Interfacial Electron Modulation to Boost Driving Force: Partial Sulfurization over Co-MOF@Fe2O3 p–n Heterojunctions for Water Splitting

Herein, a p–n junction composed of cobalt-based metal–organic frameworks (Co-MOFs) and Fe₂O₃ has been designed to provide a strong built-in electric field (B-IEF) to enhance electron transport and facilitate intermediate adsorption of oxygen during the oxygen evolution reaction. Meanwhile, partial sulfurization surface modulation is envisioned to achieve a switchable phase transformation, and the B-IEF has been further broadened to 1.535 V. The Co-MOF@Fe₂O₃–S bearing partial sulfurization delivered a lower overpotential of 300 mV at 50 mA cm^–2, a modest Tafel slope of 83.8 mV dec^–1, and remarkable long-term stability. Density functional theory calculations and in situ Raman analysis have indicated charge redistribution, accelerated electron transfer and OH^– ion diffusion, and the modest adsorption/desorption energy of oxygen-containing intermediates. This interfacial p–n heterojunction and sulfurization treatment without losing the microstructure lays the foundation for the production of clean energy.