Adsorption Of H2 Molecules Research Articles

Ab initio study of hydrogen storage on metal-decorated GeC monolayers

Bidimensional nanostructures have been proposed as hydrogen-storage systems owing to their large surface-to-volume ratios. Germanium carbide monolayers (GeC-MLs) can offer attractive opportunities for H2 adsorption compared to graphene. However, this possibility has not been explored in detail. In this work, the adsorption of H2 molecules on GeC-MLs decorated with alkali metal (AM) and alkaline earth metal (AEM) adatoms was investigated using the density functional theory. Results showed that the AM adatoms were chemisorbed on the GeC-ML, whereas AEM adatoms were physisorbed. The H2 molecules presented negligible adsorption energies on the weakly adsorbed AEM adatoms. Conversely, the AM adatoms improved the H2 adsorption, possibly due to a large charge transfer from the adatoms to the GeC-ML. The potassium-decorated GeC-ML exhibited the most optimal H2 storage capacity, adsorbing up to six molecules and with a lower possibility of forming metal clusters than the other studied cases. These results may aid in the development of new efficient hydrogen-storage materials.

Ultrahigh Hydrogen Uptake in an Interpenetrated Zn 4 O-Based Metal–Organic Framework

As a highly promising candidate for hydrogen storage, crucial to vehicles powered by fuel cells, metal–organic frameworks (MOFs) have attracted the attention of chemists in recent decades. H2 uptak...

C60Con complexes as hydrogen adsorbing materials

An active line of contemporary research is dedicated to the adsorption and storage of hydrogen on metal-doped carbon materials. Using density functional theory and van der Waals corrections we have studied molecular and dissociative adsorption of H2 on neutral and cationic C60Con complexes with n = 1–8. The Co atoms form compact clusters on the surface of the fullerene. Dissociative chemisorption of one H2 molecule is more stable than molecular adsorption on neutral C60Con, with the only exception of C60Co. When C60Con is ionized, the electronic charge deficit remains localized in the cobalt cluster. The molecular and dissociative adsorption features on cationic C60Con+ and neutral C60Con complexes are in general similar, but some differences can be highlighted. Molecular and dissociative H2 adsorption on C60Co2+ are competitive; in fact, molecular adsorption is slightly more stable as a result of the localized electronic charge deficit on the Co dimer. Another difference is that the dissociative adsorption energies on some of the neutral C60Con complexes are substantially larger than the dissociative adsorption energies on the corresponding C60Con+ cationic complexes by amounts between 0.2 and 0.5 eV. Activation barriers for dissociation of the adsorbed H2 molecule strongly depend on the charge state and cluster size. These barriers help to interpret the adsorption state (molecular or dissociated) of experimentally produced hydrogenated C60Con+ complexes. Hydrogen saturation has been studied in two cases. C60Co adsorbs three H2 units in molecular form, and C60Con adsorbs up to thirteen H2 units, four dissociated and nine in molecular form.

An aromatic Ca2B8 complex for reversible hydrogen storage

Ca2B8 cluster which shows high stability is predicted to be a symmetrical 3-dimension complex at coupled-cluster method. Charge analysis shows that the great charge transfers from Ca to B8 ring result in the formation of (Ca)22+(B8)4- complex. The aromaticity of this complex is identified through the negative nucleus-independent chemical shifts (NICS) and delocalized σ and π molecular orbitals. Importantly, the aromatic Ca2B8 is found to be a promising hydrogen storage material with moderate adsorption energy and high gravimetric density (10.6%). The adsorbed H2 molecules on Ca2B8 can be efficiently released at ambient temperature revealed by ab initio molecular dynamics (AIMD) simulation.

DFT study of the H2 molecules adsorption on pristine and Ni doped graphite surfaces

The adsorption of H2 on graphite is of great interest because this material is the most abundant carbon polymorph, making it attractive for hydrogen storage. It is also known that Ni is a good candidate to catalyze the adsorption of H2 on different materials. In this work, we tested the adsorption of H2 on a pristine (001) graphite surface, being 1.71 eV the minimum energy required. The addition of nickel to the graphite surface was tested on three different configurations, being the center of the hexagonal-graphite ring the most favorable site with a ΔE = −2.47 eV. The adsorption of H2 molecules on Ni atoms was also tested on three configurations: Ni on a C atom, on a C vacancy and on the center of the C-ring, being the first configuration the most favorable geometry for the adsorption of up to two H2 molecules. In all the tested configurations, the adsorption of three molecules derived on the removal of the Ni as NiH6.

