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Chemical hydrogen storage is the sought after hydrogen storage media for automotive applications because of the expected low pressure operation ( 0.05 kg H 2 /kg system ), and system volumetric capacities (>0.05 kg H 2 /L system ). Currently, the primary shortcomings of chemical hydrogen storage are regeneration efficiency, fuel cost and fuel phase (i.e., solid or slurry phase). Understanding the required material properties to meet the DOE Technical Targets for Onboard Hydrogen Storage Systems is a critical knowledge gap in the hydrogen storage research community. This study presents a set of fluid-phase chemical hydrogen storage material property guidelines for automotive applications meeting the 2017 DOE technical targets. Viable material properties were determined using a boiler-plate automotive system design. The fluid-phase chemical hydrogen storage media considered in this study were neat liquids, solutions, and non-settling homogeneous slurries. Material properties examined include kinetics, heats of reaction, fuel-cell impurities, gravimetric and volumetric hydrogen storage capacities, and regeneration efficiency. The material properties, although not exhaustive, are an essential first step in identifying viable chemical hydrogen storage material properties—and most important, their implications on system mass, system volume and system performance.

Unsupported nickel was evaluated as an electrocatalyst material in an electrochemical hydrogen pump using the superprotonic solid acid CsH 2 PO 4 as a proton exchange membrane. In humidified hydrogen at 250 °C, Ni-based electrodes display a stable proton reduction current of 207 mA cm −2 at a −0.2 V cell potential. Electrodes utilizing carbon-supported Pt catalysts evolved hydrogen at 558 mA cm −2 under identical conditions. Hydrogen evolution and oxidation are reversible on Pt, but hydrogen oxidation activity is virtually absent on Ni.

The Pd nanoparticles of 10 nm have been prepared by dealloying method. They can absorb/desorb hydrogen or deuterium completely in a few seconds at room temperature. There is no apparent isotope effect on the sorption kinetics. The activation energies of hydrogen and deuterium absorption are 23.2 and 23.7 kJmol −1 , respectively. The diffusion coefficients of hydrogen and deuterium in the Pd nanoparticles are similar at 423 K. However, the deuterium isotherm shows higher plateau pressure and narrower gap than the hydrogen isotherm at the same temperature. When the temperature increases to 473 K, no phase transformation can be detected for both hydrogen and deuterium. The particle size and structure effects on the hydrogen/deuterium sorption process are discussed.

This study investigates the performances of hydrogen adsorption on activated carbon separated by TiO 2 nanoparticles with the presence of an electric potential. Four species with different TiO 2 contents were prepared. Hydrogen adsorption measurements on those TiO 2 -coated materials, with or without an external electric field, were made, respectively. The results showed that the adsorption capacity could be enhanced by introducing the electric potential and the enhancement increased with increasing amount of TiO 2 nanoparticles. The hydrogen adsorption capacity on TiO 2 particles is negligible, and thus there is no increase in hydrogen adsorption on TiO 2 particles alone when an electric field is applied. The effect of the dielectric coating is demonstrated.

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.

Direct hydrogen fuel cell power system as an alternative of current batteries is promising for portable applications because of its potential better energy and power density. Straight feeding hydrogen, which is generated from a chemical reaction process, to a fuel cell system requires a load-response hydrogen generation rate which is generally not easy to obtain. Hydrogen generation from the reaction between aluminum and water offers a simple way to acquire hydrogen which can be directly fed to a fuel cell power system, however, the oxide film formed on the surface of aluminum particles will generally stop the reaction to proceed. In the present review, metal aluminum activated by various techniques, namely by the addition of alkaline solutions, carbon materials, oxides and by alloying with other elements, are summarized. The effects of the additives on the hydrogen generation characteristics are evaluated. The available hydrogen generators based on the reaction between aluminum and water are discussed and some recommendations for future work are also proposed.

