Modelling the effects of measured anode triple-phase boundary densities on the performance of micro-tubular hollow fiber SOFCs

The percolated or active triple phase boundary (TPB) length per unit volume of Ni-YSZ anode hollow fibers (HFs) containing 60 wt.% initial NiO and a spatially varying microstructure were measured using a focused ion beam (FIB)-SEM technique. The measured values of contiguous TPB density were interfaced with a 2-D distributed finite element model of a hollow fiber solid oxide fuel cell. The model was applied to simultaneously solve the ionic and electronic charge balances in the electrodes, which were modelled as overlying continuum materials with effective electronic and ionic conductivities. The model was used to predict the effects of anode microstructure on the distribution of current density, and anode activation polarization. Active TPB lengths of 2.63-8.63 mu m(-2) were measured for the anode depending on location in the fiber wall and local microstructure. The effective anode ionic conductivity was predicted to be crucial to spreading the reaction zone from the anode/electrolyte interface toward the anode current collector. For equal TPB distributions, faster electrochemical kinetics was predicted to constrain anode reaction current generation to within a few micrometers of the anode/electrolyte interface. (C) 2009 Elsevier B.V. All rights reserved.