The application of cobalt-free spinel Ni1.4Mn1.6O4 as a cathode in intermediate temperature solid oxide fuel cells

Abstract

In this study, a series of cobalt-free spinels Ni_1+xMn_2-xO₄ (x = 0, 0.2, 0.4, 0.6) were prepared by the solid-liquid composite method. After preparing them into full-cell tests, it was found that Ni_1.4Mn_1.6O₄ (NMO) exhibited the best performance when x = 0.4, and subsequent in-depth research was focused on NMO. NMO has good thermal expansion matching with the electrolyte layer below 700 ℃, as well as excellent mixed ionic-electronic conductivity. When employed as a cathode material in an solid oxide fuel cell (SOFC), the cell achieves a discharge power density of 1150.25 mW cm⁻² at 800 ℃. However, as the oxygen ion conduction rate decreases with decreasing temperature, the power densities at medium and low temperatures are significantly lower, with only 248.97 mW cm⁻² at 650 ℃ and 33.55 mW cm⁻² at 600 ℃. The combination of NMO with the electrolyte material 8YSZ results in a significant increase in power density at 650 °C and 600 °C, achieving 330.21 mW cm⁻² and 157.81 mW cm⁻², respectively. An SOFC with NMO-YSZ64 as the cathode demonstrates excellent long-term stability, and the voltage degradation rate is less than 1 % after 110 hours of galvanostatic discharge at 650 °C and 200 mA cm⁻². SEM analysis reveals that the microstructure of the cell remains intact after prolonged discharge and has good adhesion at the cathode-electrolyte interface. These results suggest that Ni_1.4Mn_1.6O₄ and its composite cathodes are highly promising cathode materials.