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Design of novel catalysts for the reduction of N2 to ammonia has been urgently pursued because of various issues related to the industrial reduction technology. In this work, we perform first-principles calculations on the basis of the density-functional theory to control the edges of two-dimensional (2D) transition-metal disulfides (TMDs), including MoS2, WS2, VS2, NbS2, TiS2, and TaS2, for the achievement of optimal efficiency in nitrogen-fixation. Our calculations show that nitrogen molecules prefer to stay at the bridge-on sites of the metal edges of TMD nanoribbons because of exothermic reactions. The calculated energy barrier at each step illustrates that VS2 has the lowest potential-determining step of 0.16 eV in the distal pathway, leading to its best catalytic activity in the N2 reduction reaction (NRR). Additionally, we find that the trend of catalytic activity of 2D TMD nanoribbons is as follows: VS2 > NbS2 > TiS2 > MoS2 > WS2 > TaS2. We show that charge transfer is critical to the reduction reaction. We further demonstrate that the edges of TMDs, especially VS2, show a higher selectivity for NRR over the hydrogen evolution reaction (HER) by investigating the competition between HER and NRR. Our findings not only reveal the effect of the edges of TMDs on NRR, but also provide theoretical support to the reported experimental results in the literature. It is expectable that the 2D TMD nanoribbons, especially VS2, may find application for efficient N2-fixation. At the same time, our work may guide the design of new catalysts for NRR.

We carry out our first-principles calculations within density functional theory to study the 3d transition metal (TM) doped AlN nanosheets. The calculated results indicate that a stoichiometric AlN nanosheet is graphene-like structure and nonmagnetic. The TM impurities can induce magnetic moments, localized mainly on the 3d TM atoms and neighboring N atoms. Our calculated results of TM-doped nanosheet systems indicate a strong interaction between 3d orbit of TM atom and the 2p orbit of N atoms. In addition, the Mn- and Ni-doped AlN nanosheet with half-metal characters seems to be good candidates for spintronic applications. When substituting two Al atoms, the relative energies of the states between ferromagnetic and antiferromagnetic coupling are investigated sufficiently. The exchange coupling of Co- and Ni-doped AlN nanosheets exhibits a transformation with different distances of two TM atoms and that of Cr-, Mn-, and Fe-doped AlN nanosheets is not changed.

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