Boosting antioxidation efficiency of nonstoichiometric CeO_x nanoparticles via surface passivation toward robust polymer electrolyte membrane fuel cells

Nonstoichiometric cerium oxide (CeO_x) nanomaterials are considered the most efficient radical scavengers with regenerative redox behavior and are emerging as a pivotal ingredient to secure long-lasting energy conversion devices. However, the environment of energy conversion reactions, which hampers a regeneration of Ce chemical states and severely degrades CeO_x antioxidation efficiency, engenders the thirst for CeO_x surface passivation strategies that confer high colloidal stability, robust chemical durability, and efficient radical scavenging performance. Here, as a proof-of-concept study, we suggest that chemically durable mesoporous silica (mSiO₂) shells with high colloidal stability in polar media boost CeO_x antioxidation efficiency. The mSiO₂ enabled the even dispersion of the CeO_x nanoparticles (NPs) in polar media, effectively mitigated radical scavenging activity degradation, and an increased ratio of highly active Ce(III) states. Importantly, a proton exchange membrane (PEM) based on the CeO_x/mSiO₂ core/shell exhibited a much lower disintegration rate during the Fenton's test than the CeO_x-based PEM and the pristine one. Furthermore, in fuel cell tests, the CeO_x/mSiO₂-based PEM demonstrated excellent durability preserving 91.7% of initial maximum power density after 100 h-durability tests, while other PEMs underwent drastic performance degradation. In addition, systematic modulation of structural factors in CeO_x/mSiO₂ allowed demonstrating the multifunctionality of the mSiO₂ shell.