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Summary The gravimetric hydrogen storage efficiency of silicon has been widely reported as 14 wt.%, suggesting that this material should be an excellent hydrogen generation source for portable applications. However, in the case of the reaction of silicon powder with 20 wt.% sodium hydroxide solution at 50 °C, the observed production of hydrogen fails to realize these high expectations unless a large excess of basic solution is used during the reaction, rendering the use of silicon in such systems uncompetitive compared with chemical hydride based technologies. By investigating the molar ratio of water:silicon from a large excess of water towards the stoichiometric 2:1 ratio dictated by the reaction equation, this study shows that for the reaction of silicon in 20 wt.% sodium hydroxide solution, the quantity of hydrogen produced decreases as the 2:1 ratio expected from the equation for the reaction is approached. Furthermore, in order to reach 80% of the theoretical efficacy, a molar ratio of 20:1, or 12 mL of 20 wt.% sodium hydroxide solution per gram of silicon, would be required. These results suggest that the actual gravimetric hydrogen storage capacity is less than 1%, casting doubts as to whether the use of silicon for hydrogen generation in real systems would be possible. © 2016 The Authors. International Journal of Energy Research published by John Wiley & Sons Ltd.

Deuterium desorption in an automotive-scale hydrogen storage tube was studied in-situ using neutron diffraction. Gradients in the concentration of the various alanate phases were observed along the length of the tube but no significant radial anisotropy was present. In addition, neutron radiography and computed tomography showed large scale cracks and density fluctuations, confirming the presence of these structures in an undisturbed storage system. These results demonstrate that large scale storage structures are not uniform even after many absorption/desorption cycles and that movement of gaseous hydrogen cannot be properly modeled by a simple porous bed model. Furthermore, the evidence indicates that there is slow transformation of species at one end of the tube indicating loss of catalyst functionality. These observations explain the unusually fast movement of hydrogen in a full scale system and shows that loss of capacity is not occurring uniformly in this type of hydrogen-storage system.

With the increasing use of hydrogen in energy process engineering and as chemical reactant, the importance of hydrogen sensors is rising. However, there are few established methods to measure the hydrogen concentration of a gas-mixture at high temperatures. Also the in situ measurement at these temperatures in chemical reactors is challenging. A sensor, which is based on hydrogen permeation, could be a cheap and practical solution for the in situ measurement at high temperatures. A permeation hydrogen sensor for the measurement of the hydrogen partial pressure was developed and built. The concept of the sensor is a small, hermetically sealed nickel tube working as a hydrogen permeable membrane filled with pure hydrogen. It is in contact with the measurement gas and connected to a pressure sensor. Under stationary conditions a equilibrium between the hydrogen partial pressure of the tube and the measurement gas will be established. Since the tube is filled only with hydrogen, the pressure sensor connected with the nickel-tube measures the hydrogen partial pressure of the measurement gas. Such a sensor was modeled, developed, built and characterized. The most important calculations, the general design of the sensor as well as the most important results of the experiments are presented in this paper. The sensor worked with a good accuracy and showed a response time of about 1000 s at 60 °C and 200 s at 900 °C. A response time lower than 200 s for temperatures above 600 °C is possible with an improved sensor design. Also, an in-situ measurement of the steam content inside a shift reactor was conducted, the results matched the calculated steam contents from a reactor balance very precisely.

The thermodynamics of three pathways of the hydrogen sulfide decomposition reaction is considered. In the thermal process, the gas-phase dissociation of hydrogen sulfide yields hydrogen and diatomic singlet sulfur. Over sulfide catalysts, the reaction proceeds via the formation of disulfane (H2S2) as the key surface intermediate. This intermediate then decomposes to release hydrogen into the gas phase, and adsorbed singlet sulfur recombines into cyclooctasulfur. Over metal catalysts, H2S decomposes via dissociation into surface atoms followed by the formation of gaseous hydrogen and gaseous triplet disulfur. The last two pathways are thermodynamically forbidden in the gas phase and can take place at room temperature only on the surface of a catalyst. An alternative mechanism is suggested for hydrogen sulfide assimilation in the chemosynthesis process involving sulfur bacteria. To shift the hydrogen sulfide decomposition equilibrium toward the target product (hydrogen), it is suggested that the reaction should be conducted at room temperature as a three-phase process over a solid catalyst under a layer of a solvent that can dissolve hydrogen sulfide and sulfur. In this case, it is possible to attain an H2S conversion close to 100%. Therefore, hydrogen sulfide can be considered as an inexhaustible source of hydrogen, a valuable chemical and an environmentally friendly energetic product.

The combination of unstable hydrogen storage materials with a high pressure tank provides a potential solution to on-board hydrogen storage system for fuel cell vehicles. However, none of the available solid-state materials can fulfill all the requirements. In this work, Zr Fe V-based alloys were systematically investigated for the possible use in such kind of hybrid storage devices. Among these alloys studied here, the composition (Zr0.7Ti0.3)1.04Fe1.8V0.2 shows the best overall properties with a reversible hydrogen capacity of 1.51 wt%, and a hydrogen desorption pressure of 11.2 atm at 0 °C. Besides, this alloy also shows excellent stability without obvious capacity loss even after 200 hydrogen absorption/desorption cycles. Calculated results show that the gravimetric density of the hybrid storage system combining a 35 MPa high pressure tank with (Zr0.7Ti0.3)1.04Fe1.8V0.2 alloy is 1.95 wt% when the volumetric density reaches 40 kg/m3.