Stability and hydrogen storage properties of various metal-decorated benzene complexes have been studied using a first-principles method. According to our results, most metals from the first to the third period of the periodic table can be strongly adsorbed on the benzene surfaces, except Be, Na, Mg, K, and Zn. Among the metals we studied Ca is the most promising adsorbate for hydrogen storage. Two Ca atoms prefer to be isolated on the benzene surfaces, one on each side, and each adsorbed Ca can adsorb up to four H 2 molecules, thus yielding a H 2 uptake of 9.2 wt%. The calculated binding energy is 0.45 eV/H 2 , suitable for reversible hydrogen storage. The adsorbed Li and Sc can also adsorb a large number of H 2 molecules with suitable H 2 binding energies, but they are likely to dimerize on the benzene surfaces. Other metal adsorbates we studied are not suitable for hydrogen storage, because they will suffer from the large H 2 binding energy or the low hydrogen storage capacity.

LiBH 4 has a high hydrogen storage capacity and could potentially serve as a superior hydrogen storage material. However, during the hydrolysis process for hydrogen generation, the agglomeration of the hydrolysis product of LiBH 4 limits its full utilization. In order to completely release the stoichiometric amount of H 2 from LiBH 4 hydrolysis, multiwalled carbon nanotubes (MWCNTs) were doped with LiBH 4 by mechanical milling. The results show that MWCNT carried LiBH 4 can slowly react with water vapor at room temperature which is 25 °C lower than the reaction temperature of neat LiBH 4 . Agglomeration can be avoided when the addition of MWCNTs exceeds 7 wt.%, which results in a complete hydrolysis process. The total hydrogen capacity is 7.5 wt.%. The enhanced hydrolysis of LiBH 4 can be attributed to the MWCNTs which increased the contact areas between LiBH 4 and water and created gas channels for hydrogen diffusion. The performance of a micro proton exchange membrane fuel cell connected to MWCNT-doped LiBH 4 powder packed-bed reactor was examined. The result demonstrates that doping with MWCNTs enhanced the hydrogen generation of LiBH 4 hydrolysis. MWCNT-doped LiBH 4 can be applied as hydrogen source of fuel cells.

The objective of this work was to develop a hydrogen storage module for onboard electrical power sources suitable for use in micro power systems and micro-electro-mechanical systems (MEMS). Hydrogen storage materials were developed as thin-film inks to be compatible with an integrated manufacturing process. Important design aspects were (a) ready activation at sub-atmospheric hydrogen pressure and room temperature and (b) durability, i.e. capable of hundreds of absorption/desorption cycles and resistance to deactivation on exposure to air. Inks with palladium-treated intermetallic hydrogen storage alloys were developed and are shown here to be compatible with a thin-film micro-fabrication process. These hydrogen storage modules absorb hydrogen readily at atmospheric pressure, and the absorption/desorption rates remained fast even after the ink was exposed to air for 47 weeks.

To meet the requirements of fuel cell power system for electric bike, the influence of partial substitution of Zr and Cr on hydrogen storage performance of TiMn1.5V0.2-based alloys is investigated first, and a hydrogen storage tank is then built using the developed TiMn1.5V0.2-based alloy as metal hydride bed and its hydrogen supply ability is further evaluated. It is found that for TiMn1.5V0.2-based alloys, the Zr substitution for Ti effectively reduces the plateau pressure but increases the plateau slope, while the partial substitution of Mn by Cr decreases the absorption plateau pressure, leading to a smaller hysteresis factor. After the optimization of components, 6 kg of Ti0.95Zr0.05Mn1.4Cr0.1V0.2 alloy powder with 5 wt.% aluminum foam is mixed uniformly to form a metal hydride bed inside the tank. The measurements show that the tank releases up to 82 g of hydrogen to produce a 200 W fuel cell output for 300 min and has a stable cyclic capacity, indicating that hydrogen storage system of TiMn1.5V0.2-based alloys for fuel cell power system of electric bike is applicable.

