Density functional theory study on hydrogen storage capacity of yttrium decorated graphyne nanotube

The hydrogen storage capacity of yttrium decorated graphyne nanotubes is calculated using spin polarized DFT method. The stabilities, electronic properties and the structures of Y attachment on graphyne tube are investigated. It is revealed that Y can be separately adsorbed on graphyne tube with the binding energy of 6.76 eV and the clustering of metal atoms is hindered. The geometry optimization shows that Y atoms decorated graphyne tube can capture 42H₂ molecules through Dewar-Kubas like interaction and the polarization under the electrostatic potential formed by Y and graphyne tubes. The weight percent capacity is 5.71 wt%, with an average hydrogen adsorption energy of −0.153 eV per H₂, indicating its potential application on hydrogen storage candidates.     

A comparative study of the reversible hydrogen storage behavior in several metal decorated graphyne

In virtue of the first-principle calculations, the hydrogen storage behavior in several metal decorated graphyne was investigated. It is found that the hydrogen storage capacity can be as large as 18.6, 10.5, 9.9 and 9.5 wt% with average adsorption energy of about −0.27, −0.36, −0.76 and −0.70 eV/H₂ for Li, Ca, Sc, Ti decorated graphyne, respectively. The results suggest potential candidates for hydrogen storage at ambient condition. The adsorption mechanism for H₂ on metal coated graphyne was mainly attributed to the polarization induced by electrostatic field of metal atoms on graphyne and the hybridization between the metal atoms and hydrogen molecules. Furthermore, the formation of super-molecules of hydrogen can enhance the adsorption energy.     

Doping sp-hybridized B atoms in graphyne supported single cobalt atoms for hydrogen evolution electrocatalysis

Electrochemical water splitting to hydrogen is considered as a promising approach for clean H₂ production. However, developing highly active and inexpensive electrocatalysts is an important part of the hydrogen evolution reaction (HER). Herein, we present a multifaceted atom (sp²-and sp-hybridized boron) doping strategy to directly fine-modify the electronic structures of the active site and the HER performance by the density functional theory calculations. It is found that the binding strength between the Co atom and the B doped graphyne nanosheets can be enhanced by doping B atoms. Meanwhile, the Co@B₁-GY and Co@B₂-GY catalysts exhibit good thermodynamic stability and high HER catalytic activity. Interestingly, the Co@B₂-GY catalyst has an ideal HER performance with the ΔG_H* value of −0.004 eV. Moreover, the d-band center of the Co atoms is upshifted by the sp²-or sp-hybridized B dopants. The concentrations of the sp-hybridized B atoms have a positive effect on the electrons transformation of the Co atoms. The interaction between the H and Co atoms becomes strong with the increase of the concentrations of the sp-hybridized B atoms and thus the corresponding catalysts show sluggish HER kinetics. This investigation could provide useful guidance for the experimental groups to directly and continuously control the catalytic activity towards HER by precisely doping multifaceted atoms.     

Interaction of molecular hydrogen with Ni doped ethylene and acetylene complex

This work reports the interaction of molecular hydrogen with C₂H₂Ni, C₂H₄Ni complex and also with their dimer using density functional method. Maximum of two H₂ molecules can interact with both C₂H₂Ni and C₂H₄Ni complex which corresponds to the gravimetric uptake capacity of 4.54 and 4.44 wt% respectively. No significant difference is observed either in structural parameters or in the adsorption energies after H₂ adsorption on C₂H₂Ni and C₂H₄Ni complex. The calculated adsorption energies show that, the hydrogen molecules are strongly bound to both C₂H₂Ni and C₂H₄Ni complex. The Gibb’s corrected adsorption energies are positive for C₂H₂Ni(2H₂) and C₂H₄Ni(2H₂) complex even at higher temperature. Dimerization of C₂H₂Ni and C₂H₄Ni complex was carried out, which has reduced the gravimetric uptake capacity in case of C₂H₂Ni complex. A strong metal aggregation is observed during the dimerization process. The results from electronic structure method are confirmed using atom-centered density matrix propagation molecular dynamics simulations.     

