Search

The storage of hydrogen in metal hydride reactors is examined experimentally and numerically in this paper. In this respect, as-received LaNi 5 powders are coated with different amounts of copper by using copper sulphate solution to accelerate the hydrogen charging processes. The thermal conductivity of the copper-coated storage material is found to reach up to 8 times of the uncoated powders. A two-dimensional axisymmetric model regarding complex heat and mass transfer occurring during hydrogen charging process in metal hydride reactors is numerically solved at macro level. The developed model is validated by using experimental data related to the amount of hydrogen stored and the reactor temperatures. In accordance with the experimental results, the simulation results show that more homogenous temperature distribution in the reactor can be obtained with the copper coating due to improved thermal properties. Moreover, charging time is also improved by the copper coating. However, since the reactor is loaded with coated/uncoated LaNi 5 powders at the same weight of 65 g, the total amount of hydrogen stored decreases with the copper coating due to reduced amount of LaNi 5. • LaNi 5 powders are coated with copper to improve hydrogen storage performance. • Thermal conductivity is notably improved with copper additive. • Hydrogen charging time is significantly shortened with copper additive. • A 2D axisymmetrical model is developed to simulate the hydrogen storage. • The experimental and numerical results are in good agreement. [ABSTRACT FROM AUTHOR]

The execution of metal hydride reactor (MHR) for storage of hydrogen is greatly affected by thermal effects occurred throughout the sorption of hydrogen. In this paper, based on different governing equations, a numerical model of MHR filled by MmNi 4.6 Al 0.4 is formed using ANSYS Fluent for hydrogen absorption process. The validation of model is done by relating its simulation outcomes with published experimental results and found a good agreement with a deviation of less than 5%; hence present model accuracy is considered to be more than 95%. For extraction or supply of heat, water or oil is extensively used in MHR during the absorption or the desorption process so as to improve the competency of the system. Since nanofluid (mixture of base fluid and nanoparticles) has a higher heat transfer characteristics, in this paper the nanofluid is used in place of the conventional heat transfer fluid in MHR. Further the numerical model of MHR is modified with nanofluid as heat extraction fluid and results are presented. The Al 2 O 3 /H 2 O, CuO/H 2 O and MgO/H 2 O nanofluids are selected and simulations are carried out. The results are obtained for different parameters like nanoparticle material, hydrogen concentration, supply pressure and cooling fluid temperature. It is seen that 5 vol% CuO/H 2 O nanofluid is thermally superior to Al 2 O 3 /H 2 O and MgO/H 2 O nanofluid. The heat transfer rate improves by the increment in the supply pressure of hydrogen as well as decrement in temperature of nanofluid. The CuO/H 2 O nanofluid increases the heat transfer rate of MHR up to 10% and the hydrogen absorption time is improved by 9.5%. Thus it is advantageous to use the nanofluid as a heat transfer cooling fluid for the MHR to store hydrogen. • Developed and validated numerical model of metal hydride reactor for hydrogen storage. • Selected various nanofluids for heat and mass transfer enhancement. • Presented performance for Al 2 O 3 /H 2 O, CuO/H 2 O and MgO/H 2 O nanofluid. • Reported 10% improvement in the heat transfer rate for CuO/H 2 O nanofluid. • Absorption time is lowered by 9.5% for given conditions. [ABSTRACT FROM AUTHOR]

The hydrogen storage phase of an energy storage plant based on metallic hydrides has a strong influence on the total efficiency of storage power plants as well as on their response time. The technique presented in this paper uses a hydrogen-metal chemical bond during its storage. This paper describes a metal hydride cylinder modeled and simulated by using the main quantities involved in the adsorption and desorption processes as well as in an analysis of the influence of thermal quantities involved in these processes. As a result, a proposal for automation of the thermal exchange of the modeled cylinder is presented and the possibilities of evaluation of this technique. [ABSTRACT FROM AUTHOR]

