Search

Aiming to elucidate the hydrogen absorption/desorption cycling properties of Mg-based alloys with in-situ formed Mg2Ni and LaHx (x = 2, 3) nanocrystallines, the hydrogen storage cycle stability, hydriding/dehydriding cycling kinetics and thermodynamic stability of the experimental alloys have been investigated in detail. The results show that the Mg–Ni–La alloys exhibit improved hydrogen storage cycling properties and can remain storage hydrogen above 5.5 wt% after 200 cycles. With the increase of cycling numbers, the dehydrogenation rates of the experimental samples increase firstly and then gradually decrease, and eventually maintain relative stable state. Microstructure observation reveals that powders sintering and hydrogen decrepitation both exist during hydrogen absorption/desorption cycles due to repeated volume expansion and contraction. Meanwhile, the in-situ formed LaHx (x = 2, 3) and Mg2Ni nanocrystallines stabilize the microstructures of the particles and hinder the powders sintering. After 200 cycles, the average particle size of the experimental samples decreases and the specific surface area apparently increases, which leads to the decomposition temperatures of MgH2 and Mg2NiH4 slightly shift to lower temperatures. Moreover, Mg2Ni and LaHx (x = 2, 3) have been proven to be stable catalysts during long-term cycling, which can still uniformly distribute within the powders after 200 cycles.

Ultrasonic treatment has great contributions on modifying the morphology, dimension and distribution of constituent phases during solidification, which serve as dominate factors influencing the hydrogen storage performance of Mg-based alloys. In this research, ultrasonic treatment is utilized as a novel method to enhance the de-/hydriding properties of Mg-2Ni (at.%) alloy. Due to ultrasonic treatment, the microstructure of as-cast alloy is significantly refined and homogenized. Ascribing to the increased eutectic boundaries and shortened distance inside α-Mg for hydrogen atoms diffusion, the hydrogen uptake capacities and isothermal de-/hydriding rates improve effectively, especially at lower temperature. The peak desorption temperature reduces from 392.99 °C to 345.56 °C, and the dehydriding activation energy decreases from 101.93 kJ mol−1 to 88.65 kJ mol−1. Weakened hysteresis of plateau pressures and slightly optimized thermodynamics are determined from the pressure-composition isotherms. Owing to the refined primary Mg, a larger amount of hydrogen with the higher hydriding proportion is absorbed in the first stage when hydrides nucleate in eutectic region and grow on primary Mg periphery subsequently before MgH2 colonies impinging, resulting in the enhancement of hydrogenation rates and capacities.

The work presented herein describes the synthesis and characterization of metal–organic frameworks (MOFs) and their application for gas separations and hydrogen storage. Metal–organic frameworks are crystalline, porous materials that offer a high degree of synthetic tunability and can be thought of as designer zeolites. With an upfront investment in material design, followed by discovery of the appropriate synthetic conditions, new materials with specific properties optimized for a target application can be realized. Herein a new framework, V2Cl2.8(btdd), is synthesized and its unprecedented properties for gas separations and hydrogen storage is described. Other frameworks are also discussed, and overall designing orbital interactions to engender specific adsorption behavior is discussed as a relatively underexplored frontier to develop adsorbents for various important use cases.Chapter 1 introduces metal–organic frameworks, highlights how bulk properties can be controlled at the molecular level, and notable examples are provided. Key concepts of adsorption, gas separations, and hydrogen storage are discussed. Emphasis is placed on the various mechanisms of gas binding and the implications for gas separations and storage applications. The limitations of adsorbents today are discussed, and some of the outstanding challenges in gas separations are outlined. The idea of expanding the functionality of adsorbents based on orbital interactions is established.Chapter 2 describes the first example of a porous material with coordinatively unsaturated vanadium(II) sites, V2Cl2.8(btdd). The material is characterized by powder X-ray diffraction (PXRD), K-edge X-ray absorption spectroscopy, infrared spectroscopy, solid-state NMR, and gas adsorption experiments. The exposed vanadium sites are capable of backbonding with industrially- relevant π-acids, such as N2. This orbital-mediated binding and high-density of binding sites gives rise to record N2 uptake capacities and importantly enables selective capture of N2 in the presence of CH4. This work expands the functionality available to adsorbents to now include the ability to discriminate gas mixtures based on π-acidities. This has immensely important implications for industrial use, as many industrial processes utilize π-acidic gases.Chapter 3 explores the hydrogen adsorption properties of V2Cl2.8(btdd). While hydrogen is a promising zero-emission transportation fuel, its implementation is limited in part by the difficulty in its storage. Current approaches require high pressures or cryogenic temperatures to reach sufficiently high storage densities. An adsorbent with an optimal binding enthalpy for ambient-temperature hydrogen storage could transform the transportation sector. In this chapter, we show that V2Cl2.8(btdd) is the first porous material that exhibits an optimal binding enthalpy, −21kJ/mol. The orbital-mediated binding, or Kubas-type complexation, is characterized by neutron diffraction, infrared spectroscopy, and electronic structure calculations. Ultimately, the pursuit of MOFs containing high densities of weakly π-basic metal sites may enable storage capacities under ambient conditions that far surpass those accessible with compressed gas storageChapter 4 details a spectrochemical walk of relevant industrial adsorbates (H2, C3H8, C2H6, CH4, CO2, N2, C3H6, and C2H4) with V2Cl2.8(btdd). Thermodynamic binding values are obtain and electronic structure calculations are used to understand orbital interactions and their contributions to binding. Notably, V2Cl2.8(btdd) exhibits a higher enthalpy for methane than ethane and propane, in contrast to traditional adsorbents with open metal sites. This surprising result is explained by the unique orbital-mediated binding as well as steric effects. Importantly, this binding mechanism establishes a new design principle to realize selective capture of methane over other paraffins. Methane binding is characterized further by high pressure gas adsorption experiments.Chapter 5 presents a perspective on oxygen-selective adsorbents for air separations. The need for small-scale, low-capital air separation units is described. Limitations of current adsorbents are discussed and molecular principles for O2 capture are highlighted. The bulk of the chapter details with key considerations for designing oxygen-selective adsorbents that can greatly outperform incumbent technologies. A thermodynamic analysis is described which is used to benchmark materials based on the ∆G of O2 binding. The importance of entropy of O2 binding and its effect on working capacities is emphasized. Promising research direction are described, and calculation results are included which substantiate some of the proposed directions.