This paper conducts a three-dimensional (3D) modeling study to investigate the hydrogen absorption process and associated mass and heat transport in a metal hydride (LaNi5) hydrogen storage tank. The 3D model is further implemented numerically for validation purpose and the detailed investigation on absorption process. Results indicate that at the very initial absorption stage the bed temperature evolves almost uniformly, while it varies greatly spatially at the latter stage. At the initial seconds, most hydrogen is absorbed in the region near the cooling wall due to the better heat removal. The absorption in the core is slow at the beginning, but becomes important at the very end stage. It also shows that the initial hydrogen flow in the bed is several-fold larger than the latter stage and the flow may provide extra cooling to the hydriding process. By analyzing the Peclet number, we find that the heat convection by the hydrogen flow may play an important role in local heat transfer. This work provides an important platform beneficial to the fundamental understanding of multi-physics coupling phenomena during hydrogen absorption and the development of on-board hydrogen storage technology.

Practical challenges of metal hydrides for hydrogen storage such as magnesium hydride, lie predominantly in improving hydrogen absorption kinetics and capacity. Approaches to improving kinetics of Mg commonly include changing particle geometry, reducing crystallite size and coating with catalytic transition metals such as Ni. This study is aimed at improving the hydrogen storage kinetics and capacity of Mg by a novel approach utilizing high aspect ratio powders (thin metal flakes with large diameters) coated with a Ni nano-catalyst. A high speed orbiting ball media (HSOBM) processor was utilized to fabricate the flake-shaped materials. Mg flakes effectively coated with Ni nano-catalyst using dry mechanical coating were found to possess more favorable hydrogen absorption/desorption characteristics and improved hydrogen storage capacity than traditional spherical particles. Geometric shape was shown to be a vital factor in hydrogen absorption kinetics and its effects proved to be dominant over those of crystallite size.

The development of efficient and reliable energy storage systems based on hydrogen technology represents a challenge to seasonal storage based on renewable hydrogen. State of the art renewable energy generation systems include separate units such as electrolyzer, hydrogen storage vessel and a fuel cell system for the conversion of H 2 back into electricity, when required. In this work, a novel electrochemical system has been developed which integrates hydrogen production, storage and compression in only one device, at relatively low cost and high efficiency. The developed prototype comprises a six-electrode cell assembly using an AB 5 -type metal hydride and Ni plates as counter electrodes, in a 35-wt% KOH solution. Metal hydride electrodes with chemical composition LaNi 4.3 Co 0.4 Al 0.3 were prepared by high frequency vacuum melting followed by high temperature annealing. X-ray phase analysis showed typical hexagonal structure and no traces of other intermetallic compounds belonging to the La–Ni phase diagram. Thermodynamic study has been performed in a Sieverts type of apparatus produced by Labtech Int. During cycling, the charging/discharging process was studied in situ using a gas chromatograph from Agilent. It is anticipated that the device will be integrated as a combined hydrogen generator and storage unit in a stand-alone system associated to a 1-kW fuel cell.

A safe and simple hydrogen generator, which produced hydrogen by chemical reaction of aluminum and sodium hydroxide solution, was proposed for proton exchange membrane fuel cells. The effects of concentration, dropping rate and initial temperature of sodium hydroxide solution on hydrogen generation rate were investigated. The results showed that about 38 ml min −1 of hydrogen generation rate was obtained with 25 wt.% concentration and 0.01 ml s −1 dropping rate of sodium hydroxide solution. The cell fueled by hydrogen from the generator exhibited performance improvement at low current densities, which was mainly due to the humidified hydrogen reduced the protonic resistivity of the proton exchange membrane. The hydrogen generator could stably operate a single cell under 500 mA for nearly 5 h with about 77% hydrogen utilization ratio.

The mechanism for safe and reversible storage of hydrogen in porous carbonaceous materials by electrochemical decomposition of water in alkaline electrolyte is proposed. Atomic H was found to be inserted into the microdomains of defective graphene layers. Hydrogen storage capacity increases with increasing interlayer distance between carbon sheets. Hydrogen insertion in carbonaceous materials occurs at ambient conditions. Static potential acts as an electrochemical valve which can retain the hydrogen in the carbon structure, thus preventing leakage during storage.

