Photocatalytic robust solar energy reduction of dinitrogen to ammonia on ultrathin MoS₂

The crux for solar N₂ reduction to ammonia is activating N₂ into its high-energy intermediate. Applying a simultaneous multi-electron reduction process could avoid intermediate generation and decrease the thermodynamic barrier. However, this process is extremely difficult from a kinetic view and experiments so far have not shown it is accessible. Here we show the first direct evidence of trion induced multi-electron N₂ reduction on ultrathin MoS₂. By applying light induced trions, N₂ molecular was activated and transformed into ammonia by a simultaneous six-electron reduction process, with a high ammonia synthesis rate of 325 μmol/g h without the assistant of any organic scavengers or co-catalyst. Bulk MoS₂ without trions did not exhibit any activity. This demonstrates multi-electron reduction may be realized in electron-rich semiconductors with high concentration of localized electrons such as trions. The methodology of simultaneous multi-electron reduction has wide implications for reactions beyond N₂ reduction and for materials beyond MoS₂.