The chemical behavior and degradation mitigation effect of cerium oxide nanoparticles in perfluorosulfonic acid polymer electrolyte membranes |
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Authors: | Benjamin P Pearman Nahid Mohajeri Darlene K Slattery Michael D Hampton Sudipta Seal David A Cullen |
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Institution: | 1. Florida Solar Energy Center, University of Central Florida, 1679 Clearlake Rd, Cocoa, FL 32922, USA;2. Department of Chemistry, University of Central Florida, Orlando, FL 32816, USA;3. Advanced Materials Processing and Analysis Center, Department of Mechanical Materials and Aerospace Engineering, University of Central Florida, Orlando, FL 32816, USA;4. Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA |
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Abstract: | Perfluorosulfonic acid membranes are susceptible to degradation during hydrogen fuel cell operation due to radical attack on the polymer chains. Mitigation of this attack by cerium-based radical scavengers is an approach that has shown promise. In this work, two formulations of crystalline cerium oxide nanoparticles, with an order of magnitude difference in particle size, are incorporated into said membranes and subjected to proton conductivity measurements and ex-situ durability tests. We found that ceria is reduced to Ce(III) ions in the acidic environment of a heated, humidified membrane which negatively impacts proton conductivity. In liquid and gas Fenton testing, fluoride emission is reduced by an order of magnitude, drastically increasing membrane longevity. Sideproduct analysis demonstrated that in the liquid Fenton test, the main point of attack is weak polymer end groups, while in the gas Fenton test, there is additional side-chain attack. Both mechanisms are mitigated by the addition of the ceria nanoparticles, whereby the extent of the concentration-dependent durability improvement is found to be independent of particle size. |
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Keywords: | Cerium oxide Perfluorosulfonic acid Polymer electrolyte membrane (PEM) Fuel cell Fenton test Degradation mitigation |
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