Redox-Driven Exsolution and Dissolution Behavior of High-Entropy Spinel Catalysts: A Comparative Study of MnFeCoNiCuO and MnCoNiCuZnO.

High-entropy oxides (HEOs) offer tunable redox chemistry and thermal stability for catalytic applications. Here, we compare two spinel-type HEOs, MnFeCoNiCuO and MnCoNiCuZnO, with similar configurational entropy but different redox behaviors under reverse water-gas shift (RWGS) conditions. Only MnFeCoNiCuO exhibits reversible exsolution and reincorporation of Fe/Co/Ni/Cu alloy nanoparticles (NPs) during H-CO cycling, as confirmed by in situ X-ray absorption spectroscopy and wavelet-transformation. This dynamic restructuring correlates with higher concentrations of oxygen vacancy and exsolved Fe/Co/Ni/Cu alloy NPs, resulting in higher RWGS activity above 400 °C. In contrast, redox-inert Zn in MnCoNiCuZnO suppresses lattice flexibility and alloy formation. These findings underscore that redox-active cations, rather than entropy alone, govern the regenerative behavior and catalytic performance in HEO systems.