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The use of NaAlH 4 as a practical hydrogen storage material has seen extensive progress. However, it is still difficult to control the hydrogen storage properties of NaAlH 4 and in particular its hydrogen thermodynamics. Herein, we demonstrate the potential of core-shell NaAlH 4 @Ti nanostructures in altering the hydrogen storage properties of NaAlH 4. To this aim, a facile solvent evaporation method was developed to enable the making of freestanding NaAlH 4 nanoparticles and their individual encapsulation within a Ti shell. These core-shell nanostructures enabled: (i) an effective confining environment for NaAlH 4 and its dehydrogenation products, and (b) fast hydrogen kinetics due to a weakening of the Al–H bond and the shorter diffusion lengths. At 180 °C, a reversible hydrogen storage capacity of 4.4 mass% was observed. More remarkably, this core-shell approach enabled a shift in the equilibrium plateau pressure, therefore demonstrating the possibility to control the hydrogen thermodynamics of NaAlH 4 at the nanoscale. [Display omitted] • Core-shell NaAlH 4 @Ti nanostructures have been successfully synthesized. • This enables fast NaAlH 4 hydrogen kinetics and a reversible hydrogen storage capacity of 4.4 mass%. • This also enables a shift in the plateau pressure and control over the hydrogen thermodynamics of NaAlH 4. [ABSTRACT FROM AUTHOR]

Solid-state metal hydrides are prime candidates to replace compressed hydrogen for fuel cell vehicles due to their high volumetric capacities. Sodium aluminum hydride has long been studied as an archetype for higher-capacity metal hydrides, with improved reversibility demonstrated through the addition of titanium catalysts; however, atomistic mechanisms for surface processes, including hydrogen desorption, are still uncertain. Here, operando and ex situ measurements from a suite of diagnostic tools probing multiple length scales are combined with ab initio simulations to provide a detailed and unbiased view of the evolution of the surface chemistry during hydrogen release. In contrast to some previously proposed mechanisms, the titanium dopant does not directly facilitate desorption at the surface. Instead, oxidized surface species, even on well-protected NaAlH4 samples, evolve during dehydrogenation to form surface hydroxides with differing levels of hydrogen saturation. Additionally, the presence of these oxidized species leads to considerably lower computed barriers for H2 formation compared to pristine hydride surfaces, suggesting that oxygen may actively participate in hydrogen release, rather than merely inhibiting diffusion as is commonly presumed. These results demonstrate how close experiment-theory feedback can elucidate mechanistic understanding of complex metal hydride chemistry and potentially impactful roles of unavoidable surface impurities.

The introduction of silver into the Sm3+-doped sodium-aluminosilicate glasses prepared by Ag+-Na+ ion exchange leads to the formation of different ionic silver species. Under 270 nm/250 nm excitation, effective enhancement of Sm3+ luminescence is ascribed to radiative energy transfer from isolated Ag+ to Sm3+. Under 355 nm excitation, white light emission was realized by combining red orange light emission of Sm3+ with green light emission of Ag+-Ag+ and blue light emission of (Ag2)+. Silver nanoparticles formed by further heat treatment are effective quenchers of luminescence from the corresponding excited states of Sm3+ ions. [ABSTRACT FROM AUTHOR]

The concept of light activation for triggering hydrogen release or uptake in hydrogen storage materials was investigated with the aid of gold (Au) nanoparticles dispersed at the surface of typical hydrides including magnesium hydride (MgH2), lithium hydride (LiH) and sodium alanate (NaAlH4). Upon Xe lamp illumination, the overall temperature of the materials reached ca. 100 °C owing to the plasmonic heating effect of the Au nanoparticles. Direct‐heat‐driven hydrogen storage at the same temperature with a conventional electrical furnace was found to be less effective with a smaller fraction of hydrogen released from Au/LiH and no phase conversion for Au/NaAlH4 or for Au/Mg under hydrogen pressure. The better efficiency of the observed light‐driven hydrogen storage is attributed to the higher temperature in the vicinity of the Au nanoparticles owing to their plasmonic effect. With further improvements, light‐activated hydrogen storage could lead to an effective approach for hydrogen uptake and release from hydrides at low temperatures. In the spotlight: For some hydrogen storage materials, hydrogen uptake and release is temperature dependent. When Au nanoparticles, which display local plasmonic heating upon light illumination, are dispersed on the surface of hydrogen storage materials such as Mg, LiH and NaAlH4, these materials display light‐activated hydrogen uptake and release (see figure). [ABSTRACT FROM AUTHOR]

The concept of light activation for triggering hydrogen release or uptake in hydrogen storage materials was investigated with the aid of gold (Au) nanoparticles dispersed at the surface of typical hydrides including magnesium hydride (MgH2), lithium hydride (LiH) and sodium alanate (NaAlH4). Upon Xe lamp illumination, the overall temperature of the materials reached ca. 100 °C owing to the plasmonic heating effect of the Au nanoparticles. Direct‐heat‐driven hydrogen storage at the same temperature with a conventional electrical furnace was found to be less effective with a smaller fraction of hydrogen released from Au/LiH and no phase conversion for Au/NaAlH4 or for Au/Mg under hydrogen pressure. The better efficiency of the observed light‐driven hydrogen storage is attributed to the higher temperature in the vicinity of the Au nanoparticles owing to their plasmonic effect. With further improvements, light‐activated hydrogen storage could lead to an effective approach for hydrogen uptake and release from hydrides at low temperatures. In the spotlight: For some hydrogen storage materials, hydrogen uptake and release is temperature dependent. When Au nanoparticles, which display local plasmonic heating upon light illumination, are dispersed on the surface of hydrogen storage materials such as Mg, LiH and NaAlH4, these materials display light‐activated hydrogen uptake and release (see figure). [ABSTRACT FROM AUTHOR]

