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Hydrogen Storage Capacity of Low-Lying Isomer of C24 Functionalized with Ti
Abstract
Hydrogen energy is a sustainable and eco-friendly substitute for reducing fossil fuel dependency and boost the air quality index. High-density reversible hydrogen storage as a vehicular fuel is the biggest challenge. Hydrogen storage capacity in Jahn-Teller distorted C24 fullerene functionalized with Ti is studied by using density functional theory. It is found that Ti atoms form two hexagonal pyramidal clusters due to high cohesive energy. Four hydrogen molecules are adsorbed by each Ti through Kubas interaction with adsorption energies in the range of 0.33–0.76 eV/H2. Our findings of practical hydrogen storage capacity and the van ‘t Hoff desorption temperature reveal that hydrogen molecules are reversibly stored under operable thermodynamic conditions with 10.5 hydrogen weight %. Storage parameters meet the US Department of Energy targets making it a prospective hydrogen storage material.
... Adsorption of 6H 2 molecules on a Sc-doped C 24 structure is reported with a gravimetric density of 13.02 wt% [16]. Sathe et al. have reported the formation of hexagonal pyramidal clusters of 14Ti atoms on C 24 fullerene because of the high cohesive energy of the Ti atom, and the whole structure can adsorb 56H 2 molecules with a 10.5 wt% H 2 uptake capacity [17]. Sahoo et al. have studied the hydrogen storage properties of C 8 N 8 Li 2 and C 8 N 8 Sc 2 cages and confirmed reversibility by performing MD simulations [18]. ...
... We have compared our work with previously studied Ti-doped nanocages and nanocluster materials. For that, we have considered Tidoped C 24 [17], C 24 B 24 [24], C 60 [28], C 24 N 24 [31] and B 8 [33] clusters and Li-doped B 12 C 6 N 6 nanocage [41]. The distance between H 2 molecules and Ti atoms from this work is comparable with earlier findings whereas for the Li doped it is in the range of 2.21-2.43 ...
... The adsorption energy values from this work are comparable with the Ti doped cages studied earlier, which fall in the range of 0.2-0.6 eV and point toward the best reversibility of H 2 molecules. The adsorption energy values from this work are in a range of 0.273 to 0.514 whereas it is found to be in a range of 0.33 to 0.76 eV/H 2 for Ti doped C 24 cage [17]. The H 2 uptake capacity from this work for I12 (6.54 wt%) is lower than that for Ti doped C 24 cage (10.5 wt%) [17]. ...
The hydrogen storage properties of Ti-doped B12C6N6 nanocage are investigated using density functional theory with wB97XD functional and 6-311++G(d,p) basis set. Two lowest energy isomers of B12C6N6 with different Ti doping sites are considered. Five stable structures of Ti doped B12C6N6 are obtained by doping different number of Ti atoms and named as I11, I12, I21, I22, and I23. The structures I11, I12, I21, I22, and I23 show hydrogen uptake capacity of 3.54, 6.54, 2.34, 2.34, and 1.77 wt% respectively with respective average H2 adsorption energy with zero-point energy correction (ΔEZPE) of 0.258, 0.222, 0.250, 0.345, and 0.150 eV. Only I12 structure satisfies the target set by the U.S. Department of Energy (5.5 wt% by 2025). The obtained negative values of formation energy show that all the structures are thermodynamically favorable. Gibbs free energy corrected adsorption energy plots indicate that H2 adsorption on Ti-doped B12C6N6 cages is energetically favorable over a wide range of pressures at room temperature and below 277, 240, 260, 337 and 177 K at 1 atm pressure for I11, I12, I21, I22 and I23, respectively. The H2 desorption temperature is found to be 331, 284, 320, 442 and 191 K for I11, I12, I21, I22 and I23, respectively. An increase in gap between the highest occupied molecular orbital and the lowest unoccupied molecular orbital after hydrogen adsorption and the calculated vibrational spectra with no soft modes confirms the stability of the cages.
... Moreover, the only byproduct of hydrogen combustion is water. Furthermore, Hydrogen has higher utilization efficiency, high environmental compatibility and is also the most suitable fuel for vehicle application [3]. Therefore, hydrogen can be considered as a best alternative to replace fossil fuels. ...
... The bond length of 1.42 A is observed for b6,5, whereas the two types of bond lengths (1.53 A and 1.36 A) are observed in case of b5,5 (see Fig. 1), which are in good agreement with previously reported results [3]. Initially, TM is placed at different positions (b6,5 and b5,5 interfaces) on the surface of C24 fullerene (hexahedral) to find the most stable TM@C24 nanocage complex. ...
... kJ/mol per hydrogen molecule. The van 't Hoff desorption temperature for this complex is in the range of 245e526 K [7]. The process of sequential hydrogen adsorption over Ti functionalized C 24 fullerene followed in Ref. [7] has been summarized in Fig. 10. ...
... The van 't Hoff desorption temperature for this complex is in the range of 245e526 K [7]. The process of sequential hydrogen adsorption over Ti functionalized C 24 fullerene followed in Ref. [7] has been summarized in Fig. 10. When decorated with Pd and Co, C 24 fullerene shows desirable hydrogen adsorption energies, yet stability is a bit issue in such cases [263]. ...
... Recently, the transition metaldecorated nanostructures are widely used as Kubas-type hydrogen storage material because of their high capacity and reversibility. [53] Through density functional theory (DFT) calculations, [54] it is predicted that these materials can provide significant hydrogen storage (9-12 wt %) with lower adsorption energy (-0.4 to À 0.2 eV). ...
... [65a] Similarly, using DFT, it is shown that Ti-doped fullerene surprisingly results in 10.5 wt % of uptake at temperature 100-300 K and pressure 0-50 atm. [54] They found that a maximum of 56 hydrogen molecules can be adsorbed onto the surface. The desorption temperature is predicted to be 245-526 K. ...
It is estimated that all fossil fuels will be depleted by 2060 if we continue to use them at the present rate. Therefore, there is an unmet need for an alternative source of energy with high calorific value. In this regard, hydrogen is considered the best alternative renewable fuel that could be used in practical conditions. Accordingly, researchers are looking for an ideal hydrogen storage system under ambient conditions for feasible applications. In many respects, carbon‐based sorbents have emerged as the best possible hydrogen storage media. These carbon‐based sorbents are cost‐effective, eco‐friendly, and readily available. In this Review, the present status of carbon‐based materials in promoting solid‐state hydrogen storage technologies at the operating temperature and pressure was reported. Experimental studies have shown that some carbon‐based materials such as mesoporous graphene and doped carbon nanotubes may have hydrogen storage uptake of 3–7 wt %, while some theoretical studies have predicted up to 13.79 wt % of hydrogen uptake at ambient conditions. Also, it was found that different methods used for carbon materials synthesis played a vital role in hydrogen storage performance. Eventually, this Review will be helpful to the scientific community for finding the competent material and methodology to investigate the existing hydrogen uptake issues at operating conditions.
... The reversible adsorption and desorption of H 2 molecules under environmental conditions are crucial for the storage and transportation of H 2 in practical applications [71]. The van't Hoff equation is used to calculate the desorption temperature (T D ) for the adsorption system, which can be determined with the following equation [72][73][74]: ...
The promise of using 2D materials for hydrogen storage has broad prospects, ascribe to their significant specific surface area and lightweight properties. In this work, the hydrogen storage capability and reversible storage mechanism of 2D penta-SiCN material are investigated based on the first-principles computational method. Thermal stability of penta-SiCN is calculated by the ab-initio molecular dynamics (AIMD) simulation and root-mean-square displacement (RMSD) algorithm. It has been found that penta-SiCN is thermodynamically stable even after adsorbing hydrogen molecules. Taking into account the benchmarks of average and continuous adsorption energies of the adsorption systems, a pristine 2 × 2 × 1 penta-SiCN substrate has the ability to adsorb up to 26H 2 molecules, which results in a maximum hydrogen storage capacity of 10.80 wt%. According to the semi-empirical calculation method that based on the thermodynamic analysis, the penta-SiCN adsorption system has a high reversible hydrogen storage capacity of 9.57 wt% within the adsorption and desorption application working conditions. The results proposed in this study demonstrates that penta-SiCN exhibits considerable promise for hydrogen storage with its substantial hydrogen storage capacity, exceptional reversibility, and eco-friendly characteristics.
... The optimized structure of C24 nanocage (D 6 symmetry) consists of three 3 distinct C-C bonds: one bond is b6,5 (1.42 Å) present at the interface of pentagon and hexagon rings, and other two C-C bonds are b5,5 bond, present at the interfaces of two pentagon rings (1.53 Å & 1.36 Å). The observed bond lengths are consistent with the early reported results [45]. ...
The development of highly active and precious metal free catalysts is of great interest for electrocatalytic hydrogen evolution reaction. A lot of efforts have been devoted for catalyzing HER process through single atom catalysis (SAC), but search for robust electrocatalytic system remains a massive challenge. In this work, transition metal (TM) doped on C24 complexes have been investigated simultaneously for thermodynamic and kinetic aspects to describe the HER activity. The interaction energies of TM@C24 catalysts suggested that all the designed catalysts are thermodynamically stable (− 0.15 to − 5.60 eV). The best catalytic performance for HER is observed for Mn@C24 catalyst with Gibbs's free energy (ΔG H) value of 0.07 eV. FMO analysis reveals that significant change in HOMO-LUMO gap is observed in case of HTM@C24 and validated through density of states analysis. Exchange current is obtained through volcano plot as a function Gibbs free energy for hydrogen evolution over designed SAC. The volcano plot indicates the near thermoneutral activity of Mn@C24 catalyst for HER. The kinetic aspect of the study reveals that Mn@C24 catalyst has a smaller energy barrier than reported for Pt(111) surface for both elementary reactions of HER. The key findings nominate that Mn@C24 catalyst can act as potential electrocatalyst for hydrogen evolution with low overpotential.
... The energy storage domain constitutes another important application. Actually, the hydrogen storage capability in fullerene constitutes an increasingly significant area of interest, and the hydrogen storage properties of C 24 fullerene were studied using the DFT recently [31][32][33], where this capacity was found to approximate 10-12 wt. %. ...
