Quantification of Ni-YSZ Anode Microstructure Based on Dual Beam FIB-SEM Technique

Abstract

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.

Connected Three-Phase Boundary Length Evaluation in Modeled Sintered Composite Solid Oxide Fuel Cell Electrodes

“…Furthermore, calculation of the total and connected TPBL from the identified three-phase boundary ͑TPB͒ voxels requires verification with well-defined test cases to validate the algorithm because the true values are not known a priori in real electrodes. Iwai et al 16 have recently described two methods for determining TPBL of FIB-SEM reconstructed anodes and found that comparable results are obtained for electrode structures having a characteristic length ͑e.g., particle or pore size͒ discretized by approximately 10 voxels.…”

“…For example, Wilson et al 14 modified the Tanner-Fung-Virkar model 15 to include phase connectivity and tortuosity obtained from reconstruction of La 0.8 Sr 0.2 MnO 3 -Y 2 O 3 -stabilized ZrO 2 ͑YSZ͒ cathodes, improving the agreement between measured and calculated polarization resistance. The development of electrode performance models that make direct use of 3D microstructural models 3,9,11,16 rather than volume averaged properties may provide further insight into the relationships between electrode performance and material composition and microstructure at the cost of increased computation time.…”

Quantifying Percolated Triple Phase Boundary Density and Its Effects on Anodic Polarization in Ni-Infiltrated Ni/YSZ SOFC Anodes

“…The resulting labeled volume was analyzed in Python using an inhouse program. TPBs were isolated with the commonly-used volume expansion method, 7 and particle sizes were quantified with the intercept method, as described by Lee. 15 Since the particles are assumed to be spherical, a stereographic coefficient of 1.5 is incurred, and multiplied by every calculated size.…”

“…While this infiltration technique has been shown to improve anode performance at low temperatures, the complexity of the infiltrated microstructure and interplay of various catalytic processes in the anode, including ion conduction, gas transport, and reactions at the TPBs, have made it difficult to precisely explain these performance improvements. Advanced microstructural characterization techniques such as 3-D reconstruction have been used in detailed investigations of anode microstructure, [7][8][9] anode degradation, 10 the microstructure of MIEC-infiltrated electrodes, 11 and the microstructure of LSM-infiltrated YSZ electrodes. 12 This work builds on these previous analyses by using 3-D reconstruction in combination with other characterization techniques to estimate TPB density in Ni infiltrated Ni-YSZ anodes.…”

Electrode Reconstruction by FIB/SEM and Microstructure Modeling

“…resolution in z-direction). Generally the resolution of the SEM images and the slicing resolution differ from each other (4,5,7,13). This can be readjusted by applying a re-sample step on the FIB/SEM data.…”