Electronic Structure Calculations of Hydrogen Storage in Lithium-Decorated Metal-Graphyne Framework

Density functional study of physisorption of H2 molecules on scandium and yttrium decorated C20 fullerene: prospect for hydrogen storage

CONTEXT

Hydrogen storage in porous nanostructured compounds have recently attracted a lot of attention due to the fact that the underlying adsorption mechanism and thermodynamics provide suitable platform for room temperature adsorption and desorption of H2 molecules. This work reports the findings of a study on the reversible hydrogen storage capacities of Sc and Y decorated C20 fullerene, conducted using dispersion-corrected density functional theory (DFT) calculation. The transition metal (TM) atoms, such as Sc and Y, are identified to attach to the C-C bridge position of the C20 fullerene through non-covalent closed-shell interactions. This suggests that the interaction between the TM atoms and the fullerene occurs via weak van der Waals forces rather than stronger covalent bonds. The thermodynamic stability of the decorated fullerene structures is assessed using different reactivity descriptors. Each Sc and Y atom attached to the C20 fullerene is capable of absorbing maximum of 6 and 7 numbers of hydrogen molecules, respectively. This results in practical gravimetric densities of up to 4.0 wt% and 4.04 wt% at a temperature of 300 K and a pressure of 60 bar. These findings highlight the significant hydrogen storage capacities of the decorated fullerene structures, indicating their potential for practical use in hydrogen storage systems. The average adsorption energy of H2 molecules is found lying in the range of 0.332-0.276 eV implying the adsorption process to be physisorptive. Overall, the study provides valuable insights into the hydrogen storage capabilities of Sc and Y decorated C20 fullerene complexes, offering a promising avenue for the development of efficient and reversible hydrogen storage materials for clean energy applications.

METHODS

Geometry optimization and other electronic structure calculations was performed by Gaussian 09 software using density functional theory (DFT) with the B3LYP-D3 and M06-2X functionals and the basis set 6-311 + G(d,p). The dispersion-corrected and hybrid meta-exchange correlation functionals were employed because of their accuracy in describing non-covalent interactions, rendering them appropriate for investigating hydrogen adsorption on surfaces.

Reversible hydrogen storage and release mechanism of a B2N monolayer: a first-principles insight

It was found the physical adsorption could be an efficient strategy for high capacity, high efficiency and high safety in hydrogen storage. In this research, a systematic investigation into the potential of the B2N monolayer as an excellent physical adsorption hydrogen storage material is conducted by utilizing the first-principles calculation method. The findings of the investigation demonstrate that the B2N monolayer has a planar lattice and excellent structural stability. It is possible for H2 molecules to adsorb onto the B2N monolayer spontaneously. Both the individual adsorption and saturation adsorption corresponded to average adsorption energies ranging from -0.221 to -0.194 eV, fulfilling the physical adsorption criteria. In the case of saturation adsorption, a 1 × 2 × 1 B2N supercell can store a total of 24 H2 molecules, with the hydrogen gravimetric density up to 14.511 wt% and volumetric density up to 138 g L-1. A semi-empirical calculation method is used to research the performance of the system in terms of adsorption and desorption with actual temperature and pressure conditions. Under the actual conditions with adsorption carried out at 30 atm/233 K and desorption carried out at 3 atm/358 K, the maximal reversible hydrogen storage capacity of the hydrogen storage system based on the B2N monolayer can still reach 12.157 wt%, which is superior to that of many other boron-nitrogen compounds and metal-free functionalized hydrogen storage materials. The findings of this work indicate that the pristine B2N monolayer is one of the promising physical adsorption materials which could achieve excellent reversible hydrogen storage under defined conditions.