As a promising hydrogen storage material, the practical application of magnesium is obstructed by the stable thermodynamics and sluggish kinetics. In this paper, three kinds of NiTiO3 catalysts with different mole ratio of Ni to Ti were successfully synthesized and doped into nanocrystalline Mg to improve its hydrogen storage properties. Experimental results indicated that all the Mg-NiTiO3 composites showed prominent hydrogen storage performance. Especially, the Mg-NiTiO3/TiO2 composite could take up hydrogen at room temperature and the apparent activation energy for hydrogen absorption was dramatically decreased from 69.8 ± 1.2 (nanocrystalline Mg) kJ/mol to 34.2 ± 0.2 kJ/mol. In addition, the hydrogenated sample began to release hydrogen at about 193.2 °C and eventually desorbed 6.6 wt% H2. The desorption enthalpy of the hydrogenated Mg-NiTiO3-C was estimated to be 78.6 ± 0.8 kJ/mol, 5.3 kJ/mol lower compared to 83.9 ± 0.7 kJ/mol of nanocrystalline Mg. Besides, the sample revealed splendid cyclic stability during 20 cycles. No obvious recession occurred in the absorption and desorption kinetics and only 0.3 wt% hydrogen capacity degradation was observed. Further structural analysis demonstrates that nanosizing and catalyst doping led to a synergistic effect on the enhanced hydrogen storage performance of Mg-NiTiO3-C composite, which might serve as a reference for future design of highly effective hydrogen storage materials.

Carbon materials have excellent catalytic effects on the hydrogen storage performance of MgH2. Here, carbon-supported Ni3S2 (denoted as Ni3S2@C) was synthesized by a facile chemical route using ion exchange resin and nickel acetate tetrahydrate as raw materials and then introduced to improve the hydrogen storage properties of MgH2. The results indicated the addition of 10 wt.% Ni3S2@C prepared by macroporous ion exchange resin can effectively improve the hydrogenation/dehydrogenation kinetic properties of MgH2. At 100 °C, the dehydrogenated MgH2 Ni3S2@C-4 composite could absorb 5.68 wt.% H2. Additionally, the rehydrogenated MgH2 Ni3S2@C-4 sample could release 6.35 wt.% H2 at 275 °C. The dehydrogenation/hydrogenation enthalpy changes of MgH2 Ni3S2@C-4 were calculated to be 78.5 kJ mol−1/−74.7 kJ mol−1, i.e., 11.0 kJ mol−1/7.3 kJ mol−1 lower than those of MgH2. The improvement in the kinetic properties of MgH2 was ascribed to the multi-phase catalytic action of C, Mg2Ni, and MgS, which were formed by the reaction between Ni3S2 contained in the Ni3S2@C catalyst and Mg during the first hydrogen absorption–desorption process.

