Isotope engineering achieved by local coordination design in Ti-Pd co-doped ZrCo-based alloys

Deuterium/Tritium (D/T) handling in defined proportions are pivotal to maintain steady-state operation for fusion reactors. However, the hydrogen isotope effect in metal-hydrogen systems always disturbs precise D/T ratio control. Here, we reveal the dominance of kinetic isotope effect during desorption. To reconcile the thermodynamic stability and isotope effect, we demonstrate a quantitative indicator of Tgap and further a local coordination design strategy that comprises thermodynamic destabilization with vibration enhancement of interstitial isotopes for isotope engineering. Based on theoretical screening analysis, an optimized Ti-Pd co-doped Zr0.8Ti0.2Co0.8Pd0.2 alloy is designed and prepared. Compared to ZrCo alloy, the optimal alloy enables consistent isotope delivery together with a three-fold lower Tgap, a five-fold lower energy barrier difference, a one-third lower isotopic composition deviation during desorption and an over two-fold higher cycling capacity. This work provides insights into the interaction between alloy and hydrogen isotopes, thus opening up feasible approaches to support high-performance fusion reactors.

Atomic reconstruction for realizing stable solar-driven reversible hydrogen storage of magnesium hydride

Reversible solid-state hydrogen storage of magnesium hydride, traditionally driven by external heating, is constrained by massive energy input and low systematic energy density. Herein, a single phase of Mg2Ni(Cu) alloy is designed via atomic reconstruction to achieve the ideal integration of photothermal and catalytic effects for stable solar-driven hydrogen storage of MgH2. With the intra/inter-band transitions of Mg2Ni(Cu) and its hydrogenated state, over 85% absorption in the entire spectrum is achieved, resulting in the temperature up to 261.8 °C under 2.6 W cm-2. Moreover, the hydrogen storage reaction of Mg2Ni(Cu) is thermodynamically and kinetically favored, and the imbalanced distribution of the light-induced hot electrons within CuNi and Mg2Ni(Cu) facilitates the weakening of Mg-H bonds of MgH2, enhancing the "hydrogen pump" effect of Mg2Ni(Cu)/Mg2Ni(Cu)H4. The reversible generation of Mg2Ni(Cu) upon repeated dehydrogenation process enables the continuous integration of photothermal and catalytic roles stably, ensuring the direct action of localized heat on the catalytic sites without any heat loss, thereby achieving a 6.1 wt.% H2 reversible capacity with 95% retention under 3.5 W cm-2.

Experimentally validated design principles of heteroatom-doped-graphene-supported calcium single-atom materials for non-dissociative chemisorption solid-state hydrogen storage

Non-dissociative chemisorption solid-state storage of hydrogen molecules in host materials is promising to achieve both high hydrogen capacity and uptake rate, but there is the lack of non-dissociative hydrogen storage theories that can guide the rational design of the materials. Herein, we establish generalized design principle to design such materials via the first-principles calculations, theoretical analysis and focused experimental verifications of a series of heteroatom-doped-graphene-supported Ca single-atom carbon nanomaterials as efficient non-dissociative solid-state hydrogen storage materials. An intrinsic descriptor has been proposed to correlate the inherent properties of dopants with the hydrogen storage capability of the carbon-based host materials. The generalized design principle and the intrinsic descriptor have the predictive ability to screen out the best dual-doped-graphene-supported Ca single-atom hydrogen storage materials. The dual-doped materials have much higher hydrogen storage capability than the sole-doped ones, and exceed the current best carbon-based hydrogen storage materials.

On the Use of Solomon Echoes in 27 Al NMR Studies of Complex Aluminium Hydrides

The quadrupole coupling constant CQ and the asymmetry parameter η have been determined for two complex aluminium hydrides from 27 Al NMR spectra recorded for stationary samples by using the Solomon echo sequence. The thus obtained data for KAlH4 (CQ =(1.30±0.02) MHz, η=(0.64±0.02)) and NaAlH4 (CQ =(3.11±0.02) MHz, η<0.01) agree very well with data previously determined from MAS NMR spectra. The accuracy with which these parameters can be determined from static spectra turned out to be at least as good as via the MAS approach. The experimentally determined parameters (δiso , CQ and η) are compared with those obtained from DFT-GIPAW (density functional theory - gauge-including projected augmented wave) calculations. Except for the quadrupole coupling constant for KAlH4 , which is overestimated in the GIPAW calculations by about 30 %, the agreement is excellent. Advantages of the application of the Solomon echo sequence for the measurement of less stable materials or for in situ studies are discussed.

