Gravimetric Hydrogen Capacity Research Articles

Enhance hydrogen storage in lightweight solid-state systems based on Poly(vinylnaphthalene)

This article highlights the potential of poly(2-vinylnaphthalene) (PVN) as a novel light-weight solid-state hydrogen storage system for various applications. With an impressive theoretical gravimetric hydrogen capacity of 5.2 wt.-%, PVN stands out for its attractiveness as a hydrogen carrier. The material possesses advantageous characteristics, including moldability, low toxicity, and ease of storage, making it a promising candidate for both stationary and mobile hydrogen storage applications. Experimental findings demonstrate that PVN can be hydrogenated by up to 76 % utilizing an Ru/Al2O3 catalyst at 250 °C for 24 h. Confirmation of the hydrogenation reaction, which results in poly(2-vinyldecalin), was achieved through characterization techniques such as FTIR, 1H NMR, and spectroscopic ellipsometry. The study of the effects of hydrogen pressure and reaction time identified moderate conditions as favorable, though a further exploration of different catalysts is suggested for optimal conversion. A palladium-based catalyst was employed to release hydrogen from the hydrogenated polymer, demonstrating almost complete reversibility of the hydrogenation of poly(2-vinylnaphthalene) with a dehydrogenation yield of 90 %.

Density functional analysis of structural, mechanical, electronic, and hydrogen storage properties of thermodynamically stable lead-free hydrides [formula omitted](X = Cs, Fr): A perspective of clean energy and fuel

A density functional theory based calculations are performed to investigate structural, hydrogen storage, mechanical, electronic and thermodynamical properties of lead-free hydride perovskites XGeH3 (X=Cs, Fr). The optimized lattice constant and hence volume against the minimum energy is obtained and found to be 4.176 Å and 4.184 Å for CsGeH3 and FrGeH3 respectively. The gravimetric and volumetric hydrogen storage capacity of 1.43% and 1.00%, 72.81(g.H2/L) and 73.21(g.H2/L) for CsGeH3 and FrGeH3 respectively. The density of states and electronic band structure predicted the metallic nature of both hydrides which was affirmed by the Fermi Surfaces. The calculation of Poisson’s, Pugh’s ratio and Cauchy’s pressure suggested their brittle nature. The Debye temperature decreases with the increase of temperature while volume and entropy increase by increasing applied temperature. The present study shows the potential of lead-free hydride perovskites in hydrogen storage applications due to rather suitable gravimetric hydrogen capacity and high stability.

AlH3 as High-Energy Fuels for Solid Propellants: Synthesis, Thermodynamics, Kinetics, and Stabilization

Aluminum hydride (AlH3) has attracted wide attention due to its high gravimetric and volumetric hydrogen capacity. AlH3 can easily release hydrogen when heated at relatively low temperature. Such high hydrogen density and low dehydrogenation temperature make it one of the most promising high-energy fuels for solid propellants. In particular, AlH3 as a component of solid propellants may greatly increase the specific impulse of rocket engines. However, AlH3 exhibits low chemical and thermal stability in an ambient atmosphere. In this paper, the research progress about the synthesis, dehydrogenation thermodynamics, and kinetics, the stabilization of AlH3 over the past decades are reviewed, with the aim of exploring more a economical synthesis and suitable stabilization methods for large-scale use in solid propellants. Finally, some suggestions regarding future research directions in this filed are proposed.

Electrolytic Hydrogen Release from Hydrogen Boride Sheets.

Solid-state hydrogen storage materials are safe and lightweight hydrogen carriers. Among the various solid-state hydrogen carriers, hydrogen boride (HB) sheets possess a high gravimetric hydrogen capacity (8.5 wt%). However, heating at high temperatures and/or strong ultraviolet illumination is required to release hydrogen (H2) from HB sheets. In this study, the electrochemical H2 release from HB sheets using a dispersion system in an organic solvent without other proton sources is investigated. H2 molecules are released from the HB sheets under the application of a cathodic potential. The Faradaic efficiency for H2 release from HB sheets reached >90%, and the onset potential for H2 release is -0.445V versus Ag/Ag+, which is more positive than those from other proton sources, such as water or formic acid, under the same electrochemical conditions. The total electrochemically released H2 in a long-time experiment reached ≈100% of the hydrogen capacity of HB sheets. The H2 release from HB sheets is driven by a small bias; thus, they can be applied as safe and lightweight hydrogen carriers with economical hydrogen release properties.

