Development of a Multiscale SOFC Model and Application to Axially-Graded Electrode Design

A multiscale model is built to understand how microscale characteristics and the thermo‐chemical and electrochemical phenomena, occurring in the electrode and electrolyte assembly, may affect the overall performance of a solid oxide fuel cell (SOFC) stack. This study presents the integration of two‐dimensional finite volume models: a 1D microscale model and a 1D (or 2D) macroscale (channel/cell) model. The new tool is calibrated against the experimental data of a short‐stack via a numerical procedure aiming at the minimisation of the mean square deviation of the model from the measured data. Subsequently, the distribution of electrochemical active thickness in a state‐of‐the‐art solid oxide cell channel is calculated; the result is limited between 3% and 7% of the electrode thickness. An axially graded electrode is studied by changing the particle radii in order to locally control the triple phase boundary length distribution along the cell channel. The performances of a four‐section graded electrode is estimated in comparison to a reference non‐graded electrode. The average current density increases by approximately 6% in the short‐stack. If such a graded design was introduced into a state‐of‐the‐art cogeneration system, the extrapolation of these results suggests that a power output increase up to 13.5% is attainable.