Electro-chemo-mechanical Studies of Perovskite-Structured Mixed Ionic-Electronic Conducting SrSni-₁₋xFexO₃₋x/₂₊[epsilon]

Thesis: S.M., Massachusetts Institute of Technology, Department of Materials Science and Engineering, 2015.

Bibliografische gegevens
Hoofdauteur: Kim, Chang Sub, Ph.D. Massachusetts Institute of Technology
Andere auteurs: Massachusetts Institute of Technology. Department of Materials Science and Engineering.
Formaat: Thesis
Taal:eng
Gepubliceerd in: Massachusetts Institute of Technology 2016
Onderwerpen:
Online toegang:http://hdl.handle.net/1721.1/101562
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author Kim, Chang Sub, Ph.D. Massachusetts Institute of Technology
author2 Massachusetts Institute of Technology. Department of Materials Science and Engineering.
author_facet Massachusetts Institute of Technology. Department of Materials Science and Engineering.
Kim, Chang Sub, Ph.D. Massachusetts Institute of Technology
author_sort Kim, Chang Sub, Ph.D. Massachusetts Institute of Technology
collection MIT
description Thesis: S.M., Massachusetts Institute of Technology, Department of Materials Science and Engineering, 2015.
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spelling mit-1721.1/1015622019-09-19T22:06:15Z Electro-chemo-mechanical Studies of Perovskite-Structured Mixed Ionic-Electronic Conducting SrSni-₁₋xFexO₃₋x/₂₊[epsilon] Kim, Chang Sub, Ph.D. Massachusetts Institute of Technology Massachusetts Institute of Technology. Department of Materials Science and Engineering. Massachusetts Institute of Technology. Department of Materials Science and Engineering Materials Science and Engineering. Thesis: S.M., Massachusetts Institute of Technology, Department of Materials Science and Engineering, 2015. Cataloged from PDF version of thesis. In title on title page, "[epsilon] appear as lower case Greek letters. Includes bibliographical references (pages 55-57). High efficiency and fuel flexibility make solid oxide fuel cells (SOFCs) attractive. However, when operating at reduced temperatures, there is significant loss in efficiency, of which slow surface reaction kinetics at the cathode are most responsible. Previously, the mixed ionic and electronic conducting (MIEC) perovskite-structured SrSni-₁₋xFexO₃₋x/₂₊[epsilon] (STF) materials system was identified as a promising candidate for SOFC cathodes given rapid oxygen surface exchange kinetics. The exchange kinetics were correlated with the minority electron charge density in STF, which in turn depends on its defect chemistry and band structure. In this work, an alternate B site host cation, Sn, was selected to replicate and extend the STF studies, due to its distinct band structure and higher electron mobility. Oxygen nonstoichiometry and the defect chemistry of the SrSni-₁₋xFexO₃₋x/₂₊[epsilon] (SSF) system were examined by means of thermogravimetry as a function of oxygen partial pressure in the temperature range of 973-1273 K. Marginally higher reducibility was observed compared to corresponding compositions in STF system. The bulk electrical conductivity was measured in parallel to examine how changes in defect chemistry and electronic band structure associated with the substitution of Ti by Sn impact carrier density and ultimately electrode performance. Bulk chemical expansion was measured by dilatometry as a function of oxygen partial pressure while surface kinetics were examined by means of AC impedance spectroscopy. The electrochemo- mechanical properties of SSF were found not to differ significantly from the corresponding composition in STF. It is believed that Fe dominates the character of the valence and conduction bands and thus governs the electronic properties in SSF. Though slightly shifted by Sn's larger size, the defect equilibria - including the oxygen vacancy concentration - were found to also be largely dominated by Fe and thus differed only in a limited way from that in STF. Key thermodynamic parameters of SrSn₀.₆₅Fe₀.₃₅O₂ ₈₂₅₊ SSF35 obtained include the reduction enthalpy (4.30 eV) the electronic band gap (1.72 eV) and the anion Frenkel enthalpy (0.52 eV). Key kinetic parameters include the migration enthalpy of oxygen vacancies (0.70 eV), the activation energy of area-specific-resistance (1.65 eV) and the electron (0.0002±0.00005 cm²/V-s) and hole (0.0037±0.0015 cm²/V-s) mobilities. With the surface exchange rate nearly identical to the STF35 counterpart, the main advantage of SSF35 as a SOFC electrode would be its enhanced chemical stability and slower degradation. by Chang Sub Kim. S.M. 2016-03-03T21:09:09Z 2016-03-03T21:09:09Z 2015 2015 Thesis http://hdl.handle.net/1721.1/101562 940570333 eng M.I.T. theses are protected by copyright. They may be viewed from this source for any purpose, but reproduction or distribution in any format is prohibited without written permission. See provided URL for inquiries about permission. http://dspace.mit.edu/handle/1721.1/7582 57 pages application/pdf Massachusetts Institute of Technology
spellingShingle Materials Science and Engineering.
Kim, Chang Sub, Ph.D. Massachusetts Institute of Technology
Electro-chemo-mechanical Studies of Perovskite-Structured Mixed Ionic-Electronic Conducting SrSni-₁₋xFexO₃₋x/₂₊[epsilon]
title Electro-chemo-mechanical Studies of Perovskite-Structured Mixed Ionic-Electronic Conducting SrSni-₁₋xFexO₃₋x/₂₊[epsilon]
title_full Electro-chemo-mechanical Studies of Perovskite-Structured Mixed Ionic-Electronic Conducting SrSni-₁₋xFexO₃₋x/₂₊[epsilon]
title_fullStr Electro-chemo-mechanical Studies of Perovskite-Structured Mixed Ionic-Electronic Conducting SrSni-₁₋xFexO₃₋x/₂₊[epsilon]
title_full_unstemmed Electro-chemo-mechanical Studies of Perovskite-Structured Mixed Ionic-Electronic Conducting SrSni-₁₋xFexO₃₋x/₂₊[epsilon]
title_short Electro-chemo-mechanical Studies of Perovskite-Structured Mixed Ionic-Electronic Conducting SrSni-₁₋xFexO₃₋x/₂₊[epsilon]
title_sort electro chemo mechanical studies of perovskite structured mixed ionic electronic conducting srsni ₁₋xfexo₃₋x ₂₊ epsilon
topic Materials Science and Engineering.
url http://hdl.handle.net/1721.1/101562
work_keys_str_mv AT kimchangsubphdmassachusettsinstituteoftechnology electrochemomechanicalstudiesofperovskitestructuredmixedionicelectronicconductingsrsni1xfexo3x2epsilon