Phonon transport characteristics of α, β, and γ crystalline phases of magnesium hydride from first-principles-based anharmonic lattice dynamics

The superior gravimetric and volumetric hydrogen capacities of magnesium hydride (MgH2) make it a promising candidate material for solid-state hydrogen storage. However, the slow kinetics of hydrogen atoms and the high thermodynamic stability of MgH2 hinder its practical application. To address the challenging issue of adsorption–desorption in MgH2, structural engineering involving nanostructuring has been used to improve the hydrogen-storage characteristics of this material. However, although structural engineering and thermal management significantly influence material properties, no microscopic understanding of the heat conduction property of pristine MgH2 exists. Further advances in the thermal engineering of MgH2-based hydrogen-storage materials require a better understanding of heat conduction in pristine MgH2, particularly knowledge of how the crystalline phases of MgH2 depend on the hydrogen concentration and external pressure. This study uses first-principles-based anharmonic lattice dynamics to quantitatively investigate the intrinsic thermal conductivity of heat-carrying phonons in pristine MgH2 with three different crystalline phases α, β, and γ. The results show that the thermal conductivity of MgH2 depends on the crystalline phase and that the magnitude of the thermal conductivity increases in the order α, γ, and β. In contrast, the volumetric heat capacity and mean squared displacements of the constituent atoms are similar for all three phases. Furthermore, as observed for the pressure dependence of phonon transport, increasing the pressure reduces the thermal conductivity of all phases. However, for the γ and β phases, these reductions are relatively moderate because of the competing effects of group velocity and relaxation time, which have opposite dependencies on pressure. Finally, modal analysis indicates that the spectral features of the phonon transport properties under an applied external pressure are comparable to those at atmospheric pressure. These results should help tailor the heat dissipation of MgH2 while maintaining its hydrogen adsorption–desorption performance through structural engineering.

Supported Manganese Organic Framework as Catalyst for Hydrogen Evolution Reaction

The dependence on fossil fuels has caused significant harmful impact on the environment. The combustion of fossil fuels increases the harmful greenhouse gases including carbon dioxide and methane. The pollution not only worsens the impact of global warming but also affects human health. Many renewable energy sources have been discovered to replace fossil energy, but it is a challenge to find a cheap and effective energy source. Hydrogen arises as a potential candidate due to its high energy density and abundance. However, hydrogen was difficult to store. Hydrogen was often stored in liquid form at high pressure and extremely low temperature conditions. Another method of effectively storing hydrogen is by using hydrogen feedstock materials such as sodium borohydride. Sodium borohydride can be stored at room temperature and has a high gravimetric hydrogen capacity of 10% by weight. However, the process of extracting hydrogen from the materials was slow so it required catalysts. Many precious metal catalysts such as gold and silver catalyst have been applied to improve hydrogen generation reaction, but those metal catalysts were expensive to create. Additionally, those metal catalysts were often agglomerate and impossible to reuse. In this study, we used a non-precious metal complex supported over carbon-based materials to catalyze the hydrogen evolution reaction. We discovered a novel method of synthesizing manganese terephthalate complex at room temperature. The metals complex was coupled with graphene (G) and multiwalled carbon nanotubes (MWCNT) to increase its durability and efficiency. Each material was characterized by Powdered X-ray diffraction (P-XRD), Fourier Transform Infrared (FTIR) spectroscopy, Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM). During the reaction with sodium borohydride, we discovered that the manganese terephthalate complex converted to manganese boride and further improved the catalysis process. In the first trial, the reaction catalyzed by Mn complex coupled with MWCNT produced 25ml of hydrogen. At the fifth reuse trials, the amount of generated hydrogen (~44 ml) was nearly doubled. A similar phenomenon was observed in Mn complex coupled with graphene. This study introduces a novel method in synthesizing a stable, cheap and efficient catalyst for hydrogen evolution.