Theoretical Study on Tuning Band Gap and Electronic Properties of Atomically Thin Nanostructured MoS2/Metal Cluster Heterostructures.

Nano-heterostructures have attracted immense attention recently due to their remarkable interfacial properties determined by the heterointerface of different nanostructures. Here, using first-principles density functional theory (DFT) calculations, we examine what range the variable electronic properties such as the electronic band gap can be tuned by combining two dissimilar nanostructures consisting of atomically thin nanostructured MoS2 clusters with small silver and gold nanoparticles (Ag/Au NPs). Most interestingly, our calculations show that the electronic band gap of the nanostructured MoS2 cluster can be tuned from 2.48 to 1.58 and 1.61 eV, by the formation of heterostructures with silver and gold metal nanoclusters, respectively. This band gap is ideal for various applications ranging from flexible nanoelectronics to nanophotonics applications. Furthermore, the adsorption of H2 molecules on both nano-heterostructures is investigated, and the computed binding energies are found to be within the desirable range. The reported theoretical results provide inspiration for engineering various optoelectronic applications for nanostructured MoS2-based heterostructures.

Ultrahigh hydrogen storage capacity of holey graphyne

Holey graphyne (HGY), a novel two-dimensional (2D) single-crystalline carbon allotrope, was recently synthesized by Castro–Stephens coupling reaction. The naturally existing uniform periodic holes in the 2D carbon–carbon network demonstrate its promising potential in energy storage. Herein, we conduct density functional theory (DFT) calculation and ab initio molecular dynamics simulations (AIMD) to predict the H storage properties of a single-layer HGY sheet modified by Li metal atoms. The DFT calculations demonstrate that Li atoms can bind strongly to the HGY sheet without forming clusters, and each Li atom can anchor four H2 molecules with an average adsorption energy of about −0.22 eV/H2. The largest H storage capacity of the doped HGY sheet can reach as high as 12.8 wt%, showing that the Li/HGY complex is an ideal H storage material at ambient conditions. In addition, we investigate the polarization mechanism of the storage media and find that the polarization originates from the electric field induced by both the ionic Li atoms and the weak polarized H2 molecules. Finally, the desorption mechanism of the adsorbed H2 molecules is thoroughly investigated using a kinetic AIMD method.

Hexagonal boron nitride ([formula omitted]-BN) nanosheet as a potential hydrogen adsorption material: A density functional theory (DFT) study

The hydrogen storage capacity of Boron Nitride nanosheet has been performed by using density functional theory (DFT). All the structural and electronic properties of a monolayer BN nanosheet are in well agreement with the previously reported results. Out of the four possible adsorption sites, centre is the most favourable adsorption site for H2 molecule with binding energy ∼0.212 eV/H2. We have proceeded our calculations considering this adsorption site. The calculated direct band gap within GGA and HSE for pristine h-BN monolayer are found to be 4.669 eV and 5.63 eV, respectively. In our calculation the Hydrogen storage capacity of BN nanosheet was found to be 6.7 wt.% well within benchmark value (6.0%) with an average adsorption energy of (∼0.128 eV/H2). Bader analysis revealed that the charge transfer from BN nanosheet to the H2 molecule is very low (0.004–0.065∣ e ∣) leading to weak binding of the H2 molecule. The calculated desorption temperature was found to be low due to low average adsorption energy of the H2 molecule. Also, upon increasing the number of H2 molecule adsorption a feeble tuning of the band gap has been observed due to the contribution of the 1s orbital of H2 molecule.

Sc/Ti-decorated and B-substituted defective C60 as efficient materials for hydrogen storage

Doping heteroatoms and producing defects are perfect methods to improve the hydrogen storage property of TM-decorated carbon materials. In this view, four novel Sc/Ti-decorated and B- substituted defective C60 fullerenes (B24C24) are explored. The special stability, large specific surface, uniform distribution of the metal and positively charged states make these four fullerenes have high hydrogen storage capacities. Especially, each Sc atom in Sc6B24C24(B4) can adsorb up to five H2 molecules with a storage capacity of 6.80 wt %. The adsorbed H2 molecules in Sc6B24C24(B4)–30H2 begin to relax at 190 K and are 100% released at 290 K. Moreover, a comparative study is carried out for hydrogen storage properties of Sc-decorated B4, C4, or N4 coordination environments. These results provide a new focus on the nature of B-, and N-substituted defective carbon nanomaterials.

