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Properties of the adsorbed hydrogen phase have been studied for hydrogen adsorption in three carbide derived carbons: SiC-CDC, steam/CO2 activated SiC-CDC and TiC-CDC. Using the excess hydrogen uptake isotherm at hydrogen pressures above 120 MPa where adsorption has finished, the adsorbate volume has been determined and the adsorbate density has been calculated at ambient temperatures. Absolute adsorption isotherms have been constructed by assuming the adsorbate volume is equivalent to the pore volume and is therefore constant. This study indicates that all three CDCs had the same maximum adsorbate density, with the adsorption proportional to the total pore volume.

Artículo escrito por un elevado número de autores, solo se referencian el que aparece en primer lugar, el nombre del grupo de colaboración, si le hubiere, y los autores pertenecientes a la UAM, Hydrides based on magnesium and intermetallic compounds provide a viable solution to the challenge of energy storage from renewable sources, thanks to their ability to absorb and desorb hydrogen in a reversible way with a proper tuning of pressure and temperature conditions. Therefore, they are expected to play an important role in the clean energy transition and in the deployment of hydrogen as an efficient energy vector. This review, by experts of Task 40 'Energy Storage and Conversion based on Hydrogen' of the Hydrogen Technology Collaboration Programme of the International Energy Agency, reports on the latest activities of the working group 'Magnesium- and Intermetallic alloys-based Hydrides for Energy Storage'. The following topics are covered by the review: multiscale modelling of hydrides and hydrogen sorption mechanisms; synthesis and processing techniques; catalysts for hydrogen sorption in Mg; Mg-based nanostructures and new compounds; hydrides based on intermetallic TiFe alloys, high entropy alloys, Laves phases, and Pd-containing alloys. Finally, an outlook is presented on current worldwide investments and future research directions for hydrogen-based energy storage

To calculate a gas sorption isotherm from measurements made using the manometric (Sieverts) technique requires accurate knowledge of the sample cell void volume, the volume able to be occupied by the free gas. For many combinations of material and morphology, this volume changes as the sample expands or compresses, swells, undergoes chemical change or adsorbs gas. For gas adsorption measurements on porous materials, the volume of the adsorbate is often accepted as the pore volume, and the adsorbate density changes as the material adsorbs. For materials exhibiting IUPAC type I isotherms, including many carbons, the uptake saturates at high pressures and additional information about the volume (adsorption space) and density of the adsorbate can be extracted at high pressure, provided adsorption has finished. For hydrogen, this typically requires cryogenic temperatures at pressures up to 10 MPa. In this work, hydrogen isotherms are conducted at pressures up to 200 MPa, in order to investigate the properties of the adsorbate at ambient temperatures. In addition, the manometric method gas uptake equations for absolute, excess and net isotherms are revisited and extrapolated to high pressure in order to extract information on the adsorbate volume and density, and enable the construction of the absolute isotherm.

Artículo escrito por un elevado número de autores, solo se referencian el que aparece en primer lugar, el nombre del grupo de colaboración, si le hubiere, y los autores pertenecientes a la UAM, Industrial and public interest in hydrogen technologies has risen strongly recently, as hydrogen is the ideal means for medium to long term energy storage, transport and usage in combination with renewable and green energy supply. In a future energy system, the production, storage and usage of green hydrogen is a key technology. Hydrogen is and will in future be even more used for industrial production processes as a reduction agent or for the production of synthetic hydrocarbons, especially in the chemical industry and in refineries. Under certain conditions material based systems for hydrogen storage and compression offer advantages over the classical systems based on gaseous or liquid hydrogen. This includes in particular lower maintenance costs, higher reliability and safety. Hydrogen storage is possible at pressures and temperatures much closer to ambient conditions. Hydrogen compression is possible without any moving parts and only by using waste heat. In this paper, we summarize the newest developments of hydrogen carriers for storage and compression and in addition, give an overview of the different research activities in this field

Efficient storage of hydrogen is one of the biggest challenges towards a potential hydrogen economy. Hydrogen storage in liquid carriers is an attractive alternative to compression or liquefaction at low temperatures. Liquid carriers can be stored cost-effectively and transportation and distribution can be integrated into existing infrastructures. The development of efficient liquid carriers is part of the work of the International Energy Agency Task 40: Hydrogen-Based Energy Storage. Here, we report the state-of-the-art for ammonia and closed CO2-cycle methanol-based storage options as well for liquid organic hydrogen carriers.