In situ formed MgTi2O4 from MgO improving the cycling stability of MgH2

Magnesium hydride (MgH2) is a potential candidate for hydrogen storage due to its high gravimetric and volumetric hydrogen capacities. However, high operating temperature and reversible H2 capacity attenuation inhibit its commercial application. To overcome these issues, we synthesized an N ion-doped Na2TiO3 (denoted as N-NaTiO) catalyst by reducing TiO2 with NaNH2. Experimental results show that the addition of 5 wt% N-NaTiO can lower the dehydrogenation peak temperature of MgH2 from 328 to 239 °C, and 6.0 wt% H2 is quickly released in ca. 4 min at 300 °C. In particular, the modified MgH2 exhibits a high reversible hydrogen capacity of 6.7 wt% which is equal to a retention of 94.4% after 250 cycles. Reaction mechanism investigations reveal that hydrogen insertion and removal during the ab/desorption processes are consistent with the reversible change of titanium valence states in the catalyst. In addition, it is observed that there is an irreversible evolution of MgO to MgTi2O4 at the interface between the catalyst and MgH2 during the cycling process, which is linked to the improvement of the ab/desorption kinetics and cycle stability.

Core-Shell, Critical-Temperature-Suppressed V Alloy-Pd Alloy Hydrides for Hydrogen Storage—A Technical Evaluation

Hydrogen storage for energy applications is of significant interest to researchers seeking to enable a transition to lower-pollution energy systems. Two of the key drawbacks of using hydrogen for energy storage are the low gas-phase storage density and the high energy cost of the gas-phase compression. Metal hydride materials have the potential to increase hydrogen storage density and decrease the energy cost of compression by storing the hydrogen as a solid solution. In this article, the technical viability of core-shell V90Al10-Pd80Ag20 as a hydrogen storage material is discussed. LaNi5, LaNi5/acrylonitrile-butadiene-styrene copolymer mixtures, core-shell V-Pd, and core-shell V90Al10-Pd80Ag20 are directly compared in terms of reversible hydrogen-storage content by weight and volume. The kinetic information for each of the materials is also compared; however, this work highlights missing information that would enable computational dynamics modelling. Results of this technical evaluation show that V90Al10-Pd80Ag20 has the potential to increase gravimetric and volumetric hydrogen capacity by 1.4 times compared to LaNi5/acrylonitrile-butadiene-styrene copolymer mixtures. In addition, the literature shows that Pd80Ag20 and V90Al10 both have similarly good hydrogen permeabilities, thermal conductivities, and specific heats. In summary, this evaluation demonstrates that core-shell V90Al10-Pd80Ag20 could be an excellent, less-expensive hydrogen storage material with the advantages of improved storage capacity, handleability, and safety compared to current AB5-polymer mixtures.

Thermodynamics of hydrogen storage: LOHC system 1-alkyl-indole/octahydro-1-alkyl-indole

The environmental advantages of the hydrogen economy are obvious, but the limiting factor in its development is finding an optimal storage system with high gravimetric and volumetric hydrogen capacities. The most efficient technology for storing and consequently using hydrogen is that with organic compounds that are able to enrich hydrogen by forming bonds with the hydrogen. In this study, we considered 1-alkyl-indoles as suitable LOHC systems because of their high thermal stability and high boiling points. The thermochemical studies of these compounds were performed, including vapour pressure measurements and combustion calorimetry. The experimental data obtained are compared with the results of theoretical quantum chemical methods. In addition, a thermodynamic analysis of the hydrogenation/dehydrogenation of the LOHC systems based on 1-alkyl-indoles was performed.

