Hydrogen storage properties of light metal adatoms (Li, Na) decorated fluorographene monolayer

Enhanced H2 Storage Capacity of Bilayer Hexagonal Boron Nitride (h-BN) Incorporating van der Waals Interaction under an Applied External Electric Field

Lightweight two-dimensional materials are being studied for hydrogen storage applications due to their large surface area. The characteristics of hydrogen adsorption on the h-BN bilayer under the applied electric field were investigated. The overall storage capacity of the bilayer is 6.7 wt % from our theoretical calculation with E _ads of 0.223 eV/H₂. The desorption temperature to remove the adsorbed H₂ molecules from the surface of the h-BN bilayer system in the absence of an external electric field is found to be ∼176 K. With the introduction of an external electric field, the E _ads lies in the range of 0.223-0.846 eV/H₂ and the desorption temperature is from 176 to 668 K. Our results show that the external electric field enhances the average adsorption energy as well as the desorption temperature and thus makes the h-BN bilayer a promising candidate for hydrogen storage.

Capacity enhancement of polylithiated functionalized boron nitride nanotubes: an efficient hydrogen storage medium

By using first principles density functional theory simulations, we report detailed geometries, electronic structures and hydrogen (H₂) storage properties of boron nitride nanotubes (BNNTs) doped with selective polylithiated molecules (CLi₂). We find that unsaturated bonding of Li-1s states with BNNT significantly enhances the system stability and hinders the Li-Li clustering effect, which can be detrimental for reversible H₂ storage. The H₂ adsorption mechanism is explained on the basis of polarization caused by the cationic Li⁺ of CLi₂ molecules bonded with BNNT. The incident H₂ molecules are adsorbed with BNNT-nCLi₂ through electrostatic and van der Waals interactions. We find that with a maximum of 5.0% of CLi₂ coverage on BNNT, an H₂ gravimetric density of up to 4.41 wt% can be achieved with adsorption energies in the range of -0.33 eV per H₂, which is suitable for ambient condition H₂ storage applications.

Graphitic carbon nitride nano sheets functionalized with selected transition metal dopants: an efficient way to store CO2

Proficient capture of carbon dioxide (CO₂) is considered to be a backbone for environment protection through countering the climate change caused by mounting carbon content. Here we present a comprehensive mechanism to design novel functional nanostructures capable of capturing a large amount of CO₂ efficiently. By means of van der Waals corrected density functional theory calculations, we have studied the structural, electronic and CO₂ storage properties of carbon nitride (g-C₆N₈) nano sheets functionalized with a range of transition metal (TM) dopants ranging from Sc to Zn. The considered TMs bind strongly to the nano sheets with binding energies exceeding their respective cohesive energies, thus abolishing the possibility of metal cluster formation. Uniformly dispersed TMs change the electronic properties of semiconducting g-C₆N₈ through the transfer of valence charges from the former to the latter. This leaves all the TM dopants with significant positive charges, which are beneficial for CO₂ adsorption. We have found that each TM's dopants anchor a maximum of four CO₂ molecules with suitable adsorption energies (-0.15 to -1.0 eV) for ambient condition applications. Thus g-C₆N₈ nano sheets functionalized with selected TMs could serve as an ideal sorbent for CO₂ capture.

Light metal decorated graphdiyne nanosheets for reversible hydrogen storage

The sensitive nature of molecular hydrogen (H₂) interaction with the surfaces of pristine and functionalized nanostructures, especially two-dimensional materials, has been a subject of debate for a while now. An accurate approximation of the H₂ adsorption mechanism has vital significance for fields such as H₂ storage applications. Owing to the importance of this issue, we have performed a comprehensive density functional theory (DFT) study by means of several different approximations to investigate the structural, electronic, charge transfer and energy storage properties of pristine and functionalized graphdiyne (GDY) nanosheets. The dopants considered here include the light metals Li, Na, K, Ca, Sc and Ti, which have a uniform distribution over GDY even at high doping concentration due to their strong binding and charge transfer mechanism. Upon 11% of metal functionalization, GDY changes into a metallic state from being a small band-gap semiconductor. Such situations turn the dopants to a partial positive state, which is favorable for adsorption of H₂ molecules. The adsorption mechanism of H₂ on GDY has been studied and compared by different methods like generalized gradient approximation, van der Waals density functional and DFT-D3 functionals. It has been established that each functionalized system anchors multiple H₂ molecules with adsorption energies that fall into a suitable range regardless of the functional used for approximations. A significantly high H₂ storage capacity would guarantee that light metal-doped GDY nanosheets could serve as efficient and reversible H₂ storage materials.

Effect of Li Termination on the Electronic and Hydrogen Storage Properties of Linear Carbon Chains: A TAO-DFT Study

Accurate prediction of the electronic and hydrogen storage properties of linear carbon chains (C n ) and Li-terminated linear carbon chains (Li2C n ), with n carbon atoms (n = 5-10), has been very challenging for traditional electronic structure methods, due to the presence of strong static correlation effects. To meet the challenge, we study these properties using our newly developed thermally-assisted-occupation density functional theory (TAO-DFT), a very efficient electronic structure method for the study of large systems with strong static correlation effects. Owing to the alteration of the reactivity of C n and Li2C n with n, odd-even oscillations in their electronic properties are found. In contrast to C n , the binding energies of H2 molecules on Li2C n are in (or close to) the ideal binding energy range (about 20 to 40 kJ/mol per H2). In addition, the H2 gravimetric storage capacities of Li2C n are in the range of 10.7 to 17.9 wt%, satisfying the United States Department of Energy (USDOE) ultimate target of 7.5 wt%. On the basis of our results, Li2C n can be high-capacity hydrogen storage materials that can uptake and release hydrogen at temperatures well above the easily achieved temperature of liquid nitrogen.

Manipulating energy storage characteristics of ultrathin boron carbide monolayer under varied scandium doping

We report, for the first time we believe, a detailed investigation on hydrogen storage efficiency of scandium (Sc) decorated boron carbide (BC₃) sheets using spin-polarized density functional theory (DFT).