In this study, we have performed a comprehensive theoretical analysis of C 24 isomers in the gaseous phase using the PBE-D3/cc-pVTZ, B3LYP/cc-pVTZ, B3LYP-D3/cc-pVTZ and MP2/6-31G methods. We have also considered the basis set cc-pVTZ for the MP2 method, and carried out optimized (single point) calculations in three isomers (in the remaining two isomers where the convergence was too time consuming) in order to reveal the potentiality of the method. Our investigation covered a wide range of properties, including geometry optimizations, chemical stability, polarizabilities, nuclear screening constants, Fermi (FE), gap (GE) and atomization energies (AE), thermodynamic analysis, reactivity index, as well as IR and NMR spectra. These calculations were performed for the ring (D 12h), sheet (D 6h) and two cage (D 6d and O h) configurations. Interestingly, we also proposed a new structure, the bracelet (D 2d) arrangement, which appeared to be stable according to the PBE, B3LYP and B3LYP-D3 methods, but was classified as a transition state by the MP2 method. The results consistently indicated that the D 6h isomer is the most stable one among the C 24 isomers studied, while the D 2d isomer was found to be the least stable. Regarding the gap energy (GE), the B3LYP and B3LYP-D3 methods consistently yielded higher values compared to the PBE's, with an average DFT (PBE and B3LYP) GE of 1.89 eV, whereas the MP2 method showed a substantially higher GE value of 7.6 eV, representing an increase of approximately 75%. Additionally, the polarizabilities of the C 24 isomers were found to be overestimated by the PBE, B3LYP and B3LYP-D3 methods when compared to the corresponding MP2 values. The PBE-D3 method consistently produced higher polarizabilities for the C 24 isomers in comparison to the B3LYP, B3LYP-D3 and MP2 methods. The investigation confirms that the O h (D 12h) isomer has the smallest (largest) polarizability, as agreed upon by all methods. Moreover, the polarizability of D 12h is notably affected by the selected DFT method, while that of O h displays lower sensitivity but shares similarities with D 6d. However, for the newly proposed D 2d isomer, the polarizability is ranked third (fourth) in ascending order with the PBE-D3 (B3LYP-D3) method. This highlights the importance of considering the electronic correlation and dispersion effects in accurately predicting polarizabilities. The results obtained from the different methods shed light on the impact of the methodology choice on the predicted properties, emphasizing the need for careful consideration when analyzing and interpreting theoretical results for such various geometries.
... The current technology for storing hydrogen in liquid and gaseous forms have restrictions in terms of weight, size, safety, and cost. A potential remedy for this issue, however, is the reversible storage of hydrogen in solid form [11][12][13][14][15][16]. The following two crucial considerations should be taken into account when selecting the hydrogen storage technique. The average adsorption energy (E ad ) of adsorbed hydrogen on the possible adsorptive medium (−0.1 to −0.6 eV) is the first crucial factor [17]. ...
One of the critical techniques for developing hydrogen storage applications is the advanced research to build novel two-dimensional materials with significant capacity and effective reversibility. In this work, we perform first-principles unbiased structure search simulations to find a novel AsC5 monolayer with a variety of functionally advantageous characteristics. Based on theoretical simulations, the proposed AsC5 has been found to be energetically, dynamically, and thermally stable, supporting the viability of experiment. Since the coupling between H2 molecules and the AsC5 monolayer is quite weak due to physisorption, it is crucial to be enhanced by thoughtful material design. Hydrogen storage capacity can be greatly enhanced by decorating the AsC5 monolayer with Li atoms. Each Li atom on the AsC5 substrate is shown to be capable of adsorbing up to four H2 molecules with an advantageous average adsorption energy (Ead) of 0.19 eV/H2. The gravimetric density for hydrogen storage adsorption with 16Li and 64 H2 of a Li-decorated AsC5 monolayer is about 9.7 wt%, which is helpful for the possible application in hydrogen storage. It is discovered that the desorption temperature (TD) is much greater than the hydrogen critical point. Therefore, such crucial characteristics make AsC5-Li be a promising candidate for the experimental setup of hydrogen storage.
... However, there are serious issues with these substrate materials, such as high desorption temperature for metal hydrides, lower hydrogen uptake for zeolites, instability at high temperatures, clustering of the metal atoms, etc. Metal doped carbon nanomaterials such as fullerenes [8,[21][22][23][24], carbon nanotubes [25][26][27][28][29][30][31][32][33][34], graphene [35][36][37][38][39], graphyne [40][41][42][43], advanced 2d materials [44][45][46][47] have also been studied widely for hydrogen storage due to their low molecular mass and high surface area. Pristine carbon nanomaterials are not suitable for hydrogen storage as they bind the hydrogen molecules only by the weak van der Waals forces at ambient conditions [48,49], hence desorption temperature is lower than the room temperature. ...
By applying density functional theory (DFT) and ab-initio molecular dynamics (AIMD) simulations, we predict the ultrahigh hydrogen storage capacity of K and Ca decorated single-layer biphenylene sheet (BPS). We have kept various alkali and alkali earth metals, including Na, Be, Mg, K, Ca, at different sites of BPS and found that K and Ca atoms prefer to bind individually on the BPS instead of forming clusters. It was found that 2x2x1 supercell of biphenylene sheet can adsorb eight K, or eight Ca atoms, and each K or Ca atom can adsorb 5 H$_2$, leading to 11.90 % or 11.63 % of hydrogen uptake, respectively, which is significantly higher than the DOE-US demands of 6.5 %. The average adsorption energy of H$_2$ for K and Ca decorated BPS is -0.24 eV and -0.33 eV, respectively, in the suitable range for reversible H$_2$ storage. Hydrogen molecules get polarized in the vicinity of ionized metal atoms hence get attached to the metal atoms through electrostatic and van der Waals interactions. We have estimated the desorption temperatures of H$_2$ and found that the adsorbed H$_2$ can be utilized for reversible use. We have found that a sufficient energy barrier of 2.52 eV exists for the movement of Ca atoms, calculated using the climbing-image nudged elastic band (CI-NEB) method. This energy barrier can prevent the clustering issue of Ca atoms. The solidity of K and Ca decorated BPS structures were investigated using AIMD simulations.
... However, there are serious issues with these substrate materials, such as high desorption temperature for metal hydrides, lower hydrogen uptake for zeolites, instability at high temperatures, clustering of the metal atoms, etc. Metal doped carbon nanomaterials such as fullerenes [8,[21][22][23][24], carbon nanotubes [25][26][27][28][29][30][31][32][33][34], graphene [35][36][37][38][39], graphyne [40][41][42][43], advanced 2d materials [44][45][46][47] have also been studied widely for hydrogen storage due to their low molecular mass and high surface area. Pristine carbon nanomaterials are not suitable for hydrogen storage as they bind the hydrogen molecules only by the weak van der Waals forces at ambient conditions [48,49], hence desorption temperature is lower than the room temperature. ...
By applying density functional theory (DFT) and ab-initio molecular dynamics (AIMD) simulations, we predict the ultrahigh hydrogen storage capacity of K and Ca decorated single-layer biphenylene sheet (BPS). We have kept various alkali and alkali-earth metals, including Na, Be, Mg, K, Ca, at different sites of BPS and found that K and Ca atoms prefer to bind individually on the BPS instead of forming clusters. It was found that 2⨯2⨯1 supercell of biphenylene sheet can adsorb eight K, or eight Ca atoms, and each K or Ca atom can adsorb 5H2, leading to 11.90% or 11.63% of hydrogen uptake, respectively, which is significantly higher than the DOE-US demands of 6.5%. The average adsorption energy of H2 for K and Ca decorated BPS is −0.24 eV and −0.33 eV, respectively, in the suitable range for reversible H2 storage. Hydrogen molecules get polarized in the vicinity of ionized metal atoms hence get attached to the metal atoms through electrostatic and van der Waals interactions. We have estimated the desorption temperatures of H2 and found that the adsorbed H2 can be utilized for reversible use. We have found that a sufficient energy barrier of 2.52 eV exists for the movement of Ca atoms, calculated using the climbing-image nudged elastic band (CI-NEB) method. This energy barrier can prevent the clustering issue of Ca atoms. The solidity of K and Ca decorated BPS structures were investigated using AIMD simulations.
... The hydrogen storage capacity of the low-lying isomer of C 24 functionalized with Ti has also been studied. 32 The hydrogenation mechanism in smaller fullerene cages was studied by EL-Barbary, 33 who focused on the corresponding energy parameters. Li +encapsulated fullerenes are quite unique among various endohedral metallofullerenes (EMFs). ...
Mechanistic investigations into the functionalization of three fullerene cages, viz. C 60 , C 70 , and C 36 through dehydrogenation of ammonia-borane (AB) have been conducted using Density Functional Theory (DFT). In this process of functionalization, different ring fusions, namely (6-6), (6-5) positions for C 60 and C 70 , and an additional (5-5) for C 36 fullerene have been investigated. The optimized geometries of all the complexes and transition states have been characterized using the M06-2X functional in conjunction with the 6-31G(d) basis set. The effect of Li +-encapsulation on the energetics and activation barriers of H 2 attachment has also been examined. Although the process of functionalization of neutral fullerenes proceeds extensively through concerted pathways, a step-wise route has been observed for the encapsulated systems. NPA charge analysis and Wiberg bond index (WBI) have been used in order to detect the change in the nature of participating hydrogen atoms and validate the variation in the bond order of the CC connectivity respectively upon hydrogenation. GCRD parameters have also been calculated to explicate the electronic properties of the hydrogenated products. The (6-6) hydrogenation is observed to be favoured thermodynamically and kinetically for both neutral and Li +-encapsulated C 60 and C 70 , while (5-5) is found to be the most preferred site for C 36 systems. Our theoretical exploration suggests that the covalent functionalization of the fullerene cages can be done successfully via AB resulting in the stabilization of these systems. In short, the present work will provide a general idea about the detailed mechanism related to the functionalization of fullerene cages, which will further motivate researchers in fullerene chemistry.
... Hydrogen storage in Pd and Co-decorated C24 fullerene was reported by Soltani et al. 43 , but they have not investigated the solidity of the structure at high temperatures. Sathe et al. 44 have investigated hydrogen storage in Ti-doped C24 fullerene recently. They observed that a single titanium atom adsorbs 4 H2 molecules with 10.5 wt % of hydrogen for their system, but the issue was the higher maximum desorption temperature (562 K). ...
