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DOI: 10.1017/S1431927607073473
Microsc Microanal 13(Suppl 2), 2007
Copyright 2007 Microscopy Society of America
Three-Dimensional Analysis of Solid Oxide Fuel Cells
Using Focused Ion Beam – Scanning Electron Microscopy
Scott Barnett,* James Wilson,* Worawarit Kobsiriphat,* Hsun-Yi Chen,** Roberto Mendoza,**
Jon Hiller,*** Dean Miller,*** Katsuyo Thornton,** Peter Voorhees,* Stuart Adler****
*
Department of Materials Science and Engineering, Northwestern University, Evanston,
IL
**
Department of Materials Science and Engineering, University of Michigan, Ann Arbor,
MI
***
Argonne National Laboratory, Argonne, IL
**** Department of Chemical Engineering, University of Washington, Seattle, WA
Typical solid oxide fuel cell (SOFC) electrodes consist of contiguous electronically and ionically
conducting solid phases in an interconnected porous structure. Quantitatively analyzing this
microstructure remains a key challenge for connecting materials processing with microstructure
and microstructure with electrode performance. A number of macrohomogeneous structural
parameters are needed for use in electrochemical models, including solid and pore volume
fractions, interface areas, tortuosities, and triple-phase boundary lengths (contact lines between
electronically conducting, ionically conducting, and vapor phases).
This paper will describe the application of focused ion beam – scanning electron microscopy for
doing three-dimensional reconstruction of SOFC electrodes, including Ni-YSZ anodes (YSZ =
yttria-stabilized zirconia) and (La,Sr)CoO3 cathodes. The images were collected using a Zeiss
1540XB FIB-SEM. The configuration allows simultaneous collection of a series of 2D crosssectional SEM images as the specimen is sectioned by the FIB along the third axis. The spacing
between consecutive images was usually 40-50 nm, depending on the sample and microstructure.
Typically 50-200 images were collected to produce a total analyzed volume of ~100 µm3.
Different methods for segmentation – i.e. converting images to 3D data sets – were compared in
order to determine the tradeoff between calculation accuracy and analysis time.
Results are described for Ni-yttria-stabilized zirconia (Ni-YSZ) anodes in anode-supported solid
oxide fuel cells (SOFCs) [1]. The SOFCs were made using standard techniques and yielded
performance typical of such cells: e.g. a maximum power density of ≈1.2 W/cm2 at 800°C. The
3D reconstruction data indicates that the Ni, YSZ, and pore phases were very well
interconnected, providing relatively low tortuosity transport paths. Figure 1 shows an image of
the triple-phase boundary lines in a typical anode. The triple-phase boundary (TPB) density
obtained from the 3D reconstruction was 4.28 x 106 m/cm3. This number was found to be
consistent with the measured anode area-specific resistance for this SOFC and independent
measurements of the area specific resistance per unit Ni-YSZ-vapor TPB length [2]. A finiteelement calculation of the gas diffusion through the pore structure of a typical Ni-YSZ active
layer was carried out, yielding a gas-phase tortuosity of ~2.
Single-phase mixed-conducting (La,Sr)CoO3 (LSC) cathodes were also reconstructed to
determine gas, solid, and surface tortuosities, and then correlated with electrochemical test
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http://dx.doi.org/10.1017/S1431927607073473
Microsc Microanal 13(Suppl 2), 2007
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results. Figure 2 shows an example of a 3D cathode image and an image of the interface
between the cathode and a Gd-doped Ceria (GDC) electrolyte.
References
[1]
J. R. Wilson, W. Kobsiriphat, R. Mendoza, H.-Y. Chen, J. M. Hiller, D. J. Miller, K.
Thornton, P. W. Voorhees, S. B. Adler, and S. A. Barnett, Nat. Mater. 5, 541-544 (2006).
[2]
A. Bieberle, L. P. Meier, L. J. Gaukler, J. Electrochem. Soc., 148(6), A646-A656 (2001).
Figure 1. 3D map of the three-phase boundaries in the anode. From Reference [1].
Figure 2. (a) 3D reconstruction of an LSC cathode on a GDC electrolyte, and (b) the interface
between LSC and GDC (black areas represent the LSC/GDC contact areas).
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http://dx.doi.org/10.1017/S1431927607073473