Structurally tuned nitrogen doped cerium oxide as a superior free radical scavenger for mitigating polymer electrolyte membrane degradation

Commercial cerium oxide (CeO₂) and as-prepared high-surfacearea CeO₂ 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 Ce³⁺ surface concentration and oxygen vacancies upon nitrogen doping (Ndoping) were determined using x-ray photoelectron spectroscopy (XPS) and Raman spectroscopy respectively. In-situ fluorescence experiments suggested that the N-doped samples (both commercial and high-surface area CeO₂) showed continuous scavenging activity for at least 34 hours during fuel cell operation at 80°C and 75% RH (experiments were stopped at this point). The increase in Ce³⁺ surface concentration and oxygen vacancy are the primary reasons for an improved scavenging property of CeO₂ upon N-doping as evidenced by XPS and Raman measurements.