An integration of CO2 -free hydrogen generation through methane decomposition coupled with hydrogen/methane separation and chemical hydrogen storage through liquid organic hydrogen carrier (LOHC) systems is demonstrated. A potential, very interesting application is the upgrading of stranded gas, for example, gas from a remote gas field or associated gas from off-shore oil drilling. Stranded gas can be effectively converted in a catalytic process by methane decomposition into solid carbon and a hydrogen/methane mixture that can be directly fed to a hydrogenation unit to load a LOHC with hydrogen. This allows for a straight-forward separation of hydrogen from CH4 and conversion of hydrogen to a hydrogen-rich LOHC material. Both, the hydrogen-rich LOHC material and the generated carbon on metal can easily be transported to destinations of further industrial use by established transport systems, like ships or trucks.

The Heatpipe Reformer provides an allothermal gasification process for the generation of hydrogen-rich synthesis gas. This synthesis gas can be used for generation of hydrogen for applications like fuel cells, engines, storage or the chemical industries. Conventional processes for hydrogen production involve CO Shift reactors to enhance hydrogen yield followed by hydrogen separation using gas scrubbing technology. The Institute of Energy Process Engineering (FAU-EVT) follows the approach to apply hydrogen permeable membranes as separation step directly in the reformer. This also allows higher hydrogen yields due to an additional shift of the gasification reactions to the product side as one product is continuously removed. This paper gives an overview on membranes in high temperature applications. It focuses on the temperature range from 750 to 900 °C required for biomass gasification processes. Existing approaches to high temperature hydrogen separation like palladium composite membranes or ceramic materials show advantages and disadvantages mainly regarding stability and prices. The presented approach applies commercial nickel capillary tubes as membranes. Vacuum increases the partial pressure difference between permeate and retentate. This remedies the need for a sweep gas, which is needed with all membranes that cannot withstand a physical pressure difference. In the experimental section several commercial nickel capillaries were tested for their hydrogen permeability and the results from a parameter study regarding the influence of synthesis gas components like CO, CH4 and H2O on permeation are shown. The nickel membranes were also tested in hydrogen containing H2S, which can be present in synthesis gas in concentrations of up to 1000 ppm.

The regularities of the effect exerted by gas molecules from the residual atmosphere in the vacuum chamber on the absorption characteristics of V 0.9 Ti 0.1 N x thin-film were investigated. It is shown that the open nanoporous structure actively absorbs not only the hydrogen molecules but also the larger molecules. The saturation with hydrogen at 20 °C leads to the reduction of absorption capacity of the material (no more than 3 wt.%) and the increasing of the temperature of hydrogen desorption (500 °C) are observed. High temperature (250 °C) of hydrogen saturation may reduce the temperature of desorption up to 275 °C and increase the gravimetric capacity to 7 wt.%. It is shown that the hydrogen in the porous nanocrystalline structures can be maintained both in the intergranular and interparticle pores and at grain boundaries and in not filled by nitrogen sites of V 0.9 Ti 0.1 N x grains. At that, the greatest amount of hydrogen is held just in the interparticle pores and vacant sites.

Hydrogen fuel provided via green method is renewable and environmentally friendly. However, the lack of practical storage methods has restricted its use to such an extent that hydrogen storage is currently a crucial obstacle in the development of a hydrogen economy. For mobile applications hydrogen storage system needs to be lightweight and compact. Current technologies such as compressed gas or liquefied hydrogen have severe disadvantages especially in volumetric terms compared to fossil fuels and the storage of hydrogen in light weight solids could be the solution to further enhances the energy density of hydrogen tanks. This article reveals overview of novel solid hydrogen storage materials, highlighting their main advantages and drawbacks.

Metal-organic frameworks (MOFs) are an emerging class of porous, crystalline materials with potential application as hydrogen storage media in fuel cell vehicles. Unlike lower capacity adsorbents such as zeolites and carbons, some MOFs are expected to degrade due to attack by impurities present in the hydrogen fuel stream. Hydrogen intended for use in fuel cell vehicles should satisfy purity standards, such as those outlined in SAE J2719. This standard limits the concentration of certain species in the fuel stream based primarily on their deleterious effects on PEM fuel cells. However, the impact of these contaminants on MOFs is mostly unknown. In the present study MOF-5 is adopted as a prototypical moisture-sensitive hydrogen storage material. Five “impure” gas mixtures were prepared by introducing low-to-moderate levels (i.e., up to ∼200 times greater than the J2719 limit) of selected contaminants (NH3, H2S, HCl, H2O, CO, CO2, CH4, O2, N2, and He) to pure hydrogen gas. Subsequently, MOF-5 was exposed to these mixtures over hundreds of adsorption/desorption pressure-swing cycles and for extended periods of static exposure. The impact of exposure was assessed by periodically measuring the hydrogen storage capacity of an exposed sample. Hydrogen chloride was observed to be the only impurity that yielded a measurable, albeit small, decrease in hydrogen capacity; no change in H2 uptake was observed for the other impurities. Post-cycling and post-storage MOF-5 samples were also analyzed using infrared spectroscopy and x-ray diffraction. These analyses reveal slight changes in the spectra for those samples exposed to HCl and NH3 compared to the pristine material. These measurements suggest that MOF-5 – and likely many other MOFs – exhibit sufficient robustness to withstand prolonged exposure to ‘off-spec’ hydrogen fuel.

A numerical model for a cryogenic adsorption hydrogen storage with enhanced heat distribution structure is presented and validated by experiments. The investigations cover charging, discharging and dormancy at cryogenic conditions. Metal foam was implemented as heat distribution enhancement structure. The prediction of the effective thermal conductivity, keff_foam, over the entire storage working range was carried out using an experimentally validated unit cell approach. An increase of keff_foam by +33% was observed by lowering the temperature from 295 K to 77 K, given keff_foam = 4.87 W/(m·K). The novel 2D axis-symmetric storage model developed applies two energy equations, one for the storage bed and one for the foam. Further, important thermal effects such as hydrogen isomer conversion were considered in the model. The storage model predictions were within the measurement uncertainties. A 95% storage filling was measured after 300 s charging. The enhanced heat transfer in the storage allowed highly transient charging. The volumetric and gravimetric storage capacity increased after 300 s charging by 21.5% and 9.3%, respectively. This behavior compensated for the volume and mass penalties for the implemented foam structure. However, further storage material improvements and a storage optimized heat distribution structure, including cooling fluid piping, are foreseen to meet overall storage requirements.

