Hydrogen adsorption on C3H3–TM (TM = Sc, Ti) organometallic compounds

This work reports hydrogen adsorption on C₃H₃–TM (TM = Sc, Ti) organometallic compounds using second-order Møller–Plesset perturbation theory method. Two types of organometallic compounds are considered viz. transition metal-capped and transition metal-inserted. Maximum five and four hydrogen molecules were adsorbed on Sc-capped ScC₃H₃ and Ti-capped TiC₃H₃ complexes, thereby giving gravimetric hydrogen uptake capacity of 10.71 and 8.5 wt%, respectively. The gravimetric H₂ uptake capacity 10.71 wt% of ScC₃H₃ complex is higher by 1.41 wt% than that of Sc-capped ScC₄H₄ organometallic complex reported earlier. The hydrogen uptake capacity 8.5 wt% of TiC₃H₃ is in between the uptake capacity of 6.61 and 9.1 wt% shown by Ti-capped TiC₅H₅ and TiC₄H₄ organometallic complexes, respectively. The Sc-capped and Sc-inserted ScC₃H₃ adsorb same number of H₂ molecules whereas Ti-inserted TiC₃H₃ complex adsorbs less number of H₂ molecules than that of Ti-capped TiC₃H₃ complex. Nature of interactions between different molecules in hydrogen-adsorbed complexes is studied. The binding energy per H₂ molecules differ by about 0.1 eV in transition metal-capped and transition metal-inserted structures.     

Hydrogen storage in chemically reducible mesoporous and microporous Ti oxides

Chemically reducible micro- and mesoporous Ti oxides with controlled pore sizes from 12 to 26 A were synthesized. The hydrogen storage and adsorption capacity at 77 K was tested as a function of surface area, pore size, and reducing agent. Surprisingly, the oxidation state of the surface Ti species had an even greater effect on the storage densities than surface area or pore size. For example, the 12 A material reduced with bis(toluene) Ti possesses a surface area of less than 300 m2/g, but absorbs up to 4.94 wt % and 40.46 kg/m3 of H2 reversibly at 77 K and 100 atm. This volumetric storage capacity is higher than that of AX-21, which has a much higher surface area. The H2 binding enthalpies increased from 4.21 kJ/mol to 8.08 kJ/mol as the surface oxidation state of the Ti decreased. These results suggest that a Kubas-type sigma H2 complex may be involved and that further tuning of the H2 binding enthalpies through use of appropriate organometallic reagents may achieve even higher storage levels at more moderate temperature.     

Reversible transient hydrogen storage in a fuel cell-supercapacitor hybrid device

A new concept is investigated for hydrogen storage in a supercapacitor based on large-surface-area carbon material (Black Pearls 2000). Protons and electrons of hydrogen are separated on a fuel cell-type electrode and then stored separately in the electrical double layer, the electrons on the carbon and the protons in the aqueous electrolyte of the supercapacitor electrode. The merit of this concept is that it works spontaneously and reversibly near ambient pressure and temperature. This is in pronounced contrast to what has been known as electrochemical hydrogen storage, which does not involve hydrogen gas and where electrical work has to be spent in the loading process. With the present hybrid device, a H(2) storage capacity of 0.13 wt% was obtained, one order of magnitude more than what can be stored by conventional physisorption on large-surface-area carbons at the same pressure and temperature. Raising the pressure from 1.5 to 3.5 bar increased the capacity by less than 20%, indicating saturation. A capacitance of 11 μF cm(-2), comparable with that of a commercial double layer supercapacitor, was found using H(2)SO(4) as electrolyte. The chemical energy of the stored H(2) is almost a factor of 3 larger than the electrical energy stored in the supercapacitor. Further developments of this concept relate to a hydrogen buffer integrated inside a proton exchange membrane fuel cell to be used in case of peak power demand. This serial setup takes advantage of the suggested novel concept of hydrogen storage. It is fundamentally different from previous ways of operating a conventional supercapacitor hooked up in parallel to a fuel cell.     