Magnesium hydride (MgH2) is one of the most promising hydrogen storage materials for practical application due to its favorable reversibility, low cost and environmental benign; however, it suffers from high dehydrogenation temperature and slow sorption kinetics. Exploring proper catalysts with high and sustainable activity is extremely desired for substantially improving the hydrogen storage properties of MgH2. In this work, a composite catalyst with high-loading of ultrafine Ni nanoparticles (NPs) uniformly dispersed on porous hollow carbon nanospheres is developed, which shows superior catalytic activity towards the de-/hydrogenation of MgH2. With an addition of 5 wt% of the composite, which contains 90 wt% Ni NPs, the onset and peak dehydrogenation temperatures of MgH2 are lowered to 190 and 242 °C, respectively. 6.2 wt% H2 is rapidly released within 30 min at 250 °C. The amount of H2 that the dehydrogenation product can absorb at a low temperature of 150 °C in only 250 s is very close to the initial dehydrogenation value. A dehydrogenation capacity of 6.4 wt% remains after 50 cycles at a moderate cyclic regime, corresponding to a capacity retention of 94.1%. The Ni NPs are highly active, reacting with MgH2 and forming nanosized Mg2Ni/Mg2NiH4. They act as catalysts during hydrogen sorption cycling, and maintain a high dispersibility with the help of the dispersive role of the carbon substrate, leading to sustainably catalytic activity. The present work provides new insight into designing stable and highly active catalysts for promoting the (de)hydrogenation kinetics of MgH2.

There are different types of materials comprising of carbon and nitrogen elements. Typical materials are the cyanogen family, beta carbon nitride, graphitic carbon nitride, azafullerenes, and heterofullerenes, N-containing heterocycles. Except cyanogen (C2N2) is a gas, most others are solid. Among these solids, the graphitic carbon nitride, with the general chemical formula of C3N4, is widely studied in heterogeneous catalysis and energy storage. Such applications exploit the resiliency of the material in different environments due to its labile protons and Lewis acid functionalities, as well as its layered structure. The structure of graphitic C3N4 allows it to store a significant amount of hydrogen. Furthermore, it offers the space for dopants, which are used purposely for tuning the band gap and the electronic properties of C3N4 to make it suitable for water splitting using sun light, or many other applications in waste water treatment under radiation. We think that the material is important and it is not being exploited at its highest capability, especially in hydrogen production via water splitting technique. This review aims to summarize recent outcomes using the carbon nitride material in hydrogen production, and a brief about hydrogen storage. We also highlight future research directions which might worth being persuaded.

The superlattice La-Y-Ni-based hydrogen storage alloys have high discharge capacity and are easy to prepare. However, there is still a gap in commercial applications because of the severe corrosion of the alloy in electrolyte and poor high-rate dischargeability (HRD). Therefore, (LaSmY)(NiMnAl)3.5 alloy was prepared by magnetic levitation induction melting, and then the alloy was coated with different contents (0.1 wt%–1.0 wt%) of nano-carbons by low-temperature sintering with sucrose as the carbon source in this work. The results show that the cyclic stability and HRD of the alloy first increase and then decrease with the increase of carbon contents. The kinetic results show that the electrocatalytic activity and conductivity of the alloy electrodes can be enhanced by carbon coating. The electrochemical properties of the alloy are the best when the carbon coating content is 0.3 wt%. Compared with the uncoated alloy, the maximum discharge capacity (Cmax) improves from 354.5 to 359.0 mAh/g, the capacity retention rate after 300 cycles (S300) enhances from 73.15% to 80.01%, and the HRD1200 of the alloy enhances from 74.39% to 74.39%.

Electrochemical storage of neutralised protons in porous carbon materials such as activated carbons and multi-layer graphene is becoming possible using novel technologies such as the proton battery and proton flow reactor. This set-up is a promising option for electrical energy storage at various scales, and possibly for exporting a zero-emission hydrogen-based fuel. This paper focusses on understanding and identifying the contributions to hydrogen storage in activated carbon from phenolic resin (aC PR) from processes such as electric double layer capacitance, electrosorption, cationic concentration by intercalation in ultramicropores, and reversible faradaic (redox) reactions between hydronium, and negatively-charged carbon surfaces inside pores with and without intermediary oxygen groups. A combination of XPS, Raman, and infrared spectroscopy is employed to identify the forms of C ⋯ H reactions involved, together with temperature programmed desorption, cyclic voltammetry and galvanostatic charging and discharging. Experimental evidence for the formation of C⋯H bonding in aC PR is presented, which promises to be sufficient for use of this and similar carbon materials as a solid-state hydrogen storage material with competitive energy density.

Functionalized single-walled carbon nanotubes into HKUST-1 ([Cu3-(btc)2]; btc = 1,3,5-benzenetricarboxylate) metal organic framework composite materials were synthesized by solvothermal method and characterized using different techniques such as XRD, BET,TG, SEM, and in situ Raman spectroscopy. It is important to mention that for the first time the thermal stability of the materials was determined by in situ Raman spectroscopy. Our results demonstrated that the incorporation of functionalized SWCNTs into HKUST-1 a slight increase in the thermal stability of MOF was observed. Too, a significant enhancement in the hydrogen adsorption capacity from 23.5% at 77 K and 1 bar of in the composite materials was observed. After of 5 cycles, hydrogen uptake is still above 2.98 wt% for 0.5SW/HKUST-1 sample. The hydrogen adsorption isotherms in the composite materials were completely reversible, reflecting only the physisorption of hydrogen molecule in the structure surface. Our results showed that the composite material with small amount of carbon nanotubes can be a promising candidate for the hydrogen storage.

