Phase‐Regulated Active Hydrogen Behavior on Molybdenum Disulfide for Electrochemical Nitrate‐to‐Ammonia Conversion

Abstract Electrochemical reduction of nitrate waste is promising for environmental remediation and ammonia preparation. This process includes multiple hydrogenation steps, and thus the active hydrogen behavior on the surface of the catalyst is crucial. The crystal phase referred to the atomic arrangements in crystals has a great effect on active hydrogen, but the influence of the crystal phase on nitrate reduction is still unclear. Herein, enzyme‐mimicking MoS 2 in different crystal phases (1T and 2H) are used as models. The Faradaic efficiency of ammonia reaches ≈90 % over 1T‐MoS 2 , obviously outperforming that of 2H‐MoS 2 (27.31 %). In situ Raman spectra and theoretical calculations reveal that 1T‐MoS 2 produces more active hydrogen on edge S sites at a more positive potential and conducts an effortless pathway from nitrate to ammonia instead of multiple energetically demanding hydrogenation steps (such as *HNO to *HNOH) performed on 2H‐MoS 2 .