Hydrogen sulfide (H 2 S) methane (CH 4 ) reformation (H 2 SMR) (2H 2 S + CH 4 = CS 2 + 4H 2 ) is a potentially viable process for the removal of H 2 S from sour natural gas resources or other methane containing gases. Unlike steam methane reformation that generates carbon dioxide as a by-product, H 2 SMR produces carbon disulfide (CS 2 ), a liquid under ambient temperature and pressure—a commodity chemical that is also a feedstock for the synthesis of sulfuric acid. Pinch point analyses for H 2 SMR were conducted to determine the reaction conditions necessary for no carbon lay down to occur. Calculations showed that to prevent solid carbon formation, low inlet CH 4 to H 2 S ratios are needed. In this paper, we analyze H 2 SMR with either a cryogenic process or a membrane separation operation for production of either liquid or gaseous hydrogen. Of the three H 2 SMR hydrogen production flowsheets analyzed, direct liquid hydrogen generation has higher first and second law efficiencies of exceeding 80% and 50%, respectively.

This communication describes a new hybrid method for storing hydrogen in solid inorganic hydride materials as well as producing it from water based on the reaction between LiOH/LiOH·H 2 O and LiH. As a hydrogen storage method, the release and uptake of hydrogen in this method are accomplished via a series of simple reactions with good kinetics within a practically reasonable temperature range. The reversible hydrogen storage capacity of the material system is 6–8.8 wt.% at

Sodium borohydride (NaBH 4 ) in the presence of sodium hydroxide as a stabilizer is a hydrogen generation source with high hydrogen storage efficiency and stability. It generates hydrogen by self-hydrolysis in aqueous solution. In this work, a Co–B catalyst is prepared on a porous nickel foam support and a system is assembled that can uniformly supply hydrogen at >6.5 L min −1 for 120 min for driving 400-W polymer electrolyte membrane fuel cells (PEMFCs). For optimization of the system, several experimental conditions were changed and their effect investigated. If the concentration of NaBH 4 in aqueous solution is increased, the hydrogen generation rate increases, but a high concentration of NaBH 4 causes the hydrogen generation rate to decrease because of increased solution viscosity. The hydrogen generation rate is also enhanced when the flow rate of the solution is increased. An integrated system is used to supply hydrogen to a PEMFCs stack, and about 465 W power is produced at a constant loading of 30 A.

Fuel cells (FC) can produce electricity through electrochemical reaction of hydrogen with oxygen with the use of a membrane and electrode assembly (MEA). In other words, the hydrogen pressure difference between the anode and cathode can produce electricity via an electrochemical process. Conversely, when we supply electricity to MEA from an external power source, we can pump up or separate hydrogen from the low pressure anode to the high pressure cathode according to the principle of the “concentration cell”. The depleted hydrogen from the FC can be recovered by the hydrogen separation pump proposed herein, or low pressure hydrogen can be pumped to high pressure hydrogen by the hydrogen compression pump proposed herein. In this study we preliminarily tested the hydrogen separation pump and hydrogen compression pump, and demonstrated their good performance. The tested performances were analyzed with the use of our simulation model of a hydrogen pump, which was made by modifying our FC simulation model, and the test results agreed well with the calculated results.

Vertically oriented nanotubular TiO2 arrays were formed by a simple anodization process. Hydrogen storage studies were carried out on the TiO2 nanotubular arrays having different diameters by charging and discharging hydrogen with potentiostatic/galvanostatic control. The hydrogen storage capacities of the nanotubes were only marginally affected by the tube diameter. Concentration of oxygen vacancies as defects influenced the hydrogen storage of the nanotubes. Annealing of the TiO2 nanotubes in argon atmosphere increased the defect density and decreased the hydrogen discharge during initial charge–discharge cycles. Hydrogen storage studies through electrochemical route did not show significant storage capacity of TiO2 nanotubes. Diffusion of hydrogen as protons and interference of the double layer capacitance of nanotubes could be attributed to the lower hydrogen storage capacity.

