Equilibration Process in Response to a Change in the Anode Gas Using Thick Sm-Doped Ceria Electrolytes in Solid-Oxide Fuel Cells

Abstract

The electronic conductivity of Sm-doped ceria is very low in air but increases substantially in H2 gas. Conventional models can explain the equilibration processes of yttria-stabilized zirconia electrolytes and thin mixed ionic-electronic conducting electrolytes in response to variations in the fuel composition. However, the equilibration processes of thick samaria-doped ceria electrolytes have not yet been explained. We measured and attempted to explain the equilibration process of a very thick (6.6 mm) samaria-doped ceria electrolyte in response to a change in the anode gas. The measured open-circuit voltage gradually increased to an equilibrium voltage of 0.80 V within 5 min. However, based on the chemical diffusion coefficient equation for the electron diffusion current, the equilibrium time should have been much longer than 5 min. When we assumed a current-independent constant anode voltage loss (0.35 V), the calculations were substantially improved for determining the experimental results.