Boosting the Dehydrogenation Properties of LiAlH4 by Addition of TiSiO4

Given its significant gravimetric hydrogen capacity advantage, lithium alanate (LiAlH4) is regarded as a suitable material for solid-state hydrogen storage. Nevertheless, its outrageous decomposition temperature and slow sorption kinetics hinder its application as a solid-state hydrogen storage material. This research's objective is to investigate how the addition of titanium silicate (TiSiO4) altered the dehydrogenation behavior of LiAlH4. The LiAlH4-10 wt% TiSiO4 composite dehydrogenation temperatures were lowered to 92 °C (first-step reaction) and 128 °C (second-step reaction). According to dehydrogenation kinetic analysis, the TiSiO4-added LiAlH4 composite was able to liberate more hydrogen (about 6.0 wt%) than the undoped LiAlH4 composite (less than 1.0 wt%) at 90 °C for 2 h. After the addition of TiSiO4, the activation energies for hydrogen to liberate from LiAlH4 were lowered. Based on the Kissinger equation, the activation energies for hydrogen liberation for the two-step dehydrogenation of post-milled LiAlH4 were 103 and 115 kJ/mol, respectively. After milling LiAlH4 with 10 wt% TiSiO4, the activation energies were reduced to 68 and 77 kJ/mol, respectively. Additionally, the scanning electron microscopy images demonstrated that the LiAlH4 particles shrank and barely aggregated when 10 wt% of TiSiO4 was added. According to the X-ray diffraction results, TiSiO4 had a significant effect by lowering the decomposition temperature and increasing the rate of dehydrogenation of LiAlH4 via the new active species of AlTi and Si-containing that formed during the heating process.

Nanoporous adsorbents for hydrogen storage

Hydrogen storage in absorbents as activated carbons has been rarely investigated; however, about 25 years ago, the development of new nanomaterials, initiated by Iijima’s discovery of carbon microtubules, started new hopes. Unfortunately, initial results on high hydrogen uptake in carbon nanotubes at ambient conditions could not be independently reproduced; however, at cryogenic conditions, these novel nanomaterials just behaved as activated carbons with an uptake proportional to the surface area. Shortly after, the development of coordination polymers with permanent porosity opened a new route to nanoporous materials with ultra-high internal surfaces. Mainly metal–organic frameworks (MOFs) have been attracting a great deal of attention in recent years, as very high gravimetric hydrogen capacities can be achieved at 77 K. Cryogenic storage by physisorption of hydrogen molecules will safely operate at low pressures, is fully reversible, and possesses fast kinetics. This mini-review shows the rapid development in this field over the past 25 years. Exemplarily, the main focus is on results obtained in the hydrogen storage laboratory in Stuttgart and their connection to Applied Physics A.

In situ formation of TiB2 and TiH2 catalyzed Li/Mg based dual-cation borohydride with a low onset dehydrogenation temperature below 100 °C

Chemical complex borohydride is a promising hydrogen storage material due to its large gravimetric and volumetric hydrogen capacities. However, the high dehydrogenation temperature and sluggish kinetics still place strong restrictions on its practical application in the hydrogen storage field. In this work, a synergetic approach of partial cation substitution and catalysis is developed to enhance the hydrogen storage properties of LiBH4. The Li/Mg based dual-cation borohydride (LiMg2(BH4)5, LMBH) was successfully synthesized by wet chemical ball milling of LiBH4 and MgCl2. The optimal (LMBH (4.5:1) sample, LiBH4 and MgCl2 in molar ratios of 4.5:1, possesses a maximum hydrogen desorption capacity (11.27 wt%) and the outstanding initial decomposition temperature (∼250 °C). Importantly, the LMBH (4.5:1) doped with TiF3 shows a remarkable onset dehydrogenation temperature as low as 97.2 °C, which is about 190 °C lower than that of pristine LiBH4. The LMBH (4.5:1) doped with TiF3 system releases 7.98 wt% H2 within 170 min below 350 °C. And the dehydrogenation product of doped composite can reversibly absorb ∼4.72 wt% H2 at a relatively moderate temperature of 280 °C, which is substantially lower than the reversible hydrogen absorption temperature of previous modified borohydride systems. Based on the structural characteristic analyses, the TiF3 reacts with LMBH (4.5:1) to in-situ form actual catalytic components of TiB2 and TiH2 as the actual catalysts for LMBH (4.5:1), resulting in the improved hydrogen re/dehydrogenation properties. The synergetic modification of Li/Mg dual-cation substitution and TiB2/TiH2 catalysis may lead to the development of light-metal borohydrides with outstanding hydrogen storage properties.

