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dc.contributor.advisorBirss, Viola
dc.contributor.authorAbhayawardhana, Anusha Dilhani
dc.date2018-11
dc.date.accessioned2018-10-05T21:29:52Z
dc.date.available2018-10-05T21:29:52Z
dc.date.issued2018-09-21
dc.identifier.citationAbhayawardhana, A. D. (2018). Ta-Based Nanostructured Materials for Proton Exchange Membrane Fuel Cells (Unpublished doctoral thesis). University of Calgary, Calgary, AB. doi:10.11575/PRISM/33130en_US
dc.identifier.urihttp://hdl.handle.net/1880/108778
dc.description.abstractThe focus of this work has been to assess the suitability of nanostructured TaOxNy, primarily as nanotubes (NTs), as a catalyst and/or catalyst support material for proton exchange membrane fuel cell (PEMFC) applications. It was found that this n-type material could be switched between an insulating state at > 0.6 V vs RHE to a conducting state at < 0.6 V in both aqueous and organic media. In the conducting state, the redox activity was proposed to be due to the Ta4+/5+ reaction, along with insertion/de-insertion of solution cations. The conductivity switching behavior was correlated with electrochromism, with the NTs being yellow-orange in the oxidized state and blue-black when reduced. TaOxNy was then tested for its activity in catalyzing hydrogen oxidation (HOR) and oxygen reduction (ORR) in acidic medium. Although TaOxNy alone is inactive towards these reactions, the presence of Pt nanoparticles (NPs) changed its behaviour. When deposited on a thin compact TaOxNy film, normal Pt electrochemistry was seen with a ~60 mV⋅decade-1 ORR Tafel slope. When Pt NPs were deposited on TaOxNy NTs, a 105 mV⋅decade-1 ORR Tafel slope was seen attributed to porosity or resistance of the TaOxNy. Both the TaOxNy NTs alone and the Pt NPs/TaOxNy NTs material were found to be very resistant to corrosion under PEMFC operating conditions, evaluated through an in-house accelerated durability test. Further, due to its conductivity switching characteristics, the HOR showed better performance than the ORR, but not as good as for state-of the art Pt/Carbon. Interestingly, some hydrogen oxidation was seen even when TaOxNy is non-conducting, attributed to stabilization of the Ta4+ state in H2. TaOxNy was also anchored on colloid imprinted carbon (CIC) to improve its conductivity and durability. Although the CIC improved the conductivity, all CIC-based materials failed the corrosion accelerated durability tests (ADT). The presence of TaOxNy or N-doping of CIC (N is doped during synthesis) also did not improve the corrosion resistance. Overall, TaOxNy was shown to be a very durable material, resistant to corrosion even at very high anodic potentials. It is also a promising support material for Pt NPs for the catalysis of the HOR, but its conductivity likely needs to be improved further in order to catalyze the ORR.en_US
dc.language.isoeng
dc.rightsUniversity of Calgary graduate students retain copyright ownership and moral rights for their thesis. You may use this material in any way that is permitted by the Copyright Act or through licensing that has been assigned to the document. For uses that are not allowable under copyright legislation or licensing, you are required to seek permission.
dc.subject.classificationEnergyen_US
dc.subject.classificationMaterials Scienceen_US
dc.titleTa-Based Nanostructured Materials for Proton Exchange Membrane Fuel Cells
dc.typedoctoral thesis
dc.publisher.facultyGraduate Studies
dc.publisher.facultyScience
dc.publisher.institutionUniversity of Calgaryen
dc.identifier.doihttp://dx.doi.org/10.11575/PRISM/33130
thesis.degree.nameDoctor of Philosophy (PhD)
thesis.degree.disciplineChemistry
thesis.degree.grantorUniversity of Calgary
dc.contributor.committeememberSutherland, Todd C.
dc.contributor.committeememberShimizu, George K. H.
dc.contributor.committeememberCo, Anne
dc.contributor.committeememberPonnurangam, Sathish
dc.publisher.placeCalgaryen
ucalgary.item.requestcopytrue


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University of Calgary graduate students retain copyright ownership and moral rights for their thesis. You may use this material in any way that is permitted by the Copyright Act or through licensing that has been assigned to the document. For uses that are not allowable under copyright legislation or licensing, you are required to seek permission.