H2 Uptake Capacity Research Articles

Ti doped [1,1,1,1] paracyclophane and its derivatives for hydrogen storage: A Computational Insight

Ti-doped [1,1,1,1] paracyclophane(PCP) and its derivatives have been designed by substituting heteroatoms boron and nitrogen and studied their hydrogen storage properties using density functional theory. Heteroatom substitution is important for stronger Ti-binding whereas Ti-doping for light weight, almost empty d-orbital and its stronger interaction with H2 molecules. Six configurations are obtained: PB1,PB2(boron substitution), PN1,PN2 (nitrogen substitution) and PBN1,PBN2(boron and nitrogen co-substitution). Stability of all Ti-doped structures has been confirmed using cohesive and formation energy. PCP, PB1, PB2, PN1, PN2, PNB1 and PNB2 show gravimetric hydrogen uptake capacity(adsorption energy) as 5.52(0.67),6.90(0.5),6.90(0.53),5.37(0.6),5.37(0.61), 5.48(0.7) and 5.48(0.74 eV) wt% respectively. Ti-doped boron substituted structures show required H2 uptake capacity, suitable adsorption energy, thermodynamically favorable H2 adsorption at ambient conditions, moderate desorption temperature, structural and thermodynamic stability, thus more suitable for hydrogen storage than nitrogen substituted and boron and nitrogen co-substituted structures. Ti-doped boron substituted PCP is a promising reversible hydrogen storage candidate.

Be/Li doped C24 and C12B12 nanocages for hydrogen storage: A comparison

The hydrogen storage on Be/Li doped C24 and its boron substituted derivative(C12B12) is studied using density functional theory(DFT). Doping of four and six Be atoms on tetragonal rings of C24 and C12B12 nanocage, respectively is possible. This difference is due to lower(higher) binding energy of Be atoms with C24(C12B12) than its cohesive energy in bulk. Doping of six Be atoms on C24 disturbs the cage. Doping of six Li atoms on tetragonal rings of C24 and C12B12 is possible without disturbing the cage as binding energy of Li atoms with both the cages is higher than its cohesive energy in bulk. Metal doped C12B12 shows higher H2 uptake capacity than C24. H2 molecules interact more strongly with Be doped nanocages than Li doped nanocages. The metal atoms bind more strongly with C12B12 nanocage than C24. From formation energy, metal doped C12B12 are more stable than metal doped C24. Though Li doped nanocages show higher H2 uptake capacity, they are not suitable for hydrogen storage at ambient conditions. Be doped nanocages are more suitable for hydrogen storage at ambient conditions.

Novel Graphene-Based Reversible Physisorption Materials for High Hydrogen Uptake

Carbon-based nanomaterials (graphene, carbon nanotube, microporous carbon, graphitic carbon etc.) are excellent H2 storage materials due to high molecular H2 uptake at the micropores and large H2 adsorption at the graphene network via the formation of dipoles in H2 molecules through London dispersion forces. On the other hand, incorporation of transition metal nanoparticles within the nanocarbon network facilitates dissociation of H2 molecules into constituents H-atoms over the metal nanoparticles, followed by diffusion into the carbon nano-matrix via ‘spill-over’ effect for polarization/hybridization of metal-hydrogen to create high H2 binding energy for high hydrogen adsorption. Therefore, a nanocomposite of graphene-microporous carbon-metal nanoparticle network is expected to deliver excellent H2 uptake capacity and acts as a novel reversible physisorption material for hydrogen storage applications, which is very important for sustainable renewable energy integration.A simple, cost effective sputtering method is used to fabricate metal incorporated graphitic microporous carbon film and differential resistance measurement showed high H2 uptake. Average number of graphene layer formation is dependent on sputtering parameters, which manifest bi-to-multilayer graphene. With increase in graphene layers, H2 adsorption also increases due to a fourfold effect: higher molecular hydrogen uptake at the graphene layers, more active sites into the micropores, promotion of molecular dissociation into atomic hydrogen by the metal nanoparticles, and the formation of hydrogenated carbon via destruction of the π-bonds.

