Mechanism for Degradation of Nafion in PEM Fuel Cells from Quantum Mechanics Calculations.
We report results of quantum mechanics (QM) mechanistic studies of Nafion membrane degradation in a polymer electrolyte membrane (PEM) fuel cell. Experiments suggest that Nafion degradation is caused by generation of trace radical species (such as OH•, H•) only when in the presence of H, O, and Pt....
| Publicado en: | Journal of the American Chemical Society Vol. 133; no. 49; pp. 19857 - 19864 |
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| Autores principales: | , , , , , |
| Formato: | Artículo |
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American Chemical Society
12/14/2011
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| Materias: | |
| Acceso en línea: | Ver este registro en EBSCOhost |
| fields | @attributes: recordID: 1 pdfLink: plink: https://search.ebscohost.com/login.aspx?direct=true&db=hlh&AN=70200717&site=ehost-live header: @attributes: shortDbName: hlh uiTerm: 70200717 longDbName: Humanities International Complete uiTag: AN controlInfo: bkinfo: jinfo: jid: 00027863 ACS jtl: Journal of the American Chemical Society issn: 00027863 maglogo: N pubinfo: dt: 12/14/2011 vid: 133 iid: 49 pid: 997 pub: American Chemical Society artinfo: ui: 70200717 10.1021/ja2074642 ppf: 19857 ppct: 7 formats: tig: atl: Mechanism for Degradation of Nafion in PEM Fuel Cells from Quantum Mechanics Calculations. aug: au: Yu, Ted H. Yao Sha Wei-Guang Liu Merinov, Boris V. Shirvanian, Pezhman Goddard, III, William A. affil: Materials and Process Simulation Center, California Institute of Technology, MC 139-74, Pasadena, California 91125, United States Research & Advanced Engineering, Ford Motor Co., 2101 Village Road, Dearborn, Michigan 48104, United States su: Proton exchange membrane fuel cells Quantum theory Polyelectrolytes Density functionals Potential energy surfaces sug: subj: Proton exchange membrane fuel cells Quantum theory Polyelectrolytes Density functionals Potential energy surfaces ab: We report results of quantum mechanics (QM) mechanistic studies of Nafion membrane degradation in a polymer electrolyte membrane (PEM) fuel cell. Experiments suggest that Nafion degradation is caused by generation of trace radical species (such as OH•, H•) only when in the presence of H, O, and Pt. We use density functional theory (DFT) to construct the potential energy surfaces for various plausible reactions involving intermediates that might be formed when Nafion is exposed to H (or H) and O in the presence of the Pt catalyst. We find a barrier of 0.53 eV for OH radical formation from HOOH chemisorbed on Pt(111) and of 0.76 eV from chemisorbed OOH, suggesting that OH might be present during the ORR, particularly when the fuel cell is turned on and off. Based on the QM, we propose two chemical mechanisms for OH radical attack on the Nafion polymer: (1) OH attack on the S-C bond to form HSO plus a carbon radical (barrier: 0.96 eV) followed by decomposition of the carbon radical to form an epoxide (barrier: 1.40 eV). (2) OH attack on H crossover gas to form hydrogen radical (barrier: 0.04 eV), which subsequently attacks a C-F bond to form HF plus carbon radicals (barrier as low as 1.00 eV). This carbon radical can then decompose to form a ketone plus a carbon radical with a barrier of 0.86 eV. The products (HF, OCF, SCF) of these proposed mechanisms have all been observed by F NMR in the fuel cell exit gases along with the decrease in pH expected from our mechanism. pubtype: Academic Journal doctype: Article src: R language: English refInfo: copyright: @attributes: flag: Y dt: @attributes: year: 2011 holdings: @attributes: islocal: N |
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