CORRELATED RESISTOR NETWORK STUDY OF POROUS SOLID OXIDE FUEL-CELL ANODES

A resistor network model is developed for solid oxide fuel cell (SOFC) composite anodes, in which solid electrolyte grains, metal particles, and pores are considered on the same footing. The model is studied by a Monte Carlo simulation on a face-centered cubic lattice, with a ran dom distribution of the three components over the lattice sites. The c oncept of active bonds is used; the bond between a metal and an electr olyte site is conductive (reaction-active) if the sites belong to clus ters connected to the solid-electrolyte membrane or metal current coll ector, respectively, and if the bond has at least one neighbor site wh ich is a part of a pore cluster connected with the fuel supplying gas channels. Active bonds are characterized by an elementary reaction res istance, inactive bonds are blocking. The total inner resistance of th e anode is calculated as a function of composition and the elementary reaction resistance, R-r, vs. ion transport resistance, R-e (of a ''bo nd'' between two solid-electrolyte grains). Compositions which provide the lowest inner resistance for a given R-r/R-e ratio are revealed. A cross-the-sample distribution of the current through the three-phase b oundary is investigated. The higher the R-r/R-e, ratio, the larger are as of the three-phase boundary are used; however if the ratio is low, the reaction occurs only very close to the anode /membrane interface t o avoid ion transport limitations. A scaling law for the reaction pene tration depth inside the anode, N-f proportional to(R-r/R-e)(beta) (wh ere beta less than or equal to 0.5) is suggested in accordance with th e Monte Carlo results. In line with the existing experimental data, th e simulation and scaling estimates reveal the interplay between the re action penetration depth and the anode thickness, which determines the thickness effect-on the inner resistance.