Enhancement of hydrogen storage using functionalized MoSe2/Graphene monolayer and bilayer systems: DFT study

Utilizing the spin-polarized density-functional theory (DFT), we present an investigation of the adsorption properties of hydrogen-gas molecules on ten different substrates, which are based upon defected and TM-doped MoSe2 monolayer (ML) and MoSe2/graphene bilayer (BL) systems (TM = Ni, Cu). Particularly, Ni, and Cu substitutional doping at Se site showed distinct high H2 uptake capacity and thus to be good candidates for H2 storage. On these latter catalysts, H2 molecule exhibited physisorption with moderate respective energies Eads = −0.307 and −0.362 eV, attributed to the enhancement in electric dipole moment and spin splitting (magnetism) induced in the substrate. The desorption processes of the H2 molecule are found to cost energies of about 0.46 and 0.44 eV, respectively. Moreover, the H2 molecule can move parallel to the substrate after crossing potential barriers of 0.56 and 0.65 eV, respectively. Furthermore, the gravimetric uptake density can further be improved by increasing the dopants concentrations. For instance, by increasing the number of Ni dopants from one to two atoms in the computational sample 4 × 4 PCs of MoSe2 ML, the gravimetric density raises from 1.28 wt% to 3.6 wt% (almost triple). This should corroborate the candidacy of TM-doped @Se MoSe2 for hydrogen storage applications. PAC Numbers31.15.E; 68.43.-h; 68.43.Mn; 68.65.Pq; 73.43.Cd; 75.70.Rf.

Melamine assisted preparation of nitrogen doped activated carbon from sustainable biomass for H2 and CO2 storage

Activated carbon (AC), as an effective solid adsorbent, is extensively employed in H2 and CO2 storage. To enhance its adsorption capability and selectivity, it is necessary to increase its surface area and dope heteroatoms by a simple and environment-friendly method. In this work, nitrogen doped activated carbon (NAC) has been synthesized from sustainable biomass by direct activation with the assistance of melamine. The obtained NAC with 2.1 wt% N dopants possesses a high surface area (2477.27 m2/g) and pore volume (1.93 cm3/g). The NAC displayed enhanced H2 uptake capacity (2.29 wt% at 77 K, 1 bar and 0.83 wt% at 298 K, 100 bar) and adequate CO2 uptake capacity (2.85 mmol/g at 298 K, 1 bar and 4.49 mmol/g at 273 K, 1 bar). Activation mechanism with the assistance of melamine was proposed in accordance with the experimental data. The facile method of preparing NAC is potential for large-scaled production.

Concurrent Enhancement of Acetylene Uptake Capacity and Selectivity by Progressive Core Expansion and Extra-Framework Anions in Pore-Space-Partitioned Metal-Organic Frameworks.

A multi-stage core-expansion method is proposed here as one component of the integrative binding-site/extender/core-expansion (BEC) strategy. The conceptual deconstruction of the partitioning ligand into three editable parts draws our focus onto progressive core expansion and allows the optimization of both acetylene uptake and selectivity. The effectiveness of this strategy is shown through a family of eight cationic pore-partitioned materials containing three different partitioning ligands and various counter anions. The optimized structure, Co3 -cpt-tph-Cl (Hcpt=4-(p-carboxyphenyl)-1,2,4-triazole, H-tph=(2,5,8-tri-(4-pyridyl)-1,3,4,6,7,9-hexaazaphenalene) with the largest surface area and highest C2 H2 uptake capacity (200 cm3 /g at 298 K), also exhibits (desirably) the lowest CO2 uptake and hence the highest C2 H2 /CO2 selectivity. The successful boost in both C2 H2 capacity and IAST selectivity allows Co3 -cpt-tph-Cl to rank among the best crystalline porous materials, ionic MOFs in particular, for C2 H2 uptake and C2 H2 /CO2 experimental breakthrough separation.

De-Linker-Enabled Exceptional Volumetric Acetylene Storage Capacity and Benchmark C2H2/C2H4 and C2H2/CO2 Separations in Metal-Organic Frameworks.