Using first-principles density functional theory simulations, we have observed that the scandium decorated C$_{24}$ fullerene can adsorb up to six hydrogen molecules with an average adsorption energy of -0.35 eV per H$_2$ and average desorption temperature of 451 K. The gravimetric wt % of hydrogen for the scandium decorated C$_{24}$ fullerene system is 13.02%, which is sufficiently higher than the Department of Energy, United States demand. Electronic structure, orbital interactions, and charge transfer mechanisms are explained using the density of states, spatial charge density difference plots, and Bader charge analysis. A total amount of 1.44e charge transfer from the 3d and 4s orbitals of scandium to the 2p carbon orbitals of C$_{24}$ fullerene. Hydrogen molecules are attached to scandium decorated C$_{24}$ fullerene by Kubas type of interactions. Diffusion energy barrier calculations predict that the existence of a sufficient energy barrier will prevent metal-metal clustering. Ab-initio molecular dynamics (A.I.M.D.) simulations confirm the solidity of the structure at the highest desorption temperature. Therefore, we believe that the scandium decorated C$_{24}$ fullerene system is a thermodynamically stable, promising reversible high-capacity hydrogen storage device.
... Although many theoretical and experimental studied have been performed for hydrogen storage in various carbon nanostructure, very few works have been reported so far for C 20 , the smallest fullerene [40,41]. Thus it is a good idea to investigate the C 20 fullerene decorated with AM to answer some of the questions like 1) where do the Li/Na atoms bound in C 20 fullerene? ...
This work reports the reversible hydrogen storage capacities of Li and Na decorated C20 fullerene using dispersion corrected density functional theory calculation. The alkali metal (AM) atoms are found to bind on the C–C bridge position of C20 through non-covalent closed-shell interaction. Their thermodynamic stabilities are verified through HOMO-LUMO gaps and different reactivity descriptors. Each Li and Na atoms decorated on C20 adsorb maximum up to five H2 molecules through Niu-Rao-Jena interaction. The adsorption energy decreases with successive addition of H2 molecules with average binding energy lying in the range of 0.12 eV–0.13 eV. The systems can have a maximum gravimetric density of 13.08 wt% and 10.82 wt% for C20Li4–20H2 and C20Na4–20H2 respectively. ADMP molecular dynamic simulations illustrate the reversibility of adsorbed hydrogen molecules at higher temperature (≧ 300 K). The calculated thermodynamic useable hydrogen capacity shows the room temperature H2 desorption condition of AM decorated C20. Consistent with criteria set by the US-DOE, C20Li4 and C20Na4 can be used as promising hydrogen storage materials.
... Hydrogen storage in Pd and Co-decorated C24 fullerene was reported by Soltani et al. 43 , but they have not investigated the solidity of the structure at high temperatures. Sathe et al. 44 have investigated hydrogen storage in Ti-doped C24 fullerene recently. They observed that a single titanium atom adsorbs 4 H2 molecules with 10.5 wt % of hydrogen for their system, but the issue was the higher maximum desorption temperature (562 K). ...
Using first principles density functional theory simulations, we have observed that the scandium decorated C24 fullerene can adsorb up to six hydrogen molecules with an average adsorption energy of −0.35 eV per H2 and average desorption temperature of 451 K. The gravimetric wt% of hydrogen for the scandium decorated C24 fullerene system is 13.02%, which is sufficiently higher than the Department of Energy, United States demand. Electronic structure, orbital interactions, and charge transfer mechanisms are explained using the density of states, spatial charge density difference plots, and Bader charge analysis. A total amount of 1.44e charge transfer from the 3d and 4s orbitals of scandium to the 2p carbon orbitals of C24 fullerene. Hydrogen molecules are attached to scandium decorated C24 fullerene by Kubas type of interactions. Diffusion energy barrier calculations predict that the existence of a sufficient energy barrier will prevent metal–metal clustering. Ab-initio molecular dynamics (A.I.M.D.) simulations confirm the solidity of structure at the highest desorption temperature. Therefore, we believe that the scandium decorated C24 fullerene system is a thermodynamically stable, promising reversible high-capacity hydrogen storage device.
... At present, the common solid hydrogen storage materials belong to two main classes: materials for physical storage based on adsorption and for chemical storage based on bonding. Materials used for physical hydrogen storage usually have a large surface area or are porous, such as metal-organic frameworks (MOFs) [5][6][7], covalent-organic frameworks (COFs) [8][9][10][11], carbon-based materials [12][13][14][15][16][17][18], MXene [19][20][21], and other monolayer structures [22][23][24][25][26][27][28]. Based on the type of bonding, chemical hydrogen storage materials can be divided into metal hydrides [29][30][31][32][33][34], complex hydrides [35][36][37][38][39][40] and other chemical hydrides [41,42]. ...
The exploitation of solid hydrogen storage materials is an essential part of the large-scale utilization of hydrogen energy. However, existing hydrogen storage materials cannot have both high hydrogen density and great stability at ambient temperature. Herein, we develop transition metal-decorated boron doped twin-graphene as a novel hydrogen storage material based on first-principles calculations. Ten different twin graphene adsorbents with Ti-decorated and doped with five boron atoms are examined. Metal decorating has a decisive influence on whether the twin graphene can be used for hydrogen storage. As the amount of boron atoms doping increases, the binding interaction between metal and substrate becomes more stable while the hydrogen adsorption strength weakens. The best structure can stably adsorb eight hydrogen molecules with a gravimetric density of 4.95 wt%. From thermodynamic calculations, the material is stable at reasonable conditions, e.g. 0.1 MPa, 238.5 K and 2.1 MPa, 298.15 K. Considering its outstanding hydrogen storage performance, we believe that Ti-decorated boron doped twin-graphene provides new inspirations to the discovery of carbon-based hydrogen storage materials.
... This is consistent with a lengthening of the H-H bond without breakage. Though hydrogen storage in Ticapped carbon clusters is reported by many authors, the number of H 2 molecules bond to the Ti adsorbents is found to be system dependent and no specific rule is available in literature [58,59]. The reason might be due to the systemdependent steric hindrance developed because of sequential H 2 adsorption on the surface of the host clusters. ...
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 Å, 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.
... Theoretical predictions yield very high magnitudes of gravimetric densities for H 2 storage (up to 24 wt%), 12 however, most papers reported more moderate values for hydrogen uptake. For instance, several theoretical works show 5.7 wt% for Ti-decorated chains-terminated C 20 fullerene, 13 9.52 wt% for defected C 4 N nanosheets, 14 10.5 wt% for Ti-functionalized C 24 nanoclusters, 15 or even 11.21 wt% for boron-substituted carbon-based cluster decorated with alkali metal cations. ...
Hydrogen adsorption on different benzenes, both organic and inorganic, decorated with Li cations (Li+) was systematically studied by using quantum chemistry techniques. Our calculations demonstrate that Li+-decoration enhances the hydrogen storage ability of the complexes. MP2 calculations reveal that one to five hydrogen molecules per Li+ have high adsorption energies (Ead), up to -4.77 kcal/mol, which is crucial for effective adsorption/desorption performance. The assessed hydrogen capacity of studied complexes is in the range of 10.0 – 10.6 wt%. SAPT2 calculations confirmed that induction and electrostatic interactions play the major role for H2 adsorption of the investigated systems, whereas London dispersion contributes to Ead moderately only in the cases of large number of hydrogen molecules adsorbed. Independent gradient model (IGM) analysis showed that there exists non-covalent bonding between Li+ and H2. The obtained van't Hoff desorption temperatures substantially exceed the temperature of liquid nitrogen. Ab initio molecular dynamics simulations confirmed the stability of the studied complexes. Our investigations establish the high potential of the studied complexes for usage in systems for hydrogen storage.
Over recent years, hydrogen (H2) has become the most sought-after sustainable energy carrier by virtue of its high energy content and carbon-free emission. The practical implementation of hydrogen as an...
Solid-state hydrogen storage is crucial for the widespread applications of hydrogen energy. It is a grand challenge to find appropriate materials that provide high hydrogen density and ambient temperature stability. Herein, we investigated the potential of Ti-decorated Irida-Graphene, a promising effective hydrogen storage system, as a novel hydrogen storage material using first-principles calculation. Irida-Graphene is a two-dimensional isomer of carbon consisting of tri-, hexa-, and octagon rings of carbon. Ti atoms are tightly bounded to the hexagonal rings. Binding energy analysis reveals that a single Ti atom in the primitive unit-cell of Ti-decorated Irida-Graphene is capable to bind up with 5 H2 molecules and the average adsorption energy was -0.41 eV/H2. It indicates the gravimetric density of 7.7 wt%. The stability is attributed to Kubas-type interactions and ensured by a 5.0 eV diffusion energy barrier that prevents the Ti-Ti clustering. Further, ab initio molecular dynamics simulations results illustrate that the system remains stable at 600 K, higher than the desorption temperature of 524 K, implying the stability of the system during hydrogen recharge and discharge. The exceptional hydrogen storage performance suggests that Ti-decorated Irida-Graphene is an outstanding candidate for hydrogen storage materials.
This article presents the hydrogen storage capacity of Ar encapsulated and Li functionalized Si 12 C 12 heterofullerene using state-of-the-art Density Functional Theory (DFT) simulations. We find that the Li atom regioselectively prefers to bind at the top of the tetragonal sites of Ar encapsulated Si 12 C 12 heterofullerene with a maximum binding energy of 2.02 eV. Our study reveals that inert gas Ar encapsulation inside bare Si 12 C 12 provides greater stability to the heterofullerene by reducing the distortion. Hence, it provides a steady platform for Li decoration and successive H 2 adsorption. The adsorption energies of sequentially hydrogen-adsorbed Si 12 C 12 Li 6 , Ne@Si 12 C 12 Li 6 , and Ar@Si 12 C 12 Li 6 are compared, and it is observed that H 2 molecules prefer to adsorb over Li decorated Ar@Si 12 C 12 with maximum adsorption energy. Each Li atom decorated over Ar@Si 12 C 12 adsorbs a maximum of 5 H 2 molecules with an optimum adsorption energy of 0.11−0.22 eV, resulting in a gravimetric density of 9.7 wt % which is well above the US-DoE target. The adsorption mechanism of H 2 molecules over Ar@Si 12 C 12 Li 6 has been thoroughly investigated using the electrostatic map and topological analyses. The type of interaction involved in the adsorption of H 2 molecules over the Ar@Si 12 C 12 Li 6 surface is found to be a weak noncovalent interaction. Thermodynamic study reveals that almost all the 30 H 2 molecules remain adsorbed over the system at a low temperature of 100−120 K and undergo maximum desorption at 250−400 K, maintaining the structural integrity, which infers that the Ar@Si 12 C 12 Li 6 nanocage can be considered as a potential hydrogen storage material.
