Unraveling medium-entropy alloy–ceria heterostructures for oxygen reduction reaction electrocatalysis

The development of highly efficient medium-entropy alloy (MEA)-based electrocatalysts for the oxygen reduction reaction (ORR) is of paramount importance in advancing sustainable energy technologies, including fuel cells and metal–air batteries. Nevertheless, realizing the structural integration of MEAs with non-noble metal species remains a significant challenge, particularly in achieving well-defined heterointerfaces that enable synergistic electronic interactions. Moreover, the lack of mechanistic clarity regarding how these components collectively modulate reaction pathways hinders rational catalyst design. Herein, the aim is to overcome this challenge by fabricating FeCoNi MEA–ceria heterostructures into N-doped carbon nanofibers (FeCoNi/CeO2@N-CNFs). The synergistic integration of x-ray absorption spectroscopy and in situ characterization techniques reveals that intrinsic lattice distortions inherent in medium-entropy systems profoundly reshape the electronic environment of active sites, while the incorporation of CeO2 species significantly enhances ORR kinetics by achieving an exquisite balance between the adsorption and desorption of oxygen-related intermediates. As resultant, the FeCoNi/CeO2@N-CNFs demonstrate enhanced ORR electrochemical performance than that of single-component counterparts. This study provides a deeper understanding of how electronic characteristics and dynamic evolution of adsorbed intermediate species at the MEA metal centers can be modulated via CeO2 to enhance ORR electrocatalytic performance and durability.