Summary Metal hydrides are considered as promising candidates for hydrogen storage as they exhibit higher energy densities than compressed gas storage storages. This study represents a theoretical thermodynamic analysis of metal hydride-based hydrogen storage systems, focusing mainly on the energy demand to operate the storage system and the resulting efficiency. The main energy demand occurs during hydrogen release. This energy demand is composed of three contributions: the heat required to heat the hydride up to desorption temperature, the heat of reaction and the work of compression to reach the targeted outlet pressure. A sensitivity analysis was performed to demonstrate the impact of several parameters, for example, heat of reaction and hydrogen uptake on the energy balance. The most influential parameter is the heat of reaction. The hydrogen uptake does not have a noticeable influence as long as it is not too low. Several possibilities to improve the efficiency of the storage system are discussed (heat integration and the application of a heat storage system). Heat integration can significantly improve the overall efficiency, whereas the application of a heat storage system does not seem realistic. Compared with other hydrogen storage technologies, metal hydrides can feature higher efficiencies than low-temperature hydrogen storage concepts, for example, liquefied or cryo-adsorbed hydrogen. The efficiencies of a metal hydride storage system are similar to those reached with a system based on liquid organic hydrogen carriers. Copyright © 2016 John Wiley & Sons, Ltd.

Hydrogen is considered as an environmental friendly energy carrier because it generates no pollution. Chlorides are promising catalyst for the hydrogen desorption in sodium alanate. All reactions and operations were performed under argon atmosphere in glove box. Crystalline NaAlH 4 and catalyst TiCl 3 , Nb 2 O 5 PbCl 2 and CeCl 3 were mixed in a ratio of (1, 2) wt%. Due to the air sensitivity of the samples they were covered with a kapton tape layer to minimize any contamination for characterization purpose. Structural characterizations and phase compositions of the samples were studied by XRD. The hydrogen storage capacity is measured by seivert type apparatus. Amount of desorbed hydrogen was found to be 3.6 wt % to 5.5 wt% at 250 °C with different type of catalyst. In the present work effect of doping of TiCl 3 , Nb 2 O 5 PbCl 2 and CeCl 3 catalysis in NaAlH 4 are investigated to understand the hydrogen desorption kinetics. It is concluded that enhanced storage capacity of NaAlH 4 can be achieved due to various catalysts with reduction in temperature 285 °C–250 °C for desorption.

Hydrogen is considered a potential future energy source. Among other applications of hydrogen, hydrogen-rich water is emerging as a new health care product in industrial areas. Water electrolysis is typically used to generate a hydrogen rich water system. We annealed 10AA carbon paper in air to use it as an electrode of a hydrogen rich water generator. Driven by annealing, structural changes of the carbon paper were identified by secondary electron microscope analysis. Depending on the various annealing temperatures, changes of the hydrophilic characteristics were demonstrated. The crystal structures of pristine and heat-treated carbon paper were characterized by X-ray diffraction. Improvement of the efficiency of the electrochemical oxygen evolution reaction was measured via linear voltammetry. The optimized annealing temperature of 10AA carbon paper showed the possibility of using this material as an effective hydrogen rich water generator.

In this article, we investigate the hydrogen storage capacity of Mg-decorated γ-graphyne (Mg-G) based on DFT calculations. Our results indicate that an external electric field can effectively prevent Mg atoms aggregating on γ-graphyne sheet. The Mg-G, after electric field (F = 0.05 V/nm) treatment, can store up to ten H 2 molecules and the hydrogen storage capacity is 10.64 wt%, with the average adsorption energy of 0.28 eV/H 2 . Our calculations demonstrate that Mg-G is a potential material for hydrogen storage with high capacity and might motivate active experimental efforts in designing hydrogen storage media.

A hydrogen storage medium, using a dehydrogenation reaction of naphthene in a membrane reactor, is proposed for fuel cell systems. In this system, the permeation rate of hydrogen is not high so that the residual hydrogen, not passing through the membrane, must be recovered. A gas-liquid separator and an adsorption column were evaluated. For the design of the separator, the hydrogen solubility has been already reported for aromatic hydrocarbon, naphthenes, and equimolar mixtures. In this study, adsorption on activated carbon was measured in hydrogen flow saturated with pure benzene, cyclohexane, methycyclohexane, and toluene, and the equimolar mixtures, benzene+cyclohexane and methycyclohexane+toluene. The measurement was carried out by a new apparatus specially designed for this study, based on a flow type method, and equipped with gas chromatograph with both FID and TCD. In the measurement, the breakthrough curve and the specific mass adsorbed were measured at 347 kPa and 303.15 K. The adsorption mechanism was also discussed based on the breakthrough curves for the pure adsorbates and mixtures. Finally, the required mass of adsorbate, activated carbon, was estimated for the system by assuming the reaction rate and the hydrogen permeation ratio in the membrane reactor.

International audience; The role of fundamental characteristics of porous systems (binding energy, specific surface area and multilayer adsorption) in designing an efficient hydrogen adsorbent is discussed. We analyze why the amount of hydrogen adsorbed in all known materials is much lower than required for mobile applications and what are possible strategies to increase it. Further we report new ab initio calculations demonstrating possible ways of chemical modification of graphene fragments which can lead to the substantial increase of hydrogen binding to the graphene-based surface. Such Open Carbon Frameworks, substituted and functionalized at the fragments' edge may theoretically adsorb, at ambient temperature and relatively low pressure (60-100 bar), the amount of hydrogen necessary for mobile applications.

