Hydrogen storage in advanced solid state materials has been an intense area of research due to many drawbacks in conventional high pressure or cryogenic liquid hydrogen storage methods. A practical hydrogen storing material is required to have high storage capacity and fast dehydrogenation kinetics. Among many solid state materials for hydrogen storage, magnesium hydride (MgH2) combines a hydrogen capacity of 7.6 wt % with the benefit of the low cost of production and abundance. The main difficulties for implementing MgH2 are slow absorption/desorption kinetics and high reactivity towards air and oxygen, which are also common issues in most lightweight metal hydrides. Previously, improvements in hydrogen storage and release properties have been reported by using nanostructured magnesium that can be obtained through various fabrication methods including ball-milling, mechanical alloying, and vapor transport. In this study, we investigate the hydrogen absorption and desorption properties of magnesium “nanotrees” fabricated by glancing angle deposition (GLAD) technique, and also conventional Mg thin films deposited at normal incidence. Mg nanotrees are about 15 μm long, 10 μm wide, and incorporate “nanoleaves” of about 20 nm in thickness and 1,2 μm in lateral width. A quartz crystal microbalance (QCM) gas absorption/desorption measurement system has been used for our hydrogen storage studies. Nanostructured and thin film Mg have been deposited directly on the surface of the gold coated unpolished quartz crystal samples. QCM hydrogen storage experiments have been performed at temperatures ranging between 100-300 °C, and at H2 pressures of 10 and 30 bars. Our QCM measurements revealed that Mg nanotrees can absorb hydrogen at lower temperatures and also at a faster rate compared to Mg thin film. In addition, Mg nanotrees can reach hydrogen storage values of about 4.80 wt% at 100 °C, and up to about 6.71 wt% (which is close to the theoretical maximum storage value of Mg) at temperatures lower than 150 °C. The significant enhancement in hydrogen absorption properties of our Mg nanotrees is believed to originate from novel physical properties of their nanoleaves. These nanoleaves are very thin (∼20 nm) and both surfaces are exposed to hydrogen enhancing the diffusion rate of hydrogen together with a decreased diffusion length. Based on X-ray diffraction measurements, individual nanoleaves have non-close-packed crystal planes that can further enhance the hydrogen absorption kinetics. In addition, our nanostructured Mg have been observed to quite resistant to surface oxidation, which is believed to due to the single crystal property of the Mg nanoleaves, which further improves the absorption kinetics of hydrogen.

For a formation of metal hydride of MgH2 or AlH3 under room temperature and ambient pressure, the cathode electrodes of metal and lithium hydride are electrochemically charged with Li anode electrodes in the system of Li-ion extraction. For MgH2 formation, the VC (Voltage-Composition) curve of Mg + 2LiH during charge shows a plateau voltage at 0.6 V until the final composition of 1.05 Li extraction. After charge MgH2 phase is observed by the XRD measurement. Therefore MgH2 is produced by the electrochemical charge from Mg and LiH. For AlH3 formation, Al + 3LiH is charged until the final composition of 0.6 Li at a plateau voltage of 0.8 V which corresponds to the reaction between Al and LiH for the formation of AlH3. In the XRD profile after charge AlH3 phase is not detected although the intensities of Al and LiH decrease compared with these before charge, which suggests the reaction leading to the formation of AlH3.

Metallographic information has been used to support the kinetic analysis and the relative experimental findings in the phase transformation from Mg to MgH2, by absorption of hydrogen gas. In particular the method provides detailed information on the role of localized features like catalyst particles and defects present in the sample, which is obtained from ball milled MgH2 enriched with 5wt% Fe. In this work we have compared the kinetics of the hydrogenation reaction carried out at two different temperatures while keeping constant the thermodynamic force driving the reaction. This last was achieved by carefully controlling the hydrogen gas pressure. Despite this fact, the sample microstructure shows a marked effect of the temperature on the nucleation mechanism. In particular we have noticed that the density of sites active for nucleation is higher at lower temperature.

Instant nucleation deduced by the kinetic analysis was confirmed by comparing the microstructure of samples at different reaction stages.

Nanoporous carbon is a widely studied material due to its potential applications in hydrogen storage or for filtering undesirable products. Most of the developments have been experimental although some simulation work has been carried out based on the use of graphene sheets and/or carbon chains and classical molecular dynamics. The slit pore model is one of the oldest models proposed to describe porous carbon. Developed by Emmet in 1948 [1] it has been recurrently used and in its most basic form consists of two parallel graphene layers separated by a distance that is taken as the width of the pore. Its simplicity limits its applicability since experimental evidence suggests that the walls of the carbon pores have widths of a few graphene layers [2], but it still is appealing for computational simulations due to its low computational cost. Using a previously developed ab initio approach to generate porous semiconductors [3] we have obtained porous carbonaceous materials with walls made up of a few graphene layers (four layers), in agreement with experimental results; these walls are separated by distances comparable to those used in the slit pore model [4]. This validates the idea of a modified slit pore model obtained without the use of ad hoc suppositions. Structures will be presented, analyzed and compared to available experimental results.

In this paper we report on kinetics studies of the growth rates of a hydride phase during the metal-hydride phase transformation of Mg films doped with transition metals (=Ti, Fe). Infrared emission imaging of wedge-shaped thin films during hydrogen loading reveals different effects of Ti and Fe additives on Mg hydride growth rates. Compared to hydrogenation of pure Mg, Ti addition (atomic fraction 1.6 % and 2.3 %) does not increase the Mg hydride growth rate. However, this doping results in the formation of a thicker hydride layer residing on top of the films. The hydrogenation rate is increased by an order of magnitude for addition of atomic fraction 3.1 % of Fe and the thickness of Mg hydride layer is more than twice that of the hydride layer during hydrogenation of pure Mg. Results obtained here can be used to guide powder design for hydrogen storage applications.

