2D Hydrogenated graphene-like borophene as a high capacity anode material for improved Li/Na ion batteries: A first principles study

Fast-growing electronics industry and future energy storage needs have encouraged the design of rechargeable batteries with higher storage capacities, and longer life times. In this regard, two-dimensional (2D) materials, specifically boron and carbon nanosheets, have garnered enthusiasm due to their fascinating electronic, optical, mechanical and chemical properties. Recently, a hydrogen boride (HB) nanosheet was successfully fabricated showing remarkable stability and superior physical properties. Motivated by this experimental study, we used first principle electronic structure calculations to study the feasibility of this nanosheet to serve as an anode material for Li/Na/Ca/Mg/Al ion batteries. Most active adsorption sites for single adatoms were evaluated and next adatoms were gradually inserted into the anode surface accordingly. The charge transfer, electronic density of sates, storage capacity, structural stability, open-circuit potential and diffusion energy barriers were explored. Our theoretical study predicts that HB shows outstanding electrode properties for Li and Na ion batteries. The intercalation of both Li and Na adatoms into the HB monolayer can lead to a high identical storage capacity of 1133.8 mAh/g which is promising compared to the capacities of the traditional anode materials; such as graphite (372 mAh/g) and TiO2 (200 mAh/g), and other 2D materials; such as germanene (369 mAh/g), stanene (226 mAh/g), and phosphorene (432.8 mAh/g) nanosheets. These results may open a new horizon for the design of rechargeable batteries with higher storage capacitates

N-Graphdiyne two-dimensional nanomaterials: Semiconductors with low thermal conductivity and high stretchability

We conducted density functional theory (DFT) and molecular dynamics simulations to explore the mechanical/failure, thermal conductivity and stability, electronic and optical properties of three N-graphdiyne nanomembranes. Our DFT results of uniaxial tensile simulations reveal that these monolayers can yield remarkably high stretchability or tensile strength depending on the atomic structure and loading direction. Studied N-graphdiyne nanomembranes were found to exhibit semiconducting electronic character, with band-gap values ranging from 0.98 eV to 3.33 eV, based on the HSE06 estimations. The first absorption peak suggests that these 2D structures can absorb visible, IR and NIR light. Ab initio molecular dynamics results reveal that N-graphdiyne 2D structures can withstand at high temperatures, like 2000 K. Thermal conductivities of suspended single-layer N-graphdiyne sheets were predicted to be almost temperature independent and about three orders of magnitude smaller than that of the graphene. The comprehensive insight provided by this work highlights the outstanding physics of N-graphdiyne 2D nanomaterials, and suggest them as highly promising candidates for the design of novel stretchable nanodevices

Atomistic Simulations and Computations of Clay Minerals at Geologic Carbon Sequestration Conditions

Classical atomistic simulations are carried out to study carbon sequestration at deep underground formations. In classical simulations, formulas and equations are inherently different from those used in continuum and quantum calculations. Here, in contrast to continuum approaches such as the finite element method, interactions of atomic particles are computed, and unlike quantum techniques such as the density functional theory, calculations are not restricted to a limited number of atoms, therefore a balance between accuracy and computational cost makes classical atomistic techniques the best candidate to study layered materials in numerous situations. The success of CO2 sequestration depends on diverse parameters related to the depth and type of the underground formations. In this work, chemical, physical, and geometrical characteristics of formations are investigated. Different types of interlayer cation (Na+ and Ca2+), intercalated molecule (water and CO2), and clay structure (montmorillonite (MMT) and beidellite (BEI), and pyrophyllite (PPT)) are investigated as chemical parameters. Rotational degree of layers, pressure, temperature and chemical potential are considered as geometrical and physical variables. Using free energy calculations, stable energy states due to the intercalation of water and carbon dioxide to smectite structures are predicted. For hydrated systems, three states consisting of interlayer spacing values 9-10, 11.5-12.5 and 14.5-15.5 A, respectively called 0W, 1W and 2W hydration state are found. For systems including mixed H2O-CO2 intercalation, the amount of adsorbed CO2 alters and reaches its peak at the sub-first hydration levels. Another fascinating result emerges by simulating the binary MMT-CO2 system. The global minimum is found at the dry (0W) state which explains why there is no experimental observation of pure CO2 adsorption on the MMT surface. Finally, ternary smectite-H2O-CO2 simulations show that the amount of adsorbed CO2 in the clay phase is higher than that of bulk phase suggesting that the underground formation is a proper option to store extensive volumes of the green house gas carbon dioxide