Investigation of hydrogen storage on Sc/Ti-decorated novel B24N24

Inspired by the TM−N₄ coordination environment in single-atom catalysts, four novel TM-decorated B₂₄N₂₄ (TM = Sc, Ti) fullerenes with six TM−N₄ or TM−B₄ units are designed. Molecular dynamic simulations confirm that the four TM₆B₂₄N₂₄ fullerenes are thermodynamically stable. Their hydrogen storage properties were investigated using density functional theory calculations. Sc/Ti atoms bind to the N₄/B₄ cavities with an average interaction energy of 6.30–11.96 eV. Hence, the problem of clustering can be avoided. 36H₂ could be adsorbed with average hydrogen adsorption energies of 0.18–0.55 eV. The lowest hydrogen desorption temperatures at atmospheric pressure for Sc₆B₂₄N₂₄(N₄)–36H₂, Sc₆B₂₄N₂₄(B₄)–36H₂, Ti₆B₂₄N₂₄(N₄)–36H₂, and Ti₆B₂₄N₂₄(B₄)–36H₂ are 255 K, 318 K, 243 K, and 408 K, respectively. The maximum hydrogen gravimetric densities of the Sc₆B₂₄N₂₄ and Ti₆B₂₄N₂₄ systems are 7.74 wt% and 7.50 wt%, respectively. Therefore, the novel Sc₆B₂₄N₂₄ and Ti₆B₂₄N₂₄ could be suitable as potential hydrogen storage materials at ambient temperature.     

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

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

Revealing the interfacial phenomenon of metal-hydride formation and spillover effect on C48H16 sheet by platinum metal catalyst (Pt (n=1-4)) for hydrogen storage enhancement

Hydrogen is a worldwide green energy carrier, however due its low storage capacity, it has yet to be widely used as an energy carrier. Therefore, the quantum chemical method is being employed in this investigation for better understand the hydrogen storage behaviour on Pt _(n = 1-4) cluster decorated C₄₈H₁₆ sheet. The Pt_(n = 1-4) clusters are strongly bonded on the surface of C₄₈H₁₆ sheet with binding energies of ?3.06, ?4.56, ?3.37, and ?4.03 eV respectively, while the charge transfer from Pt_(n = 1-4) to C₄₈H₁₆ leaves an empty orbital in Pt atom, which will be crucial for H₂ adsorption. Initially, the molecular hydrogen is adsorbed on Pt_(n = 1-4) decorated C₄₈H₁₆ sheet through the Kubas interaction with adsorption energies of ?0.85, ?0.66, ?0.72, and ?0.57 eV respectively, while H–H bond is elongated due to the transfer of electron from σ (HH) orbital to unfilled d orbital of the Pt atom, resulting in a Kubas metal-dihydrogen complexes. Furthermore, the dissociative hydrogen atoms adsorbed on Pt_(n = 1-4) decorated C₄₈H₁₆ sheet have adsorption energies of ?1.14 eV, ?1.02 eV, ?0.95 eV, and ?1.08 eV, which are greater than the molecular hydrogen adsorption on Pt_(n = 1-4) cluster supported C₄₈H₁₆ sheet with lower activation energy of 0.007, 0.109, 0.046, and 0.081 eV respectively. To enhance the dissociative hydrogen adsorption energy, positive and negative external electric fields are applied in the charge transfer direction. Increasing the positive electric field makes H–H bond elongation and good adsorption, whereas increasing the negative electric field results H–H bond contraction and poor adsorption. Thus, by applying a sufficient electric field, the H₂ adsorption and desorption processes are can be easily tailored.     

