Two-dimensional Dirac TiB2C2 as a potential anode material for Li-ion batteries: a first-principles study.

The development and design of anode materials with good stability, high capacity, low diffusion barrier and excellent cyclability is an important challenge for further improvement of the battery industry. In this context, a promising 2D anode material TiB2C2 with Dirac cone states is investigated through the first-principles prediction. We found this material to be thermodynamically, dynamically, and thermally stable, suggesting the possibility of its experimental synthesis. Considering its lightweight, planar structure and Dirac cone features, we systematically investigated the feasibility of the TiB2C2 monolayer as an anode material for Li-ion batteries (LIBs). Based on the adsorption energy of lithium on the monolayer surfaces, we determined the sites that can hold lithium ions with high adsorption energy. Moreover, TiB2C2 exhibits good ionic and electronic conductivity, a suitable voltage profile, and high structural stability upon the Li-loading process; it also shows 1.12% change in cell parameters. Importantly, a high storage capacity of up to 1075 mA h g-1 was found. All these criteria conclude the appealing electrochemical performance of the TiB2C2 monolayer as a promising anode material for LIBs.

Enhancement in photocatalytic water splitting using van der Waals heterostructure materials based on penta-layers.

Recently, van der Waals heterostructures (vdWHs) have been used to improve the performance of 2D materials, enabling more applications. By using first-principles calculations, we have studied the electronic and optical properties of vdWHs composed of penta-siligraphene and other penta-layers (p-Si2C4/p-X; X = Si2N4, ZnO2, Ge2C4 or SiGeC4). The stability of the vdWHs is verified by computing their binding energy, vibrational phonon spectra and ab initio molecular dynamics simulations. By assessing the electronic properties, we have found that the p-Si2C4/p-ZnO2, p-Si2C4/p-Ge2C4 and p-Si2C4/p-SiGeC4 vdWHs are semiconductors with an indirect band gap characterized by type-I band alignment. Meanwhile, the p-Si2C4/p-Si2N4 vdWH is a quasi-direct band gap semiconductor characterized by type-II band alignment. Bader charge analysis and charge density of p-Si2C4/p-Si2N4 vdWHs showed that photogenerated electrons move from the p-Si2N4 monolayer to the p-Si2C4 monolayer limiting the recombination of photogenerated charges and improving the photocatalytic efficiency. Furthermore, the p-Si2C4/p-Si2N4 vdWH exhibits suitable band edge positions compared to isolated monolayers suggesting its potential applicability in photocatalytic water splitting. The calculated optical absorption revealed that the p-Si2N4 monolayer exhibits substantial optical absorption in the ultraviolet (UV) range, while the p-Si2C4 monolayer and the p-Si2C4/p-Si2N4 vdWH show outstanding optical absorption on the order of 105 cm-1 in the visible and UV ranges. More importantly, the p-Si2C4/p-Si2N4 vdWH can greatly improve the optical absorption in these regions, which leads to high-efficiency usage of solar energy. Our study provides a route to design new vdWHs based on pentagonal monolayers, as well as an efficient photocatalyst for photocatalytic water splitting and optical devices.

Shape transition and coalescence of Au islands on Ag (110) by molecular dynamics simulation.

We have used molecular dynamics simulations based on many body semi-empirical potentials described by the embedded atom method, to analyze and understand the diffusion and coalescence phenomena of Au-clusters during the heteroepitaxial growth on Ag (110) surface. Temperature ranging from 300 to 700 K were considered. In this study, we examined the heterogeneous system Aun/Ag(110), where n is the number of atoms in each cluster/island (with n = 15, ….35). Our results show that the clusters diffuse on the Ag (110) surface via different diffusion processes, namely, the exchange mechanism and the simple jump, which generate a 2D to 3D transition. Formation and adsorption energies of clusters with different sizes have been computed using static simulations. The dynamic study of coalescence for two islands of system Au15; Au0 - 9/Ag(110) at different temperatures makes it possible to deduce the detail of cluster shape and the influence of its temperature on the stability of the system and its growth during this evolution.