Papers by Keyword: Metal Hydride

Abstract: A holistic approach is required for the development of materials and systems for hydrogen storage, embracing all the different steps involved in a successful advance of the technology. The several engineering solutions presented in this work try to address the technical challenges in synthesis and application of solid-state hydrogen storage materials, mainly metal hydride based compounds. Moving from the synthesis of samples in lab-scale to the production of industrial sized batches a novel process development is required, including safety approaches (for hazardous powders), and methods to prevent the contamination of sensitive chemicals. The reduction of overall costs has to be addressed as well, considering new sources for raw materials and more cost-efficient catalysts. The properties of the material itself influence the performances of the hydride in a pilot storage tank, but the characteristics of the system itself are crucial to investigate the reaction limiting steps and overcome hindrances. For this, critical experiments using test tanks are needed, learning how to avoid issues as material segregation or temperature gradients, and optimizing the design in the aspects of geometry, hull material, and test station facilities. The following step is a useful integration of the hydrogen storage system into real applications, with other components like fuel cells or hydrogen generators: these challenging scenarios provide insights to design new experiments and allow stimulating demonstrations.

Abstract: A modified Hough transform algorithm for the study of metal hydride orientations was developed, and optimum parameter for the transform was obtained based on numerical analysis result. By assigning an orientation to each hydride pixel, the algorithm removes the ambiguities in handling interconnected hydrides. It is expected that the algorithm will find applications in particle orientations measurement in composites and precipitation reinforced materials in general.

Abstract: The hydrogenation of TbNi_0.4Co_0.6 was studied by means of neutron diffraction and calorimetric method with use of the differential heat-conducting Tian-Calvet type calorimeter. It was determined that TbNi_0.4Co_0.6H_3.8 crystallized in orthorhombic CrB-type structure (S.G. Cmcm). The hydride formation is accompanied with strong lattice expansion. In the structure TbNi_0.4Co_0.6D_3.4 deuterium atoms occupy tetrahedral 8f-intersices, trigonal bipyramidal 4c-interstices and octahedral 4b-interstices. Dependence of the differential molar enthalpy of absorption (ΔH_abs) vs. the hydrogen concentration in the metallic matrix was obtained at 50°C. It was ascertained that in the range of 0<X<2.0 (X=H/ TbNi_0.4Co_0.6) ΔH_abs =-102.0±2.3 kJ mol^-1H_2. The value of the integral enthalpy of hydrogen absorption by TbNi_0.4Co_0.6 equals -99.5kJ mol^-1H₂ for the composition TbNi_0.4Co_0.6H_3.8.

Abstract: As hydrogen generation technologies using renewable energy sources are being developed, considerable attention is paid to storage and transportation of hydrogen gas. Metal hydride alloys are considered as promising materials because they are viewed as an attractive alternative to conventional hydrogen storage cylinders and mechanical hydrogen compressors. Compared to storing in a classic gas cylinder, which requires compression of hydrogen at high pressures, metal hydride alloys can store the same amount of hydrogen at nearly room pressure. However, this hydrogen absorption necessitates an effective way to reject the heat released from the exothermic hydriding reaction. In this paper, fin structures are employed to enhance the heat transfer of metal hydride alloys in a cylindrical reactor. Numerical simulations are performed based on a multiple-physics modeling to analyze the transient heat transfer during the hydrogen absorption process. The objective is to minimize the time elapsed for the process and to reduce the hotspot temperature by determining the number and shape of rectangular fins while the total volume of fins used are fixed. The simulation results show that the more fins are applied the better heat transfer is achieved and that there exists an optimal length of the fins.

Abstract: Nowadays hydrogen as an important source of energy is still produced from fossil fuel processing largely, hence the separation of hydrogen from the gas mixture with high recovery ratio and purity arises as an important issue. In this paper we proposed a hydrogen recovery/production process from half-coke oven gas, and the material LaNi_4.3Al_0.7 was considered for use due to its low plateau pressure and good resistance to impurities. We use a Sieverts type volumetric apparatus to investigate the material properties,including P-C-T properties and hydriding/ dehydriding kinetics under different conditions. Based on the results obtained, the feasibility of using the material for gas separation purpose was discussed.Keywords: Gas separation; metal hydride; reaction kinetics; P-C-T properties; Sieverts method

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: 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: 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: This study analyzed and discussed the hydrogen storage reaction in the metal hydride hydrogen storage tank with internally fined heat tube. As the heat transfer and hydrogen storage efficiency of internal temperature control system are better than external temperature control, this study created a hydrogen storage simulation method to discuss the effect of thermistor fins on hydrogen storage. The results showed that the fins have significant effect on increasing the hydrogen storage efficiency, and the hydrogen storage time decreases as the thermistor fluid velocity increases, but the drawback is not apparent when the fluid velocity reaches a threshold.

Abstract: With the expansion of application fields of the high purity hydrogen (hydrogen content>99.9999%), its preparation methods, in particular recovery from multi-component mixture,have attracted wide attentions. This paper describes the principle of hydrogen separation and purification process based on metal hydride, and some key issues involved in it, such as the alternatives of raw gas, the processing of hydride materials, the design of metal hydride reactor are discussed according to the literature reports. Finally, the current problems encountered in hydride based gas separation are presented, and future trends are also predicted.