Selective decoration of nitrogenated holey graphene (C2N) with titanium clusters for enhanced hydrogen storage application

For an envisioned hydrogen (H₂) economy, the design of new multifunctional two-dimensional (2D) materials have been a subject of intense research for the last several decades. Here, we report the thriving H₂ storage capacity of 2D nitrogenated holey graphene (C₂N), functionalized with Ti_n (n = 1–5) clusters. By using spin polarized density functional theory (DFT) calculations implemented with the van der Waals corrections, the most favourable adsorption site for the Ti_n clusters on C₂N has been revealed. With the monomer Ti, the functionalization was evenly covered on C₂N having 5% doping concentration (C₂N–Ti). For C₂N–Ti sheet, Ti binds to C₂N with a strong binding energy of ~6 eV per Ti which is robust enough to hinder any Ti–Ti clustering. Bader charge analysis reveals that the Ti_n clusters donate significant charges to C₂N sheet and become cationic to polarize the H₂ molecules, thus act as efficient anchoring agents to adhere multiple H₂ molecules. Each Ti in C₂N–Ti could adsorb a maximum of 10H₂ molecules, with the adsorption energies in the range of ?0.2 to ?0.4 eV per H₂ molecule, resulting into a high H₂ storage capacity of 6.8 wt%, which is promising for practical H₂ storage applications at room temperature. Furthermore, Ti_m (m = 2, 3, 4, 5) clusters have been selectively decorated over C₂N. However, with Ti_m functionalization H₂ storage capacities fall short of the desirable range due to large molecular weights of the systems. In addition, the H₂ desorption mechanism at different conditions of pressure and temperature were also studied by means of thermodynamic analysis that further reinforce the potential of C₂N–Ti as an efficient H₂ storage material.     

A theoretical research of dihydrogen storage in ScxNy (x+y=4) compounds

The dihydrogen storage capacity of Sc_xN_y (x + y = 4) compounds have been theoretically investigated at different levels. At B3LYP-D3/6-311G(3df,3pd) level, ScN₃ has multiple isomers with similar energies, which is an interference of hydrogen storage research. Sc₂N₂ and Sc₃N has four and three isomers, respectively. For both systems, the lowest-lying isomers are planar Sc₂N₂ 01 and Sc₃N 01, which are energetically much low-lying by at least 20 kcal/mol than the other isomers, respectively. Sc₃N 01 can adsorb 8H₂ with gravimetric uptake capacity of 9.77 wt %. It satisfies the target specified by US DOE, however, some hydrogen molecules will dissociate and bond atomically on scandium atoms. The strong binding energy (0.66 eV/H₂) exceeds the reversible adsorption range (0.1–0.4 eV/H₂), which will cause high operating temperature to desorb hydrogen during the application process. Sc₂N₂ 01 can adsorb 9H₂ in the molecular form. The H₂ gravimetric uptake capacity of Sc₂N₂ 01 (9H₂) (13.33 wt %) exceeds the target set by US Department of Energy, moreover, its average adsorption energy (0.32 eV/H₂) is in the reversible adsorption range. The interaction of Sc₂N₂ 01 with H₂ molecules is considered by means of the bond critical points (bcp) in the quantum theory of atoms in molecules (QTAIM). The Gibbs free energy corrected adsorption energy points that the adsorption of Sc₂N₂ 01(9H₂) is energetically favorable below 240 K. Therefore, in Sc_xN_y (x + y = 4), the planar compound Sc₂N₂ 01 is more suitable to be a dihydrogen adsorption material.     

Hydrogen capability of bimetallic boron cycles: A DFT and ab initio MD study

Bimetallic boron cycle, B₆C₂TM₂ (TM = scandium, titanium), was recently predicted to have high stability and aromaticity. The hydrogen capabilities of these clusters were studied in the present work. Our computational results indicate that the gravimetric hydrogen uptake capacity of B₆C₂Sc₂ and B₆C₂Ti₂ and clusters are 11.7% and 11.4%, respectively. The adsorption energies of H₂ molecules on B₆C₂Sc₂ and B₆C₂Ti₂ clusters are predicted with different calculational schemes to meet the criteria of reversible hydrogen storage. The interaction of H₂ with B₆C₂Ti₂ cluster is a little stronger than that with B₆C₂Sc₂. Ab initio molecular dynamics simulations indicate that H₂ molecules can be efficiently released from the metal sites of B₆C₂TM₂ clusters at room temperature. The bulk-like B₆C₂Sc₂ and B₆C₂Ti₂ tetramer can also efficiently adsorb H₂ molecules.     

