Structurally Tuned Nitrogen Doped Cerium Oxide as a Superior Free Radical Scavenger for Mitigating Polymer Electrolyte Membrane Degradation

Commercial cerium oxide (CeO 2 ) and as-prepared high-surface-area CeO 2 (220 m 2 /g) were doped with nitrogen and the ROS (reactive oxygen species ) scavenging efficacy of the samples was evaluated using in-situ fluorescence spectroscopy. Changes in the Ce 3+ surface concentration and oxygen vacancies upon nitrogen doping (N-doping) were determined using x-ray photoelectron spectroscopy and Raman spectroscopy. In-situ fluorescence experiments suggested that the N-doped commercial CeO 2 lose its scavenging properties after 41 hours during fuel cell operation at 90 o C and 50% RH. However, N-doped high-surface-area CeO 2 showed at least 100 hours of continuous scavenging properties under a similar fuel cell operating condition. XPS and Raman measurements suggested that the improved scavenging property of CeO 2 upon N-doping was attributed to the increase in Ce 3+ surface concentration and oxygen vacancy.