Understanding and Preventing Ni Oxidation in Ni-YSZ Anode-Supported SOFCs

Young, Jason Lee

Understanding and Preventing Ni Oxidation in Ni-YSZ Anode-Supported SOFCs

atmire.migration.oldid	2018
dc.contributor.advisor	Birss, Viola I.
dc.contributor.author	Young, Jason Lee
dc.date.accessioned	2014-04-17T17:21:49Z
dc.date.available	2014-06-16T07:00:31Z
dc.date.issued	2014-04-17
dc.date.submitted	2014	en
dc.description.abstract	Ni-yttria-stabilized zirconia (YSZ) anode-supported cell architectures are the current state-of-the-art in solid oxide fuel cells (SOFCs), but their lifetime is too short due to sulphur (S) poisoning, coking and deleterious Ni oxidation. The aim of this work was to understand the mechanisms by which Ni oxidation (‘redox cycling’) damages the cell and develop solutions to this problem. It was shown that degradation due to air exposure increases as the temperature was increased from 600 to 900˚C and as pO2 was decreased. The severity of degradation was correlated to the steepness of the NiO gradient in the anode layer. It was also shown that when oxidation is homogeneous in the anode, some NiO particles were pushed out of the air-anode interface. A pre-oxidation cycle, aimed at intentionally forcing NiO out onto the surface, increased the oxidation tolerance at 600˚C from 74% to 80%, but the tolerance at 800˚C was not changed by the process, although the severity of the electrolyte degradation was lowered. Raman spectroscopy was used to quantitatively map the NiO gradient across partially oxidized anodes. It is shown that this technique can quickly and accurately map the NiO distribution through the thickness of a Ni-YSZ anode layer and even showed 20% NiO content in regions of the anode that were not expected to contain any NiO. A reverse bias (a negative bias applied to the Ni-YSZ anode) technique was also used during air exposure to attempt to prevent Ni oxidation. Ex situ microscopy showed that Ni adjacent to the electrolyte is protected preferentially. A new technique, in operando TGA, that allows electrochemical evaluation while concurrently monitoring cell mass was developed. It was shown that the application of > -1.5 V or > -13 mA∙cm-2 to a Ni-YSZ electrode during air exposure (800˚C) can prevent a large fraction of Ni oxidation. It was also demonstrated with in operando TGA that S-define could be removed by an air exposure with a reverse bias applied, although it may be necessary to oxidize the Ni surface in the region of the electrolyte to fully remove the S.	en_US
dc.identifier.citation	Young, J. L. (2014). Understanding and Preventing Ni Oxidation in Ni-YSZ Anode-Supported SOFCs (Doctoral thesis, University of Calgary, Calgary, Canada). Retrieved from https://prism.ucalgary.ca. doi:10.11575/PRISM/28557	en_US
dc.identifier.doi	http://dx.doi.org/10.11575/PRISM/28557
dc.identifier.uri	http://hdl.handle.net/11023/1420
dc.language.iso	eng
dc.publisher.faculty	Graduate Studies
dc.publisher.institution	University of Calgary	en
dc.publisher.place	Calgary	en
dc.rights	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.
dc.subject	Chemistry--Physical
dc.subject.classification	Ni Oxidation	en_US
dc.subject.classification	Solid Oxide Fuel Cells (SOFC)	en_US
dc.subject.classification	Reverse Bias	en_US
dc.subject.classification	Redox Cycling	en_US
dc.subject.classification	Anode-Supported	en_US
dc.subject.classification	Electrolyte Cracking	en_US
dc.title	Understanding and Preventing Ni Oxidation in Ni-YSZ Anode-Supported SOFCs
dc.type	doctoral thesis
thesis.degree.discipline	Chemistry
thesis.degree.grantor	University of Calgary
thesis.degree.name	Doctor of Philosophy (PhD)
ucalgary.item.requestcopy	true