In this work, a Mg-Al-Li solid solution was prepared and the influence of the preparation process on its hydrogen storage properties was investigated. The Mg17Al12 (Li) solid solution was obtained by sintering, annealing at liquid nitrogen temperature and mechanical ball milling using a molar ratio of Mg:Al:LiH = 6.5:1.5:2.0. The maximum hydrogen storage capacity of the Mg17Al12 (Li) solid solution reached 3.7 wt.% at 300 °C in 80 min. The enthalpy of the solid solution hydride decomposition was 53 kJ mol−1 H2, much lower than that of bulk Mg hydride decomposition (75 kJ mol−1 H2). The solid solution had higher hydrogen storage capacity and better hydrogen absorption kinetics than Mg17Al12 alloy.

Beryllium intermetallic compounds show a variety of excellent properties such as neutron multiplication, refractory function, hydrogen storage, and superconductivity. Be 12 M compounds (M = Ti, V, and Zr) have been investigated as neutron multipliers for fusion reactors, while Be 17 M 2 compounds have been explored as refractory materials. Furthermore, Be 2 Ms are known to have Laves phases, which are characterized by an A 2 B type compound having high H 2 gas storage potential. Because of its low density, the hydrogen properties of Be 2 Ms have attracted great interest from viewpoints of reactivity with H 2 O, trap site of hydrogen, and amount of H 2 gas in this compound. However, few studies have dealt with Be 2 M, and its database remains unsatisfactory. Preliminary synthesis of a beryllium intermetallic compound (=Be 2 Ti) as a hydrogen storage material was conducted to clarify its reactivity with water vapor at high temperatures and high hydrogen storage capacity. X-ray diffraction profiles and electron-probe microanalysis results confirmed that the preliminary synthesis of single-phase Be 2 Ti by homogenization treatment and plasma sintering was successful. The hydrogen generation rate of Be 2 Ti by reaction with 1% H 2 O increased as the test temperature increased. High temperature exposure to H 2 O led to the formation of TiO 2 on the surface. Furthermore, the hydrogen gas storage concentration of Be 2 Ti, evaluated using the pressure–concentration–temperature curve, was 0.56 wt.% (=0.125 H/M) at 298 K, which is relatively low considering that H 2 pressure was increased up to 13 MPa. Based on additional pressure–composition–temperature measurements, it does not appear to have particle size dependence with regard to hydrogen capacity. A simulation based on first-principles calculation indicated the presence of two hydrogen trap sites, tetrahedral and center of triangle with solution energies of −0.52 and −0.05 eV, respectively, implying that the maximum trap site of hydrogen with 5.4 wt.%. This dissimilarity might be attributed to the fact that the Be 2 Ti sample contained a large fraction of surface oxide layer, which disturbed the surface penetration of hydrogen.

Lithium is a material of choice for batteries, but it has also the potential to store energy with high density as a hydrogen storage material, i.e. via the formation of its hydride (LiH). However, the high thermodynamic stability of LiH has so far precluded the use of lithium as an effective hydrogen storage material owing the high temperature 700 °C for hydrogen release. Herein, we report on a novel method to enable the reversible storage of hydrogen with lithium under mild conditions of pressure (6 MPa) and temperature (350 °C). Through the catalytic hydrogenation of lithium, LiH particles were restricted to a few nanometres (

Hydrogen is a kind of promising clean energy with huge potential values for human being. Developing a convenient real-time and on-demand hydrogen production and utilization method is critical for its wide practices. Liquid metal was recently found to be able to easily activate aluminum in aqueous solution to continuously and quickly generate hydrogen at room temperature, and thus provides a straightforward hydrogen production way. To further improve this technology, we are dedicated here to investigate the effects of the container substrate on such hydrogen generation process. An interesting phenomenon was found that metal substrate material would evidently enhance the hydrogen generation rate. For conceptual illustration purpose, comparative experiments were conducted to demonstrate the different hydrogen evolution modes between the present method and former approach, and the enhancement mechanism lying behind was revealed. In addition, the influence of the surface roughness of the substrate on the hydrogen production performance was also clarified. The present finding would help motivate an improved extremely simple, straightforward and low cost way for the liquid metal assisted aluminum hydrogen production.

Porous materials have potential hydrogen storage properties. MOFs have been widely used because of porous, structural diversity, higher surface area and lower crystal density. Zr-based MOFs can be regarded as ideal hydrogen storage materials because of good thermal and chemical stability. Here we predicted the hydrogen storage properties of Zr-based MOFs (MOF-801, MOF-802, MOF-808, and MOF-841) at 77 K by means of GCMC method, mainly analyzed the adsorption isotherm and isosteric heat of H 2 in several Zr-based MOFs and explored the influence factors of hydrogen storage properties. The results showed that the isosteric heat was the factor of hydrogen storage at low pressures, while the surface area and porosity were the factors at high pressures. MOF-808 had a high mass and volume adsorption capacity both at low pressure and high pressure, which can be regarded as an ideal hydrogen storage material in the future.

Hydrogen production and toluene hydrogenation were performed with a hydrogen-permeable Pd–Ag membrane as a cathode by using permeated pure hydrogen produced from the electrolysis of aqueous potassium hydroxide. For hydrogen production, the hydrogen flow rate on the permeation side increased with temperature because of the increased hydrogen permeability of the palladium membrane. The increase in pressure applied to the electrolysis side from 0.1 MPa to 0.8 MPa enhanced hydrogen production and hydrogen permeation through the membrane by reducing the effects of bubble formation, and achieved a high hydrogen permeation yield of 93% at 373 K regardless of the amount of hydrogen produced. Hydrogenation of toluene with 5 wt% Pt/Al2O3 and with 0.8 MPa of pressure applied to the electrolysis side yielded methylcyclohexane as a product, and the conversion increased to 95% at 393 K with increasing contact time. This electrolysis system is effective for producing pure hydrogen and for hydrogenating aromatics to synthesize chemical hydrides.