An ideal adsorbent for separation requires optimizing both storage capacity and selectivity, but maximizing both or achieving a desired balance remain challenging. Herein, a de-linker strategy is proposed to address this issue for metal-organic frameworks (MOFs). Broadly speaking, the de-linker idea targets a class of materials that may be viewed as being intermediate between zeolites and MOFs. Its feasibility is shown here by a series of ultra-microporous MOFs (SNNU-98-M, M = Mn, Co, Ni, Zn). SNNU-98 exhibit high volumetric C2H2 uptake capacity under low and ambient pressures (175.3 cm3 cm-3 @ 0.1 bar, 222.9 cm3 cm-3 @ 1 bar, 298 K), as well as extraordinary selectivity (2405.7 for C2H2/C2H4, 22.7 for C2H2/CO2). Remarkably, SNNU-98-Mn can efficiently separate C2H2 from C2H2/CO2 and C2H2/C2H4 mixtures with a benchmark C2H2/C2H4 (1/99) breakthrough time of 2325 min g-1, and produce 99.9999% C2H4 with a productivity up to 64.6 mmol g-1, surpassing values of reported MOF adsorbents.

Enhanced hydrogen storage performance of Li and Co functionalized h-GaN nanosheets: DFT study

Based on the density functional theory (DFT) computations, we investigated the hydrogen storage performances of alkali metal (Li) and transition metal (Co) decorated the defective GaN nanosheets. Fundamental aspects including the interaction properties, bonding characteristics, adsorption ability, frontier orbital, HOMO–LUMO energy gaps, natural bond orbital (NBO) analysis, projected densities of states (PDOS) and statistical thermodynamic stability have been demonstrated to analyze the interaction properties of H2 molecules. As a theoretical strategy, non-covalent interactions (NCI) and the atoms in molecules (QTAIM) descriptors were performed to depict weak interactions. The LiN-GaN and CoN-GaN systems and the H2 uptake capacity revealed to be 7.78% and 5.55%, respectively. Our results demonstrated that H2 molecules are introduced sequentially on the Li and Co that functionalized both sides of VN-GaN nanosheets yielded the gravimetric densities up to 8.158% (2Co-VN-GaN) that well above the gravimetric DOE achieve. The 2LiN-GaN and 2CoN-GaN are energetically more effective for the H2 adsorption, stable and preferred than pristine GaN nanosheet.Additionally, two binding mechanisms including polarization of the hydrogen molecules and σ orbitals hybridization of H2 molecules have been investigated to explain the interaction of H2 molecules. The hydrogen desorption enthalpy and desorption temperatures of hydrogen molecules, indicating the H2 molecules are easy to desorb from Li and Co decorated defective GaN nanosheets. These results suggest the possibility of an excellent and promising nanostructural material to improve the performance of hydrogen storage for in fuel cells application at ambient temperature.

Metal doped tetrahedral silsesquioxane cages for hydrogen storage

The hydrogen adsorption properties of Tetrahedral Silsesquioxane Si4O6H4 (TS) cages doped with Be, Li, Sc and Ti atoms are studied in different spin state using density functional theory with M062X functional. Initially-one of the four hydrogen atoms in TS cage was substituted by metal atoms. Doublet and singlet are the lowest energy state for TS-Be and TS-Li respectively with respective H2 uptake capacity of 1.79 and 3.56 wt%. Triplet and quartet are the lowest energy state for TS-Sc and TS-Ti respectively. TS-Sc (singlet) and TS-Ti (doublet) cage interacts with seven and six hydrogen molecules respectively with respective gravimetric H2 capacity of 5.25 and 4.51 wt%. TS-Sc in triplet state could adsorb six H2 molecules whereas TS-Ti in quartet state could adsorb five H2 molecules with respective H2 uptake capacity of 4.5 wt% and 3.7 wt%. Then all the four hydrogen atoms in a TS cage are substituted by four Be, Li or Sc atoms (lowest energy state is Singlet for all the three) with respective hydrogen uptake capacity of 6.19, 12.69 and 12.01 wt%. When all the four hydrogens in TS cage are substituted by four Ti atoms, clustering of Ti atoms occurs and the cage structure gets distorted and therefore not considered for H2 adsorption. H2 adsorption on one Be(doublet), Sc(triplet) and Ti(quartet) atom doped TS cage is thermodynamically favourable below 210, 160 and 320 K respectively at 1 atm. pressure. At room temperature, it is thermodynamically favourable at higher pressure also. Four Sc and Be atom doped TS cages are found to be thermodynamically suitable for hydrogen storage below 210 K at 1 atm pressure. It is also suitable at room temperature but at higher pressure. One as well as four Li atom doped TS cages are not suitable for hydrogen storage for the entire temperature and pressure range considered. Molecular dynamics simulations performed using atom centered density matrix propagation (ADMP) show that the loosely bonded H2 molecules fly away during the simulations.