Dual-cation K2TaF7 catalyst improves high-capacity hydrogen storage behavior of MgH2

MgH2 has been extensively regarded as a low-cost hydrogen storage material with high gravimetric hydrogen capacity of approximately 7.6 wt%. However, the hydrogen release and absorption kinetics in MgH2 still needs further improving. For the first time, the catalytic impacts of a new dual-cation metal fluoride K2TaF7 upon the hydrogen storage characteristics of MgH2 have been investigated in this work. With only 1 wt% K2TaF7 dopant, the initial dehydrogenation temperature of MgH2 was lowered by about 130 °C, releasing more than 7.3 wt% hydrogen totally. The desorption activation energy of MgH2 + 1 wt% K2TaF7 composite was decreased to 107.2 ± 1.2 kJ mol−1. Besides, at 190 °C, the dehydrogenated MgH2 + 1 wt% K2TaF7 sample could absorb 6.56 wt% H2, while pristine MgH2 re-absorbed only 3.45 wt% H2. Further studies revealed that K2TaF7 could react with MgH2 during dehydrogenation and produce symbiotic hydrides KMgH3 and TaH0.8, which could play the role of hydrogen pumps during hydrogen release and uptake. The cooperative catalysis between the hydrogen pump effect and the active interface in the multi-hydride area significantly enhanced the reversible hydrogen storage in the MgH2+1 wt% K2TaF7 composite. This study provides new thinking for novel catalysts to elevate the hydrogen storage performance of MgH2.

Effect of isostructural phase transition on cycling stability of ZrCo-based alloys for hydrogen isotopes storage

ZrCo alloy as a promising candidate for hydrogen isotopes storage and delivery in the international thermonuclear experimental reactor (ITER) has attracted considerable attention. However, its capacity retention after 50 cycles is 22.4%, resulting from the disproportionation reaction during repeated phase transitions between cubic ZrCo phase and orthorhombic ZrCoH3 phase. Herein, a single isostructural phase transition with high thermal stability and structural stability in ZrCo-H system is achieved by multicomponent substitution for the first time. Considering the computational screening results, cost and gravimetric hydrogen capacity, a series of Zr0.8Nb0.2Co0.6Cu0.4−xNix (x = 0.2–0.3) alloys are designed and synthesized. The compositional dependence of phase component is further discussed in detail. Specifically, Zr0.8Nb0.2Co0.6Cu0.15Ni0.25 alloy with single orthorhombic phase exhibits high thermal stability (up to 550 °C) and maintains the orthorhombic structure during the de-/hydrogenation process at 380 °C. Thermodynamic destabilization of hydride (ΔH = 71.95 kJ·mol−1 H2) and nearly no de-/hydrogenation hysteresis contribute to a significantly low desorption temperature of 283 °C at 100 kPa. Thanks to superior thermal stability and structural stability, no attenuation of hydrogen storage performances including thermodynamics and kinetics can be observed during 200 de-/hydrogenation cycles, and the supereminent cycling stability of 100% and cyclic hydrogen capacity of 1.65 wt% are achieved. Combined with first-principles calculations, the improved cycling stability of Zr0.8Nb0.2Co0.6Cu0.15Ni0.25 alloy can be ascribed to the reduced lattice expansion and atomic motion during the orthorhombic isostructural phase transition.