The diffusion of hydrogen molecules adsorbed in a highly porous carbon aerogel has been studied with quasi-elastic neutron scattering. Hydrogen diffusion in this carbon substrate followed an activated jump process with a single activation barrier. The temperature dependence of the diffusion rate agrees well with previous results from activated carbons and other highly porous carbons. The carbon aerogel sample showed a strongly enhanced conversion between the ortho- and para-hydrogen spin states. The ortho-para conversion process, however, was inhibited for a fraction of the hydrogen molecules. This inhibition process is attributed to a rotational confinement of the hydrogen molecules at the nanometre scale.

Interest in hydrogen fuel is growing for automotive applications; however, safe, dense, solid-state hydrogen storage remains a formidable scientific challenge. Metal hydrides offer ample storage capacity and do not require cryogens or exceedingly high pressures for operation. However, hydrides have largely been abandoned because of oxidative instability and sluggish kinetics. We report a new, environmentally stable hydrogen storage material constructed of Mg nanocrystals encapsulated by atomically thin and gas-selective reduced graphene oxide (rGO) sheets. This material, protected from oxygen and moisture by the rGO layers, exhibits exceptionally dense hydrogen storage (6.5 wt% and 0.105 kg H2 per litre in the total composite). As rGO is atomically thin, this approach minimizes inactive mass in the composite, while also providing a kinetic enhancement to hydrogen sorption performance. These multilaminates of rGO-Mg are able to deliver exceptionally dense hydrogen storage and provide a material platform for harnessing the attributes of sensitive nanomaterials in demanding environments., Hydrogen fuel cell electric vehicles are poised to transform the automotive industry, but the lack of safe, high density solid state hydrogen storage solutions is stifling progress. Here, the authors develop a graphene oxide/magnesium nanocomposite which appears to overcome many of the existing challenges.

An enhanced 3-D numerical model, described in Part 1 [1] of this two part work, has been employed to study a metal-hydrogen storage system. In this manuscript we investigate the effect of varying the hydrogen in-flow rate and total amount of hydrogen inserted on the time taken to absorb/store the hydrogen and the temperature excursions. In addition, the ability to vary the temperature of the thermal management fluid has been used to examine the relative effect of a fixed fluid temperature and one which is hotter for desorption and colder for absorption. It was found that a shorter time and a greater amount of hydrogen injection to the tank leads to a higher driving pressure and, as a result, higher rate of absorption. This must be moderated by constraints such as the pressure rating of the tank. Furthermore, compared to using the same constant temperature thermal fluid for absorption and desorption, switching the fluid temperature between 283 K for absorption and 343 K for desorption leads to faster hydrogen cycling and more complete hydrogen desorption in the tank. However, a constant fluid temperature of 313 K gives a reasonable performance over the same time duration, without the additional energy expenditure associated with switching the fluid temperature.

Generation of electrical energy with renewable sources is interruptible due to the primary energy characteristics (sun, wind, hydro, etc.). In these cases, it is necessary to use energy storage so increasing penetrability of these sources connected to the distribution system. This paper discusses in details some equipment and accessories of an integrated power plant using fuel cell stack, electrolyzer and metal hydrides. During the plant operation were collected the power consumption data and established the efficiency of each plant component. These data demonstrated an overall efficiency of about 11% due to the low efficiencies of the commercial electrolyzers and power inverters used in the experiments.

The present communication deals with the hydrogen storage performance of ambient pressure dried pristine as well as platinum doped carbon aerogel (CA-0.10 Pt). These carbon aerogels (CAs) have been prepared from resorcinol-formaldehyde (R–F) through sol–gel synthesis route with sodium carbonate as a catalyst (C). The synthesis parameters adapted led to the formation of CA having preponderance of submicropores. Structural and microstructural characteristics of these carbon aerogels have been investigated through XRD, SEM, TEM, nitrogen adsorption and Raman spectroscopic techniques. Nitrogen adsorption and TEM studies confirm the large density of micropores with the majority of pores having sizes between 0.30 and 1.46 nm (submicropores). The hydrogen storage characteristics of as synthesized carbon aerogels have been investigated by monitoring the hydrogen ad/desorption curves. At room temperature and at pressure upto 22 atm the CA and CA-0.1 Pt have hydrogen storage capacity of 0.40 wt.% and 0.33 wt.% respectively. However, under the same pressure but at liquid nitrogen temperature CA and CA-0.10 Pt have hydrogen storage capacity of 5.65 wt.% and 5.15 wt.%. Feasible reasons for the high hydrogen storage capacities at liquid nitrogen temperature for the present CAs have been put forward.

The processes of hydrogen charging to and discharging from a 3-L cryogenic tank have been studied experimentally and numerically. This study investigated the impacts of factors such as mass flow rate, outlet opening time, bed density, and heating power on the hydrogen charging and discharging processes. For charging, it was found that the flow-through cooling technique could remove the adsorption heat in the process, but some issues such as channeling phenomenon and large thermal mass of the system need to be addressed. Low initial bed temperature is beneficial for hydrogen storage in terms of the efficiency of charging operation. When the bed density of metal organic framework-5 (MOF-5) is increased from 164 kg/m3 to 174 kg/m3, the total storage of hydrogen within the tank increases accordingly. It is found that pressure is the major factor that determines the storage of hydrogen, which increases significantly with the pressure within the tank. For discharging, high pressure in the storage tank can be used to release hydrogen for a certain period of time without heating. However, in order to maintain the desired hydrogen discharge rate, a heat source is eventually needed. This heat must be supplied in order to desorb the additional hydrogen from the system. To deal with the channeling phenomenon in the charging process, cyclic charging was tested and adopted.

