Gravimetric Hydrogen Density Research Articles

Density functional theory study of the interaction of hydrogen with TMC2H2(TM=Sc-Ni)

Different aspects of the hydrogen storage properties of TMC2H2 (TM = Sc-Ni) were evaluated using density functional theory and ab initio molecular dynamics calculations. Hydrogen saturation conformations indicate that the hydrogen gravimetric density of TMC2H2 (TM = Sc-Ni) is 4.54–12.43%. The free energy profiles and first-principles molecular-dynamics (MD) simulations showed that when the first H2 molecule attaches to TMC2H2 (TM = Sc, Ti), the H2 molecule is first dissociated over Ti/Sc, and then, one of the H atoms goes to a carbon atom, forming a CH2 group. That is, there are two types of hydrogen bonding in TiC2H2 and ScTiC2H2: the first set of hydrogen binds to C, and the subsequent set of hydrogen binds to Ti/Sc. Importantly, TiC2H2 is able to bind five H2 molecules with the hydrogen gravimetric density of 12.00%, regardless of CH2 group formation. However, ScC2H3H can bind only three H2 molecules, reducing the gravimetric uptake capacity of ScC2H2 from 12.43% to 10.13%. For TMC2H2 (TM = V, Cr, Mn), the first hydrogen molecule is dissociated, but there is no “spillover effect”. For TMC2H2 (TM = Fe, Co, Ni), the first hydrogen molecule is bound quasi-molecularly. Most of our findings, such as those regarding H2 dissociation and TMC2H3H formation, should be valid for other TM-decorated nanostructures.

Ca-decorated borophene as potential candidates for hydrogen storage: A first-principle study

Based on density functional theory calculation, we have investigated the hydrogen storage properties of three types of Ca-decorated borophene which have been recently synthesized experimentally. It is found that Ca atoms have strong bonding strength with borophene without the problem of aggregation. The configuration of borophene has an important effect on the H2 storage capacity. Ca-decorated borophene of S2 and S3 are promising materials system for high-capacity hydrogen storage with gravimetric hydrogen density 9.5 wt% and 7.2 wt% while that of S1 are not. Not only the polarization mechanism but also the orbital hybridization are involved in the adsorption of H2. The temperature and pressure have also been taken into consideration. All the hydrogen adsorbed structures of S2 and S3 are stable at room temperature under mild pressure. Our results indicate that Ca-decorated borophene of S2 and S3 structures could be expected to be promising H2 storage materials for H2 fuel battery.

Lithium Hydrazinidoborane Ammoniate LiN₂H₃BH₃·0.25NH₃, a Derivative of Hydrazine Borane.

Boron- and nitrogen-based materials have shown to be attractive for solid-state chemical hydrogen storage owing to gravimetric hydrogen densities higher than 10 wt% H. Herein, we report a new derivative of hydrazine borane N2H4BH3, namely lithium hydrazinidoborane ammoniate LiN2H3BH3·0.25NH3. It is easily obtained in ambient conditions by ball-milling N2H4BH3 and lithium amide LiNH2 taken in equimolar amounts. Both compounds react without loss of any H atoms. The molecular and crystallographic structures of our new compound have been confirmed by NMR/FTIR spectroscopy and powder X-ray diffraction. The complexation of the entity LiN2H3BH3 by some NH3 has been also established by thermogravimetric and calorimetric analyses. In our conditions, LiN2H3BH3·0.25NH3 has been shown to be able to release H2 at temperatures lower than the parent N2H4BH3 or the counterpart LiN2H3BH3. It also liberates non-negligible amounts of NH3 at temperatures lower than 100 °C. This is actually quite detrimental for chemical H storage, but alternatively LiN2H3BH3·0.25NH3 might be seen as a potential NH3 carrier.

High temperature metal hydrides for energy systems Part A: Numerical model validation and calibration

Metal hydrides have become more and more significant both as hydrogen storage devices and as basic elements in energy conversion systems. Magnesium hydride (MgH2) shows very interesting characteristics – i.e. high enthalpy of reaction and hydrogen gravimetric density – making it capable of being employed in the field of energy production. So there is interest in investigating the behaviour of this kind of hydride, placed in an energy system. In order to examine MgH2 in depth, its main kinetic parameters must be found and this can be accomplished by means of the calibration of a model previously realised by author Marco Gambini in his 1989–1994 works.In the light of this, an assessment of the activation energies (Ea = 72,200 kJ/kmol, Ed = 89,000 kJ/kmol) and kinetic constants (k0a = 15,000 s−1, k0d = 198,500 s−1) in both absorption and desorption phase of magnesium hydride has been provided. Thanks to these values, the behaviour of MgH2 can be modelled, making the performance of a magnesium hydride-based energy system estimable.