A Theoretical Perspective to Decipher the Origin of High Hydrogen Storage Capacity in Mn(II) Metal-Organic Framework.

Herein, we report a detailed periodic DFT investigation of Mn(II)-based [(Mn4 Cl)3 (BTT)8 ]3- (BTT3- =1,3,5-benzenetristetrazolate) metal-organic framework (MOF) to explore various hydrogen binding pockets, nature of MOF…H2 interactions, magnetic coupling and, H2 uptake capacity. Earlier experiments found an uptake capacity of 6.9 wt % of H2, with the heat of adsorption estimated to be ∼10 kJ/mol, which is one among the highest for any MOFs reported. Our calculations unveil different binding sites with computed binding energy varying from -6 to -15 kJ/mol. The binding of H2 at the Mn2+ site is found to be the strongest (site I), with H2 found to bind Mn2+ ion in a η2 fashion with a distance of 2.27 Å and binding energy of -15.4 kJ/mol. The bonding analysis performed using NBO and AIM reveal a strong donation of σ (H2 ) to the dz 2 orbital of the Mn2+ ion responsible for such large binding energy. The other binding pockets, such as -Cl (site II) and BTT ligands (site III and IV) were found to be weaker, with the binding energy decreasing in the order I>II>III>IV. The average binding energy computed for these four sites put together is 9.6 kJ/mol, which is in excellent agreement with the experimental value of ∼10 kJ/mol. We have expanded our calculations to compute binding energy for multiple sites simultaneously, and in this model, the binding energy per site was found to decrease as we increased the number of H2 molecules suggesting electronic and steric factors controlling the overall uptake capacity. The calculated adsorption isotherm using the GCMC method reproduces the experimental observations. Further, the magnetic coupling computed for the unbound MOF reveals moderate ferromagnetic and strong antiferromagnetic coupling within the tetrameric {Mn4 } unit leading to a three-up-one-down spin configuration as the ground state. These were then coupled ferromagnetically to other tetrameric units in the MOF network. The magnetic coupling was found to alter only marginally upon gas binding, suggesting that both exchange interaction and the spin-states are unlikely to play a role in the H2 uptake. This is contrary to the O2 uptake studied lately, where strong dependence on exchange-coupling/spin state was witnessed, suggesting exchange-coupling/magnetic field dependent binding as a viable route for gas separation.

Triptycene based fluorinated polymers with improved carbon dioxide capture and hydrogen/methane storage

The use of direct arylation polymerization (DArP) as a viable strategy to obtain porous organic polymers (POPs) has not been explored to its full potential. Instead, other strategies (such as conventional cross-coupling reactions) are usually employed to yield POPs that employ expensive organometallic monomers whose syntheses require multiple steps. Herein, using DArP, three fluorinated porous organic polymers (fPOPs: TFPP1, TFPP2 and TFPP3) were obtained that represent unique examples of triptycene motif containing fluorine rich network polymers. These thermally stable polymers (Td > 400 °C with high char yields at 800 °C) are predominantly microporous with high surface areas (up to 1295 m2/g) and thus satisfy the requirement for facilitating superior adsorption of small gas molecules. The recorded CO2, CH4, and H2 uptake capacities of fPOPs are superior than several previously reported fluorinated/non-fluorinated POPs. High CO2 uptake capacities of fPOPs are due to the incorporation of ample triptycene motifs and polar C–F bonds in the polymeric backbone. Overall, the high thermal stability, surface area and sorption capacities demonstrated by these fluorinated polymers render them potential materials for the applications in capture of CO2 and storage of CH4/H2.