Exploring the Potential of Chemically Modified Graphyne Nanodots as an Efficient Adsorbent and Sensitive Detector of Environmental Contaminants: A First Principles Study

In this study, we investigated the reactivity of γ-graphyne (Gp) and its derivatives, Gp-CH3, Gp-COOH, Gp-CN, Gp-NO2, and Gp-SOH, for the removal of toxic heavy metal ions (Hg+ 2, Pb+ 2, and Cd+ 2) from wastewater. From the analysis of the optimized structures, it was observed that all the compounds exhibited planar geometry. The dihedral angles (C9-C2-C1-C6 and C9-C2-C1-C6) were approximately 180.00°, indicating planarity in all molecular arrangements. To understand the electronic properties of the compounds, the HOMO (EH) and LUMO (EL) energies were calculated, and their energy gaps (Eg) were determined. The EH and EL values ranged between - 6.502 and - 8.192 eV and - 1.864 and - 3.773 eV, respectively, for all the compounds. Comparing the EH values, Gp-NO2 exhibited the most stable HOMO, while Gp-CH3 had the least stable structure. In terms of EL values, Gp-NO2 had the most stable LUMO, while Gp-CH3 was the least stable. The Eg values followed the order: Gp-NO2 < Gp-COOH < Gp-CN < Gp-SOH < Gp-CH3 < Gp, with Gp-NO2 (4.41 eV) having the smallest energy gap. The density of states (DOS) analysis showed that the shape and functional group modifications affected the energy levels. Functionalization with electron-withdrawing (CN, NO2, COOH, SOH) or electron-donating (CH3) groups reduced the energy gap. To specifically target the removal of heavy metal ions, the Gp-NO2 ligand was selected for its high binding energy. Complexes of Gp-NO2-Cd, Gp-NO2-Hg, and Gp-NO2-Pb were optimized, and their properties were analyzed. The complexes were found to be planar, with metal-ligand bond distances within the range of 2.092→3.442 Å. The Gp-NO2-Pb complex exhibited the shortest bond length, indicating a stronger interaction due to the smaller size of Pb+ 2. The computed adsorption energy values (Eads) indicated the stability of the complexes, with values ranging from - 0.035 to -4.199 eV. Non-covalent interaction (NCI) analysis was employed to investigate intermolecular interactions in Gp-NO2 complexes. The analysis revealed distinct patterns of attractive and repulsive interactions, providing valuable insights into the binding preferences and steric effects of heavy metals.

Hydrogen physisorption on the (BeO)n, B2H4(Be,Ti), and B6Ti3 metal clusters: a computational study of energies and atomic charges

The equilibrium structures of BeO clusters and Be,Ti-decorated boranes were computed with the ωB97X-D method and the 6-31G + (2d,2p) and aug-cc-pVTZ basis sets to study their intermolecular interactions with hydrogen molecules. Thermochemical and molecular properties such as the harmonic vibrational frequency, dipole and quadrupole moments, and atomic charges are employed to understand the attractive interactions that control the adsorption process. Comparison of molecular properties and atomic charges of the studied compounds before and after H₂ molecule adsorption shows that most of the interactions among the BeO clusters and boranes with H₂ molecules constitute a combination of dispersion, electrostatic, and weak charge transfer interactions. Calculated values of Hirschfeld atomic charges and ΔE_e (in parenthesis) (BeO)₄.8H₂ (0.028 e and -2.0 kcal.mol^-1), (BeO)₂.12H₂ (0.030 e and -2.8 kcal.mol^-1), B₆Ti₃.10H₂ (0.045 e and -15.4 kcal.mol^-1), and B₆Ti₃⁺.10H₂ (0.058 e and -15.3 kcal.mol^-1) show qualitative correlation between hydrogen atomic charges and electronic energy of hydrogen interaction. The ωB97X-D/6-31 + G(2d,2p) values of Gibbs free energy at 298.15 K for (BeO)₄.8H₂ B₂H₄Ti.4H₂ and B₆Ti₃.10H₂ clusters are equal to -5.0, -4.9, and -5.1 kcal.mol^-1, respectively, which are within the range of energy parameters of materials that could be employed in hydrogen storage tanks for light vehicles.

