Electrochemical performance of Nd_0.6Sr_0.4Co_0.5Fe_0.5O_{3- δ}-Ag composite cathodes in intermediate temperature solid oxide fuel cells

The electrochemical performances of Nd_0.6Sr_0.4Co_0.5Fe_0.5 O_3-δ-Ag composite cathodes have been investigated in intermediate temperature solid oxide fuel cells. The Nd_0.6Sr_0.4Co_0.5Fe_0.5 O_3-δ-Ag cathodes prepared by ball milling followed by firing at 920 °C show the maximum performance (power density: 0.15 W cm^-2 at 800 °C) at 3 wt.% Ag. On the other hand, the Nd_0.6Sr_0.4Co_0.5Fe_0.5 O_3-δ-Ag composite cathodes with 0.1 mg cm^-2 (∼0.5 wt.%) Ag that were prepared by an impregnation of Ag into Nd_0.6Sr_0.4Co_0.5Fe_0.5 O_3-δ followed by firing at 700 °C (but the electrolyte-Nd_0.6Sr_0.4Co_0.5 Fe_0.5O_3-δ assembly was prepared first by firing at 1100 °C) exhibit much better performance (power density: 0.27 W cm^-2 at 800 °C) than the composite cathodes prepared by ball milling, despite a much smaller amount of Ag due to a better dispersion and an enhanced adhesion. AC impedance analysis indicates that the Ag catalysts dispersed in the porous Nd_0.6Sr_0.4Co_0.5Fe_0.5 O_3-δ cathode reduce the ohmic and the polarization resistances due to an increased electronic conductivity and enhanced electrocatalytic activity.