Hydrogen Storage in Complex Metal Hydrides NaBH4: Hydrolysis Reaction and Experimental Strategies

Worldwide, hydrogen is gaining ground since it is a promising alternative energy source to conventional fuels, which include fossil fuel. Thus, numerous techniques to generate hydrogen have been suggested. This literature review describes the challenges and obstacles identified through a series of the publications that target the hydrolysis of sodium borohydride. This review present several catalysts and reactor systems for the generation of hydrogen gas using the hydrolysis of sodium borohydride, selecting articles in the literature that show a promising future for this technology, although some challenges lie ahead. Sodium borohydride has been widely considered as a low-cost hydrogen storage material with high gravimetric hydrogen capacity of about 10 wt.%. However, its thermodynamic stability seriously hinders the application of sodium borohydride to obtain hydrogen. The performances of the reviewed systems of sodium borohydride hydrolysis include analysis from both the thermodynamic and kinetic points of view. The feasibility of an efficient hydrogen generation system, where a mixture of sodium borohydride and catalysts is hydrolyzed, is considered. This review aims to provide a useful resource to aid researchers starting work on the generation of hydrogen gas using the hydrolysis of sodium borohydride, so they can select the catalysts and reactor systems that best suit them. Thus far, no single catalyst and reactor system can simultaneously meet all of the required standards for efficient practical applications.

Effect of the particle size evolution on the hydrogen storage performance of KH doped Mg(NH2)2 + 2LiH

In recent years, many solid-state hydride-based materials have been considered as hydrogen storage systems for mobile and stationary applications. Due to a gravimetric hydrogen capacity of 5.6 wt% and a dehydrogenation enthalpy of 38.9 kJ/mol H2, Mg(NH2)2 + 2LiH is considered a potential hydrogen storage material for solid-state storage systems to be coupled with PEM fuel cell devices. One of the main challenges is the reduction of dehydrogenation temperature since this system requires high dehydrogenation temperatures (~ 200 °C). The addition of KH to this system significantly decreases the dehydrogenation onset temperature to 130 °C. On the one hand, the addition of KH stabilizes the hydrogen storage capacity. On the other hand, the capacity is reduced by 50% (from 4.1 to 2%) after the first 25 cycles. In this work, the particle sizes of the overall hydride matrix and the potassium-containing species are investigated during hydrogen cycling. Relation between particle size evolution of the additive and hydrogen storage kinetics is described by using an advanced synchrotron-based technique: Anomalous small-angle X-ray scattering, which was applied for the first time at the potassium K-edge for amide-hydride hydrogen storage systems. The outcomes from this investigation show that, the nanometric potassium-containing phases might be located at the reaction interfaces, limiting the particle coarsening. Average diameters of potassium-containing nanoparticles double after 25 cycles (from 10 to 20 nm). Therefore, reaction kinetics at subsequent cycles degrade. The deterioration of the reaction kinetics can be minimized by selecting lower absorption temperatures, which mitigates the particle size growth, resulting in two times faster reaction kinetics.

Potassium hydride reduced black TiO2−x for boosting the hydrogenation of magnesium at room temperature

MgH2 has attracted intense interest as one of the most efficient solid-state materials to reversibly store hydrogen owing to its large gravimetric and volumetric hydrogen capacities of about 7.6 wt% and 110 g/L, respectively. However, the high thermodynamic stability of ca. 76 kJ/mol-H2, and slow kinetics of H2 de/absorption at temperatures ca. 300 °C, have challenged the broad applications of MgH2 in the field of energy storage. In an attempt to solve these challenges, this study presents the catalytic effects of adding black TiO2−x reduced by KH (denoted as K-TiO2−x) on the hydrogen storage performance of MgH2. As compared with pristine and ball-milled MgH2, the addition of 5 wt% of K-TiO2−x into MgH2 significantly improves the absorption/desorption behaviors. The doped system respectively absorbs 4.0, and 6.0 wt% H2 within the first 6 min, and after 180 min of charging at room temperature; the hydrogen can be reversibly released off starting from 194 °C which is ca. 96 °C lower than the additive-free ball-milled MgH2. The system can also produce ca. 6.5 wt% H2 upon cycling. Investigations into the improved performance and the structural patterns of MgH2 +K-TiO2−x reveal the presence of “K2Ti2O3” pseudo-complex of Ti2+ that is liberated in situ during the sorption process of MgH2; this pseudo-complex is believed to act as a catalyst by providing nucleation sites, oxygen vacancies, and hydrogen diffusion channels at its boundaries with Mg/MgH2 for the enhanced hydrogen sorption performance observed in the catalyzed MgH2 composite.