Ca and K decorated germanene as hydrogen storage: An ab initio study

The hydrogen storage capacity and performance of Ca and K decorated germanene were studied using density functional theory calculation. The Ca and K adatoms were found to be sufficiently bonded to the germanene without clustering at the hollow site. Further investigation has shown an ionic bonding is apparent based on the charge density difference and Bader charge analysis. Upon adsorption of H₂ on the decorated germanene, it was found that the Ca and K decorated systems could adsorb 8 and 9 H₂ molecules, respectively. The adsorption energies of H₂ molecules were within the Van der Waals energy (400–435 meV), suggesting weak physisorption. The charge density profile revealed that the electron of H₂ moved toward the adatom decoration without leaving the local region of H₂. This suggests that a dipole-dipole interaction was apparent and consistent with the energy range found. Finally, the gravimetric density obtained from the adsorption of H₂ on the decorated germanene shows that this material is a potential for H₂ storage media.     

First-principles study of potassium-doped PC61BM for hydrogen storage

It is known that metal-doped C₆₀ molecule has suitable adsorption energy for H₂ adsorption/release around room temperature. However, the gravimetric storage capacity achieved on solid samples is too low (<1 wt%). In this work we study the hydrogen storage property of a metal-doped C₆₀ derivative, K₇PC₆₁BM, with density functional theory calculations. The complex of K₇PC₆₁BM is selected because it has been observed experimentally. The calculations are performed for an isolated K₇PC₆₁BM molecule, but the limited size of interstitial space for solid phase is taken into consideration in finding the adsorption structure. It is found that K₇PC₆₁BM can at least adsorb 31H₂ molecules (5.07 wt%) due to a compact adsorption structure. The averaged adsorption energy is 0.119 eV/H₂, indicating a desorption temperature near room temperature.     

Density functional theory study of reversible hydrogen storage in monolayer beryllium hydride by decoration with boron and lithium

The hydrogen storage capacity of M-decorated (M = Li and B) 2D beryllium hydride is investigated using first-principles calculations based on density functional theory. The Li and B atoms were calculated to be successfully and chemically decorated on the Surface of the α-BeH₂ monolayer with a large binding energy of 2.41 and 4.45eV/atom. The absolute value was higher than the cohesive energy of Li and B bulk (1.68, 5.81eV/atom). Hence, the Li and B atoms are strongly bound on the beryllium hydride monolayer without clustering. Our findings show that the hydrogen molecule interacted weakly with B/α-BeH₂(B-decorated beryllium hydride monolayer) with a low adsorption energy of only 0.0226 eV/H₂ but was strongly adsorbed on the introduced active site of the Li atom in the decorated BeH₂ with an improved adsorption energy of 0.472 eV/H₂. Based on density functional theory, the gravimetric density of 28H₂/8li/α-BeH₂) could reach 14.5 wt.% higher than DOE's target of 6.5 wt. % (the criteria of the United States Department of Energy). Therefore, our research indicates that the Li-decorated beryllium hydride monolayer could be a candidate for further investigation as an alternative material for hydrogen storage.     

An effective method to screen carbon (boron,nitrogen) based two-dimensional hydrogen storage materials

The current critical environmental pollution caused by the huge fossil fuel burning together with the increasingly scarce energy source has inspired much attention on the renewable clean hydrogen energy. Thus, the hydrogen storage materials are very vital for the hydrogen application and will be screened by the high-throughput computational screening procedure in this paper. Generally, metal-modified carbon (boron, nitrogen) nanomaterials can exhibit excellent hydrogen storage capacities. An effective procedure is designed to screen the potential metal decorated carbon (boron, nitrogen) hydrogen storage materials from the Materials Project database, which can be proved to be easily realized and reliable. Totally six ideal structures are obtained for hydrogen storage by considering the thermodynamic stability, the metal decorating, the theoretical hydrogen gravimetric density larger than 5.5 wt%, the PBE band gap smaller than 1.0 eV, and the two-dimensional structure restriction. Furthermore, the binding energy of the metal atom to the screened 2D materials, the average adsorption energy per H₂ adsorbed by the metal, the density of states, the difference charge densities are calculated by the density functional method. We believe that our screening procedure can effectively and accurately search for hydrogen storage materials, which should be the theoretical basis for experimental researches.     