Silicon-based nanosheets (SNS) were synthesised via a mild (60 °C) and time-saving (8 h) modified topochemical method. Then, Cu3(BTC)2 and SNS@Cu3(BTC)2 were successfully synthesised by microwave irradiation, and their characteristics and hydrogen storage performance were analysed by multiple techniques. The accordion-like SNS exhibited void spaces, a unique low buckled structure, and ultrathin, almost transparent, loosely stacked layers with a high specific surface area (362 m2/g). After in-situ synthesis with Cu3(BTC)2, the SNS compound achieved a high specific surface area (1526 m2/g), outstanding hydrogen storage performance (5.6 wt%), and a desirable hydrogen diffusion coefficient (10−7). Thus, SNS doping improved the hydrogen storage performance of Cu3(BTC)2 by 64% through electron transfer reactions with Cu enabled by the unique composite nanostructure of SNS@Cu3(BTC)2. This study presents a promising method of synthesising SNS and porous composite materials for hydrogen storage.

Density functional theory (DFT) calculations have been performed to investigate the hydrogen dissociation and diffusion on Mg (0001) surface with Ni incorporating at various locations. The results show that Ni atom is preferentially located inside Mg matrix rather than in/over the topmost surface. Further calculations reveal that Ni atom locating in/over the topmost Mg (0001) surface exhibits excellent catalytic effect on hydrogen dissociation with an energy barrier of less than 0.05 eV. In these cases, the rate-limiting step has been converted from hydrogen dissociation to surface diffusion. In contrast, Ni doping inside Mg bulk not only does little help to hydrogen dissociation but also exhibits detrimental effect on hydrogen diffusion. Therefore, it is crucial to stabilize the Ni atom on the surface or in the topmost layer of Mg (0001) surface to maintain its catalytic effect. For all the case of Ni-incorporated Mg (0001) surfaces, the hydrogen atom prefers firstly immigrate along the surface and then penetrate into the bulk. It is expected that the theoretical findings in the present study could offer fundamental guidance to future designing on efficient Mg-based hydrogen storage materials.

Safe, compact, lightweight and cost-effective hydrogen storage is one of the main challenges that need to be addressed to effectively deploy the hydrogen economy. LiAlH4, as a solid-state hydrogen storage material, presents several advantages such as high hydrogen storage capacity, low price and abundant sources. Unfortunately, neither thermodynamic nor kinetic properties of dehydrogenation for LiAlH4 can fulfill the requirements of practical application. Thus, a series of spinel ferrite nanoparticles such as XFe2O4 (X = Ni, Co, Mn, Cu, Zn, Fe) were prepared by using the modified thermal decomposition method, and then doped into LiAlH4 by using ball milling. Our results show that LiAlH4 doped with 7 wt% NiFe2O4 starts to release hydrogen at 69.1°C, and the total amount of hydrogen released is 7.29 wt% before 300°C. The activation energies of the two-step hydrogen release reactions of LiAlH4 doped with 7 wt% NiFe2O4 are 42.32 kJ mol−1 and 71.42 kJ mol−1, which are 59.0% and 63.6% lower than those of as-received LiAlH4, respectively. Combining the density functional theory calculations, we reveal that both the presence of NiFe2O4 and in-situ formed Al4Ni3 in ball-milling decrease the desorption energy barrier of Al-H bonding in LiAlH4 and accelerate the breakdown of Al-H bonding through the interfacial charge transfer and the dehybridization of the Al-H cluster. Thus, the experimental and theoretical results open a new avenue toward designing high effective catalysts applied to LiAlH4 as a candidate for hydrogen storage.

In this study, hydrogen-storage glass microballoons were introduced into emulsion explosives to improve the detonation performance of the explosives. The effect of hydrogen-storage pressure on the detonation characteristics of emulsion explosives was systematically investigated. Detonation velocity experiments shows that the change of sensitizing gas and the increase of hydrogen pressure have different effects on the detonation velocity. The experimental parameters of underwater explosion increase first and then decreases with the increase of hydrogen pressure. The decrease of these parameters indicates that the strength of glass microballoons is the limiting factor to improve the detonation performance of hydrogen-storage emulsion explosives. Compared with the traditional emulsion explosives, the maximum peak pressure of shock wave of hydrogen-storage emulsion explosives increases by 10.6% at 1.0 m and 10.2% at 1.2 m, the maximum values of shock impulse increase by 5.7% at 1.0 m and 19.4% at 1.2 m. The stored hydrogen has dual effects of sensitizers and energetic additives, which can improve the energy output of emulsion explosives.