The electronic properties and structural stability of LaFeO3 oxide by niobium doping: A density functional theory study

The niobium doping perovskite has been used in anode materials of solid oxide fuel cell. The electronic properties and structural stability of LaFeO3 (LFO) oxide by Nb-doping and the adsorption of H2 molecule at the clean and Nb-doped LFO (001) surface are investigated by theoretical calculations. The calculated results reveal that the band gap of the orthorhombic LFO is 2.04 eV and the gap disappears after the Nb-doping, which improves the electrical conductivity. The Nb-doping increases the formation energy of oxygen vacancy in orthorhombic LFO. The calculated results of binding energy and formation enthalpy imply that the structural stability is strengthened after Nb-doping, which provides a theoretical explanation for recent experimental observations. This result can be attributed to the change of electronic structure after the Nb-doping. The bond mechanisms for LFO and Nb-doped LFO are obtained by analyzing density of states, Mulliken charges and bond population. Based on adsorption properties, it can be found that the adsorption of H2 molecule is slightly enhanced after Nb-doping and the Nb-doping facilitates that H2 molecule dissociates to H atoms. These results could provide powerful interpretations for the origin of experimental phenomenon.

High-Throughput Screening of Metal-Organic Frameworks for the Impure Hydrogen Storage Supplying to a Fuel Cell Vehicle

Metal-organic frameworks (MOFs), as typical porous materials, have been widely used for gas storage. However, impurities usually coexist in the stored gas, which will affect the deliverable capacity of the target gas. In this work, H2 gas (the target gas) adsorption process in 504 MOFs accompanied by impurities is screened by using a grand canonical Monte Carlo simulation method. The effects of the impurities, namely, CH4, O2, CO2, He, N2, Ar, and H2O, on the H2 deliverable capacity and regenerability are examined in the pressure between 35,000 kPa and 160 kPa at 298 K. The relationships between deliverable capacities of 504 MOFs and their material properties such as porosities, pore size, pore volumes, and surface areas are identified. Results show that the gravimetric deliverable capacity of 504 MOFs increases with porosity and surface area. XAWVUN is the best for the gravimetric deliverable capacity, and meanwhile, it has a fairly high volumetric deliverable capacity of H2 among 504 MOFs. The distributions of the adsorbed H2 molecules in XAWVUN display randomly. The impurities have no effect on the H2 adsorption in XAWVUN. The above results can guide to screen the best adsorbent for H2 storage supplying to a fuel cell vehicle.

Catalytic Reactions on Pd-Au Bimetallic Model Catalysts.

ConspectusThe enhanced catalytic activity of Pd-Au catalysts originates from ensemble effects related to the local composition of Pd and Au. The study of Pd-Au planar model catalysts in an ultrahigh vacuum (UHV) environment allows the observation of molecular level catalytic reactions between the Pd-Au surface and target molecules. Recently, there has been progress in understanding the behavior of simple molecules (H2, O2, CO, etc.) employing UHV surface science techniques, the results of which can be applied not only to heterogeneous catalysis but also to electro- and photochemical catalysis.Employing UHV methods in the investigation of Pd-Au model catalysts has shown that single Pd atoms can dissociatively adsorb H2 molecules. The recombinative desorption temperature of H2 varies with Pd ensemble size, which allows the use of H2 as a probe molecule for quantifying surface composition. In particular, H2 desorption from Pd-Au interface sites (or small Pd ensembles) is observed from 150-300 K, which is between the H2 desorption temperature from pure Au (∼110 K) and Pd (∼350 K) surfaces. When the Pd ensembles are large enough to form Pd(111)-like islands, H2 desorption occurs from 300-400 K, as with pure Pd surfaces. The different H2 desorption behavior, which depends on Pd ensemble size, has also been applied to the analysis of dehydrogenation mechanisms for potential liquid storage mediums for H2, namely formic acid and ethanol. In both cases, the Pd-Au interface is the main reaction site for generating H2 from formic acid and ethanol with less overall decomposition of the two molecules (compared to pure Pd).The chemistry behind O2 activation has also been informed through the control of Pd ensembles on a gold model catalyst for acetaldehyde and ethanol oxidation reactions under UHV conditions. O2 molecules molecularly adsorbed on continuous Pd clusters can be dissociated into O adatoms above 180 K. This O2 activation process is improved by coadsorbed H2O molecules. It is also possible to directly (through a precursor mechanism) introduce O adatoms on the Pd-Au surface by exposure to O2 at 300 K. The quantity of dissociatively adsorbed O adatoms is proportional to the Pd coverage. However, the O adatoms are more reactive on a less Pd covered surface, especially at the Pd-Au interface sites, which can initiate CO oxidation at temperatures as low as 140 K. Acetaldehyde molecules can be selectively oxidized to acetic acid on the Pd-Au surface with O adatoms, in which the selectivity toward acetic acid originates from preventing the decarboxylation of acetate species. Moreover, the O adatoms on the Pd-Au surface accelerate ethanol dehydrogenation, which causes the increase in acetaldehyde production. Hydrogen is continuously abstracted from the formed acetaldehyde and remaining ethanol molecules, and they ultimately combine as ethyl acetate on the Pd-Au surface.Using Pd-Au model catalysts under UHV conditions allows the discovery of molecular level mechanistic details regarding the catalytic behavior of H and O adatoms with other molecules. We also expect that these findings will be applicable regarding other chemistry on Pd-Au catalysts.