A DFT Investigation on Hydrogen Adsorption Based on Alkali-metal Organic Complexes

Using density functional theory calculation based on the B3LYP method,we have studied the interactions of H2 molecules with alkali-metal organic complexes C6H6-nLin(n = 1～3),C6H5Na and C6H5K.A significant part of the electronic charge of M s orbital(Li 2s,Na 3s,K 4s) is donated to phenyl and is accommodated by H2 bonding orbital.For all the complexes considered,each bonded alkali-metal atom can adsorb up to five H2 in molecular form with the mean binding energy of 0.59,0.55 and 0.56 eV/H2 molecule for C6H6-nLin(n = 1～3),C6H5Na and C6H5K,respectively.The kinetic stability of these hydrogen-covered organometallic complexes is discussed in terms of energy gap between HOMO and LUMO.It is remarkable that these alkali-metal organic complexes can store up to 23.80 wt% hydrogen.Therefore,the complexes studied may be used as hydrogen storage materials.     

High-capacity Hydrogen Storage on Novel Sandwich- like Binuclear Compounds： N4-M2-N4 （M - Sc and Ti）

With respect to the first principle calculations, we predicted that two pairs of transition metals (e.g., Sc2 and Ti2) can be interbedded between two tetranitrogen rings to form two sandwich-like binuclear complexes respectively (e.g. N4Sc2N4 and N4Ti2N4). These two complexes can adsorb up to eight and ten hydrogen molecules, corresponding to a gravimetric storage capacity of 7.7 and 9.9 wt%, respectively. These sandwich-type complexes proposed in this work are favorable for reversible adsorption and desorption of hydrogen at ambient conditions. The results are helpful for the development of a new class of high-capacity hydrogen-storage media.     

Catalytic methanolysis of hydrazine borane: a new and efficient hydrogen generation system under mild conditions

Safe and efficient hydrogen storage is a major obstacle for using hydrogen as an energy carrier. Therefore, intensive efforts have been focused on the development of new materials for chemical hydrogen storage. Of particular importance, hydrazine borane (N(2)H(4)BH(3)) is emerging as one of the most promising solid hydrogen carriers due to its high gravimetric hydrogen storage capacity (15.4 wt%) and low molecular weight. Herein, we report metal catalyzed methanolysis of hydrazine borane (N(2)H(4)BH(3), HB) as a fast hydrogen generation system under mild conditions. When trace amounts of nickel(ii) chloride (NiCl(2)) is added to the methanol solution of hydrazine borane ([HB]/[Ni] ≥ 200) the reaction solution releases 3 equiv. of H(2) with a rate of 24 mol H(2) (mol Ni min)(-1) at room temperature. The results reported here also includes (i) identification of the reaction products by using ATR-IR, DP-MS, (1)H and (11)B NMR spectroscopic techniques and the establishment of the reaction stoichiometry, (ii) investigation of the effect of substrate and catalyst concentrations on the hydrogen generation rate to determine the rate law for the catalytic methanolysis of hydrazine borane, (iii) determination of the activation parameters (E(a), ΔH(#), and ΔS(#)) for the catalytic methanolysis of hydrazine borane by using the temperature dependent rate data of the hydrogen generation.     

Derivated titanate nanotubes and their hydrogen storage properties

Titanate nanotubes and their derivates, Pd-loaded and Co²⁺, Zn²⁺, Cu²⁺, and Ag⁺ ion-exchanged titanate nanotubes, were respectively prepared and characterized by XRD, HR-TEM, and EDS. Their hydrogen storage properties were investigated, and the results revealed that the derivated titanate nanotubes had better hydrogen storage characters. Pd-loaded titanate nanotubes exhibited the highest hydrogen storage capacity of 1.03 wt%, which is three times higher than that of raw titanate nanotubes. The ion-exchanged titanate nanotubes also showed enhanced capacity. Especially, Co-TiNT reached a storage capacity of 0.80 wt%. The reason why hydrogen storage capacity was enhanced in titanate nanotubes was a pilot study. These results indicated that oxide nanotubes provided some new opportunities for hydrogen energy applications.     