Zr3Fe and Ni-substituted Zr3Fe alloys with 30 and 50 at.% Ni were synthesized and their hydrogen absorption/desorption characteristics were compared experimentally (pressure–composition isotherms, thermal desorption spectroscopy, in-situ neutron diffraction) and by computational methods (ab-initio molecular dynamics (AMD), nudged elastic band theory (NEB)). All the alloys absorbed hydrogen to a hydrogen-to-metal atomic ratio of about 1.7, but the hydrides formed were stable at room temperature. The Zr3Fe0.5Ni0.5 alloy and its hydrided form were multi-phase. The Zr3Fe0.7Ni0.3 alloy was single-phase and retained the C m c m structure of the parent intermetallic. In-situ neutron diffraction with D2 in place of H2 showed that the hydride formed in the isotherm measurements, Zr3Fe0.7Ni0.3H6.88, had the same structure ( C m c m ) as Zr3FeH7, while disproportionation was observed in the hydrogenation of Zr3Fe. The kinetics of hydride formation was slower in both the Ni-substituted alloys. Thermal desorption spectroscopy showed that substitution of 0.3Ni significantly destabilized the hydride, lowering the temperature of the principal desorption peak by about 300 K relative to Zr3Fe–H2, without loss of hydrogen capacity, and avoiding disproportionation. Based on the structures determined by neutron diffraction, AMD and NEB calculations were conducted to compare Zr3Fe and Zr3Fe0.7Ni0.3 and their hydrides. The AMD calculations predicted that H diffusion was slower in Ni-substituted Zr3Fe, in agreement with the experimental observation of slower kinetics, implying a higher activation energy for H migration. The NEB calculations also predicted a higher energy barrier for H migration in Ni-substituted Zr3Fe.

An intrinsically microporous high surface area (772 m2 g–1) hexaazatrinaphthylene-based network polymer has been synthesized. Additionally, the material was postmodified via the introduction of palladium ions to determine the effect of metalation on the properties of the assembly. Both the unmodified as-synthesized and metal-modified polymers were characterized using elemental analysis, Fourier transform infrared spectroscopy, solid-state 13C cross-polarization-magic-angle spinning NMR spectroscopy, Brunauer–Emmett–Teller surface area analysis, X-ray photoelectron spectroscopy, X-ray diffraction analysis (XRD), small-angle X-ray scattering, and thermogravimetric analysis techniques. The hydrogen uptake capacities of these materials were determined for a wide range of pressures up to 2000 bar. The palladium functionalization changed the intermolecular chain distances in the polymer, enhanced the microporosity, and increased the hydrogen uptake at ambient temperature.

Hydrogen storage in nanoporous materials has been attracting a great deal of attention in recent years, as high gravimetric H2 capacities, exceeding 10 wt% in some cases, can be achieved at 77 K using materials with particularly high surface areas. However, volumetric capacities at low temperatures, and both gravimetric and volumetric capacities at ambient temperature, need to be improved before such adsorbents become practically viable. This article therefore discusses approaches to increasing the gravimetric and volumetric hydrogen storage capacities of nanoporous materials, and maximizing the usable capacity of a material between the upper storage and delivery pressures. In addition, recent advances in machine learning and data science provide an opportunity to apply this technology to the search for new materials for hydrogen storage. The large number of possible component combinations and substitutions in various porous materials, including Metal-Organic Frameworks (MOFs), is ideally suited to a machine learning approach; so this is also discussed, together with some new material types that could prove useful in the future for hydrogen storage applications.

Physisorption of hydrogen in nanoporous materials offers an efficient and competitive alternative for hydrogen storage. At low temperatures (e.g. 77 K) and moderate pressures (below 100 bar) molecular H2 adsorbs reversibly, with very fast kinetics, at high density on the inner surfaces of materials such as zeolites, activated carbons and metal–organic frameworks (MOFs). This review, by experts of Task 40 ‘Energy Storage and Conversion based on Hydrogen’ of the Hydrogen Technology Collaboration Programme of the International Energy Agency, covers the fundamentals of H2 adsorption in nanoporous materials and assessment of their storage performance. The discussion includes recent work on H2 adsorption at both low temperature and high pressure, new findings on the assessment of the hydrogen storage performance of materials, the correlation of volumetric and gravimetric H2 storage capacities, usable capacity, and optimum operating temperature. The application of neutron scattering as an ideal tool for characterising H2 adsorption is summarised and state-of-the-art computational methods, such as machine learning, are considered for the discovery of new MOFs for H2 storage applications, as well as the modelling of flexible porous networks for optimised H2 delivery. The discussion focuses moreover on additional important issues, such as sustainable materials synthesis and improved reproducibility of experimental H2 adsorption isotherm data by interlaboratory exercises and reference materials.

The hydrogen storage behaviour of a PIM-1–polyaniline nanocomposite was studied for the first time at both ambient and cryogenic temperature. The porosity of the polymers was investigated using nitrogen sorption measurements. A high BET surface area of 875 m2 g−1 was obtained for the synthesised PIM-1. Though the BET surface area decreased upon doping the PIM-1 with PANi, the mean micropore size decreased and micropore volume increased. Maximum excess hydrogen uptake capacities of 2.3 ± 0.5 wt% (298 K and 316 bar) and 6.5 ± 0.3 wt% (77 K and 110 bar) were demonstrated. These results are a significant improvement over the hydrogen uptake of either of the constituent polymers, and this has been attributed to a combination of the active sites present in polyaniline and the microporous nature of PIM-1.

A study of the effect of the ball-milling gas environment on the kinetic enhancement of MgH2 with different additives was conducted using argon and hydrogen. The as-sourced MgH2 was milled for 20 h and then milled for a further 2 h after adding 1–2 mol% of one of the additives titanium isopropoxide, niobium oxide or carbon buckyballs, varying the gas environment for both ball-milling stages. The milling environment had little or no effect on the desorption kinetics in most cases. However, in some cases, the absorption uptake differed by up to 2 wt%, depending on the gas used. This effect was not consistent among the composite samples surveyed, demonstrating the importance of reporting all information about the ball-milling processes used, including the gas environment.

