Assessment of Ba_0.5Sr_0.5Co_1-yFe_yO_3-δ (y = 0.0-1.0) for prospective application as cathode for IT-SOFCs or oxygen permeating membrane

The influence of iron doping level in Ba_0.5Sr_0.5Co_1-yFe_yO_3-δ (y = 0.0-1.0) (BSCF) oxides on their phase structure, oxygen nonstoichiometry, electrical conductivity, performance as symmetrical cell electrode and oxygen permeating membranes was systematically investigated. A cubic perovskite structure was observed for all the compositions with the presence of iron. The increase of iron doping level resulted in the decrease of the lattice constant, room-temperature oxygen nonstoichiometry, total electrical conductivity, and the increase of area specific resistance (ASR) as cathode with samaria doped ceria electrolyte. However, promising cathode performance with an ASR as low as 0.613 Ω cm² was still obtained at 600 °C for Ba_0.5Sr_0.5FeO_3-δ (BSF). The ceramic membranes composing of BSCF with various iron doping level are all oxygen semi-permeable at elevated temperatures. The increase of iron doping level resulted in the decrease of oxygen permeation flux from J_O2 = 2.28 μmol cm^-2 s^-1 (STP) for Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3-δ (BSCF5582) to ∼0.45 μmol cm^-2 s^-1 (STP) at 900 °C for BSF (y = 1.0) with the same membrane thickness of 1.1 mm, alongside with the change of the rate-determination step from the oxygen surface exchange to the slow oxygen bulk diffusion. The formation of composite oxide with a proper electronic conducting phase and the thin film technology are important for their prospective application as cathode in IT-SOFCs and oxygen permeating membrane, respectively.