Evaluation of Ba_0.6Sr_0.4Co_0.9Nb_0.1O_3-δ mixed conductor as a cathode for intermediate-temperature oxygen-ionic solid-oxide fuel cells

A perovskite-type Ba_0.6Sr_0.4Co_0.9Nb_0.1O_3-δ (BSCN) oxide is investigated as the cathode material of oxygen-ionic solid-oxide fuel cells (SOFCs) with Sm_0.2Ce_0.8O_3-δ (SDC) electrolyte. Powder X-ray diffraction and SEM characterization demonstrate that solid phase reactions between BSCN and SDC are negligible at temperatures up to 1100 °C. The results of thermal-expansion and electrical conductivity measurements indicate the introduction of Ba²⁺ into the A-site of SrCo_0.9N_0.1O_3-δ (SCN) led to a decrease in the thermal-expansion coefficient (TEC) and electrical conductivity of the compound. A TEC of 14.4 × 10^-6 K^-1 is observed for BSCN within a temperature range of 200-500 °C. The chemical diffusion coefficient (D_chem) and surface exchange constant (k_ex) of BSCN and SCN are obtained using an electrical conductivity relaxation technique and BSCN prove to have higher D_chem and k_ex than SCN. An area-specific resistance of 0.1 Ω cm^-2 is achieved for BSCN cathodes at 600 °C based on symmetric cells test. Peak power density of ∼1150 mW cm^-2 is reached for a thin-film electrolyte cell with BSCN cathode at 600 °C, which is higher than a similar cell with SCN cathode (∼1008 mW cm^-2). BSCN is a promising cathode material for oxygen-ionic IT-SOFCs.