A model has been developed for a metal-hydride tank for hydrogen storage, based on linked modular mathematical models in Simulink®. The objective of the work was a tank-level model suitable for incorporation into a whole-of-system model, implying modest computing demands and reduced complexity. Finite-element analysis was not used. Because the apparent kinetics of a practicable metal-hydride tank is dominated by heat flow originating in the enthalpy of hydrogen absorption/desorption, particular attention was paid to modelling the effective thermal conductivity, based on a detailed description of the thermal resistance between hydride particles. The model was tested against our own experimental data for a pair of tanks with 6.4 kg total hydrogen capacity, and compared with a published 2D model and published experimental data. In all cases, the new model performed very well. The incorporation of a physical model of the effective thermal conductivity means that the tank model can also be used as a research tool to investigate ways of improving tank performance by altering the physical characteristics of the metal-hydride itself to achieve an optimal thermal design and enhanced reaction kinetics.

Large photovoltaic arrays are becoming common as the world moves to replace fossil-fuelled electricity generators. As the array size and project cost increase, it becomes increasingly important to know accurately what the array’s performance will be before it is built. Large arrays inevitably contain modules with a spread of performance characteristics such as short-circuit current and open-circuit voltage, and suffer from temperature differences between modules. In this first study of these problems, a model has been developed that accurately predicts the behaviour of a photovoltaic array subject to variability between modules and inhomogeneity of cell temperature across the array. The model was applied to a real rooftop array consisting of 912 modules (298 kW nominal peak power). Based on measured string currents, the predicted average string temperature was compared the temperature measured by a radiometric survey using a drone-mounted IR camera and matched very well. The five-parameter model of cell I - V characteristics was fitted to manufacturer’s data, with highest weighting given to the region around the maximum-power point (MPP) where a real array should operate via active MPP tracking. The model was used to explore separately the effects of a spread in module characteristics arising in the manufacturing process and of temperature inhomogeneity across the array. The current in each module of a string was constrained to be the same, and the voltage of every parallel-connected string was also constrained to be the same. These constraints lead to greater power loss than is predicted based on an average module at an average temperature. Compared to a hypothetical array assembled from identical average modules at the same average temperature, variability caused a loss of power of about 2%, depending on the detailed form of the distribution function chosen to represent the spread of characteristics in the manufacturer’s tolerance band. As a rule of thumb, de-rating the maximum power to the lower end of the manufacturer’s tolerance band is recommended to account for module variability during the design phase. The effect of temperature inhomogeneity is more serious, because temperature affects V oc strongly, causing parallel-connected strings to be pulled away from their ideal operating points to obey the constraint of equal voltage. A modest 10 °C temperature gradient across the studied array was predicted to cause about a 4% loss of power at the MPP. Much higher real temperature differences could be expected in summer and were observed. The study confirmed that temperature inhomogeneity poses a serious design problem for large arrays, requiring careful thermal design to achieve not only acceptably low average array temperature, but also the least possible temperature spread.

An enhanced one-dimensional model has been developed for an alkaline electrolyser cell for hydrogen production, based on linked modular mathematical models in Simulink®. Where possible, the model parameters were derived on a physical basis and related to the materials of construction and the configuration of its components. This means that the model can be applied to many alkaline electrolyser cells, whereas existing semi-empirical models were generally developed for a specific cell. In addition to predicting the overall equilibrium electrolyser cell performance, the model is a powerful tool for understanding the contributions to cell voltage from the various internal components. It is thus useful as a guide to researchers aiming for improved performance through modified geometry and enhanced electrode materials. The model performed very well when compared to published models tested against the same sets of experimental data.

A high-pressure Sieverts apparatus, specifically designed to investigate carbon and other low-density materials for hydrogen storage, has been constructed and used to investigate potential storage materials for which the volume of the sample is uncertain or difficult to define. The apparatus can be managed from a computer via a graphical interface and used to measure gas sorption isotherms from 77 K to 873 K, utilising a computer driven piston pressure booster to compress the gas to 340 bar. Based on measurements of activated carbons and graphene-like samples, this article demonstrates the low sensitivity of the apparatus to uncertainty in the sample volume and the quality of data obtained for H2 adsorption isotherms measured at 296 K and 77 K at pressures up to 300 bar.

An in-situ neutron investigation of the spatial variation in hydride composition of LaNi5 after a single absorption pressure step was performed. Compositional inhomogeneities are formed due to the strong temperature gradients created by the rapid absorption process coupled with the pressure and temperature hysteresis of the metal–hydrogen interaction. The hydride fraction of LaNi5 in a cylindrical cell was mapped using the ENGIN-X stress/strain instrument and quantitative phase analysis performed using the Rietveld technique. The material was observed to preferentially absorb hydrogen close to the edges of the cell where heat transfer out of the material was more efficient. This spatial variation was maintained even after thermal equilibration. The experimental results are compared to predictions of a 3D multiphysics model solved by the software package COMSOL. The good agreement achieved demonstrates the suitability of this model for optimisation of metal hydride tank systems.