Single-crystal ZrCo nanoparticle for advanced hydrogen and H-isotope storage

Hydrogen-isotope storage materials are essential for the controlled nuclear fusion. However, the currently used smelting-ZrCo alloy suffers from rapid degradation of performance due to severe disproportionation. Here, we reveal a defect-derived disproportionation mechanism and report a nano-single-crystal strategy to solve ZrCo's problems. Single-crystal nano-ZrCo is synthesized by a wet-chemistry method and exhibits excellent comprehensive hydrogen-isotope storage performances, including ultrafast uptake/release kinetics, high anti-disproportionation ability, and stable cycling, far superior to conventional smelting-ZrCo. Especially, a further incorporation of Ti into nano-ZrCo can almost suppress the disproportionation reaction. Moreover, a mathematical relationship between dehydrogenation temperature and ZrCo particle size is established. Additionally, a microwave method capable of nondestructively detecting the hydrogen storage state of ZrCo is developed. The proposed disproportionation mechanism and anti-disproportionation strategy will be instructive for other materials with similar problems.

Corrosion-resistant cobalt phosphide electrocatalysts for salinity tolerance hydrogen evolution

Seawater electrolysis is a viable method for producing hydrogen on a large scale and low-cost. However, the catalyst activity during the seawater splitting process will dramatically degrade as salt concentrations increasing. Herein, CoP is discovered that could reject chloride ions far from catalyst in electrolyte based on molecular dynamic simulation. Thus, a binder-free electrode is designed and constructed by in-situ growth of homogeneous CoP on rGO nanosheets wrapped around the surface of Ti fiber felt for seawater splitting. As expected, the as-obtained CoP/rGO@Ti electrode exhibits good catalytic activity and stability in alkaline electrolyte. Especially, benefitting from the highly effective repulsive Cl- intrinsic characteristic of CoP, the catalyst maintains good catalytic performance with saturated salt concentration, and the overpotential increasing is less than 28 mV at 10 mA cm-2 from 0 M to saturated NaCl in electrolyte. Furthermore, the catalyst for seawater splitting performs superior corrosion-resistance with a low solubility of 0.04%. This work sheds fresh light into the development of efficient HER catalysts for salinity tolerance hydrogen evolution.

PdNi Biatomic Clusters from Metallene Unlock Record-Low Onset Dehydrogenation Temperature for Bulk-MgH2

Hydrogen storage has long been a priority on the renewable energy research agenda. Due to its high volumetric and gravimetric hydrogen density, MgH2 is a desirable candidate for solid-state hydrogen storage. However, its practical use is constrained by high thermal stability and sluggish kinetics. Here, PdNi bilayer metallenes are reported as catalysts for hydrogen storage of bulk-MgH2 near ambient temperature. Unprecedented 422 K beginning dehydrogenation temperature and up to 6.36 wt.% reliable hydrogen storage capacity are achieved. Fast hydrogen desorption is also provided by the system (5.49 wt.% in 1 h, 523 K). The in situ generated PdNi alloy clusters with suitable d-band centers are identified as the main active sites during the de/re-hydrogenation process by aberration-corrected transmission electron microscopy and theoretical simulations, while other active species including Pd/Ni pure phase clusters and Pd/Ni single atoms obtained via metallene ball milling, also enhance the reaction. These findings present fundamental insights into active species identification and rational design of highly efficient hydrogen storage materials.