The reversible hydrogen storage abilities of metal Na (Li, K, Ca, Mg, Sc, Ti, Y) decorated all-boron cage B28

The density functional theory is used to study the hydrogen storage abilities of alkali metal Li (Na, K), alkaline-earth metal Mg (Ca), and transition metal Ti (Ti, Sc, Y) decorated B28, which is the possible smallest all-boron cage and contains one hexagonal hole and two octagonal holes. The most stable structure of B28 explored by the calypso search is as same as that explored by Zhao et al. [Nanoscale 7(2015)15086]. It is calculated that the hollow sites outside of the cavities should be the most stable for all metals except for Ti. The average adsorption energy of H2 molecules (Ead) adsorbed by each Na (Ca, K, Mg, Sc, Y and Li) atom outside of the B28 cage are in the range from 0.2 to 0.6 eV, which is suitable for hydrogen storage under near-ambient conditions. However, the largest hydrogen gravimetric density (HGD) for the B28Sc3-12H2 structure is smaller than the target of 5.5 wt% by the year 2017 specified by the US Department of Energy (DOE). Therefore, the metal Ti (Sc) decorated all-boron cage B28 should not be good candidates for hydrogen storage. The calculated desorption temperature and the molecular dynamic simulation indicate that the B28M3-nH2 (M = Na, Li, Ca, K, Mg, Y) structures are easy to desorb the H2 molecules at the room temperature (T = 300 k). Furthermore, the B28 cages bridged by the sp2-terminated B5 chain can hold Na (Li, Ca, K, Mg, Y) atoms to capture hydrogen molecules with moderate Ead and HGD. These findings suggest a new route to design hydrogen storage materials under the near-ambient conditions.

Synthesis of novel hydride Li3AlFeH8 at high temperature and pressure

Iron-containing complex hydrides are a fascinating class of materials for hydrogen storage applications because they consist of abundant iron and usually contains [FeH6]4− complexes, resulting in high hydrogen densities. In this study, we synthesized theoretically predicted Li3AlFeH8, which has the highest gravimetric hydrogen density of all transition metal complex hydrides, through a hydrogenation reaction of LiH, AlH3, and pure iron powder mixture under high pressure. The reaction process was observed in situ using a synchrotron radiation x-ray diffraction technique to clarify its reaction kinetics. The reaction temperature and pressure were changed to optimize reaction conditions for obtaining single phase Li3AlFeH8. Unfortunately, we did not obtain single phase Li3AlFeH8 because the reaction was slow. In addition, there were other phases with similar thermodynamic stabilities to that of Li3AlFeH8. Another novel hydride, LiAlFeH6, was found to be synthesized above 850 °C at 9 GPa.

Effects of electron doping on the stability of the metal hydride NaH

Alkali and alkali-earth metal hydrides have high volumetric and gravimetric hydrogen densities, but due to their high thermodynamic stability, they possess high dehydrogenation temperatures which may be reduced by transforming these compounds into less stable states/configurations. We present a systematic computational study of the electron doping effects on the stability of the alkali metal hydride NaH substituted with Mg, using the self-consistent version of the virtual crystal approximation to model the alloy Na1−xMgxH. The phonon dispersions were studied paying special attention to the crystal stability and the correlations with the electronic structure taking into account the zero point energy contribution. We found that substitution of Na by Mg in the hydride invokes a reduction of the frequencies, leading to dynamical instabilities for Mg content of 25%. The microscopic origin of these instabilities could be related to the formation of ellipsoidal Fermi surfaces centered at the L point due to the metallization of the hydride by the Mg substitution. Applying the quasiharmonic approximation, thermodynamic properties like heat capacities, vibrational entropies and vibrational free energies as a function of temperature at zero pressure are obtained. These properties determine an upper temperature for the thermodynamic stability of the hydride, which decreases from 600 K for NaH to 300 K at 20% Mg concentration. This significant reduction of the stability range indicates that dehydrogenation could be favoured by electron doping of NaH.

