Evaluation of Ba0.6Sr0.4Co0.9Nb0.1O3-δ mixed conductor as a cathode for intermediate-temperature oxygen-ionic solid-oxide fuel cells

A perovskite-type Ba0.6Sr0.4Co0.9Nb0.1O3-delta (BSCN) oxide is investigated as the cathode material of oxygen-ionic solid-oxide fuel cells (SOFCs) with Sm0.2Ce0.8O3-delta (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 degrees C. The results of thermal-expansion and electrical conductivity measurements indicate the introduction of Ba2+ into the A-site of SrCo0.9N0.1O3-delta (SCN) led to a decrease in the thermal-expansion coefficient (TEC) and electrical conductivity of the compound. A TEC of 14.4 x 10(-6) K-1 is observed for BSCN within a temperature range of 200-500 degrees 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 Omega cm(-2) is achieved for BSCN cathodes at 600 degrees C based on symmetric cells test. Peak power density of similar to 1150 mW cm(-2) is reached for a thin-film electrolyte cell with BSCN cathode at 600 degrees C, which is higher than a similar cell with SCN cathode (similar to 1008 mW cm(-2)). BSCN is a promising cathode material for oxygen-ionic IT-SOFCs. (C) 2010 Elsevier B.V. All rights reserved.