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A three-dimensional numerical simulation of the solid oxide fuel cell ͑SOFC͒ anode overpotential is conducted in a microstructure which is reconstructed by dual-beam focused ion beam-scanning electron microscopy ͑FIB-SEM͒. Gaseous, ionic, and electronic transport equations are solved by a lattice Boltzmann method with electrochemical reaction at the three-phase boundary. The predicted anode overpotential agrees with the experimental data at the fuel supply of 1.2% H 2 O-98.8% H 2 , while it is larger than the data at 10% H 2 O-90% H 2 . The dependence of exchange current density on steam partial pressure, gas diffusion modeling, as well as computational domain size must be further investigated in the future. Local three-dimensional distributions of electrochemical potential and current density inside the anode microstructure are obtained. Their nonuniformities are attributed to the scattered three-phase boundaries and complex transport paths through the solid phases.Solid oxide fuel cell ͑SOFC͒ is anticipated to play a major role in future energy utilization because of its superior efficiency and fuel flexibility. 1 However, its cost effectiveness and durability must be further improved before market introduction. The electrode microstructure has significant effects on the cell performance and durability of SOFCs. Thus, a basic understanding of the microscopic features of the electrode is indispensable. Quantitative investigations that relate the electrode microstructural parameters obtained from two-dimensional images and the polarization resistances have been reported. Wilson and Barnett 2 related anode polarization resistances to the three-phase boundary ͑TPB͒ densities of Ni-yttria-stabilized zirconia ͑YSZ͒ active layers by means of stereology. Shikazono et al. 3 also used stereology as well as the concept of contiguity theory to investigate the relationship between polarization characteristics and microstructural parameters such as TPB length and effective conductivities. However, a random mixture is assumed in stereology and the concept of contiguity theory, which has to be validated for further investigation. Furthermore, dead ends of the phases and electrochemically inactive TPBs should be rationally removed to quantitatively discuss the effects of microstructure on polarization characteristics. To overcome these issues, it is necessary to establish a method that can directly predict the polarization resistance in the real three-dimensional ͑3D͒ microstructure.Recently, direct measurements of a 3D SOFC electrode microstructure have been carried out using focused ion beam-scanning electron microscopy ͑FIB-SEM͒ 4-10 and X-ray computed tomography ͑XCT͒. 11 As a result, useful quantitative data such as TPB length and tortuosity factor are obtained from the reconstructed 3D microstructures. However, difficulty remains in removing errors that arise from a discretization process and insufficient sample volume size. 9,10,12 In addition to the above experimental studies, numerical simulations have the possibility ...

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Three-dimensional microstructure of a conventional Ni-8YSZ anode is quantified by means of dual beam FIB-SEM system equipped with EDX. The microstructure of the anode is virtually reconstructed in a computational field using a series of two-dimensional SEM images acquired. Three-phase-boundary (TPB) density and tortuosity factors are carefully evaluated applying two different evaluation methods to each parameter. TPB density is evaluated by volume expansion method and centroid method, while tortuosity factor is evaluated by Lattice Boltzmann Method calculation and by random walk approach. The estimations of each parameter by two methods match well each other showing the reliability of analyzing methods proposed in this study.