In Situ Surface-Selective Oxidation-Induced Construction of a Mo ₂ C@MoO _{2+ <i>x</i>} Heterostructure for Enhanced Electrosynthesis of Ammonia via Nitrogen Reduction

Ammonia (NH3) is a cornerstone of modern agriculture, energy storage, and clean fuel, yet its production via the conventional Haber–Bosch process consumes vast amounts of energy and emits severe greenhouse gas. Electrochemical nitrogen reduction reaction (NRR) offers a carbon-neutral alternative but faces challenges in N2 activation and competition from the hydrogen evolution reaction (HER). Herein, the Mo2C@MoO2+x heterostructure is designed via a novel in situ surface selective oxidation transformation strategy, leveraging synergistic MXene–oxide interactions to enhance NRR efficiency. The heterostructure achieves an exceptional NH3 yield of 13.6 μg h–1 mg–1 with 40% Faradaic efficiency (FE) at −0.35 V vs reversible hydrogen electrode (RHE) and maintains stability for 72 h. Density functional theory (DFT) reveals widened conduction/valence bands and elevated Fermi levels at the MXene–MoO2+x interface, with MoO2+x optimizing the electron density to suppress the HER and boost N2 activation. This work demonstrates a novel in situ strategy for designing MXene–metal oxide heterostructures, advancing sustainable NH3 synthesis.