Ion transport in dry and hydrated Ba0.95La0.05(Fe1-xYx)O3-δ and implications for oxygen electrode kinetics of protonic ceramic cells

Abstract

The ion transport of triple-conducting Ba0.95La0.05(Fe1-xYx)O3-δ perovskites (x=0 and 0.2) containing mobile protons, oxygen vacancies and electron holes is investigated. Proton diffusion coefficients are determined from hydration with D2O and secondary ion mass spectroscopy line scans, the oxygen vacancy conductivity is measured in an oxygen pumping cell. Oversized Y3+ dopants on the Fe site are found to decrease the effective proton as well as oxygen vacancy mobility. At 300-500 °C in 20 mbar H2O, the proton conductivity amounts to 3∙10-6 to 10-4 S/cm (activation energy 0.3 eV for x=0, and 0.5 eV for x=0.2), the vacancy conductivity covers a larger range of 3∙10-6 to 10-2 S/cm with activation energies of 0.9-1 eV. The consequences of these conductivities for the kinetics of porous oxygen electrodes on protonic electrolytes are discussed. Importantly, both the proton and vacancy conductivity contribute to extend the active zone for the O2 <-> H2O reaction.