A series of materials based on the perovskite Ln(0.435)Ba(0.145)Sr(0.4)Fe(0.8)Co(0.2)O(3-delta) system (Ln = La1-x-yPrxSmy) has been characterized as intermediate temperature solid oxide fuel cell (IT-SOFC) cathodes. Among the different La, Pr, and Sm combinations, those containing at a time Sm and La or alternatively Pr and La show the lowest polarization resistance values. Within the same substitution degree, praseodymium-based compositions have lower electrode resistance than samarium-based ones. Promising electrode compositions based on different ratios of Pr and La were tested in fully assembled fuel cells, comprising a Ni-yttria-stabilized zirconia (YSZ) anode and a YSZ/gadolinium-doped ceria bilayered electrolyte, and they were compared to a cell with a Pr0.58Sr0.4Fe0.8Co0.2O3-delta cathode. A maximum power density of 0.45 W cm(-2) was achieved at 650 degrees C for the most promising La0.2175Pr0.2175Ba0.145Sr0.4Fe0.8Co0.2O3-delta cathode-based fully assembled fuel cell. A systematic electrochemical study based on electrochemical impedance spectroscopy is shown for the fully assembled cells as a function of pH(2), pO(2), applied current, and operating temperature. (C) 2010 The Electrochemical Society. [DOI: 10.1149/1.3465646] All rights reserved.