Defected MoS2: An efficient electrochemical nitrogen reduction catalyst under mild conditions

•The sulfur-vacancies defected MoS2 (VS-MoS2) nanoflowers with excessive Mo atoms are synthesized for the first time.•VS-MoS2 (5:2) exhibited a high NH3 yield of 46.1 × 10−11 mol s−1 cm−2 and a prominent faraday efficiency of 4.58% .•VS-MoS2 (010)-2 can effectively facilitate electrocatalytic NRR as attributes to a low energy barrier of the RDS is 0.06 eV.•The introduction of excessive Mo into MoS2 can markedly enhance the NRR catalytic performance of MoS2. Although the electrochemical N2 reduction reaction (NRR) to NH3 provides a promising avenue for artificial N2 fixation, building of efficient NRR electrocatalysts with high activity and stability remains a tremendous challenge. The combined experimental results and theoretical calculation reveal that MoS2 with sulfur-vacancy defect (VS-MoS2) is an admirable NRR catalyst. Electrochemical results demonstrate that VS-MoS2 (5:2) possesses outstanding NRR performances, including a superior NH3 average yield rate (46.1 × 10−11 mol s−1 cm−2 at -0.5 V vs reversible hydrogen electrode (RHE)), an excellent faraday efficiency (FE: 4.58% at -0.4 V vs RHE), good electrochemical stability (at least 24 h), and high selectivity (no by-product of N2H4). Density functional theory (DFT) calculations demonstrate that the rate determining steps (RDSs) of all VS-MoS2 (010)-2, VS-MoS2 (010)-1, and MoS2 (010) are the first hydrogenation step to form *NNH intermediate, as reflected by the energy barriers of 0.06 eV, 0.20 eV, and 0.93 eV, the significantly charge transfer (1.02e, 0.45e vs. 0.41e) from two Mo atoms to N2, as well as the stretching of NN bond (1.200 Å, 1.140 Å vs. 0.970 Å), respectively. These results reveal that VS-MoS2 (010)-2 can effectively activate inert N2 molecule and have the potential application in nitrogen fixation under mild conditions. VS-MoS2 (5:2) possesses a superior NH3 average yield rate (46.1 × 10−11 mol s−1 cm−2 at -0.5 V vs RHE and a low energy barrier of the rate determining step for VS-MoS2 (010)-2 is 0.06 eV. [Display omitted]