Nanoconfinement of NaAlH 4 inside a nanoporous carbon material and its effect on the reversible hydrogen storage has been studied. NaAlH 4 has been deposited into/onto a highly microporous carbon material by solution impregnation method. The structure of the deposited NaAlH 4 and H 2 release from NaAlH 4 after deposition and after 10 dehydrogenation/hydrogenation cycles has been investigated. Materials with smaller NaAlH 4 particles and a higher ratio of amorphous NaAlH 4 phase start releasing hydrogen at ambient temperatures (>23 °C). Hydrogen release takes place from nanostructured NaAlH 4 with a more even rate over a larger temperature interval. During repetitive cycling, the crystalline NaAlH 4 had been converted into amorphous nanoconfined phase or irreversibly decomposed into bulk phases, crystalline Al and Na 3 AlH 6 , which have been detected by X-ray diffraction method. Hydrogen release from nanoconfined amorphous NaAlH 4 started already at ambient temperatures. Improved reversibility of H 2 storage has been demonstrated. The data for nanoconfined material has been compared to bulk NaAlH 4 . [ABSTRACT FROM AUTHOR]

In this work, the hydrogen storage properties of different molar ratio (in mole of 1:3 and 1:4) Na 3 AlH 6 LiBH 4 system is investigated for the first time. X-ray diffraction and Fourier transform infrared results show that the Na 3 AlH 6 LiBH 4 with molar ratio of 1:3 and 1:4 composite was transformed to Li 3 AlH 6 and NaBH 4 phases via a metathesis reaction during a ball-milling process for 6 h. Temperature-programmed-desorption (TPD) results show three stages of decomposition for the Na 3 AlH 6 LiBH 4 (in mole ratio of 1:3 and 1:4) composite resulting from Li 3 AlH 6 and NaBH 4 phases. From the TPD graph, the Na 3 AlH 6 LiBH 4 composite with molar ratio of 1:4 had showed better performance of hydrogenation properties compared to with molar ratio of 1:3. The composite began to release hydrogen at 180 °C in relation to decomposition of the Li 3 AlH 6 stage into LiH and Al. The NaBH 4 stage then began to decompose at approximately 380 °C, after reacting with Al to form an intermetallic phase, AlB 2 , which occurred at 100 °C lower than as-milled NaBH 4 . At 430 °C, the un-reacted NaBH 4 was decomposed after catalysing with AlB 2 . Kissinger analysis shows the apparent activation energy of NaBH 4 decomposition in the hydrides composite was reduced by about 75 kJ/mol compared to the as-milled NaBH 4 . The rehydrogenation process evidenced the reversibility of NaBH 4 . Based on these results, the intermetallic phase, AlB 2 , is considered to have played an important role by lowering the operating temperature and providing access to the full hydrogen content in the Na 3 AlH 6 LiBH 4 composite system. [ABSTRACT FROM AUTHOR]

Sodium aluminum (iron) phosphate glass ceramics containing of up to 20 wt.% rare earth (RE) oxides simulating pyroprocessing waste were produced by melting at 1250 °C followed by either quenching or slow cooling to room temperature. The iron-free glass-ceramics were composed of major glass and minor phosphotridymite and monazite. The iron-bearing glass-ceramics were composed of major glass and minor monazite and Na-Al-Fe orthophosphate at low waste loadings (5–10 wt.%) and major orthophosphate and minor monazite as well as interstitial glass at high waste loadings (15–20 wt.%). Slowly cooled samples contained higher amount of crystalline phases than quenched ones. Monazite is major phase for REs. Leach rates from the materials of major elements (Na, Al, Fe, P) are 10 −5 -10 −7  g cm −2  d −1 , RE elements – lower than 10 −5  g cm −2  d −1 . [ABSTRACT FROM AUTHOR]

As a prototypical high-capacity complex hydride, sodium alanate (NaAlH4) has attracted significant attention because of its favorable thermodynamics and the potential low cost of its raw materials (NaH and Al). However, a high desorption temperature and slow kinetics preclude its practical use, particularly in mobile applications. The introduction of appropriate catalysts has been demonstrated to reduce the operating temperature and to improve the reversibility of hydrogen storage in NaAlH4 effectively. In this Review, we survey the development of various catalytic additives and their effects on the hydrogen-storage behavior of NaAlH4. First, the basic physical and chemical characteristics of NaAlH4 and its catalyst- doping methods are briefly summarized. Then, the catalytically enhanced hydrogen-storage properties and the corresponding mechanistic understanding are highlighted. Finally, the remaining challenges and the directions of future research efforts are discussed. [ABSTRACT FROM AUTHOR]

This work reports an efficient co-catalyst of AgRu nanoparticles supported on γ-Al2O3 for highly selective hydrogenation of the C=C bond of cinnamaldehyde (CAL) at 443 K, uncovering a catalytic route for selective hydrocinnamaldehyde production from the CAL. This kind of chemo-selectivity of AgRu/γ-Al2O3 catalyst seems unique since any competitive hydrogenation at the conjugated C=O bond was significant. [ABSTRACT FROM AUTHOR]

A simple and cost-effective method for the synthesis of a porous Al scaffold has been optimised using only NaAlH and TiCl. The starting materials were compacted into a pellet and sintered under dynamic vacuum to remove the Na and H. The sintering conditions, such as vacuum level, temperature, and time, were the key factors that influenced both the extraction of Na and H from the pellet and the overall porosity. Quantitative phase analysis by X-ray diffraction revealed that after the sintering process, the as-prepared porous Al scaffold consisted primarily of Al. Morphological observations conducted by scanning electron microscopy showed that the scaffold exhibited an open network of pores with a small number of mesopores and no formation of micropores. The specific surface area of the scaffold was determined to be 7.9 ± 0.1 and 6.0 ± 0.5 m/g by the Brunauer-Emmet-Teller method and from small-angle X-ray scattering measurements, respectively. The total porosity of the Al scaffold was 44.6%. [ABSTRACT FROM AUTHOR]

NaAlH 4 is a promising anode material for lithium-ion batteries due to its high theoretical capacity of 1985 mAh g −1 . However, the practical application of NaAlH 4 anode is hindered by its low charge reversibility and poor cycle performance. To improve the Li-storage performance of NaAlH 4 anode, the regeneration and degradation mechanism of NaAlH 4 have been revealed in this work. Firstly, the results show that decreasing the crystalline size would result in the direct regeneration of NaAlH 4 from Na and Al without any intermediate phases (such as LiNa 2 AlH 6 ), which dramatically enhances the reversibility of NaAlH 4 anode. Secondly, a new cycle degradation mechanism is demonstrated that NaAlH 4 would decompose above 1.42 V during the charge process, which leads to a rapid degradation of cycle capacity. Therefore, the reversible capacity of NaAlH 4 anode after 20 cycles could be significantly increased from 89 mAh g −1 to 456 mAh g −1 by decreasing the cut-off voltage from 3 V to 1 V, showing an improved cycle stability. [ABSTRACT FROM AUTHOR]

