Search

The hydrogen storage capacity of a novel permeable material viz Yttrium (Y) decorated zeolite templated carbon (ZTC) has been investigated using ab-initio DFT based simulations. The study reveals that each Y atom bonded on ZTC can attach at the most of 7H 2 molecules with average binding energy of −0.35 eV/H 2. The gravimetric hydrogen storage capacity of ZTC with full decoration of Y atom comes about to 8.61 wt% which is sufficiently higher than the limit of 6.5 wt% set by the energy department of the United States of America. The desorption temperature of the system is 437 K. The stability of the structure over such an elevated temperature has been ensured via molecular dynamics (MD) simulations. The stability of the structure at room temperature and presence of sufficient energy barrier for the diffusion of Y atom signifies that the chances of metal-metal clustering are negligible. It has been discerned that it is the Kubas interaction which plays the key role in the interaction between Y and H 2 molecules. The outcomes show that ZTC adorned with Y is a capable material for hydrogen storage which will inspire the instrumentalists to fabricate ZTC based fuel cell device. [Display omitted] • Y attached on ZTC can adsorb 7H 2 with BE of ∼ −0.35 eV/H 2 leading to 8.61 wt% of H 2. • Almost uniform desorption temperature of 437 K, ideal for fuel cell applications. • The system qualifies for integrity at high temperature. • The system also avoids metal-metal clustering. • The system can act as high capacity reversible hydrogen storage device. [ABSTRACT FROM AUTHOR]

Here, CO gas environment has been used for reduction of graphene oxide (GO) and Pd precursor for preparation of varieties of Pd Nanostructures (PdNSs) with different shapes, size and surface morphologies on graphene support (RG-PdNSs). The extensive ab-initio Molecular Dynamics (MD) simulations and electronic structure calculations have been carried to get theoretical insight for the reduction process of GO by CO. The reduction of GO by CO as observed in experiment are confirmed by ab-initio MD snapshots at different time steps, energetic of the process and the Partial Density of States character of O2p orbital of GO before and after interaction with CO. The discrete states in the Partial Density of States of O2p orbital after CO attack indicates detachment of O from GO. The as-prepared RG-PdNSs are thoroughly characterized by different techniques. The simulation reveals the change in electronic properties from semi-metallic in pristine graphene to metallic due to the attachment of Pd in RG-PdNSs. The electrocatalytic activity of the as-synthesized nanostructures has been investigated toward the multi-functional energy conversion applications, the methanol oxidation reaction, formic acid oxidation reaction and oxygen reduction reaction. The RG-PdNSs exhibit excellent electrocatalytic performance compared to that of unsupported PdNSs and commercial Pd/C. Image 1 [ABSTRACT FROM AUTHOR]