This work explored the feasibility of Li decoration on the B4CN3 monolayer for hydrogen (H2) storage performance using first-principles calculations. The results of density functional theory (DFT) calculations showed that each Li atom decorated on the B4CN3 monolayer can physically adsorb four H2 molecules with an average adsorption energy of −0.23 eV/H2, and the corresponding theoretical gravimetric density could reach as high as 12.7 wt%. Moreover, the H2 desorption behaviors of Li-decorated B4CN3 monolayer at temperatures of 100, 200, 300 and 400 K were simulated via molecular dynamics (MD) methods. The results showed that the structure was stable within the prescribed temperature range, and a large amount of H2 could be released at 300 K, indicative of the reversibility of hydrogen storage. The above findings demonstrate that the Li-decorated B4CN3 monolayer can serve as a favorable candidate material for high-capacity reversible hydrogen storage application.
Solid chemisorption technologies for hydrogen storage, especially high-efficiency hydrogen storage of fuel cells in near ambient temperature zone defined from −20 to 100°C, have a great application potential for realizing the global goal of carbon dioxide emission reduction and vision of carbon neutrality. However, there are several challenges to be solved at near ambient temperature, i.e., unclear hydrogen storage mechanism, low sorption capacity, poor sorption kinetics, and complicated synthetic procedures. In this review, the characteristics and modification methods of chemisorption hydrogen storage materials at near ambient temperature are discussed. The interaction between hydrogen and materials is analyzed, including the microscopic, thermodynamic, and mechanical properties. Based on the classification of hydrogen storage metals, the operation temperature zone and temperature shifting methods are discussed. A series of modification and reprocessing methods are summarized, including preparation, synthesis, simulation, and experimental analysis. Finally, perspectives on advanced solid chemisorption materials promising for efficient and scalable hydrogen storage systems are provided.
Based on density functional theory (DFT) calculations, we have comprehensively studied H2 adsorption behaviors on superalkali NLi4 decorated γ-graphyne (GY). Our result shows that the binding energy of NLi4 cluster can reach −4.109 eV for single side of NLi4 decorated GY and −4.041 eV for both sides of NLi4 decorated GY at the hollow site of carbon 12-membered ring, respectively. Such large binding energies significantly reveal NLi4 cluster can be tightly bound onto the surface of GY. Moreover, 2NLi4/GY complex can maximally adsorb 24 H2 molecules with adsorption energy for peer H2 molecule of −0.167 eV/H2, indicating the reversible H2 storage can be realized under ambient conditions. In addition, the hydrogen storage gravimetric density reaches 6.78 wt%, which is higher than the U.S. DOE's latest standard of 6.5 wt%. Furthermore, ab initio molecular dynamic (AIMD) simulations are carried out by using the canonical ensemble (NVT) under massive Nose-Hoover (NH) thermostat and the result exhibits H2 molecules quickly escape from the 2NLi4/GY complex under room temperature of 300 K. Our investigation confirms that NLi4 decorated γ-graphyne can act as an outstanding H2 storage media.
Developing novel materials with high-capacity and reversible properties for storing hydrogen (H2) is crucial for energy treatments. We here investigated comprehensively the H2 storage performance of the Ca-decorated g-CN ([email protected]) monolayers using first-principles calculations. The Ca atoms can be uniformly decorated into the center of the pores of g-CN monolayers without aggregation. The [email protected] monolayer has an average H2 adsorption energy of around 0.163–0.228 eV as well as high H2 storage capacity of 10.1 wt%. The stabilities of the H2 adsorption systems are confirmed by high hardness and low electrophilicity. The temperature of desorption is anticipated to be near the room temperature and ideal for fuel cell devices. The thermodynamic analysis along with desorption temperature reveal that the [email protected] monolayer has promising potentials as reversible and high capacity hydrogen storage materials (HSM), which will motivate experimental efforts to synthesize the high-efficient HSM.
H2 storage capabilities of penta-octa-graphene (POG) adorned by lightweight alkali metals (Li, Na, K), alkali earth metals (Be, Mg, Ca) and transition metals (Sc, Ti, V, Cr, Mn) are studied by density functional theory. Metals considered, with the exception of Be and Mg, can be stably adsorbed to POG, effectively avoiding metal clustering. The average H2 adsorption energies are calculated in a range from 0.14 to 0.95 eV for Li (Na, K, Ca, Sc, Ti, V, Cr, Mn) decorated POG. Because the H2 adsorption energies for reversible physical adsorption lie in the range of 0.15–0.60 eV and the desorption temperatures fall in the range of 233–333 K under the delivery pressure, [email protected] and [email protected] are found to be the most suitable for H2 storage at ambient temperature. By polarization and hybridization mechanisms, up to 3 and 5 hydrogen molecules are stably adsorbed around each Li and Ti, respectively. The H2 gravimetric densities can reach up to 9.9 wt% and 6.5 wt% for Li and Ti decorated POG, respectively. Our findings suggest that, with metal decoration, such a novel two-dimensional carbon-based structure could be a promising medium for H2 storage.
Aiming to unravel the effect of alloying on the hydrogen adsorption mechanism, we perform a comparative analysis of the sequential hydrogen loading over Ti11, binary Ti10V, and Ti6VAl4 ternary alloy clusters. For each cluster, the variation of adsorption energy as a function of hydrogen atom coverage was calculated up to 20 hydrogen molecules. The results show that the adsorption of H2 on pure and alloy clusters occurs in a similar fashion including three phases; (i) three-fold and subsequent two-fold dissociative adsorption, (ii) non-dissociative hydrogen adsorption through the Kubas interaction, (iii) non-dissociative physisorption. Our calculations reveal that Ti11, binary Ti10V, and Ti6VAl4 can adsorb at least 20 H2 molecules with the adsorption energies in the range of chemisorption and physisorption. The gravimetric density of H2 adsorbed on these clusters exceeds the ultimate 7.5 wt% limits, recommended for practical applications. However, the magnitude of adsorption energies for Ti6VAl4 are much smaller than those of pure Ti11 binary Ti10V clusters that favor its operating as hydrogen storage media around ambient temperature and pressure.
The potential hydrogen storage performance of the constructed Y-decorated MoS2 was investigated via first-principles density functional theory (DFT) calculations. The Y could be stably decorated on the MoS2 monolayer with adsorption energy being −4.82 eV, the absolute value of which was higher than the cohesive energy of bulk Y. The introduced H2 interacted strongly with the Y-decorated MoS2 with an elongated bond length and reasonable adsorption energy being 0.792 Å and −0.904 eV, respectively. There would be four H2 in maximum adsorbed and stored on the Y-decorated MoS2 with average adsorption energy being −0.387 eV. Moreover, the hydrogen gravimetric capacity of the MoS2 with full Y coverage on each side could be improved to be 4.56 wt% with average adsorption energy being −0.295 eV. Our study revealed that the MoS2 decorated with Y could be a potential material to effectively store H2 with promising gravimetric density.
We have investigated the hydrogen storage capabilities of scandium decorated holey graphyne, a recently synthesized carbon allotrope, by applying density functional theory and molecular dynamics simulations. We have observed that one unit cell of holey graphyne can adsorb 6 Sc atoms, and each Sc atom can adsorb up to 5 H$_2$ molecules with an average binding energy and average desorption temperature of -0.36 eV/H$_2$ and 464 K, respectively. The gravimetric weight percentage of hydrogen is 9.80 %, which is considerably higher than the Department of Energy, United-States requirements of 6.5 %. We have found that a total amount of 1.9e charge transfers from the 3d and 4s orbitals of Sc atom to the C-2p orbitals of holey graphyne by performing the Bader charge analysis. Hydrogen molecules are bonded with the scandium atom by Kubas interactions. The ab-initio molecular dynamics simulations confirm the structural integrity of scandium decorated holey graphyne system at the high desorption temperatures. The presence of sufficient diffusion energy barriers for the Sc atom ensure the avoidance of metal-metal clustering in the system.
We have investigated the hydrogen storage capabilities of scandium decorated holey graphyne, a recently synthesized carbon allotrope, by applying density functional theory and molecular dynamics simulations. We have observed that one unit cell of holey graphyne can adsorb 6 Sc atoms, and each Sc atom can adsorb up to 5H2 molecules with an average binding energy and average desorption temperature of −0.36 eV/H2 and 464 K, respectively. The gravimetric weight percentage of hydrogen is 9.80%, which is considerably higher than the Department of Energy, United-States requirements of 6.5%. We have found that a total amount of 1.9e charge transfers from the 3d and 4s orbitals of Sc atom to the C-2p orbitals of holey graphyne by performing the Bader charge analysis. Hydrogen molecules are bonded with the scandium atom by Kubas interactions. The ab-initio molecular dynamics simulations confirm the structural integrity of scandium decorated holey graphyne system at the high desorption temperatures. The presence of sufficient diffusion energy barriers for the Sc atom ensure the avoidance of metal-metal clustering in the system.
By employing the state-of-the-art density functional theory, we report the hydrogen storage capability of yttrium decorated C$_{24}$ fullerene. Single Y atom attached on C$_{24}$ fullerene can reversibly adsorb a maximum number of 6 H$_2$ molecules with average adsorption energy -0.37 eV and average desorption temperature 477 K, suitable for fuel cell applications. The gravimetric weight content of hydrogen is 8.84 %, which exceeds the target value of 6.5 wt % H by the department of energy (DoE) of the United States. Y atom is strongly bonded to C$_{24}$ fullerene with a binding energy of -3.4 eV due to a charge transfer from Y-4d and Y-5s orbitals to the C-2p orbitals of C$_{24}$ fullerene. The interaction of H$_2$ molecules with the Y atom is due to the Kubas type interaction involving a charge donation from the metal d orbital to H 1s orbital, and back donation causing slight elongation of H-H bond length. The stability of the system at the highest desorption temperature is confirmed by ab-initio molecular dynamics simulations, and the metal-metal clustering formation has been investigated by computing the diffusion energy barrier for the movement of Y atoms. We have corrected all the calculated energies for the van der Waals (vdW) interactions by applying the dispersion energy corrections, in addition to the contribution of the GGA exchange-correlation functional. The C$_{24}$+Y system is stable at room temperature, and at the highest desorption temperature, the presence of a sufficient diffusion energy barrier prevents metal-metal clustering. Furthermore, binding energies of H$_2$ are within the target value by DoE (-0.2-0.7 eV/H$_2$ ), while H$_2$ uptake (8.84 % H) is higher than DoE's criteria. Therefore, we propose that Y decorated C$_{24}$ fullerene can be tailored as a practically viable potential hydrogen storage candidate.