Bonding states of hydrogen for supported Ti clusters on pristine and defective graphene

To determine whether graphene-supported Ti clusters can synergistically store hydrogen through Kubas and spillover effect, we systematically investigate the growth pattern of Ti_n (n = 1–10) clusters on pristine and defective graphene and analyze multiple types of bonding states of hydrogen in detail. For pristine graphene, the most stable Ti_n (n = 1–10) clusters are the quasi-planar structure except for supported Ti₄ and Ti₅. The Ti dissociation energies and the binding energy of Ti_n clusters gradually increase with increasing n, which indicates that larger Ti_n clusters tend to form. Efficient spillover will occur on single-site Ti Catalysts at low hydrogen concentration due to the lower hydrogen spillover energy barrier (3.05 eV), while the energy barrier of hydrogen migration from Tin (n = 2–7) clusters to graphene on the cluster is 5.34–6.82 eV. The Ti: H ratio is a maximum of 1:8 for the single-site Ti catalyst, while decreases with the Tin cluster increases. Therefore, the pristine graphene-supported Ti nanoclusters are more suitable as substrates for hydrogen adsorbent rather than spillover. The introduced defects make Ti_n clusters have three-dimensional conical configurations from n = 4. Ti₃ and Ti₆ are the most stable clusters. Moreover, the migration energy barriers of H atoms on them decrease from 6.54 eV to 6.82 eV–4.32 eV and 3.42 eV, respectively. Our results explain recent experimental phenomena [Appl Phys Lett 2015; 106: 083,901. ACS Energy Lett 2022; 7 (7): 2297–2303] in depth at the molecular level.     

Enhanced low temperature hydrogen desorption properties and mechanism of Mg(BH4)2 composited with 2D MXene

Mg(BH₄)₂ occupies a large hydrogen storage capacity of 14.7 wt%, and has been widely recognized to be one of the potential candidates for hydrogen storage. In this work, 2D MXene Ti₃C₂ was introduced into Mg(BH₄)₂ by a facile ball-milling method in order to improve its dehydrogenation properties. After milling with Ti₃C₂, Mg(BH₄)₂–Ti₃C₂ composites exhibit a novel “layered cake” structure. Mg(BH₄)₂ with greatly reduced particle sizes are found to disperse uniformly on Ti₃C₂ layered structure. The initial dehydrogenation temperature of Mg(BH₄)₂ has been decreased to 124.6 °C with Ti₃C₂ additive and the hydrogen liberation process can be fully accomplished below 400 °C. Besides, more than 10.8 wt% H₂ is able to be liberated from Mg(BH₄)₂–40Ti₃C₂ composite at 330 °C within 15 min, while pristine Mg(BH₄)₂ merely releases 5.3 wt% hydrogen. Moreover, the improved dehydrogenation kinetics can be retained during the subsequent second and third cycles. Detailed investigations reveal that not only Ti₃C₂ keeps Mg(BH₄)₂ particles from aggregation during de/rehydrogenation, but also the metallic Ti formed in-situ serves as the active sites to catalyze the decomposition of Mg(BH₄)₂ by destabilizing the B–H covalent bonds. This synergistic effect of size reduction and catalysis actually contributes to the greatly advanced hydrogen storage characteristics of Mg(BH₄)₂.     

The enhancement of hydrogen storage capacity in Li,Na and Mg-decorated BC3 graphene by CLICH and RICH algorithms

New hydrogen adsorption states on Li, Na, and Mg-decorated graphene-type BC₃ sheet have been investigated by first-principles calculations. The structural, electronic and binding properties, metal binding and nH₂ (n = 1–10) adsorption states of these systems are studied in detail with the Mulliken analysis, charge density differences, and partial density of states. To enhance the number of the adsorbed H₂ molecules per metal atom, and also to generate the better initial coordinates for reducing the simulation time, we present two masthematical algorithms (CLICH and RICH). The tested results on BC₃ sheet and boron-doped graphene (C₃₀B₂) show that these algorithms can increase the number of adsorbed hydrogen molecules by minimizing the computational time. It is seen that nH₂ (n = 1–10) adsorbed Li,/Na and/Mg-decorated BC₃ single- and double-sided systems are industrial materials for hydrogen storage technology, their adsorption energies fall into the acceptable adsorption energy range (0.20–0.60 eV/H₂). It is concluded from the optimized geometries and charge density differences for the higher number of H₂ adsorbed systems that not only decorated metal atom but also the sheet plays an important role in hydrogen storage process, because the boron atoms in the sheet expand the induced electric field between the adatoms and BC₃ sheet. From Mulliken analysis, there is a charge transfer mechanism between H₂ molecules and metal atoms. Moreover, the resonant peaks for the sheet, metal atoms and H₂ molecules in partial density of states curves indicate the possible hybridizations. Additionally, these adsorption processes are supported by charge density difference plots.     