Pristine B3CN4 monolayer for hydrogen storage: A first-principles approach

This work reports hydrogen storage properties of pristine B3CN4 monolayer using first-principles calculations. We predict that the pristine B3CN4 monolayer can be a promising candidate for H2 storage purpose which can adsorb up to six H2 molecules with a hydrogen storage capacity of 10.7 wt%. The hydrogen adsorption energies fall within a range of 0.214-0.474 eV, which is an ideal range for the hydrogen storage. Hydrogen desorption can occur at 275 K and P =1 atm from B3CN4(6H2) system. The interaction between H2 molecules and B3CN4 nanosheet is strong enough to show significant changes in the TDOS of B3CN4 nanosheet before and after hydrogen storage. With an increase in the number of adsorbed H2 molecules on B3CN4 nanosheet, there is an increase in hybridization between the two.

First-principles study of hydrogen storage on Ca-decorated defective boron nitride nanosheets

Hydrogen storage on the Ca-decorated defective boron nitride nanosheets (BNNSs) is investigated by first-principle calculation based on density functional theory. Four types of experimentally available defects, B vacancy (VB), N vacancy (VN), Stone-Wales defect (SW) and B–N divacancy (VNB), are considered. It is found that the binding energy of Ca atom on BNNSs with VN and SW defects is smaller than the cohesive energy of bulk Ca. While the Ca atom has strong bonding strength with BNNSs with VB and VBN defects without the problem of aggregation. Six H2 molecules can be absorbed by a Ca atom with the average adsorption energy of 0.206–0.242 eV/H2. The Ca decorated on both sides of BNNSs with VB and VBN defects leads to the hydrogen gravimetric density of 7.6 wt% and 8.0 wt%, respectively. Both the polarization mechanism and the weaker hybridization of Ca-3d orbitals with H-s orbitals are responsible for the adsorption of H2 molecules. The effect of temperature and pressure on the hydrogen storage performance is also investigated, and the results indicate that the hydrogen adsorbed structures of Ca-decorated BNNSs with VB and VBN defects are stable at room temperature under mild pressure.

Sensing mechanism of hydrogen storage on Li, Na and K-decorated Ti2C

The adsorption of H2 molecules on Li, Na and K-decorated MXenes (Ti2C) has been investigated with first-principles calculations. A detailed examination of the adsorption mechanism of the Li, Na and K-decorated systems was presented by charge population analysis, electron density and partial density of states calculations. The results show that Li-decorated Ti2C system was found suitable for hydrogen storage. The maximum storage capacity about 4.33 wt% with a suitable average adsorption energy of − 0.26 eV/H2 can be obtained for two Li atoms, which adsorbed on both sides of the Ti2C. It indicates that Li-decorated Ti2C is of great significance for the wide application of MXenes in the field of hydrogen absorption.

On the hydrogen storage performance of Cu-doped and Cu-decorated graphene quantum dots: a computational study

Hydrogen gas is a promising renewable energy source. The hydrogen storage performance of two differently modified graphene surfaces, particularly Cu-doped and Cu-decorated circumcoronene (CC), is investigated using density functional theory, 6-311G* basis set and Bader's quantum theory of atoms in molecules (QTAIM). It is found that the Cu-doped CC is able to bind three H2 molecules on one Cu atom, while the Cu-decorated CC is able to bind up to five H2 molecules on one Cu atom. Changes in the topology of charge density upon the H2 adsorption are evaluated under the formalism of QTAIM analysis. The QTAIM analysis of bond critical points as well as the density of states analysis show that the interaction between Cu and adsorbed H2 molecules can be considered as a physisorption (a van der Waals type interaction). Overall, the results presented in this study point out that the Cu-decorated graphene surfaces are more suitable potential candidates for hydrogen storage than the Cu-doped ones. Furthermore, the inclusion of diffuse functions in the basis set is critically considered.

