Localization of high-entropy metal oxide in iron oxide nanoparticles for efficient oxygen evolution reaction

Abstract The development of efficient, durable, and cost-effective oxygen evolution reaction (OER) electrocatalysts is essential for advancing renewable energy technologies. Herein, a novel strategy is reported that spatially confines a nanoscale localized high-entropy oxide (LHEO) consisting of Fe, Co, Ni, Zn, and Mn within α-Fe 2 O 3 , forming a unique α-Fe 2 O 3 @LHEO nanoarchitecture. The catalyst exhibits outstanding OER performance for alkaline water splitting, achieving a current density of 10 mA/cm 2 at a low overpotential of 229 mV with a small Tafel slope of 34.4 mV/dec, significantly outperforming commercial RuO 2 (326 mV, 118.8 mV/dec). It also shows excellent long-term stability over 1000 h at 100 mA/cm 2 without notable activity degradation. Applied in rechargeable zinc–air batteries with natural seawater, the α-Fe 2 O 3 @LHEO cathode delivers a high power density of 88.3 mW/cm 2 and stable operation over 600 cycles, substantially surpassing the benchmark Ru-Pt electrocatalyst (74.7 mW/cm 2 , 170 cycles). Combined experimental and theoretical studies reveal that LHEO induces lattice strain in α-Fe 2 O 3 , modulates its electronic structure, and lowers the crystal field splitting energy to stabilize high-spin Fe 3+ . These effects enhance metallic character for efficient charge transfer and optimize the adsorption/desorption of key oxygen reaction intermediates, thus shifting the OER pathway from the conventional adsorbate evolution mechanism (AEM) to the more energetically favorable lattice oxygen mechanism (LOM) with the energy barrier reduced from 1.85 to 1.71 eV. Overall, this work proposes a novel localized high-entropy engineering approach that overcomes key bottlenecks in designing efficient and durable OER electrocatalysts based on earth-abundant materials.