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.
By employing the state-of-the-art density functional theory, we report the hydrogen storage capability of yttrium doped C24 fullerene. Single Y atom attached on C24 fullerene can reversibly adsorb a maximum number of 6 H2 molecules with average adsorption energy -0.37 eV and average desorption temperature 477 K, suitable for fuel cell applications. The gravimetric weight content of hydrogen is 8.84%, which exceeds the target value of 6.5 wt % H by the department of energy (DoE) of the United States. Y atom is strongly bonded to C24 fullerene with a binding energy of -3.4 eV due to a charge transfer from Y-4d and Y-5s orbitals to the C-2p orbitals of C24 fullerene. The interaction of H2 molecules with Y atom is due to the Kubas type interaction involving a charge donation from the metal d orbital to H 1 s orbital, and back donation causing slight elongation of H-H bond length. The stability of the system at the highest desorption temperature is confirmed by ab-initio molecular dynamics simulations, and the metal-metal clustering formation has been investigated by computing the diffusion energy barrier for the movement of Y atoms. We have corrected all the calculated energies for the van der Waals (vdW) interactions by applying the dispersion energy corrections, in addition to the contribution of the GGA exchange-correlation functional. The C24+Y system is stable at room temperature, and at the highest desorption temperature, the presence of a sufficient diffusion energy barrier prevents metal-metal clustering. Furthermore, binding energies of H2 are within the target value by DoE (-0.2-0.7 eV/H2), while H2 uptake (8.84% H) is higher than DoE’s criteria. Therefore, we propose that Y doped C24 fullerene can be tailored as a practically viable potential hydrogen storage candidate.
The hydrogen storage performances of the pure MoS2 monolayer and the one decorated with Ti atoms were studied via the first-principles DFT calculations. The Ti atom was calculated to be successfully and chemically decorated on the surface of MoS2 monolayer with a large binding energy of -4.979 eV, the absolute value of which was higher than the cohesive energy of Ti bulk (4.85 eV). The hydrogen molecule interacted weakly with the pure MoS2 with a low adsorption energy of only -0.0226 eV but was strongly adsorbed on the introduced active site of the Ti atom in the decorated MoS2 with an improved adsorption energy of -0.472 eV. There were four hydrogen molecules in maximum stored on the modified MoS2 monolayer via chemical interactions with an average adsorption energy being -0.413 eV. Moreover, the adsorbed hydrogen molecules released 1.29 e to the substrate of decorated MoS2 during the storage process. The stored hydrogen molecules of the MoS2 decorated with two Ti atoms were further improved to be eight with transferred charges being 2.42 e. Finally, the gravimetric density of hydrogen storage of the Ti-decorated MoS2 with a full coverage being 1 on its both sides could be enhanced to be as high as 5.93 wt%, well meeting the criteria of the United States Department of Energy. Our research indicates that the MoS2 monolayer decorated with Ti atoms is promising to effectively store the hydrogen molecules and is potentially applied as an excellent hydrogen gas sensor.
Searching advanced materials with high capacity and efficient reversibility for hydrogen storage is a key issue for the development of hydrogen energy. In this work, we studied systematically the hydrogen storage properties of the pure C7N6 monolayer using density functional theory methods. Our results demonstrate that H2 molecules are spontaneously adsorbed on the C7N6 monolayer with the average adsorption energy in the range of 0.187–0.202 eV. The interactions between H2 molecules and C7N6 monolayer are of electrostatic nature. The gravimetric and volumetric hydrogen storage capacities of the C7N6 monolayer are found to be 11.1 wt% and 169 g/L, respectively. High hardness and low electrophilicity provides the stabilities of H2–C7N6 systems. The hydrogenation/dehydrogenation (desorption) temperature is predicted to be 239 K. The desorption temperatures and desorption capacity of H2 under practical conditions further reveal that the C7N6 monolayer could operate as reversible hydrogen storage media. Our results thus indicate that the C7N6 monolayer is a promising material with efficient, reversible, and high capacity for H2 storage under realistic conditions.
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.
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 TD 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.
After highlighting the fundamental contributions of van’t Hoff to the emergence of modern physical chemistry, we bring out the relevance of his ideas to a problem of great contemporary interest—storageof hydrogen in nanomaterials.
Two types of hybrid metallofullerene framework are theoretically designed, and their structural stabilities are examined using the density functional theory (DFT) computation. Both frameworks are constructed by connecting exohedral metallofullerene nodes with conjugated organic linkers, akin to the common metal–organic framework (MOF). The DFT calculations suggest that hydrogen molecules can be adsorbed in the frameworks with the hydrogen binding energies ranging from 0.15–0.50 eV, satisfying the optimal adsorption condition for hydrogen storage. Moreover, our computation suggests that the frameworks can entail molecular H2 binding in the range of 8.0–9.2 wt%, meeting the Department of Energy (DOE) target of 2010 or 2015.
Hydrogen desorption from a LiH + NH(3) mixture is very difficult due to the formation of the stable LiNH(4) compound. Using cluster models and first-principles theory, we demonstrate that the C(60) molecule can in fact significantly improve the thermodynamics of ammonia-mediated hydrogen desorption from LiH due to the stabilization of the intermediate state, LiNH(4). The hydrogen desorption following the path of LiNH(4)-C(60) → LiNH(3)-[Formula: see text] is exothermic. Molecular dynamic simulations show that this reaction can take place even at room temperature (300 K). In contrast, the stable LiNH(4) compound cannot desorb hydrogen at room temperature in the absence of C(60). The introduction of C(60) also helps to restrain the NH(3) gas which is poisonous in proton exchange membrane fuel cell applications.
Using first-principles calculations based on the density-functional theory, we perform a detailed study of the dihydrogen H 2 binding in cis-and trans-polyacetylene decorated with transition metal atoms. First, we investigate the origin of metal-dihydrogen bonding and observe the hybridization of e g t 2g orbitals of the Ti atom with the * orbitals of the H 2 molecules in octahedral geometries, which is consistent with the Kubas model. Second, using a statistical model parametrized by the results of ab initio calculations and experimental data, the adsorption and desorption of molecular hydrogens are calculated at ambient temperature and pressure. We find that the usable capacity at ambient conditions is dramatically reduced from the maximum capacity, the zero-point energy affects the storage capacity significantly, and the optimal binding energy of H 2 molecules under practical conditions is 0.3 eV/ H 2 . Third, we examine the effects of the aggregation and intercalation of the Ti atoms on H 2 adsorption.
For any potential hydrogen-storage system, raw uptake capacity must be balanced with the kinetics and thermodynamics of uptake and release. Metal-organic frameworks (MOFs) provide unique systems with large overall pore volumes and surface areas, adjustable pore sizes, and tunable framework-adsorbate interaction by ligand functionalization and metal choice. These remarkable materials can potentially fill the niche between other physisorbents such as activated carbon, which have similar uptake at low temperatures but low affinity for hydrogen at ambient temperature, and chemical sorbents such as hydrides, which have high hydrogen uptakes but undesirable release kinetics and thermodynamics.
On the basis of density functional theory calculations, we show that edge-decorated graphene nanoribbons (GNRs) by scandium can bind multiple hydrogen molecules in a quasi-molecular fashion. The average adsorption energy of H(2) on Sc ranges from 0.17 to 0.23 eV, ideally suited to hydrogen storage. For the narrowest GNR with either armchair or zigzag edges, the predicted weight percentage of H(2) is >9 wt%, exceeding the gravimetric target value set by the Department of Energy (DOE). The bonding energy between Sc and the GNR is significantly greater than the cohesive energy of bulk Sc so that clustering of Sc will not occur once Sc is bonded with carbon atoms at the edge of GNRs. Moreover, the adsorption energy of H(2) can be modestly tuned (either enhanced or reduced) by applying an external electric field.
A Lagrangian generalization of time-reversible Born-Oppenheimer molecular dynamics Niklasson et al. [Phys. Rev. Lett. 97, 123001 (2006)10.1103/PhysRevLett.97.123001] is proposed. The formulation enables the application of higher-order symplectic or geometric integration schemes that are stable and energy conserving even under incomplete self-consistency convergence. It is demonstrated how the accuracy is improved by over an order of magnitude compared to previous formulations at the same level of computational cost. The proposed Lagrangian includes extended electronic degrees of freedom as auxiliary dynamical variables in addition to the nuclear coordinates and momenta. While the nuclear degrees of freedom propagate on the Born-Oppenheimer potential energy surface, the extended auxiliary electronic degrees of freedom evolve as a harmonic oscillator centered around the adiabatic propagation of the self-consistent ground state.
The method of dispersion correction as an add-on to standard Kohn-Sham density functional theory (DFT-D) has been refined regarding higher accuracy, broader range of applicability, and less empiricism. The main new ingredients are atom-pairwise specific dispersion coefficients and cutoff radii that are both computed from first principles. The coefficients for new eighth-order dispersion terms are computed using established recursion relations. System (geometry) dependent information is used for the first time in a DFT-D type approach by employing the new concept of fractional coordination numbers (CN). They are used to interpolate between dispersion coefficients of atoms in different chemical environments. The method only requires adjustment of two global parameters for each density functional, is asymptotically exact for a gas of weakly interacting neutral atoms, and easily allows the computation of atomic forces. Three-body nonadditivity terms are considered. The method has been assessed on standard benchmark sets for inter- and intramolecular noncovalent interactions with a particular emphasis on a consistent description of light and heavy element systems. The mean absolute deviations for the S22 benchmark set of noncovalent interactions for 11 standard density functionals decrease by 15%-40% compared to the previous (already accurate) DFT-D version. Spectacular improvements are found for a tripeptide-folding model and all tested metallic systems. The rectification of the long-range behavior and the use of more accurate C(6) coefficients also lead to a much better description of large (infinite) systems as shown for graphene sheets and the adsorption of benzene on an Ag(111) surface. For graphene it is found that the inclusion of three-body terms substantially (by about 10%) weakens the interlayer binding. We propose the revised DFT-D method as a general tool for the computation of the dispersion energy in molecules and solids of any kind with DFT and related (low-cost) electronic structure methods for large systems.