The paper investigates the samples of Ni–B and Ni–In composites in the form of films synthesized by an electrochemical method having a 3high degree of defectiveness and shows the electrochemical processes for their preparation, in which the experimental data of the influence doping additions of boron and indium on the hydrogen permeability of synthesized electrochemical complexes based on nickel Ni x -B y -H z and Ni x -In y -H z are given. It is shown that by creating traps (structural, impurity) for hydrogen by introducing additional elements into the metal structure or by changing the structure (intermetallides), also by other methods, the hydrogen solubility of the metal can be changed to a greater or lesser extent depending on the technical requirements. Ni–B samples were obtained in the sulfamate nickel electrolyte using boron compounds of the class of higher polyhedral borates Na 2 B 10 H 10. The use of nanoforming boron additives provides measured hydrogen content in Ni x -B y -H z samples about of 600 cm3/100 g. Nickel-indium composites were obtained by electrolytic deposition on copper substrates (0,05 mm thick), with electrolyte composition: NiSO 4 × 7H 2 O = 140 g/L; Na 2 SO 4 × 10H 2 O = 20 g/L; and In 2 (SO 4) 3 which concentration varied from 1 g/L to 12 g/L. Variations in the amount of In 2 (SO 4) 3 ensured the production of Ni–In composites with different component ratios. The obtained data made it possible to select the optimal mode of deposition of Ni–In plating in the In 2 (SO 4) 3 electrolyte. In order to determine the effect of each of the electrodepositing parameters on the properties of the samples, only one parameter varies: either the cathode current density or the concentration of indium in the electrolyte. The samples of different concentrations of In are synthesized and studied. Their phase composition was determined. X-Ray phase analysis reveals in the Ni–In composites synthesized from electrolytes with In 2 (SO 4) 3 concentration of more than 2 g/L, a phase corresponding to the intermetallide η-In 27 Ni 10. For the first time in the practice of studying sorption, electrochemical composites Ni x -In y , including subsequent thermal desorption of hydrogen, are studied by implanting deuterium into the samples. It is demonstrated spectra of deuterium thermal desorption from Ni 70 In 30 D x composites, which allowed determining the temperature ranges of desorption of ion-implanted deuterium depending on the dose of implantation. It is confirmed that a Ni 70 In 30 composite capable of retaining doped deuterium (hydrogen) has been obtained. It is shown that it is permissible to obtain samples of a Ni x -In y -D z composite with a deuterium content of up to 2 at. D/at. Met., that corresponds to 5,3 wt% (for composites of this composition). [ABSTRACT FROM AUTHOR]

Recently, there has been growing interest in multi-principal element alloys for hydrogen storage. However, most of the papers published so far report compositions based only on transition metal elements, which limit the gravimetric storage capacities due to their densities. Since Mg is a low-density element promising for hydrogen storage, the study of Mg-containing multi-principal element compositions is opportune. In the present work, we report for the first time the structural characterization and hydrogen storage properties of the A 2 B type MgTiNbCr 0.5 Mn 0.5 Ni 0.5 alloy and its derivative Mg 0.68 TiNbNi 0.55 alloy. These Mg-containing multi-principal element alloys form major BCC phase (W-type, Im 3 ¯ m) and major FCC hydride (MH 2 with CaF 2 -type structure) when synthesized by mechanical alloying (MA) and reactive milling (RM), respectively. Hydrogen is desorbed from both RM samples in two steps, with some overlap, from different hydrides formed during synthesis. The microstructure of the Mg 0.68 TiNbNi 0.55 composition is more homogeneous (less secondary phases), but both alloys present a total gravimetric capacity of around 1.6 wt% H 2. • Two new Mg-containing multicomponent alloys were investigated for hydrogen storage. • Multicomponent hydrides were synthesized directly via reactive milling. • In-situ synchrotron XRD showed a phase transition during hydrogen sorption. • Different hydrides were formed during synthesis. • The Mg 0.68 TiNbNi 0.55 alloy is suggested as a good candidate for hydrogen storage. [ABSTRACT FROM AUTHOR]