Adsorption ability of pristine C24N24 nanocage promising as high hydrogen storage material: A DFT-D3 investigation

Adsorption of eight numbers of H₂, (H₂)_n where n = 1, 2, 4, 6, 8, 12, 18, 24, adsorbed on the C₂₄N₂₄ nanocage (CNNC) surface was investigated using three different DFT methods. Adsorption energies of various numbers of H₂ adsorbed on the CNNC surface were obtained. Adsorption strength of the CNNC was found depending on the adsorbed H₂ numbers and is in order: the H₂ numbers of (H₂) > (H₂)₂ > (H₂)₄ > (H₂)₆ > (H₂)₈ > (H₂)₁₂ > (H₂)₁₈ > (H₂)₂₄. The most stable adsorption configuration of (H₂)₁₂/CNNC, all adsorbed H₂ molecules formed as the full monolayer (ML) coverage, are dissociative chemisorption. The bilayer of (H₂)₂₄/CNNC was found that the first and second layers are composed of 12H₂ as dissociative chemisorption and 12H₂ as physisorption, respectively. The high hydrogen storage capacity of the CNNC formed as (H₂)₂₄/CNNC, around 7.75 wt% was found.     

A theoretical study on cage-like clusters (C12Ti6 and C12Ti62+) for dihydrogen storage

This work reports the dihydrogen adsorption and storage capacity of cage-like clusters (C₁₂Ti₆ and C₁₂Ti₆²⁺) using density functional theory calculations. The neutral system C₁₂Ti₆ can adsorb 15 hydrogen molecules, however, some hydrogen molecules will dissociate and bond atomically on titanium atoms. The strong binding energy will cause high operating temperature to desorb hydrogen during the application process. Fortunately, the cationic system C₁₂Ti₆²⁺ can adsorb up to 16H₂ all in molecular form. Moreover, the predicted maximal hydrogen storage density is 6.96 wt% and the average adsorption energies of C₁₂Ti₆²⁺ (nH₂) (n = 1–16) are in the desirable range of reversible hydrogen storage at the 6-311G(d,p)-B3LYP and M06-2X levels. The interaction of C₁₂Ti₆²⁺ with hydrogen molecules is considered by means of the bond critical points (bcp) in the quantum theory of atoms in molecules (QTAIM). With respect to Gibbs free energy corrected H₂ adsorption energy, C₁₂Ti₆²⁺ adsorbs 16H₂ molecules should be at low temperature (190 K). These predictions show that cationic C₁₂Ti₆²⁺ is more suitable as a material for adsorbing dihydrogen.     

The effect of charge on the dihydrogen storage capacity of Sc2–C6H6

The effect of charge on the dihydrogen storage capacity of Sc₂–C₆H₆ has been investigated at B3LYP-D3/6-311G(d,p) level. The neutral system Sc₂–C₆H₆ can store 8H₂ with gravimetric density of 8.76 wt %, and one H₂ dissociates and bonds atomically on the scandium atom. The adsorption of 8H₂ on Sc₂–C₆H₆ is energetically favorable below 155 K. The atom-centered density matrix propagation (ADMP) molecular dynamics simulations show that Sc₂–C₆H₆ can adsorb 3H₂ within 1000 fs at 300K. Compared with Sc₂–C₆H₆, the charged systems can adsorb more hydrogen molecules with higher gravimetric density, and all the H₂ are adsorbed in the molecular form. The gravimetric densities of Sc₂–C₆H₆⁺ and Sc₂–C₆H₆²⁺ are 9.75 and 10.71 wt%. Moreover, the maximum adsorption of charged systems are favorable in wider temperature range. Most importantly, the ADMP-MD simulations indicate that Sc₂–C₆H₆²⁺ can adsorb 6 hydrogen molecules within 1000 fs at 300K. It can be found that the gravimetric density (6.72 wt%) of Sc₂–C₆H₆²⁺ still exceeds the target of US Department of Energy (DOE) under ambient conditions.     