Li decorated penta-silicene as a high capacity hydrogen storage material: A density functional theory study

The H₂ adsorption characteristics of Li decorated single-sided and double-sided penta-silicene are predicted via density functional theory (DFT). The orbital hybridization results in Li atom strongly bind onto the surface of the penta-silicene with a large binding energy and it keeps the decorated Li atoms from aggregation. Moreover, Li decorated double-sided penta-silicene can store up to 12H₂ molecules with the average hydrogen adsorption energy of ?0.220 eV/H₂ and hydrogen uptake capacity of 6.42 wt%, respectively. The ab initio molecular dynamics (AIMD) simulations demonstrate the H₂ molecules are released gradually from the substrate material with the increasing simulation time and the calculated desorption temperature T_D is 281 K in the suitable operating temperature range. Our explorations confirm that Li decorated penta-silicene can be regarded as a promising hydrogen storage candidate for hydrogen storage applications.     

Effect of boron substitution on hydrogen storage in Ca/DCV graphene: A first-principle study

By using density functional calculations, the effects of boron are investigated in the new hydrogen storage systems, which are formed by substituting different numbers of boron atoms to the first (BDDCV-F) and the second (BDDCV-S) neighbor of double carbon-vacancy (DCV). The layered host systems of boron-substituted DCV graphene are decorated with Ca metal to increase the number of adsorbed H₂ molecules. Storing of H₂ applications are performed by using two coordinate algorithms as CLICH (Cap-Like Initial Conditions for Hydrogens) and RICH (Rotational Initial Conditions for Hydrogens). The adsorption properties of (1–14) H₂ molecules on the constructed systems are examined. The results for BDDCV-F and BDDCV-S boron-doped systems are compared with each other and those of the pure-DCV graphene. To compare the stabilities of BDDCV-systems, the formation energies are calculated. It is concluded from Mulliken charge analysis, the partial density of states and electron density differences that boron substitution process to different locations of the DCV graphene plays a crucial role on the charge transfer between Ca atom the layered host system, ionic nature and the binding properties of the systems. The herringbone-like anisotropic electron density is transformed to isotropic density with the substitution of the boron atoms. Then, the electric field, which is induced by ionic interactions and governs H₂ adsorption processes, is changed and intensified along with the sheet. In this way, it can be achieved more effective H₂ adsorption. It is seen from the adsorption energies of single- and double-side Ca-decorated systems that the processes of boron-substitution and Ca-decoration can considerably improve the hydrogen storage capability of pure-DCV graphene system, thus (8 and 10)H₂ can be adsorbed per Ca-atom in these-type systems. The high gravimetric density of 5.80% is calculated, although larger cell and empty surface states. Moreover, the average desorption temperatures are calculated by using van't Hoff equation, and it is seen that the DCV including boron-substituted systems have closer desorption temperatures to the room temperature than pure-DCV. To check the H₂ desorption of the systems, molecular dynamics simulations are performed at 200 K and 300 K temperatures.     

Li-decorated porous graphene as a high-performance hydrogen storage material: A first-principles study

Development of novel carbon-based nanoporous materials with high reversible capacity and excellent cycling stability is a hot topic in the field of hydrogen delivery and storage. In this work, first-principles calculations are carried out to discuss the hydrogen storage properties of Li-decorated porous graphene (Li-PG). The binding energies, electronic structures, storage capacities of hydrogen on different sites are investigated in details. The computational results show that with the increase of lithium doping concentration, the electron concentration of donor atoms exceeds the N_c value, and as a consequence, the PG changes from the p-type semiconductor to the n-type degenerate semiconductor. The maximum hydrogen adsorption configurations of H1a-H'1b and H2a-H'2b systems are obtained, and the average binding energy of per H₂ molecule is 0.245 eV and 0.263 eV, respectively. Furthermore, ab inito MD simulation results show that the H1-H'1 and H2-H'2 systems can hold up to sixteen and fifteen H₂ molecules, which corresponds to a hydrogen storage capacity of 10.89 wt% and 10.79 wt% at T = 300 K (no external pressure), respectively.     

An investigation of Li-decorated N-doped penta-graphene for hydrogen storage

By making use of first principles calculations, lithium-decorated (Li-decorated) and nitrogen-doped (N-doped) penta-graphene (PG) was investigated as a potential material for hydrogen storage. The geometric and electronic structures of two types of N-doped PG were studied, and the band gaps were 1.86 eV and 2.06 eV, respectively, depending on the positions of the substitution. The probable adsorption sites for Li atoms on topside and downside were calculated. Hydrogen molecules were added one by one to Li-decorated N-doped PG to research the maximum hydrogen gravimetric density. It is found that up to 5 hydrogen molecules on topside and 8 hydrogen molecules on downside can be adsorbed around a Li atom, and the average adsorption energies are in the range of physical adsorption processes (0.1–0.4 eV). The gravimetric densities can reach 7.88 wt% for N-doped PG with Li decoration. Our results suggest that Li-decorated N-doped PG is a significantly promising material for hydrogen storage.     

