Numerical modeling of ceria-based SOFCs with bi-layer electrolyte free from internal short circuit: Comparison of two cell configurations

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A numerical model for ceria-based solid oxide fuel cells (SOFCs) with bi-layer electrolyte is proposed to evaluate the internal short circuit by the comparison of two cell configurations: the electronic barrier electrolyte adjacent to cathode and anode, respectively. In this model, the activation polarization of the electrode reaction and the charge transport of the electrolyte with both n/p-type electronic and oxygen ion conductivity are considered. The activation polarization and the charge transport are described by the Butler-Volmer equation and the Nernst-Planck equation, respectively. Parametric simulations are performed to compare the two bi-layer electrolyte configurations in terms of the open circuit voltage, I–V relationship, leakage current density, power density at 0.7V, oxygen partial pressure distribution and electrochemical efficiency as functions of the temperature and thickness ratio of the electronic barrier electrolyte. From our modeling results, the cell configuration of which the barrier electrolyte is adjacent to cathode has significant p-type leakage current, leading to the lower open circuit voltages and electrochemical efficiency than the other one. The oxygen partial pressure distribution under the open circuit displays the “S” type in the barrier layer, which is related to the change of the n/p-type conductivity of the barrier layer. Besides, the activation polarization greatly influences the open circuit voltage and the oxygen partial pressure distribution between boundaries of electrolytes under open circuit. It is also found that the thickness ratio of the electronic barrier electrolyte can be optimized to maximize the electrochemical performance by balancing the open circuit voltage and ohmic polarization loss.