Platinum deposition onto g-C3N4 with using of labile nitratocomplex for generation of the highly active hydrogen evolution photocatalysts

The chemisorption of the labile dimeric platinum nitratocomplex [Pt₂(μ-OH)₂(NO₃)₈]^2- onto graphene oxide doped graphitic C₃N₄ (g–C₃N₄–GO) was performed for the first time to prepare PtO_x/g–C₃N₄–GO composites with ionic platinum species (Pt(II)) bonded with N-donor groups of the g-C₃N₄. The thermal treatment of the obtained composites in the hydrogen atmosphere results in a gradual reduction of Pt(II) species with the formation of Pt/g–C₃N₄–GO photocatalysts. The Pt/g–C₃N₄–GO catalysts paired with TEOA sacrificing agent in an aqueous solution were tested in a photoinduced hydrogen evolution reaction under visible light (λ = 425 nm). The photocatalytic activity of prepared materials strongly influenced by the temperature of the reduction stage so that the maximal rate of H₂ evolution was revealed for the catalyst (0.5 wt% of Pt) reduced at 400 °C with a quantum efficiency of 3.0% and rate of HER of 5.1 mmol h^?1 per 1 g of photocatalysts. The photocatalytic activity of this sample was much higher than the activity of 0.5% Pt/g–C₃N₄–GO photocatalysts prepared by conventional photoreduction of H₂PtCl₆ or reduction of this precursor with NaBH₄. The Pt/g–C₃N₄–GO photocatalyst with Pt concentration of 0.1 wt% was prepared using the described protocol and shown specific activity of about 1.4 mol h^?1 per 1 g of Pt outperforming analogous material reported to date.     

Novel sandwich-type dimetallocenes: Toward promising candidate media for high-capacity hydrogen storage

With respect to first-principles calculations, the sandwich-type dinuclear organometallic compounds as (C₅H₅)₂TM₂ (M = Sc and Ti) can adsorb up to eight hydrogen molecules. The corresponding gravimetric hydrogen-storage capacity is 6.7 wt% for (C₅H₅)₂Ti₂ and 6.8 wt% for (C₅H₅)₂Sc₂. The multimetallocenes (e.g., CpTi₃Cp and CpTi₄Cp) complexes can further increase the H₂ adsorption capacity to 8.7 wt% and 10.4 wt%, respectively. These sandwich-type organometallocenes proposed in this work are favorable for reversible adsorption and desorption of hydrogen under ambient conditions. These predictions will likely provide a new route for developing novel high-capacity hydrogen-storage materials.     

C7N6 monolayer as high capacity and reversible hydrogen storage media: A DFT study

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.     

Improvement of desorption performance of Mg(BH4)2 by two-dimensional Ti3C2 MXene addition

Magnesium borohydride (Mg(BH₄)₂) is an attractive materials for solid-state hydrogen storage due to its high hydrogen content (14.9 wt%). In the present work, the dehydrogenation performance of Mg(BH₄)₂ by adding different amounts (10, 20, 40, 60 wt%) of two-dimensional layered Ti₃C₂ MXene is studied. The Mg(BH₄)₂-40 wt% Ti₃C₂ composite releases 7.5 wt% hydrogen at 260 °C, whereas the pristine Mg(BH₄)₂ only releases 2.9 wt% hydrogen under identical conditions, and the onset desorption temperature decreases from 210 °C to a relative lower temperature of 82 °C. The special layered structure of Ti₃C₂ MXene and fluorine plays an important role in dehydrogenation process especially at temperatures below 200 °C. The main dehydrogenation reaction is divided into two steps, and activation energy of the Mg(BH₄)₂-40 wt% Ti₃C₂ composite is 151.3 kJ mol⁻¹ and 178.0 kJ mol⁻¹, respectively, which is much lower than that of pure Mg(BH₄)₂.     

