Hydrogen Storage Devices Research Articles

THE USE OF WIND-HYDROGEN UNINTERRUPTED POWER SUPPLY PLANT IN DIFFERENT CLIMATIC CONDITIONS

The paper presents the project of the autonomous power complex on the basis of wind-power plant and hydrogen module with a capacity in 3 kW with further replication to 50 kW and shows the possibilities of operation of the present plant in different climatic conditions of Russia: Siberia, the Far East, the Northern Caucasus, Krasnodar territory, and also for universal use in climatic zones of the Arctic and Antarctic, deserts of Africa and the isolated islands with typical destructive sea salt fogs.This paper carries out the study, comprehensive analysis and comparison of known types and classes of wind plants, as a result of which the authors have developed an innovative multi-tier scalable vertically-axial wind power plant. This unit is used as the main power source, the uninterrupted part of which is based on a cyclically operating hydrogen module, contains an electrolytic cell, a fuel cell system and a hydrogen storage device with a communication and control system. The components of the power plant developed by the authors’ team operate at a single DC voltage and can be connected to a common bus bar with an increase of power in this complex. Flexible control algorithms allow optimizing the operation of the power complex to reduce the start-stop frequency, thereby increasing both the service life and time intervals between maintenance. Remote control provides monitoring and management of electricity output processes and hydrogen storage with the help of Internet technologies in long-term modes.The study has shown that this equipment is long-lived, reliable and environmentally friendly, and the system is modular and flexible because it is easily scaled under consumer’s control including the personal power consumption and small business. Moreover, the developed power plant is accessible in purchase, mounting and operation for remote energy consumers as far as the assessed value of equipment is correlating with the cost of power line installation and the operation of equipment does not require large engineering and technological skills.

Photochemical Synthesis of Naked Palladium Nanoparticles

Palladium nanoparticles are widely used in catalysis, sensors, coatings and hydrogen storage devices. This paper reports the one-pot photochemical reduction of Pd(II) alcohol solutions into Pd0 nanoparticle suspensions. The synthesis involves the reduction of [PdCl4][Formula: see text] dissolved in EtOH/2-PrOH mixtures by the ketyl radicals (Me)2(HO)C[Formula: see text] generated from 254[Formula: see text]nm irradiation, in the absence of other chemical reducing agents. Clusters of [Formula: see text][Formula: see text]nm Pd0 particles thus produced could be separated from their suspensions by microfiltration. Preliminary tests are reported on the catalytic potential of such particles for the thermal dehydrogenation of alcohols.

Numerical simulation of the effect of aluminum foam on sorption induced wall strain in vertical, metal hydride based hydrogen storage container

Low thermal conductivity of metal hydride alloys significantly affects the sorption performance of hydrogen storage devices. Upon hydrogenation they also exert significant stresses on the containers due to volume changes and thermal cycling. Aluminum foam has been widely accepted as a means to enhance heat transfer and thereby improve sorption performance of metal hydride storage devices. In addition to this, such foams can also serve to homogenize the container strains. In this study, numerical simulation of the wall strain development upon hydrogenation of a vertically aligned metal hydride storage device is performed. The device contains LaNi5 as the storage alloy embedded with aluminum foam. Role of aluminum foam on hydrogenation and consequent development of wall strains is studied. Effect of controlled spatial variation of foam density as a means for strain reduction is also investigated.

Enhancement of band gap and evolution of in-gap states in hydrogen-adsorbed monolayer graphene on SiC(0001)

We have performed high-resolution angle-resolved photoemission spectroscopy (ARPES) on hydrogen-exposed monolayer graphene grown on SiC(0001). In the valence-band region, we observed the π and σ bands of graphene together with the buffer-layer bands, which hybridize with each other at specific momentum points. Upon hydrogen exposure, the ARPES-spectral intensity of buffer layer is reduced and the band hybridization is weakened, suggesting the intercalation of hydrogen atoms between graphene and buffer layer. On further hydrogen exposure, we observed the enhancement of the band gap accompanied with the evolution of in-gap states. These results are interpreted in terms of the partial transformation of C 2pz orbitals into the sp3 hybridized orbitals with covalent bonding between carbon and hydrogen atoms. The present results pave an important path toward feasible application of graphene-based hydrogen-storage devices.

