High-entropy oxides (HEOs) have emerged as promising electrocatalysts for the oxygen evolution reaction (OER) owing to their tunable electronic structures and compositions. Herein, a quinary high-entropy spinel oxide (HE-SOs) composed of Mn, Fe, Co, Ni, and Zn was synthesized via a supercritical hydrothermal process, and its element-specific behavior under OER potentials in alkaline solution was systematically investigated using in situ X-ray absorption spectroscopy (XAS). Under applied anodic potentials, distinct responses among the constituent metals were observed. Mn, Co, and Ni exhibited redox changes at the same potential range, whereas Fe and Zn exhibited no redox changes, serving as redox-inactive framework elements. The high-entropy matrix effectively suppresses structural reconstruction, balancing redox activity with structural stability. This study elucidates that the synergistic effect of the constituent elements is the origin of the high OER activity and durability of HEOs, providing fundamental insight into the design of multicomponent oxide electrocatalysts.
Iwase et al. (2026) studied this question.