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The geometric, electronic, and catalytic properties of transition-metal dichalcogenide WS 2 and WSe 2 monolayers and nanotubes as well as the ternary WSSe nanotube have been investigated using density functional theory. Their potential as catalysts for the hydrogen evolution reaction (HER) have been examined. We show that there is a significant decrease in the band gap of the nanotubes relative to their monolayer counterparts, improving the electrical contacts between these materials and the metallic conductors due to the reduction of the Schottky barrier. We also show that there is a significant decrease in the free energies for H adsorption at different sites of the nanotubes as compared to the monolayers, indicating a better performance of these materials as catalysts for hydrogen production in HER. Further, an improvement in the free energy for H adsorption was observed in the ternary WSSe structure relative to the pristine WS 2 and WSe 2 nanotubes. These results suggest that winding up monolayers of transitionmetal dichalcogenides into nanotubes and/or producing ternary nanotubes with different chalcogen atoms may significantly improve the performance of these materials for hydrogen production purposes.

First-principles calculations within DFT have been performed to investigate the use of a recently synthesized form of silicene, the dumbbell (DB) silicene as an anode material for Li-ion batteries (LiBs). The energetically most stable geometries for Li adsorption on DB silicene were investigated, and the energy barriers for Li-ion diffusion among the possible stable adsorption sites were calculated. We found that DB silicene can be lithiated up to a ratio of 1.05 Li per Si atom, resulting in a high storage capacity of 1002 mA h g–1 and an average open-circuit potential of 0.38 V, which makes DB silicene suitable for applications as an anode in LiBs. The energy barrier for Li-ion diffusion was calculated to be as low as 0.19 eV, suggesting that the Li ions can easily diffuse on the entire DB silicene surface, decreasing the time for the charge/discharge process of the LiBs. Our detailed investigations show that the most stable form of two-dimensional silicon has characteristic features suitable for application in high-performance LiBs.

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