جستجوی مقالات مرتبط با کلیدواژه « hydrogen storage » در نشریات گروه « شیمی »

In this present research, reduced graphene oxide (RGO) and hexagonal boron nitride (h-BN) nanoparticles decorated RGO sheets for a solid-state hydrogen storage medium are synthesized and characterized. The nanocomposite of RGO/h-BN was prepared using the ultrasonic-assisted liquid-phase exfoliation approach and the modified Hummer's method for graphene oxide (GO) synthesis. Using micro-Raman spectroscopy, XRD, SEM, CHNS elemental analysis, and TGA, the produced RGO and RGO/h-BN nanocomposite were evaluated. XRD and micro-Raman validate the RGO and the RGO decorated with h-BN nanoparticles. SEM analysis authorizes the h-BN nanoparticles to be decorated on the surface of the RGO sheet. Using a hydrogenation system akin to Sievert's, the hydrogen adsorption behavior of RGO and RGO/h-BN nanocomposite was investigated. With a maximal hydrogen absorption of 2.1 wt% at 100°C, RGO/h-BN nanocomposite performs better than bare RGO. In the temperature ranges of 109 to 140° and 115 to 149°, the RGO and RGO/h-BN nanocomposites released 100% stored hydrogen. The corresponding binding energy of RGO and RGO/h-BN nanocomposites were 0.31 and 0.32 eV, which is adequate for fuel cell applications. The RGO/h-BN nanocomposite is therefore anticipated to have a promising future in hydrogen storage situations of fuel cell applications.

Various nanostructures have been widely investigated as alternative materials for hydrogen storage using experimental and computational techniques. Combination of boron fullerenes with metals such as magnesium can be used as hydrogen storage materials. In this research, the electronic properties and topology of magnesium-doped boron fullerenes and their interaction with H2 for hydrogen storage are investigated using density functional theory. By density functional calculations with B3LYP/6-31G//M062X/6-31G** method, the structures of B80, Mg12B80, Mg20B80 and Mg30B80 were optimized and the total energy of each of them are calculated. The charge transfer from Mg to B atoms creates an electric field around Mg atoms with a positive charge. When hydrogen molecules approach the system, the hydrogen molecules become polarized and they are adsorbed to these boron fullerenes doped with Mg atoms. Adding one hydrogen molecule to the B80, Mg12B80, Mg20B80 and Mg30B80 structures, adsorption energies, electronic properties and some molecular descriptors were calculated. The results showed that Mg12B80 has the lowest gap energy (ΔEH-L), the lowest hardness (ƞ), and the highest adsorption energy, which indicates the reactivity and the hydrogen storage ability of this structure is higher than B80, Mg20B80 and Mg30B80.

Due to the increase in fuel consumption in the world and the creation of a lot of pollution by fossil fuels, hydrogen has received much attention as a clean fuel. Extensive studies have been conducted on hydrogen production from small-scale to large-scale. Moreover, many studies have been done on the storage of this valuable gas. In this review, various methods of hydrogen production, especially the photoelectrochemical method, have been investigated on a laboratory and industrial scale, and references have been made to hydrogen storage.

Energy problem is one of the serious concerns in modern society; therefore, we have to take hastily an effective action. Hence, researchers are looking for some attractive materials with low-cost, lightweight, and environmentally effective. Recently, 2D materials have taken notable recognition in the field of materials science for multiple energy application, because of its unique electronic and optical properties; and borophene is one of the 2D material which is commendatories than graphene. However, it has not much experimentally explored yet. This review discusses the synthesis process of borophene and discussed energy-related application such as energy storage, optoelectronic, photocatalytic activity, and hydrogen storage. Moreover, this work provides a summary of each application that could help to understand the importance of borophene materials for energy applications.

Nuclear quadrupole resonance (NQR) spectroscopy is an accurate method for determination of electric charge distribution around quadrupolar nuclei. Using ab initio computational methods, it is possible to calculate the Nuclear Quadrupole Coupling Constants (NQCCs) with high accuracy and obtain the useful structural information by using these parameters. Sodium Borohydride, NaBH4, is a metal hydride complex which is a good candidate for being applied in fuel cells as hydrogen storage material with high capacity of 10.6 wt %. Despite the high capacity of hydrogen storage, hydrogen desorption occurs at high temperatures due to high stability and strong bonds of this compound. This problem limits the practical usage of NaBH4 in fuel cells. One way to overcome this problem is applying the high-pressure techniques and using the pressure-induced NaBH4 structures. Under ambient conditions, NaBH4 has a cubic structure (α-NaBH4) that can be converted to β- and γ-NaBH4 by increasing the pressure. In the present research, charge distribution of α-NaBH4 nanocrystal has been compared to that of high-pressure structures using calculated NQCCs, to study the effect of pressure on different NaBH4 structures and hydrogen desorption ability of them. Our results show the smaller value of 2H–NQCCs and higher value of 11B-NQCCs for β-NaBH4 respect to other structures. In other words, the B-H bond is weaker in β-NaBH4 and it is expected that dehydrogenation occur more feasible and at lower temperature in β-phase compared to other phases. NBO results are in agreement with Calculated NQCCs. Calculations performed using Gaussian 09 program in B3LYP/6-311G*.