Insights about the failure mechanism of negative electrodes based on NaAlH 4 for lithium batteries are here discussed based on electrochemical-pressure measurements, galvanostatic cycling, infrared spectroscopy and impedance spectroscopy. The accumulation of irreversible capacity in the first cycle and the capacity fading have multiple origins. Besides the mechanical instability due to volume expansions/contractions upon lithium incorporation/de-incorporation, two additional reasons for electrode failure have been disclosed, both related to active material consumption: (1) the irreversible oxidation upon charge of the alanates that leads to H 2 release, and (2) the spontaneous chemical reaction of the electrode active material with the electrolyte due to an unstable solid electrolyte interface. Both problems can be tackled by limiting the anodic voltage cutoffs in lithium cells and by the use of innovative electrolytes based on mixture of an ionic liquid and the standard carbonate-based solvent blend. The use of both strategies allowed us to assemble and demonstrate for few cycles the operation of a full Li-ion cell with a negative electrode based on NaAlH 4 and a LiFePO 4 positive electrode. [ABSTRACT FROM AUTHOR]

In this work, we have investigated the hydrogen release and uptake pathways storage properties of the MgH 2 Na 3 AlH 6 with a molar ratio of 4:1 and doped with 10 wt% of TiF 3 using a mechanical alloying method. The doped composite was found to have a significant reduction on the hydrogen release temperature compared to the un-doped composite based on the temperature-programme-desorption result. The first stage of the onset desorption temperature of MgH 2 Na 3 AlH 6 was reduced from 170 °C to 140 °C with the addition of the TiF 3 additive. Three dehydrogenation steps with a total of 5.3 wt% of released hydrogen were observed for the 4MgH 2 Na 3 AlH 6 -10 wt% TiF 3 composite. The re/dehydrogenation kinetics of 4MgH 2 Na 3 AlH 6 system were significantly improved with the addition of TiF 3 . Kissinger analyses showed that the apparent activation energy, E A , of the 4MgH 2 Na 3 AlH 6 doped composite was 124 kJ/mol, 16 kJ/mol and 34 kJ/mol lower for un-doped composite and the as-milled MgH 2 , respectively. It was believed that the enhancements of the MgH 2 Na 3 AlH 6 hydrogen storage properties with the addition of TiF 3 were due to formation of the NaF, the AlF 3 and the Al 3 Ti species. These species may played a synergetic catalytic role in improving the hydrogenation properties of the MgH 2 Na 3 AlH 6 system. [ABSTRACT FROM AUTHOR]

Alanates have recently attracted attention as new anodic materials for lithium ion batteries. The electrochemical activity of sodium alanate has been already reported and the conversion mechanism explained. Through a complex conversion reaction, this compound is able to develop almost all the theoretical capacity, achieving more than 1700 mAh/g upon first discharge with an efficiency of 70%. Nevertheless alanate undergoes to capacity fade in few cycles. This is mainly due to the severe structural reorganization following the conversion reaction, that results in electrode pulverization and loss of electric contact. Here, we present a nanocomposite material consisting of NaAlH4 confined in the nanoporous of a carbon matrix able to mitigate the effect of volume expansion and improve the cyclability. Specifically, the nanocomposite has been studied in terms of structure, morphology and hydrogen content by the means of Infrared Spectroscopy, solid state NMR, electronic microscopy and thermal analysis. Finally, its performance in lithium cells is presented. [ABSTRACT FROM AUTHOR]

The local structures of sodium aluminum silicophosphate glasses containing unique AlO6-octahedra were characterized through nuclear magnetic resonance (NMR) and modeled by topological constraint theory (TCT). Subsequent calculation results of the glass-transition temperature ( Tg) and Vickers hardness ( Hv) obtained using TCT were verified by the experimental data, which provided us evidence of the glass former role of the AlO6-octahedra and their behavior in the aluminum-containing glass systems. The glass-forming behavior of the AlO6-octahedra was identified by their displacement of SiO6-octahedra based on their corresponding NMR spectrum. The structure featured a constant total amount of AlO6 and SiO6-octahedra (AlO6-octahedra increased whereas SiO6-octahedra decreased) with an increasing aluminum content, which was caused by the mutual replacement between them. The glass former role of the AlO6-octahedra was further supported by the theoretical computation of Tg and Hv through application of TCT. Specifically, the model of the aluminum-containing glasses reported here is an extension of the conventional TCT that only incorporates the constraints of the glass formers. [ABSTRACT FROM AUTHOR]

The catalytic mechanism of Ti doped NaAlH 4 for hydrogen storage remains unconfirmed. Here, we investigated the evolution of active species in Ti doped NaAlH 4 system by XRD, XPS and TEM. The results reveal that the evolution of the Ti addition in doped NaAlH 4 is Ti 3+ → amorphous Ti 0 → Al Ti species → Al 3 Ti intermetallic. TEM results show that the average particle size of the Al Ti species and Al 3 Ti intermetallic is about 30 nm, and Ti element is uniformly distributed in Al matrix. In further, we discussed the catalytic mechanism and role of active species in Ti doped NaAlH 4 system according to experimental and theoretical calculation. The rehydrogenation process of Ti doped NaAlH 4 system can be divided into three steps: (1) H 2 dissociation, (2) H atom spillover and alanes (Al x H y ) formation and (3) complex hydrides formation. The addition of Ti can catalyze the process of H 2 dissociation, H atom spillover and formation of alanes. More importantly, the current work may provide a general approach to investigate the catalytic mechanism of other doped complex hydrides for hydrogen storage system. [ABSTRACT FROM AUTHOR]

Samples NaAlH x D 4−x (0 ≤ x ≥ 4) have been synthesized through a direct hydrogen isotope absorption/desorption cycles using Ti-doped NaAlH 4 as source material, and then the interaction between hydrogen/deuterium and obtained NaAlH x D 4−x and its hydrogen isotope effect were investigated. The results show that hydrogen isotope desorption/absorption kinetics of NaAlH x D 4−x is enhanced with increasing the hydrogen concentration. In addition, NaAlH x D 4−x exhibits kinetics isotope effect during both hydrogen isotope desorption and absorption processes, and the isotope effect keeps stable during cycling. Our study may enable NaAlH 4 to be used as hydrogen isotope separation material in future based on its kinetics isotope effect. [ABSTRACT FROM AUTHOR]

