Highly selective adsorption on WX2 (X=S, Se, Te) monolayer and effect of strain engineering: A DFT Study

A model of SO2 molecule was established, and the adsorption of SO2 by intrinsic graphene was first studied by the first principles study. The calculation results show that the intrinsic WX2 (X = S, Se, Te) has a weak adsorption of SO2 and belongs to physical adsorption. Then compare the adsorption of SO2 by the WX2 systems doped with As and Ge, and calculated by first-principles: the doped WX2 has a stronger adsorption effect on SO2. From the perspective of the degree of change in the adsorption structure, single-doped Ge/WTe2 has stronger stability when adsorbing gas molecules; from the perspective of adsorption energy, charge density, band structure, and density of states diagrams, single-doped Ge/WTe2 has a greater effect on SO2 gas has better adsorption effect.

Theoretical Study on the Lewis Acidity of the Pristine AlF3 and Cl-Doped α-AlF3 Surfaces

In the past two decades, metal fluorides have gained importance in the field of heterogenous catalysis of bond activation reaction, e.g., hydrofluorination. One of the most investigated metal fluorides is AlF3. Together with its chlorine-doped analogon aluminiumchlorofluoride (AlClxF3−x, x = 0.05–0.3; abbreviated ACF), it has attracted much attention due to its application in catalysis. Various surface models for α-AlF3 and their chlorinated analogues (as representatives of amorphous ACF) are investigated with respect to their Lewis acidity of the active centres. First-principle density functional theory (DFT) methods with dispersion correction are used to determine the adsorption structure and energy of the probe molecules CO and NH3. The corresponding vibrational frequency shift agrees well with the measured values. With this insight we predict the local structure of the active sites and can clarify the importance of secondary interactions to the local anionic surrounding of the catalytic site.

Formaldehyde Molecules Adsorption on Zn Doped Monolayer MoS2: A First-Principles Calculation

Based on the first principles of density functional theory, the adsorption behavior of H2CO on original monolayer MoS2 and Zn doped monolayer MoS2 was studied. The results show that the adsorption of H2CO on the original monolayer MoS2 is very weak, and the electronic structure of the substrate changes little after adsorption. A new kind of surface single cluster catalyst was formed after Zn doped monolayer MoS2, where the ZnMo3 small clusters made the surface have high selectivity. The adsorption behavior of H2CO on Zn doped monolayer MoS2 can be divided into two situations. When the H-end of H2CO molecule in the adsorption structure is downward, the adsorption energy is only 0.11 and 0.15 eV and the electronic structure of adsorbed substrate changes smaller. When the O-end of H2CO molecule is downward, the interaction between H2CO and the doped MoS2 is strong leading to the chemical adsorption with the adsorption energy of 0.80 and 0.98 eV. For the O-end-down structure, the adsorption obviously introduces new impurity states into the band gap or results in the redistribution of the original impurity states. All of these may lead to the change of the chemical properties of the doped MoS2 monolayer, which can be used to detect the adsorbed H2CO molecules. The results show that the introduction of appropriate dopant may be a feasible method to improve the performance of MoS2 gas sensor.

Dual-Atoms Iron Sites Boost the Kinetics of Reversible Conversion of Polysulfide for High-Performance Lithium-Sulfur Batteries

Atomically dispersed metal catalysts have offered significant potential for accelerating sluggish kinetics of transformation of lithium polysulfide(LiPS) and inhibiting the shuttle effect to achieve the long-life cycling and high rate of lithium sulfur batteries. However, the end-on adsorption structure between single metal site and polysulfide limits the adsorption capacity and catalytic activity of single atom catalysts. Here, we construct dual-atoms iron sites on nitrogen doped graphene to serve as highly efficient catalyst for lithium sulfur batteries. As expected, the dual-atoms sites can firmly bound polysulfides by forming double Fe-S bonds between polysulfides and the two adjacent iron atoms. Such double-bond adsorption structure is also favorable for the electron transfer and polysulfides activation, so as to reduce the energy barrier and accelerate the reaction kinetics. As a result, the as-obtained dual-atoms iron catalyst can effectively alleviate the shuttle effect and improve the utilization of active sulfur, thus the batteries present high initial capacity of 1615 mAh g-1 at 0.05 C and long-cycle life with a decay rate per cycle as low as 0.015% at 2C over 1000 cycles.