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dc.contributor.advisorRamanathan, Shriram
dc.contributor.authorKerman, Kian
dc.date.accessioned2014-06-06T21:04:26Z
dc.date.issued2014-06-06
dc.date.submitted2014
dc.identifier.citationKerman, Kian. 2014. Ultra-thin solid oxide fuel cells: materials and devices. Doctoral dissertation, Harvard University.en_US
dc.identifier.otherhttp://dissertations.umi.com/gsas.harvard:11418en
dc.identifier.urihttp://nrs.harvard.edu/urn-3:HUL.InstRepos:12274563
dc.description.abstractSolid oxide fuel cells are electrochemical energy conversion devices utilizing solid electrolytes transporting O2- that typically operate in the 800 - 1000 °C temperature range due to the large activation barrier for ionic transport. Reducing electrolyte thickness or increasing ionic conductivity can enable lower temperature operation for both stationary and portable applications. This thesis is focused on the fabrication of free standing ultrathin (<100 nm) oxide membranes of prototypical O2- conducting electrolytes, namely Y2O3-doped ZrO2 and Gd2O3-doped CeO2. Fabrication of such membranes requires an understanding of thin plate mechanics coupled with controllable thin film deposition processes. Integration of free standing membranes into proof-of-concept fuel cell devices necessitates ideal electrode assemblies as well as creative processing schemes to experimentally test devices in a high temperature dual environment chamber. We present a simple elastic model to determine stable buckling configurations for free standing oxide membranes. This guides the experimental methodology for Y2O3-doped ZrO2 film processing, which enables tunable internal stress in the films. Using these criteria, we fabricate robust Y2O3-doped ZrO2 membranes on Si and composite polymeric substrates by semiconductor and micro-machining processes, respectively. Fuel cell devices integrating these membranes with metallic electrodes are demonstrated to operate in the 300 - 500 °C range, exhibiting record performance at such temperatures. A model combining physical transport of electronic carriers in an insulating film and electrochemical aspects of transport is developed to determine the limits of performance enhancement expected via electrolyte thickness reduction. Free standing oxide heterostructures, i.e. electrolyte membrane and oxide electrodes, are demonstrated. Lastly, using Y2O3-doped ZrO2 and Gd2O3-doped CeO2, novel electrolyte fabrication schemes are explored to develop oxide alloys and nanoscale compositionally graded membranes that are thermomechanically robust and provide added interfacial functionality. The work in this thesis advances experimental state-of-the-art with respect to solid oxide fuel cell operation temperature, provides fundamental boundaries expected for ultrathin electrolytes, develops the ability to integrate highly dissimilar material (such as oxide-polymer) heterostructures, and introduces nanoscale compositionally graded electrolyte membranes that can lead to monolithic materials having multiple functionalities.en_US
dc.description.sponsorshipEngineering and Applied Sciencesen_US
dc.language.isoen_USen_US
dash.licenseLAA
dc.subjectMaterials Scienceen_US
dc.subjectGDCen_US
dc.subjectionic conductoren_US
dc.subjectmembraneen_US
dc.subjectsolid oxide fuel cellen_US
dc.subjectthin film oxideen_US
dc.subjectYSZen_US
dc.titleUltra-thin solid oxide fuel cells: materials and devicesen_US
dc.typeThesis or Dissertationen_US
dash.depositing.authorKerman, Kian
dc.date.available2014-06-06T21:04:26Z
thesis.degree.date2014en_US
thesis.degree.disciplineEngineering and Applied Sciencesen_US
thesis.degree.grantorHarvard Universityen_US
thesis.degree.leveldoctoralen_US
thesis.degree.namePh.D.en_US
dc.contributor.committeeMemberSpaepen, Fransen_US
dc.contributor.committeeMemberAziz, Mikeen_US
dc.contributor.committeeMemberClarke, Daviden_US
dash.contributor.affiliatedKerman, Kian


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