MORPHOLOGICAL AND ELECTROCHEMICAL MODELING OF SOFC COMPOSITE CATHODES WITH DISTRIBUTED POROSITY

Description

A steady-state mathematical model of charge and mass transport and electrochemical reaction in porous composite cathodes for solid oxide fuel cell application is presented. The model, based on local mass and charge balances, describes the domain as a continuum, characterizing kinetics as well as mass and charge transport using effective properties, related to cathode microstructure and material properties by percolation theory. The distribution of morphological properties along the electrode thickness, as experimentally observed on scanning electron microscope images of the samples investigated, is taken into account. This feature allows the model to reproduce the dependence of electrode thickness and oxygen partial pressure on polarization resistance in the range 600-850 °C. It is found that for cathodes made of strontium-doped lanthanum manganite (LSM) and yttria-stabilized zirconia (YSZ), the exchange current, which represents the kinetic constant of the oxygen reduction reaction, follows an Arrhenius behavior with respect to the temperature and it is dependent on the square root of the oxygen partial pressure.

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