Fabrication of sea urchin-shaped NiFeY oxides nanorod catalyst with rich oxygen vacancies as high-performance electrocatalyst for oxygen evolution reaction

Medium entropy oxides represent a highly promising class of electrocatalysts for the oxygen evolution reaction (OER). However, their catalytic activity and operational stability still require systematic enhancement through precise modulation of atomic structure and chemical composition. In this work, we report a novel NiFeY medium-entropy oxide (NiFeYO x MEO), which has well-defined nanorod morphology with a sea urchin-like hierarchical array. Critically, the substantial ionic radius mismatch between Y 3+ (1.019 Å) and the smaller Ni 2+ (0.69 Å) and Fe 3+ (0.645 Å) cations induces significant lattice strain, facilitating oxygen-vacancy formation and modulating lattice structure in the NiFeYO x . Electrochemical evaluation reveals enhanced OER activity, achieving a low overpotential of 370 mV to deliver a current density of 100 mA cm −2 in 1 M KOH, with a low Tafel slope of 43 mV dec −1 . The catalyst also shows good operational stability, with negligible potential increase during 50 h. This study offers a viable pathway to regulate the structural and electronic properties of NiFe-based medium-entropy oxides for advanced energy conversion electrocatalysis.