Hydrogenation catalysis is dominated by transition metals, but interest in alternative catalysts has been growing over recent years. Herein, a transition-metal-free catalyst is discussed consisting of carbon supported NaAlH 4 as a selective catalyst for hydrogenation. This is illustrated using a range of substrates, and in more detail for the case of diphenylacetylene. Catalytic activity depends on the solvent utilized; in cyclohexane the activity is 2.3 mol (DPA) mol −1 (NaAlH 4 ) h −1 at 100 bar H 2 , 150 °C with a slight preference for the formation of trans -stilbene. The catalyst selectivity is influenced by the loading, yielding a high selectivity toward the thermodynamically less stable cis -stilbene at low catalyst loadings. This proof of principle shows promise for using metal hydrides based on earth-abundant elements as effective hydrogenation catalysts. [ABSTRACT FROM AUTHOR]

Optimization experiments were carried using three-level Box–Behnken design for the adsorption of chromium onto immobilized macroalgae. The influence of independent parameters such as pH (2−8), temperature (303−333 K), and initial chromium concentration (20−100 mg/L) towards chromium ions removal has been performed. Second-order polynomial models were developed for the responses. The significance of the independent parameters and their interactions were investigated using the analysis of variance. The three-dimensional (3-D) response surface plots were used to study the interactive effects of the independent parameters on the chromium removal efficiency. The maximum Cr(VI) removal efficiency of 90.52, 90.86 was observed forEnteromorphasp. immobilized in sodium alginate (ESA),Enteromorphasp. immobilized in polysulfone (EPS), and maximum observed total chromium removal efficiency of 81.14, 79.90 was obtained for ESA, EPS, respectively. The observed value was in good agreement with the predicted values. These results indicated that immobilized macroalgae could be used for the removal of chromium from aqueous solution. [ABSTRACT FROM AUTHOR]

Sodium alanate has proven to be a feasible candidate for electrochemical applications. Within a lithium cell, NaAlH4 closely approaches its theoretical capacity of 1985 mAhg-1 upon the first discharge. Despite its high specific capacity, NaAlH4 suffers from poor cycle efficiency, mostly due to the severe volume expansion following the conversion reaction and resulting in damage to electrode mechanical integrity with loss of electrical contact. Synthesis of an appropriate composite alanate/carbon by high energy ball milling demonstrates an ability to mitigate these deleterious effects, whereby large improvements in terms of electrochemical reversibility can be achieved. In order to highlight the effects of mechanochemical treatment on the electrochemical properties of NaAlH4, new insights on such NNaAlH4/C composites are reported. Solid state NMR has been used to study the impact of ball milling on the NaAlH4 crystal structure, while, the hydrogen content and associated desorption properties have been evaluated by thermal programmed desorption measurements. Also, electrochemical features have been analyzed via the combined application of potentiodynamic cycling with galvanostatic acceleration and electrochemical impedance spectroscopy measurements. Finally, new evidence concerning the reversibility of the conversion processes has been obtained by ex-situ NMR measurements on cycled electrodes. [ABSTRACT FROM AUTHOR]

First-principles calculations were performed to study the performance of AlH 3 vacancy in the early stage of the dehydrogenation reaction of NaAlH 4 . AlH 3 vacancy tends to exist on the (001) surface rather than in the interior of NaAlH 4 . The migration of AlH 3 vacancy from the subsurface layer to the surface layer is an exothermic process, with an energy barrier of 0.33 eV. The result suggests that enhancing the mobility of AlH 3 vacancy along the surface (001) is a feasible approach to facilitate the dehydrogenation reaction of NaAlH 4 . Al H 6 3 − anion is observed in this work by importing two AlH 3 vacancies, which exists stably at T = 300 K, but decomposes when the temperature increases to 400 K. The formation mechanism of Al H 6 3 − is that two neighboring Al H 4 − units form two AlH 3 vacancies and two remaining H − anions firstly, and then the two remaining H − anions are attracted to Al H 4 − unit to form Al H 6 3 − anion. [ABSTRACT FROM AUTHOR]

In this publication the authors present an aluminium alloy tank for hydrogen storage using 1921 g of Na 3 AlH 6 doped with 4 mol% of TiCl 3 and 8 mol% of activated carbon. The tank and the heat exchangers are manufactured by extrusion moulding of Al-Mg-Si based alloys. EN AW 6082 T6 alloy is used for the tank and a specifically developed alloy with a composition similar to EN AW 6060 T6 is used for the heat exchangers. The three heat exchangers have a corrugated profile to enhance the surface area for heat transfer. The doped complex hydride Na 3 AlH 6 is densified to a powder density of 0.62 g cm −3 . The hydrogenation experiments are carried out at 2.5 MPa. During one of the dehydrogenation experiments approximately 38 g of hydrogen is released, accounting for gravimetric hydrogen density of 2.0 mass-%. With this tank 15 hydrogenation and 16 dehydrogenation tests are carried out. [ABSTRACT FROM AUTHOR]

Deuterium desorption in an automotive-scale hydrogen storage tube was studied in-situ using neutron diffraction. Gradients in the concentration of the various alanate phases were observed along the length of the tube but no significant radial anisotropy was present. In addition, neutron radiography and computed tomography showed large scale cracks and density fluctuations, confirming the presence of these structures in an undisturbed storage system. These results demonstrate that large scale storage structures are not uniform even after many absorption/desorption cycles and that movement of gaseous hydrogen cannot be properly modeled by a simple porous bed model. Furthermore, the evidence indicates that there is slow transformation of species at one end of the tube indicating loss of catalyst functionality. These observations explain the unusually fast movement of hydrogen in a full scale system and shows that loss of capacity is not occurring uniformly in this type of hydrogen-storage system. [ABSTRACT FROM AUTHOR]