Be doped carbon nanoring for hydrogen storage using density functional theory

We have studied hydrogen uptake properties of Be doped carbon nanoring structures using density functional theory. The nanoring considered consists of five six-membered carbon rings bonded through CC bond. Different doping sites are considered for Be doping. Four possible doping sites lead to four different structures named as CNR1, CNR2, CNR3, CNR4. Five, five, ten and five Be atoms are doped in CNR1, CNR2, CNR3, CNR4 respectively. All the Be doped carbon nanoring structures are thermodynamically stable as indicated by the formation energies and are more stable than undoped carbon nanoring structures as indicated by cohesive energy. The stability of all the four structures is also confirmed by performing ab initio molecular dynamics simulations and vibrational spectra. One, two, two and two H2 molecules get adsorbed per Be atom in CNR1, CNR2, CNR3, CNR4 structures respectively with respective hydrogen storage capacity of 2.42, 4.73, 9.04 and 4.73 wt%. H2 adsorption is thermodynamically favorable below 350, 175, 205 and 70 K on CNR1, CNR2, CNR3, CNR4 respectively with respective desorption temperature (desorption energy) of 652(0.72), 388(0.52), 438(0.55) and 148 K (0.33 eV). Position of doping site affects the number of hydrogen molecule adsorption per Be atom, H2 uptake capacity and other properties.

Hydrogen storage in SiC, GeC, and SnC nanocones functionalized with nickel, Density Functional Theory—Study

AbstractHydrogen is regarded as one of the most potential sustainable energy sources in the future. Applications include transportation. Still, the event of materials for its storage is difficult notably as a fuel in vehicular transport. Nanocones are a promising hydrogen storage material. Silicon, germanium, and tin carbide nanocones have recently been proposed as promising hydrogen storage materials. In the present study, we have investigated the hydrogen storage capacity of and nanocones functionalized with Ni. The functionalized Ni atom are found to be adsorbed on and with an adsorption energy of −5.56, −6.70, and −4.25 eV. The functionalized , and bind up to seven, six and four molecules of hydrogen with the adsorption energy of (−0.34, −0.35, and −0.26 eV) and an average desorption temperature of around 434, 447, and 332 K (ideal for fuel cell applications). The SiC, GeC, and SnC nanocones systems exhibit a maximum gravimetric storage capacity of 12.51, 7.78, and 4.08 wt%. We suggested that NiSiCNC and NiGeCNC systems can act as potential H2 storage device materials because of their higher H2 uptake capacity as well as their stronger interaction with adsorbed hydrogen molecules than NiSnCNC systems. The hydrogen storage reactions are characterized in terms of the charge transfer, the partial density of states, the frontier orbital band gaps, and isosurface plots. And electrophilicity are calculated for the functionalized and hydrogenated and nanocones.

Heterofullerene C48B12-impregnated MOF-5 and IRMOF-10 for hydrogen storage: A combined DFT and GCMC simulations study

The H2 storage properties of isoreticular metal-organic framework materials (IRMOFs), MOF-5 and IRMOF-10, impregnated with different numbers and types of heterogeneous C48B12 molecules were investigated using density functional theory and grand canonical Monte Carlo (GCMC) calculations. The excess hydrogen adsorption isotherms of IRMOFs at 77 K within 20 bar indicate that suitable number and type of C48B12 molecules play a crucial role in improving the H2 storage properties of IRMOFs. Among the studied pure and nC48B12 (n = 1, 2, 4, 8) in Ci symmetry impregnating into MOF-5, at 77 K under 6 bar, MOF-5-4C48B12 with a 3.5 wt% and 29.9 g/L hydrogen storage density, and at 77 K under 12 bar, the pure MOF-5 with a 4.9 wt% and 31.0 g/L hydrogen storage density has the best hydrogen storage properties. Whereas, among the studied pure and nC48B12 (n = 1, 2, 4, 8) in S6 symmetry impregnating into IRMOF-10, IRMOF-10-8C48B12 always shows the best hydrogen storage properties among the pure and C48B12-impregnated IRMOF-10 at 77 K within 20 bar. IRMOF-10-8C48B12 has a 6.0 wt% and 34.6 g/L hydrogen storage density at 77 K under 6 bar, and has a 7.1 wt% and 41.4 g/L hydrogen storage density at 77 K under 12 bar. The confinement effect of IRMOFs on C48B12 molecules, and steric hindrance effect of C48B12 molecules on IRMOFs mainly affects the H2 uptake capacity by comparing the absolute H2 molecules in individual IRMOFs units, C48B12 molecules, and IRMOFs-nC48B12 compounds. The absolute hydrogen adsorption profiles show that eight C48B12 molecules impregnating into MOF-5 can exert obvious steric effects for H2 adsorption. The saturated gravimetric and volumetric H2 densities of IRMOF-10-8C48B12 higher than those of MOF-5-8C48B12 due to with larger free volume.

