Title: Redox cycling of Ni-YSZ anodes for solid oxide fuel cells: influence of tortuosity, constriction and percolation factors on the effective transport properties
Authors : Holzer, Lorenz
Iwanschitz, Boris
Hocker, Thomas
Keller, Lukas
Pecho, Omar
Sartoris, Guido
Gasser, Philippe
Muench, Beat
Published in : Journal of Power Sources
Volume(Issue) : 242
Pages : 179
Pages to: 194
Publisher / Ed. Institution : Elsevier BV
Issue Date: 2013
License (according to publishing contract) : Licence according to publishing contract
Type of review: Not specified
Language : English
Subjects : Map; SOFC
Subject (DDC) : 621.3: Electrical engineering and electronics
Abstract: A methodology based on FIB-tomography and image analysis (IA) is proposed which allows quantification of all relevant morphological features that are necessary to predict effective transport properties in porous SOFC electrodes. These morphological Features are constrictivity, tortuosity, percolation factor and phase volume fraction. An M-factor can then be calculated which represents the ratio of effective over intrinsic conductivities. The methodology is used to describe effects of microstructure degradation in Ni–YSZ anodes which are caused by redox cycling at 950 °C. The so calculated M-factors predict that because of redox cycling the effective electronic conductivity of nickel decreases from 3 to 1.2% which is mainly due to changes of percolation and constriction factors. Based on these results the effective electrical conductivity of nickel is predicted to be 685 S/cm before redox and 243 S/cm after 8 redox cycles. The predictions fit well with the experimental measurements that reveal 600 S/cm before and 200 S/cm after redox cycling at 950 °C. For YSZ the M-factors obtained with 3D-analysis predict that the degradation causes a drop of the effective ionic conductivity from 7 to 0.6%, which is due to a change of the bottleneck dimensions. This finding contradicts the frequent interpretation of YSZ as a ‘rigid backbone’ that is not affected by microstructure degradation. Finally, the effective bulk gas diffusivity increases from 2 to 11% due to an increase of porosity associated with swelling of the anode.
Departement: School of Engineering
Organisational Unit: Institute of Computational Physics (ICP)
Publication type: Article in scientific Journal
DOI : 10.1016/j.jpowsour.2013.05.047
ISSN: 0378-7753
URI: https://digitalcollection.zhaw.ch/handle/11475/1619
Appears in Collections:Publikationen School of Engineering

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