Hybrid structures have attracted a great deal of attention because of their excellent properties, which can open up a way we could not foresee in materials science and device physics. Here, we investigate the electrical and optical behaviors of SiC(GeC)/MoS heterostructures, using first principles calculations based on density functional theory. Non-covalent bonding exists between the junctions due to the weak orbital coupling. Both junctions have optically active band gaps, smaller than that of the SiC or GeC and MoS layers, which result in enhanced optical adsorption under visible-light irradiation. A small number of electrons transfer from SiC/GeC to MoS causing its n-doping. Furthermore, the charge density states of the valence band maximum and the conduction band minimum are localized at different sides, and thus the electron-hole pairs are spatially separated. Our results provide a potential scheme for photovoltaic materials.

Na, K and Ca−ion battery electrode materials with appropriate electrochemical properties are desirable candidates for replacing lithium−ion batteries (LIBs) because of their natural richness and low cost. Recently, MoO 2 has been reported as the anode material in LIBs, but so far not received attention in Na and other ion batteries. In this paper, the behaviors of Na, K, and Ca on MoO 2 are investigated by first−principles calculations. These metal atoms strongly absorb on the hexagonal center of MoO 2 and the adsorption results in semiconducting−metallic transition. The low diffusion barrier, 0.13, 0.08, 0.22 eV for Na, K, Ca, respectively, leads to an ultrahigh diffusivity. Importantly, the maximum metal−storage phases of MoO 2 monolayer correspond to Na 4 MoO 2 , K 2.5 MoO 2 and Ca 3 MoO 2 , with considerable theoretical specific capacities of 837, 523 and 1256 mAh g −1 . The electrode materials exhibit moderate average voltage of 0.30, 0.75, 0.35 V, respectively. Our findings suggest that MoO 2 monolayer can be utilized as a promising anode material with high capacities and high rate performance for next generation ion batteries.

“Two-dimensional materials as electrodes” is believed to be one of the key solutions for the development of future battery technologies. Based on the first-principles calculations, we predict that a metallic carbon allotrope (net W), with high electrochemical performance, can be served as an anode material for Li-ion batteries (LIBs). The net W exhibits metallic conductivity, and the conductivity is excellently maintained after Li adsorption. Specifically, upon Li intercalation, only slight lattice variations (<1.5%) occur, which ensures a good cycling stability. The low diffusion barriers of 0.4 eV and the moderate average open circuit voltage of 0.42 V are in between those of the currently used anodes, graphite, and TiO2. Most remarkably, the storage capacity can be up to 1675 mA h g−1, which is about 4.5 times larger than that of the commercial graphite anode. The present findings identify that net W could be an excellent anode material for the application in LIBs.

Based on first-principles calculations, we study the hydrogen evolution reaction (HER) on metal-free C2N and make efforts to improve its catalytic performance.

Designing an efficient membrane for He purification is quite crucial in scientific and industrial applications. Ultrathin membranes with intrinsic pores are highly desirable for gas purification because of their controllable aperture and homogeneous hole distribution. Based on the first−principles density function theory and molecular dynamics simulations, we demonstrate that the compressively strained graphitic carbon nitride (CN) can effectively purify He from Ne and Ar. Under a −6% strain, the CN monolayer with a suitable pore size presents an easily surmountable barrier for He (0.11 eV) but formidable for Ne (0.51 eV) and Ar (2.45 eV) passing through the membrane, and it exhibits exceptionally high selectivity of 5.17 × 10 6 for He/Ne and 1.89 × 10 39 for He/Ar, as well as excellent He permeance of 1.94 × 10 7 GPU at room temperature, superior to those of porous graphene and C 2 N membrane. Our results confirm that strain−tuned CN membrane could be potentially utilized for He separating from other noble gases.