Hydrogen Storage Density Research Articles

Simulation and Study of PEMFC System Directly Fueled by Ammonia Decomposition Gas

Ammonia can be stored as a liquid under relatively easy conditions (Ambient temperature by applying 10 bar or Ambient pressure with the temperature of 239 K). At the same time, liquid ammonia has a high hydrogen storage density and is, therefore, a particularly promising carrier for hydrogen storage. At the same time, the current large-scale industrial synthesis of ammonia has long been mature, and in the future, it will be possible to achieve a zero-emission ammonia regeneration cycle system by replacing existing energy sources with renewable ones. Ammonia does not contain carbon, and its use in fuel cells can avoid NOx production during energy release. high temperature solid oxide fuel cells can be directly fueled by ammonia and obtain good output characteristics, but the challenges inherent in high temperature solid oxide fuel cells greatly limit the implementation of this option. Whereas PEMFC has gained initial commercial use, however, for PEMFC, ammonia is a toxic gas, so the general practice is to convert ammonia to pure hydrogen. Ammonia to hydrogen requires decomposition under high temperature and purification, which increases the complexity of the fuel system. In contrast, PEMFC that can use ammonia decomposition gas directly can simplify the fuel system, and this option has already obtained preliminary experimental validation studies. The energy efficiency of the system obtained from the preliminary validation experiments is only 34–36%, which is much lower than expected. Therefore, this paper establishes a simulation model of PEMFC directly using ammonia decomposition gas as fuel to study the maximum efficiency of the system and the effect of the change of system parameters on the efficiency, and the results show that the system efficiency can reach up to 45% under the condition of considering certain heat loss. Increasing the ammonia decomposition reaction temperature decreases the system efficiency, but the effect is small, and the system efficiency can reach 44% even at a temperature of 850°C. The results of the study can provide a reference for a more scientific and quantitative assessment of the potential value of direct ammonia decomposition gas-fueled PEMFC.

Experimental investigation on the dispersion characteristics and concentration distribution of unignited low-temperature hydrogen release

The risk assessment of hydrogen-based technologies is necessary in the coming of hydrogen economic society. At present, most studies are focused on the room-temperature hydrogen (about 300 K) and cryogenic hydrogen (30–80 K), Low-temperature (200–300 K) hydrogen storage method is another storage option of hydrogen energy due to its high hydrogen storage density and less energy loss during the cooling process, however, the dispersion characteristics and concentration distribution of unignited low-temperature hydrogen during its sudden release is still unknown. In this work, a series of hydrogen release tests are performed with storage pressure at 0.5 MPa, the dispersion characteristics of unignited low-temperature hydrogen under different temperatures (200 K, 250 K and 300 K) and pinhole nozzles (1.0 mm, 1.5 mm and 2.0 mm) are analyzed. It is found that the concentration on the axis of low-temperature hydrogen jet increases with the decrease of the temperature of the hydrogen and increase of the nozzle diameter. The inverse concentration distribution with various hydrogen temperatures and different nozzle diameters by the scaled distance is obtained. The distances to some key levels of hydrogen concentration such as flammable envelope and safe distances are evaluated and the extrapolation model to other jet conditions is proposed. The results can be available for the improvement of the hydrogen safety codes and standards of low-temperature hydrogen storage.

Advances on materials design and manufacture technology of plastic liner of type Ⅳ hydrogen storage vessel

The growing demand for type IV hydrogen tanks with long life, lightweight, high hydrogen storage density characteristics has posed new issues for liners. The paper discusses the causes of liner failure in terms of hydrogen permeation, thermal instability, and mechanical damage, as well as a focused analysis of alternative material optimization strategies. Through a detailed investigation of aggregate state structures, formulations and processes, the principles of material modification, primarily inorganic functional filler/polymer filler filling composite and laminated orientation, and their enhancing effects are sorted out. Besides, the benefits and drawbacks of blow molding, injection and welding, and the rotating technique, which were employed by some manufacturers are contrasted in the article, for overcome the problematic molding of hollow plastic liners with metal BOSS structures. This text will be a valuable resource for material exploitation as well as efficient and reliable molding of various liners. • Improve hydrogen storage density and application range by material modification. • The failure modes of the plastic liner material are discussed. • Hydrogen barrier, mechanical and thermal properties modify measures were reviewed. • Molding methods for synthetic liners containing metal inserts are compared. • The recommendations for future liner materials design and molding are presented.

