Nanostructured spinel high-entropy oxide (Fe0.2Mn0.2Co0.2Ni0.2Zn0.2)3O4 as a potential cathode for solid oxide fuel cells

Abstract

Commercial use of solid oxide fuel cells (SOFCs) requires high output performance and excellent long-term stability for cathode materials. A nanostructured spinel high-entropy oxide (Fe0.2Mn0.2Co0.2Ni0.2Zn0.2)3O4 (FMCNZ) is developed as the SOFC cathode using an impregnation method. FMCNZ nanoparticles are distributed uniformly and infiltrated into a network on the Gd0.1Ce0.9O1.95 (GDC) skeleton by modifying the impregnation content. The polarization resistance of FMCNZ with 40 wt% impregnation loading shows a minimum value of 0.018 Ω cm2 at 800 °C, which is around one-third of that for the typical Ni0.2Fe0.8Co2O4 spinel cathode with the same preparation processing. The excellent oxygen reduction reaction (ORR) is primarily attributed to the diversity of surface metal cations and the population increase of surface oxygen vacancies brought on by the high entropy design. The analysis of ORR kinetics based on the distribution of relaxation time (DRT) method reveals that the species exchange process at the electrode surface is a rate-determining step, which probably originated from the low electronic conductivity of FMCNZ. The SOFC with the nanostructured FMCNZ cathode reaches a maximum power density of 1080 mW cm−2 at 800 °C. Additionally, the nanostructures of the cathode barely change after 100 h of cell operation at 750 °C. Thus, our findings provide a novel and promising path for developing high-performance cathodes by integrating a high-entropy design strategy with the construction of nanostructured materials.