Mixed ionic-electronic conducting electrolytes: Partial currents and defect distribution

Mixed ionic-electronic conductivity in solid electrolytes gives rise to a partial internal electronic short circuit in addition to the normal ionic current. I-V characteristics and electrode overpotentials of fuel cells with mixed conducting Ce0.8Sm0.2O1.9 electrolytes in the temperature range of 873 K to 1073 K are presented. These measurements are used together with electrical conductivity and nonstoichiometry data to calculate the partial ionic and electronic currents inside the electrolyte. The defect distribution across the electrolyte is shown as a function of the fuel cell operating conditions. The ratio of ionic to electronic current can be controlled by the proper choice of electrodes, the electrolyte thickness, and the applied cell voltage.