Effect of ternary transition metal sulfide FeNi2S4 on hydrogen storage performance of MgH2

Hydrogen storage is a key link in hydrogen economy, where solid-state hydrogen storage is considered as the most promising approach because it can meet the requirement of high density and safety. Thereinto, magnesium-based materials (MgH2) are currently deemed as an attractive candidate due to the potentially high hydrogen storage density (7.6 wt%), however, the stable thermodynamics and slow kinetics limit the practical application. In this study, we design a ternary transition metal sulfide FeNi2S4 with a hollow balloon structure as a catalyst of MgH2 to address the above issues by constructing a MgH2/Mg2NiH4-MgS/Fe system. Notably, the dehydrogenation/hydrogenation of MgH2 has been significantly improved due to the synergistic catalysis of active species of Mg2Ni/Mg2NiH4, MgS and Fe originated from the MgH2-FeNi2S4 composite. The hydrogen absorption capacity of the MgH2-FeNi2S4 composite reaches to 4.02 wt% at 373 K for 1 h, a sharp contrast to the milled-MgH2 (0.67 wt%). In terms of dehydrogenation process, the initial dehydrogenation temperature of the composite is 80 K lower than that of the milled-MgH2, and the dehydrogenation activation energy decreases by 95.7 kJ·mol–1 compared with the milled-MgH2 (161.2 kJ·mol–1). This method provides a new strategy for improving the dehydrogenation/hydrogenation performance of the MgH2 material.

Light-weight solid-state hydrogen storage materials characterized by neutron scattering

As a crucial link in the application of hydrogen for an alternative clean energy, light-weight solid-state hydrogen storage materials, such as metal hydrides and complex hydrides, attract ever-growing attention, and they have a great application potential due to their high hydrogen storage densities. Intensive research performed on modifications of the composition of the materials to improve their unfavorable kinetics, the thermodynamics, and reversibility, put forward higher requirements to the characterization methods to study in-depth mechanisms of the improved hydrogen absorption and desorption performance. Fortunately, due to the high scattering cross-section of hydrogen and deuterium, neutron scattering techniques, including neutron diffraction, inelastic neutron scattering, small-angle neutron scattering, and neutron total scattering technology, have become powerful tools for characterizing hydrogen storage mechanism of metal hydrides and complex hydrides. This review summarizes the recent important outcome in developing advanced solid-state hydrogen storage materials via taking advantage of neutron scattering techniques.

Hydrophilic isopropanol/acetone‐substituted polymers for safe hydrogen storage

AbstractThe development of hydrogen carriers that are free from safety risks such as explosivity, volatility and toxicity is essential for safe hydrogen storage. In this study, we synthesize a safe and hydrophilic isopropanol/acetone‐substituted polymeric hydrogen carrier by a facile synthetic procedure that is conducted in water and only requires dialysis with water for purification. A simple nucleophilic substitution of poly(allylamine) and 2‐bromoacetone produces a hydrophilic acetone‐substituted poly(allylamine) derivative, facilitating control over the hydrophilicity of the polymer according to the degree of substitution. The polymer is readily hydrogenated using NaBH4 to obtain a hydrophilic isopropanol‐substituted poly(allylamine). The high density of the repeating units and high hydrophilicity of the amine groups enable the maximization of the mass hydrogen storage density of the redox polymer to ca 1.5 wt%. Reversible hydrogen gas fixation/release from the polymeric hydrogels via chemical bond formation/disconnection is realized with complete conversion, with dehydrogenation occurring at 65–95 °C in the presence of an iridium complex catalyst. © 2021 Society of Industrial Chemistry.