First-principles study of hydrogen storage on Li12F12 nano-cage

We use the first-principles calculation based on density functional theory (DFT) to investigate the hydrogen storage on Li12F12 nano-cage. Our result indicates the largest hydrogen gravimetric density is 7.14wt% and this is higher than the 2017 target from the US department of energy (DOE). Meanwhile, the average adsorption energy is −0.161eV/H2, which is desirable for absorbing and desorbing H2 molecules at near ambient conditions. These findings will have important implications on designing hydrogen storage materials in the future.

Hydrogen storage on bare Cu atom and Cu-functionalized boron-doped graphene: A first principles study

A detailed theoretical investigation of the structural and electronic properties of Cu-type substrates as well as the interaction between adsorbed H2 molecules and the surfaces of bare Cu, Cu-functionalized graphene (Cu-G (3 × 3)) and B-doped Cu-functionalized graphene B-Cu-G (3 × 3) have been thoroughly examined in this study using Density Functional Theory. We have observed that the aggregation of Cu atom on pristine graphene can be suppressed by boron atom. It was also revealed that the first H2 molecule could interact both in the atomic and molecular configuration with bare Cu atom. The energy required to overcome this barrier was 0.523 eV and with an energy released of 0.309 eV. In addition, the bare Cu atom appeared not to be an efficient storage adsorbent for hydrogen because of the strong H2 molecule/Cu interaction as the number of molecules accumulates, and this is suggestive of a possibility of surface discharge occurring only at elevated high temperatures. However, hydrogen adsorbed on Cu-G (3 × 3) tends to be in the molecular form while the diffusion of Cu atom from the B site to H site in the atomic configuration with an energy released of 0.115 eV with small energy barrier (0.001 eV). A gravimetric hydrogen density of 4.231 wt% was reached when H2 adsorbed on double sided Cu-functionalized graphene. These results revealed that Cu-functionalized graphene could be a potential candidate for hydrogen storage compared to bare Cu atom.

Enhanced hydrogen adsorption on Li-coated B12C6N6.

The hydrogen storage property of Li-coated B12C6N6 is investigated by density functional theory calculations. B12C6N6 is an electron deficient fullerene. Li atoms can be strongly bound to this cage by donating their valance electrons to the virtual 2p orbitals of carbon in the cluster. The binding energy (-2.90 eV) is much larger than the cohesive energy (1.63 eV) of bulk Li, and it prevents the Li atoms from aggregation. The coated Li atoms have large positive charges and the adsorbed hydrogen molecules can be moderately polarized by the Li+ ions. The computation shows that each Li atom coated on B12C6N6 can hold 2-3 H2 molecules with adsorption energies in the range of 0.21-0.24 eV/H2. The B12C6N6Li8 can adsorb 16 H2 and achieve a gravimetric hydrogen density of 8.63 wt. %. The present results indicate that alkali-metal atoms coated on electron deficient fullerenes can serve as hydrogen storage materials that can operate at ambient temperatures with high recycling storage capacity.

Fivefold increase of hydrogen uptake in MOF74 through linker decorations

We present ab initio results for linker decorations in Mg-MOF74, i.e., attaching various metals $\mathcal{M}=\text{Li}$, Na, K, Sc, Cr, Mn, Fe, Ni, Cu, Zn, Rb, Pd, Ag, and Pt near the ring of the linker, creating new strong adsorption sites and thus maximizing small-molecule uptake. We find that in most cases these decorations influence the overall form and structure of Mg-MOF74 only marginally. After the initial screening, we chose metals that bind favorably to the linker and further investigated adsorption of ${\mathrm{H}}_{2},{\mathrm{CO}}_{2}$, and ${\mathrm{H}}_{2}\mathrm{O}$ for $\mathcal{M}=\text{Li}$, Na, K, and Sc. For the case of ${\mathrm{H}}_{2}$ we show that up to 24 additional guest molecules can be adsorbed in the metal-organic framework (MOF) unit cell, with binding energies comparable to the original open-metal sites at the six corners of the channel. This leads to a fivefold increase of the molecule uptake in Mg-MOF74, with tremendous impact on many applications in general and hydrogen storage in particular, where the gravimetric hydrogen density increases from 1.63 to 7.28 mass % and the volumetric density increases from 15.10 to 75.50 g ${\mathrm{H}}_{2}\phantom{\rule{4pt}{0ex}}{\mathrm{L}}^{\ensuremath{-}1}$.

