Importance of anode microstructure in modeling solid oxide fuel cells

A one-dimensional button-cell model is developed and applied to explore the influence of anode microstructure on solid oxide fuel cell (SOFC) performance. The model couples porous-media gas transport and elementary electrochemical kinetics within a porous Ni-yttria-stabilized zirconia (YSZ) cermet anode, a dense YSZ electrolyte membrane, and a composite lanthanum strontium manganite (LSM)-YSZ cathode. In all cases the fuel is humidified H-2 and air is the oxidizer. The effects of porosity, tortuosity, and other microstructural geometric factors are evaluated with respect to their overpotential contributions. The model is used to assist interpretation of the experimental results reported by Zhao and Virkar [J. Power Sources, 141, 79 (2005)]. The model results indicate that a correct formulation of concentration-gradients' dependence on tortuosity in porous electrodes provides a means for fitting the experimental data with reasonable support-layer tortuosity values (< 5.0). Further, the fitting results indicate that there must be a physically reasonable negative correlation between support-layer porosity and tortuosity. The results also show that reducing anode porosity, which increases mass-transfer resistance, can significantly increase the thickness of the electrochemically active region. These results indicate the importance of incorporating detailed chemistry and distributed reaction zones to evaluate the design and performance of SOFC membrane electrode assemblies. (C) 2008 The Electrochemical Society.