Magnesium hydride (MgH2) is a potential material for solid-state hydrogen storage. However, the thermodynamic and kinetic properties are far from practical application in the current stage. In this work, two-dimensional vanadium carbide (V2C) MXene with layer thickness of 50−100 nm was fist synthesized by selectively HF-etching the Al layers from V2AlC MAX phase and then introduced into MgH2 to improve the hydrogen sorption performances of MgH2. The onset hydrogen desorption temperature of MgH2 with V2C addition is significantly reduced from 318 °C for pure MgH2 to 190 °C, with a 128 °C reduction of the onset temperature. The MgH2 + 10 wt% V2C composite can release 6.4 wt% of H2 within 10 min at 300 °C and does not loss any capacity for up to 10 cycles. The activation energy for the hydrogen desorption reaction of MgH2 with V2C addition was calculated to be 112 kJ mol−1 H2 by Arrhenius's equation and 87.6 kJ mol−1 H2 by Kissinger's equation. The hydrogen desorption reaction enthalpy of MgH2 + 10 wt% V2C was estimated by van't Hoff equation to be 73.6 kJ mol−1 H2, which is slightly lower than that of the pure MgH2 (77.9 kJ mol−1 H2). Microstructure studies by XPS, TEM, and SEM showed that V2C acts as an efficient catalyst for the hydrogen desorption reaction of MgH2. The first-principles density functional theory (DFT) calculations demonstrated that the bond length of Mg−H can be reduced from 1.71 A for pure MgH2 to 2.14 A for MgH2 with V2C addition, which contributes to the destabilization of MgH2. This work provides a method to significantly and simultaneously tailor the hydrogen sorption thermodynamics and kinetics of MgH2 by two-dimensional MXene materials.

As a highly promising candidate for hydrogen storage, crucial to vehicles powered by fuel cells, metal–organic frameworks (MOFs) have attracted the attention of chemists in recent decades. H2 uptak...

High hydrogen desorption temperature and sluggish reaction kinetics are the major limitations for the practical application of MgH2. In this study, Co particles with a face centered cubic (FCC) structure and a hexagonal close packed (HCP) structure were prepared facilely and proved to be good catalysts for magnesium hydride. Co particles with FCC structure presented better catalytic effect on MgH2 than that with HCP structure. Both 7% (mass) Co FCC and HCP particle modified MgH2 decreased the initial dehydrogenation temperature from 301.3 °C to approximately 195.0 °C, but 7% (mass) Co with FCC structure modified MgH2 has a faster desorption rate, and around 6.5% (mass) H2 was desorbed in 10 min at 325 °C. Hydrogen uptake was detected at 70 °C under 32.5 bar hydrogen pressure and 6.0% (mass) H2 was recharged in 40 min at 150 °C. The hydrogen desorption and absorption activation energy for 7% (mass) FCC Co modified MgH2 was significantly decreased to 76.6 (±8.3) kJ·mol−1 and 68.3 (±6.0) kJ·mol−1, respectively. Thermodynamic property was also studied, the plateau pressures of MgH2+7% (mass) FCC Co were determined to be 0.14, 0.28, 0.53 and 0.98 MPa for 300 ℃, 325 ℃, 350 ℃ and 375℃. The decomposition enthalpy of hydrogen (ΔH) for MgH2+7% (mass) FCC Co was 80.6 (±0.1) kJ·mol−1 , 5.8 kJ·mol−1 lower than that of as-prepared MgH2. Moreover, cycling performance for the first 20 cycles revealed that the reaction kinetics and capacity of MgH2-FCC Co composite remained almost unchanged. The result of density functional theory calculation demonstrated that cobalt could extract the Mg-H bond and reduced the decompose energy of magnesium hydride. Our paper can be presented as a reference for searching highly effective catalysts for hydrogen storage and other energy-related research fields.

RM3 compounds (R = rare earth metals, M = transition metals) have rarely been studied for gaseous hydrogen storage applications because of unfavorable thermodynamics. In this work, the hydrogen storage properties of a single-phase YFe3 alloy were improved by non-stoichiometric composition and alloying with Sc and Zr. Only the Y1.1–yScyFe3 (y = 0.22, 0.33) alloys consist of a single rhombohedral phase. The Sc substitution for Y leads to the reduction in the unit cell volume of the YFe3 phase, and thus significantly increases the dehydriding equilibrium pressure and decreases the dehydrogenation temperature. The alloy Y0.77Sc0.33Fe3 delivers a decomposition enthalpy change of 33.54 kJ/mol and a lowest dehydrogenation temperature of 135 °C, in comparison with 38.99 kJ/mol and 165 °C for the alloy Y1.1Fe3. The Zr substitution causes a similar thermodynamic destabilization effect, but the composition and microstructure of Y–Zr–Fe alloys need to be further optimized.