Nanoconfinement of 2LiBH4-NaAlH4 into a mesoporous carbon aerogel scaffold with a pore size, BET surface area and total pore volume of Dmax = 30 nm, SBET = 689 m²/g and Vtot = 1.21 mL/g, respectively is investigated. Nanoconfinement of 2LiBH4-NaAlH4 facilitates a reduction in the temperature of the hydrogen release by 132 °C, compared to that of bulk 2LiBH4-NaAlH4 and the onset of hydrogen release is below 100 °C. The reversible hydrogen storage capacity is also significantly improved for the nanoconfined sample, maintaining 83% of the initial hydrogen content after three cycles compared to 47% for that of the bulk sample. During nanoconfinement, LiBH4 and NaAlH4 reacts to form LiAlH4 and NaBH4 and the final dehydrogenation products, obtained at 481 °C are LiH, LiAl, AlB2 and Al. After rehydrogenation of the nanoconfined sample at T = 400 °C and p(H2) = 126 bar, amorphous NaBH4 is recovered along with unreacted LiH, AlB2 and Al and suggests that NaBH4 is the main compound that can reversibly release and uptake hydrogen. [ABSTRACT FROM AUTHOR]

Sodium alanate is an important hydrogen storage material with high hydrogen content of 7.5 wt%, but it does not release hydrogen easily. In the present work niobium oxide (Nb 2 O 5 ) and titanium cholride (TiCl 3) catalysts are used to dehydrogenate NaAlH 4. Structure and morphology of materials are characterized by XRD and SEM techniques. Sodium alanate was found to have tetragonal structure having a = 5.02 Å, b = 5.02 Å and c = 11.34 Å lattice parameters. Dehydrogenation of NaAlH 4 at 250 °C converts it to a great extent to Na 3 AlH 6 with lattice parameter a = b = c = 7.755 Å, living behind a very small amount of sodium alanate reflecting in XRD peak. Scanning electron microscopic studies shows reduction in particle size after dehydrogenation. The dehydrogenation kinetics of the samples was studied using dynamic Seivert type apparatus. The amount of desorbed hydrogen was found to be 4.8 and 5.0wt %. [ABSTRACT FROM AUTHOR]

Hydrogen is considered as an environmental friendly energy carrier because it generates no pollution. Chlorides are promising catalyst for the hydrogen desorption in sodium alanate. All reactions and operations were performed under argon atmosphere in glove box. Crystalline NaAlH 4 and catalyst TiCl 3 , Nb 2 O 5 PbCl 2 and CeCl 3 were mixed in a ratio of (1, 2) wt%. Due to the air sensitivity of the samples they were covered with a kapton tape layer to minimize any contamination for characterization purpose. Structural characterizations and phase compositions of the samples were studied by XRD. The hydrogen storage capacity is measured by seivert type apparatus. Amount of desorbed hydrogen was found to be 3.6 wt % to 5.5 wt% at 250 °C with different type of catalyst. In the present work effect of doping of TiCl 3 , Nb 2 O 5 PbCl 2 and CeCl 3 catalysis in NaAlH 4 are investigated to understand the hydrogen desorption kinetics. It is concluded that enhanced storage capacity of NaAlH 4 can be achieved due to various catalysts with reduction in temperature 285 °C–250 °C for desorption. [ABSTRACT FROM AUTHOR]

NaAlH 4 was melt infiltrated within a CO 2 activated carbon aerogel, which had been preloaded with TiCl 3 . Nanoconfinement was verified by Small Angle X-Ray Scattering (SAXS) and the nature of the Ti was investigated with Anomalous SAXS (ASAXS) and X-Ray Absorption Near Edge Structure (XANES) to determine its size and chemical state. The Ti is found to be in a similar state to that found in the bulk Ti-doped NaAlH 4 system where it exists as Al 1− x Ti x nanoalloys. Crystalline phases exist within the carbon aerogel pores, which are analysed by in-situ Powder X-Ray Diffraction (PXD) during hydrogen cycling. The in-situ data reveals that the hydrogen release from NaAlH 4 and its hydrogen uptake occurs through the Na 3 AlH 6 intermediate when confined at this size scale. The hydrogen capacity from the nanoconfined NaAlH 4 is found to initially be much higher in this CO 2 activated aerogel compared with previous studies into unactivated aerogels. [ABSTRACT FROM AUTHOR]

First-principles calculations were carried out to clarify the effect of Ti and Nb dopants on the structure, energetics, and electronic properties of NaAlH 4 in bulk and surface. Our calculations revealed that Ti preferred to substitute for the AlH site of AlH 4 unit, whereas Nb preferred to substitute for the Al atom in bulk. Structural analysis showed that the structure of Nb-doped NaAlH 4 bulk was looser than Ti-doped NaAlH 4 bulk. The analysis of density of states illustrated that Ti interacted with Al atoms in covalent bonds, whereas Nb interacted with Al atoms mainly in weak ionic bonds in Ti- and Nb-doped NaAlH 4 bulk. Thus, the diffusion of hydrogen atoms and AlH x units was more favorable in Nb-doped bulk than in Ti-doped bulk. The location of Nb atom in the NaAlH 4 (001) surface was investigated, and an active NbAl 2 H 10 –Al 2 H 6 complex was observed. The results of hydrogen removal energies of the complex indicated that the removal of H atoms, especially the H atoms in the Al 2 H 6 unit, was much simpler than in pure NaAlH 4 . [ABSTRACT FROM AUTHOR]

Complex aluminum hydrides (alanates) are among the most promising material for hydrogen storage due to their high hydrogen content and fast kinetics and sodium alanate is particularly important due to its favorable reversibility too. In the present work TiO 2 catalyst is used to improve the desorption kinetics of sodium alanate by first Ball milling it to make its powder. Powered TiO 2 catalyst and NaAlH 4 were hand milled in glove box in an argon atmosphere. It is found that catalyst is also playing its role in reducing the temperature of kinetics. XRD analysis shows that TiO 2 remains stable with NaAlH 4 after milling. Pressure–Composition–Temperature (PCT) isotherm was studied using a Sivert type apparatus to investigate hydrogen storage capacity and kinetics. It is interesting that the hydrogen storage capacity increases with increase in amount of catalyst. It was observed that TiO 2 doped NaAlH 4 has faster kinetics with improved hydrogen storage capacity of 3.6–5.1 wt% at 250 °C temperature which is higher than the other studies. [ABSTRACT FROM AUTHOR]

