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Traditionally, h -BN is used as coating material to prevent corrosion on the metal surface. In sharp contrast to this, here we show catalytic behavior of h -BN monolayer deposited on Ni(111) surface, clearly demonstrating the influence of the support in modulation of h -BN electronic structure. Using first principles density functional theory we have studied the interaction of O 2 molecules with the h -BN/Ni(111) surface. The activation of O O bond, which is the most important step for oxidative catalysis, showed dependence on the O 2 coverage. Thus this study is extremely important to predict the optimum O 2 pressure in reaction chamber for efficient catalysis. [ABSTRACT FROM AUTHOR]

To surmount the limitations of bulk MgH 2 for the purpose of hydrogen storage, we report here, a detailed first principles density functional theory (DFT) based study on the structure and stability of neutral (Mg m ) and positively charged (Mg m + ) Mg nanoclusters of different sizes ( m = 2, 4, 8 and 12) and their interaction with molecular hydrogen (H 2 ). Our results demonstrate that H 2 is weakly bound to the Mg nanoclusters through van der Waals interactions. Incorporation of Grimme’s dispersion correction (D3) in the DFT based exchange–correlation functionals leads to improved accuracy of H 2 interaction energy (IE) values that fall within an energy window (between physisorption and chemisorption) desirable for hydrogen storage. Energy decomposition analysis reveals the significance of polarization energy for these Mg–H 2 binding. Ab-initio molecular dynamics simulation shows that complete dehydrogenation from these Mg nanoclusters occur at ∼100 °C which is a significant improvement over bulk MgH 2 (∼300 °C). [ABSTRACT FROM AUTHOR]

[Display omitted] • High performance was obtained in Co 82 Zr 12 V 5 B 1 and Co 82 Zr 12 V 4 B 2 annealed ribbons. • Combinatorial addition of V and B further improves the magnetic properties. • Maximum H c (3.58 kOe) was achieved for Co 82 Zr 12 V 5 B 1 ribbons annealed at 750 °C. • M r /M 17 = 0.69, (BH) max = 4.36 MGOe and grain size (<50 nm) were achieved by B addition. • Experimental observations are in conformity with our theoretical calculations. For the development of rare-earth free permanent magnets with better performance to cost ratio, V and B dopings were employed to enhance the hard magnetic properties of Zr-Co-V-B alloys. The effect of V and B microalloying additions on the magnetic properties, phase stability and microstructure of the metastable Co 5 Zr phase have been investigated with experimental measurements together with first principles based on the DFT (Density Functional Theory) calculations. This study also investigates the effects of annealing at different temperatures on the intrinsic and extrinsic magnetic properties of Co 82 Zr 12 V 6-x B x melt-spun ribbons. Rapidly solidified Co 82 Zr 12 V 6-x B x (x = 1, 2, 3) alloy ribbons were produced by melt-spinning. For as-spun Co 82 Zr 12 V 6-x B x (x = 1, 2, 3) ribbons, the coercivity H c decreases from 2.34 kOe to 0.008 kOe with an increasing × value from 1 to 3. The amorphous alloy ribbons were annealed in a vacuum furnace at a series of temperatures of 600 °C, 650 °C, 700 °C and 750 °C each for 30 min. The XRD analysis showed the presence of two soft magnetic phases (fcc-Co and Co 23 Zr 6), accompanied with a hard phase Co 5 Zr in ribbons thus leading to the desired hard/soft structure and the amount of both (hard and soft) phases increased with the annealing temperature. Coercivity was found to increase upon annealing treatment. The phase stabilities of the Co 82 Zr 12 V 6-x B x ribbons were calculated from the total energy by the DFT calculations in this work. The calculated magnetic anisotropy energies have been compared to that of experimental coercivity values. Annealed sample Co 82 Zr 12 V 5 B 1 showed the maximum coercivity value of 3.58 kOe due to the formation of a high volume fraction of hard magnetic phase (Co 5 Zr) and evenly distributed finer grains throughout the matrix. However, annealing under the same conditions resulted in lower coercivity of about 0.088 kOe and 1.61 kOe for Co 82 Zr 12 V 3 B 3 and Co 82 Zr 12 V 4 B 2 samples, respectively. Although sample Co 82 Zr 12 V 4 B 2 exhibited higher remanence (42.80 emu/g) and maximum magnetization value with the applied field of 17 kOe (i.e. M 17 = 77.70 emu/g) compared to Co 82 Zr 12 V 3 B 3 sample. [ABSTRACT FROM AUTHOR]