This paper describes a technical feasibility study of on-board metal hydride storage systems. The main advantages of these systems would be that of being able to replace counterweights with the weight of the storage system and using the heat emissions of fuel cells for energy, making forklifts a perfect use case. The main challenge is designing a system that supplies the required energy for a sufficiently long period. A first draft was set up and analyzed to provide a forklift based on a fuel cell with hydrogen from HydralloyC5 or FeTiMn. The primary design parameter was the required amount of stored hydrogen, which should provide energy equal to the energy capacity of a battery in an electric vehicle. To account for highly dynamic system requirements, the reactor design was optimized such that the storage was charged in a short time. Additionally, we investigated a system in which a fixed amount of hydrogen energy was required. For this purpose, we used a validated simulation model for the design concepts of metal hydride storage systems. The model includes all relevant terms and parameters to describe processes inside the system's particular reactions and the thermal conduction due to heat exchangers. We introduce an embedded fuel cell model to calculate the demand for hydrogen for a given power level. The resulting calculations provide the required time for charging or a full charge depending on the tank's diameter and, therefore, the necessary number of tanks. We conclude that the desired hydrogen supply times are given for some of the use cases. Accordingly, the simulated results suggest that using a metal hydride system could be highly practical in forklifts.

MgH2-based nanocomposites were synthesized by high-energy reactive ball milling (RBM) of Mg powder with 0.5–5 mol% of various catalytic additives (nano-Ti, nano-TiO2, and Ti4Fe2Ox suboxide powders) in hydrogen. The additives were shown to facilitate hydrogenation of magnesium during RBM and substantially improve its hydrogen absorption-desorption kinetics. X-ray diffraction analysis showed the formation of nanocrystalline MgH2 and hydrogenation of nano-Ti and Ti4Fe2Ox. The possible reduction of TiO2 during RBM in hydrogen was not observed, which is in agreement with lower hydrogenation capacity of the corresponding composite, 5.7 wt% for Mg + 5 mol% nano-TiO2 compared to 6.5 wt% for Mg + 5 mol% nano-Ti. Hydrogen desorption from the as-prepared composites was studied by Thermal Desorption Spectroscopy (TDS) in vacuum. A significant lowering of the hydrogen desorption temperature of MgH2 by 30–90 °C in the presence of the additives is associated with lowering activation energy from 146 kJ/mol for nanosized MgH2 down to 74 and 67 kJ/mol for MgH2 modified with nano-TiO2 and Ti4Fe2O0.3 additives, respectively. After hydrogen desorption at 300–350 °C, these materials are able to absorb hydrogen even at room temperature. It is shown that nano-structuring and addition of Ti-based catalysts do not decrease thermodynamic stability of MgH2. The thermodynamic parameters, obtained from hydrogen desorption isotherms for the Mg–Ti4Fe2O0.3 nanocomposite, ΔHdes = 76 kJ/mol H2 and ΔSdes = 138 J/K·mol H2, correspond to the reported literature values for pure polycrystalline MgH2. Hydrogen absorption-desorption characteristics of the composites with nano-Ti remain stable during at least 25 cycles, while a gradual decay of the reversible hydrogen capacity occurred in the case of TiO2 and Ti4Fe2Ox additives. Cycling stability of Mg/Ti4Fe2Ox was substantially improved by introduction of 3 wt% graphite into the composite.

A recent commentary by Santhosh and Ravindran on our paper (Int. J. Hydrogen Energy 2014, 39:10606) demonstrated that the interaction between H2 and MXene (Sc2C and Ti2C) phases are not Kubas-type and should be of weak physisorption, and thus made a conclusion that 2D Sc2C and Ti2C are not suitable for practical hydrogen storage applications. In this responses, we recalculated hydrogen adsorption on 2D Sc2C and Ti2C by using different exchange-correlation functionals. And based on the calculated results, bare MXenes (especially the Ti2C) are suitable as hydrogen storage materials at temperatures of several tens degrees lower than room temperature. And the hydrogen adsorptions on the MXenes terminated with oxygen group were also investigated. Among the Ti2C, Sc2C and their oxygen-functional counterparts, the binding energy of H2 on Sc2CO2 surface is the closest to the ideal range of 0.16–0.42 eV/H2 at ambient conditions, and thus the Sc2C with oxygen group is expected to be more suitable as hydrogen storage materials.