We study the thermal coupling potential between a Sodium Alanate tank and a High-Temperature PEM fuel cell using a heat transfer fluid to redirect a fraction of the thermal power produced during normal fuel cell operation towards the walls of the metal hydride tank in order to maintain hydrogen desorption. The remaining thermal power is then rejected to the environment by introducing an appropriately adjusted excess of air directly to the fuel cell cathode. Assuming a typical tubular geometry for both the metal hydride tank and the fuel cell, we propose a generic physical model that accounts for heat transfer in all the components of the integrated system (fuel cell, metal hydride tank and heating jacket), as well as H 2 desorption kinetics and flow in the tank. Based on this model we study the dynamics of the coupled storage/usage system in terms of H 2 pressure in the tank and temperatures in the tank and the fuel cell. Focus is primarily placed on the parameters that lead to steady-state operating conditions (i.e. the flow rate of air towards the fuel cell and the velocity of the heat transfer fluid in the heating jacket), with respect to the electrical power of the fuel cell. [ABSTRACT FROM AUTHOR]

A new method for scandium-functionalization of carbon aerogels forming nanoparticles of a new scandiumoxochloride, ScOCl is presented. Sodium aluminiumhydride, NaAlH 4 , is successfully melt infiltrated into the nano porous scaffolds with pore sizes of D max =7, 10, 13, 21, 26 and 39 nm, containing scandium based nano particles (<2.9 wt%) confirmed by elemental analysis and scanning electron microscopy. A systematic study of hydrogen storage properties of the nano composite materials is presented. An aqueous solution of ScCl 3 was initially infiltrated and formed nanoconfined [Sc(OH)(H 2 O) 5 ] 2 Cl 4 (H 2 O) 2 , which transforms to nanoparticles of a new scandium oxochloride, ScOCl at 192 °C and to Sc 2 O 3 at 420 °C. ScOCl crystallizes in an orthorhombic unit cell a =3.4409(8), b =3.9613(6) and c =8.178(2) Å, space group Pmmn , and is built from layers of [ScO 4 Cl 2 ] octahedra forming neutral ScOCl layers. Temperature programmed desorption mass spectroscopy shows slightly improved kinetics for release of hydrogen with decreasing pore size. Continuous cycling of hydrogen release and uptake measured by the Sieverts' method reveal a larger preserved hydrogen storage capacity for scandium-functionalized aerogel with the larger pores (39 nm). [ABSTRACT FROM AUTHOR]

The first Al-based amidoborane Na[Al(NH2BH3)4] was obtained through a mechanochemical treatment of the NaAlH4-4 AB (AB=NH3BH3) composite releasing 4.5 wt % of pure hydrogen. The same amidoborane was also produced upon heating the composite at 70 °C. The crystal structure of Na[Al(NH2BH3)4], elucidated from synchrotron X-ray powder diffraction and confirmed by DFT calculations, contains the previously unknown tetrahedral ion [Al(NH2BH3)4]−, with every NH2BH3− ligand coordinated to aluminum through nitrogen atoms. Combination of complex and chemical hydrides in the same compound was possible due to both the lower stability of the AlH bonds compared to the BH ones in borohydride, and due to the strong Lewis acidity of Al3+. According to the thermogravimetric analysis-differential scanning calorimetry-mass spectrometry (TGA-DSC-MS) studies, Na[Al(NH2BH3)4] releases in two steps 9 wt % of pure hydrogen. As a result of this decomposition, which was also supported by volumetric studies, the formation of NaBH4 and amorphous product(s) of the surmised composition AlN4B3H(0-3.6) were observed. Furthermore, volumetric experiments have also shown that the final residue can reversibly absorb about 27 % of the released hydrogen at 250 °C and p(H2)=150 bar. Hydrogen re-absorption does not regenerate neither Na[Al(NH2BH3)4] nor starting materials, NaAlH4 and AB, but rather occurs within amorphous product(s). Detailed studies of the latter one(s) can open an avenue for a new family of reversible hydrogen storage materials. Finally, the NaAlH4-4 AB composite might become a starting point towards a new series of aluminum-based tetraamidoboranes with improved hydrogen storage properties such as hydrogen storage density, hydrogen purity, and reversibility. [ABSTRACT FROM AUTHOR]

One of the greatest problems to implement the use of hydrogen in automotive or stationary systems is the control in the temperature to regulate the storage capacity and the absorption and desorption process of material used to store the hydrogen. Metal organic compounds have generated a significant interest due to a high proportion of hydrogen in their structure, by this reason most of the researches are focused on the development of storage systems based on these compounds, but the regulation of temperature and mass transfer are yet a drawback to increase the efficiency of these systems. In this paper, we study the feasibility of a cooling system for a hydrogen storage system using Sodium alanate catalyzed by Titanium chloride as the hydrogen storage material in a cylindrical vessel with a suitable distribution of feed and cooling systems. A temperature of 170 °C was chosen for hydrogen input according to the storage properties of the selected storage medium looking for the increase of store capacity in terms of high density of hydrogen accumulation to obtain an adequate storage system to be implemented in automotive applications. One of the main characteristics to determine the efficiency of cooling systems is the quantity of time necessary to decrease the temperature to a normal range. In this case was obtained an effective time of 1100 s for a structure composed by a central and external system of coolant pipes, using the ethylene glycol properties as coolant to unify the use of the same coolant for hydrogen storage and engine cooling. [ABSTRACT FROM AUTHOR]

A lightweight tank for hydrogen storage based on four kilograms of sodium alanate was designed, built and tested. An improvement in gravimetric capacity of 83% and 49% in volumetric capacity over a previous tank [1] was achieved. Heat evolution and temperature spikes during hydrogen absorption were studied. Due to the high specific heat of the complex hydride, the storage material itself acts as a heat sink, aiding in the heat management of the system. The first-ever radiography with fast neutrons on an operational complex-hydride based test tank was performed. [ABSTRACT FROM AUTHOR]