Performance of a solid state hydrogen storage device with finned tube heat exchanger

In the present study, a cylindrical solid state hydrogen storage device embedded with finned heat exchanger is numerically investigated. The finned heat exchanger consists of two ‘U’ shaped tube and circular fins brazed on the periphery of the tubes. 1 kg of LaNi5 alloy is filled inside the device and 80 g of copper flakes is evenly distributed in between the fins to increase the overall thermal conductivity of the metal hydride. Water is used as heat transfer fluid. Absorption performance of the storage device is investigated at constant hydrogen supply pressure of 15 bar and cooling fluid temperature and velocity of 298 K and 1 m/s respectively. At these operating conditions, the required charging time is found to be around 610 s for a storage capacity of 12 g (1.2 wt%). The study is extended to examine the influence of different heat exchanger configurations based on number of fins, thickness of the fins, diameter of tubes, holes in fins, amount of copper flakes etc. An analysis for the same weight of the heat exchanger assembly has also been carried out by changing the number of fins at different thickness and pitch.

Numerical simulation of hydrogen desorption from high-density metal hydride hydrogen storage vessels

Metal hydride (MH) alloys are a promising type of material in hydrogen storage applications, allowing for low-pressure, high-density storage. However, while many studies are being performed on enhancing the hydrogen storage properties of such alloys, there has been little research on large-scale storage vessels which make use of the alloys. In particular, large-scale, high-density storage devices must make allowances for the temperature variations caused by the heat of reaction between hydrogen and MH alloys, which may impact the storage characteristics. In this study, we propose a numerical model for the design and evaluation of hydrogen storage devices using MH alloys. Hydrogen desorption reaction behavior for an alloy is observed in terms of temperature and reaction rate. This behavioral correlation is used as the basis for a comprehensive simulation model of the alloy system. Calculated results are found to be in good agreement with experimentally measured data, indicating that the model may be applied to multiple system geometries, scales, and alloy compositions.

Adsorption of H2 on Ga24N24 cluster; A density functional theory investigation

Molecular adsorption of hydrogen on Ga24N24 cluster is explored using Density Functional Theory. It is shown that the adsorption of H2 molecules on gallium atoms surface of the cluster is a quasi-molecular adsorption with Ead = −19.7 kJ mol−1, which is favorable for hydrogen-storage materials. This adsorption is nearly position-independent but is not dissociative. The natural bond orbital analysis, reduced density gradient scatter graphs as well as Fukui functions and density of states spectra confirm the weak interaction between σ-bonding electrons of H2 molecule with the gallium atom of the cluster. The results may open a window to new hydrogen-storage devices at moderate pressures.

Fluorine and sulfur simultaneously co-doped suspended graphene

Suspended graphene flakes are exposed simultaneously to fluorine and sulfur ions produced by the μ-wave plasma discharge of the SF6 precursor gas. The microscopic and spectroscopic analyses, performed by Raman spectroscopy, scanning electron microscopy and photoelectron spectromicroscopy, show the homogeneity in functionalization yield over the graphene flakes with F and S atoms covalently bonded to the carbon lattice. This promising surface shows potential for several applications ranging from biomolecule immobilization to lithium battery and hydrogen storage devices. The present co-doping process is an optimal strategy to engineer the graphene surface with a concurrent hydrophobic character, thanks to the fluorine atoms, and a high affinity with metal nanoparticles due to the presence of sulfur atoms.

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.

Experiments on solid state hydrogen storage device with a finned tube heat exchanger

The absorption and desorption performances of a solid state (metal hydride) hydrogen storage device with a finned tube heat exchanger are experimentally investigated. The heat exchanger design consists of two “U” shaped cooling tubes and perforated annular copper fins. Copper flakes are also inserted in between the fins to increase the overall effective thermal conductivity of the metal hydride bed. Experiments are performed on the storage device containing 1 kg of hydriding alloy LaNi5, at various hydrogen supply pressures. Water is used as the heat transfer fluid. The performance of the storage device is investigated for different operating parameters such as hydrogen supply pressure, cooling fluid temperature and heating fluid temperature. The shortest charging time found is 490 s for the absorption capacity of 1.2 wt% at a supply pressure of 15 bar and cooling fluid temperature and velocity of 288 K and 1 m/s respectively. The effect of copper flakes on absorption performance is also investigated and compared with a similar storage device without copper flakes.