Recent Progress Using Solid-State Materials for Hydrogen Storage: A Short Review

With the rapid growth in demand for effective and renewable energy, the hydrogen era has begun. To meet commercial requirements, efficient hydrogen storage techniques are required. So far, four techniques have been suggested for hydrogen storage: compressed storage, hydrogen liquefaction, chemical absorption, and physical adsorption. Currently, high-pressure compressed tanks are used in the industry; however, certain limitations such as high costs, safety concerns, undesirable amounts of occupied space, and low storage capacities are still challenges. Physical hydrogen adsorption is one of the most promising techniques; it uses porous adsorbents, which have material benefits such as low costs, high storage densities, and fast charging–discharging kinetics. During adsorption on material surfaces, hydrogen molecules weakly adsorb at the surface of adsorbents via long-range dispersion forces. The largest challenge in the hydrogen era is the development of progressive materials for efficient hydrogen storage. In designing efficient adsorbents, understanding interfacial interactions between hydrogen molecules and porous material surfaces is important. In this review, we briefly summarize a hydrogen storage technique based on US DOE classifications and examine hydrogen storage targets for feasible commercialization. We also address recent trends in the development of hydrogen storage materials. Lastly, we propose spillover mechanisms for efficient hydrogen storage using solid-state adsorbents.

Reversible Hydrogen Storage in Metal-Decorated Honeycomb Borophene Oxide

Two-dimensional (2D) boron-based materials are receiving much attention as H2 storage media due to the low atomic mass of boron and the stability of decorating alkali metals on the surface, which enhance interactions with H2. This work investigates the suitability of Li, Na, and K decorations on 2D honeycomb borophene oxide (B2O) for H2 storage, using dispersion corrected density functional theory (DFT-D2). A high theoretical gravimetric density of 8.3 wt % H2 is achieved for the Li-decorated B2O structure. At saturation, each Li binds to two H2 with an average binding energy of -0.24 eV/H2. Born-Oppenheimer molecular dynamics simulations at temperatures of 100, 300, and 500 K demonstrate the stability of the Li-decorated structure and the H2 desorption behavior at different temperatures. Our findings indicate that Li-decorated 2D B2O is a promising material for reversible H2 storage and recommend experimental investigation of 2D B2O as a potential H2 storage medium.

Graphynes: indispensable nanoporous architectures in carbon flatland

Theoretical design and experimental realization of novel nanoporous architectures in carbon membranes has been a success story in recent times. Research on graphynes, an interesting class of materials in carbon flatland, has contributed immensely to this success story. Graphyne frameworks possessing sp and sp2 hybridized carbon atoms offer a variety of uniformly distributed nanoporous architectures for applications ranging from water desalination, gas separation, and energy storage to catalysis. Theory has played a pivotal role in research on graphynes, starting from the prediction of various structural forms to the emergence of their remarkable applications. Herein, we attempt to provide an up-to-date account of research on graphynes, highlighting contributions from numerous theoretical investigations that have led to the current status of graphynes as indispensable materials in carbon flatland. Despite unsolved challenges in large-scale synthesis, the future appears bright for graphynes in present theoretical and experimental research scenarios.

Facile Synthesis and Superior Catalytic Activity of Nano-TiN@N-C for Hydrogen Storage in NaAlH4

Herein, we synthesize successfully ultrafine TiN nanoparticles (<3 nm in size) embedded in N-doped carbon nanorods (nano-TiN@N-C) by a facile one-step calcination process. The prepared nano-TiN@N-C exhibits superior catalytic activity for hydrogen storage in NaAlH₄. Adding 7 wt % nano-TiN@N-C induces more than 100 °C reduction in the onset dehydrogenation temperature of NaAlH₄. Approximately 4.9 wt % H₂ is rapidly released from the 7 wt % nano-TiN@N-C-containing NaAlH₄ at 140 °C within 60 min, and the dehydrogenation product is completely hydrogenated at 100 °C within 15 min under 100 bar of hydrogen, exhibiting significantly improved desorption/absorption kinetics. No capacity loss is observed for the nano-TiN@N-C-containing sample within 25 de-/hydrogenation cycles because nano-TiN functions as an active catalyst instead of a precursor. A severe structural distortion with extended bond lengths and reduced bond strengths for Al-H bonding when the [AlH₄]^- group adsorbs on the TiN cluster is demonstrated for the first time by density functional theory calculations, which well-explains the reduced de-/hydrogenation temperatures of the nano-TiN@N-C-containing NaAlH₄. These findings provide new insights into designing and synthesizing high-performance catalysts for hydrogen storage in complex hydrides.

Hydrogen sorption efficiency of titanium decorated calix[4]pyrroles

Ti decorated calix[4]pyrrole and octamethylcalix[4]pyrrole is explored as a potential H₂storage material.