The structural, electronic and elastic properties of LaNi 5− x Fe x (x = 0.25, 0.5, 0.75, 1, 1.25) have been investigated employing the density functional theory with the generalized gradient approximation (GGA). The optimized results indicate that Fe prefers to substitute Ni atom in the 3 g site, and Fe replaces 2c site of Ni atom up to x = 1.25. The radius of 6 m interstitial site gradually increases as x goes from 0 to 1.25 due to volume expansion, which is one of the reasons for the increase of hydrogen storage. Combined with elastic constants and elastic modulus, the anti-pulverization ability of the La–Ni–Fe system enhances, and LaNi 4.25 Fe 0.75 has the best anti-pulverization capability among six crystal structures. According to the density of states, the new peak appears at near −5 eV which is dominated by Fe-3d States. Based on the analysis of charge distributions and charge density differences, the sequence of interaction between atoms is Ni 2 c -Fe 3 g > Ni 2 c -Ni 3 g > Ni 3 g -Ni 3 g > Ni 3 g -Fe 3 g > La–Ni 2 c > La–Fe 2 c , while that of the interactions with H atom is as follows: Fe > Ni 3 g > Ni 2 c > La. The electron hybridization of H and La, Ni, Fe atoms form covalent bonds through electron transfer. To study the interaction between Ni, Fe and H atoms, the electronic densities on (0002) plane for LaNi 4.25 Fe 0.75 are plotted in Figure (a). It is obvious that the charge of H atoms overlaps well with that of iron and nickel atoms, and the corresponding electron density between H atom and Ni, Fe atoms is 0.0864, 0.0868 e/bohr3, respectively. It indicates that the chemical bond between H atom and Fe atom is the strongest, which is still shown that La-Ni-Fe system has the good hydrogen fixation capacity.To analyze the electron transfer behavior and bonding features between atoms, the (0002) plane of charge density difference contour is drawn in Figure (b). It is obvious that hydrogen gains electrons while other atoms lose electrons. Generally, the covalent bonds between H and Fe, Ni are formed. Image 1 • Fe prefers to substitute Ni atom in the 3g site, and Fe is replacing 2c site of Ni atom up to x=1.25. • The radius of 6m interstitial site increases gradually as x goes from 0 to 1.25. • The sequence of interaction between atoms is Ni 2c -Fe 3g > Ni 2c -Ni 3g > Ni 3g -Ni 3g > Ni 3g -Fe 3g > La-Ni 2c > La-Fe 2c , and the order of the interactions with H atom is as follows: Fe > Ni 3g > Ni 2c > La. • The elastic constants for LaNi 5-x Fe x (x=0.25, 0.5, 0.75, 1, 1.25) have been successfully obtained. • LaNi 4.25 Fe 0.75 has the best anti-pulverization characteristics among all structures. [ABSTRACT FROM AUTHOR]

• The detailed ab-initio electronic structure calculations were carried out on non-centrosymmetric La7Ir3 superconductor. • The theoretical results reveal the mixture of La-5d and Ir-5d orbitals to be responsible for superconductivity in La7Ir3. • Band splitting was caused by both spin-orbit and asymmetric spin-orbit couplings but the latter effect is not enough strong. • The electron-phonon coupling constant λ el-ph ∼ 0.63 was estimated, being in the weak-coupling regime of superconductivity. We have carried out the first-principles calculations of the electronic band structure properties of weakly electron correlated, non-centrosymmetric La 7 Ir 3 superconductor (Tc = 2.25 K). We have utilized the GGA-PBE exchange-correlation functionals, implemented in the FP-LAPW ELK code to determine Electronic bands, Densities of States, Fermi surfaces and Electron localization functions. A comparative analysis of scalar relativistic and fully relativistic results reveals the presence of both asymmetric spin - orbit coupling (ASOC) and ordinary spin-orbit coupling (SOC). We have shown that the ASOC with an energy of Δ E ASOC ≈ 10-60 meV, corresponding to relatively low ratio Δ E ASOC / k B T c ≈ 50-310, which is not high enough to cause deviation of the superconductivity from the standard BCS theory. [ABSTRACT FROM AUTHOR]

RbVO 3 luminescent materials have been successfully prepared by solid-state synthesis. The phase, surface morphology and photoluminescence properties of RbVO 3 have been characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and luminescence spectrophotometer, respectively. The band structure, Density of States and optical properties of RbVO 3 have been simulated by Materials Studio software based on density functional theory (DFT). According to the experimental results and the First-principles, the electronic structure and optical properties of RbVO 3 were studied. The results show that RbVO 3 crystal has a direct band gap with a band gap of 2.973 eV. Under ultraviolet excitation in the range of 210–390 nm, and the excitation spectrum peak appears at 340 nm. The emission spectrum of RbVO 3 phosphors ranges from 400 to 700 nm, and its peak emission spectrum is near 507 nm, showing white luminescence emission. • RbVO 3 has been successfully prepared by solid-state synthesis. • The RbVO 3 luminescent material is a high brightness phosphor. • PL measurements on RbVO 3 shows a broad emission centered at 507 nm. • The optical properties of RbVO 3 are studied in detail based on first-principles for the first time. • The band structure, density of States and optical properties of RbVO 3 were calculated to reveal its luminescence mechanism. [ABSTRACT FROM AUTHOR]

