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Open AccessArticle

The Detection of Monoclinic Zirconia and Non-Uniform 3D Crystallographic Strain in a Re-Oxidized Ni-YSZ Solid Oxide Fuel Cell Anode

1
The Electrochemical Innovation Lab, Department of Chemical Engineering, UCL, London WC1E 7JE, UK
2
The Faraday Institution, Quad One, Harwell Science and Innovation Campus, Didcot OX11 0RA, UK
3
Finden Limited, Merchant House, 5 East St Helens Street, Abingdon OX14 5EG, UK
4
Department of Chemistry, University College London, 20 Gordon Street, London WC1H 0AJ, UK
5
National Renewable Energy Laboratory, 15013 Denver W Parkway, Golden, CO 80401, USA
6
Research Complex at Harwell, Rutherford Appleton Laboratory, Harwell Science and Innovation Campus, Didcot OX11 0FA, UK
7
ESRF–The European Synchrotron, 71 Avenue des Martyrs, 38000 Grenoble, France
*
Authors to whom correspondence should be addressed.
Crystals 2020, 10(10), 941; https://doi.org/10.3390/cryst10100941
Received: 28 September 2020 / Revised: 9 October 2020 / Accepted: 13 October 2020 / Published: 16 October 2020
The solid oxide fuel cell (SOFC) anode is often composed of nickel (Ni) and yttria-stabilized zirconia (YSZ). The yttria is added in small quantities (e.g., 8 mol %) to maintain the crystallographic structure throughout the operating temperatures (e.g., room-temperature to >800 °C). The YSZ skeleton provides a constraining structural support that inhibits degradation mechanisms such as Ni agglomeration and thermal expansion miss-match between the anode and electrolyte layers. Within this structure, the Ni is deposited in the oxide form and then reduced during start-up; however, exposure to oxygen (e.g., during gasket failure) readily re-oxidizes the Ni back to NiO, impeding electrochemical performance and introducing complex structural stresses. In this work, we correlate lab-based X-ray computed tomography using zone plate focusing optics, with X-ray synchrotron diffraction computed tomography to explore the crystal structure of a partially re-oxidized Ni/NiO-YSZ electrode. These state-of-the-art techniques expose several novel findings: non-isotropic YSZ lattice distributions; the presence of monoclinic zirconia around the oxidation boundary; and metallic strain complications in the presence of variable yttria content. This work provides evidence that the reduction–oxidation processes may destabilize the YSZ structure, producing monoclinic zirconia and microscopic YSZ strain, which has implications upon the electrode’s mechanical integrity and thus lifetime of the SOFC. View Full-Text
Keywords: X-ray; diffraction; computed tomography; SOFC; fuel cell; anode; microstructure; YSZ; yttria; zirconia; strain X-ray; diffraction; computed tomography; SOFC; fuel cell; anode; microstructure; YSZ; yttria; zirconia; strain
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MDPI and ACS Style

Heenan, T.M.M.; Vamvakeros, A.; Tan, C.; Finegan, D.P.; Daemi, S.R.; Jacques, S.D.M.; Beale, A.M.; Di Michiel, M.; Brett, D.J.L.; Shearing, P.R. The Detection of Monoclinic Zirconia and Non-Uniform 3D Crystallographic Strain in a Re-Oxidized Ni-YSZ Solid Oxide Fuel Cell Anode. Crystals 2020, 10, 941.

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