By using a newly constructed bench-scale hydrogen energy system with renewable energy, ‘Pure Hydrogen Energy System’, the present study demonstrates the operations of a metal hydride (MH) tank for hydrogen compression as implemented through the use solar thermal energy. Solar thermal energy is used to generate hot water as a heat source of the MH tank. Thus, 70 kg of LaNi5, one of the most typical alloys used for hydrogen storage, was placed in the MH tank. We present low and high hydrogen flow rate operations. Then, the operations under winter conditions are discussed along with numerical simulations conducted from the thermal point of view. Results show that a large amount of heat (>100 MJ) is generated and the MH hydrogen compression is available.

Refueling of a single MOF-5 pellet with cryogenic hydrogen at moderate pressures is modeled in this work. A MOF-5 pellet in a discharged state is placed in a hydrogen atmosphere at refueling conditions of 80 K temperature and 30 bar pressure. The absolute adsorption isotherm for hydrogen on MOF-5 is described by the Unilan model, hydrogen is modeled as a real gas, and properties of the compressed MOF-5 pellet are obtained from polynomial fits to low temperature experimental data. Pellet properties change due to the addition of expanded natural graphite (ENG) and various levels of compaction. A parametric study is performed using COMSOL ® Multiphysics 4.2 to understand the effect of ENG and pellet compaction on refueling behavior of a single pellet. Specifically, the role of permeability and thermal conductivity, and the effect of anisotropic thermal conductivity are investigated using a two-dimensional axisymmetric model. The variation in pellet refueling time with varying pellet sizes is studied in order to determine the “optimal” pellet size for fast refueling. Results show that both stick-like geometry ( h / d ≫ 1) and flat hockey-puck geometry ( h / d ≪ 1) provide fast refueling. Conversely, pellets with h / d ≈ 0.5 show the longest refueling times and are therefore not recommended for use in a packed bed design.

An all-vanadium dual circuit redox flow battery is an electrochemical energy storage system capable to function as a conventional battery, but also to produce hydrogen and perform desulfurization when surplus of electricity is available by chemical discharge of the battery electrolytes. The hydrogen reactor chemically discharging the negative electrolyte has been designed and scaled up to kW scale, while different options to discharge the positive electrolyte have been evaluated, including oxidation of hydrazine, SO2 and H2S. The system is well suited to convert sulfur dioxide and hydrogen sulfide to harmless compounds while producing hydrogen, with overall system efficiencies from 50 to 70 % for hydrogen production.

Compressed hydrogen gas has been generated from water and iron powders via a hydrothermal method. As compared to the conventional steam–iron process, this process has the advantages of low temperature, simplicity, and high purity. Also, the direct generation of compressed hydrogen gas was favorable for its storage and utilization.

This paper, based on the analysis of possible ways of storage and transporting hydrogen, considers the construction of the device for power propulsion and vehicles. The functioning of the proposed device is to hydrogen generation by reacting the active metals, or their alloys, or metal hydrides with water in a polar aprotic organic solvent. From these products, it has been proposed to form the cartridges with internal through holes. Cartridges are placed in the hydrogen generator. The polar solvent is pumped through the hydrogen generator in which it does not react with the material of the cartridge. Water is added in this solvent in a controlled manner and used for the reaction with the cartridge material for hydrogen release. After separation of the liquid phase, hydrogen flows into the fuel system of the internal combustion engine. The spent solvent is pumped into the acceptance and storage system, and is replaced when changing the cartridge. The system can operate in a closed loop in the case organization of gathering and recycling of waste materials for reuse.

The reaction of water with hydrides (hydrolysis reaction) is very attractive for onsite hydrogen generation. Instead of using liquid water like in most cases, we demonstrate that hydrogen generation from hydrolysis reactions can also occur in the solid state. By simply heating mixtures of hydrated solids and hydrides, hydrogen generation is readily achieved through the recombination from the protonic hydrogen in the hydrated solids and the hydridic hydrogen in the hydride. The composites 5CaH2 + Na4P2O7·10H2O and NaBH4 + H2C2O4·2H2O give attainable gravimetric hydrogen storage capacity of 2.76% at 40 °C and 2.79% at 70 °C with rapid response, respectively. The dehydrogenation temperature can be controlled by the dehydration temperature of the hydrated solids. This innovative hydrogen generation approach provides a temperature activated, easy to control solution for onsite hydrogen generation.

When heat pipes are applied in atmospheres containing hydrogen, e.g. in presence of syngas, a small amount of hydrogen permeates through the wall of the containment into the heat pipe and accumulates as non-condensable at the end of the condenser. If the hydrogen is not removed during operation, this mechanism causes a rapid deactivation of the heat pipe starting from the condensation zone. This paper demonstrates the impacts of this deactivation on heat pipe operation and heat transfer rates and presents a formal description of the mechanism. Possible countermeasures to avoid this problem are presented and will be discussed, in particular the choice of safe operation conditions and the use of hydrogen windows based on metal membranes. The hydrogen deactivation was investigated both experimentally and theoretically. We will focus on the kinetics of the inactivation process as well as the equilibrium state when applying hydrogen windows for hydrogen removal. The results will be discussed in comparison with modelling approaches. The deactivation time from beginning of hydrogen sweep to complete inactivation of the heat pipe is in the range of 1–3 h. In the experiments a nickel hydrogen window was applied in a sodium heat pipe. With this measure the inactive length could be limited to 25–31% of the heat pipe length in hydrogen atmosphere.