Different Aluminum: alkaline earth metal atomic weight ratios effects on structure transformations in alanates nanopowders were studied. Changes in crystal structures from alane to alanates by increasing alkaline earth metals dopants in the mixture with slight changes in crystal structures from rhombohedral centered – trigonal (alane) to trigonal (magnesium alanate), and monoclinic (calcium alanate), while thermal behavior alters from one step dissociation at ~150 úC with ~ 8.1 wt% hydrogen release in alane to the two steps hydrogen releases in magnesium alanate at 130 and 285 úC with 7 and 2.1 wt% changes, and to the three steps hydrogen releases in calcium alanate at 127, 260, and 328 úC with 1.7, 2.1, and 4 wt% changes were indicated. Residual phases after dissociation are formed in aluminum and magnesium alloying systems and intermetallic phases like Mg2Al3 and Mg17Al12 with no sign of oxide formation and pure aluminum, Al4Ca, Al2Ca intermetallic phases and Ca in aluminum: Calcium system.

The storage capacity of hydrogen on Na-decorated born nitride nanotubes (BNNTs) is investigated by using density functional theory within Quantum Espresso and Gaussian 09. The results obtained predict that a single Na atom tends to occupy above the central region of the hexagonal rings in (5,0) and (3,3) BNNT structures with a binding energy of -2.67 and -4.28 eV/Na-atom respectively. When a single H2 molecule is absorbed by a Na decorated BNNT, electrostatic field around Na atom and consequently charge of the participating atoms in the interaction region also undergo change. According to Mulliken population and partial density of state (PDOS) analyses, it is observed that positive charge carried by Na atom decreases.Another result of this charge transfer is revealed as an increase in the magnitude of the dipole moment of BNNT-Na-1H2 with respect to BNNT-Na. The results of charge density, separation distance of atoms in adsorption region as well as the H2 binding energy show the hydrogen molecule adsorption is a physical adsorption (physisorption). In the adsorption process, a single sodium atom with losing about 0.4e of its net charge can adsorb up to six H2 molecules with the binding energy of -0.35 and -0.32 eV/ H2 molecule on (5,0) and (3,3) BNNTs respectively. A comparison of the H2 binding energy of two nanotubes implies that the (5,0) BNNT-Na is more favorable for the hydrogen molecule adsorption.

Hydrogen storage capacity of Si-coated B80 fullerene was investigated based on density functional theory calculations within local density approximation and generalized gradient approximation. It is found that Si atom prefer to be attached above the center of pentagon with a binding energy of -5.78 eV. It is inferred that this binding is due to the charge transfer between the Si atom and B80 cage, such as B80AM, B80Ca and B80Mg complexes. The media produced by 12 Si atoms coating on B80, i.e. Si12B80, which Si atoms do not cluster on the B80 surface, can store up to 96 hydrogen molecules resulting in the gravimetric density of 13.87 wt %. Binding of 96 H2 molecules adsorbed on Si12B80 is found to be -0.03 eV/H2 based on the first-principles van der Waals density functional calculations being an indication of the weak interaction (physisorption) between H2 molecules and B80. Furthermore, the adsorption behavior of 96 H2 molecules around the Si12B80 complex was studied through ab initio molecular dynamics simulation at room temperature. Our finding shows that hydrogen molecules escape from the cage, which highlights that the corresponding system easily releases the hydrogen molecules at ambient conditions.

Hydrogen storage capacity of defected graphene was studied by first-principles theory based on Density-functional calculations. Adsorption of molecular hydrogen on a defected graphene V2(5-8-5) and lithium doped defected graphene V2(5-8-5) was carried out. Hydrogen molecules are physisorbed on defected graphene V2(5-8-5) with binding energy about 21–48 meV. Whereas the binding energies increase up to 150–152 meV in Li doped defected graphene. Charge-density analysis indicated that the increasing of binding energy is due to the charge transfer from the H2 molecule to Li . The results explain the enhancement of storage capacity observed in some experimental hydrogen adsorption on defected graphene qualitatively.

In this study, we have investigated radius dependence of hydrogen storage within armchair (n,n) single walled carbon nanotubes (SWCNT) in a square arrays. To this aim, we have employed equilibrium molecular dynamics (MD) simulation. Our simulations results reveal that radius of carbon nanotubes are an important and influent factor in hydrogen distribution inside carbon nanotubes and consequently in amount of hydrogen stored in carbon nanotube array. Moreover, our results show that the SWCNTs with radius smaller than (5, 5) SWCNTs, do not have the ability of adsorption and storage of hydrogen inside themselves.