Cooperative Cu with defective MXene for enhanced nitrate electroreduction to ammonia

The electroreduction of nitrate (NO₃RR) to ammonia (NH₃) provides a promising solution to enable environmental remediation caused by ${{\text{NO}}_3}^{-}$-containing waste and also allows for energy-saving NH₃ generation. Adsorption of *NO₂ intermediate may be strengthened to decrease byproducts (e.g., ${{\text{NO}}_2}^{-}$) and favor the eight-electron NO₃RR into NH₃. In this work, copper-incorporated O-vacancy containing Ti₃C₂ MXene (Cu@Ti₃C₂O_v) is reported, which cooperatively inhibits ${{\text{NO}}_2}^{-}$ production and facilitates hydrogenation, leading to approximately 100% Faradaic efficiencies of NH₃ and high yield rates at various potentials. Density functional theory calculations show that ${{\text{NO}}_3}^{-}$ and the *NO₂ intermediates have a significant interaction with the Cu@Ti₃C₂O_v catalyst. Moreover, the formation of ${{\text{NO}}_2}^{-}$ has a high energy barrier, which explains the appealing catalytic performance of the Cu@Ti₃C₂O_v toward NO₃RR with suppressed ${{\text{NO}}_2}^{-}$ and elevated NH₃ selectivity. This work would motivate the prudent design of new catalysts for high-performance NO₃RR to NH₃ by elucidating the significance of stabilizing the *NO₂ intermediate.