Interfacial Electronic Modulation of MoO₂/Fe₃O₄-Melamine Nanorods with Abundant Oxygen Vacancies Towards...

Developing robust, efficient oxygen evolution catalysts is essential to advancing alkaline water electrolysis and sustainable hydrogen production. Herein, we present a vacancy-engineered MoO₂/Fe₃O₄-Mel nanorod composite, grown on nickel foam via a one-step solvothermal strategy. The catalyst possesses abundant oxygen vacancies and strongly coupled MoO₂/Fe₃O₄ heterointerface, while the nitrogen-rich melamine framework promotes electronic modulation of Fe active centers. During electrochemical activation, it undergoes surface reconstruction to generate an FeOOH active phase and oxygen vacancies promote interfacial charge redistribution. These structural and electronic features accelerate charge transfer and facilitate the adsorption and conversion of oxygenated intermediates during oxygen evolution reaction (OER). As a result, the optimized MoO₂/Fe₃O₄-Mel catalyst delivers ultra-low overpotential of 217 mV at 100 mA cm^-2, a small Tafel slope of 70 mV dec^-1, and maintains stable operation for 150 h. In situ Raman and in situ Fourier transform infrared spectroscopy reveal vacancy-associated surface reconstruction and dynamic oxygenated intermediate evolution, while tetramethylammonium and pH-dependent studies confirm an adsorbate evolution mechanism. A two-electrode MoO₂/Fe₃O₄-Mel⁽⁺⁾||Pt/C^(-) electrolyzer achieves a low cell voltage of 1.45 V at 100 mA cm^-2 with negligible degradation over 100 h. This work highlights the effectiveness of interfacial electronic modulation and oxygen vacancy engineering for high-performance alkaline OER catalysts.