Multiporous carbon allotropes transformed from symmetry-matched carbon nanotubes

Carbon nanotubes (CNTs) with homogeneous diameters have been proven to transform into new carbon allotropes under pressure but no studies on the compression of inhomogeneous CNTs have been reported. In this study, we propose to build new carbon allotropes from the bottom-up by applying pressure on symmetry-matched inhomogeneous CNTs. We find that the (3,0) CNT with point group C3v and the (6,0) CNT with point group C6v form an all sp3 hybridized hexagonal 3060-Carbon crystal, but the (4,0) CNT with point group D4h and the (8,0) CNT with point group D8h polymerize into a sp2+sp3 hybridized tetragonal 4080-Carbon structure. Their thermodynamic, mechanical and dynamic stabilities show that they are potential carbon allotropes to be experimentally synthesized. The multiporous structures, excellently mechanical properties and special electronic structures (semiconductive 3060-Carbon and semimetallic 4080-Carbon) imply their many potential applications, such as gases purification, hydrogen storage and lightweight semiconductor devices. In addition, we simulate their feature XRD patterns which are helpful for identifying the two carbon crystals in future experimental studies.

Si96: A New Silicon Allotrope with Interesting Physical Properties.

The structural mechanical properties and electronic properties of a new silicon allotrope Si96 are investigated at ambient pressure by using a first-principles calculation method with the ultrasoft pseudopotential scheme in the framework of generalized gradient approximation. The elastic constants and phonon calculations reveal that Si96 is mechanically and dynamically stable at ambient pressure. The conduction band minimum and valence band maximum of Si96 are at the R and G point, which indicates that Si96 is an indirect band gap semiconductor. The anisotropic calculations show that Si96 exhibits a smaller anisotropy than diamond Si in terms of Young’s modulus, the percentage of elastic anisotropy for bulk modulus and shear modulus, and the universal anisotropic index AU. Interestingly, most silicon allotropes exhibit brittle behavior, in contrast to the previously proposed ductile behavior. The void framework, low density, and nanotube structure make Si96 quite attractive for applications such as hydrogen storage and electronic devices that work at extreme conditions, and there are potential applications in Li-battery anode materials.

Reversible Activated Transport to Hopping Conduction Transition in Graphene Layers: Molecular Adsorption Induced Defect States

In this study, a transition from activated conduction mechanism to variable range carrier hopping conduction mechanism is observed on adsorption of H2, Ar and O2 molecules onto graphene layers in the temperature range from 173 K to 373 K. A fast switching (<100 s), recovery (<300 s), completely reversible behavior and lack of dependence on nature of the molecules show that physical adsorption of gas molecules results in appearance of defect states in the bandgap of graphene. These results provide further understanding of electrical conduction mechanism in graphene and are important for its applications in gas sensing and hydrogen storage devices.

Performance assessment of an integrated PEFC and an hydrogen storage device based on innovative material

Storage of hydrogen in solid materials has the potential to become a safe and efficient way to store energy, both for stationary and mobile applications. An integrated small scale system, integrating a small hydrogen tank, with a capacity of 18 cm3, and a 25 cm2 PEFC single cell, has been tested to assess the performance of an innovative hydrogen storage material based on manganese oxide anchored to a polymeric matrix having a hydrogen storage capacity of about 1 wt%. A Labview software application has been developed for data logging and control of the test set-up. Sorption process has been achieved by setting the charging time and recording pressure vs. time. The electrochemical tests were performed at 80 °C (PEFC cell temperature) and several discharge–charge cycles have been performed at different pressure and two discharge rates (i.e. 100 and 200 ml/min). The nominal power produced by the PEFC cell has been between 6 and 10 W, with an average discharge time of 400–500 s.

Long-term cycle stability of metal hydride-graphite composites

Recently, metal hydride composites (MHC) have been proposed which consist of a hydride forming metal alloy and a highly heat conduction secondary phase such as expanded natural graphite (ENG) in order to improve the thermal conductivity of metal hydride powder beds. However, only little data is available in the literature on the effects of extensive cycling on technically relevant properties of MHC.In this paper, hydrogenation characteristics, thermal conductivity and geometrical stability of Hydralloy® C5-based MHC were thoroughly investigated over 1000 cycles. The obtained results suggest that the MHC under study did not significantly alter their hydrogen uptake characteristics throughout cycling, despite the fact that their thermal conductivity decreased during the first 250 cycles but remained constant thereafter. Although the cylindrical MHC maintained their geometrical stability, radial cracks were detected after cycling. Based on these results, MHC are suitable for high-dynamic applications such as hydrogen storage or thermochemical devices.