Room-Temperature Transient Hydrogen Uptake of MgH2 Induced by Nb-Doped TiO2 Solid-Solution Catalysts

The practical applications of MgH₂ as a high-density hydrogen carrier depend heavily on efficient and low-cost catalysts to accelerate the dehydriding/hydriding reactions at moderate temperatures. In the present work, this issue is addressed by synthesizing Nb-doped TiO₂ solid-solution-type catalysts that dramatically improve the hydrogen sorption performances of MgH₂. The catalyzed MgH₂ can absorb 5 wt % of H₂ even at room temperature for 20 s, release 6 wt % of H₂ at 225 °C within 12 min, and the complete dehydrogenation can be achieved at 150 °C under a dynamic vacuum atmosphere. Density functional theory calculations reveal that Nb doping introduces Nb 4d orbitals with stronger interaction with H 1s into the density of states of TiO₂. This considerably enhances both the adsorption and dissociation ability of the H₂ molecule on the catalysts surface and the hydrogen diffusion across the specific Mg/Ti(Nb)O₂ interface. The successful implementation of solid solution-type catalysts in MgH₂ offers a demonstration and inspiration for the development of high-performance catalysts and solid-state hydrogen storage materials.

Dispersed surface Ru ensembles on MgO(111) for catalytic ammonia decomposition

Ammonia is regarded as an energy vector for hydrogen storage, transport and utilization, which links to usage of renewable energies. However, efficient catalysts for ammonia decomposition and their underlying mechanism yet remain obscure. Here we report that atomically-dispersed Ru atoms on MgO support on its polar (111) facets {denoted as MgO(111)} show the highest rate of ammonia decomposition, as far as we are aware, than all catalysts reported in literature due to the strong metal-support interaction and efficient surface coupling reaction. We have carefully investigated the loading effect of Ru from atomic form to cluster/nanoparticle on MgO(111). Progressive increase of surface Ru concentration, correlated with increase in specific activity per metal site, clearly indicates synergistic metal sites in close proximity, akin to those bimetallic N₂ complexes in solution are required for the stepwise dehydrogenation of ammonia to N₂/H₂, as also supported by DFT modelling. Whereas, beyond surface doping, the specific activity drops substantially upon the formation of Ru cluster/nanoparticle, which challenges the classical view of allegorically higher activity of coordinated Ru atoms in cluster form (B₅ sites) than isolated sites.

Solar-Driven Reversible Hydrogen Storage

The lack of safe and efficient hydrogen storage is a major bottleneck for large-scale application of hydrogen energy. Reversible hydrogen storage of light-weight metal hydrides with high theoretical gravimetric and volumetric hydrogen density is one ideal solution but requires extremely high operating temperature with large energy input. Herein, taking MgH₂ as an example, a concept is demonstrated to achieve solar-driven reversible hydrogen storage of metal hydrides via coupling the photothermal effect and catalytic role of Cu nanoparticles uniformly distributed on the surface of MXene nanosheets (Cu@MXene). The photothermal effect of Cu@MXene, coupled with the "heat isolator" role of MgH₂ indued by its poor thermal conductivity, effectively elevates the temperature of MgH₂ upon solar irradiation. The "hydrogen pump" effect of Ti and TiH_x species that are in situ formed on the surface of MXene from the reduction of MgH₂ , on the other hand, plays a catalytic role in effectively alleviating the kinetic barrier and hence decreasing the operating temperature required for reversible hydrogen adsorption and desorption of MgH₂ . Based on the combination of photothermal and catalytic effect of Cu@MXene, a reversible hydrogen storage capacity of 5.9 wt% is achieved for MgH₂ after 30 cycles using solar irradiation as the only energy source.

A Unique Nanoflake-Shape Bimetallic Ti-Nb Oxide of Superior Catalytic Effect for Hydrogen Storage of MgH2

MgH₂ is one of the most promising solid hydrogen storage materials due to its high capacity, excellent reversibility, and low cost. However, its operation temperature needs to be greatly reduced to realize its practical applications, especially in the highly desired fuel cell fields. This work synthesizes a 2D nanoflake-shape bimetallic Ti-Nb oxide of TiNb₂ O₇ , which has high surface area and shows superior catalytic effect for the hydrogen storage of MgH₂ . Incorporated with the TiNb₂ O₇ nanoflakes as low as 3 wt%, MgH₂ shows a low onset dehydrogenation temperature of 178 °C, which is lowered by 100 °C compared with the pristine one. A dehydrogenation capacity as high as 7.0 wt% H₂ is achieved upon heating to 300 °C. The capacity retention is as high as 96% after 30 cycles. The mechanism of the improved hydrogen storage properties is analyzed by density functional theory (DFT) calculation and the microstructural evolution during dehydrogenation and hydrogenation. This work provides an MgH₂ system with high available capacity and low operation temperature by a unique structural design of the catalyst. The high surface area feature of the TiNb₂ O₇ nanoflakes and the synthesis method hopefully can develop the application of TiNb₂ O₇ .