During the last years, the power densities of automotive fuel cell systems have been raised dramatically. However, a major technology improvement is still needed for the on-board fuel storage system since hydrogen exhibits a rather low volumetric energy density (regardless whether it is stored as a liquid at cryogenic temperatures or as a compressed gas). Furthermore, the cost for current hydrogen containers is far from what gasoline tanks cost. Therefore, alternatives like solid-state absorbers of hydrogen (e.g. metal hydrides or complex hydrides) are investigated for their feasibility by the car industry. These kinds of systems show very high volumetric storage densities on a materials basis. Unfortunately, the host compounds are usually quite heavy and thus possess a low gravimetric storage density. Also, the thermodynamics and kinetics of the absorption/desorption reactions and their impact on the tank design in general (and on the heat management in particular) have to be considered. Within the framework of this paper, the properties of the most promising solid-state storage systems are discussed and compared to those of the liquid and compressed gaseous hydrogen technologies.

This paper presents work on hydrogen generation from sodium borohydride (NaBH4) solution that could have great application in micro fuel cells. A hydrogen test method has been developed, which is very effective for sustained measurement of the generation rate and yield of hydrogen. The hydrogen is supplied to a proton exchange membrane fuel cell. The discharged current is measured by a computer-controlled electronic load system connecting to the fuel cell where hydrogen generation rate and yield are calculated. The study is focused on the slow release of hydrogen. The results show that if the concentration of NaBH4 solution is 10%, no solid substance is formed and the catalyst supported on the ion-exchange resin beads remains unchanged. The hydrogen generation can be controlled by inserting or removing the catalyst into/from the solution, which can be applied to a micro fuel cell. When the concentration of NaBH4 solution is 20%, however, the catalyst beads are broken up and dispersed in the solution (probably by the NaBO2 crystallization force) and give rise to uncontrollable generation of hydrogen.

For hydrogen generation from an aqueous alkaline NaBH 4 solution, Co-B catalyst was prepared by the chemical reduction method using NaBH 4 as a reduction chemical. To design a hydrogen generator, hydrogen generation rate was measured using the Co-B catalyst as a function of solution temperature, amount of catalyst loading, NaBH 4 concentration, and NaOH (a base-stabilizer) concentration. Activation energy for the hydrogen generation reaction was measured to be 64.87 kJ mol −1 . Compared to Ru catalysts previously used, the low-cost Co-B catalyst exhibited comparable activity for the hydrogen generation reaction. Using the hydrogen generation system employing the Co-B catalyst, a 2 W polymer electrolyte membrane fuel cell (PEMFC) stack was operated and successfully powered a cellular phone.

In a closed pressure vessel, the reaction of sodium borohydride (NaBH 4 ) with Pt-LiCoO 2 catalyst and a stoichiometric amount of water drastically increases the pressure owing to the generation of large quantities of hydrogen gas by synergism of hydrogen pressure and the catalyst (gravimetric hydrogen density per unit weight of NaBH 4 and H 2 O including the Pt-LiCoO 2 catalyst is 9.0 wt.%, volumetric hydrogen density per unit weight of NaBH 4 and H 2 O including the Pt-LiCoO 2 catalyst is 101 kg H 2 /m −3 ). The hydrogen densities are high enough to reach the US Department of Energy (DOE) targets for use in a fuel cell vehicle (FCV) and also for other applications such as a fuel cell uninterrupted power supply (FCUPS).