(Invited) Hydrogen Materials Advanced Research Consortium R&D Activities

The Hydrogen Materials—Advanced Research Consortium (HyMARC) is a National Lab-led consortium working to advance and develop hydrogen storage materials that meet DOE targets for energy density, kinetics and cost for a wide range of applications. The goal of HyMARC is to enable a doubling of the hydrogen storage density compared with state-of-the-art compressed storage systems. DOE’s Hydrogen and Fuel Cell Technologies Office launched HyMARC in 2015, bringing together world-class National Lab capabilities in materials modelling, characterization and synthesis; and fostering collaboration with industry and academia to overcome R&D challenges in materials-based hydrogen storage. The consortium is led by teams at Sandia National Laboratories and the National Renewable Energy Laboratory and includes groups at Lawrence Livermore, Lawrence Berkeley, and Pacific Northwest National Laboratories. HyMARC is working to develop foundational understanding of phenomena governing thermodynamics and kinetics of hydrogen release and uptake in all classes of hydrogen storage materials, including metal hydrides, adsorbents, and hydrogen carriers. It seeks to accelerate materials development by addressing critical R&D gaps in hydrogen storage—leveraging recent advances in predictive multiscale modeling, machine learning, high-resolution in situ characterization, and novel materials synthesis techniques to realize their goal to enable twice the energy density for hydrogen storage in the coming years. This presentation will describe HyMARC’s ongoing R&D activities and past accomplishments which have pushed the bar forward for materials-based hydrogen storage.

Computational screening of zeolite templated carbons for hydrogen storage

Grand Canonical Monte Carlo (GCMC) simulations were used to evaluate the hydrogen storage performance of the 68 stable ZTCs which were recently identified. The relationship between the hydrogen storage capacities and densities, accessible pore volume, specific surface area, and helium void fraction of the 68 ZTC structures at 77 K and 298 K up to100 bar pressure has been investigated. The simulation results revealed that RHO has the highest gravimetric H2 uptake (9.23 wt%) under 77 K and 100 bar condition. The RHO structure also showed better deliverable capacity than other ZTCs under room temperature (1.25 wt%) and cryogenic conditions (8.83 wt%). These results show the high potential of the ZTCs for the future ultra-lightweight hydrogen storage media. The relationship between excess hydrogen capacity and specific surface area was investigated, and it was found that 10.3 mmol/g excess hydrogen capacity per 1000 m2/g specific surface area at 77 K. It was determined that the most effective parameters on the maximum excess hydrogen capacity at 77 K were accessible pore volume and specific surface area. A multiple linear regression model was also proposed to predict maximum excess hydrogen capacity at 77 K.

Alcohol-Substituted Vinyl Polymers for Stockpiling Hydrogen

Abstract Hydrogen has a high energy density and produces only water during combustion; consequently, it has attracted considerable attention as a next-generation sustainable energy source. To be used on a daily basis, hydrogen-storage materials need to stockpile hydrogen safely and to release it using only small amounts of energy. Chemically bonded hydrogen stored in a polymer is highly safe, enabling hydrogen to be stored under ambient conditions in a non-volatile, non-toxic, and non-flammable manner. Herein, we report the dehydrogenation reactions of alcohol-substituted vinyl polymers at mild temperatures. Poly(allyl alcohol) was dehydrogenated at 65–95 °C in the presence of an iridium complex catalyst to produce poly(acrylic acid) due to the extremely low activation energy (10 kJ/mol) associated with the catalyst-specific cycle. Poly(allyl alcohol) exhibits a hydrogen-storage density of 6.8 wt% by releasing two equivalents of hydrogen gas, which demonstrates that alcohol-substituted vinyl polymers can be used to stockpile hydrogen and release it under mild conditions.