Based on the density functional theory calculations, we predict that the Yttrium-dispersed capped-carbon nanotubes (CCNY) can serve as a high-capacity hydrogen storage material. The interaction of H2 molecules with the CCNT can be significantly enhanced upon decoration by Y atoms. The H2 molecules binding to the Y-CCNT system is similar to the Y–C60 system with a maximum of six H2 molecules per Y atom and an average binding energy of −0.48 eV, which is suitable for reversible hydrogen storage at ambient conditions. With six Y atoms located, the gravimetric density of the cap is found to be 7.51 wt%, thus exceeding the 6.5 wt% target of the U.S. Department of Energy.

In the present work, the high temperature (425–575 °C) hydrogen storage properties of Ti–V alloys have been studied, both at static conditions and in a flow of hydrogen gas. The selected isothermal temperature range is considered as an optimal condition for hydrogen sorption enhanced steam reforming. When hydrogenation and dehydrogenation were performed in pure hydrogen gas and in vacuum, a large reversible hydrogen capacity of 3.95 wt. % H was obtained, demonstrating completeness of the formation and decomposition of (Ti,V)-dihydrides. However, when cycling was performed in a flow of hydrogen gas, the reversible hydrogen capacity decreased to ∼2 wt. % H caused by the formation of stable lower (Ti,V)-hydrides. A further decrease in the reversible hydrogen storage capacity took place when pure hydrogen gas was replaced by a mixture of hydrogen and carbon monoxide CO. This decrease was caused by the formation of an oxygen rich layer on the surface of the alloy, which was partially blocking the hydrogen exchange between the surface and the bulk of the sample.

We have designed, developed and fabricated a volumetric apparatus for the measurement of adsorption isotherms. The proposed design minimizes the sources of systematic errors, which are mainly due to the calibration of inner volume of the apparatus, and the stability and uniformity of temperatures and pressures. Using the volumetric instrument, the amount of methane on various MOFs is measured. These results are represented in terms of the equilibrium and dynamic characteristics of methane adsorption on three well known metal–organic frameworks (MOFs), namely MIL-101(cr), HKUST-1 and MOF-F300. The apparatus allows us to evaluate methane adsorbate uptakes for the temperatures varying from 125 K to 298 K and pressures up to 10 bar. The acquired results are in good agreement with the values reported in the literature.

Current state-of-the-art methods consist of containing high-pressure compressed hydrogen in composite cylinders, with solid-state hydrogen storage materials an alternative that could improve on storage performance by enhancing volumetric densities. A new strategy that uses cryogenic temperatures to load hydrogen (cryocharging) is proposed and analysed in this work, comparing densities and final storage pressures for empty cylinders and containers with the high-surface area materials MIL-101 (Cr) and AX-21. Results show cryocharging as a viable option, as it can substantially lower the charging (at 77 K) and final pressures (at 298 K) for the majority of the cases considered. Kinetics are an equally important requirement for hydrogen storage systems, so the effective diffusivities at these conditions for both materials were calculated, and showed values comparable to the ones estimated in metal–organic frameworks and zeolites from quasielastic neutron scattering and molecular simulations. High-surface area materials tailored for hydrogen storage are a promising route for storage in mobile applications and results show that cryocharging is a promising strategy for hydrogen storage systems, since it increases volumetric densities and avoids energy penalties of operating at high pressures and/or low temperatures. Keywords: Hydrogen storage, Nanoporous materials, Hydrogen storage systems, Adsorption

International audience; A brief review of the different methods of hydrogen storage process for application in automobile manufacturing was presented and discussed. The hydrogen storage by adsorption on super activated carbon AX21 at various thermodynamic conditions wasinvestigated. In order to describe the reality of the system, we planned a brief review, adiscussion and modeling of the different EOS equations adapted to a hydrogen gas.Different characterization tools for obtaining the physical property of AX21 were used,among them SEM, BET and Helium displacement method at high temperature. Thehydrogen storage capacity of AX21 at different temperature and pressure up to 70 MPa was investigated experimentally. In order to describe the experimental hydrogen gas excess adsorption results, the model of Chilev and a modified potential theory were selected. The comparison of the two models describing adsorption isotherms and a critical discussion of their accuracy was given. Based on the models results the absolute amount adsorbed was obtained. The difference between an absolute and an excess amount adsorbed at 77 K and 293 K was discussed. A comparison between the volumetric tank capacity obtained by pure compression and the adsorption process at both temperatures were studied. The method of hydrogen storage and optimal operating conditions were investigated.

Solid-state hydrogen storage through the reversible formation of metallic hydrides is a key issue for the development of hydrogen as an energy vector. Herein we report the hydrogen storage performances of the KSiH3 phase ball-milled with NbF5 as a catalyst. The kinetics of hydrogen absorption/desorption are strongly enhanced by the addition of a catalyst as revealed by the large decrease of activation energies for both the absorption and desorption reactions. No disproportionation phenomenon is observed, indicating that the reaction between KSiH3 and KSi is perfectly reversible with a hydrogen storage capacity of 4.1 wt% H2. The thermodynamic properties of this KSi/KSiH3 equilibrium were investigated by plotting PCI curves from 90 °C to 130 °C: an enthalpy of 24.3 kJ mol−1 H2 and a low entropy change of 59.5 J K−1 mol−1 H2 are found. This low entropy variation is related to the high mobility of the H atoms in the α-KSiH3 phase as recently demonstrated by Quasi-Elastic Neutron Scattering (QENS) experiments.

A standalone hydrogen generator (SHG) has been developed based on chemical decomposition of water in heterogeneous compositions containing finely dispersed aluminum powder and crystallohydrates of sodium metasilicate. The kinetics of hydrogen generation has been studied depending on constants of the aluminum activation and oxidation rate, and aluminum and oxygen concentrations. In the hydrogen accumulation kinetics, the length of the induction period is determined by the concentration of oxygen. The SHG design, hydrogen selection and capacity are discussed. The availability and low cost of domestically manufactured chemical agents make the SHG a promising choice as the source of hydrogen for various applications, including nuclear power plants (NPP).