Superior Dehydrogenation Performance of α-AlH3 Catalyzed by Li3 N: Realizing 8.0 wt.% Capacity at 100 °C

The high dehydrogenation temperature of aluminum hydride (AlH₃ ) has always been an obstacle to its application as a portable hydrogen source. To solve this problem, lithium nitride is introduced into the aluminum hydride system as a catalyst to optimize the dehydrogenation drastically, which reduces the initial dehydrogenation temperature from 140.0 to 66.8 °C, and provides a stable hydrogen capacity of 8.24, 6.18, and 5.75 wt.% at 100, 90, and 80 °C within 120 min by adjusting the mass fraction of lithium nitride. Approximately 8.0 wt.% hydrogen can be released within 15 min at 100 °C for the sample of 10 wt.% doping. Moderate dehydrogenation temperature slows down the inevitable self-dehydrogenation process during the ball-milling process, and the enhanced kinetics at lower temperature shows the possibility of application in the fuel cell.

2-step reaction kinetics for hydrogen absorption into bulk material via dissociative adsorption on the surface

We have demonstrated that the process of hydrogen absorption into a solid experimentally follows a Langmuir-type (hyperbolic) function instead of Sieverts law. This can be explained by independent two theories. One is the well-known solubility theory which is the basis of Sieverts law. It explains that the amount of hydrogen absorption can be expressed as a Langmuir-type (hyperbolic) function of the square root of the hydrogen pressure. We have succeeded in drawing the same conclusion from the other theory. It is a 2-step reaction kinetics (2sRK) model that expresses absorption into the bulk via adsorption on the surface. The 2sRK model has an advantage to the solubility theory: Since it can describe the dynamic process, it can be used to discuss both the amount of hydrogen absorption and the absorption rate. Some phenomena with absorption via adsorption can be understood in a unified manner by the 2sRK model.

Thermally-assisted milling and hydrogenolysis for synthesizing ultrafine MgH2with destabilized thermodynamics

A novel process has been developed to synthesize MgH₂nanoparticles by combining ball milling and thermal hydrogenolysis of di-n-butylmagnesium (C₄H₉)₂Mg, denoted as MgBu₂. With the aid of mechanical impact, the hydrogenolysis temperature of MgBu₂in heptane and cyclohexane solution was considerably lowered down to 100 °C, and the MgH₂nanoparticles with an average particle size ofca.8.9 nm were obtained without scaffolds. The nano-size effect of the MgH₂nanoparticles causes a notable decrease in the onset dehydrogenation temperature of 225 °C and enthalpy of 69.78 kJ mol^-1 · H₂. This thermally-assisted milling and hydrogenolysis process may also be extended for synthesizing other nanomaterials.

Improved Hydrogenation Kinetics of TiMn1.52 Alloy Coated with Palladium through Electroless Deposition

The deterioration of hydrogen charging performances resulting from the surface chemical action of electrophilic gases such as CO₂ is one of the prevailing drawbacks of TiMn_1.52 materials. In this study, we report the effect of autocatalytic Pd deposition on the morphology, structure, and hydrogenation kinetics of TiMn_1.52 alloy. Both the uncoated and Pd-coated materials were characterized using scanning electron microscopy/energy dispersive spectroscopy (SEM/EDS) and X-ray diffraction (XRD). XRD analyses indicated that TiMn_1.52 alloy contains C14-type Laves phase without any second phase, while the SEM images, together with a particle size distribution histogram, showed a smooth non-porous surface with irregular-shaped particles ranging in size from 1 to 8 µm. The XRD pattern of Pd-coated alloy revealed that C14-type Laves phase was still maintained upon Pd deposition. This was further supported by calculated crystallite size of 29 nm for both materials. Furthermore, a Sieverts-type apparatus was used to study the kinetics of the alloys after pre-exposure to air and upon vacuum heating at 300 °C. The Pd-coated AB₂ alloy exhibited good coating quality as confirmed by EDS with enhanced hydrogen absorption kinetics, even without activation. This is attributed to improved surface tolerance and a hydrogen spillover mechanism, facilitated by Pd nanoparticles. Vacuum heating at 300 °C resulted in removal of surface barriers and showed improved hydrogen absorption performances for both coated and uncoated alloys.

