane degradation, while the second approach (using free radical scavengers) resulted in over an order of magnitude reduction in the rate of electrolyte membrane degradation. Radical scavengers based on non-stoichiometric metal oxides were found to be regenerative. These results will be presented and discussed in conjunction with associated performance and materials characterization data.