title: CeO2 surface oxygen vacancy concentration governs in situ free radical scavenging efficacy in polymer electrolytes.
abstract: Nonstoichiometric CeO(2) and Ce(0.25)Zr(0.75)O(2) nanoparticles with varying surface concentrations of Ce(3+) were synthesized. Their surface Ce(3+) concentration was measured by XPS, and their surface oxygen vacancy concentrations and grain size were estimated using Raman spectroscopy. The surface oxygen vacancy concentration was found to correlate well with grain size and surface Ce(3+) concentration. When incorporated into a Nafion polymer electrolyte membrane (PEM), the added nonstoichiometric ceria nanoparticles effectively scavenged PEM-degradation-inducing free radical reactive oxygen species (ROS) formed during fuel cell operation. A 3-fold increase in the surface oxygen vacancy concentration resulted in an order of magnitude enhancement in the efficacy of free radical ROS scavenging by the nanoparticles. Overall, the macroscopic PEM degradation mitigation rate was lowered by up to 2 orders of magnitude using nonstoichiometric ceria nanoparticles with high surface oxygen vacancy concentrations.
authors.affiliation: Center for Electrochemical Science and Engineering, Department of Chemical and Biological Engineering, Illinois Institute of Technology, 10 W, 33rd Street, Chicago, Illinois 60616, USA.
authors.forename: Panagiotis
authors.initials: P
authors.lastname: Trogadas
authors.forename: Javier
authors.initials: J
authors.lastname: Parrondo
authors.forename: Vijay
authors.initials: V
authors.lastname: Ramani