The effect of titanium isopropoxide (TTIP) on the kinetics of absorption and desorption of magnesium hydride was compared to the benchmark additive niobium oxide (Nb2O5). A systematic survey was performed for ball-milled MgH2 mixed with up to 2 mol% TTIP or Nb2O5 additive for different ball-milling times. It was found that TTIP was just as effective as Nb2O5 for the enhancement of the kinetics of absorption and desorption and that 0.5 mol% was sufficient. The TTIP composite sample had superior hydrogen capacity compared to the Nb2O5 composite sample. As TTIP is a liquid at room temperature, 30 min ball-milling with the magnesium hydride was sufficient time for mixing. Hand mixing the TTIP with MgH2 demonstrated excellent desorption kinetics but the absorption kinetics were poorer compared to ball-milling.

Mixed-matrix membranes containing synthesised nano-sized zeolite 4A and PVAc were fabricated to investigate the effect of zeolite loading on membrane morphology, polymer-filler interaction, thermal stability and gas separation properties. SEM studies revealed that, although the membranes with 40 wt % nano-sized zeolite particles were distributed uniformly through the polymer matrix without voids, the membranes with 15 wt % zeolite loading showed agglomeration. With increasing zeolite content, the thermal stability improved, the permeability decreased and the selectivity increased. The effect of silanation on dispersion of 15 wt % zeolite 4A nanoparticles through PVAc was investigated by post-synthesis modification of the zeolite with 3-Aminopropyl(diethoxy)methylsilane. Modification of the nanoparticles improved their dispersion in PVAc, resulting in higher thermal stability than the corresponding unmodified zeolite membrane. Modification also decreased the rigidity of the membrane. Partial pore blockage of the modified zeolite nanoparticles after silanation caused a further decrease in permeability, compared to the 15 wt % unmodified zeolite membrane.

There has been recent interest in polymers of intrinsic microporosity (PIMs) for solid-state hydrogen-storage materials; however, the gas-sorption properties and conditions for hydrogen uptake are relatively unexplored. PIM-1 has been synthesised using the condensation reaction between 3,3,3,3-tetramethyl-1,1-spirobisindane-5,5,6,6-tetraol and 2,3,5,6-tetrafluorophthalonitrile as precursors. The synthesised PIM-1 was annealed at different temperatures for varying times and then characterised for hydrogen uptake at both ambient and cryogenic temperatures. The excess hydrogen PCT isotherms have been measured to high pressure (320 bar) for the first time and the effect of different annealing conditions on the hydrogen capacity is reported.

The critical component of a proton exchange membrane fuel cell (PEMFC) system is the proton exchange membrane (PEM). Perfluorosulfonic acid membranes such as Nafion are currently used for PEMFCs in industry, despite suffering from reduced proton conductivity due to dehydration at higher temperatures. However, operating at temperatures below 100 °C leads to cathode flooding, catalyst poisoning by CO, and complex system design with higher cost. Research has concentrated on the membrane material and on preparation methods to achieve high proton conductivity, thermal, mechanical and chemical stability, low fuel crossover and lower cost at high temperatures. Non-fluorinated polymers are a promising alternative. However, improving the efficiency at higher temperatures has necessitated modifications and the inclusion of inorganic materials in a polymer matrix to form a composite membrane can be an approach to reach the target performance, while still reducing costs. This review focuses on recent research in composite PEMs based on non-fluorinated polymers. Various inorganic fillers incorporated in the PEM structure are reviewed in terms of their properties and the effect on PEM fuel cell performance. The most reliable polymers and fillers with potential for high temperature proton exchange membranes (HTPEMs) are also discussed.

An advanced PEM fuel cell mathematical model is described and realised in four ancillaries in the Matlab–Simulink environment. Where possible, the model is based on parameters with direct physical meaning, with the aim of going beyond empirically describing the characteristics of the fuel cell. The model can therefore be used to predict enhanced performance owing to, for instance, improved electrode materials, and to relate changes in the measured performance to internal changes affecting influential physical parameters. Some simplifying assumptions make the model fairly light in computational demand and therefore amenable to extension to simulate an entire fuel-cell stack as part of an energy system. Despite these assumptions, the model emulates experimental data well, especially at high current density. The influences of pressure, temperature, humidification and reactant partial pressure on cell performance are explored. The dominating effect of membrane hydration is clearly revealed.

The addition of transition metal nanoparticles to carbon nanostructures has been shown to increase the hydrogen storage capacity of carbon nanostructures by dissociating molecular hydrogen and allowing adsorption via chemical means, a process known as hydrogen spillover. This paper is an overview of experimental and theoretical studies on hydrogen storage on transition metal doped carbon nanostructures via the spillover mechanism and the prospects for achieving practical hydrogen storage targets. The most promising materials are found to be high surface area hexagonal system carbons for which the π-conjugation is broken by well dispersed oxygen functional groups or lattice dopants.

