Electrochemical properties of Sr1−xCexMnO3 (0.1≤x≤0.4) - GDC composite cathodes for IT-SOFCs

The electrochemical properties of Sr1−xCexMnO3 (SCM, 0.1≤x≤0.4)-Gd0.2Ce0.8O2−x (GDC) composite cathodes were determined by impedance spectroscopy. The study focused on the doping effect of Ce in the composite cathodes. Single-phase perovskite was obtained for 0.1≤x≤0.3 in SCM. No reaction occurred between the Sr0.7Ce0.3MnO3 electrode and the GDC electrolyte at an operating temperature of 800 °C for 100 h. In the single phase perovskite region, lattice expansion occurred due to the reduction of Mn4+ to Mn3+ at B-sites, and this was attributed to an increase in Ce content. Ce doping enhanced the electrode performance of SCM-GDC composite cathodes, and best electrode performance was achieved for the Sr0.7Ce0.3MnO3-GDC composite cathode (0.93 Ω cm2 and 0.47 Ω cm2 at 750 °C and 800 °C, respectively). The improvement in electrode performance was attributed to increases in charge carriers induced by a shift of some Mn from +4 to +3 and to the formation of surface oxygen vacancies caused by Mn4+ to Mn3+ conversion at high temperatures.