First principle study of hydrogen diffusion in equilibrium rutile, rutile with deformation twins and fluorite polymorph of Mg hydride

The transport properties of hydrogen are crucial to the kinetics of hydrogen storage in MgH₂. We use first principle calculations to identify the hydrogen diffusion paths and barriers and diffusion rates in three different MgH₂ structures: equilibrium rutile, rutile with ball-milling-induced deformation twins and fluorite polymorph. Hydrogen vacancy mediated mechanism was applied when hydrogen diffusion was studied. We observed that both hydrogen diffusion barriers in deformation twins and fluorite structure are lower compared to that in the equilibrium rutile. This is because the hydrogen diffusion is facilitated by new interstitial sites in the Mg lattice: a new hexahedral site formed by the reconstruction of Mg lattice at the twinning interface in the deformation twins and the octahedral sites in the fluorite structure. Furthermore, the hydrogen vacancy density effect on the diffusion barrier was estimated. The general trend is the higher the density of hydrogen vacancies, the lower the hydrogen diffusion barrier, the higher the diffusion rate. Our results demonstrate how the hydrogen kinetics is altered by controlling the structure of the hydrides.     

Functionalized tetrahedral silsesquioxane cages for hydrogen storage

The hydrogen storage capacity of functionalized Tetrahedral Silsesquioxane (H₄Si₄O₆) cages is obtained using density functional theory (M062X) and second order Møller-Plesset (MP2) method with 6-311++G7 basis set. We labelled Tetrahedral Silsesquioxane (H₄Si₄O₆) as ‘TS’. We replaced four hydrogen in TS one by one with C₂HBe or C₂HTi group and labelled as TSR₁M_1, TSR₂M₂ TSR₃M₃ and TSR₄M₄ where RM can be either C₂HBe or C₂HTi. In TSRM when one hydrogen in a cage is replaced by C₂HBe or C₂HTi maximum of two and five hydrogen molecules, get adsorbed per Be and Ti atom respectively with respective H₂ capacity of 1.61 and 3.42 wt %. H₂ uptake capacity of TSR_mM_m (m = 1, 2, 3 and 4) has increased extensively when all the hydrogen in cage are replaced either C₂HBe or C₂HTi. TSR₄M₄ with RM = C₂HTi can adsorbs maximum of 20H₂ molecules with highest H₂ uptake of 7.46 wt % among all the studied complexes. Calculated Gibbs free energy corrected H₂ adsorption energies show that adsorption of H₂ molecules on all the complexes is thermodynamically favourable. The desorption temperature for the complexes were calculated by using the van't Hoff equation. Calculated interaction energies show that H₂ molecules interact strongly with Be atom than Ti atom. The molecular dynamics (MD) simulations have also been performed using atom centered density matrix propagation (ADMP) at ambient conditions. Interaction of hydrogen molecules and the metal atom is confirmed through the density of states (DOS) plot.     

Ab initio study on hydrogen interaction with calcium decorated silicon carbide nanotube

Ab initio study on the viability of calcium decorated silicon carbide nanotube as a hydrogen storage material was conducted. Calcium strongly adsorbs on silicon carbide nanotube (SiCNT) with a significant binding energy of ?2.83 eV, thus calcium's low cohesive energy and strong binding with SiCNT may prevent Ca to form clusters with other adsorbates. Bader charge analysis also revealed a charge transfer of 1.45e from Ca to SiCNT resulting to calcium's cationic state, which may induce charge polarization to a nearby molecule such as hydrogen. Hydrogen molecule was then allowed to interact with the calcium adatom where it exhibited charge polarization, induced by the electric field from calcium's positive charge. This resulted to a significant binding energy of ?0.22 eV for the first hydrogen molecule. Results reveal that Ca on SiCNT can hold up to 7 hydrogen molecules and can be a promising candidate for a hydrogen storage material.     

Enhancing hydrogen storage capacity of pyridine-based metal organic framework

Using first principles calculations, we show that the storage capacity as well as desorption temperature of MOFs can be significantly enhanced by decorating pyridine (a common linker in MOFs) by metal atoms. The storage capacity of metal-pyridine complexes are found to be dependent on the type of decorating metal atom. Among the 3d transition metal atoms, Sc turns out to be the most efficient storing unto four H₂ molecules. Most importantly, Sc does not suffer dimerisation on the surface of pyridine, keeping the storage capacity of every metal atom intact. Based on these findings, we propose a metal-decorated pyridine-based MOFs, which has potential to meet the required H₂ storage capacity for vehicular usage.     