This critical review covers the application of computer simulations, including quantum calculations (ab initio and DFT), grand canonical Monte-Carlo simulations, and molecular dynamics simulations, to the burgeoning area of the hydrogen storage by metal-organic frameworks and covalent-organic frameworks. This review begins with an overview of the theoretical methods obtained from previous studies. Then strategies for the improvement of hydrogen storage in the porous materials are discussed in detail. The strategies include appropriate pore size, impregnation, catenation, open metal sites in metal oxide parts and within organic linker parts, doping of alkali elements onto organic linkers, substitution of metal oxide with lighter metals, functionalized organic linkers, and hydrogen spillover (186 references).
A method for calculations of the ground-state energy and structure of finite systems and for molecular-dynamics simulations of the evolution of the nuclei on the Born-Oppenheimer ground-state electronic potential-energy surface is described. The method is based on local-spin-density functional theory, using nonlocal pseudopotentials and a plane-wave basis set. Evaluations of Hamiltonian matrix elements and the operations on the wave functions are performed using a dual-space representation. The method, which does not involve a supercell, affords accurate efficient simulations of neutral or charged finite systems which possess, or may develop, multipole moments. Since the ground-state electronic energy and the forces on the ions are calculated for each nuclear configuration during a dynammical simulation, a relatively large time step can be used to integrate the classical equations of motion of the nuclei (1-10 fs, depending on the characteristic frequencies of the ionic degrees of freedom). The method is demonstrated via a study of the energetics, structure, and dynamics of the water dimer, (H2O)2, yielding results in agreement with experimental data and other theoretical calculations. In addition to the properties of the ground state of the dimer, higher-energy transition structures involved in transformations between equivalent structures of the (H2O)2 molecule, were studied, and finite temperature simulations of the dynamics of such transformations are presented.
Transition metal (TM) atoms bound to fullerenes are proposed as adsorbents for high density, room temperature, ambient pressure storage of hydrogen. C60 or C48B12 disperses TMs by charge transfer interactions to produce stable organometallic buckyballs (OBBs). A particular scandium OBB can bind as many as 11 hydrogen atoms per TM, ten of which are in the form of dihydrogen that can be adsorbed and desorbed reversibly. In this case, the calculated binding energy is about 0.3 eV/H(2), which is ideal for use on board vehicles. The theoretical maximum retrievable H2 storage density is approximately 9 wt %.
Chemical stabilities of six low-energy isomers of C24 derived from global-minimum search are investigated. The six isomers include one classical fullerene (isomer 1) whose cage is composed of only five- and six-membered rings (56-MRs), three nonclassical fullerene structures whose cages contain at least one four-membered ring (4-MR), one plate, and one monocyclic ring. Chemical and electronic properties of the six C24 isomers are calculated based on a density-functional theory method (hybrid PBE1PBE functional and cc-pVTZ basis set). The properties include the nucleus-independent chemical shifts (NICS), singlet-triplet splitting, electron affinity, ionization potential, and gap between the highest occupied molecular orbital and the lowest unoccupied molecular orbital (HOMO-LUMO) gap. The calculation suggests that the neutral isomer 2, a nonclassical fullerene with two 4-MRs, may be more chemically stable than the classical fullerene (isomer 1). Analyses of molecular orbital NICS show that the incorporations of 4-MRs into the cage considerably reduce paratropic contributions from HOMO, HOMO-1, and HOMO-2, which are mainly responsible for the sign change in NICS from positive for isomer 1 (42) to negative (-19) for isomer 2, although C24 clusters satisfy neither 4N+2 nor 2(N+1)2 aromaticity rule. Anion photoelectron spectra of four cage isomers, one plate, one monocyclic ring, and one tadpole isomer, as well as three bicyclic ring isomers are calculated. The simulated photoelectron spectra of mono- and bicyclic rings (with C1 symmetry) appear to match the measured HOMO-LUMO gap (between the first and second band in the experimental spectra) [S. Yang et al., Chem. Phys. Lett. 144, 431 (1988)]. Nevertheless, the nonclassical fullerene isomers 3 and 4 apparently also match the measured vertical detachment energy (2.90 eV) reasonably well. These results suggest possible coexistence of nonclassical fullerene isomers with the mono- and bicyclic ring isomers of C24(-) under the experimental conditions.
We present the detailed comparative study of dihydrogen adsorption in Li, Mg, Ca, and Sc decorated γ-graphyne (Gγ) performed with density functional theory calculations. Hydrogen molecules are sequentially loaded onto metal decorated Gγ. Maximum hydrogen weight percentage for Li, Mg, Ca, and Sc decorated Gγ is found to be 8.69, 7.73, 8.10, and 6.83, respectively, with maximum 8 H2 on Li, Mg, and Sc while 10 on Ca decorated Gγ. All hydrogen molecules are physisorbed over all the complexes except that the first one on each Sc of Gγ-2Sc is chemisorbed. Orbital hybridization involved in Dewar coordination of metal decoration and the Kubas mechanism of hydrogen adsorption has been explained with the partial density of states. Lower values of adsorption and desorption energies in these complexes indicate the reversibility of adsorption. These complexes obey high hardness and low electrophilicity principles and contain no imaginary frequencies which specify their stability. In Born-Oppenheimer molecular dynamics, reversibility of adsorption is proven at various temperatures. Based on the comparative studies of hydrogen weight percentage, energetics, stability, and reversibility, Gγ-2Ca is proven to be a better hydrogen storage candidate. This comprehensive study confirms the potential of metal decorated γ-graphyne as a suitable hydrogen storage material.
Use of metal functionalized molecules for reversible hydrogen storage is well established due to their high gravimetric hydrogen storage capacity. We study BN-analogue of [2,2]paracyclophane (BNP22) containing two borazine rings and functionalized with Sc and Ti atoms to interpret its hydrogen binding capacity. First principles calculations based on density functional theory suggest that BNP22-2Sc and BNP22–2Ti systems can have a gravimetric density as high as 8.9 and 9.9 %, respectively. The BNP22-2Sc system can be operated under ambient thermodynamic conditions within the allowable pressure range of 3–30 atm and van ‘t Hoff desorption temperature range of 219–438 K as confirmed from molecular dynamics and occupation number studies. Both the systems establish Brønsted-Evans-Polanyi relation with BNP22-2Sc having significantly less activation energy of 0.38 eV. We discuss the energetic stability of these systems with respect to vibrational frequency, absolute hardness, and transition states. Consistent with 2020 targets set by the DOE, BNP22-2Sc proves to be budding hydrogen storage material.
The present work examines the host-guest interactions in H2-THF mixed hydrates in a fused dodeca-hexakaidecahedral cage at the molecular level. The host-guest interaction energies are analyzed to get insight on the occupancies of H2 and THF in different host cages. The maximum and optimum storage capacity of H2 in dodecahedral and hexakaidecahedral cages is determined. The studies show that THF in a hexakaidecahedral cage interacts with water molecules of the neighboring dodecahedral cage whereas H2 due to its smaller size does not interact with water molecules of a neighboring cage. The interaction energy and free energy associated with the encapsulation of guest species revealed that simultaneous encapsulation of H2 and THF in the large cavities of sII hydrates is feasible. Energy decomposition analysis indicates that electrostatic and dispersion interactions contribute significantly to the stability of the complexes. The occupancy of H2 in small and large cages of mixed hydrates are analyzed in terms of ¹H and ¹³C chemical shifts.
In the originally published article version the family name of first author WANG Hui was misspellt “WAND”. The original article has been corrected. © 2018, Science Press, Institute of Engineering Thermophysics, CAS and Springer-Verlag GmbH Germany, part of Springer Nature.
The hydrogen storage behavior of alkali and alkaline-earth metal (AM = Li, Na, K, Mg, Ca) atoms decorated C24 fullerene was investigated by using density functional theory (DFT) study. Our results indicate that the AM atoms prefer to adsorb atop the center of tetragon of C24 fullerene with the largest binding energy than other possible adsorption sites. Moreover, the hydrogen storage gravimetric density of 24H2/6Li/C24, 24H2/6Na/C24 and 36H2/6Ca/C24 configurations reaches up to 12.7 wt%, 10.1 wt% and 12 wt%, higher than the year 2020 target from the US department of energy (DOE). Also, the average adsorption energies of H2 molecules of the 24H2/6Li/C24, 24H2/6Na/C24 and 36H2/6Ca/C24 configurations are −0.198 eV/H2, −0.164 eV/H2 and −0.138 eV/H2, locate the desirable range under the physical adsorption at near ambient conditions. These findings will have important implications on designing new hydrogen storage materials in the future.
Storing hydrogen for commercial purpose with high gravimetric density is a major task. Li and Sc are functionalized over delocalized π electrons of [4,4]paracyclophane to explore reversible hydrogen storing capacity. Electronic structure calculations are performed with Minnesota 06 hybrid functional and 6-311G(d,p) basis set. [4,4]paracyclophane binds strongly to Sc showing Dewar coordination. Sc functionalized [4,4]paracyclophane complex has a capacity of holding 10 H2 molecules while Li functionalized complex holds 8 H2 molecules with hydrogen weight percentage of 11.8% and 13.7% respectively. Conceptual DFT parameters namely hardness and electrophilicity confirm the high stability of the complexes. Atom Density Matrix Propagation simulations at various temperatures and their desorption pattern indicate reversibility of adsorbed hydrogens. The study confirms the potential of Sc functionalized [4,4]paracyclophanes as a hydrogen storage material.
Li and Sc metals functionalized on the delocalized p-electrons of benzene rings in [2,2]paracyclophane
structure are studied for hydrogen storage efficiency by using the M06 DFT functional with 6-311G(d,p) basis
set. It is found that Sc and Li functionalized [2,2]paracyclophane complexes can hold up to 10 H2 molecules
and 8 H2 molecules by Kubas-Niu-Jena interaction and charge polarization mechanism with hydrogen
weight percentage of 11.4 and 13.5, respectively. Molecular dynamics simulation at various temperatures
showed appreciable thermal stability while the chemical potential calculation at room temperature reveals
that Sc functionalized [2,2]paracyclophane system will be a promising hydrogen storage material.