Understanding the importance of N−doping for CNT-supported Ni catalysts for CO2 methanation

The N−doping of carbon nanotubes (CNTs) is widely accepted as an effective way to enhance the catalytic performance of CNT-supported Ni catalysts for CO2 methanation. To demonstrate, in a direct systematic comparison, the importance of N−doping for producing high-performance CO2 methanation catalysts, we developed two catalysts composed of 15 wt% Ni on pristine (Ni/CNT) and N−doped CNT (Ni/CNT−N) and correlated their catalytic performance with their properties. Compared to Ni/CNT, Ni/CNT−N achieved a higher XCO2 of 81.2% with SCH4 = 99.2% at a lower temperature of 400 °C, exhibiting excellent stability over 48 h time-on-stream testing. Our comprehensive comparative study demonstrated that the N−doped CNT support featured a better distribution of the Ni sites that were strongly interacting with the support, even with atomically dispersed Ni being observed by HAADF-STEM. This higher dispersion, enabled by the anchoring sites provided by the N−doping, is one of the main reasons for the enhanced performance of Ni/CNT−N, because it increases the H2 uptake capacity.

Why Ni/CeO2 is more active than Ni/SiO2 for CO2 methanation? Identifying effect of Ni particle size and oxygen vacancy

An impregnated Ni/CeO2 catalyst with an array structure and a phyllosilicate-based Ni/SiO2 catalyst prepared by hydrothermal method were designed for CO2 methanation. The as-synthetized Ni/SiO2 catalyst exhibits a high Ni content of 25.9 wt%, while its CO2 conversion at low temperature is far lower than that of Ni/CeO2, whose Ni content is only 10.0 wt%. TEM and XRD results show that the Ni/CeO2 catalyst possesses very tiny Ni particle size of around 1.2 nm, which leads to large H2 uptake capacity. XPS and Raman analyses indicate that Ni/CeO2 obtains more oxygen vacancies resulting in promotion of the CO2 activation. The combined effect of the Ni/CeO2 catalyst to enhance chemisorption of H2 and CO2 leads to high low-temperature activity.

Ti decorated heterocyclic rings for hydrogen storage

This study uses first-principles calculations to investigate and compare the hydrogen storage properties of Ti doped benzene (C6H6Ti) and Ti doped borazine (B3N3H6Ti) complexes. C6H6Ti and B3N3H6Ti complex each can adsorb four H2 molecules, but the former has a 0.11 wt% higher H2 uptake capacity than the latter. Ti atoms bind to C6H6 more strongly than B3N3H6. The hydrogen adsorption energies with Gibbs free energy correction for C6H6Ti and B3N3H6Ti complexes are 0.17 and 0.45 eV, respectively, indicating reversible hydrogen adsorption. The hydrogen adsorption properties of C6H6Ti have also been studied after boron (B) and nitrogen (N) atom substitutions. Several B and N substituted structures between C6H6Ti and B3N3H6Ti with different boron and nitrogen concentration and at different positions were considered. Initially, one boron and one nitrogen atom is substituted for two carbon atoms of benzene at three different positions and three different structures are obtained. Seven structures are possible when four carbon atoms of benzene are replaced by two boron and two nitrogen atoms at different positions. The hydrogen storage capacity of the C6H6Ti complex increases as boron and nitrogen atom concentrations increases. The positions of substituted boron and nitrogen atoms have less impact on H2 uptake capacity for the same B and N concentration. The position and concentration of B and N affects the H2 adsorption energy as well as the temperature and pressure range for thermodynamically favorable H2 adsorption. The H2 desorption temperature for all the complexes is found to be higher than 250 K indicates the stronger binding of H2 molecules with these complexes.