To reduce the cost and modulate hydrogen storage performances of Ti-based Laves phase alloys for the application of inputting 3.2 MPa feed hydrogen and outputting 8 MPa hydrogen with water bath, three series of less-vanadium Ti–Zr–Mn–Cr–V based alloys were prepared by induction levitation melting, and their microstructure and hydrogen storage properties were systematically investigated. All alloys consist of a single C14-type Laves phase with well-distributed elements. With vanadium decreasing in Ti0.95Zr0.05Mn0.9+xCr0.9+xV0.2-2x (x = 0–0.02) and Ti0.93Zr0.07Mn1.1+yCr0.7+zV0.2-y-z (y = 0, 0.05, z = 0–0.05) stoichiometric alloys, the hydrogen equilibrium pressure increases and hydrogenation kinetics is slightly deteriorated. After introducing Ti hyper-stoichiometry, Ti0.93+wZr0.07Mn1.15Cr0.7V0.15 (w = 0–0.04) alloys show decreased hydrogen equilibrium pressure, high hydrogen capacity and enhanced kinetics. Among alloys mentioned, Ti0.95Zr0.07Mn1.15Cr0.7V0.15 has optimum performances including useable capacity of 1.07 wt% at working conditions, together with satisfactory cycling durability. This study guides for compositional design of high-density hydrogen storage multi-component alloys.

Mg(BH4)2 is a promising solid-state hydrogen storage material, releasing 14.9 wt% hydrogen upon conversion to MgB2. The rehydrogenation of MgB2 is particularly challenging, requiring prolonged exposure to high pressures of hydrogen at high temperature. Here we report an XPS study probing the influence of LiH and TiH2 on the hydrogen storage properties of MgB2 in the surface and near-surface regions, as a complementary investigation to a preceding study of the bulk properties. Surface and near-surface properties are important considerations for nanoscale and bulk hydrogen storage materials. If there are reactions occurring at the surface that modify the chemical composition in the near-surface region, species diffusion can alter the chemical composition even deep into the bulk of the material. For LiH/MgB2, metastable LiH–B and LiH–Mg species are produced that are more reactive than Bulk MgB2. With prolonged glovebox storage, the LiH/MgB2 material shows increased reactivity towards O and C and enriched levels of Li and B in the near-surface region. In addition, Li induces the growth of Li2CO3 in the surface and near surface regions. Exposing LiH/MgB2 to hydrogen at 700 bar and 280 °C for 24 h produces borohydride at a temperature 100 °C below the threshold for bulk MgB2 hydrogenation. In a specifically surface process with macroscopic implications, the hydrogenation conditions also cause Li2CO3 to react with boron hydroxide in the sample to form a Li-deficient glassy lithium borate melt at the interfaces of the particles, bonding them together. Subsequent heating to 380 °C dehydrogenates the borohydride and eliminates the Li-deficient glassy lithium borate. The LiH/MgB2 material is not reversible because desorption does not lead back to LiH/MgB2, but rather to elemental B and Mg metal in the near-surface region. In contrast to LiH, TiH2 does not react with MgB2, despite the favorable thermodynamics for destabilization via TiB2 formation. Furthermore, high pressure hydrogenation yields only unreacted TiH2 and MgB2 in the surface and near-surface regions. Thus, added TiH2 provides no benefit to MgB2 hydrogenation, in agreement with the findings of the preceding bulk study.

A discharge-type fusion neutron source generates neutrons by fusion reactions of hydrogen isotope atoms. In order to operate the fusion device based on the deuterium–tritium (D–T) fusion reaction, the tritium inventory is required to be decreased. In the present work, a self-sufficient system was installed into the fusion device for reducing the amount of hydrogen isotope fuel gas. The fuel gas was supplied and recovered with an intermetallic compound ZrCo in a sealed chamber in this system. A deuterium–deuterium operation was maintained for more than 60 min with stable discharge voltages, and the temperature of the ZrCo bed was changed to improve the neutron production rate. Factors that influenced the pressure inside the chamber were determined and optimized. Gas analysis using a quadrupole mass spectrometer indicates a dilution of the deuterium fuel was caused by hydrogen isotope exchange between the supplied deuterium gas and the absorbed protium on the chamber and electrodes surface. This system's hydrogen isotope control method and the amount of fuel were proposed for a D–T operation.

On-site produced hydrogen from ammonia decomposition can directly fuel solid oxide fuel cells (SOFCs) for power generation. The key issue in ammonia decomposition is to improve the activity and stability of the reaction at low temperatures. In this study, proton-conducting oxides, Ba(Zr,Y) O3-δ (BZY), were investigated as potential support materials to load Ni metal by a one-step impregnation method. The influence of Ni loading, Ba loading, and synthesis temperature, of Ni/BZY catalysts on the catalytic activity for ammonia decomposition were investigated. The Ni/BZY catalyst with Ba loading of 20 wt%, Ni loading of 30 wt%, and synthesized at 900 °C attained the highest ammonia conversion of 100% at 600 °C. The kinetics analysis revealed that for Ni/BZY catalyst, the hydrogen poisoning effect for ammonia decomposition was significantly suppressed. The reaction order of hydrogen for the optimized Ni/BZY catalyst was estimated as low as −0.07, which is the lowest to the best of our knowledge, resulting in the improvement in the activity. H2 temperature programmed reduction and desorption analysis results suggested that a strong interaction between Ni and BZY support as well as the hydrogen storage capability of the proton-conducting support might be responsible for the promotion of ammonia decomposition on Ni/BZY. Based on the experimental data, a mechanism of hydrogen spillover from Ni to BZY support is proposed.

