Stress analysis of solid oxide fuel cell anode microstructure reconstructed from focused ion beam tomography

The degradation and ultimately lifetime of solid oxide fuel cells (SOFCs) is determined in part by the stresses generated within the different layers of the device. For fully dense materials such as the electrolyte, when modelling these stresses on a macro-scale the material properties can be considered to be homogeneous (evenly distributed) allowing the prediction of volume average stresses due to differential thermal expansion in the layer. However, detailed stress analysis of real. multiphase porous layers such as those found in SOFC electrodes, on the micron and sub-micron scale has not been possible to date as detailed geometry and convenient methods to generate a finite element model have not been available. In this paper we present work that combines microstructural characterisation of a porous solid oxide fuel cell anode with three dimensional stress analysis to inspect the stresses within the individual phases of the anode, and at phase boundaries. The electrode microstructure has been characterised using focused ion beam (FIB) tomography and the resulting microstructure used to generate a solid mesh of three dimensional tetrahedral elements. A temperature field was applied to simulate the heating of the sample from room temperature (298 K) to operating temperature (1073 K). The maximum principal stress in the nickel phase was found to exceed the yield strength, while the minimum principal stress in the yttria-stabilized zirconia (YSZ) phase was found to exceed the characteristic strength of that volume of YSZ, indicating that the probability of failure of the YSZ matrix is significant. (C) 2011 Elsevier B.V. All rights reserved.