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.
| Main Author: | |
|---|---|
| Other Authors: | |
| Format: | Thesis |
| Language: | eng |
| Published: |
Massachusetts Institute of Technology
2016
|
| Subjects: | |
| Online Access: | http://hdl.handle.net/1721.1/101562 |
| _version_ | 1826198236691431424 |
|---|---|
| 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. |
| first_indexed | 2024-09-23T11:01:33Z |
| format | Thesis |
| id | mit-1721.1/101562 |
| institution | Massachusetts Institute of Technology |
| language | eng |
| last_indexed | 2024-09-23T11:01:33Z |
| publishDate | 2016 |
| publisher | Massachusetts Institute of Technology |
| record_format | dspace |
| 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 |