This work discusses the influence of different metal hydride storage bed configurations. The objective was to design and optimize a solid-state hydrogen storage for a nonpolluting mobility. A study of the absorption and desorption dynamics of a loose powder bed was performed first, followed by three different storage bed configurations: compacted Ti-Mn alloy powder, alternated Ti-Mn alloy compacts with stainless steel fins and compacted [Ti-Mn alloy/Stainless steel] powder mixture. A numerical model was developed to simulate the heat transfer and the hydrogen absorption and desorption rates. The alternation and compact mixture configurations gave better heat transfer efficiencies, absorption and desorption rates and increased hydrogen storage densities. Indeed, an efficient heat transfer (between the tank and its surrounding fluid), a tailored porosity of the metal hydride storage bed and the addition of high thermal conductivity materials allowed the overall storage performance to be improved. Thus, the required time for loading/unloading hydrogen was reduced drastically. The alternation configuration would offer the additional advantage of a simple, inexpensive and efficient recycling procedure.

In view of hydrogen based backup power systems or small-scale power2gas units, hydrogen storages based on metal hydrides offer a safe and reliable solution. By using Hydralloy C5 as suitable hydride forming alloy, the present tank design guarantees very simple operating conditions: pressures between 4 bar and 30 bar, temperatures between 15 degrees C and 40 degrees C and minimal efforts for thermal management in combination with fast and constant charging and discharging capabilities. The modular tank consists of 4 layers with 5 reactor tubes each that are filled with metal hydride-graphite composites of a diameter of 21 mm. Experiments show that each layer of this tank is able to desorb the desired amount of hydrogen for a fuel cell operation at electrical power of 160 W-el for 100 min reaching a utilization factor of 93% of the stored hydrogen at RC. Furthermore, the experimental results of modularity, increasing loads and the electric air ventilation are presented. (C) 2017 Elsevier B.V. All rights reserved.

This contribution shows the development of a micro fuel cell system based on the ceramic multilayer technology. All necessary components, like the hydrogen reservoir based on metal hydrides, the planar fuel cell stack, as well as all necessary micro valves were manufactured in ceramic multilayers. The target size of the system is similar to rechargeable lithium button cell batteries (CR2450) and can substitute these. By use of metal hydrides as hydrogen storage medium, a power density of up to 290 Wh / l can be achieved that exceeds the lithium battery (CR2450) by more than 50% in combination with extended operating temperatures and increased cycle stability. By the potential of miniaturization of the ceramic energy system and the scalability to the specific application dimensions and performance, completely new possibilities are offered as a long-term stable energy storage, for example, in the field of autonomous sensor systems for the Internet of Things (IoT).

Metal hydride composites (MHC), which consist of a primary hydrogen absorbing phase and secondary phases such as graphite, offer very high volumetric storage densities and operation dynamics compared to widely used metal hydride powder beds. Here, we report on the stress evolution of confined MHC during hydrogen ab- and desorption which is due to the lattice expansion of the hydrogen absorbing phase during hydrogen uptake. The stress development during hydrogenation was recorded in situ using a specially designed measuring cell. Influences of gas pressure, temperature and MHC geometry on the stress evolution were considered. In this regard, so-called pressure-stress-isotherms are proposed for the first time in thermomechanical analogy to pressure-composition-isotherms. Copyright (C) 2015, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.

Hydrogen solid-state storage in metal hydrides has attracted remarkable attention within the past decades due to their high volumetric storage densities at low operating pressures. In particular, recently emerged hydride-graphite composites (HGC) can enable a safe, reliable and very compact hydrogen storage solution for various applications. In this regard, only little is known about the activation behavior of such HGC, their cycle stability and degradation effects. Because of the high sensitivity to hydrogen, neutron imaging offers a distinctive approach to examine in operando reaction fronts, swelling effects and microstructural changes of hydrogen absorbing materials with high spatial and temporal resolution. In this contribution, a comprehensive analysis of various phenomena during activation and cycling of HGC based on a Ti–Mn hydrogen absorbing alloy and expanded natural graphite is reported for the first time. A neutron radiography and tomography set-up with a spatial resolution down to 7 μm was utilized allowing highest detection precision. During initial hydrogenation, regions with enhanced reactivity are observed which contradicts a theoretically expected homogeneous reactivity inside the HGC. These active regions grow with the number of hydrogenation-dehydrogenation cycles until the whole HGC volume uniformly participates in the hydrogen sorption reaction. With regard to long-term hydrogenation-dehydrogenation cycling, inhomogeneous swelling effects were observed from which essential conclusions for technical HGC-based tank systems can be derived.