Energy Exchange Between the Discrete Breathers in Graphane

Discrete breathers in graphane (fully hydrogenated graphene) are studied by the molecular dynamics method. It has previously been demonstrated that in graphane, there are discrete breathers in the form of single hydrogen atoms oscillating with the big amplitude in the direction perpendicular to the graphane plane with a frequency lying in the bandgap of the phonon spectrum. In this work, the possibility of the existence of longlived clusters of discrete breathers of different configurations is shown, their properties are studied, and the possibility of energy exchange between the discrete breathers in the cluster is demonstrated. These results are important for the discussion of physical processes occurring during dehydrogenation of graphane at high temperatures, which, in turn, is of great importance for the development of the hydrogen storage and transport devices based on sp2-carbon materials.

Effects of heat exchanger design on the performance of a solid state hydrogen storage device

Heat exchanger design plays a significant role in the performance of solid state hydrogen storage device. In the present study, a cylindrical hydrogen storage device with an embedded annular heat exchanger tube with radial circular copper fins, is considered. A 3-D mathematical model of the storage device is developed to investigate the sorption performance of metal hydride (MH). A prototype of the device is fabricated for 1 kg of MH alloy, LaNi5, and tested at constant supply pressure of hydrogen, validating the simulation results. Absorption characteristics of storage device have been examined by varying different operating parameters such as hydrogen supply pressure and cooling fluid temperature and velocity. Absorption process is completed in 18 min when these parameters are 15 bar, 298 K and 1 m/s respectively. A study of geometric parameters of copper fins (such as perforation, number and thickness of fin) has been carried out to investigate their effects on absorption process.

Numerical simulation of the parametric influence on the wall strain distribution of vertically placed metal hydride based hydrogen storage container

Metal hydride hydrogen storage alloys show significant thermal variations and dimensional non-homogeneity during their charge–discharge cycles. Pulverization, settling and agglomeration of these alloys and the consequent densification influence the rate of hydrogenation and wall strains on storage containers. In this study, numerical simulation of the wall strain distribution of a vertically placed hydrogen storage device is conducted with LaNi5 as the hydrogen storage alloy. The influence of salient parameters such as bed thickness, hydrogen supply pressure and coolant temperature on wall strains is studied with its already known effect on sorption performance. Effect of the densification of hydride particles during hydriding is also studied.

Synthesis of N-S Doped Graphene for Hydrogen Storage

Doping is a common and effective approach to tailor semiconductor properties. Theoretical studies predicted that doping graphene with nitrogen and sulphur can tailor its electronic properties and chemical reactivity. Hydrogen as an environment friendly fuel is a strong contender for fossil fuel based auto fuel. But the major stumbling block in realizing this is the risk involved in transporting hydrogen due to the risk of fire hazard owing to wider limits of in flammability. Hence, it is important to develop efficient hydrogen storage devices for storing and transporting hydrogen safely. Graphene in its original form do not have good hydrogen storage capacity but synthesized graphene are reported to be the best method for hydrogen storage since (Nitrogen–sulphur) doped graphene exhibit good electrical conductivity, long durability and high selectivity. CVD (Chemical vapour deposition)method is also considered one of the best method for synthesis of grapheme.

Thermal modeling of LmNi4.91Sn0.15 based solid state hydrogen storage device with embedded cooling tubes

A 2-D mathematical model is developed for predicting the minimum charging/discharging time of the metal hydride based hydrogen storage device by varying the number of cooling tubes embedded in it. This study is extended to 3-D mathematical model for predicting the hydriding and dehydriding characteristics of LmNi4.91Sn0.15 based hydrogen storage device with 60 embedded cooling tubes (ECT) using COMSOL Multiphysics 4.3. The performance of the hydrogen storage device during hydriding/dehydriding process is presented for different supply pressure (10–35 bar), hot fluid temperature (30–60 °C) and effective thermal conductivity of hydride bed (0.2–2.5 W/(m∙K)). It is observed that the rate of heat transfer and the hydriding and dehydriding rates are enhanced when the number of ECT is increased from 24 to 70. For the reactor with 60 ECT, the rate of hydrogen absorption is rapid for the supply pressure of 35 bar and hydride bed effective thermal conductivity of 2.5 W/(m∙K). The numerically predicted hydrogen storage capacity (wt%) and amount of hydrogen desorbed (wt%) are compared with experimental data and found a good accord between them.