Papers by Keyword: Hydrogen Storage

Abstract: Porous adsorbents are currently investigated for hydrogen storage application. From a practical point of view, in addition to high porosity developments, high material densities are required, in order to confine as much material as possible in a tank device. In this study, we use different measured sample densities (tap, packing, compacted and monolith) for analyzing the hydrogen adsorption behavior of activated carbon fibres (ACFs) and activated carbon nanofibres (ACNFs) which were prepared by KOH and CO₂ activations, respectively. Hydrogen adsorption isotherms are measured for all of the adsorbents at room temperature and under high pressures (up to 20 MPa). The obtained results confirm that (i) gravimetric H₂ adsorption is directly related to the porosity of the adsorbent, (ii) volumetric H₂ adsorption depends on the adsorbent porosity and importantly also on the material density, (iii) the density of the adsorbent can be improved by packing the original adsorbents under mechanical pressure or synthesizing monoliths from them, (iv) both ways (packing under pressure or preparing monoliths) considerably improve the storage capacity of the starting adsorbents, and (v) the preparation of monoliths, in addition to avoid engineering constrains of packing under mechanical pressure, has the advantage of providing high mechanical resistance and easy handling of the adsorbent.

Abstract: The H2TRUST is a Coordination and Support Action by a team of European FCH industry leaders to foster a smooth and well managed transition to a full scale commercialization of FCH applications in Europe and, to aid the process by which all industry stakeholders are informed, prepared and confident from a safety perspective. Safety is considered in all hydrogen applications: production, storage, distribution, mobility, vehicles, non-vehicles and residential power generation.Here we will present the data collection from a set of hydrogen stakeholders, recognized experts in this field, consumers and incident response bodies associated with the fuel cells and hydrogen industries. These results will be disseminated by creating an online website with all the information collected. Best practices and methodology are going to be prepared in order to improve the hydrogen safety knowledge of the society.

Abstract: Recently, Magnesium hydride MgH₂ is one of the attractive hydrogen storage materials because it reaches a high hydrogen capacity. However, the reaction kinetics is too slow and needs high temperature for progressing hydrogen absorption and desorption reactions, which hinders the process of practical applications and it is necessary to improve the hydrogen storage propesties. In this paper, most used or under research methods (Doping with metal and compound) of improving on the hydrogen storage of magnesium hydride are reviewed, in particular to elements substitution, addition of transition metal oxides or fluorine and so on. The advantages and disadvantages of vaious methods of improving on the hydrogen storage of magnesium hydride are compared. The trend of the methods of improving is also introduced.

Abstract: We report on the preparation and hydrogen desorption/absorption kinetics of nanocrystalline magnesium hydride (MgH₂) added commercial TiO₂ by high-energy ball milling. The phase and composition of the as-milled powders are characterized by X-ray diffraction (XRD). The results show that the milled sample contained MgH₂ phase, small amount of Mg and various phases of TiO₂ such as tetragonal and orthorhombic structure. The effect of the milling time (10, 20 and 30 h) on the hydrogen desorption property of MgH₂ has been investigated and found that the milling time of 20 h has excellent dehydrogenation properties, which can release 3.3 wt% H₂ within 60 min at 300 ^oC, which indicates that the kinetics of hydrogen desorption of MgH₂-TiO₂ composite has been greatly enhanced compared to the pure MgH₂. Moreover, hydrogen absorption kinetics of the sample milled 20 h has been studied and the hydrogen content is 0.7, 0.8 and 1.2 wt% H₂ at 250, 280 and 300 ^oC within 60 min, respectively.

Abstract: The nanocrystalline materials for hydrogen storage offer a breakthrough in prospects for practical applications. Their excellent properties are from the combined engineering of many factors: alloy composition, surface properties, microstructure, grain size and others. Nanoengineering can speed up the kinetics, lower the enthalpy of formation and reduce the temperature of releasing hydrogen. The main focus is on the nanostructured metal hydrides, preparing nanograined materials and the effects of nanomaterials on the hydrogen storage properties in this review.

Abstract: The catalytic hydrogenation kinetics of N-ethylcarbazole over 5 wt% Ru/Al₂O₃ was investigated at various temperatures. The results shows that the hydrogenation reaction was exothermic and high temperature is unfavorable for the reaction rate. Fully hydrogenation was achieved within 1 hour under the best reaction temperature of 170 °C. The kinetics of N-ethylcarbazole follows the first-order kinetics in terms of the reactant concentration but independent of hydrogen pressure, which was maintained as a constant in the reaction process. The apparent activation energy of N-ethylcarbazole hydrogenation reaction at 150-180 °C was found to be 71.2 kJ/mol.

Abstract: In this communication we report the effect of macro and microstructure on the hydrogen storage properties of magnesium based materials. Magnesium hydride is an attractive material for hydrogen storage applications since it has a high hydrogen volumetric density. Furthermore, the high enthalpy of hydride formation makes it attractive for thermal energy storage applications. Besides, magnesium is an abundant and low cost material. However, the Mg/MgH₂ system requires high operating temperatures due to its thermodynamic stability and slow hydrogen absorption and desorption kinetics. Magnesium’s first hydrogenation is a very long and costly process. This work aims to ameliorate this process which would effectively reduce the cost of MgH₂. Commercial pure magnesium samples were processed by cold rolling. After processing, the samples presented limited hydrogen absorption due to their small surface area to volume ratio. To overcome this problem the samples were then reduced to powder using a bastard file. The samples were characterized by scanning electron microscopy and presented different morphology. Hydrogen storage properties and morphology are discussed and correlated. Results show an important improvement on the hydrogen absorption and desorption kinetics for the comminuted samples.

Abstract: Mg, Ni, Co, Cu and Fe nanoparticles with a particle size of 30-300 nm were synthesized by hydrogen plasma metal reaction method. Nanostructured Mg-based hydrogen storage materials (Mg-H, Mg-Ni-H, Mg-Co-H, Mg-Cu-H and Mg-Fe-H systems) were synthesized from these metal nanoparticles. In this work, the kinetic and thermodynamic properties of these nanostructured hydrogen storage materials were studied. It was found that nanostructure could significantly enhance the hydrogen absorption kinetics but the thermodynamics (desorption enthalpy and entropy) does not change with downsizing in the size range of 50 to 300 nm.

Abstract: Thermal conduction capability of metal hydrides can be enhanced by 400 ~ 500% through pelletizing the metal hydride powder after a well-controlled copper-coating treatment. In this paper, pelletized LaNi5 metal hydride is studied to evaluate its heat transfer performance and hydrogen absorption rate. In order to analyze the transient heat transfer and hydriding reaction, numerical simulations are carried out based on a multiple-physics modeling. The reactor temperature variation and the dimensionless mass of absorbed hydrogen are plotted for different hydrogen gas supply pressures. The results are compared with the conventional powder-type metal hydride reactor.

Abstract: High pressure hydrate experiment device was used to research the influence of active carbon to the hydrogen storage characteristics of THF hydrates in volume 502.4 ml and 1°C. The results show that within the experimental pressure range, the induction time changes irregularly, so active carbon has no apparent effect on the induction time, but has obvious influence to the pressure drop, under same initial pressure, the pressure drops with activated carbon are larger than that without activated carbon; With activated carbon, the higher the initial pressure the larger the pressure drop. Because the pressure drop is proportional to the hydrogen storage density, so the larger the pressure drop, the higher the hydrogen storage density. When the initial pressure is 8.4 MPa, with activated carbon the hydrogen storage density (0.0082wt%) is far higher than that (0.0031wt%) without it. So activated carbon can promote the hydrogen storage density of THF hydrate.