Core–Shell Engineering Boosted Active Hydrogen Generation in Cu2–xS/MoS2 Quantum Dots for Efficient Electrocatalytic Nitrate Reduction to Ammonia

The electrochemical nitrate reduction reaction (NO3RR) emerges as a promising method for ammonia (NH3) production, which faces the dilemma of inhibiting the hydrogen evolution reaction (HER) and promoting active hydrogen (Hads) supply for hydrogenation of nitrogen intermediates. Here, a core–shell structure engineering strategy is developed for Cu2–xS/MoS2, where the strong Hads adsorption and storage capacity can accelerate the hydrogenation of nitrogen intermediates. As a result, an eminent NH3 yield of 0.178 mmol h–1 cm–2 and a Faradaic efficiency of 84.5% were achieved. A series of electrochemical tests demonstrate that the tuning of the Cu2–xS/MoS2 interface can improve the electrochemical activity and the conversion of NO2–, while avoiding the strong HER that can effectively retain the Hads. The density functional theory calculation further demonstrates that the Cu2–xS/MoS2 interface has a strong *H retention and adsorption ability to promote the NO3RR process. This work offers a novel perspective on the manipulation of Hads generation for the NO3RR.