Engineering Oxygen Vacancies in MoO 2 for Enhanced Photocatalytic Nitrogen Reduction to Ammonia

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Photocatalytic ammonia synthesis is considered one of the most promising fields as the sustainable, which will attract increasing attention. In this work, grayish‐white MoO 3 was first synthesized using one‐step hydrothermal calcination method under an inert atmosphere. It was then subjected to secondary calcination in pure hydrogen, ultimately yielding black MoO 2 photocatalysts with abundant oxygen vacancies (OVs). The reduced MoO 2 achieves a maximum photocatalytic ammonia synthesis rate of 46.29 μmol·h −1 ·g −1 . Electron paramagnetic resonance and X‐ray photoelectron spectroscopy characterization confirmed the formation of OVs. Photoelectrochemical testing demonstrated that compared to MoO 3 , MoO 2 enhanced light absorption and suppressed carrier recombination, thereby improving nitrogen fixation efficiency. Density functional theory calculations show a lower adsorption energy for MoO 2 (0.16 eV) than for MoO 3 (0.95 eV), highlighting the crucial role of OVs in tuning the reaction kinetics. The dynamic role of OVs in catalytic reactions is demonstrated in this work.