CHAPTER 8:Three‐Dimensional Numerical Modelling of Ni‐YSZ Anode

A three-dimensional numerical simulation of the anode overpotential is conducted in a microstructure which is reconstructed by a dual-beam focused ion beam-scanning electron microscope. Gaseous, ionic and electronic transport equations are solved by a lattice Boltzmann method with electrochemical reaction at the three-phase boundary. The effects of reconstructed sample volume size on the three phase boundary length, tortuosity factors and overpotential are first evaluated. The YSZ tortuosity factor became nearly constant for the samples with the cross-sectional area larger than approximately 200 μm2, whilst the pore tortuosity factor is almost independent of the sample volume size. On the other hand, the Ni tortuosity factor shows very large variation regardless of the sample volume size. Two exchange current models based on patterned electrodes are assessed. However, both models gave weaker dependence on the steam concentration than the experimental data. From the predicted three-dimensional current stream lines, it is found that the mirrored computational structure gives a thinner reactive layer because of the factitious connection of Ni phase. Thus, it is recommended to use larger volume size samples which can cover whole reactive thickness when discussing the local potential and flux distributions.