Tailoring dual redox pairs strategy on a defective spinel Mg0.4NixMn2.6-xO4+δ cathode for the boosting of SOFCs performance

The oxygen hopping through oxygen defect site plays an extremely important role in cathode catalysts of solid oxide fuel cells (SOFC) application. Herein, a dual Ni2+/Ni3+ and Mn2+/Mn3+/Mn4+ redox pairs strategy is developed to construct a series of defective spinel Mg0.4NixMn2.6−xO4+δ (abbreviated MN(x)MO) to gain insights in terms of oxygen nonstoichiometry. By regulating the stoichiometric proportion of Ni and Mn, it is possible to optimize electronic conductivity and oxygen-vacancy concentration. The optimized MN(1.4)MO provides electrical conductivity as high as 68 S·cm−1 at 800 °C, 2.72 folds that of MN(1.0)MO. Based on oxygen transport performance, the surface exchange coefficient of MN(1.4)MO at 900 °C is 162 folds that of commercial La0.7Sr0.3MnO3-δ (LSM). When a MN(1.4)MO cathode was used, the resulted SOFC exhibited extraordinarily high maximum power density of 0.34 W·cm−2 at 600 °C and 2.02 W·cm−2 at 800 °C. To the best of our knowledge, the performance is the best among the spinel-based cathodes ever reported for SOFC application. Endowed with optimal properties, MN(1.4)MO-based SOFC displays peak power density which is 2.27 and 1.44 folds that of LSM-based SOFC at 600 °C and 800 °C, respectively. A test of 50 h revealed the MN(1.4)MO-based SOFC is remarkably stable at 800 °C, continuously offering 2.02 W·cm−2 at 0.5 V. The excellent performance and stability of MN(1.4)MO-based SOFC suggests that MN(1.4)MO is a promising cathode material for the development of intermediate temperature SOFC technology.