Hydrogen is separated from a hydrogen/nitrogen/carbon dioxide mixture by an electrochemical separation method. By applying a direct current to a proton-conducting membrane, hydrogen can be electrochemically dissociated on the platinum catalyst of the anode, transported across the hydrated cation exchange membrane, and then recovered on the catalytic cathode. The operating principles and advantages of the electrochemical hydrogen separation method are described. The effects of temperature and pressure are examined and the optimum operating conditions are determined. Increase in cell temperature enhances the purity of hydrogen and the power efficiency. The pressure of the feeding gas increases both the performance and the amount of hydrogen product, but decreases the purity of the hydrogen because of the increasing permeation flux of impurities, i.e., nitrogen and carbon dioxide. High purity, (99.72%) hydrogen can be achieved from a low purity (30%) feed via a two-stage separation process at 700 mA cm −2 .

The challenge in the research on hydrogen storage materials is to pack hydrogen atoms or molecules as close as possible. The density of liquid and solid hydrogen is 70.8 and 70.6 kg m −3 , respectively. Hydrogen absorbed in metals can reach a density of more than 150 kg m −3 (e.g. Mg 2 FeH 6 ) at atmospheric pressure. However, due to the large atomic mass of the transition metals the gravimetric hydrogen density is limited to less than 5 mass%. Light weight group 3 metals, e.g. Al, B, are able to bind four hydrogen atoms and form together with an alkali metal an ionic or at least partially covalent compound. These compounds are rather stable and often desorb the hydrogen only above their melting temperature. Complex hydrides like NaAlH 4 , when catalyzed, decompose already at room temperature. We have investigated LiBH 4 , a complex hydride which consists of 18 mass% of hydrogen. The hydrogen desorption from LiBH 4 was successfully catalyst with SiO 2 and 13.5 mass% of hydrogen were liberated starting already at 200 °C.

Studies are focused on the hydrogen adsorption on carbon materials at ambient temperature. The hydrogen adsorption from the gas phase was measured by isothermal gravimetric analysis, using a microbalance at hydrogen pressures up to 125 bar at 23°C. In this work, the hydrogen adsorption reached values of approximately 1.5 wt.% at ambient temperature and 125 bar.

The objective of this work was to demonstrate a micro-fabricated hydrogen storage module for micro-power systems. Hydrogen storage materials were developed as thin-film inks to be compatible with an integrated manufacturing process. Performance and durability of storage modules were evaluated. Further, applications were demonstrated for a nickel-hydrogen battery and a micro-fabricated hydrogen-air PEM fuel cell. The ink making process, in which polymer binders and solvents were added to the palladium-treated alloys, slightly decreased the storage capacities, but had little effect on the activation properties of the treated alloys. After 5000 absorption/desorption cycles under hydrogen, the hydrogen storage capacities of the thin-film inks remained high. Absorption/desorption behavior of the ink was tested in the environment of a new type nickel-hydrogen battery, in which it would in contact with 26wt% KOH solution, and the ink showed no apparent degradation. Storage modules were used as the successfully as hydrogen source for PEM fuel cell.

A method for manufacturing hydrogen storage alloy particles comprises steps of obtaining a melt of the hydrogen storage alloy and pulverizing the hydrogen storage alloy by water atomizing process, whereby the melt is pulverized by contacting or colliding with high-speed jetting thereto to be dispersed in the form of solidified fine particles. By employing an aqueous solution of hypophosphorous acid or an alkali aqueous solution in place of water during the water atomizing process, or by etching the oxide films once formed on the surface of the hydrogen storage alloy particles with an aqueous solution of a strong acid, the thickness of the oxide film can be made thinner, and thus a high discharge capacity of a battery configured with a negative electrode comprising the alloy particles can be realized.

A hydrogen storage alloy electrode comprising, an electrically conductive support made of a punched or perforated metal sheet, a mixture supported on said conductive support and a water-repellent agent for giving a water-repellent property on the surface of the electrode, said mixture including; a hydrogen storage alloy powder, a styrene-butadiene copolymer having a styrene to butadiene weight ratio in a range of 100:30 to 100:100 as a binder, a polymeric material for giving a hydrophilic property inside the electrode, and carbon black for giving a hydrophobic property inside the electrode.