This review focuses on a new generation of polymers with intrinsic microporosity (PIMs) and their hydrogen storage applications. PIMs are a novel microporous material attracting attention due to their potentially useful functional properties. In this review, the methods of synthesis, suitable characterisation techniques and applications are briefly described. Importantly, the hydrogen capacity of PIMs that have been investigated recently is highlighted and the hydrogen uptake is compared to other microporous materials such as hypercrosslinked polymers (HCPs), metal organic frameworks (MOFs) and activated carbons. This review brings H2 storage-applicable PIMs that have been reported in different studies together for the first time, providing a reference for better comparison of H2 storage in PIMs.

We present an overview of hydrogen-containing superconductors, including metallic, cuprate, pnictide and carbon-based materials. Particularly in BCS-like superconductors, hydrogen introduces new phonon modes and these may lead to better or worse superconducting properties, with anharmonicity of the H potential being a decisive factor. The availability of the deuterium isotope, in addition to protium, makes hydrogen an extremely useful extra probe of mechanisms of superconductivity. While hydrogen modification has not so far led to any confirmed remarkable improvement in already existing metallic superconductors, hydrogen plays an important role in the synthesis of novel iron-based superconductors and as a substitutional impurity appears to increase the transition temperature. Most recently, a new record for the superconducting transition temperature of 203 K has been claimed for a metallic hydride under high pressure, H 2 S. We survey elemental hydrides and superconductors, discuss techniques for introducing hydrogen into materials, then review and summarise published knowledge about hydrogen-containing superconductors.

Metal hydrides, particularly those based on intermetallic alloys, are effective, safe and efficient for storage of hydrogen. While their low gravimetric energy density is unsuited to mobile applications, this is seldom a problem for stationary hydrogen storage. In this review we focus on developments in the newest AB3 class of intermetallic hydrides, in the context of a renewable energy system in which hydrogen is supplied at relatively low pressure and delivered to a fuel cell. AB3 alloys are of interest because their characteristics are roughly speaking intermediate between those of the long-established AB5 and AB2 types. AB3 alloys offer promise of coming closer to satisfying important performance criteria than do the classic types, through tuning of their hydrogen absorption characteristics. Modification of the nominal composition by element substitution, leading to structural changes affecting all hydriding properties, is the most effective approach. After establishing performance criteria for the present application, conventional elemental and alloy hydrides are briefly compared, followed by a comprehensive survey of research on AB3 hydrides and the opportunities to tune their performance.

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.

The complexity of the metal-hydrogen interaction and the critical role of thermal management in a metal-hydride storage tank necessitate comprehensive mathematical modelling before a suitable design can be chosen and subsequently implemented. Existing models have been analysed and integrated into an enhanced model which incorporates several features more suited to practical applications using an intermetallic metal-hydride tank. These include matching initial conditions of the model to physically achievable experimental conditions, the ability to vary the cooling system fluid temperature and realistic modelling of hydrogen injection and extraction from the tank as well as incorporating the non-ideal gas equation and modifying the equilibrium pressure and effective thermal conducting equation based on experimental data.

Metal-hydrides have been of great interest as one of the most promising materials for hydrogen storage applications. For widespread use, the most appropriate container and thermal management systems to minimise the time of absorption and desorption and maximise the amount of stored hydrogen must be designed. In recent years, many attempts have been made to identify the relationship between different operating and design variables and the resultant performance of metal-hydride systems. In this review, features of mathematical models of metal-hydride reactors including the assumptions, different applied equations and solution methods which have been developed in previous studies are presented. The evolution of the reactor geometries and configurations of cooling systems as well as different effective factors of metal-hydride performance are also discussed.

Palladium hydride was discovered more than 150 years ago and remains one of the most-studied interstitial metal hydrides because of the richness of its physical behaviours, which include ordered phases and anomalous properties at temperatures below 100 K, a superabundant-vacancy (SAV) phase with stoichiometry Pd3H4 formed at high temperature and pressure, and quenching of the enhanced Pauli paramagnetism of palladium. One of the most fascinating properties of palladium hydride is superconductivity at about 10 K without external pressure, in contrast to the newly-discovered polyhydride room-temperature superconductors that require megabar pressures. Moreover, the superconductivity exhibits an inverse isotope effect. Remarkably, modern first-principles approaches are unable to accurately predict the superconducting transition temperature by calculating the electron–phonon coupling constant within Migdal-Eliashberg theory. Anharmonicity of the hydrogen site potential is a key factor and poses a great challenge, since most theoretical approaches are based on the harmonic approximation. This review focuses on the electron and phonon band structures that underpin all such calculations, with palladium as a reference point. While the electron band structures of palladium and its monohydride are uncontroversial, the phonon band structure of palladium hydride in particular is problematic, with a realistic treatment of anharmonicity required – and largely yet to be achieved – to reproduce the results of inelastic neutron scattering experiments. In addition to the monohydride and SAV phases, possible higher hydrides are surveyed and the origin of the famous “50-K” anomaly in specific heat and other physical properties is critically reviewed.