Enabling easy and efficient hydrogen release below 80 °C from NaBH4 with multi-hydroxyl xylitol

NaBH4 has been widely considered as a low-cost hydrogen storage material with high gravimetric hydrogen capacity of about 10 wt%. However, its strong thermodynamic stability severely hinders the application of NaBH4 to obtain hydrogen. In this study, multi-hydroxyl xylitol, for the first time, was chosen as a protic hydrogen carrier to destabilize and react with NaBH4. The NaBH4-xylitol composites were easily prepared through hand-milling, which leads to the fast liberation of hydrogen from moderate temperatures lower than 80 °C with more than 3.6 wt% hydrogen desorption capacity. Besides, over 80% of hydrogen could be efficiently released in NaBH4-xylitol composite. The dehydrogenation process is proved to be completely impurity-free and controllable by altering the NaBH4/xylitol ratios and operating temperatures. The reaction between NaBH4 and xylitol is investigated to be similar to an alcoholysis procedure, however no observable liquid phase takes place before and after the dehydrogenation of NaBH4-xylitol composite, showing a great potential to produce hydrogen under low temperatures through solid-state carriers.

Engineering Challenges of Solution and Slurry-Phase Chemical Hydrogen Storage Materials for Automotive Fuel Cell Applications.

We present the research findings of the DOE-funded Hydrogen Storage Engineering Center of Excellence (HSECoE) related to liquid-phase and slurry-phase chemical hydrogen storage media and their potential as future hydrogen storage media for automotive applications. Chemical hydrogen storage media other than neat liquid compositions will prove difficult to meet the DOE system level targets. Solid- and slurry-phase chemical hydrogen storage media requiring off-board regeneration are impractical and highly unlikely to be implemented for automotive applications because of the formidable task of developing solid- or slurry-phase transport systems that are commercially reliable and economical throughout the entire life cycle of the fuel. Additionally, the regeneration cost and efficiency of chemical hydrogen storage media is currently the single most prohibitive barrier to implementing chemical hydrogen storage media. Ideally, neat liquid-phase chemical hydrogen storage media with net-usable gravimetric hydrogen capacities of greater than 7.8 wt% are projected to meet the 2017 DOE system level gravimetric and volumetric targets. The research presented herein is a collection of research findings that do not in and of themselves warrant a dedicated manuscript. However, the collection of results do, in fact, highlight the engineering challenges and short-comings in scaling up and demonstrating fluid-phase ammonia borane and alane compositions that all future materials researchers working in hydrogen storage should be aware of.

Hydrogen storage in organosilicon ionic liquids

New structures of ionic liquids have been studied as liquid organic hydrogen carriers. The hydrogenation of organosilicon compounds containing a carbazole fragment was carried out for the first time. The N–(CH2)3–Si fragment in the composition of the hydrogen carrier based on organosilicon moieties was found to be more suitable than the N–CH2–Si bond. Ionic liquids with a carbazole fragment containing silicon atoms were synthesized for the first time. It was possible to significantly reduce the melting point of such ionic liquids by introducing an organosilicon linker between carbazole nitrogen and imidazolium ion. The synthesized ionic liquid is a liquid at room temperature. Hydrogenation-dehydrogenation experiments demonstrated that such ionic liquids are thermally stable up to at least 220 °C, and nearly quantitative conversion can be achieved. Both the hydrogenation and dehydrogenation processes were carried out using the same Pd/C catalyst. The theoretical total gravimetric hydrogen capacities for synthesized ionic liquids are 2.05% and 1.58%.