Effect of Few-Layer Ti3C2Tx Supported Nano-Ni via Self-Assembly Reduction on Hydrogen Storage Performance of MgH2

For the first time, few-layer Ti₃C₂T_x (FL-Ti₃C₂T_x) supporting highly dispersed nano-Ni particles with an interconnected and interlaced structure was elaborated through a self-assembly reduction process. FL-Ti₃C₂T_x not only acts as a supporting material but also self-assembles with Ni²⁺ ions through the electrostatic interaction, assisting in the reduction of nano-Ni. After ball milling with MgH₂, Ni₃₀/FL-Ti₃C₂T_x (few-layer Ti₃C₂T_x supported 30 wt % nano-Ni via self-assembly reduction) shows superior catalytic activity for MgH₂. For example, MgH₂-5 wt % Ni₃₀/FL-Ti₃C₂T_x can release approximately 5.83 wt % hydrogen within 1800 s at 250 °C and absorb 5 wt % hydrogen within 1700 s at 100 °C. The combined effects of finely dispersed nano-Ni in situ-grown on FL-Ti₃C₂T_x, large specific area of FL-Ti₃C₂T_x, multiple-valence Ti (Ti⁴⁺, Ti³⁺, Ti²⁺, and Ti⁰) derived from FL-Ti₃C₂T_x, and the electronic interaction between Ni and FL-Ti₃C₂T_x can explain the superb hydrogen storage performance. Our results will attract more attention to the elaboration of the metal/FL-Ti₃C₂T_x composite via self-assembly reduction and provide a guideline to design high-efficiency composite catalysts with MXene in hydrogen storage fields.

Rechargeable proton exchange membrane fuel cell containing an intrinsic hydrogen storage polymer

Proton exchange membrane fuel cells (PEMFCs) are promising clean energy conversion devices in residential, transportation, and portable applications. Currently, a high-pressure tank is the state-of-the-art mode of hydrogen storage; however, the energy cost, safety, and portability (or volumetric hydrogen storage capacity) presents a major barrier to the widespread dissemination of PEMFCs. Here we show an 'all-polymer type' rechargeable PEMFC (RCFC) that contains a hydrogen-storable polymer (HSP), which is a solid-state organic hydride, as the hydrogen storage media. Use of a gas impermeable SPP-QP (a polyphenylene-based PEM) enhances the operable time, reaching up to ca. 10.2 s mg_HSP^-1, which is more than a factor of two longer than that (3.90 s mg_HSP^-1) for a Nafion NRE-212 membrane cell. The RCFCs are cycleable, at least up to 50 cycles. The features of this RCFC system, including safety, ease of handling, and light weight, suggest applications in mobile, light-weight hydrogen-based energy devices.

A Unique Double-Layered Carbon Nanobowl-Confined Lithium Borohydride for Highly Reversible Hydrogen Storage

Poor reversibility and high desorption temperature restricts the practical use of lithium borohydride (LiBH₄ ) as an advanced hydrogen store. Herein, a LiBH₄ composite confined in unique double-layered carbon nanobowls prepared by a facile melt infiltration process is demonstrated, thanks to powerful capillary effect under 100 bar of H₂ pressure. The gradual formation of double-layered carbon nanobowls is witnessed by transmission electron microscopy (TEM) observation. Benefiting from the nanoconfinement effect and catalytic function of carbon, this composite releases hydrogen from 225 °C and peaks at 353 °C, with a hydrogen release amount up to 10.9 wt%. The peak temperature of dehydriding is lowered by 112 °C compared with bulk LiBH₄ . More importantly, the composite readily desorbs and absorbs ≈8.5 wt% of H₂ at 300 °C and 100 bar H₂ , showing a significant reversibility of hydrogen storage. Such a high reversible capacity has not ever been observed under the identical conditions. The usable volumetric energy density reaches as high as 82.4 g L^-1 with considerable dehydriding kinetics. The findings provide insights in the design and development of nanosized complex hydrides for on-board applications.

