CeO2(111) Surface with Oxygen Vacancy for Radical Scavenging: A Density Functional Theory Approach

CeO2 has been established as an effective scavenger for destructive oxygen radicals in fuel cell membranes. The effect of ceria (CeO2) surface defect on (OH)-O-center dot and (OOH)-O-center dot radical scavenging efficacy is investigated using density functional theory (DFT). Our calculations suggest that both (OH)-O-center dot and (OOH)-O-center dot can be bound to oxygen vacancies on the CeO2(111) surface. Intriguingly, binding to the triangular defect ((OH)-O-center dot binding energy = -4.54 eV; (OOH)-O-center dot binding energy = -3.20 eV) is more favorable than binding to the linear defect ((OH)-O-center dot binding energy = -4.12 eV; (OOH)-O-center dot binding energy = -2.80 eV). This is likely due to Coulombic repulsive interaction from the additional oxygen atom adjacent to the linear defect. This is also potentially due to the greater localization of electrons to defect-adjacent cerium atoms in the triangular defect, as demonstrated via a Mulliken population analysis. Confirming this observation, it is shown that the density of states (DOS) for the Ce 4f band undergoes a significant alteration near the Fermi level due to this electron localization. As such, it is demonstrated that the triangular defect possesses a superior radical scavenging capability compared to the linear defect. Based on the results of this study, we suggest that future experimental studies aim to synthesize ceria nanoparticles with a greater percentage of triangular defects to enhance the particle radical scavenging capability.