The removal of fluoride from water using adsorption on a low-cost mineral such as kaolinite is an important research topic. The present communication uses Density Functional Theory (DFT) and Molecular Dynamics (MD) based simulations to comprehensively investigate the adsorption behaviour of HF, one of the most predominant species of fluoride in the aqueous solutions, on the (0 0 1) surface of kaolinite. The optimum geometric configurations of adsorption of HF on different possible sites on the mineral surface have been established, and the corresponding adsorption energies, bond distances, Partial Density of States (PDOS), Mulliken charges and electron density difference plots have been analyzed to understand the interaction at each site. To explore the site-dependent adsorption behaviour, the interaction of HF has been investigated on different sites such as aluminium centres, surface oxygen atoms (both lying and upright) and cavity site (void space encircled by six aluminium centres). The analysis shows that the F atom has a strong tendency to form hydrogen bonds with the surface H atom on kaolinite. Among the three aforementioned types of adsorption sites considered, the "cavity" site is found to offer the greatest adsorption strength. Further, MD simulations have been undertaken to explain the effect of water on the adsorption and substantiate the bonding mechanism. • Adsorption of HF on the kaolinite (0 0 1) surface was investigated by DFT-D simulation. • Optimum adsorption configurations of HF on different possible sites are established. • MD simulations reveal effect of solvent on the behaviour of HF adsorption. • Complex structure, preferred adsorption position and adsorption bonding pattern were solved. • Among all the adsorption sites considered, the "cavity" site is found to offer the greatest adsorption strength. [ABSTRACT FROM AUTHOR]

In the present approach, we have successfully synthesized wormlike Ni 3 S 2 and Ni 3 S 2 -RGO hybrids on nickel (Ni) foam by a facile and highly reproducible one-step chemical vapor deposition (CVD) method. We have demonstrated that Ni 3 S 2 and Ni 3 S 2 -RGO hybrids can be grown directly on the current collector of energy storage devices without using any binder, which may lead to serve industry for large-scale production of the material. We have studied the pseudocapacitive energy storage performance of the CVD grown Ni 3 S 2 and its hybrids with variable concentration of RGO. The Ni 3 S 2 -RGO hybrid with 0.5 mg GO showed a maximum areal specific capacitance of 1.4 F·cm−2 at a current density of 1 mA·cm−2 (approximately 1124 Fg−1 at a current density of 1 Ag−1). The enhanced supercapacitive performance of Ni 3 S 2 -RGO predominantly due to its high surface area and high conductivity as compared to bare Ni 3 S 2. The electrochemical impedance spectroscopic analysis revealed Ni 3 S 2 -RGO possess enhanced charge-transfer characteristics as compared to bare Ni 3 S 2. Furthermore, Density Functional Theory (DFT) simulations infer the strong hybridization between C p orbital and Ni d orbital lead to enhanced electrochemical property and Density of States (DOS) is crucially responsible for the improved charge storage performance of Ni 3 S 2 -RGO hybrids. Unlabelled Image • A naive, convinient, cost effective and less time-consuming CVD based synthesis technique is developed for the synthesis of binder free Ni 3 S 2 /RGO electrode. • Resultant Ni 3 S 2 /RGO hybrid exhibit maximum capacitance of 1124 Fg−1 at a current density of 1 Ag−1. • Cycling stability was good even after 5000 charge/discharge cycles with capacitance retention of 78% of the initial specific capacitance. • Theoretical DFT simulation studies support the experimental data and explain the mechanisms responsible for the enhanced supercapacitor property of Ni 3 S 2 /RGO hybrid. [ABSTRACT FROM AUTHOR]