Monodisperse palladium-cobalt alloy nanocatalyst supported on activated carbon (AC) as highly effective catalyst for the DMAB dehydrocoupling

In the study, activated carbon (AC) supported palladium/cobalt (Pd/Co) nanocatalyst was synthesized to achieve hydrogen release from dimethylamine boron (DMAB). Nanocatalyst were produced by the reduction of Pd2+ and Co2+ cations by the ultrasonic double reduction method. Analytical studies of the synthesized nanomaterials were characterized by X-ray photoelectron spectroscopy, Raman spectroscopy, X-ray diffraction, transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HR-TEM), electron energy loss spectroscopy, ultraviolet-visible spectroscopy. In this research, nanomaterials exhibited high catalytic activity and reusability, and great performance at low temperatures and concentrations. For the dehydrogenation reaction of dimethylamine borane, TOF and Ea were calculated as 379.5 h-1 and 75.86 kJ mol-1, respectively. The PdCo@AC nanocatalyst can be used as a promising catalyst for the hydrogen production reaction from DMAB.

Dehydrogenation Performances of Different Al Source Composite Systems of 2LiBH4 + M (M = Al, LiAlH4, Li3AlH6)

Hydrogen has become a promising energy source due to its efficient and renewable properties. Although promising, hydrogen energy has not been in widespread use due to the lack of high-performance materials for hydrogen storage. Previous studies have shown that the addition of Al-based compounds to LiBH₄ can create composites that have good properties for hydrogen storage. In this work, the dehydrogenation performances of different composite systems of 2LiBH₄+ M (M = Al, LiAlH₄, Li₃AlH₆) were investigated. The results show that, under a ball to powder ratio of 25:1 and a rotation speed of 300 rpm, the optimum ball milling time is 50 h for synthesizing Li₃AlH₆ from LiH and LiAlH₄. The three studied systems destabilized LiBH₄ at relatively low temperatures, and the 2LiBH₄-Li₃AlH₆ composite demonstrated excellent behavior. Based on the differential scanning calorimetry results, pure LiBH₄ released hydrogen at 469°C. The dehydrogenation temperature of LiBH₄ is 416°C for 2LiBH₄-Li₃AlH₆ versus 435°C for 2LiBH₄-LiAlH₄ and 445°C for 2LiBH₄-Al. The 2LiBH₄-Li₃AlH₆, 2LiBH₄-LiAlH₄, and 2LiBH₄-Al samples released 9.1, 8, and 5.7 wt.% of H₂, respectively. Additionally, the 2LiBH₄-Li₃AlH₆ composite released the 9.1 wt.% H₂ within 150 min. An increase in the kinetics was achieved. From the results, it was concluded that 2LiBH₄-Li₃AlH₆ exhibits the best dehydrogenation performance. Therefore, the 2LiBH₄-Li₃AlH₆ composite is considered a promising hydrogen storage material.

Flexible, Water-Resistant and Air-Stable LiBH4 Nanoparticles Loaded Melamine Foam With Improved Dehydrogenation

Flexible, water-resistant, and air-stable hydrogen storage material (named PMMA-LiBH₄/GMF), consisting of LiBH₄ nanoparticles confined by poly (methylmethacrylate) (PMMA) and reduced graphene oxide (rGO) modified melamine foam (GMF), were prepared by a facile method. PMMA-LiBH₄/GMF can recover original shape after compression at the strain of 50% and exhibits highly hydrophobic property (water contact angle of 123°). Owing to the highly hydrophobic property and protection of PMMA, PMMA-LiBH₄/GMF demonstrates outstanding water-resistance and air-stability. Significantly, the onset dehydrogenation temperature of PMMA-LiBH₄/GMF at first step is reduced to 94°C, which is 149°C less than that of LiBH₄/GMF, and the PMMA-LiBH₄/GMF desorbs 2.9 wt% hydrogen within 25 min at 250°C, which is obviously more than the dehydrogenation amount of LiBH₄/GMF under the same conditions. It's our belief that the flexible, water-resistant and air-stable PMMA-LiBH₄/GMF with a simple preparation route will provide a new avenue to the research of hydrogen storage materials.