We present here results from detailed investigation on the adsorption property of H2 on the surface of B12N12 (BN) and Ni-decorated B12N12 (Ni-BN) nano-clusters through density functional theory (DFT) methods. First, the adsorption of Ni on BN nano-cage resulted in optimization of two distinct geometries (P1 and P2) differing in
orientation of nickel on the surface of the nano-cage. The binding properties have been calculated and analyzed theoretically for both geometries of Ni-BN (P1 and P2) in terms of binding energies, band structures, total density of states, and natural bond orbital (NBO) charges. The nickel binds more strongly to BN nano-cage in P1 compared to P2, as revealed from energetic and electronic properties. Hydrogen adsorption has also been studied on Ni-BN (both P1 and P2), and compared with that of bare BN nano-cage. H2 adsorption capacity for nickel decorated BN nano-cage (Ni-BN) is considerably enhanced while there is very low adsorption capacity for pristine BN. Although, decoration of Ni in P1 geometry releases slightly higher energy (~444 kJ/mole versus ~399
kJ/mole for P2), the latter is better adsorbent for H2 molecule. H2 adsorption on Ni-BN in P2 geometry is more exothermic (~144 kJ/mole versus ~108 kJ/mole for position P1).The band gap of Ni-BN nano-cages
increases upon interaction with hydrogen, and the effect is more pronounced for P2 geometry compared to P1. Incorporation of Ni enhances the H2 adsorption capacity of BN cluster, significantly.
An emissions trajectory for the US consistent with 2 °C warming would require marked societal changes, making it crucial to understand the associated benefits. Previous studies have examined technological potentials and implementation costs and public health benefits have been quantified for less-aggressive potential emissions-reduction policies (for example, refs,), but researchers have not yet fully explored the multiple benefits of reductions consistent with 2 °C. We examine the impacts of such highly ambitious scenarios for clean energy and vehicles. US transportation emissions reductions avoid ∼0.03 °C global warming in 2030 (0.15 °C in 2100), whereas energy emissions reductions avoid ∼0.05-0.07 °C 2030 warming (∼0.25 °C in 2100). Nationally, however, clean energy policies produce climate disbenefits including warmer summers (although these would be eliminated by the remote effects of similar policies if they were undertaken elsewhere). The policies also greatly reduce damaging ambient particulate matter and ozone. By 2030, clean energy policies could prevent ∼175,000 premature deaths, with ∼22,000 (11,000-96,000; 95% confidence) fewer annually thereafter, whereas clean transportation could prevent ∼120,000 premature deaths and ∼14,000 (9,000-52,000) annually thereafter. Near-term national benefits are valued at ∼US$250 billion (140 billion to 1,050 billion) per year, which is likely to exceed implementation costs. Including longer-term, worldwide climate impacts, benefits roughly quintuple, becoming ∼5-10 times larger than estimated implementation costs. Achieving the benefits, however, would require both larger and broader emissions reductions than those in current legislation or regulations.
The calculation results show that H2O monomer prefers to adsorb at two top sites (t1, t2) of the icosahedral Ru55 nanoparticle. When two H2O molecules coadsorb on Ru55, they choose to adsorb at the two adjacent vertex and edge sites to form a H2O dimer. The energy barrier for H2O monomer dissociation is 0.43 eV on t1 site and 0.34 eV on t2 site after DFT-D2 correction, indicating the t2 site is more active than the t1 site. The energy barrier for H2O dimer dissociation on t2 site is only 0.11 eV after DFT-D2 correction. During H2O dimer dissociation, the H atom from the H2O locating on the t1 site can automatically transfer to the H2O locating on the more active t2 site. The low energy barriers for the dissociation of H2O monomer and dimer illustrate that Ru55 nanoparticles have a high catalyst activity for H2O dissociation to produce hydrogen.
Ab initio DFT (density functional theory) is used to investigate the hydrogenation energy and hydrogenation mechanism of Cn and CnHn fullerene cages from n = 20 to n = 60. All calculations have been performed using G03W package, with B3LYP exchange-functional and applying basis set 6-31G(d, p). It is found that the most stable hydrogenation sites on the Cn fullerene cages are (black small square) and (black small square) sites and on the CnHn fullerene cages are (black small square), (black small square) and (black small square) sites. The calculations show that the required energy to initiate the hydrogen migration on the surface of Cn fullerene cages between two metastable structures of C54H is ∼1.5 eV and on the surface of CnHn fullerene cages between metastable and stable structures of the C60H61 fullerene cage is ∼2.35 eV. Also, it is found that the energy release from hydrogen migration is always enough to direct the hydrogenation process towards the most stable structures and it reduces the number of hydrogen atoms bonded to the fullerene cage via forming H2 molecules.
Graphene has been intensively investigated as a possible hydrogen storage medium due to the spectacular properties granted by its two-dimensional nature. Since graphene's discovery, several new two-dimensional carbon allotropes have been theorized and synthesized. We investigated the hydrogen storage ability of six such allotropes: C65, C64, C63, C62, C31 and C41. The ability to anchor lithium metal atoms over each allotrope and the hydrogen binding energies for each lithium decorated allotrope were studied with density functional theory using LDA, GGA and vdW-DF2 (for describing van der Waals interactions) functionals. All the allotropes were able to achieve double sided lithium decoration and hydrogen adsorption. Every allotrope other than C31 possesed lithium binding energies stronger than bulk lithium's cohesive energy which indicates that adsorbed lithium atoms will not cluster on the allotrope surface. Furthermore, every structure produced hydrogen binding energies stronger than that of lithium decorated graphene, suggesting the potential of use of these structures in practical hydrogen storage media. The C41 structure was able to adsorb far more hydrogen molecules than any other structure with a maximum hydrogen gravimetric density of 7.12 wt.% using the vdW-DF2 functional.
A study is conducted to demonstrate quantum-chemical characterization of the properties and reactivities of metal-organic frameworks (MOF). MOFs exhibit important properties from a technology standpoint, as they are thermally stable, crystalline, and characterized by high porosities and possess record-breaking surface areas. These properties make them good candidates as gas adsorbents. The chemical functional groups found in their pores, along with the shapes and sizes of those pores can be tuned in a controlled fashion. The MOFs' porosities are systematically tuned by increasing the sizes of the organic carboxylate linkers.
Hydrogen is considered as a potential candidate for future energy source in automobile industry. Hydrogen storage is the major problem in achieving this goal. In this study, metal–organic framework (MOF) with organic linker is replaced with BN linker namely borazocine (B4N4H8) and is functionalized with Ti, enhancing the stability and storage capacity of the framework. A first-principles electronic structure calculation using spin polarized generalized gradient approximation with Perdew–Burke–Ernzerhof functional, structural optimization and molecular dynamics (MD) simulations have been performed for hydrogen sorption efficiency of the Ti-functionalized Mg4O–BN framework (MBF). Low adsorption and desorption energies suggest the high hydrogen reversibility of the system. BN ring coordinates strongly with the Ti metal by Dewar interaction while each Ti metal adsorbs 4 H2 molecules by Kubas interaction. In MD simulations, 75% of the physisorbed H2 molecules are desorbed at 300 K while at 373 K chemisorbed hydrogen also began to desorb with the MBF framework remaining structurally stable. The average hydrogen desorption temperature using van’t Hoff equation is predicted to be 323 K with hydrogen storage capacity of 7.8 wt %. For the first time, the H2 sorption efficiency of the Ti-functionalized metal–BN framework has been studied and is found to be better than MOF or metal-functionalized MOF with respect to storage capacity, stability, and reversibility, making it a potential hydrogen storage material.
Density functional techniques are used to investigate the relative energies of seven different structural isomers of C24. The traditional local density approximation yields the fullerene-like isomer to be the most stable. As in the case of C20, the inclusion of gradient corrections has a dramatic effect on the relative energies. The gradient-corrected B-LYP method yields the monocyclic ring and graphite-like isomers to be almost isoenergetic (and most stable) while the bicyclic ring, fullerene-like, and bowl-like isomers are progressively higher in energy. The Hartree—Fock results are quite similar to the B-LYP results. Implications to fullerene growth mechanisms are pointed out.
The energy difference between the ring and fullerene forms of C24 have been calculated by means of ab initio methods, and compared to density functional methods. The calculations strongly suggest that the fullerene form is favored by ~80 kcal/mol over a monocyclic ring structure, which is at variance with experimental findings. Density functional results vary considerably, although functionals including exact exchange (B3LYP and B3PW91) give reasonable results when basis sets of at least triple zeta quality are employed.
The discovery of dihydrogen complexes, Ln
M(H2), pointed to direct transfer of hydrogen from coordinated H2 ligands to substrates as an operable pathway in catalysis both in homogeneous and heterogeneous systems. Sigma complexes, Ln
M(η
2-H–X) (X=H, Si, C, etc), are indeed relevant in hydrogenation as well as silane alcoholysis and methane conversion.
Hückel model calculations have been performed for small fullerene cages with 20–50 atoms. The closed-shell electronic structures for the small cages are emphasized. The relatively high stability of C24, C28, C32, C44 and C50 clusters observed in the early laser vaporization experiments is explained. These clusters have pseudo closed-shell or half-filled electronic structures with a relatively large HOMO-LUMO gap. Based on the Hückel results, we propose a large number of other possible stable clusters formed by adding hydrogens, replacing carbons with other atoms which have an appropriate number of valence electrons, or encapsulating metal atoms capable of donating a given number of valence electrons.
The ground-state structures of small fullerenes below C70 were
determined by tight-binding molecular-dynamics total energy
optimization. An efficient simulated annealing scheme was used to
generate closed, hollow, spheroidal cage structures for all
even-numbered carbon clusters from C20 to C70. As a general trend,
fullerenes prefer geometries which separate the pentagonal rings as far
apart as possible. Except for C60, C70, and C50, most fullerenes have
relatively low symmetries.
The effect of light metal (M = Li, Be, Mg, and Al) decoration on the stability of metal organic framework MOF-5 and its hydrogen adsorption is investigated by ab initio and periodic density functional theory (DFT) calculations by employing models of the form BDC:M2:nH2 and MOF-5:M2:nH2, where BDC stands for the benzenedicarboxylate organic linker and MOF-5 represents the primitive unit cell. The suitability of the periodic DFT method employing the GGA-PBE functional is tested against MP2/6-311 + G* and MP2/cc-pVTZ molecular calculations. A correlation between the charge transfer and interaction energies is revealed. The metal-MOF-5 interactions are analyzed using the frontier molecular orbital approach. Difference charge density plots show that H2 molecules get polarized due to the charge generated on the metal atom adsorbed over the BDC linker, resulting in electrostatic guest-host interactions.Our solid state results show that amongst the four metal atoms, Mg and Be decoration does not stabilize the MOF-5 to any significant extent. Li and Al decoration strengthened the H2-MOF-5 interactions relative to the pure MOF-5 exhibited by the enhanced binding energies. The hydrogen binding energies for the Li- and Al-decorated MOF-5 were found to be sensible for allowing reversible hydrogen storage at ambient temperatures. A high hydrogen uptake of 4.3 wt.% and 3.9 wt.% is also predicted for the Li- and Al-decorated MOF-5, respectively.Highlights► We examine light metals as novel dopants for hydrogen storage properties in MOF-5. ► For MOF-5, our results show good agreement with results of MP2 method. ► We analyze FMO and charge density of MOF-5 with metals and H2.