Presence of curvature is considered as a tuning parameter to activate the hydrogen storage capability of carbon nanostructures. Here, we explicate the role of 'intra-curvature' in a set of single-walled carbon nanohorns (SWCNHs), to adsorb light metal ad-atoms (M) e.g. Li, Na, Ca and subsequently explore the metal-doped systems for hydrogen storage application using density functional theory. The binding strength of ad-atoms on SWCNHs of different curvature is correlated with the π electron occupancy of the corresponding carbon ring. Higher π electron occupancy causes significantly high binding energy of the metal ad-atoms (M), thereby indicating high stability of those M−C bonds for intra-curvature values more than 11⁰, even at a higher temperature. After full hydrogenation, Li-doped SWCNHs are found to contain a maximum of 7.5 wt % of hydrogen. Overall, our results indicate that Li-doped SWCNHs with intra-curvature values higher than 11⁰, is a potential candidate for hydrogen storage. Image 1 • Exploring metal-doped single-walled carbon nanohorns for hydrogen storage. • Intra-curvature of nanohorns is exploited to tune the metal-carbon bond strength. • π electron occupancy of the hexagonal rings acts as the main descriptor. • Higher stability of metal-carbon bonds for intra-curvature values more than 11°. • Li-doping with intra-curvature more than 11° is suitable for hydrogen storage. [ABSTRACT FROM AUTHOR]

First principles density functional theory based calculations have been performed to investigate the strain and temperature induced tunability of the thermoelectric properties of monolayer (ML) MoS 2. Modifications in the electronic and phononic transport properties, under two anisotropic uniaxial strains along the armchair (AC) and zigzag (ZZ) directions, have been explored in detail. Considering the intrinsic carrier-phonon scattering, we found that the charge carrier mobility (μ) and relaxation time (τ) increase remarkably for strains along the ZZ direction. Concomitantly, strain along the ZZ direction significantly reduces the lattice thermal conductivity (κ L) of ML-MoS 2. The combined effect of shortened phonon relaxation time and group velocity, and the reduced Debye temperature is found to be the driving force behind the lowering of κ L. The large reduction in κ L and increase in τ , associated with the strains along the ZZ direction, act in unison to result in enhanced efficiency and hence, improved thermoelectric performance. Nearly 150% enhancement in the thermoelectric efficiency can be achieved with the optimal doping concentration. We, therefore, highlight the significance of in-plane tensile strains, in general, and strains along the ZZ direction, in particular, in improving the thermoelectric performance of ML-MoS 2. [Display omitted] • DFT based study on the strain engineered thermoelectric performance of ML-MoS 2. • Tensile strain driven anisotropic enhancement in the thermoelectric efficiency. • Charge carrier mobility and relaxation time increases remarkably with strain. • Significant strain induced reduction in lattice thermal conductivity. • Tensile strain along the zigzag direction in particular results in large increase in ZT. [ABSTRACT FROM AUTHOR]

Using state-of-the-art density functional theory (DFT) based approach; we investigated the catalytic activity of electron doped C 2 N monolayer (O → N) for CO oxidation. Large surface-to-volume ratio and uniformly distributed holes of recently synthesized planar 2D C 2 N have made it a potential candidate as noble metal-free catalyst. However, pristine C 2 N monolayer is chemically inert and hinders the adsorption of O 2 and CO molecule on it. Oxygen doping in C 2 N brings additional electrons to the system and introduces donor state below E F . Thus the reactivity of O-doped C 2 N (2OC 2 N) monolayer gets significantly enhanced, thereby opening up the possibility of its usage as a catalyst. This reactive 2OC 2 N surface adsorbs an incoming O 2 molecule along with the elongation of O O bond, making it chemically active. Presence of this pre-adsorbed active O 2 greatly impedes the adsorption of another incoming CO, favoring Eiley-Rideal (ER) mechanism for CO oxidation. [ABSTRACT FROM AUTHOR]