Isolating hydrogen in hexagonal boron nitride bubbles by a plasma treatment

Atomically thin hexagonal boron nitride (h-BN) is often regarded as an elastic film that is impermeable to gases. The high stabilities in thermal and chemical properties allow h-BN to serve as a gas barrier under extreme conditions. Here, we demonstrate the isolation of hydrogen in bubbles of h-BN via plasma treatment. Detailed characterizations reveal that the substrates do not show chemical change after treatment. The bubbles are found to withstand thermal treatment in air, even at 800 °C. Scanning transmission electron microscopy investigation shows that the h-BN multilayer has a unique aligned porous stacking nature, which is essential for the character of being transparent to atomic hydrogen but impermeable to hydrogen molecules. In addition, we successfully demonstrated the extraction of hydrogen gases from gaseous compounds or mixtures containing hydrogen element. The successful production of hydrogen bubbles on h-BN flakes has potential for further application in nano/micro-electromechanical systems and hydrogen storage.

Hydrogen Desorption Properties of LiBH4/xLiAlH4 (x = 0.5, 1, 2) Composites

A detailed analysis of the dehydrogenation mechanism of LiBH₄/xLiAlH₄ (x = 0.5, 1, 2) composites was performed by thermogravimetry (TG), differential scanning calorimetry (DSC), mass spectral analysis (MS), powder X-ray diffraction (XRD) and scanning electronic microscopy (SEM), along with kinetic investigations using a Sievert-type apparatus. The results show that the dehydrogenation pathway of LiBH₄/xLiAlH₄ had a four-step character. The experimental dehydrogenation amount did not reach the theoretical expectations, because the products such as AlB₂ and LiAl formed a passivation layer on the surface of Al and the dehydrogenation reactions associated with Al could not be sufficiently carried out. Kinetic investigations discovered a nonlinear relationship between the activation energy (E_a) of dehydrogenation reactions associated with Al and the ratio x, indicating that the E_a was determined both by the concentration of Al produced by the decomposition of LiAlH₄ and the amount of free surface of it. Therefore, the amount of effective contact surface of Al is the rate-determining factor for the overall dehydrogenation of the LiBH₄/xLiAlH₄ composites.

Reversible Hydrogen Uptake/Release over a Sodium Phenoxide-Cyclohexanolate Pair

Hydrogen uptake and release in arene-cycloalkane pairs provide an attractive opportunity for on-board and off-board hydrogen storage. However, the efficiency of arene-cycloalkane pairs currently is limited by unfavorable thermodynamics for hydrogen release. It is shown here that the thermodynamics can be optimized by replacement of H in the -OH group of cyclohexanol and phenol with alkali or alkaline earth metals. The enthalpy change upon dehydrogenation decreases substantially, which correlates with the delocalization of the oxygen electron to the benzene ring in phenoxides. Theoretical calculations reveal that replacement of H with a metal leads to a reduction of the HOMO-LUMO energy gap and elongation of the C-H bond in the α site in cyclohexanolate, which indicates that the cyclohexanol is activated upon metal substitution. The experimental results demonstrate that sodium phenoxide-cyclohexanolate, an air- and water-stable pair, can desorb hydrogen at ca. 413 K and 373 K in the solid form and in an aqueous solution, respectively. Hydrogenation, on the other hand, is accomplished at temperatures as low as 303 K.

