Synergistic Defect and Surface Engineering in Mesoporous MgFe ₂ O ₄ : A Quenching‐Driven Strategy for Enhanced Oxygen Evolution Reaction Performance

Metal oxides composed of earth‐abundant elements such as Mg and Fe are promising candidates for water electrolysis; however, MgFe 2 O 4 (MFO) suffers from low electrical conductivity and limited active sites. Herein, we report a binder‐free synthesis of mesoporous MFO directly on carbon cloth using a molten salt‐assisted self‐assembly approach. Quenching the calcined material at 500 °C in ice water or 0.1 M Ni 2+ solution induces surface defects, oxygen vacancies, and Ni incorporation. In addition, phosphate incorporation via phosphoric acid treatment is explored to enhance stability and activity. The optimized sample exhibits an overpotential of 300 mV at 10 mA cm −2 and 350 mV at 100 mA cm −2 , along with stable operation for 84 h. The enhanced performance is attributed to modified electronic structure and increased active site density arising from defect formation and surface Ni incorporation. These results demonstrate an effective strategy for improving MFO‐based electrocatalysts.