Dusty-Gas Model with Uniform Pressure: A Numerical Study on the Impact of a Frequent Inconsistent Assumption in SOFC Electrode Modeling

One of the most popular models adopted to describe the gas transport in porous electrodes is the dusty-gas model. Such a model is commonly applied in the literature under the assumption of uniform pressure. However, as we recently summarized in a short communication [A. Bertei, C. Nicolella, J. Power Sour. 279 (2015) 133-137], this assumption is incompatible with the dusty-gas model formulation and leads to serious inconsistencies, for example, fluxes that do not obey reaction stoichiometry. In such a case the model fails to predict partial pressure profiles, concentration overpotentials and limiting currents.

In this study, we report the quantification of the error in the prediction of partial pressure profiles and concentration overpotential due the inconsistent assumption of uniform pressure in a broad range of conditions, focusing mainly on SOFC anodes. Simulations show that an inconsistent use of the dusty-gas model may lead to relative errors in the prediction of concentration overpotential as large as 60%. In H₂/H₂O/N₂ mixtures, the error increases as the molar fraction of the inert species decreases and is maximum in binary H₂/H₂O mixtures. In addition, the error increases as porosity, pore size and water molar fraction increase while it decreases as the current density and the electrode thickness increase. These results are helpful to quantify the impact of an inconsistent use of the dusty-gas model in the literature and to promote a coherent gas transport modeling.