Boosting the dehydrogenation efficiency of dodecahydro-N-ethylcarbazole by assembling Pt nanoparticles on the single-layer Ti3C2Tx MXene

As the candidates for large-scale hydrogen storage, liquid organic hydrogen carriers (LOHCs) exhibit evident advantages in hydrogen storage density and convenience of storage and transportation. Among them, NECZ (N-ethylcarbazole)/12H-NECZ (dodecahydro-N-ethylcarbazole) is considered as a typical system with the lower hydrogenation/dehydrogenation temperature. However, the low dehydrogenation efficiency restrict its commercial applications. In this work, the single-layer Ti₃C₂T_x MXene was employed as the support to load the Pt nanoparticles for the 12H-NECZ dehydrogenation reaction. The effect of transition metals, loading amounts and morphologies of catalysts were analyzed. It was found that the 3 wt% Pt/S–Ti₃C₂T_x catalyst exhibited the best catalytic performance with 100% conversion, 91.55% selectivity of NECZ and 5.62 wt% hydrogen release amount at 453 K, 101.325 kPa for 7 h. The product distributions and kinetics analysis suggested that the elementary reaction from 4H-NECZ to NECZ was the rate-limiting step. The selectivity of NECZ is sensitive to the dehydrogenation temperature. Combined with the XRD, SEM, HRTEM, XPS, BET and FT-IR results, it could be indicated that the special two-dimension structure of S–Ti₃C₂T_x and electronic effect between Pt and S–Ti₃C₂T_x enhanced the dehydrogenation efficiency of 12H-NECZ. The measurements of cyclic dehydrogenation indicated that the Pt/S–Ti₃C₂T_x catalyst exhibited good stability after 42 h. This work brought a new strategy for the design of efficient catalysts using two-dimensional materials in the applications of the liquid organic storage hydrogen technology.     

The effect of Sc addition on the hydrogen storage capacity of Ti0.32Cr0.43V0.25 alloy

The effect of the addition of 4th element on the hydrogen storage capacity of Ti_0.32Cr_0.43V_0.25 alloy was evaluated by simulation and confirmed experimentally. The crystal lattice volume, phase formation energy, and hydrogen absorption energy of the alloys were calculated by ab initio calculation for the alloys containing the third-period transition metals as Sc, Cr, Mn, Fe, Co, Ni, Cu, and Zn. It was postulated that the hydrogen absorption would be favored by large crystal volume and low hydrogen absorption energy. The calculation suggested Sc as the most suitable element and the hydrogen capacities of a series of Ti_0.32Cr_0.43−xV_0.25Sc_x alloys (x = 0.02–0.1) were determined accordingly. Among the alloys, the capacities of Ti_0.32Cr_0.41V_0.25Sc_0.02 and Ti_0.32Cr_0.39V_0.25Sc_0.04 alloys were higher than that of the Ti_0.32Cr_0.43V_0.25 alloy. The capacity of both alloys could be enhanced further by the heat treatment at 1250 °C due to the elimination of the second-phase TiCr₂.     

The optimal adsorption pathway of H2 molecules on Ti-Acetylene/ ethylene compounds: A DFT study

Ti-Acetylene/Ethylene complexes were used to be considered as a potential high capacity hydrogen storage media by physisorption. Here, special attentions have been paid to the optimal adsorption pathway of H₂ molecules on TiC₂H₂/TiC₂H₄ compounds by using CCSD(T) and B3LYP functionals. An interesting result is that some most stable configurations of TiC₂H₂(nH₂)(n = 1–7) complexes are not the structures coordinated by H₂ molecules but plausible hydrogenation intermediates. Based on the potential energy profiles and MD simulations, the optimal adsorption pathway is considered as TiC₂H₂(T) → 1b → 2c → 2b → 2a → 3b → 3a → 4a → 5a → 5b → 6d → C₂H₆ + Ti(H₂)₅ for TiC₂H₂ and TiC₂H₄(1c) → 2a → 3b → 3a → 4a → 5a → 5b → 6d → C₂H₆+Ti(H₂)₅ for TiC₂H₄. It indicates that the adsorptions of H₂ molecules on TiC₂H₂/TiC₂H₄ contain chemisorption and physisorption. The product C₂H₆+Ti(H₂)₅ exhibits 14 wt% uptake of H₂, which is completely consistent with the experimental results.