An equivalent circuit model is developed for interpreting the behavior of a fuel cell based on a BaZr_0.1Ce_0.7Y_0.1Yb_0.1O_3-δ (BZCYYb)-NiO anode-supported thin Sm-doped ceria (SDC) electrolyte.  The reason behind the high open cell voltage and high peak power density of the cell are explained using the proposed circuit, which facilitated the separation of the polarization processes and the corresponding characteristic frequencies, especially those for oxygen ion diffusion through the interlayer at the anode/electrolyte interface. Theoretical analysis and data fitting based on the presented circuit model indicate that the inter-diffusion layer between Ni-BZCYYb and SDC effectively suppresses electronic conduction while maintaining the catalyst activity and ionic conductivity. More importantly, careful analysis of the characteristic frequencies offers a powerful approach to assigning a specific part of the impedance data (e.g., an impedance arc or loop) to the corresponding physicochemical process. Further, any change in the characteristic frequency for a physicochemical process also reflects a change in the inherent nature of that process under the testing conditions. Once validated by more experimental results under a broader range of testing conditions, the presented equivalent circuit model, in turn, maybe used to predict fuel cell performances and optimize the operating conditions.

Key words: Solid oxide fuel cell; Mixed conductor; Impedance spectroscopy; Equivalent circuit