Modeling mass transfer in solid oxide fuel cell anode: I. Comparison between Fickian, Stefan-Maxwell and dusty-gas models

Fickian, Stefan-Maxwell and dusty-gas model have been widely used in modeling mass transfer in porous electrodes of solid oxide fuel cells. Suwanwarangkul et al. (J. Power Sources 122 (2003) 9-18) implement a survey for performance comparison among these models to predict the concentration overpotential of a solid oxide fuel cell anode. In their work, the flux ratio of species is calculated by Graham's law and contradictorily the equimolar counter transport is used for isobaric assumption. Focused on the flux-ratio approaches and usually neglected pressure gradient, a comparison between Fickian, Stefan-Maxwell and dusty-gas model is done again in this article. The dusty gas model combined with the 'Stoich' flux-ratio approach, i.e. the species flux is dictated by its stoichiometry of the electrochemical reaction, is validated to make the best performance. And all models by the 'Graham' flux-ratio approach, i.e. the flux of species satisfies Graham's law, underestimate the concentration overpotential when the molecular weights of species are quite different. The extended Stefan-Maxwell model is an alternative, although it generally exaggerates the role of Knudsen diffusion. The effect of pore size on the Knudsen diffusion and pressure gradient is also discussed.