Metal hydrides are known as a potential efficient, low-risk option for high-density hydrogen storage since the late 1970s. In this paper, the present status and the future perspectives of the use of metal hydrides for hydrogen storage are discussed. Since the early 1990s, interstitial metal hydrides are known as base materials for Ni – metal hydride rechargeable batteries. For hydrogen storage, metal hydride systems have been developed in the 2010s [1] for use in emergency or backup power units, i. e. for stationary applications. With the development and completion of the first submarines of the U212 A series by HDW (now Thyssen Krupp Marine Systems) in 2003 and its export class U214 in 2004, the use of metal hydrides for hydrogen storage in mobile applications has been established, with new application fields coming into focus. In the last decades, a huge number of new intermetallic and partially covalent hydrogen absorbing compounds has been identified and partly more, partly less extensively characterized. In addition, based on the thermodynamic properties of metal hydrides, this class of materials gives the opportunity to develop a new hydrogen compression technology. They allow the direct conversion from thermal energy into the compression of hydrogen gas without the need of any moving parts. Such compressors have been developed and are nowadays commercially available for pressures up to 200 bar. Metal hydride based compressors for higher pressures are under development. Moreover, storage systems consisting of the combination of metal hydrides and high-pressure vessels have been proposed as a realistic solution for on-board hydrogen storage on fuel cell vehicles. In the frame of the “Hydrogen Storage Systems for Mobile and Stationary Applications” Group in the International Energy Agency (IEA) Hydrogen Task 32 “Hydrogen-based energy storage” different compounds have been and will be scaled-up in the near future and tested in the range of 500 g to several hundred kg for use in hydrogen storage applications, The research for the lab-scale compressor is part of the activities of SCCER HaE, which is financially supported by Innosuisse - Swiss Innovation Agency . The authors thank the Alexander von Humboldt Foundation in the frame of the post-doctoral fellowship of Dr. J. Puszkiel (No. 1187279 STP ) as well as the European Union for their funding of projects STORHY (contract Nr. SES6-CT-2004-502667 , FP6-2002-Energy-1, 6.1.3.2.2), NESSHY (contract Nr. 518271 , FP6-2004-Energy-3, 6.1.3.2.2) and the EU Horizon 2020 /RISE project HYDRIDE4MOBILITY. Financial support from the S02 and KP8 S05), the European Union's Seventh Framework Programme ( FP7/2007e2013 ) for the Fuel Cells and Hydrogen Joint Technology Initiative under grant agreement no. 256653 (SSH2S), from the European Fuel Cells and Hydrogen Joint Undertaking in the framework of BOR4STORE (Grant agreement no. 303428 ), from the Australian Research Council for grants LP120101848 , LP150100730 , and LE0989180 , The Innovation Fund Denmark (project HyFill-Fast), DST within Hydrogen South Africa/HySA programme (projects KP3 National Research Foundation/NRF of South Africa , incentive funding grant number 109092 and the Research Council of Norway (project 285147 ) is thankfully acknowledged

An enhanced model of a PEM electrolyser cell is presented, based on linked modular mathematical models of the anode, cathode, membrane and cell voltage. In addition to predicting the overall equilibrium electrolyser cell performance, based on parameters related to the materials of construction and the configuration of its components, the model is a powerful tool for exploring control strategies and understanding the contributions to cell voltage from the various internal components as a guide to researchers aiming for improved performance.

Magnesium hydride remains an attractive hydrogen storage material due to the high hydrogen capacity and low cost of production. A high activation energy and poor kinetics at practical temperatures for the pure material have driven research into different additives to improve the sorption properties. This review details the development of catalytic additives and their effect on the activation energy, kinetics and thermodynamic properties of magnesium hydride.

A systematic survey of the catalytic effect of up to 10 wt% C 60 carbon buckyballs on the kinetics of hydrogen desorption and subsequent absorption of magnesium hydride has been made. It was found that there was an optimum amount of C 60 additive for the best desorption kinetics as well as an optimum time of ball-milling, improving the desorption kinetics over that of ball-milling alone. A comparison with the additive Nb 2 O 5 under the same conditions indicated that desorption kinetic enhancement was relatively minor. The subsequent absorption kinetics were always poorer than the un-catalysed samples.

An in-situ structural study of three Mg–Zn samples with nominal composition Mg0.9963Zn0.0037, Mg0.89Zn0.11 and Mg0.73Zn0.27 was performed using neutron diffraction to investigate what phases are formed during the hydrogen absorption process. It was found that at the temperatures needed for reasonable kinetics, a Mg–Zn liquid phase was present. This aspect of the reaction mechanism has not been revealed by previous ex-situ investigations in the literature. The only hydride formed was tetragonal MgH2. No Mg–Zn–H hydride phase was found and the Zn did not appear to play any part in the reaction.