Numerical simulation of hydrogen filling process in novel high-pressure microtube storage device

Novel high-pressure microtube hydrogen storage device has higher hydrogen storage density and safety than conventional hydrogen tanks. A one-dimensional numerical model for hydrogen filling process in microtubes is established, with reasonable calculation methods and accurate physical properties adopted. Based on the analysis of flow parameters variations, three stages of the filling process are summarized. At the beginning of the filling process, the maximum temperature appears at the inlet, but the average temperature does not rise significantly during the whole process. The effects of microtube length, filling pressure and environmental temperature are investigated and discussed. The results show that excessively long microtubes greatly increase the filling time and higher filling pressure reduces the filling time and improves the filling efficiency. The microtube hydrogen storage device achieves higher hydrogen storage density and filling efficiency in lower temperature mediums. It reveals that high filling pressure, low temperature encapsulation and reasonable microtube size design are the future development directions of microtube hydrogen storage for better application.

Influence of noble metals on the electronic and optical properties of LiH hydride: First-principles calculations

Lithium hydride (LiH) has attracted attention because of its high density hydrogen storage energy. However, the poor dehydrogenation properties cannot be used as an effective hydrogen storage material. In this paper, we apply the first-principles calculations to study the influence of noble metals on the electronic and optical properties of LiH hydride. Here, five noble metals TM(TM = Ag, Au, Pd, Pt and Ru) are considered. The calculated result shows that the noble metals are thermodynamic stability in LiH hydride. In particular, it is found that only the Pt-doped LiH is a dynamical stability compared to the other noble metals doping. Here, the calculated band gap of the pure LiH is 3.002 eV. Interestingly, these noble metals are beneficial to improve the electronic transfer (near Fermi level) of LiH because the introduction of noble metal induces the H-1s state to the Fermi level, making the band gap of the noble metal doped LiH disappear. In addition, we study the influence of noble metal Pt on the optical properties of LiH. It is found that the Pt doping can enhance the optical activity of LiH for visible light and infrared light, presumably caused by the addition of d state.

Hydrogen storage on Li-decorated B4N: a first-principle calculation insight

The hydrogen storage performance of Li functionalized B4N re-entrant honeycomb monolayer is investigated by using density functional theory calculations. The calculated results indicate that dispersed Li atoms can strongly bond with two N atoms with a large average binding energy. It is found that each Li atom on B4N monolayer can capture up to four H2 molecules with a desirable average adsorption energy of 0.16 eV/H2. In the fully loaded case, forming B32N8Li4–16H2 compounds, the hydrogen storage density is up to 6.23 wt%. Ab initio molecular dynamics results manifest that Li-decorated B4N has a good reversible adsorption performance on H2 molecules. The Bader charge and density of states analysis demonstrates that hydrogen molecules are physically adsorbed on the Li atoms via the electrostatic interactions. These findings suggest that Li decorated B4N monolayer can be a very potential hydrogen storage material.

Li-decorated B2O as potential candidates for hydrogen storage: A DFT simulations study

Two-dimensional (2D) B2O monolayer is considered as a potential hydrogen storage material owing to its lower mass density and high surface-to-volume ratio. The binding between H2 molecules and B2O monolayer proceeds through physisorption and the interaction is very weak, it is important to improve it through appropriate materials design. In this work, based on density functional theory (DFT) calculations, we have investigated the hydrogen storage properties of Lithium (Li) functionalized B2O monolayer. The B2O monolayer decorated by Li atoms can effectively improve the hydrogen storage capacity. It is found that each Li atom on B2O monolayer can adsorb up to four H2 molecules with a desirable average adsorption energy (Eave) of 0.18 eV/H2. In the case of fully loaded, forming B32O16Li9H72 compound, the hydrogen storage density is up to 9.8 wt%. Additionally, ab initio molecular dynamics (AIMD) calculations results show that Li-decorated B2O monolayer has good reversible adsorption performance for H2 molecules. Furthermore, the Bader charge and density of states (DOS) analysis demonstrate H2 molecules are physically absorbed on the Li atoms via the electrostatic interactions. This study suggests that Li-decorated B2O monolayer can be a promising hydrogen storage material.

