A novel cobalt-free high-entropy spinel oxide (Ni0.2Fe0.2Cr0.2Zn0.2Mg0.2)3O4 for solid oxide fuel cell cathode

As an innovative material synthesis strategy, high-entropy design offers a novel approach for the development of solid oxide fuel cell cathodes. In this study, we employed microwave heat treatment combined with solution combustion to synthesize five-component, cobalt-free high-entropy spinel oxides, specifically (Ni 0.2 Fe 0.2 Cr 0.2 Zn 0.2 Mg 0.2 ) 3 O 4 , where the molar ratio of the metal elements is nearly equal. The synthesized (Ni 0.2 Fe 0.2 Cr 0.2 Zn 0.2 Mg 0.2 ) 3 O 4 exhibits a porous network structure with a notably high specific surface area of 25.013 m 2 /g, enhancing its effectiveness in facilitating the oxygen reduction reaction. The high-entropy strategy, combined with microwave heat treatment, facilitates the formation of oxygen vacancies in (Ni 0.2 Fe 0.2 Cr 0.2 Zn 0.2 Mg 0.2 ) 3 O 4 , thereby enhancing its oxygen ion conductivity. The synergistic interactions among multiple metal cations significantly enhance the activity of the oxygen reduction reaction. (Ni 0.2 Fe 0.2 Cr 0.2 Zn 0.2 Mg 0.2 ) 3 O 4 exhibits excellent chemical compatibility with GDC, SDC, and YSZ. Electrochemical impedance spectroscopy analysis reveals that the high-entropy spinel, synthesized through microwave heat treatment at 800 °C, exhibits a polarization impedance as low as 0.12 Ω cm 2 and a power density of 611.53 mW cm −2 . These findings underscore its considerable potential for application as a cathode material in intermediate-temperature SOFCs. This study highlights the potential of the high-entropy strategy and microwave synthesis to improve the performance of spinel oxide cathodes. These approaches offer innovative directions for developing cobalt-free, intermediate-temperature SOFCs cathodes.