Hydrogen storage in a layered flexible [Ni2(btc)(en)2]n coordination polymer

[Ni2(btc)(en)2]n coordination polymer exhibits a layered two-dimensional structure with weak interaction between the layers. Correlation of experimental measurements, DFT calculations and molecular simulations demonstrated that its structural features, primarily the inherent flexibility of the layered polymeric structure, lead to improved hydrogen storage performance at room temperature, due to significant enhancement in isosteric heats of hydrogen adsorption. Volumetric measurements of hydrogen adsorption at room temperature show up to 0.3 wt.% hydrogen absorbed at 303 K and 2.63 bar of hydrogen pressure, with isosteric heats of adsorption of about 12.5 kJ mol−1. Predicted performance at room temperature is 1.8 wt.% at 48 bar and 3.5 wt.% at 100 bar, better than both MOF-5 and NU-100, with calculated values of isosteric heats for adsorption of hydrogen in 8–13 kJ mol−1 range at both 77 K and 303 K. Grand canonical Monte Carlo calculations show that this material, at 77 K, exhibits gravimetric hydrogen densities of more than 10 wt.% (up to 8.3 wt.% excess) with the corresponding volumetric density of at least 66 gL−1, which is comparable to MOF-5, but achieved with considerably smaller surface area of about 2500 m2 g−1. This study shows that layered two-dimensional MOFs could be a step towards MOF systems with significantly higher isosteric heats of adsorption, which could provide better room temperature hydrogen storage capabilities.

Hydrogen adsorption and storage on Palladium – functionalized graphene with NH-dopant: A first principles calculation

We conducted a detailed theoretical investigation of the structural and electronic properties of single and double sided Pd-functionalized graphene and NH-doped Pd-functionalized graphene, which are shown to be efficient materials for hydrogen storage. Nitrene radical dopant was an effective addition required for enhancing the Pd binding on the graphene sheet as well as the storage of hydrogen. We found that up to eight H2 molecules could be adsorbed by double-sided Pd-functionalized graphene at 0K with an average binding energy in the range 1.315–0.567eVA gravimetric hydrogen density of 3.622wt% was reached in the Pd-functionalized graphene on both sides. The binding mechanism of H2 molecules came not only the polarization mechanism between Pd and H atoms but also from the binding of the Pd atoms on the graphene sheet and the orbital hybridization. The most crucial part of our work is measuring the effect of nitrene radical on the H2 adsorption on Pd-functionalized graphene. Our calculations predicted that the addition of NH radicals on Pd-functionalized graphene enhance the binding of H2 molecules, which helps also to avoid the desorption of Pd(H2)n (n=1–5) complexes from graphene sheet. Our results also predict Pd-functionalized NH-doped graphene is a potential hydrogen storage medium for on-board applications.

Hydrogen adsorption on Li-decorated BN analogs of γ-graphyne: A DFT study

Li-decorated BN analogs of γ-graphyne have a potential for high density hydrogen storage. We investigate the structural stabilities of Li decorated double-sided BN analogs of γ-graphyne (2Li/BN-yne and 2Li/BNC-yne) and the hydrogen storage capacities based on density-functional theory (DFT) including van der Waals interactions. The two materials both are able to absorb six hydrogen molecules with a maximum hydrogen gravimetric density of 6.865 and 8.797wt%, respectively. And the average binding energies are 0.335 and 0.342eV/H2 using the vdW-DF2 functional, respectively. The hydrogen binding mechanisms are investigated by analyzing the partial density of state (PDOS) and charge transfer of the complexes.