H2 storage in carbon materials

In this work a series of commercial carbons with different structural and textural properties were characterised and evaluated for their application in hydrogen storage. The results showed that temperature has a greater influence on the storage capacity of carbons than pressure. The highest H₂ storage capacity at 298 K and 90 bar was 0.5 wt%, while at 77 K and atmospheric pressure it was 2.9 wt%. It is also showed that, in order to predict the hydrogen storage capacity of carbon material both at cryogenic and ambient temperature, the only use of BET surface area or total micropore volume obtained from N₂ adsorption isotherm may be insufficient, the characterization of the narrow microporosity is needed due to its high contribution to hydrogen adsorption capacity. The process involved in hydrogen storage in pure carbon materials seems to be physisorption. Morphological or structural characteristics have no influence, at least on gravimetric storage capacity.     

Hydrogen adsorption on Ce/SWCNT systems: a DFT study

The adsorption of H(2) on Ce doped single-walled carbon nanotubes (SWCNT) and graphene are investigated by using density functional theory. For both systems, it is found that Ce preferentially occupies the hollow site on the outside. The results indicate that Ce/SWCNT system is a good candidate for hydrogen storage where six H(2) per Ce can be adsorbed and 5.14 wt% H(2) can be stored in the Ce(3)/SWCNT system. Among metal-doped SWCNTs, Ce exhibits the most favorable hydrogen adsorption characteristics in terms of the adsorption energy and the uptake capacity. The hybridization of the Ce-4f and Ce-5d orbitals with the H orbital contributes to the H(2) binding where Ce-4f electrons participate in the hybridization due to the instability of the 4f state. The interaction between H(2) and Ce/SWCNT is balanced by the electronic hybridization and electrostatic interactions. Curvature of SWCNT changes the size of the binding energy of Ce and C and the adsorption energy of H(2) on Ce.     

Hydrogen binding property of Co- and Ni-based organometallic compounds

The binding property of hydrogen on organometallic compounds consisting of Co, and Ni transition metal atoms bound to C _m H _m rings (m = 4, 5) is studied through density functional theory calculation. CoC _m H _m and NiC _m H _m complexes can store up to 3.49 wt% hydrogen with an average binding energy of about 1.3 eV. The adsorption characteristics of hydrogen to organometallic compounds are investigated by analyzing vibrational spectra of CoC₄H₄(H₂) _n and NiC₄H₄(H₂) _n (n = 0, 1, 2). The kinetic stability of these hydrogen-covered organometallic complexes is assured by analyzing the energy gap between the highest occupied molecular orbitals and the lowest unoccupied molecular orbitals. It is also discussed the application of 18-electron rule in predicting maximum number of hydrogen molecules that could be adsorbed by these organometallic compounds.     

Hydrogen storage in nanoporous carbon materials: myth and facts

We used Grand canonical Monte Carlo simulation to model the hydrogen storage in the primitive, gyroid, diamond, and quasi-periodic icosahedral nanoporous carbon materials and in carbon nanotubes. We found that none of the investigated nanoporous carbon materials satisfy the US Department of Energy goal of volumetric density and mass storage for automotive application (6 wt% and 45 kg H(2) m(-3)) at considered storage condition. Our calculations indicate that quasi-periodic icosahedral nanoporous carbon material can reach the 6 wt% at 3.8 MPa and 77 K, but the volumetric density does not exceed 24 kg H(2) m(-3). The bundle of single-walled carbon nanotubes can store only up to 4.5 wt%, but with high volumetric density of 42 kg H(2) m(-3). All investigated nanoporous carbon materials are not effective against compression above 20 MPa at 77 K because the adsorbed density approaches the density of the bulk fluid. It follows from this work that geometry of carbon surfaces can enhance the storage capacity only to a limited extent. Only a combination of the most effective structure with appropriate additives (metals) can provide an efficient storage medium for hydrogen in the quest for a source of "clean" energy.     