Abstract: Design of hydrogen storage systems aims at minimal weight and volume while fulfilling performance criteria. In this paper, the tubular tank configuration for hydrogen storage based on light weight hydrides is optimized towards its total weight using the predictions of a newly developed simulation model. Sodium alanate is taken as model material. A clear definition of the optimization is presented, stating a new optimization criterion: a defined total mass of hydrogen has to be charged in a given time, instead of prescribing percentages of the total hydrogen storage capacity. This yields a wider space of possible solutions. The effects of material compaction, addition of expanded graphite and different tubular tank diameters were evaluated. It was found that compaction of the material is the most influential factor to optimize the storage system. In order to obtain lighter storage systems one should concentrate on improving the ratio mass of hydride bed to mass of tank wall by screening lighter materials for the tank wall and developing hydrogen storage materials exhibiting both higher gravimetric and volumetric storage capacities. [Copyright &y& Elsevier]

Abstract: Small hybrid wind systems are capable of storing and supplying power for residential applications. In this paper, the excess wind energy is converted into hydrogen by electrolysis and is stored in a metal hydride. Metal hydride beds are known for their high volumetric capacity compared to the compressed hydrogen storage, and offers hydrogen storage at a reasonable operating temperature and pressure. A system simulation model is developed in Matlab/Simulink platform for the dynamics of the metal hydride hydrogen storage system, which is charged by the wind energy. The thermal loads of the metal hydride storage system is met by passing water at ambient temperature for cooling the bed while hydrogen is being absorbed. The effect of the transient turbulent wind velocity profile on the storage system is analyzed. The thermal management of the storage system plays an important role in the overall design, and hence it is discussed in detail. [Copyright &y& Elsevier]

Abstract: The major challenge of complex hydride for hydrogen storage is to release hydrogen at a moderate temperature with rapid kinetics. This paper reports a new composite system (NaBH4/ZnF2) to generate hydrogen at a low temperature below 100 °C. The NaBH4 and ZnF2 mixture was prepared by a mechanical milling in a 2:1 M ratio. Dehydrogenation of the mixture during a heating process shows that the initial dehydrogenation temperature was below 100 °C with favorable kinetics. The structural analysis confirmed the formation of NaBF4 and Zn in the reaction products. The study concerning the reaction mechanism reveals that ZnF2 plays a role of reagent rather than catalyst. The produced intermediate of NaZnF3, however, affects the decomposition of the emitted B2H6. This work suggests that the extension of the decomposition mechanism of NaBH4/ZnF2 composite system would favor the development of new catalysts for complex hydride systems. [Copyright &y& Elsevier]

Abstract: Two metal hydride containers were built at the laboratory respecting a simple and modular design for the purpose of getting useful knowledge about the similarity of elements of metal hydride containers relevant in the prediction of larger size storage unit behaviour. In this paper, we present a description of the containers and an investigation of the parameters influencing the hydrogen storage performance. [Copyright &y& Elsevier]

Abstract: On-board hydrogen storage systems employing high-pressure metal hydrides promise advantages including high volumetric capacities and cold start capability. In this paper, we discuss the development of a system simulation model in Matlab/Simulink platform. Transient equations for mass balance and energy balance are presented. Appropriate kinetic expressions are used for the absorption/desorption reactions for the Ti1.1CrMn metal hydride. During refueling, the bed is cooled by passing a coolant through tubes embedded within the bed while during driving, the bed is heated by pumping the radiator fluid through same set of tubes. The feasibility of using a high-pressure metal hydride storage system for automotive applications is discussed. Drive cycle simulations for a fuel cell vehicle are performed and detailed results are presented. [ABSTRACT FROM AUTHOR]

