Using a focused ion beam to characterize the microstructure of porous lanthanum strontium manganite (LSM) electrodes A. Chen, J.R.Smith, R. T. DeHoff, and K.S. Jones Department of Materials Science and Engineering, University of Florida, Gainesville, FL 32611 The relationship between the microstructure and electrochemical performance of lanthanum strontium manganite (LSM) /yttria stabilized zirconia (YSZ) solid oxide fuel cells (SOFC) was studied with respect to the isochronal sintering at temperatures between 950°C and 1400°C for times between 1 hour and 6 hours. Previous studies have shown that the performance of this materials system varies tremendously with materials properties and microstructure [1, 2] However, it is not clear how cathode polarization, the major component of the SOFC performance, depends on the different aspects of the microstructure. This study was focused on how two aspects of the microstructure: 1) triple-phase boundary (TPB) length, which represents number density of sites for the charge transfer reaction at the LSM/YSZ interface, and 2) pore area, which determines the area exposed for dissociative adsorption of oxygen, affects the cathode activation polarization. A technique using a dual-beam focused ion beam (FIB) system was developed to automatically slice serial sections of the electrode parallel to the surface and perpendicular to the surface with a narrow (760Å) thickness per slice as shown in FIG 1. Software was used to reconstruct the 3-D pore structure from SEM images of each slice as shown in FIG 2. The homogeneity of the sample was studied by dissector analysis [3] to ensure an unbiased quantification of the cathode microstructure. The line intercept count [4, 5] was used to calculate TPB length per area and pore surface area per volume based on two dimensional sections. Porosity was quantified based on two dimensional images and 3-D pore structure, respectively. The electrochemical property of the sintered LSM cathodes was characterized by electrochemical impedance spectroscopy (EIS) measured in air at various temperatures ranging from 250 ºC to 900 ºC. It was found that TPB length was reduced from 1.41±0.07 um/um 2 to 0.21±0.01 um/um 2 as the 1 hour sintering temperature increased from 950°C to 1400°C, and pore surface area at 1400 ºC was eight times smaller than that at 950 ºC. In addition, cathode activation polarization was reduced with the increasing pore surface area as shown in FIG 3. This study shows that both microstructure evolution and the corresponding changes in cathode polarization changed dramatically above 1200°C. The effect of isothermal sintering at 1200°C on both the cathode microstructure and cathode polarization will be presented. References [1] H. H. Mobius, J. Solid State Electrochem. 1 (1997) 2. [2] M. J. Jorgensen et al., J. Appl. Electrochem. 30 (2000) 411. [3] J.C. Russ, R.T. DeHoff, Practical Stereology, 2nd Edition, Plenum Press, New York, 2000 [4] S.A.Saltykov, Stereometric Metallography, Metallurgizdat,Moscow (1958) [5] C.S.Smith, and L.Guttman:Measurement of Internal Boundaries in Three-Dimensional Structures by Random Sectioning, Trans.AIME,197 (1953) 81 [5] The aid of Jerry Bourne, MAIC at University of Florida is gratefully acknowledged. Microsc Microanal 12(Supp 2), 2006 Copyright 2006 Microscopy Society of America DOI: 10.1017/S1431927606068152 1286 CD https://doi.org/10.1017/S1431927606068152 Downloaded from https://www.cambridge.org/core. IP address: 54.162.69.248, on 14 Jun 2020 at 10:10:57, subject to the Cambridge Core terms of use, available at https://www.cambridge.org/core/terms.