Mathematical modeling of the operation of SOFC Nickel-cermet anodes

A surface diffusion–reaction model is developed and solved to describe the steady-state operation of Nickel-cermet anodes in solid oxide fuel cells. The model accounts for the migration (backspillover) and diffusion of oxygen ions from the solid electrolyte onto the nickel surface and the concomitant reaction with the fuel over a finite reaction zone extending from the three-phase boundaries onto the Ni–gas interface. The model is developed for various nickel particle geometries and is compared with existing anode model predictions for flat geometries. The performance of the anode, expressed by an anodic effectiveness factor, is found to depend on two dimensionless numbers, which contain all the operational and structural information of the anode. The model is validated with literature experimental data regarding the dependence of the anode performance on the fuel partial pressure and predicts correctly the observed deviation from linearity of the dependence of cell current on fuel partial pressure.