Systematic evaluation of Co-free LnBaFe2O5+δ (Ln = Lanthanides or Y) oxides towards the application as cathodes for intermediate-temperature solid oxide fuel cells

Co-free oxides with a nominal composition of LnBaFe(2)O(5+delta), where Ln = La, Pr, Nd, Sm, Gd, and Y, were synthesized and phase structure, oxygen content, electronic conductivity, oxygen desorption, thermal expansion, microstructure and electrochemical performance were systematically investigated. Among the series of materials tested, LnBaFe(2)O(5+delta) oxide showed the largest electronic conductivity and YBaFe2O5+delta oxide had the smallest thermal expansion coefficient (TEC) of 14.6 x 10(-6) K-1 within a temperature range of 200-900 degrees C. All LnBaFe(2)O(5+delta) oxides typically possess the TEC values smaller than 20 x 10(-6) K-1. The oxygen content, electronic conductivity and TEC values are highly dependent on the cation size of the Ln(3+) dopant. The lowest electrode polarization resistance in air under open circuit voltage condition was obtained for SmBaFe2O5+delta electrode and was approximately 0.043, 0.084, 0.196, 0.506 and 1.348 Omega cm(2) at 800, 750, 700, 650 and 600 degrees C, respectively. The SmBaFe2O5+delta oxide also demonstrated the best performance after a cathodic polarization. A cell with a SmBaFe2O5+delta cathode delivered peak power densities of 1026, 748, 462, 276 and 148 mW cm(-2) at 800, 750, 700, 650 and 600 degrees C, respectively. The results suggest that certain LnBaFe(2)O(5+delta) oxides have sufficient electrochemical performance to be promising candidates for cathodes in intermediate-temperature solid oxide fuel cells. (C) 2012 Elsevier Ltd. All rights reserved.