This work focused on the high pressure PCT and in situ neutron powder diffraction studies of the LaMg 2 Ni 9 -H 2 (D 2 ) system at pressures up to 1,000 bar. LaMg 2 Ni 9 alloy was prepared by a powder metallurgy route from the LaNi 9 alloy precursor and Mg powder. Two La 3−x Mg x Ni 9 samples with slightly different La/Mg ratios were studied, La 1.1 Mg 1.9 Ni 9 (sample 1) and La 0.9 Mg 2.1 Ni 9 (sample 2). In situ neutron powder diffraction studies of the La 1.09 Mg 1.91 Ni 9 D 9.5 (1) and La 0.91 Mg 2.09 Ni 9 D 9.4 (2) deuterides were performed at 25 bar D 2 (1) and 918 bar D 2 (2). The hydrogenation properties of the (1) and (2) are dramatically different from those for LaNi 3 . The Mg-containing intermetallics reversibly form hydrides with DH des = 24.0 kJ/mol H2 and an equilibrium pressure of H 2 desorption of 18 bar at 20 °C (La 1.09 Mg 1.91 Ni 9 ). A pronounced hysteresis of H 2 absorption and desorption, ~100 bar, is observed. The studies showed that LaNi 5 -assisted hydrogenation of MgNi 2 in the LaMg 2 Ni 9 hybrid structure takes place. In the La 1.09 Mg 1.91 Ni 9 D 9.5 (1) and La 0.91 Mg 2.09 Ni 9 D 9.4 (2) (a = 5.263/5.212; c = 25.803/25.71 Å) D atoms are accommodated in both Laves and CaCu 5 -type slabs. In the LaNi 5 CaCu 5 -type layer, D atoms fill three types of interstices; a deformed octahedron [La 2 Ni 4 ], and [La(Mg) 2 Ni 2 ] and [Ni 4 ] tetrahedra. The overall chemical compositions can be presented as LaNi 5 H 5.6/5.0 + 2*MgNi 2 H 1.95/2.2 showing that the hydrogenation of the MgNi 2 slab proceeds at mild H 2 /D 2 pressure of just 20 bar. A partial filling by D of the four types of the tetrahedral interstices in the MgNi 2 slab takes place, including [MgNi 3 ] and [Mg 2 Ni 2 ] tetrahedra.

Bulk graphene was prepared by the method of magnesium combustion in a CO 2 atmosphere, producing large quantities of material which had a different morphology and importantly, a more ordered carbon lattice than reduced graphene oxide and other bulk graphene synthetic methodologies. Despite a low surface area of 235.5 m 2 /g and ca 9 at.% of magnesium and its oxides which do not contribute to hydrogen adsorption, we observe 0.85 wt.% of H 2 at 65 bar and 77 K, and 0.9 wt.% of H 2 at 300 bar and 293 K. As this methodology readily produces many-gram quantities with cheap starting materials, we anticipate that with further enhancements to the synthetic methodology, improving both surface area and reducing reaction by-products, this material will provide a robust platform for further H 2 adsorption investigations.

A full analysis of the uncertainties in the calculation of the amount of gas absorbed or desorbed by a sample using the gravimetric technique has been made. The gravimetric technique provides a near direct measurement of the uptake of gas by continuously measuring the weight of the sample plus absorbed gas and is frequently used to characterise the uptake of hydrogen in potential hydrogen storage materials. These calculations provide the capability to determine the uncertainty in the final gas uptake measurement given knowledge of the measurement uncertainties. Uptake of hydrogen gas on activated carbon has been modelled to allow individual constants such as the buoyancy volumes as well as measurement uncertainties to be changed while determining the effect on the uptake uncertainty. The measurement uncertainties critical to minimising the overall uptake uncertainty have been identified and a comparison with another popular gas uptake method, the Sieverts technique, has been made.

The Sieverts technique is a popular method of measuring the uptake of gas on a sample and is an important tool for the characterisation of hydrogen uptake by potential hydrogen storage materials. An analysis of the consequences of errors in the calibration of volumes in this technique has been made using hydrogen absorption on an AB2 alloy as an example. Trends in the error in the uptake as a function of errors in the volumes have been explained in terms of the equations for uptake. Significant advantages are found for calibration techniques for which the ratio of volumes is an intrinsic measurement.

The Mg–Si–H system is economically favorable as a hydrogen storage medium for renewable energy systems while moving toward sustainable energy production. Hydrogen desorption from MgH2 in the presence of Si is achievable, forming magnesium silicide (Mg2Si). However, absorbing hydrogen into Mg2Si remains problematic due to severe kinetic limitations. The objective of this study is to reduce these kinetic limitations by synthesizing Mg2Si nanoparticles to limit the migration distance for magnesium atoms from the Mg2Si matrix to produce MgH2 and Si, thus improving the reversibility of the Mg–Si–H system. Mg2Si nanoparticles were synthesized using a reduction reaction undertaken by solid–liquid mechanochemical ball milling. Particle size was controlled by adding a reaction buffer (lithium chloride) to the starting reagents to restrict particle growth during milling. The reaction buffer was removed from the nanoparticles using tetrahydrofuran and small-angle X-ray scattering revealed an average Mg2Si particle s...

An analysis of the uncertainties in the calculation of the amount of gas absorbed or desorbed by a sample has been made for the manometric or Sieverts technique, commonly used for the determination of hydrogen uptake on potential hydrogen storage materials. The analytical derivations provide a means to calculate the uncertainty in each step of a hydrogen absorption isotherm. In addition, a Sieverts system is modelled to allow a detailed investigation of the effect of volumes and other parameters as well as the relative impact of the different measurement uncertainties. Reliable uncertainty estimates are especially important for authoritative measurements of gas uptake by carbons and other nanostructured materials used for hydrogen storage.

The hydrogen cycled (H) planetary milled (PM) NaAlH4 + xM (x TiN > TiC > Ti, with rapid hydrogenation kinetics of ca. 23 wt.% H/hour for TiO2 enhanced NaAlH4, equivalent to TiCl3 enhanced NaAlH4. The TiN and TiC are partially reduced by ca. 7 and 22% respectively, and the TiO2 is completely reduced. The location of the reduced Ti cannot be discerned by X-ray diffraction at these minor proportions.