Synthesis, characterization and hydrogen storage capacity of MS2 (M = Mo, Ti) nanotubes

The structure, morphology and hydrogen-storage capacity of MS₂ (M = Mo, Ti) nanotubes prepared by different experimental methods were studied. It was found that the MoS₂ nanotubes treated by KOH displayed the gaseous storage capacity of 1.2 wt% hydrogen (under the hydrogen pressure of 3 MPa and 25°C) and the electrochemical discharge capacity of 262 mAh/g (at the discharge current density of 50 mA/g and 25°C) that corresponds to about 1.0 wt % hydrogen. In comparison, TiS₂ nanotubes can store 2.5 wt% hydrogen under the hydrogen pressure of 4 MPa and 25°C. The results show that MS₂ compound nanotubes are promising materials for hydrogen storage. __________ Translated from Acta Scientiarum Naturalium Universitatis Nankaiensis, 2005, 38(4) (in Chinese)     

Titanium-capped carbon chains as promising new hydrogen storage media

The capacity of Ti-capped sp carbon atomic chains for use as hydrogen storage media is studied using first-principles density functional theory. The Ti atom is strongly attached at one end of the carbon chains via d-p hybridization, forming stable TiC(n) complexes. We demonstrate that the number of adsorbed H(2) molecules on Ti through Kubas interactions depends upon the chain types. For polyyne (n even) or cumulene (n odd) structures, each Ti atom can hold up to five or six H(2) molecules, respectively. Furthermore, the TiC(5) chain effectively terminated on a C(20) fullerene can store hydrogen with an optimal binding energy of 0.52 eV per H(2) molecule. Our results reveal a possible way to explore high-capacity hydrogen storage materials in truly one-dimensional carbon structures.     

Novel dithiocarbamate–Hg(II) complexes containing mixed ligands: Synthesis,spectroscopic characterization,and H2 storage capacity

A tetrahedral Hg(II) diethyl dithiocarbamate (Et₂Dt) complex containing triphenylphosphine (PPh₃) of the composition [HgCl(κ²-Et₂Dt)₂(PPh₃)] ( 1 ) is prepared. Furthermore, complex ( 1 ) is used as a synthone to prepare a novel series of complexes of the following composition [Hg(Et₂Dt)L(PPh₃)] {L = saccharinate ( 2 ), thiosaccharinate ( 3 ), benzisothiazolinate ( 4 ), benzothiozole-2-thiolate ( 5 ), and benzooxazole-2-thiolate ( 6 ) anions}. The resulted complexes ( 1 )–( 6 ) are characterized by elemental analysis, molar conductivity, powder X-ray diffraction, fourier transform Infrared, and NMR (¹H and ³¹P) spectroscopic techniques. The Et₂Dt ligand is coordinated as bidentate chelate through the sulfur atoms, whereas the L ligands are bonded as monodentate ligands to afford a tetrahedral geometry around the Hg(II) ion. Nitrogen adsorption–desorption isotherm for two of as-prepared complexes ( 2 ) and ( 3 ) are measured first to get their Brunauer–Emmett–Teller surface area. Moreover, the mentioned two complexes are evaluated for their ability to store hydrogen gas at 77 K. However, the results of the hydrogen storage tests proved that the selected complexes are all capable of storing hydrogen, but in varying degrees, where complex ( 2 ) exhibited a storage capacity of 4.22 wt% under 88 bar.     

氢气在单壁碳纳米管束的吸附的密度泛函研究

作者利用密度泛函理论（DFT）计算了氢气在单壁碳纳米管束（SWNTs)中管内 和管间的吸附。考察了温度,孔径以及压力对吸附的分子数密度,重量百分比,单 位体积储存能力以及超额吸附量的影响。DFT计算发现,较大的孔径有利于氢气在 SWNTs中的吸附且氢气在管隙中的吸附不可忽略。计算表明在77 K和6 MPa时,氢气 在2.719 mm的SWNTs的总的吸附的重量百分比分别可达到13.2 wt%,这约是美国能 源部（DOE）目标值的两倍,而单位体积储存能力在DOE目标值附近,而在300 K和 6 MPa时,氢气在2.719 nm的SWNTs的总的吸附的重量百分比仅为1.5 wt%。通过实 验结果与计算结果的比较表明,密度泛函理论的计算结果支持SWNTs有较高的吸附 储氢能力的实验结论。     

