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 Ba_0.95La_0.05(Fe_1−xY_x)O_3−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 time-of-flight 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⁻¹ with an 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⁻¹ with activation energies of 0.9–1 eV. The consequences of these conductivities for the kinetics of porous triple-conducting oxygen electrodes on protonic electrolytes are discussed. Importantly, both the proton and vacancy conductivity contribute to extending the active zone for the O₂ ↔ H₂O reaction.