As a promising alternative to the Haber-Bosch process for producing NH3, the electrocatalytic nitrogen reduction reaction (NRR) in the aqueous electrolyte has attracted much attention. However, the presence of sluggish reaction kinetics and competitive hydrogen evolution could result in poor activity and unsatisfactory selectivity. Herein, self-supported NbSe2 nanosheet arrays have been prepared and tested as electrocatalysts for NH3 electrosynthesis with a Faradaic efficiency of 13.9 +/- 1.0% at -0.4 V versus the reversible hydrogen electrode (vs RHE) and a yield rate of 89.5 +/- 6.0 mu g h (1) mg(1)(cat) at -0.45 V vs RHE in 0.1 M Na2SO4 under ambient conditions. Moreover, this electrocatalyst showed excellent durability during the 60-h electrolysis (no stable decay of Faradaic efficiencies and NH3 yield rates). Furthermore, density functional theory calculations disclosed that NbSe2 can effectively catalyze the dissociation of the adsorbed N-2 molecule and thus promote the NRR process. (C) 2019 Elsevier Inc. All rights reserved.