A numerical methodology for evaluating the three-phase boundary length ͑TPBL͒ in sintered composite solid oxide fuel cell electrodes is developed. Three-dimensional models of a representative volume element of sintered composite electrodes are generated for which the mean particle diameter, composition, and total porosity may be specified as input parameters. Tomographic methods are used to reconstruct the modeled electrode and the percolation for each phase is evaluated. The connected TPBL is calculated for a range of electrode designs and comparisons are made with calculated TPBL values available in the literature. The maximum connected TPBL occurred at a porosity of 0.21 and at equal solid volume fractions of ionic and electronic conducting phases for particles having the same mean diameter and particle size variance. A cubic envelope having a minimum length of 14 times the mean particle diameter was necessary to adequately represent the electrode structure.Design and fabrication of solid oxide fuel cell ͑SOFC͒ electrodes require careful attention to the relationships between electrode performance and both material composition and microstructure. One method of gaining insight into these relationships is the development of detailed three-dimensional ͑3D͒ electrode geometry models, either numerically 1-6 or by constructing representations of real electrodes using methods such as focused ion beam-scanning electron microscopy ͑FIB-SEM͒ 7-10 or X-ray computed tomography ͑XCT͒. 11,12 Key microstructural parameters such as the connected three-phase boundary length ͑TPBL͒ density 1,4 and effective transport properties such as electronic and ionic conductivities and gas diffusivity 13 can be extracted from the resulting geometrical models. These volume averaged properties can then be used in continuum electrode models for electrochemical performance evaluation. 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.Numerical generation of electrode microstructure models and the digital reconstruction of electrodes each have advantages and disadvantages pertaining to the elucidation of electrode structureperformance relationships. Numerical generation of electrode structures allows comparatively rapid evaluation of a wide range of electrode parameters. The resulting structures are deterministic in the sense that microstructural parameters such as the total TPBL can be determined analytically. However, the connectivity of the pore space is difficult to evaluate due to the presence...

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In multi‐component materials, triple phase boundary (TPB) is the location where reactions occur. A typical example is the TPB encountered in solid oxide fuel cells at the cathode–electrolyte interface. We proposed a tomographic approach that was developed based on serial sectioning using a focused dual ion beam (FIB) system. For image capture, FIB tomography was coupled with scanning electron microscopy, and differentiation of the composite cathode materials was possible through image contrast adjustment. An algorithm, built on the Hoshen–Kopelman theory, was then applied to measure TPB length. The percentage of the connected TPB line was also calculated with the algorithm for 3D computation. © 2011 Canadian Society for Chemical Engineering

A numerical methodology for evaluating the three-phase boundary length in sintered composite electrode layers is developed. Three dimensional models of sintered composite electrodes are generated for which the mean particle diameter, composition, and total porosity may be specified as input parameters. Tomographic methods are used to reconstruct the modeled electrode and the percolation for each phase is evaluated. The connected three-phase boundary length is calculated for a range of electrode designs.