Solid oxide fuel cells ! SOFCs are efficient, environmentally friendly, and fuel-flexible electrochemical devices for the generation of electrical power and heat. They consist of three basic layers: cathode, electrolyte, and anode. The cathode is a porous, conductive catalyst for the reduction of O2 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 is 2 O2 +V o ·· +2 e! =O o x ! 1 Current 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. 2-4 In this initial study a dual-beam focused ion beam/scanning electron microscope ! was utilized to reconstruct an actual three-dimensional ! model of a La0.8Sr0.2Co0.2Fe0.8O3! ! ! LSCF cathode and its interface with a dense yttrium-stabilized zirconia ! YSZ 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. 7-11 With the advent of 3D modeling software, nanotomography utilizing the dual-beam FIB/SEM technique was used to quantify nanoceramic suspended powders. 10-12 This technique was applied to SOFC cermet anodes to quantify microstructural properties such as porosity, triple-phase-boundary ! TPB 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.