Perturbing d-band center via high-entropy modulation within spinel lattices toward enhanced oxygen evolution reaction catalysis

With a multimetallic composition featuring diverse oxidation states and coordination environments, high-entropy oxides (HEOs) provide tunable affinities toward oxygen intermediates, thereby alleviating the intrinsic kinetic barriers of oxygen evolution reaction (OER). This compositional and structural diversity allows modulation of the reaction pathway and reduction of the activation barrier for the inherently sluggish four-electron OER process. Herein, we report the synthesis of a nanobelt-shaped, single-phase pentametallic spinel oxide (Co_1.8Cr_0.3Rh_0.3Fe_0.3Ni_0.3)O₄ as an entropy-engineered electrocatalysts with tunable electronic structures for efficient OER. The multimetallic synergy upshifts the metal d-band center toward the Fermi level, optimizing oxygen intermediate binding and thereby reducing the OER overpotential. Compared to commercial IrO₂ in 1 M KOH, the spinel oxide exhibits a lower overpotential (1.58 V vs. RHE at 10 mA cm^–2), a smaller Tafel slope (66.1 mV dec^–1) and excellent durability maintaining stable performance over 12 h. These results highlight the potential of high-entropy spinel oxides, rationally engineered through multimetallic design, to achieve superior OER activity by finely tuning adsorption energetics and mitigating kinetic limitations.