Determination of Charge Carriers in Solid Electrolyte SrCe<SUB>0.95</SUB>Yb<SUB>0.05</SUB>O<SUB>3−δ</SUB> by DC Polarization

Abstract

In order to make clear the conduction mechanism of a new type proton conductive solid electrolyte SrCe0.95Yb0.05O3−δ, DC-polarization characteristics of a hydrogen concentration cell based on this electrolyte were investigated in the temperature range 973-1123 K. The cell was designed to have asymmetrical electrodes; one was reversible for both oxygen and hydrogen, and the other was irreversible for hydrogen. By polarization, only the movement of proton was blocked and the steady-state current due to the sum of the oxygen ion and the positive hole was measured. The current resulted from the migration of oxygen ion was separated from it by measuring the mass of transported oxygen with the volumetric method. Observed oxygen ion and positive hole currents were both negatively dependant on the hydrogen potentials of the reversible electrode. With increasing applied voltage, these currents increase exponentially in the small potential region and linearly in the high potential region. From a comparison between the theoretically derived and the observed voltage-current relationships, the conduction mechanism was examined and the parameters controlling the imperfection equilibria and the value of carrier mobilities were estimated. Based on these values, the partial conductivities and transport numbers of positive hole and oxygen vacancy were evaluated. In the electrolyte equilibrated with air containing 1% water vapour, the transport numbers of positive hole and oxygen vacancy were found to be in the range 0.2-0.6 and 0.01-0.15, respectively. They were found to increase with the temperature and decrease with the hydrogen partial pressure.