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++G∗∗ 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 TSR1M1, 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 TSRmMm (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.

Adsorption of H2 and CO2 gas molecules on Li/Na decorated Si2BN nano-sheet for energy harvesting applications – A density functional study

The Li and Na decorated Si2BN are investigated as electrodes for energy applications. At first, Na and Li decorated Si2BN is used to adsorb H2 molecules and the obtained adsorption energy values are in the range of −0.278–0.506eVs which are ideal for Hydrogen storage in practical applications. The desorption temperatures of H2 molecule on Li and Na decorated Si2BN are 449 K and 355 K respectively. As of now, this may be the first theoretical work where the Li and Na decorated Si2BN is used to adsorb CO2 molecule, and the adsorption energy values on Li and Na decorated Si2BN are −0.500 eV and −0.431 eV respectively. Due to the Li and Na decoration, the adsorption energy is more enhanced than three times of CO2 adsorption on Si2BN mono-layer. The quasi molecular interaction between the Li/Na and CO2 amplifies the bond distance between C and O, can induce catalyst reaction. The obtained results show that the Li and Na decorated Si2BN can also be used in CO2 capture and conversion technology such as Li-CO2 and Na-CO2 batteries. The desorption temperatures of CO2 on the Li and Na decorated Si2BN are 308 K and 265 K respectively, and the calculated desorption temperatures are desirable for storage medium.

Adsorption of H2 molecules on B/N-doped defected graphene sheets—a DFT study

Adsorption of hydrogen molecules on the surface of two-dimensional sheets is extremely challenging due to the non-polar nature of the molecules. Though the adsorption occurs on the surface of the two-dimensional sheets, the adsorption energy tends to be weak. There are a few factors such as delocalized electrons, adsorption sites, the curvature of adsorbent and adsorption orientation which play a vital role in the adsorption of hydrogen molecule. Thus, the primary objective of the present work is focusing on the adsorption factors and giving a range of ideas to increase the adsorption of hydrogen molecules on the surface of two-dimensional defected graphene sheets. In order to explore in a wide range, four different graphene defects such as 5-8-5, 55-77, 555-777 and 5555-6-7777 sheets are taken and each sheet is doped with B and N atoms. Interestingly, the obtained results show that hydrogen orientation and adsorption sites are playing a vital role in hydrogen storage. Addition of N atom in the sheets increases the delocalized electrons and the addition of B atoms increase the localized electrons in the system. The N-doped sheets are behaving as a donor (n-type semiconductor) and B-doped sheets are behaving as acceptors (p-type semi-conductors). The bandgap of H-terminated bare 5-8-5, 55-77, 555-777 and 5555-6-7777 sheets are in the order of 5-8-5 and 55-77 > 5555-6-7777 > 555-777. The hydrogen adsorption values on the specific sheet with the perpendicular orientation of hydrogen molecule provide maximum adsorption energy value of − 80 meV. Similarly, the specific sheet with a parallel orientation of hydrogen provides the minimal adsorption energy value of − 9 meV. The overall B/N-doped 5-8-5, 55-77, 555-777 and 5555-6-7777 ranges from − 9 to − 80 meV which is lesser than the required adsorption energy value of 100 meV. Though the results are slightly low, the exploration provides clear insights on the Hydrogen adsorption on the surface of graphene defects and a possible way to enlarge the adsorption energy. The obtained results further show that the fusion points of pentagonal and hexagonal rings possess more delocalized electrons which are favourable for hydrogen adsorption.

Alkali and transition metal atom-functionalized germanene for hydrogen storage: A DFT investigation

In this work, we have performed density functional theory-based calculations to study the adsorption of H2 molecules on germanene decorated with alkali atoms (AM) and transition metal atoms (TM). The cohesive energy indicates that interaction between AM (TM) atoms and germanene is strong. The values of the adsorption energies of H2 molecules on the AM or TM atoms are in the range physisorption. The K-decorated germanene has the largest storage capacity, being able to bind up to six H2 molecules, whereas the Au and Na atoms adsorbed five and four H2 molecules, respectively. Li and Ag atoms can bind a maximum of three H2 molecules, while Cu-decorated germanene only adsorbed one H2 molecule. Formation energies show that all the studied cases of H2 molecules adsorbed on AM and TM atom-decorated germanene are energetically favorable. These results indicate that decorated germanene can serve as a hydrogen storage system.