Hydrogen adsorption on metal‐functionalized benzene and B‐substituted benzene

Hydrogen storage properties of metal doped benzene complexes vary with positions of boron atom substitution in a benzene ring at MP2/6-311++g(d,p) level. Two carbon atoms of a benzene (C6H6) ring positioned at 1-2, 1-3 and 1-4 are replaced by two boron atoms and the structures named as BB1-2, BB1-3 and BB1-4, respectively. Further, pristine as well as boron substituted benzene complexes are decorated with Li, Be,Ti and Ca atoms. C6H6Li, BB1-2Li, BB1-3Li and BB1-4Li complexes can interact with three, three, two and three H2 molecules, respectively, with 6.64, 6.82, 4.65 and 6.82 wt% H2 uptake capacities. Only one H2 molecule gets adsorbed on each C6H6Be, BB1-2Be, BB1-3Be and BB1-4Be complexes with respective H2 uptake capacity of 2.26, 2.32, 2.32 and 2.32 wt%. One additional hydrogen molecule gets adsorbed on Ti(Ca) decorated boron substituted benzene than C6H6Ti(C6H6Ca) with respective H2 uptake capacity 7.54(7.98) and 6.02(9.46) wt%. Electron density of metal atom gets altered significantly after adsorption of H2 molecules. The averaged H2 adsorption energies with Gibbs free energy correction ΔEG are found to be negative for all Li- and Ca-doped complexes indicates thermodynamically unfavorable H2 adsorption where ΔEG values are positive for all Ti- and Be-doped complexes at room temperature indicating thermodynamically favorable H2 adsorption. Interaction between H2 molecules and Be- as well as Ti-doped complexes is found to be stronger than Li- and Ca-doped complexes. Be-doped complexes considered do not satisfy the target set by DOE regarding H2 uptake capacity. Boron substitution improves molecular hydrogen uptake of Benzene-Ti complex by 1.52 wt% and satisfy the target set by DOE. C6H6Li, BB1-2Li, BB1-3Li and BB1-4Li complexes cannot be used for hydrogen storage since hydrogen adsorption on these complexes is endothermic. Ti-doped boron substituted complexes are found to more promising H2 storage material because of their higher H2 uptake capacity as well as their strong interaction with adsorbed hydrogen molecules than Li-, Be- and Ca-doped complexes.

A first principle study of hydrogen storage in titanium-doped small carbon clusters (C2nTin, n = 2–6)

Hydrogen storage in Ti-doped small carbon clusters, C2nTin (n = 2–6), has been studied using density functional theory. Using the principle of maximum hardness (η) and minimum electrophilicity (ω), stabilities of the clusters are confirmed. The average adsorption energies of all complexes are found in the range of 0.2–0.5 eV/H2 and average Ti-H2 bond length is in the range of 1.953 to 2.145 A, inferring the adsorption process to be physisorption type. All the studied clusters are found to adsorb hydrogen in molecular form through Kubas type of interaction with H2 uptake capacity in the range of 5.31–10.09 wt% which is well above the target set by US-DOE (5.5 wt%). Bader’s topological analyses confirm the closed-shell type interaction among H2 molecules and Ti atoms. Desorption temperature calculated using Van’t-hoff equation is found above the liquid nitrogen temperature.

Synopsis of Factors Affecting Hydrogen Storage in Biomass-Derived Activated Carbons

Hydrogen (H2) is largely regarded as a potential cost-efficient clean fuel primarily due to its beneficial properties, such as its high energy content and sustainability. With the rising demand for H2 in the past decades and its favorable characteristics as an energy carrier, the escalating USA consumption of pure H2 can be projected to reach 63 million tons by 2050. Despite the tremendous potential of H2 generation and its widespread application, transportation and storage of H2 have remained the major challenges of a sustainable H2 economy. Various efforts have been undertaken by storing H2 in activated carbons, metal organic frameworks (MOFs), covalent organic frameworks (COFs), etc. Recently, the literature has been stressing the need to develop biomass-based activated carbons as an effective H2 storage material, as these are inexpensive adsorbents with tunable chemical, mechanical, and morphological properties. This article reviews the current research trends and perspectives on the role of various properties of biomass-based activated carbons on its H2 uptake capacity. The critical aspects of the governing factors of H2 storage, namely, the surface morphology (specific surface area, pore volume, and pore size distribution), surface functionality (heteroatom and functional groups), physical condition of H2 storage (temperature and pressure), and thermodynamic properties (heat of adsorption and desorption), are discussed. A comprehensive survey of the literature showed that an “ideal” biomass-based activated carbon sorbent with a micropore size typically below 10 Å, micropore volume greater than 1.5 cm3/g, and high surface area of 4000 m2/g or more may help in substantial gravimetric H2 uptake of >10 wt% at cryogenic conditions (−196 °C), as smaller pores benefit by stronger physisorption due to the high heat of adsorption.