Calcium decorated two dimensional carbon allotropes for hydrogen storage: A first-principles study

Graphene has attracted tremendous interest as a potential hydrogen storage medium due to its extraordinary properties granted by its two-dimensional nature. In this study, we investigated the hydrogen storage ability of five 2D carbon allotropes: C40, C41, C63, C64 and C65 with calcium decoration by adopting the first-principles method based on density functional theory. The probable adsorption sites for a Ca atom and different Ca coverages were examined, and the hydrogen molecules were added one by one to investigate the maximum hydrogen gravimetric density. Our results show that Ca atom prefers to stay on the hollow site above the largest polygons instead of small polygons. Up to 6 hydrogen molecules can be adsorbed on one single Ca atom with the average adsorption energy in the reasonable range. The hydrogen gravimetric density for these carbon allotropes with Ca decoration are 3.53–4.48wt.% at low Ca coverage and 7.5–8.57wt.% at high Ca coverage.

Synthesis of Ni/Graphene Nanocomposite for Hydrogen Storage

We have designed a Ni-graphene composite for hydrogen storage with Ni nanoparticles of 10 nm in size, uniformly dispersed over a graphene substrate. This system exhibits attractive features like high gravimetric density, ambient conditions, and low activation temperature for hydrogen release. When charged at room temperature and an atmospheric hydrogen pressure of 1 bar, it could yield a hydrogen capacity of 0.14 wt %. When hydrogen pressure increased to 60 bar, the sorbent had a hydrogen gravimetric density of 1.18 wt %. The hydrogen release could occur at an operating temperature below 150 °C and completes at 250 °C.

Catalytic decomposition of carbon-based liquid-phase chemical hydrogen storage materials for hydrogen generation under mild conditions

The increasing demand of energy requires the development of sufficient and sustainable energy sources. However, the upcoming hydrogen economy is suffering from challenges which need to be solved. In this context, the search for liquid hydrogen storage materials and successful utilisation is crucial due to the high gravimetric and volumetric hydrogen densities, easy recharging, low capital investment, and low potential risks. In this review, we survey the progress made in hydrogen generation from carbon-based liquid-phase chemical hydrogen storage materials, focusing mainly on the catalytic decomposition of formic acid for hydrogen production.

Design and operation of an aluminium alloy tank using doped Na3AlH6 in kg scale for hydrogen storage

In this publication the authors present an aluminium alloy tank for hydrogen storage using 1921 g of Na3AlH6 doped with 4 mol% of TiCl3 and 8 mol% of activated carbon. The tank and the heat exchangers are manufactured by extrusion moulding of Al-Mg-Si based alloys. EN AW 6082 T6 alloy is used for the tank and a specifically developed alloy with a composition similar to EN AW 6060 T6 is used for the heat exchangers. The three heat exchangers have a corrugated profile to enhance the surface area for heat transfer. The doped complex hydride Na3AlH6 is densified to a powder density of 0.62 g cm−3. The hydrogenation experiments are carried out at 2.5 MPa. During one of the dehydrogenation experiments approximately 38 g of hydrogen is released, accounting for gravimetric hydrogen density of 2.0 mass-%. With this tank 15 hydrogenation and 16 dehydrogenation tests are carried out.

First principle predictions of new crystal structures for hydrogen reservoirs

The demand for clean energies grows rapidly, therefore, research into new materials to be used as hydrogen reservoirs are necessary. With this work we try to provide some understanding on complex hydrides. The compounds studied are of the type Li–X–H, where X are lighter elements in the periodic table. With the participation of these elements we can obtain a high gravimetric hydrogen density. We performed a systematic study on these materials. In this work we used different ab-initio codes. The predictive power of first principle calculations have shown their importance in determining properties of new materials not yet synthesized. The ab-initio calculations help to shorten development times of new materials such as those proposed in this paper. Additionally, new data on materials studied in the past and others designed in this work are shown here.

Ca-decorated novel boron sheet: A potential hydrogen storage medium

We studied hydrogen storage properties of Ca-decorated a novel boron sheet through first-principles calculations. It was found that up to six H2 molecules can be captured by a Ca atom at 0 K with an average binding energy in a better range of −0.20 to −0.32 eV/H2. The gravimetric hydrogen density of 12.68 wt.% is reached when Ca is adsorbed on both sides of the boron sheet. The mechanism for binding the attached H2 molecules comes from not only the polarization mechanism but also the orbital hybridization. The effect of temperature and pressure on hydrogen storage performance of the Ca-decorated boron sheet was also evaluated. At room temperature, all the hydrogen adsorbed structures are stable at mild pressure. Our results indicate that Ca-decorated boron sheet is a potential hydrogen storage medium for on-board vehicle application.