Additional Voltage Loss to Explain an Equilibration Process in Response to a Change in the Anode Gas Using Sm-Doped Ceria Electrolytes

Abstract

The electronic conductivity of Sm-doped ceria is very low in air and increases substantially under hydrogen gas. We measured the equilibration process using a very thick (6.6 mm) samarium-doped ceria electrolyte in response to a change in the anode gas. The open circuit voltage gradually increased to an equilibrium voltage of 0.80 V within 5 minutes. The time constant was only 1 minute. However, according to Weppner’s approach, the equilibrium time should be much longer than 5 minutes. It is impossible to calculate the open current voltage during equilibration in response to a change in the oxygen activity of the anode gas. With the assumption of a current-independent constant anode voltage loss, the calculation results provided a significantly improved explanation of the experimental results, both quantitatively and qualitatively. Consequently, both Weppner’s approach and Wagner’s equation can coexist with this method. This proposed voltage loss does not contradict the model for very thin films but is necessary for improvement to explain the experimental results. Furthermore, a current-independent constant anode voltage loss is a general topic in electrochemistry and important to explain physical phenomena not only in the area of solid oxide fuel cells.