The electrocatalytic activity of T6[100] surface containing both sp 3 (C 1 ) and sp 2 (C 2 ) hybridized carbon atoms is explored using first-principles density functional theory based approach. The top layered C 1 atom of the surface is found to be more active towards the oxygen reduction reaction (ORR), as compared to that of C 2 atom. This is attributed to the presence of dangling σ bond in the corresponding C 1 atom, leading to the high electron density near the Ferrmi level. Whereas, the π electron in the top layered C 2 atom forms a weak out of plane network. As estimated from free energy profile, the overpotential is much lower when C 1 is considered as the active site and the final step i.e desorption of final OH − ion is found to be the potential determining step. We have also reported the effect of Si dopant on the catalytic activity of T6[100] surface and explained the origin of high overpotential value in this case. Thus in this report, we propose a new metal-free catalyst i.e T6[100] surface, having both sp 2 (maintains the high metallicity needed to reduce ohmic loss) and sp 3 (helps in capturing the upcoming molecules) hybridized carbon atoms, as a potential candidate for ORR. [ABSTRACT FROM AUTHOR]

Employing first principles density functional theory (DFT) based approach, the structure, stability and hydrogen storage efficiency of a hydrogenated hexagonal boron nitride sheet (BHNH chair conformer) functionalized by the lightest alkali metal atom Li has been explored here in details. Substituting one hydrogen atom from both B and N sides of BHNH sheet by a Li atom, we have found that Li becomes cationic and acts as a binding site to adsorb hydrogen molecules. The stability of this Li-substituted BHNH sheet has been indicated via Ab-initio Molecular Dynamics (AIMD) simulation upto 400 K. The binding energy (∼0.18–0.3 eV/H 2 molecule) and gravimetric density (∼6 wt %) (upto ∼200 K) of the hydrogen molecules fall in the required window for practical hydrogen storage. AIMD simulation indicates complete dehydrogenation from this system occurs at ∼400 K, thereby predicting the suitability of this system from the point of view of efficient hydrogen storage. [ABSTRACT FROM AUTHOR]

• Hf addition stabilizes the 1:7H phase. • Grain refinement is achieved by B addition. • The maximum coercivity (H c) of the ribbons is achieved at Hf ≃ 3 at.%. • The remanent magnetization increases with increasing B content. • Experimental observations are in conformity with our theoretical calculations. The effect of Hf and B additions on the phase stability, microstructure and magnetic properties of the metastable SmCo 7 (1:7H) ribbons has been investigated with a combined approach of experimental measurements and first principle DFT (density functional theory) calculations. A series of (Sm 0.12 Co 0.88) 95 Hf 5−x B x (x = 0, 1, 2, 3, 4 and 5) alloys were arc-melted in a TIG (tungsten inert gas) arc melting furnace, followed by melt-spinning onto a copper roller at a wheel velocity of 40 m/s. Characterization based on X-ray diffraction indicates that the major phase is SmCo 7 having meta-stable (TbCu 7 -type) structure. From the total energy calculations using DFT, the phase stability of (Sm 0.12 Co 0.88) 95 Hf 5−x B x ribbons have been confirmed. Moreover, Hf and B addition results in an effective grain refinement; average grain size being as low as ~ 80 nm. The reduction in grain size leads to significant changes (increase or decrease) in magnetic properties depending on the Hf/B ratio. The coercivity value (H c) varies between 7 kOe and 12 kOe as x (at.% B) increases from 0 to 5 at.%. The experimental coercivity values have been compared with the computed anisotropy energies. The saturation magnetization (M s) increases from ~ 54 emu/g to 77 emu/g with increasing B concentration (x). [ABSTRACT FROM AUTHOR]