Challenges in the electrochemical modelling of solid oxide fuel and electrolyser cells

Computational fluid dynamics (CFD) tools for the modelling of solid oxide fuel cells (SOFC), solid oxide electrolyser cells (SOEC) or solid oxide regenerative fuel cells (SORFC) nearly always require a fitting process prior to its application for cell design or optimisation purposes. In this fitting, a set of experimental data is used to guess the value of those parameters of the model that cannot be either modelled or measured experimentally. This is crucially the case of the charge transfer coefficients (αb,a,αf,a,αb,c,αf,c) and the exchange current densities (io,a,io,c) in the Butler–Volmer equation (i.e. electrochemical model).

The fitting of the electrochemical parameters in the SOFC, SOEC and SORFC modelling literature is reviewed in this work. It is found that this process is only vaguely discussed, if mentioned at all. In the authors׳ opinion, this practice contributes with uncertainty rather than guidance, since this fitting process is of utmost significance for making reliable quantitative predictions.

In this work, we further introduce a comprehensive model for the simulation of solid oxide regenerative fuel cells, i.e. a model that simulates, without any ad hoc adjustments or tuning, both the SOFC and SOEC modes. We also describe in detail how the electrochemical parameters are fitted, and discuss the applicability of the values commonly used in the literature for these fitted parameters and their proper validation. Finally, the validity of the proposed model and fitted parameters is shown by comparison of the numerical results with experimental data.