Abstract: MgH2 is one of the most promising hydrogen storage materials due to its high capacity and low cost. In an effort to develop MgH2 with a low dehydriding temperature and fast sorption kinetics, doping MgH2 with NiCl2 and CoCl2 has been investigated in this paper. Both the dehydrogenation temperature and the absorption/desorption kinetics have been improved by adding either NiCl2 or CoCl2, and a significant enhancement was obtained in the case of the NiCl2 doped sample. For example, a hydrogen absorption capacity of 5.17 wt% was reached at 300 °C in 60 s for the MgH2/NiCl2 sample. In contrast, the ball-milled MgH2 just absorbed 3.51 wt% hydrogen at 300 °C in 400 s. An activation energy of 102.6 kJ/mol for the MgH2/NiCl2 sample has been obtained from the desorption data, 18.7 kJ/mol and 55.9 kJ/mol smaller than those of the MgH2/CoCl2, which also exhibits an enhanced kinetics, and of the pure MgH2 sample, respectively. In addition, the enhanced kinetics was observed to persist even after 9 cycles in the case of the NiCl2 doped MgH2 sample. Further kinetic investigation indicated that the hydrogen desorption from the milled MgH2 is controlled by a slow, random nucleation and growth process, which is transformed into two-dimensional growth after NiCl2 or CoCl2 doping, suggesting that the additives reduced the barrier and lowered the driving forces for nucleation. [Copyright &y& Elsevier]

Abstract: In this paper, a novel 3D flexible tool for simulation of metal hydrides-based (LaNi5) hydrogen storage tanks is presented. The model is Finite Element-Based and considers coupled heat and mass transfer resistance through a non-uniform pressure and temperature metal hydride reactor. The governing equations were implemented and solved using the COMSOL Multiphysics simulation environment. A cylindrical reactor with different cooling system designs was simulated. The shortest reactor fill time (15min) was obtained for a cooling design configuration consisting of twelve inner cooling tubes and an external cooling jacket. Additional simulations demonstrated that an increase of the hydride thermal conductivity can further improve the reactor dynamic performance, provided that the absorbent bed is sufficiently permeable to hydrogen. [Copyright &y& Elsevier]

Abstract: This paper describes the direct synthesis of magnesium hydride (MgH2) nanofibers by hydriding chemical vapor deposition (HCVD), in which the effect of hydrogen pressure on the production rate, the composition and the shape of products obtained were examined by using X-ray diffraction (XRD), scanning electron microscopy (SEM) and Brunauer–Emmett–Teller (BET). The XRD patterns showed that the main product in each case was MgH2; in particular, the products formed at 2, 3 and 4MPa were highly pure. In contrast, at a hydrogen pressure of 1MPa, unhydrided Mg was deposited along with MgH2. The SEM images also revealed orientation of the as-deposited products; higher pressures of 3 and 4MPa caused the formation of straight and curved nanofibers, and lower ones of 1 and 2MPa, highly curved nanofibers and nanorods with a few straight nanofibers. With pressurizing hydrogen, not only the BET specific surface areas of the products but also the production rate increased. The results also appealed that HCVD could control the shape/size of MgH2 nanofibers by changing the pressure via only a single operation. [Copyright &y& Elsevier]

Abstract: This paper presents a heat transfer fin optimization for a LaNi5 hydrogen storage container. In this simplified approach, a one-dimension fin model is proposed in order to avoid geometrical restrictions and constrains associated to a particular technological solution. Therefore, the presented model can be utilized as a general framework for the development of containers with inner fins. The hydrogen absorption reaction was simulated using a developed finite difference method. On this base, the heat transfer fin design was optimized for different absorption times and container diameters applying the gradient method. Numerical outcomes were then confirmed by comparison with experimental measurements, showing good agreement between the theoretical model and the experimental result. [Copyright &y& Elsevier]

Abstract: The effect of Cu-doping on the hydrogen storage properties of Mg95Ni5Cu x (x =0, 0.5, 1, 2) prepared by hydriding combustion synthesis and mechanical milling (HCS+MM) was studied. For dehydriding properties, the dehydriding temperature onset decreases from 450K for Mg95Ni5 to 420K for Mg95Ni5Cu2. Additionally, the activation energy for dehydriding decreases from 116kJ/mol for Mg95Ni5 to 98kJ/mol for Mg95Ni5Cu2, indicating that the dehydriding reaction is activated by the catalytic effect of Cu. Moreover, the hydrogen absorption capacity of Mg95Ni5Cu2 at 373K in 100s increases from 0.95 to 4.16wt.% by MM pretreatment before HCS. The factors for the improvement of the hydrogen storage properties are discussed in this paper. [Copyright &y& Elsevier]