Scavenging of Hydroxyl Radicals by Ceria Nanoparticles

Bosnjakovic, Admira, Marek Danilczuk, and Shulamith Schlick

Due to unique auto-catalytic and redox properties, cerium oxide (CeO2) nanoparticles have been widely investigated in various applications such as catalysis [1,2], polymer electrolyte fuel cells [3], and biological systems [4]. The high performance of ceria is attributed to oxygen vacancy sites at the surface of the nanoceria fluorite structure, which allow rapid change of oxidation state between Ce(III) and Ce(IV) [5]. In the past decades proton exchange membrane fuel cells (PEMFCs) have received growing interest, but problem remain, due to membrane degradation under the strong oxidizing conditions inside the fuel cell. Our group recently reported experiments in an in situ fuel cell (FC) with a membrane-electrode assembly (MEA) based on Nafion 10% neutralized by Ce(III). The results obtained by Electron Spin Resonance (ESR) showed hydroxyl radicals scavenging by Ce(III). Ce(III) proved to be an effective stabilizer because of the Ce(III)/Ce(IV) couple redox chemistry [6]. This redox chemistry is facilitated in ceria nanoparticles and it is more pronounced in smaller particle size due to increased surface area. Here we report the preliminary ESR study showing the scavenging of hydroxyl radicals by ceria nanoparticles. The hydroxyl radicals were generated by UV irradiation of hydrogen peroxide solution containing various concentrations of ceria nanoparticles and 5,5-dimethyl-1-pyrroline-N-oxide (DMPO) as a spin trap. The UV irradiation and detection of DMPO/OH adduct were done in situ. The results showed that the intensity of the DMPO/OH adduct decreases with the increasing the ceria concentration from 0.5 µM to 8 µM. Based on these results it is expected that the proton exchange membrane with incorporated ceria nanoparticle would be more stable during fuel cell operation.

Acknowledgements

This research was supported by Polymers Program of the U.S. National Science Foundation. We thank Dr. Mariana Spulber for the synthesis of Ceria nanoparticles.

References

  1. Ou, D.R.; Mori, T.; Fugane, K.; Togasaki, H.; Ye, F.; Drennan, J. Stability of ceria supports in Pt-CeOx/C catalysts. J. Phys. Chem. C 2011, 115, 19239-19245.
  2. Kockrick, E.; Borchardt, L.; Schraget, C.; Gaudillere, C.; Ziegler, C.; Freudenberg, T.; Farrusseng, D.; Eychmu, A.; Kaskel, S. Ce2O/Pt catalyst nanoparticle containing carbide-derived carbon composites by a new in situ functionalization strategy. Chem. Mater. 2011, 23, 57-66.
  3. Trogadas, P.; Parrondo, J.; Ramani, V. Degradation mitigation in polymer electrolyte membranes using cerium oxide as a regenerative free-radical scavenger. Electrochem. Solid-State Lett. 2008, 11, B113-B116.
  4. Xue, Y.; Luan, Q.; Yang, D.; Yao, X.; Zhou, K. Direct evidence for hydroxyl radical scavenging activity of cerium oxide nanoparticles. J. Phys. Chem. C 2011, 115(11), 4433-4438.
  5. Heckert, E.; Karakoti, A.; Seal, S.; Self, W.T. The role of cerium redox state in the SOD mimetic activity of nanoceria. Biomater. 2008, 29(18), 2705-2709.
  6. Danilczuk, M.; Schlick, S.; Coms, F.D. Cerium (III) as a stabilizer of perfluorinated membranes used in fuel cells: in situ detection of early events in the ESR resonator. Macromolecules 2009, 42, 8943-8949.