Magnetically Coupled Intergranular Interactions and Synergistic Effects on the Oxygen Evolution Reaction in Ferrimagnetic–Antiferromagnetic Heteronanostructures

The ferrimagnetic (FM)–antiferromagnetic (AFM) heterostructured NiFe 2 O 4 /LaFeO 3 (NL) can act as an electrocatalyst due to magnetically coupled intergranular interactions and synergistic effects, which can be explored as facile descriptors for deciphering the intrinsic field-free OER performance in an alkaline medium. Studying OER under field-free conditions allows us to assess the natural electronic and magnetic interactions at the heterojunction interface, providing a baseline understanding of how FM–AFM coupling influences charge transfer and catalytic activity without the effects of externally applied magnetic fields. Magnetic investigations reveal that saturation magnetization ( M s ) decreases with increasing LaFeO 3 (LFO) loading. Pristine NiFe 2 O 4 (NFO) exhibits a high M s of 41.126 emu/g, and the N7L3 (30 wt % LaFeO 3 ) composite shows a significantly lower M s of 28.873 emu/g, along with very low effective coercivity (∼7 Oe) compared to all other synthesized samples. The N8L2 (20 wt % LaFeO 3 ) heterostructure exhibits the highest squareness ratio (0.11), indicative of a multidomain structure and comparatively stronger magnetically coupled intergranular magnetostatic interactions among all the synthesized composite materials. The N8L2 heterostructure material exhibited an overpotential of 378 mV at a current density of 10 mA/cm 2 for the oxygen evolution reaction (OER) with a Tafel slope of 86 mV dec –1 in 1 M KOH electrolyte solution. N8L2 exhibited 93.49% faradaic efficiency and long-term stability for OER performance. The alignment of nonvolatile spins and modified Fe–O–Ni superexchange pathways at the heterojunction interface alters the electronic structure and magnetic properties, thereby contributing to the enhanced OER performance for the N8L2 heterostructure material, indicating a strong potential for electrochemical energy conversion technologies.