High performance material for hydrogen storage: Graphenelike Si2BN solid

Recently, two dimensional graphenelike i.e. Si₂BN solid monolayer have attracted much attention for the use of hydrogen developments. The work is based on first principles calculations using density functional theory with long range van der Waal (vdW) interactions. The optimized structure is energetically more stable due to high formation energy 45.39 eV with PBE and 50.82 eV with HSE06 functionals, respectively. Our ab-initio studies show that Pd (palladium) adatoms secured graphenelike Si₂BN solid via two types of interactions; physisorption and chemisorptions reactions, which engrossing up to 3H₂ molecules signifying gravimetric limits of ≈6.95–10.21 wt %. The absorption energies vary from ?0.31 eV to ?1.93 eV with Pd-adatom and without Pd-adatom respectively, and it varies up to ?1.24 eV. The work function of pure Si₂BN is 5.36 eV while metal-adatom on monolayer Si₂BN with (1 to 6)H₂ molecules is 3.53 eV–4.99 eV and reaches up to 5.85 eV. The theoretical study suggests that the functionalized graphenelike Si₂BN is efficient for hydrogen storage and propose a possible improvement for advantageous storage of hydrogen at ambient conditions.     

The adsorption of H2 on Fe-coated C5H5 and its application in hydrogen storage

Based on density functional theory, the capacities of FeC₅H₅, Fe₂C₅H₅ and one-dimensional (FeC₅H₅)_∞ nanowire as hydrogen storage media were investigated. The results show that FeC₅H₅ and Fe₂C₅H₅ can adsorb five and ten H₂ molecules, respectively, and form stable FeC₅H₅(H₂)₅ and Fe₂C₅H₅(H₂)₁₀ systems. The hydrogen storage capacities of the two systems are 7.63 wt% and 10.15 wt%, while the average adsorption energies are 0.49 and 0.73 eV/H², indicating that FeC₅H₅ and Fe₂C₅H₅ are excellent hydrogen storage media. In addition, (FeC₅H₅)_∞ nanowire can also adsorb H₂ molecules (1.62 wt%). Most importantly, the magnetic and electrical properties of the nanowire are sensitive to the additional H₂, thus (FeC₅H₅)_∞ can be used for selecting and detecting H₂ molecules.     

Divulging the electrochemical hydrogen storage of ternary BNP-doped carbon derived from biomass scaled to a pouch cell supercapacitor

Activated carbon materials have been studied extensively as electrode materials for supercapacitors (SCs), but their poor capacitance and energy density have hampered their growth. We present a one-step synthesis of a ternary boron-nitrogen-phosphorous-doped carbon (BNPC) from biomass hemp fibre to determine its electrochemical hydrogen storage ability using SC applications. FESEM micrographs reveal mixed morphologies like square, diamond and cylindrical-shaped nanosheets, confirming the hetero-atom doping into the carbon skeleton. The optimized BNPC electrode delivers a half-cell specific capacitance and hydrogen-storage capacity of 520 Fg^-1 (1 Ag^-1) and 360 mAhg⁻¹ (10 mVs⁻¹), respectively. To demonstrate the practicability of the as-prepared BNPC electrode, a symmetric pouch-cell supercapacitor device was assembled which exhibits a full-cell specific capacitance of 262.56 Fg^-1 at 1 Ag^-1 and a specific energy of ~118 Wh kg⁻¹ at a specific power of ~5759 Wkg^-1 with an operating potential window of 1.8 V and 99.7% capacitance retention over 10,000 cycles. This excellent electrochemical performance can be ascribed to the synergetic properties of fast-electrolyte-ion diffusion due to the doping of heteroatoms into the carbon matrix, high conductivity and high specific surface area and effective microporosity of BNPC (1555.5 m²g^-1). Also, the chemical stability of the BNPC materials, was investigated with density functional theory (DFT)-single point calculations, where the least molecular orbital energy gap was obtained by the BNPC, which confirms its structural stability. Thus, the prepared ternary BNP-doped carbon derived from biomass has provided a new direction to enhance the electrochemical energy storage potential.