Most bauxite-producedalumina is obtained by the Bayer process,but the production efficiency is limited by the slow gibbsite crystalgrowth due to the high concentration of NaOH in sodium aluminate solution.Here electrodialysis (ED) and electro-electrodialysis (EED) are coupledto separate NaOH from the sodium aluminate solution so as to enhancethe gibbsite crystal growth rate and achieve high alumina productionefficiency. The ED or EED process is also investigated before thecoupling process to find the optimal operating conditions. The EDprocess indicates that the optimized current density is in the rangeof 45–60 mA cm–2and the optimal membranesare CMV/AMV. The current density of 60 mA cm–2canachieve a high recovery ratio (ηOH–92.6%), low energy consumption (2.38 kW h kg–1), but a relatively high Al(OH)4–leakageratio (ηAl(OH)4–15.1%). The EEDprocess indicates that with the optimized current density of 30 mAcm–2and membrane CMV, the ηAl(OH)4–can be “zero” and the energy consumptioncan be as low as 2.07 kW h kg–1, but the treatmentcapability is low since OH–ions cannot be recovereddirectly and a single cation exchange membrane is used. The couplingprocess can combine the advantages of ED and EED, so that the ηOH–can keep a high value of 90.9%, the ηAl(OH)4–decreases to a low value of ∼5%,and the energy consumption remains low at 2.25 kW h kg–1. Overall, the coupling process of ED and EED is an excellent methodto separate NaOH from the sodium aluminate solution. [ABSTRACT FROM AUTHOR]

The dilational properties of the anionic gemini surfactant, ethanediyl-1,2-bis(sodium N-decanoyl-β-alaninate), and the comparable conventional surfactant were investigated via the oscillation barrier technique. The oscillation frequency was varied between 0.0033 and 0.1 Hz. The dilational moduli of the gemini surfactant at low surfactant concentration show less dependence on the frequency at the air/water interface compared with the decane/water interface. The interface layer is basically elastic. The dilational moduli at the air/water interface are remarkably higher than those at the decane/water interface. The dilational moduli of the gemini surfactant show two maxima with increasing concentration, originating from the reorientation and compression of the surfactant molecules adsorbed at the interfaces. A possible schematic diagram of the adsorption of the gemini surfactant at the air/water and decane/water interfaces is proposed. [ABSTRACT FROM AUTHOR]

Here we present the development of an aluminium alloy based hydrogen storage tank, charged with Ti-doped sodium aluminium hexahydride Na 3 AlH 6 . This hydride has a theoretical hydrogen storage capacity of 3 mass-% and can be operated at lower pressure compared to sodium alanate NaAlH 4 . The tank was made of aluminium alloy EN AW 6082 T6. The heat transfer was realised through an oil flow in a bayonet heat exchanger, manufactured by extrusion moulding from aluminium alloy EN AW 6060 T6. Na 3 AlH 6 is prepared from 4 mol-% TiCl 3 doped sodium aluminium tetrahydride NaAlH 4 by addition of two moles of sodium hydride NaH in ball milling process. The hydrogen storage tank was filled with 213 g of doped Na 3 AlH 6 in dehydrogenated state. Maximum of 3.6 g (1.7 mass-% of the hydride mass) of hydrogen was released from the hydride at approximately 450 K and the same hydrogen mass was consumed at 2.5 MPa hydrogenation pressure. 45 cycle tests (rehydrogenation and dehydrogenation) were carried out without any failure of the tank or its components. Operation of the tank under real conditions indicated the possibility for applications with stationary HT-PEM fuel cell systems. [ABSTRACT FROM AUTHOR]

Abstract: An ordered mesoporous carbon scaffold (CMK-1) has been synthesized and infiltrated with NaAlH4 nanoparticles by solvent- and melt-infiltration techniques. Small angle X-ray scattering (SAXS), powder X-ray diffraction (XRD), scanning electron microscopy (SEM), Transmission Electron Microscopy (TEM) and energy dispersive spectroscopy (EDS) are used to characterize the structure, composition and morphology before and after thermal treatment. This study illuminates some of the problems that can be associated with nanoconfinement of hydrogen storage materials including scaffold contamination, residual solvent contamination, sample morphology changes after heating, and other factors that can be detrimental to the application of these systems. Of particular interest is the expulsion of NaAlH4 decomposition products from the scaffold after heating beyond its melting point under vacuum. This results in the surface of mesoporous carbon particles having arrays of multi-micron-long Al filaments that are >100 nm in diameter. [Copyright &y& Elsevier]

The large-scale mechanically agitated tank has been widely used in the decomposition process of sodium aluminate solution in the alumina industry. The mixing process in three types of seed precipitation tanks (Robin, Ekato, and improved Ekato) stirred with multiple impellers was compared by using computational fluid dynamics, respectively. The flow field, solid distribution, mixing time, and power consumption were numerically simulated by adopting a Eulerian granular multiphase model and a standard k- ε turbulence model. A steady multiple reference frame approach was used to represent impeller rotation. Compared with the Robin tank, the Ekato tank can generate an axial circulation loop, which is better for fluid mixing and solid suspension; meanwhile about half of the power can be saved. With future improvements in the Ekato tank, the fluid mixing and exchanging can be enhanced under the interaction of a lengthened Intermig impeller coupled with sloped baffles. With a little increase in power consumption, the maximum of the relative solid concentration difference in the whole tank can be maintained within 3%, which meets the design requirement. [ABSTRACT FROM AUTHOR]

Abstract: For practical solid-state hydrogen storage, reversibility under mild conditions is crucial. Complex metal hydrides such as NaAlH4 and LiBH4 have attractive hydrogen contents. However, hydrogen release and especially uptake after desorption are sluggish and require high temperatures and pressures. Kinetics can be greatly enhanced by nanostructuring, for instance by confining metal hydrides in a porous carbon scaffold. We present for a detailed study of the impact of the nature of the carbon–metal hydride interface on the hydrogen storage properties. Nanostructures were prepared by melt infiltration of either NaAlH4 or LiBH4 into a carbon scaffold, of which the surface had been modified, varying from H-terminated to oxidized (up to 4.4 O/nm2). It has been suggested that the chemical and electronic properties of the carbon/metal hydride interface can have a large influence on hydrogen storage properties. However, no significant impact on the first H2 release temperatures was found. In contrast, the surface properties of the carbon played a major role in determining the reversible hydrogen storage capacity. Only a part of the oxygen-containing groups reacted with hydrides during melt infiltration, but further reaction during cycling led to significant losses, with reversible hydrogen storage capacity loss up to 40% for surface oxidized carbon. However, if the carbon surface had been hydrogen terminated, ∼6 wt% with respect to the NaAlH4 weight was released in the second cycle, corresponding to 95% reversibility. This clearly shows that control over the nature and amount of surface groups offers a strategy to achieve fully reversible hydrogen storage in complex metal hydride-carbon nanocomposites. [Copyright &y& Elsevier]

