Mass transfer in graded microstructure solid oxide fuel cell electrodes

A computational model is presented in which performance of a solid oxide fuel cell with functionally graded electrodes can be predicted. The model calculates operational cell voltages at varying electrode porosity and operational parameters, accounting for losses from mass transport through the porous electrodes, ohmic losses from current flow through the electrodes and electrolyte, and activation polarization. Specifically the physical phenomena that occur when the electrode is designed with a change in microstructure along its thickness are studied. Cell polarizations are investigated to find arrangements for which the minimal polarization occurs. Both diluted hydrogen fuel and partially reformed methane streams with internal reforming are investigated. It is concluded that performance benefits are seen when the electrodes are given an increase in porosity near the electrolyte interface for certain fuels and with satisfactory material properties. Enhanced reformation is observed in high tortuosity structures due to increased gas residence time within the electrode.