Scavenging of Hydroxyl Radicals by Ceria Nanoparticles: Effect of Particle Size and Concentration
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- 作者：Shulamith Schlick ; Marek Danilczuk ; Andrew R. Drews ; Ratandeep S. Kukreja
- 刊名：Journal of Physical Chemistry C
- 出版年：2016
- 出版时间：March 31, 2016
- 年：2016
- 卷：120
- 期：12
- 页码：6885-6890
- 全文大小：386K
- ISSN：1932-7455
文摘
The most commonly used proton exchange membranes (PEMs) for hydrogen and direct methanol fuel cells are the perfluorosulfonic acid ionomers (PFSA) such as Nafion, which are based on a Teflon-like backbone with side chains containing sulfonic groups. These materials exhibit good mechanical, chemical, and thermal stability in both oxidative and reductive media; however, the fuel cell is a reactor with strong oxidizing power, capable of reducing the durability of the PEMs. The centrality of hydroxyl radicals, HO·, in the degradation mechanism of PFSA is well documented in numerous papers, including our work. Therefore, membrane durability remains a critical issue for further development of fuel cell applications. We present the use of ceria nanoparticles (NPs) for mitigating the chemical degradation process and describe their effectiveness for scavenging hydroxyl radicals as a function of their size and concentrations. The hydroxyl radicals were generated by UV-irradiation of hydrogen peroxide, and the radicals were detected by spin trapping electron spin resonance (ESR) with 5,5-dimethyl-1-pyrroline-N-oxide (DMPO) as the spin trap. The size of the ceria NPs was in the range 7.1–14.7 nm, as determined by X-ray diffraction (XRD), and the molar concentration of ceria was varied between 0 and 200 μM. The ESR results indicated that larger NPs are more effective scavengers of the HO· radicals. Transmission electron microscopy (TEM) data measured in the scanning TEM (STEM) mode showed pronounced agglomeration of the smaller NPs. Consideration of both TEM and ESR results suggests that the agglomerated particles do not contribute fully to radical scavenging. This conclusion is due to the short diffusion distances of short-lived species such as hydroxyl radicals, typically 4–6 nm, compared to 10–20 nm for stable species. The results of this study indicated that scavenging of hydroxyl radicals is more effective for larger NPs.