H2在K0-MWCNTs上储存和吸附/脱附特性研究

利用高压容积法辅以卸压升温脱附排水法, 测定金属K修饰多壁碳纳米管对H₂的吸附储存容量. 结果表明, 在室温(25 ℃), 7.25 MPa实验条件下, x%K⁰-MWCNTs (x%＝30%～35%, 质量百分数)对H₂的吸附储存容量可达3.80 wt%(质量百分数), 是相同条件下单纯MWCNTs氢吸附储量的2.5倍; 室温下卸至常压的脱附氢量为3.36 wt%(占总吸附氢量的～88%), 后续升温至673 K的脱附氢量为0.41 wt%(占总吸附氢量的～11%). 利用LRS和H₂-TPD-GC/MS等谱学方法对H₂/K⁰-MWCNTs吸附体系的表征研究表明, H₂在K⁰-MWCNTs上吸附存在非解离 (即分子态)和解离(即原子态)两种吸附态; 在≤723 K温度下, H₂/K⁰-MWCNTs体系的脱附产物几乎全为H₂气; 723 K以上高温脱附产物不仅含H₂, 也含有CH₄, C₂H₄和C₂H₂等C₁/C₂-烃.     

Adsorption of molecular hydrogen on inorganometallic complexes B<Subscript>2</Subscript>H<Subscript>4</Subscript>M (M=Li,Be, Sc,Ti, V)

Molecular interaction between hydrogen molecules and B₂H₄M (M=Li, Be, Sc, Ti, V) complexes has been studied using the DFT method (M06 functional) and 6-311++G** basis set. The hydrogen uptake capacity of the complexes considered is higher than the target set by the US Department of Energy (5.5 wt% by 2020). The metal atom bound strongly to the B₂H₄ substrate. Adsorption of molecular hydrogen on Be-, Ti-, and V-decorated complexes is thermodynamically possible for all the pressures and temperatures considered whereas it is unfavorable for Li-decorated complexes for all the pressure and temperatures. For the Sc-doped complexes, adsorption of molecular hydrogen is favorable below 330 K and entire pressure range considered. All the H₂ adsorbed complexes are kinetically stable. For all the complexes, the interaction between the inorganometallic complexes and the H₂ molecules adsorbed is attractive whereas that between adsorbed H₂ molecules is repulsive. We have also performed molecular dynamics simulations to confirm the same number of H₂ molecule adsorption from the simulations and DFT calculations.     

Research of Nanomaterials as Electrodes for Electrochemical Energy Storage

This paper has experimentally proved that hydrogen accumulates in large quantities in metal-ceramic and pocket electrodes of alkaline batteries during their operation. Hydrogen accumulates in the electrodes in an atomic form. After the release of hydrogen from the electrodes, a powerful exothermic reaction of atomic hydrogen recombination with a large energy release occurs. This exothermic reaction is the cause of thermal runaway in alkaline batteries. For the KSL-15 battery, the gravimetric capacity of sintered nickel matrix of the oxide-nickel electrode, as hydrogen storage, is 20.2 wt%, and cadmium electrode is 11.5 wt%. The stored energy density in the metal-ceramic matrix of the oxide-nickel electrode of the battery KSL-15 is 44 kJ/g, and in the cadmium electrode it is 25 kJ/g. The similar values for the KPL-14 battery are as follows. The gravimetric capacity of the active substance of the pocket oxide-nickel electrode, as a hydrogen storage, is 22 wt%, and the cadmium electrode is 16.9 wt%. The density of the stored energy in the active substance oxide-nickel electrode is 48 kJ/g, and in the active substance of the cadmium electrode it is 36.8 kJ/g. The obtained results of the accumulation of hydrogen energy in the electrodes by the electrochemical method are three times higher than any previously obtained results using the traditional thermochemical method.     

LiAlH4与LiNH2的相互作用机理及储氢特性

将LiAlH4和LiNH2按摩尔比1：2进行球磨复合,随后将复合物进行加热放氢特性研究,然后对其完全放氢后的产物进行再吸氢特性研究。通过X射线衍射分析(XRD)、热分析(DSC)和红外 (FTIR)分析等测试手段对其反应过程进行了系统分析研究。研究结果表明,LiAlH4/2LiNH2加热放氢分为3个反应阶段,放氢后生成Li3AlN2,总放氢量达到8.65wt%。放氢生成的Li3AlN2在10MPaH2压力和400℃条件下,可以可逆吸氢5.0wt%,吸氢后的产物为 LiNH2 、AlN和LiH,而不能再生成LiAlH4。本文对LiAlH4/2LiNH2复合物放氢/再氢化过程机理进行了分析。