This paper reports synthesis of several nanoporous polymers containing stereocontorted cores for hydrogen storage. The spirobifluorene and tetraphenylmethane cores were used as the building blocks for the cross-linked polymers. Trimerizations of acetylinic compounds or oxidative coupling of thiophenyl compound were used for the polymerization. Characterizations on structures and hydrogen storage capacities of the resulting polymers were performed. It was found that the polymers thus prepared generally have a narrow pore size distribution, and specific surface areas up to 1000 m2/g were obtained. It was shown that the reaction conditions affect the size of nanopores and the surface areas. Hydrogen adsorption capacities at liquid nitrogen and ambient temperatures were measured using a Sievert isotherm apparatus.
The sequential growth of small titanium clusters with up to 15 atoms and the dissociative chemisorption of H2 on the minimum energy clusters have been studied within density functional theory under the generalized gradient approximation. It has been found that the low-energy clusters grow three dimensionally from Ti4 and follow a pentagonal growth pattern. The clusters Ti7 and Ti13 show a higher stability than other clusters with a configuration of pentagonal bipyramid and icosahedron structures, respectively. The second difference of binding energy plot indicates that these two clusters are highly stable; this agrees with the experimental collision-induced dissociation studies and previous theoretical calculations. For the first time, a systematic study of chemical reactivity of small Tin clusters, with n = 2−15, toward dissociative chemisorption of H2 is performed. It is found that the chemisorption occurs preferentially at the two adjacent edges of any Ti atom. The chemisorption energy as a function of the cluster size shows considerable structural changes in the Tin clusters due to H2 dissociation and adsorption, and the chemisorption energy of Ti13 cluster is found to be the highest.
Using density functional theory we show that a recently synthesized silsesquioxanes (SQ) nano complex [RSiO3/2]n with R = −C5H5 provides a novel material for hydrogen storage. Grafting cyclopentadienyl on SQ totally changes its electronic structure and chemistry: cyclopentadienyl becomes a reactive site where a transition metal atom (e.g., Sc) can be doped to serve as an effective adsorption site for hydrogen molecules. This nano complex has the following advantages: (1) The storage capacity in the fully grafted case is 5 wt % where hydrogen is bound molecularly with a binding energy of about 0.6 eV/H2 molecule. (2) The structure of SQ itself is stable. Our study shows for the first time that the functionalized SQ complexes can be an effective and practical material for hydrogen storage.
The coordination of extra-framework Li + in faujasite (FAU) and the interaction between H 2 and Li-FAU were studied by the generalized-gradient approximation (GGA) of density functional theory (DFT) with the Perdew–Burke–Ernzerhof (PBE) exchange-correction functional. Four adsorption sites have been found to be stable for Li + : site SI , the most stable one, in the sodalite cage; site SII in the six-ring windows of the sodalite unit and sites SIII and SIII in the supercage. Hydrogen interacting with these sites prefers the side-on coordination geometry. Calculated adsorption energies decrease in the sequence of SIII > SIII > SI > SII, consistent with the calculated Li–H distance and the charge on H 2 . The H–H stretching frequencies of adsorbed species at 4286–4346 cm −1 are by about 7–67 cm −1 lower than in the free hydrogen molecules. The small bathochromic harmonic H 2 frequency shift is in agreement with the small H 2 bond elongation.
First principles calculations based on gradient corrected density functional theory and molecular dynamics simulations of Ca decorated fullerene yield some novel results: (1) C 60 fullerene decorated with 32 Ca atoms on each of its 20 hexagonal and 12 pentagonal faces is extremely stable. Unlike transition metal atoms that tend to cluster on a fullerene surface, Ca atoms remain isolated even at high temperatures. (2) C 60 Ca 32 can absorb up to 62 H 2 molecules in two layers. The first 30 H 2 molecules dissociate and bind atomically on the 60 triangular faces of the fullerene with an average binding energy of 0.45 eV/H, while the remaining 32 H 2 molecules bind on the second layer quasi-molecularly with an average binding energy of 0.11 eV/H 2 . These binding energies are ideal for Ca coated C 60 to operate as a hydrogen storage material at near ambient temperatures with fast kinetics. (3) The gravimetric density of this hydrogen storage material can reach 6.2 wt %. Simple model calculations show that this density is the limiting value for higher fullerenes.
In the synchronous-transit method, a model linear synchronous transit pathway is first constructed and is then refined by optimizing one or more intermediate structures subject to the constraint that the optimized structure retain the same relative position along the path (orthogonal optimization). The method yields a series of energy estimates which progressively bound the energy of the transition state from above and from below. High computational efficiency is attainable, and sufficient flexibility is provided to deal with asynchronous processes. Comparisons are made to the alternative “reaction-coordinate” approach, which is shown to be subject to several serious deficiencies. The method is applied to a model two-dimensional energy surface and to the allowed electrocyclic interconversions of the cyclopropyl and allyl cations and of cyclobutene and cis-butadiene.
The structure and stability of four possible isomers of C24 and B12N12 have been investigated by means of ab initio calculations at the MP2/DZP level. The four geometries are a monocyclic ring, a graphite-like sheet and two fullerene structures. For C24 it is found that the graphite-like isomer is lowest in energy, while a B12N12 fullerene consisting of 4- and 6-membered rings appears to be quite stable. It is possible that this fullerene plays the same role for boron nitride as C60 does for carbon.
The declared objective of this book is to provide an introductory review of the various theoretical and practical aspects of adsorption by powders and porous solids with particular reference to materials of technological importance. The primary aim is to meet the needs of students and non-specialists who are new to surface science or who wish to use the advanced techniques now available for the determination of surface area, pore size and surface characterization. In addition, a critical account is given of recent work on the adsorptive properties of activated carbons, oxides, clays and zeolites.
New materials capable of storing hydrogen at high gravimetric and volumetric densities are required if hydrogen is to be widely employed as a clean alternative to hydrocarbon fuels in cars and other mobile applications. With exceptionally high surface areas and chemically-tunable structures, microporous metal-organic frameworks have recently emerged as some of the most promising candidate materials. In this critical review we provide an overview of the current status of hydrogen storage within such compounds. Particular emphasis is given to the relationships between structural features and the enthalpy of hydrogen adsorption, spectroscopic methods for probing framework-H(2) interactions, and strategies for improving storage capacity (188 references).
Using self-consistent field molecular-orbital theory, we show that the interaction of hydrogen molecules with a Ni{sup +} ion is characteristically different from that with a neutral Ni atom. While hydrogen chemisorbs dissociatively on the neutral metal atom, it is bound to the cation in its molecular form. The atomic bonding is a consequence of the Pauli exclusion principle whereas the bonding of the molecular hydrogen results from an electrostatic interaction. We predict that a Ni{sup +} ion can bind at least six hydrogen molecules.
Generalized gradient approximations (GGA{close_quote}s) for the exchange-correlation energy improve upon the local spin density (LSD) description of atoms, molecules, and solids. We present a simple derivation of a simple GGA, in which all parameters (other than those in LSD) are fundamental constants. Only general features of the detailed construction underlying the Perdew-Wang 1991 (PW91) GGA are invoked. Improvements over PW91 include an accurate description of the linear response of the uniform electron gas, correct behavior under uniform scaling, and a smoother potential. {copyright} {ital 1996 The American Physical Society.}
We report a first-principles study, which demonstrates that a single Ti atom coated on a single-walled nanotube (SWNT) binds up to four hydrogen molecules. The first H2 adsorption is dissociative with no energy barrier while the other three adsorptions are molecular with significantly elongated H-H bonds. At high Ti coverage we show that a SWNT can strongly adsorb up to 8 wt % hydrogen. These results advance our fundamental understanding of dissociative adsorption of hydrogen in nanostructures and suggest new routes to better storage and catalyst materials.
Recent efforts in finding materials suitable for storing hydrogen with large gravimetric density have focused attention on carbon-based nanostructures. Unfortunately, pure carbon nanotubes and fullerenes are unsuitable as hydrogen storage materials because of the weak bonding of the hydrogen molecules to the carbon frame. It has been shown very recently that coating of carbon nanostructures with isolated transition metal atoms such as Sc and Ti can increase the binding energy of hydrogen and lead to high storage capacity (up to 8 wt % hydrogen, which is 1.6 times the U.S. Department of Energy target set for 2005). This prediction has led to a great deal of excitement in the fuel cell community [see The Fuel Cell Review, http://fcr.iop.org/articles/features/2/7/4]. However, this prediction depends on the assumption that the metal atoms coated on the fullerene surface will remain isolated. Using first-principles calculations based on density functional theory, we show that Ti atoms would prefer to cluster on the C60 surface, which can significantly alter the nature of hydrogen bonding, thus affecting not only the amount of stored hydrogen but also their thermodynamics and kinetics.
Binding energies of selected hydrogen bonded complexes have been calculated within the framework of density functional theory (DFT) method to discuss the efficiency of numerical basis sets implemented in the DFT code DMol3 in comparison with Gaussian basis sets. The corrections of basis set superposition error (BSSE) are evaluated by means of counterpoise method. Two kinds of different numerical basis sets in size are examined; the size of the one is comparable to Gaussian double zeta plus polarization function basis set (DNP), and that of the other is comparable to triple zeta plus double polarization functions basis set (TNDP). We have confirmed that the magnitudes of BSSE in these numerical basis sets are comparative to or smaller than those in Gaussian basis sets whose sizes are much larger than the corresponding numerical basis sets; the BSSE corrections in DNP are less than those in the Gaussian 6-311+G(3df,2pd) basis set, and those in TNDP are comparable to those in the substantially large scale Gaussian basis set aug-cc-pVTZ. The differences in counterpoise corrected binding energies between calculated using DNP and calculated using aug-cc-pVTZ are less than 9 kJ/mol for all of the complexes studied in the present work. The present results have shown that the cost effectiveness in the numerical basis sets in DMol3 is superior to that in Gaussian basis sets in terms of accuracy per computational cost.