We have studied the complex decomposition mechanism of cubic γ-Mg(BH4)2 (Ia3d, a = 15.7858(1) A) by in-situ synchrotron X-ray diffraction, temperature-programmed desorption, visual observation of the melt, and Fourier transform infrared (FTIR) spectroscopy. The decomposition and release of hydrogen proceeds through eight distinct steps, including two polymorphic transitions before melting, with a new e-Mg(BH4)2 phase at ca. 150 °C. After melting, strong changes in sample color from yellow to brown to gray are consistent with the unknown Mg–B–H phase(s) (that diffract with high d-spacing halos) in the sample changing from an average composition of MgB2H5.3 at 325 °C, to MgB2.9H3.2 at 350 °C, and to MgB4.0H3.7 by 450 °C. From 350 to 450 °C, the crystalline Mg proportion increases. No combination of previously assigned anionic BnHm species (including MgB12H12 and Mg(B3H8)2) can account for the average composition of the unknown proportion of the sample. This is supported by FTIR spectra showing an absence o...

Diffraction-based methods offer unique advantages for elucidating the pathways by which materials absorb and desorb hydrogen, especially when a phase change or the formation of new compounds is involved. In this case, the hydriding reaction may be followed via the changing crystallography of the phases involved in response to a change in temperature or hydrogen pressure. By using a fast diffractometer, the reaction kinetics may also be correlated to environmental conditions and the degree of completion of the reaction. In this paper we consider and model quantitatively the essential elements of a successful in-situ diffraction experiment with neutrons or X-rays under hydrogen pressures up to several kilobars: a gas manifold to accurately measure hydrogen uptake; a pressure cell designed for maximum detected intensity; means to exclude scattering arising in the cell as much as possible; methodology to correct for attenuation and subtract background intensity from the cell and environment.

Reversible hydrogen storage capacity of the La(3-x)Mg(x)Ni(9) alloys, charged by gaseous hydrogen or by electrochemical methods, reaches its maximum at composition La(2)MgNi(9). As (La,Mg)Ni(3-3.5) alloys are the materials used in advanced metal hydride electrodes in Ni-MH batteries, this raises interest in the study of the structure-properties interrelation in the system La(2)MgNi(9)-H(2) (D(2)). In the present work, this system has been investigated by use of in situ synchrotron X-ray and neutron powder diffraction in H(2)/D(2) gas and by performing pressure-composition-temperature measurements. The saturated La(2)MgNi(9)D(13.1) hydride forms via an isotropic expansion and crystallizes with a trigonal unit cell (space group R3m (No.166); a = 5.4151(1) Å; c = 26.584(2) Å; V = 675.10(6) Å(3)). The studied hybrid structure is composed of a stacking of two layers resembling existing intermetallic compounds LaNi(5) (CaCu(5) type) and LaMgNi(4) (Laves type). These are occupied by D to form LaNi(5)D(5.2) and LaMgNi(4)D(7.9). The LaNi(5)D(5.2) slab has a typical structure observed for all reported LaNi(5)-containing hybrid structures of the AB(5) + Laves phase types. However, the Laves type slab LaMgNi(4)D(7.9) is different from the characterized individual LaMgNi(4)D(4.85) hydride. This results from the filling of a greater variety of interstitial sites in the La(2)MgNi(9)D(13)/LaMgNi(4)D(7.9), including MgNi(2), Ni(4), (La/Mg)(2)Ni(2), and (La/Mg)Ni(3), in contrast with individual LaMgNi(4)D(4.85) where only La(2)MgNi(2) and Ni(4) interstitials are occupied. Despite a random distribution of La and Mg in the structure, a local hydrogen ordering takes place with H atoms favoring occupation of two Mg-surrounded sites, triangles MgNi(2) and tetrahedra LaMgNi(2). A directional bonding between Ni, Mg, and hydrogen is observed and is manifested by a formation of the NiH(4) tetrahedra and MgH(6) octahedra, which are connected to each other by sharing H vertexes to form a spatial framework.

The MgH2 + 0.02Ti-additive system (additives = 35 nm Ti, 50 nm TiB2, 40 nm TiC

Isotopic Mg11B2 has been deuterated at 400 °C and 800 bar, with the production of β-Mg(11BD4)2 observed by in situ neutron diffraction. A natural MgB2 sample has been deuterated under similar condi...

Magnesium silicide (Mg2Si) has attracted interest as a hydrogen storage material due to favorable thermodynamics (ΔHdesorption = 36 kJ/mol H2) for room temperature operation. To date, direct hydriding of Mg2Si under hydrogen gas to form MgH2 and Si has only been attempted at low pressure and has been hindered by poor kinetics of absorption. In this paper we study the dehydrogenation reaction with in-situ neutron powder diffraction and present results of our attempts to hydrogenate Mg2Si under both hydrogen and deuterium gas up to temperatures of 350 °C and pressures of 1850 bar. Even under these extreme absorption conditions Mg2Si does not absorb any measureable quantity of hydrogen or deuterium.