Improvement of Hydrogen Desorption Characteristics of MgH₂ With Core-shell Ni@C Composites

Magnesium hydride (MgH₂) has become popular to study in hydrogen storage materials research due to its high theoretical capacity and low cost. However, the high hydrogen desorption temperature and enthalpy as well as the depressed kinetics, have severely blocked its actual utilizations. Hence, our work introduced Ni@C materials with a core-shell structure to synthesize MgH₂-x wt.% Ni@C composites for improving the hydrogen desorption characteristics. The influences of the Ni@C addition on the hydrogen desorption performances and micro-structure of MgH₂ have been well investigated. The addition of Ni@C can effectively improve the dehydrogenation kinetics. It is interesting found that: i) the hydrogen desorption kinetics of MgH₂ were enhanced with the increased Ni@C additive amount; and ii) the dehydrogenation amount decreased with a rather larger Ni@C additive amount. The additive amount of 4 wt.% Ni@C has been chosen in this study for a balance of kinetics and amount. The MgH₂-4 wt.% Ni@C composites release 5.9 wt.% of hydrogen in 5 min and 6.6 wt.% of hydrogen in 20 min. It reflects that the enhanced hydrogen desorption is much faster than the pure MgH₂ materials (0.3 wt.% hydrogen in 20 min). More significantly, the activation energy (E_A) of the MgH₂-4 wt.% Ni@C composites is 112 kJ mol⁻¹, implying excellent dehydrogenation kinetics.

Trimeric cluster of lithium amidoborane-the smallest unit for the modeling of hydrogen release mechanism

A detailed first-principle DFT M06/6-311++G(d.p) study of dehydrogenation mechanism of trimeric cluster of lithium amidoborane is presented. The first step of the reaction is association of two LiNH2 BH3 molecules in the cluster. The dominant feature of the subsequent reaction pathway is activation of H atom of BH3 group by three Li atoms with formation of unique Li3 H moiety. This Li3 H moiety is destroyed prior to dehydrogenation in favor of formation of a triangular Li2 H moiety, which interacts with protic H atom of NH2 group. As a result of this interaction, Li2 H2 moiety is produced. It features N(-) H(+) H(-) group suited near the middle plane between two Li(+) in the transition state that leads to H2 release. The transition states of association and hydrogen release steps are similar in energy. It is concluded that the trimer, (LiNH2 BH3 )3 , is the smallest cluster that captures the essence of the hydrogen release reaction.

Facile formation of thermodynamically unstable novel borohydride materials by a wet chemistry route

A novel wet synthetic method utilizing weakly coordinating anions that yields LiCl-free Zn-based materials for hydrogen storage has recently been reported. Here we show that this method may also be applied for the synthesis of the pure yttrium derivatives, M[Y(BH4)4] (M = K, Rb, Cs). Moreover, it can be extended to the preparation of previously unknown thermodynamically unstable derivatives, Li[Y(BH4)4] and Na[Y(BH4)4]. Importantly, these two H-rich phases cannot be accessed by standard dry (mechanochemical) or solid/gas synthetic methods due to the thermodynamic obstacles. Here we describe their crystal structures and selected important physicochemical properties.

Superior dehydrogenation/hydrogenation kinetics and long-term cycling performance of K and Rb cocatalyzed Mg(NH(2))(2)-2LiH system

The coaddition of KH and RbH significantly improves the hydrogen storage properties of the Mg(NH2)2-2LiH system. An Mg(NH2)2-2LiH-0.04KH-0.04RbH composite was able to reversibly store 5.2 wt % H2 when the dehydrogenation operates at 130 °C and the hydrogenation operates at 120 °C. The isothermal dehydrogenation rate at 130 °C was approximately 43 times that of a pristine sample. During ball-milling, KH reacts with RbH to form a K(Rb)H solid solution. Upon heating, RbH first separates from the K(Rb)H solid solution and participates in the first step of dehydrogenation reaction, and then the remaining KH participates in the second dehydrogenation reaction. The presence of RbH and KH provide synergetic effects, which improve the thermodynamics and kinetics of hydrogen storage in the Mg(NH2)2-2LiH system. In particular, more than 93% of the hydrogen storage capacity (4.4 wt %) remains after cycling a sample with 0.04 mol of KH and RbH for 50 cycles, indicating notably better cycling stability compared with any presently known Li-Mg-N-H systems.