Structural rules have been formulated for the molecular crystal of ammonia borane (AB, NH3BH3) and clathrates thereof. These rules are similar to the “ice rules” in water. Periodic structures of possible clathrates of AB have been predicted. A rigorous analysis of the uniform space filling tessellations of 3D space has been performed resulting in the identification of two promising structures for AB clathrates. Additional five structures have been identified exploiting features and properties of AB molecules. The screening, or evaluation, of proposed periodic structures has been performed on the basis of their stability determined at the density functional level of theory. Hydrogen capacity of the most stable periodic structure (cantitruncated cubic honeycomb) is estimated to be 21 wt%, 19% chemically bound in AB and 2 wt% of H2 physisorbed in the cages of AB.

Metal tetrahydroborates remain interesting materials as potential hydrogen storage media. In the present paper, we analyze thermodynamic stability of borohydrides of Al and Zr by means of extensive density functional calculations. We show that solid phases of these compounds are formed by dispersive Van der Waals forces. These compounds are thermodynamically unstable at room temperature with respect to decomposition to boron and hydrogen. Their stability is explained by formation of diborane as a necessary step in the decomposition path, pointing out to the kinetic factors that are important for the stability analysis of metal borohydrides.

Mg has 7.6 mass% of high gravimetric hydrogen density, an abundance of resources and inexpensive price compared with other functional materials. Owing to these merits, it has been the major subject of hydrogen storage study. However, it is unsuitable for practical application due to thermodynamic stability and slow kinetics of Mg hydride. Therefore, many ways such as fabrication of nanocrystalline or addition of catalyst have been proposed to solve the problems of Mg hydride system. Copper and aluminum are inexpensive and can obtain easily as well as Mg. Each eutectic alloy could be produced by sintering process and observed improvement of reaction with hydrogen. Mg2Cu laminate, one phase of Mg-Cu eutectic alloy, could also be produced by cold-rolling process, and it showed reversible reaction with hydrogen, at this study.

A novel class of secondary battery comprising MH and air electrodes was developed for potential uses in high power density and high energy density applications such as electric or hybrid vehicles and power storage units supporting fuel cell and solar power systems. The air electrode consisted of nickel-based gas diffusion electrode using Ir2Bi2O7-z as oxygen evolution and reduction catalyst. Coin-type of cells using alkaline solutions as electrolyte were designed and fabricated, and the charge-discharge behaviors were evaluated with constant current operation. The discharge voltage and power density were improved by using a thin film membrane, in which the electrolyte was impregnated, between the air and MH electrodes, and the maximum power density was comparable to that of commercially available Ni-MH secondary battery. The MH utilization and the current efficiency of a charge-discharge cycle were found to be more than 90%.

Hydrogen is a reliable energy vector and its storage is strongly connected to the costs, performance and level of safety of the storage system components. Several materials for physical and chemical hydrogen storage have been proposed, but few research works were devoted to polymers, that generally are low cost and weight materials, easy to be managed and manufactured. In this work, a functionalised Poly(ether ether ketone) (PEEK) polymer was studied and chosen as a base polymeric matrix with the aim to produce both a low cost and low weight hydrogen storage material. The polymer was in situ functionalised starting from a manganese oxide precursor. The obtained oxide, bonded to the polymer chain, allows the hydrogen storage. In this work, the functionalisation process and preliminary results of the hydrogen storage capability are reported.

From Scanning Electron Microscopy (SEM) and surface area measurements (BET), it has been verified that the metallic compound introduction modifies the morphology of the material, supplies an increased surface area for hydrogen chemisorption, revealing a 1.2%wt/wt hydrogen adsorption capability at 77 K. Preliminary results by Gravimetric Hydrogen Absorption measurements show that by increasing the temperature, the hydrogen storage capability is reduced and a value of 0.3%wt/wt at 50°C and 80 absolute bar was obtained. The reversibility cycles of hydrogen adsorption-desorption seem to be confirmed. For this reason such approach has been considered as a promising pathway and deeper studies are in progress.

Compound formation properties of very finely layered Mg/Al laminate composite (“super laminate composite”) were investigated. Almost uniform Mg17Al12 compound was obtained by heat treatment of the super laminate at 673K in less than 0.6ks(10 minutes). The rate control process of the compound formation is thought to be the diffusion of Mg in Al. Hydrogenation properties of thus obtained Mg17Al12 compound were also studied and its absorption capacity and dissociation pressure were almost the same as those previously reported material, which was prepared by a longer time heat treatment.

This paper uses an efficient and accurate approach to estimate the hydrogen physical adsorption in various carbon structures. By comparing with previous Grand Canonical Monte Carlo (GCMC) and other methods on expanded graphite, the introduced method is shown to be accurate, but the calculation is much faster and more intuitive. Our preliminary results in amorphous carbons show high hydrogen uptake close to 0.8% at 300 K and moderate pressure.

This work is aimed at the interactions between hydrogen atoms contained in high concentrations in metal lattices. Effects of metals on hydrogen interactions are surveyed by carrying out molecular dynamics (MD) simulations on hydrogen fluids containing palladium atoms, from a viewpoint in contrast to previous simulations on low concentrations of hydrogen in metal lattices. Some results of these simulations reveal the dissociation of H2 molecules to H atoms due to the presence of Pd atoms under densification, and therefore imply the change of attractive H-H interactions in H2 molecules to repulsive interactions of H atoms in Pd lattices. These repulsive interactions are consistent with an empirical “2-Å rule” of hydrogen atoms in metal lattices, and impose limits on hydrogen-storage capacities of metals.