Abstract: Due to its thermodynamic properties and high reversibility, Ti doped sodium alanate is considered as a prototype hydrogen storage material. In this work we show how sodium alanate can be synthesized by reactive ball milling using aluminum particles obtained from recycled waste incineration slag. The synthesis was monitored with an in situ milling vial and characterized stepwise by PXD and DTA analyses. The sorption properties of the material were investigated using in situ synchrotron radiation PXD and volumetric analyses. A complete conversion of the starting reactants was obtained. [Copyright &y& Elsevier]

Abstract: First-principles calculations based on density functional theory have been performed to study the effects of La atom on the structural, electronic, and dehydrogenation properties of NaAlH4 (001) surface. A LaAl4H18 complex structure is found in the La atom doped NaAlH4 (001) surface. Two new peaks are imported into the density of state of La-doped NaAlH4 (001) surface at −1.46 and Fermi level due to the effect of La d orbitals. The analyses of bond length and electronic properties show that it is favorable to form LaAl phase. The average hydrogen removal energy of La-doped NaAlH4 (001) surface decreases to 2.390 eV, which is smaller than that of pristine NaAlH4 (001) surface. The characteristic illustrates that doping La favors the dehydrogenation reaction of NaAlH4. The improved dehydrogenation in the La-doped NaAlH4 (001) surface may be attributed to the weakening of Al–H bond. [Copyright &y& Elsevier]

In this paper, we report the hydrogen storage properties and reaction mechanism of NaAlH4–MgH2–LiBH4 (1:1:1) ternary-hydride system prepared by ball milling. It was found that during ball milling, the NaAlH4/MgH2/LiBH4 combination converted readily to the mixture of LiAlH4/MgH2/NaBH4 and there is a mutual destabilization among the hydrides. Three major dehydrogenation steps were observed in the system, which corresponds to the decomposition of LiAlH4, MgH2, and NaBH4, respectively. The onset dehydrogenation temperature of MgH2 in this system is observed at around 275 °C, which is over 55 °C lower from that of as-milled MgH2. Meanwhile, NaBH4-relevant decomposition showed significant improvement, starts to release hydrogen at 370 °C, which is reduced by about 110 °C compared to the as-milled NaBH4. The second and third steps decomposition enthalpy of the system were determined by differential scanning calorimetry measurements and the enthalpies were changed to be 61 and 100 kJ mol−1 H2 respectively, which are smaller than that of MgH2 and NaBH4 alone. From the Kissinger plot, the apparent activation energy, E A, for the decomposition of MgH2 and NaBH4 in the composite was reduced to 96.85 and 111.74 kJ mol−1 respectively. It is believed that the enhancement of the dehydrogenation properties was attributed to the formation of intermediate compounds, including Li–Mg, Mg–Al, and Mg–Al–B alloys, upon dehydrogenation, which change the thermodynamics of the reactions through altering the de/rehydrogenation pathway. [ABSTRACT FROM AUTHOR]

Coal fly ash (CFA) was used as a raw material for the synthesis of zeolite molecular sieve. The synthesis began with the pretreatment of CFA to remove impurities (e.g., Fe2O3, CaO, etc.) under various acid types (HCl, H2SO4, and HNO3) and acid/CFA ratios (5–25 mLacid/gCFA). High product purity (up to 97%) was achieved with HCl (20%wt), and acid/CFA ratio of 20 mLHCl/gCFA. The treated CFA was then converted to zeolite by the fusion reaction under various Si/Al molar ratios (0.54–1.84). Zeolite type A was synthesized when the Si/Al molar ratios were lower than 1, whereas sodium aluminum silicate hydrate was formed when the Si/Al molar ratio were higher than 1. The highest water adsorption performance of the zeolite product, i.e., the outlet ethanol concentration of 99.9%wt and the specific adsorption capacity of 2.31 × 10−2gwater/gzeolite, was observed with the Si/Al molar ratio of 0.82. The zeolite was tested for its water adsorption capacity repeatedly 10 times without deactivation.Implications: This work evaluated the technical feasibility in the conversion of CFA to zeolite, which would help reduce the quantity of waste needed to be landfilled. This adds value to the unwanted material by converting it into something that can be further used. The synthesized products were shown to be quite stable as water adsorbent for the dehydration of ethanol solution. [ABSTRACT FROM PUBLISHER]

Sodium aluminum hydride (NaAlH4) was directly synthesized by ball milling NaH/Al co-doped with CeCl3 + KH under a hydrogen pressure of 3 MPa at room temperature. Out of various samples corresponding to xNaH/Al + 0.02CeCl3 + yKH (x + y = 1; y = 0, 0.02, 0.04 mol%) composites, the composite with y = 0.02 exhibits the optimum de/hydrogenation properties. It shows that the addition of KH can effectively improve the dehydrogenation properties of second step reaction of NaAIH4 system. The composite with y = 0.02 starts to release hydrogen from 87 °C and completes dehydrogenation within 20 min at 170 °C, with good cycling de/hydrogenation kinetics at relatively lower temperature (100–140 °C). After ball milling, the CeCl3 precursor can be changed into CeH2 catalytic active component in the first several de/hydrogenation cycles. Apparent activation energy of the second decomposition step of NaAIH4 system can be effectively decreased by addition of KH, resulting in the decrease of desorption temperatures. Based on the microstructure analyses combined with hydrogen storage performances, the improved dehydrogenation properties of sodium aluminum hydride system are ascribed to the lattice volume expansion of Na3AlH6 during the dehydrogenation process resulted from the addition of KH. Moreover, by analyzing the reaction kinetics of CeCl3 + KH co-doped sample, both of the decomposition steps of composite with y = 0.02 were conformed to the two-dimension phase-boundary growth mechanism. The mechanistic investigations gained here could help to understand the de/rehydrogenation behaviors of catalyzed complex metal hydride systems. [ABSTRACT FROM AUTHOR]