Abstract

In this initial study the electrochemically active region of a La 0.8 Sr 0.2 Co 0.2 Fe 0.8 O 3−␦ ͑LSCF͒ cathode was reconstructed in three dimensions using a focused ion beam/scanning electron microscope. The reconstructed volume totaled 1065 m 3 from the free air surface to the dense yttria-stabilized zirconia electrolyte interface. Various microstructural properties were measured, including overall porosity, closed porosity, graded porosity, surface area, tortuosity, triple-phase boundary length, and pore size. Electrochemical impedance spectroscopy data was correlated to microstructure. © 2007 The Electrochemical Society. ͓DOI: 10.1149/1.2794672͔ All rights reserved. Solid oxide fuel cells ͑SOFCs͒ are efficient, environmentally friendly, and fuel-flexible electrochemical devices for the generation of electrical power and heat.1 They consist of three basic layers: cathode, electrolyte, and anode. The cathode is a porous, conductive catalyst for the reduction of O 2 and for the oxidation of fuel. Between the cathode and anode is the dense electrolyte. The circuit is completed via cathode and anode contacts to an external load.The basic chemical formula for the cathodic reduction reaction isCurrent SOFC performance is limited by cathode polarization, which increases with decreasing operational temperatures. 2,3 Cathode microstructure and morphology have a strong effect on this polarization. [2][3][4] In this initial study a dual-beam focused ion beam/scanning electron microscope ͑FIB/SEM͒ was utilized to reconstruct an actual three-dimensional ͑3D͒ model of a La 0.8 Sr 0.2 Co 0.2 Fe 0.8 O 3−␦ ͑LSCF͒ cathode and its interface with a dense yttrium-stabilized zirconia ͑YSZ͒ electrolyte. This highresolution, 3D technique advances the understanding of the cathode microstructure's effect on performance. The identification of critical microstructural properties such as surface area, tortuosity, and interfacial porosity may be correlated with the ionic, electronic, and catalytic processes for a better fundamental understanding of electrochemical performance. With this tool, SOFC material and microstructural design can be more effective in reducing cathodic polarization at lower operational temperatures.The semiconductor industry has used the FIB since the 1980s to deposit, etch, micromachine, and image specimens during different stages of circuit processing. 5,6 This technology was brought forward to reconstruct 3D, geometrically complex submicrometer structures. [7][8][9][10][11] With the advent of 3D modeling software, nanotomography utilizing the dual-beam FIB/SEM technique was used to quantify nanoceramic suspended powders. [10][11][12] This technique was applied to SOFC cermet anodes to quantify microstructural properties such as porosity, triple-phase-boundary ͑TPB͒ length, and degree of anisotropy via tortuosity.13 Such a technique has never before been applied to reconstruct a cathode and the cathode/ electrolyte interface. ExperimentalSquare LSCF symmetric cell cathodes ͑8 ϫ 8 mm͒ were screen printed using prem...

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The use of in situ analytical electron microscopy for probing nanoscale electrochemistry enables us to understand dynamic changes in the chemistry and structure of bulk materials and interfaces over the course of electrochemical processes. Analytical transmission electron microscopy (TEM) has been used extensively to study electrode materials ex situ in the past. This article describes the use of a novel instrumental system that combines analytical electron microscopy with advanced spectroscopy to probe dynamic phenomena in an all solid-state battery. The intricacies of the experimental set-up are discussed, and the and in-situ results obtained at the nanometer scale are discussed.