Nitrogen Vacancies on 2D Layered W₂ N₃ : A Stable and Efficient Active Site for Nitrogen Reduction Reaction

Electrochemical nitrogen reduction reaction (NRR) under ambient conditions provides an avenue to produce carbon-free hydrogen carriers. However, the selectivity and activity of NRR are still hindered by the sluggish reaction kinetics. Nitrogen Vacancies on transition metal nitrides are considered as one of the most ideal active sites for NRR by virtue of their unique vacancy properties such as appropriate adsorption energy to dinitrogen molecule. However, their catalytic performance is usually limited by the unstable feature. Herein, a new 2D layered W₂ N₃ nanosheet is prepared and the nitrogen vacancies are demonstrated to be active for electrochemical NRR with a steady ammonia production rate of 11.66 ± 0.98 µg h^-1 mg_cata ^-1 (3.80 ± 0.32 × 10^-11 mol cm^-2 s^-1 ) and Faradaic efficiency of 11.67 ± 0.93% at -0.2 V versus reversible hydrogen electrode for 12 cycles (24 h). A series of ex situ synchrotron-based characterizations prove that the nitrogen vacancies on 2D W₂ N₃ are stable by virtue of the high valence state of tungsten atoms and 2D confinement effect. Density function theory calculations suggest that nitrogen vacancies on W₂ N₃ can provide an electron-deficient environment which not only facilitates nitrogen adsorption, but also lowers the thermodynamic limiting potential of NRR.