Metal hydride composites (MHC) with expanded natural graphite (ENG) exhibiting enhanced thermal conductivity and reduced porosity compared to metal hydride powders can enable a reversible, compact and safe way for hydrogen storage.In this study, neutron imaging during cyclic hydrogenation was utilized to investigate the structural stability and the spatial-temporal hydrogen concentration of application-oriented MHC with 40 mm in diameter compared to a loose metal hydride powder. In particular, swelling and shrinking effects of a radially confined MHC which could freely expand upwards were studied. It was found that the loose powder bed was easily torn apart during dehydrogenation, which leads to increased thermal resistance within the hydride bed. In contrast, the thermal resistance between MHC and container wall was minimized since the initial gap closes during initial hydrogenation and does not reopen thereafter. Further cyclic hydrogenation caused MHC volume changes, i.e. an almost reversible swelling/shrinking (so-called "MHC breathing"). Moreover, neutron imaging allowed for the observation of reaction fronts within the MHC and the powder bed that are governed by the heat transfer. (C) 2015 Elsevier B.V. All rights reserved.

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 (R) 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. Copyright (C) 2015, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.

It is of high technical importance to consider the loading and unloading dynamics of hydride-based hydrogen storage tanks, which are mainly influenced by the heat and gas transfer properties inside the reaction bed. In this regard, hydride-graphite composites offer improved heat transfer properties and higher volumetric storage capacities compared to commonly used powder beds.In this contribution, we report on the cycle stability of densified hydride-graphite composites based on melt-spun Mg90Ni10. The results reveal superior heat conduction properties compared to loose Mg90Ni10 flakes. Furthermore, this work deals with the hydrogenation behavior of such composites and their evolution throughout cyclic hydrogenation. Cycles at different temperatures and hydrogen pressures were conducted. High gas permeability in radial direction and sufficient thermal conductivity in combination with a stable composite structure underline the potential of such composites for hydrogen storage applications with high un-/loading dynamics. Copyright (C) 2014, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.

The design of hydride-based hydrogen storage systems is non-trivial because numerous physical, chemical and engineering principles have to be considered. In particular, gas and heat transport properties of the hydride bed are crucial for a high-dynamic tank operation. Since most hydrides show low intrinsic heat conductivities, auxiliary materials or structures inside the reaction zone are beneficial. For that purpose, hydride-graphite composites with strong anisotropic thermal conductivities have been developed recently.Here, a comprehensive numerical model to simulate the dynamics of hydrogen storage tanks based on pelletized hydride-graphite composites is presented. Among other common characteristics it includes anisotropic thermal conduction properties, convective heat transport as well as local shrinkage and swelling effects in the hydride bed. For experimental validation, a room temperature AB(2)-type hydrogen storage alloy was used in form of alloy-graphite pellets whose specific materials parameters were experimentally obtained and implemented into the computer simulation. In view of the thermodynamic properties of the AB(2)-type alloy, a novel mathematical formalism was developed to describe realistic pressure-composition isotherms. The comparison of experimental and simulation results reveals a good agreement. Thus, the validated model allows predictive studies on tank design and operation scenarios. Copyright (c) 2013, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.

Determining the thermal conductivity is crucial whenever heat transfer issues are considered which play a major role in many technological applications. However, various materials are sensitive to oxygen or moisture and, therefore, cannot be examined with commonly used equipment under ambient conditions. Here, we present a novel approach which combines the inert requirements of ambient-sensitive specimens with the flash method in which the apparatus, a Netzsch LFA 447 NanoFlash®, is placed under ambient conditions. A new measuring cell with flash-transparent windows was constructed which resembles a gas-tight specimen chamber. This device can be easily adapted to other apparatuses based on the flash method. The thermal conductivities of reference materials in inert and ambient conditions were examined in a temperature range from 25 to 275 °C. In general an excellent agreement was found. Further, the usability of this special sample cell is demonstrated for the investigation of the thermal conductivities of two complex hydride systems which are important for solid-state hydrogen storage applications.

Complex hydrides are attractive candidates for solid-state hydrogen storage because of their high hydrogen storage capacities and moderate operation temperatures. However, the fast and efficient transport of reaction heat through the hydride bed is an unsolved problem clue to the low intrinsic heat conductivities of complex hydrides.Here, we report on increasing the effective thermal conductivities of a NaAIH(4)- and a LiNH2-MgH2-based material by admixing expanded natural graphite (ENG) up to 25 mass% and compaction with up to 400 MPa. Thermal conductivities in radial and axial direction, microstructure and phase fractions of these pellets were determined. With increasing ENG content the heat transfer characteristics of both systems were enhanced from less than 1 W m(-1) K-1 up to 38 W m(-1) K-1. The pelletized hydride-graphite composites can be processed easily and safely compared to loose powders. Further, they have increased volumetric storage capacities of up to 59g-H-2 l(-1) and 54g-H-2 l(-1) compared to the loose powders with 19 g-H-2 l(-1) and 18 g-H-2 l(-1) for the NaAlH4- and a LiNH2-MgH2-based material, respectively, and they are very suitable for a tubular hydride tank design due to anisotropic heat transfer characteristics. (C) 2012 Elsevier B.V. All rights reserved.