Aiming to gain insight on the hydrogen storage properties of Mg-based alloys, partial hydrogenation and hydrogen pressure related de-/hydrogenation kinetics of Mg–Ni–La alloys have been investigated. The results indicate that the phase boundaries, such as Mg/Mg2Ni and Mg/Mg17La2, distributed within the eutectics can act as preferential nucleation sites for β-MgH2 and apparently promote the hydrogenation process. For bulk alloy, it is observed that the hydrogenation region gradually grows from the fine Mg–Ni–La eutectic to primary Mg region with the extension of reaction time. After high-energy ball milling, the nanocrystalline powders with crystallite size of 12∼20 nm exhibit ameliorated hydrogen absorption/desorption performance, which can absorb 2.58 wt% H2 at 368 K within 50 min and begin to desorb hydrogen from ∼508 K. On the other side, variation of hydrogen pressure induced driving force significantly affects the reaction kinetics. As the hydrogenation/dehydrogenation driving forces increase, the hydrogen absorption/desorption kinetics is markedly accelerated. The dehydrogenation mechanisms have also been revealed by fitting different theoretical kinetics models, which demonstrate that the rate-limiting steps change obviously with the variation of driving forces.

TiCr2 with adding different amount of Mn (0, 2, 4 and 8 wt.%) alloys have been investigated. All alloys have C14-type main phase (gray color in SEM) and Ti minor phase (dark gray color in SEM). Rietveld fitting results proved that the lattice parameter a and cell volume of C14-type phase decreased with increasing Mn content. The first hydrogenation measurement manifest that all alloys have best activation properties and could be activated without any prior heat treatment and hydrogen exposure. However, introducing Mn led to the decrease of the first hydrogen absorption rate of TiCr2 alloy, which may be due to the decrease of cell volume of C14-type main phase. The first hydrogenation properties at low temperature and effect of air exposure of the alloy were discussed. The results showed that the maximum hydrogen absorption capacity at 0 °C was obviously higher than that at room temperature. In addition, TiCr2 alloy doped with minor amounts of Mn after long-time air exposure showed better hydrogenation performance. This may be due to the Mn additive acting as a deoxidizer. Finally, the first hydrogenation kinetic mechanisms of all alloys at different temperature were also studied by using the rate limiting step.

Co2B alloy was synthesized via the method of high temperature solid phase. Carbon fiber (CF) was prepared from cotton by calcination process. The addition of carbon fiber and Co3O4 improves corrosion resistance and charge transfer speed of the composite material electrode. The Rct value of Co2B + 1 wt.% CF was 360 mΩ, lower than the other composite electrode could reduce charge transfer resistance. The overall electrochemical performance of Co2B + 2 wt.% Co3O4 + 1 wt.% CF was best among all the electrodes, and its Cmax could reach 715.3 mAh/g. The high conductivity and multiple reaction sites provided by carbon fiber and the catalytic effect of Co3O4 may be the main reasons for the improvement of electrochemical performance, which enhance the kinetic performance of electrochemical reactions. The synergistic effect of carbon fiber and Co3O4 improves the electrochemical hydrogen storage properties of Co2B alloy. This work presents a simple and effective method to improve the electrochemical hydrogen storage performance of cobalt-boron alloys by adding transition metal oxides and carbon materials derived from biomass.

An optimal hydrogen storage reactor should have a higher chemical reaction rate by which the heat can be exchanged as fast as possible. The configuration of heat exchanger structure design plays a crucial role in improving heat and mass transfer effect in metal hydride beds. Consequently, a variety of different metal hydride bed configurations have been investigated in experimental and simulation works for the improvement of absorption/desorption rate. In this work, the development of metal hydride bed design in recent decades has been reviewed to help the readers summarize and optimize the reactor configuration. The summarization and review of metal hydrides design can be broadly classified into five distinct categories, which are: 1) design of cooling tubes, 2) design of fins, 3) increasing and arrangement of cooling tubes, 4) other geometric design, and 5) utilization of phase change material. This work is concentrated on assessing the heat and mass transfer effectiveness of various reactor structure configurations. The superiority and weakness of different configurations are summarized to give a comparison of the heat exchange effects. Moreover, the structural parameter analysis for each configuration is also reviewed from the heat and mass transfer aspect. Finally, some recommendations are provided for future metal hydride bed structural designs.