A nanocrystalline CeO2@C-containing NaAlH4 composite is successfully synthesized in situ by hydrogenating a NaH-Al mixture doped with CeO2@C. Compared with NaAlH4 , the as-prepared CeO2@C-containing NaAlH4 composite, with a minor amount of excess Al, exhibits significantly improved hydrogen storage properties. The dehydrogenation onset temperature of the hydrogenated [NaH-Al-7 wt % CeO2@C]-0.04Al sample is 77 °C lower than that of the pristine sample because of a reduced kinetic barrier. More importantly, the dehydrogenated sample absorbs ∼4.7 wt % hydrogen within 35 min at 100°C and 10 MPa of hydrogen. Compositional and structural analyses reveal that CeO2 is converted to CeH2 during ball milling and that the newly formed CeH2 works with the excess of Al to synergistically improve the hydrogen storage properties of NaAlH4. Our findings will aid in the rational design of novel catalyst-doped complex hydride systems with low operating temperatures, fast kinetics, and long-term cyclability.

Kinetic parameters of the process of thermal decomposition of the MgH2 hydride (obtained by the method of the mechanoactivation of magnesium in a hydrogen atmosphere) and of the commercial AlH3 hydride have been studied upon the rapid heating in the range of temperatures of 150–510°C at hydrogen pressures of 0–2 atm. The time dependences of the amount of hydrogen released by the metal hydrides at different temperatures and pressures have been determined. It has been shown that the activation energies of the hydrogen desorption are 135 kJ/mol for MgH2 and 107 kJ/mol for AlH3. The maximum rates of hydrogen desorption from the investigated metal hydrides have been established, and the temperatures and initial pressures that ensure the maximum rate and maximum volume of the hydrogen release have been determined.

In order to provide with novel composites with high specific surface area for hydrogen storage, FeNiCr-carbon composites were prepared by an alcohol chemical vapor deposition (ACCVD) method with methanol as a carbon source, wherein the abbreviation FeNiCr denoted powdery mixture of hydrogenated Fe, Ni and Cr. After the ACCVD synthesis, the composites were optionally ground to expose inner sorption sites. The peak temperature of hydrogen desorption from as-prepared FeNiCr-carbon composite hydrogenated at 653 K under 1.1 MPa of hydrogen was 723 K, as recorded by temperature programmed desorption (TPD). The peak temperature of hydrogen desorption from ground FeNiCr-carbon composite hydrogenated under the same conditions was as low as 423 K. HD molecules were detected by TPD, after the ground FeNiCr-carbon composite was similarly hydrogenated at 653 K under mixed H2 plus D2 gas. Such was also the case, after the ground composite was hydrogenated at room temperature. It was evidenced that atomic hydrogen took part in hydrogen sorption by the ground composite. The maximum hydrogen concentrations of the FeNiCr-carbon composites were 0.59 mass% and 1.16 mass%, before and after grinding, respectively, at 77 K under 0.77 MPa of hydrogen.

Hydrogen storage and transportation or distribution is closely linked together. Hydrogen can be distributed continuously in pipelines or batch wise by ships, trucks, railway or airplanes. All batch transportation requires a storage system but also pipelines can be used as pressure storage system. Hydrogen exhibits the highest heating value per weight of all chemical fuels. Furthermore, hydrogen is regenerative and environment friendly. There are two reasons why hydrogen is not the major fuel of toady’s energy consumption: First of all, hydrogen is just an energy carrier. And, although it is the most abundant element in the universe, it has to be produced, since on earth it only occurs in the form of water. This implies that we have to pay for this energy, which results in a difficult economic task, because since the industrialization we are used to consuming energy for free. The second difficulty with hydrogen as an energy carrier is the low critical temperature of 33 K, i.e. hydrogen is a gas at room temperature. For mobile and in many cases also for stationary applications the volumetric and gravimetric density of hydrogen in a storage system is crucial. Hydrogen can be stored by six different methods and phenomena: high pressure gas cylinders (up to 800 bar), liquid hydrogen in cryogenic tanks (at 21 K), adsorbed hydrogen on materials with a large specific surface area (at T < 100 K), absorbed on interstitial sites in a host metal (at ambient pressure and temperature), chemically bond in covalent and ionic compounds (at ambient pressure), oxidation of reactive metals e.g. Li, Na, Mg, Al, Zn with water. These metals easily react with water to the corresponding hydroxide and liberate the hydrogen from the water. Finally, the metal hydroxides can be thermally reduced to the metals in a solar furnace.

Hydrogen absorption is a crucial process in energy storage (microscopic or macroscopic) and management and here a porous organic cage (POC) material is shown to bind and release hydrogen when deposited directly onto a platinum electrode and immersed into aqueous electrolyte. Preliminary voltammetry experiments for the POC CC3 deposited onto a platinum disc electrode reveal uptake and release of hydrogen gas (probably coupled to water release and uptake, respectively) in the vicinity of the electrode. Significant pH effects on the rate of binding and release are reported and explained with a change in H2 binding rate. In future, “wet” POCs or POCs dispersed in aqueous solution could be employed for enhancing hydrogen capture/transport in energy applications. N.H. and J.I. thank MINICINN, Spain (projects CTQ2013-48280-C3-3-R and CTQ2016-76231-C2-2-R (AEI/FEDER, UE)) for financial support and the University of Alicante for support for a PhD exchange visit. J.-S.M.L., M.E.B., and A.I.C. thank EPSRC (EP/H000925/1) for financial support.