A reversible hydrogen storage material of Li-decorated two-dimensional (2D) C4N monolayer: First principles calculations

Two-dimensional (2D) materials can be regarded as potential hydrogen storage candidates because of their splendid chemical stability and high specific surface area. Recently, a new dumbbell-like carbon nitride (C4N) monolayer with orbital hybridization of sp3 is reported. Motivated from the above exploration, the hydrogen adsorption properties of Li-decorated C4N monolayer are comprehensively investigated via first principles calculations based on the density functional theory (DFT). It is found that the Dirac points and Dirac cones exists in the Brillouin zone (BZ) from the calculated electronic structure and indicates the C4N can be used as an excellent topological material. Also, the calculated phonon spectra demonstrate that the C4N monolayer owns a strong stability. Moreover, the calculated binding energy of decorated Li atom is bigger than its cohesive energy and results in Li atoms disperse over the surface of C4N monolayer uniformly without clustering. In addition, the Li8C4N complex can capture up to 24H2 molecules with an optimal hydrogen adsorption energy of −0.281 eV/H2 and achieves the hydrogen storage density of 8.0 wt%. The ab initio molecular dynamics (AIMD) simulations suggest that the H2 molecules can be desorbed quickly at 300 K. This study reveals that Li-decorated C4N monolayer can be served as a promising hydrogen storage material.

A DFT study on the outstanding hydrogen storage performance of the Ti-decorated MoS2 monolayer

The hydrogen storage performances of the pure MoS2 monolayer and the one decorated with Ti atoms were studied via the first-principles DFT calculations. The Ti atom was calculated to be successfully and chemically decorated on the surface of MoS2 monolayer with a large binding energy of -4.979 eV, the absolute value of which was higher than the cohesive energy of Ti bulk (4.85 eV). The hydrogen molecule interacted weakly with the pure MoS2 with a low adsorption energy of only -0.0226 eV but was strongly adsorbed on the introduced active site of the Ti atom in the decorated MoS2 with an improved adsorption energy of -0.472 eV. There were four hydrogen molecules in maximum stored on the modified MoS2 monolayer via chemical interactions with an average adsorption energy being -0.413 eV. Moreover, the adsorbed hydrogen molecules released 1.29 e to the substrate of decorated MoS2 during the storage process. The stored hydrogen molecules of the MoS2 decorated with two Ti atoms were further improved to be eight with transferred charges being 2.42 e. Finally, the gravimetric density of hydrogen storage of the Ti-decorated MoS2 with a full coverage being 1 on its both sides could be enhanced to be as high as 5.93 wt%, well meeting the criteria of the United States Department of Energy. Our research indicates that the MoS2 monolayer decorated with Ti atoms is promising to effectively store the hydrogen molecules and is potentially applied as an excellent hydrogen gas sensor.

Acid-assisted synthesis of nitrogen-deficient mesoporous graphitic carbon nitride for hydrogen storage

Defect engineering is an important strategy to tune the surface physical and chemical properties of carbon nitride materials. Herein, a nitrogen-deficient mesoporous graphitic carbon nitride (ND-MCN) with a high specific surface area of 62.6 m2 g−1 was synthesized via hydrochloric acid-assisted thermal polycondensation of melamine and its potential application in hydrogen storage was investigated. Hydrochloric acid acting as activation agent can increase the specific surface area of carbon nitride, and introduce nitrogen-vacancy defects into the framework, leading to a stronger interaction between ND-MCN and hydrogen molecules. As a result, the ND-MCN shows a high hydrogen storage density of 6.39 × 10−3 wt%·g m−2 at 298 K under 20 bar.

