The catalytic activity for the hydrogen evolution reaction (HER) at the anion vacancy of 40 2D transition-metal dichalcogenides (TMDs) is investigated using the hydrogen adsorption free energy (Δ G) as the activity descriptor. While vacancy-free basal planes are mostly inactive, anion vacancy makes the hydrogen bonding stronger than clean basal planes, promoting the HER performance of many TMDs. We find that ZrSe and ZrTe have similar Δ G as Pt, the best HER catalyst, at low vacancy density. Δ G depends significantly on the vacancy density, which could be exploited as a tuning parameter. At proper vacancy densities, MoS, MoSe, MoTe, ReSe, ReTe, WSe, IrTe, and HfTe are expected to show the optimal HER activity. The detailed analysis of electronic structure and the multiple linear regression results identifies the vacancy formation energy and band-edge positions as key parameters correlating with Δ G at anion vacancy of TMDs.

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Interchain interactions in arrays of metal–organic hybrid chains were studied using scanning tunneling microscopy and ab initio calculations. The array of hybrid chains having a Ag–anthryl biradical were self-assembled by catalytic scission of Br–C bonds in 9,10-dibromoanthracene on Ag(111). An atomic model for the observed chain structures was proposed. Ag atoms in chains were alternatingly located at hollow sites, making slightly zigzaging structures. Between the hybrid chains, Br atoms located at hollow sites to form Br···H intermolecular bonds. Anthryl biradicals had two different apparent heights; this was explained by considering Br···H intermolecular bonds and intrachain steric repulsion. When a hybrid chain was laterally moved by manipulation techniques, Br adsorbates moved together with the chain, implying that they are stabilized by Br···H intermolecular bonds.

Intermolecular structures of porous two-dimensional supramolecular networks are studied using scanning tunnelling microscopy combined with density functional theory calculations. The local configurations of halogen bonds in polymorphic porous supramolecular networks are directly visualized in support of previous bulk crystal studies.

Using the multiscale simulation combining ab initio calculations and kinetic Monte Carlo (KMC) simulations, we theoretically investigate the hydrogen evolution reaction (HER) on the sulfur vacancy of a MoS 2 monolayer. Unlike metal catalysts, the protonation step and the charging step proceed independently in semiconducting MoS 2 . Interestingly, the barrier for hydrogen evolution decreases when the vacancy site is hyper-reduced with extra electrons. The turnover frequency and polarization curve obtained from the KMC simulation agree well with extant experimental data, and the major HER paths underscore the role of hyper-reduced states, particularly when the overpotential is applied. The strain effect is also simulated, and it is found that the tensile strain enhances HER by reducing the energy cost of hyper-reduced states. The estimated reduction in the overpotential agrees favorably with the experiment while the hydrogen binding energy alone cannot account for it, suggesting that the full-blown KMC simulation should be used to accurately predict the variation of HER performance under various conditions. By uncovering the nature of the catalytic reaction at the sulfur vacancy of MoS 2 and revealing a design principle in which the facile formation of hyper-reduced states plays an important role, the present work will pave the way for developing HER catalysts that may replace Pt.

Two-dimensional (2D) molybdenum disulfide (MoS2) has been attracting rapidly increasing interest for application in chemoresistive gas sensors owing to its moderate band gap energy and high specific surface area.

Using all-atom simulation of vapor deposition, we theoretically investigate how the molecular orientation depends on various factors such as the substrate temperature, molecular shape, and material composition.

The structure of glassy GeSe9 was investigated by combining neutron diffraction with density-functional-theory-based first-principles molecular dynamics. In the simulations, three different models of N = 260 atoms were prepared by sampling three independent temporal trajectories, and the glass structures were found to be substantially different from those obtained for models in which smaller numbers of atoms or more rapid quench rates were employed. In particular, the overall network structure is based on Sen chains that are cross-linked by Ge(Se4)1/2 tetrahedra, where the latter are predominantly corner as opposed to edge sharing. The occurrence of a substantial proportion of Ge-Se-Se connections does not support a model in which the material is phase separated into Se-rich and GeSe2-rich domains. The appearance of a first-sharp diffraction peak in the Bhatia-Thornton concentration-concentration partial structure factor does, however, indicate a non-uniform distribution of the Ge-centered structural motifs on an intermediate length scale.