Hydrogen-based power systems require safe, efficient and robust hydrogen storage solutions. In this regard, metal hydrides become increasingly important because of their extremely high volumetric hydrogen capacity and their moderate operation pressures. The loading and unloading dynamics of hydride-based hydrogen tanks is mainly influenced by the intrinsic hydrogen sorption kinetics of the storage material as well as by the heat and gas transport properties of the hydride bed.In this contribution, pelletized composites of the room-temperature hydrogen storage material Hydralloy C5(2) (AB(2)-type) with expanded natural graphite (ENG) are discussed in view of high-dynamic hydrogen solid-state storage applications. Powdery Hydralloy C5(2) is blended with up to 12.5 wt.% ENG. The blend is pelletized at compaction pressures up to 600 MPa. The Hydralloy ENG pellets exhibit an increased effective thermal conductivity and provide an increased volumetric H-2 storage capacity compared to loose powders. The hydrogenation behavior at different temperatures and for various hydrogenation dehydrogenation cycles is discussed. Furthermore, the stability of the pellets throughout cyclic hydrogenation is evaluated. High gas permeability in radial direction and sufficient thermal conductivity in combination with a stable pellet structure underline the potential of Hydralloy ENG composites for hydrogen storage applications with high loading dynamics. (C) 2012 Elsevier B.V. All rights reserved.

Metal hydrides are suitable for the compact, efficient and safe storage of hydrogen. Considering hydride-based hydrogen storage tanks, the enhancement of the heat and gas transport properties of the hydride bed is crucial for increased (un-)loading dynamics of the tank.In this contribution, pelletized composites of different hydrogen storage materials (lithium amide, sodium alanate, magnesium hydride and transition metal hydride Hydralloy C5) with expanded natural graphite (ENG) are discussed. The materials were admixed with up to 25 wt.% ENG and compacted at compaction pressures up to 600 MPa. The resulting hydride-ENG pellets exhibit an increased effective thermal conductivity which can be tuned in a wide range. The pellets have an increased volumetric H-2 storage capacity compared to loose hydride powders. High gas permeability in radial direction and sufficient thermal conductivity (>10 W m(-1) K-1) in combination with a stable pellet structure indicate a high potential to use suchlike prepared hydride-ENG composites for hydrogen storage applications with high loading dynamics. Copyright (C) 2012, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.

In recent years, melt-spun magnesium alloys have attracted a lot of attention due to their excellent (de)hydrogenation characteristics resulting from their nanoscale crystal structure and the homogeneous distribution of minor catalyst phases. Besides reaction kinetics, the heat conductivity of the storage material is important to transfer the reaction enthalpies in a controlled manner. Due to the inferior heat conduction properties of magnesium hydride, composites containing melt-spun Mg90Ni10 flakes and expanded natural graphite (ENG) up to 25.5 wt.% have been examined. Mixtures of those starting materials were compacted to cylindrical pellets using compaction pressures up to 600 MPa. Investigations of thermal conductivities in radial and axial directions, microstructure and phase fractions were carried out upon all sets of specimens. The heat transfer characteristics were tuned in a wide range from 1 up to 47 W m(-1) K-1. Furthermore, cyclic (de-)hydrogenation was carried out upon the compacts showing a hydrogen uptake of up to 4 wt.%-H-2 within 10 min. During the hydrogen loading process, the Mg90Ni10-ENG pellets remained mechanically stable. (C) 2010 Elsevier B.V. All rights reserved.

Melt spun magnesium alloys that contain catalytically active constituents have become attractive hydrogen storage materials due to their ultra fine and homogeneous micro structure and their excellent (de)hydrogenation characteristics However their heat conduction properties have to be improved for practical applications For this purpose composites of melt spun magnesium alloys and expanded natural graphite (ENG) were examined in this work Melt spun flakes were mixed with different amounts of up to 25 5 wt % ENG These mixtures were compacted to cylindrical pellets using compaction pressures up to 600 MPa For comparison, pellets of pure magnesium hydride and ENG were equally processed All sets of specimens were investigated regarding their thermal conductivities in radial and axial direction, their microstructure and phase fractions It was found that the heat transfer characteristics can be tailored in a wide range e g the thermal conductivity of magnesium alloy ENG compacts were tuned from 1 up to 47 W m(-1) K-1 For the system MgH2 ENG the thermal conductivity can be adjusted from 1 up to 43 W m(-1) K-1 Therefore a hydrogen storage material with homogeneous heat transfer properties can be anticipated which only slightly depend on the hydrogenated fraction (C) 2010 Professor T Nejat Veziroglu Published by Elsevier Ltd All rights reserved