Theoretical study on the structural evolution and hydrogen storage in NbHn (n = 2–15) clusters

Niobium hydrides are attractive superconductors. Exploring the formation process of niobium hydrides is essential to elucidate the mechanism of superconductivity. One of the key issues is to clarify the atomic stacking patterns of Nb and H atoms, i.e., the structural evolution of Nb–H clusters. Here, the low-energy structural isomers of NbHn (n = 2–15) clusters are determined using the CALYPSO method combined with density functional theory calculations. Geometries were fully optimized at the B3LYP/LANL2DZ/6–311++G(d) level of theory to determine global minimum structures for each size. The results indicate that NbH13 is the most stable cluster in this size range. The 4d atomic orbital of Nb and the hydrogen 1s atomic orbital participate largely to the internal binding of the NbH13 cluster. They hydrogen storage density and adsorption energy of this cluster are calculated to be 12.4 wt% and 2.58 eV, respectively. The high hydrogen storage density, suitable hydrogen adsorption energy, and high stability of NbH13 shows promise as a hydrogen storage material. These results provide fundamental information for further design of metal hydrogen storage materials.

Synthesis of vinyl polymers substituted with 2-propanol and acetone and investigation of their reversible hydrogen storage capabilities

Developing a safe hydrogen carrier without the risks of high pressures and toxicities is an issue of significant urgency. In this study, we prepared a polymeric hydrogen carrier with high thermal stability by incorporating 2-propanol and acetone units into polymers. Poly(methyl vinyl ketone) with a high molecular weight (~105) was synthesized via bulk polymerization of methyl vinyl ketone and then dehydrogenated in one step to give poly(3-buten-2-ol) in high yield. Reversible hydrogen fixation and release by these polymers were achieved with full conversion under mild conditions (80–180 °C, ≦3 atm hydrogen pressure). A simple temperature-dependent hydrogenation/dehydrogenation cycle that operated at temperatures higher than the boiling points of 2-propanol and acetone in the presence of an iridium complex catalyst was established by virtue of having these groups as pendants of the vinyl chain, with a compact repeating unit to maximize the mass hydrogen storage density of 2.8 wt%. Polymeric hydrogen carrier with high thermal stability was prepared by incorporating isopropanol and acetone units into polymers via a facile reaction process. Reversible hydrogen fixing and releasing were achieved with full conversion under mild conditions. Temperature-dependent facile hydrogenation and dehydrogenation cycle that operated at temperatures higher than the boiling points of isopropanol and acetone, in the presence of an iridium complex catalyst, was established by virtue of having these groups as pendants of the vinyl chain, with a compact repeating unit to maximize the mass hydrogen storage density of 2.8 wt%.

Mulch-assisted ambient-air synthesis of oxygen-rich activated carbon for hydrogen storage: A combined experimental and theoretical case study

Most existing manufacturing protocols of functional carbon materials highly rely on inert media, which usually make them complicated and costly. In this work, an inert gas-free method for synthesizing oxygen-rich activated carbon has been developed. The inert gas-free synthesis is conducted simply by mixing the carbon precursor with chemical activator into a sand covered vessel followed by elevated temperature treatment under ambient atmosphere. Owing to the blocking effect of sand mulch and the overflow of self-generated pyrolysis volatiles, an in-situ pressure difference is built up to prevent air penetration, forming a local air-isolated atmosphere. Lignite-based activated carbon derived from the ambient-air process exhibits hierarchical pores with specific surface area of 823 m2/g. The hydrogen storage density of this ambient-air synthesized activated carbon is determined to be up to 0.34 wt% under 35 bar at 303 K, which is mainly attributed to the enriched oxygen-containing surface groups. DFT calculations suggest the adsorption enhancement of hydrogen follows the order of cis-COOH functionalized ≥ trans-COOH > OH functionalized activated carbon surfaces. This ambient-air strategy is potentially applicable all kind of precursors, and may open up a new avenue towards the low-cost synthesis of functional carbon materials.

Materials for safe and high density hydrogen storage

Materials for safe and high density hydrogen storage