Low-Temperature, Rapid Synthesis of Plasma-Exsolved FeNi/NiFe₂O₄ Composites for Enhanced Oxygen Evolution Reaction

Exsolution of active nanoparticles (NPs) on substrate surfaces is a promising route to enhance the oxygen evolution reaction (OER) efficiently. However, conventional exsolution methods often suffer from protracted long processing times (4-10 h), substantial energy consumption, and high-temperature (500-1000 °C) reduction under H₂/Ar atmospheres. To address these limitations, this work introduces a hydrogen plasma treatment that facilitates rapid exsolution of NPs in a few minutes at low temperatures (∼200 °C), resulting in NPs-modified spinel structures. The resulting FeNi/NiFe₂O₄ composite structure exhibits remarkable OER activity, demonstrating an overpotential of 290 mV at 10 mA cm^-2 and a Tafel slope of 68.18 mV dec^-1, superior to pristine NiFe₂O₄ (315 and 98.97 mV dec^-1, respectively). The catalyst also presents robust stability, maintaining its initial current density for over 240 h. This work offers valuable insights into plasma-induced exsolution for enhancing the electrocatalytic activity of spinel structures.