(468a) Mathematical Modeling and Steady-State Analysis of a Hybrid Solid Oxide Fuel Cell

Electrolytes in solid oxide fuel cells (SOFCs) are typically based on stabilized  zirconia, which has good oxygen-anion conductivity at high temperatures [1].  One disadvantage of this type of fuel cells is their high operation temperature. Many efforts are currently being made to develop novel lower temperature SOFCs that use electrolytes with high conductivity at intermediate temperatures. Among these electrolytes are the ones that have high proton conductivity at low temperatures between 600-800°C [2] or have mixed proton and oxygen ion conductivity in the temperature range of 600-1000°C [1, 3].

In this study, a mathematical model of a SOFC based on BaCe _1-xSm _xO _3-α and two platinum electrodes are developed. This type of electrolytes exhibit both proton and oxygen anion conductivity [4]. In the modeling, heat transfer, mass transfer and electrochemical processes are taken into account. The model is then validated using the experimental data reported in [1]. The existence of steady-state multiplicity in this type of fuel cells is investigated under three modes of constant ohmic load, potentiostatic and galavanostatic operations. The cell shows up to three steady states under constant ohmic load and potentiostatic modes. Under galvanostatic mode, the cell exhibits a unique steady state, as in oxygen-ion conducting SOFCs [5].The effects of changes in the heat convection coefficient and the inlet fuel and air flow rates on the multiplicity are studied. The increase in the heat convection coefficient shifts the multiplicity region to lower values of load resistance and cell voltage in the constant ohmic load and potentiostatic modes, respectively. Interestingly, this study shows that thermal and concentration multiplicities can coexist. Ignition in the solid temperature is accompanied by extinction in the reactant concentrations and ignition in the product concentration.

References:

[1] H. Iwahara, T. Yajima, T. Hibino, H. Ushida, Journal of the Electrochemical Society, 140 (1993) 1687.

[2] H. Iwahara, Solid State Ion., 28 (1988) 573-578.

[3] N. Bonanos, Journal of Physics and Chemistry of Solids, 54 (1993) 867-870.

[4] H. Iwahara, H. Uchida, K. Morimoto, Journal of the Electrochemical Society, 137 (1990) 462.

[5] M. Mangold, M. Krasnyk, K. Sundmacher, J. of Applied Electrochemistry 36(3) (2006),  265-275.