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

Abstract

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.