Hydrogen Storage in Complex Metal Hydrides

This paper reports the catalytic activity of several metal oxide nanoparticles such as TiO for NaAlH 4 . TiO 2 was found to be the most effective catalyst. In order to find the size dependence of TiO 2 nanoparticles on the catalytic activity, TiO 2 nanoparticles of different sizes such as 5 nm, 25 nm, 150 nm and 200 nm have been used. TiO 2 nanoparticles lower the desorption temperature of sodium alanate (NaAlH 4 ) from w 473 K to w373 K. Using 5 nm and 25 nm TiO 2 catalysts w3 wt% hydrogen could be released within 5e7 min at 423 K. TiO 2 (25 nm) catalyst lowers the activation energy of NaAlH 4 to 67 kJ/mol H 2 , as compared to 119 kJ/mol H 2 for the pristine material. This is better than Ti nanoparticles catalyst of similar size which lowers the activation energy up to 77 kJ/mol H 2 . The long-term reversible characteristics of 25 nm TiO 2 admixed NaAlH 4 up to 35 cycles and the phase structural features of the cycled samples are discussed.

Gymnema  sylvestre  (Asclepiadaceae) is  a  good  source  of  large
number  of  bioactive  substances.  It  has  deep  roots  in  history,  being
one  of  the  major  botanicals  used  in  traditional  medicine  to  treat
conditions ranging from diabetes, malaria, to snakebites. This study
was conducted to quantitatively evaluate anti-haemolytic activity of
aqueous  extract  of  stem,  leaf  and  flower  parts  of  this  plant,  against
hydrogen  peroxide  induced  haemolysis  using  human  erythrocyte  in
an in vitro  assay. Prior to the addition of H
2O2
to induce haemolysis,
different concentrations (50-500 mg/ml) of the extract was added to
2ml  of  4%  erythrocyte  suspension  and  allowed  to  incubate  for  5
minutes  at  room  temperature.  The  mixture  was  centrifuged  and  the
colour  density  of  the  supernatant  was  measured
spectrophotometrically.  Quercetin  was  used  as  standard.  The
percentage haemolysis and IC
50
values were calculated. The extracts
were  potent  against  haemolysis  of  the  erythrocyte  in  concentration
dependent  manner.  The  leaf  extract  exhibited  the  highest  antihaemolytic  effect  with  IC
50 =  29.83  mg/ml  followed  by  the  flower
with IC50= 34.96 mg/ml and the least was the stem with IC50
= 37.75
mg/ml. the IC50
value of Quercetin was 386.72 mg/ml. The lower the
IC
50
the more protection offered against haemolysis by  the extracts.
These results suggest that the plant extracts are better anti-haemolytic
agents  and  offered  significant  biological  action  compared  with
standard compound used.

En utilisant les calculs ab-initio basé sur la théorie densité de la fonctionnelle
(DFT), nous avons étudié la stabilité de structure, les propriétés thermodynamiques
et cinétiques de déshydrogénation d’hydrure complexe LiBH4 sous différentes
contraintes mécanique biaxiale en utilisant GGA-PBE pour l’optimisation
et les calculs dans la structure cristalline de LiBH4, Les résultats montrent que le
contrainte traction biaxiale ou contrainte de compression de la structure LiBH4
diminue son enthalpie de désorption d’hydrogène et sa température de déshydrogénation
, en outre, l’énergie d’activation de diffusion d’atome d’hydrogène
en LiBH4 est également diminué, ces améliorations thermodynamique et cinétique
pourraient conduire à utiliser le borohydrure de lithium LiBH4 dans les
applications de stockage de l’hydrogène.

A promising alternative to hydrogen storage in high pressure cylinders and cryogenic tanks is the hydrogen storage in solid form as metal hydrides or complex metal hydrides. However, much research is still necessary in this direction. In particular, the optimal pressure and temperature of operation for the use of a hydride-based tank in a PEM fuel cell-powered vehicle should remain in the of 1-10 atm and 25-120 °C, respectively. The further difficulty is related to the weight of the storing materials, which is still too high for efficient mobile applications compared to the amount of stored hydrogen.
The work reported in this thesis deals with systems belonging to several hydride classes such as complex hydrides, interstitial metal hydrides and magnesium-based hydrides. Improvements from the point of view of thermodynamic and kinetic properties are proposed and discussed on systems almost ready for niche applications and on other very promising systems but still far from hydrogen storage applications. Among the classical interstitial hydrides-forming alloys, the interaction of hydrogen with TiCr1.78-xMnx alloys, one of the most promising for the use in high pressure-solid state hybrid tanks, has been studied. Among the Mg-based hydrides, a compacted Mg-Al-based material is proposed in order to overcome the degradation problems found during the scaling up of MgH2 as hydrogen storage medium. Concerning the complex hydrides, the kinetics improvement of the Li-Mg-N-H system by high energy ball milling processing is discussed and the problem of reversibility and slow decomposition kinetics of LiBH4 has been faced.

In this study, hydroxy gas (HHO) was produced by the electrolysis process of different electrolytes (KOH(aq), NaOH(aq), NaCl(aq)) with various electrode designs in a leak proof plexiglass reactor (hydrogen generator). Hydroxy gas was used as a supplementary fuel in a four cylinder, four stroke, compression ignition (CI) engine without any modification and without need for storage tanks. Its effects on exhaust emissions and engine performance characteristics were investigated. Experiments showed that constant HHO flow rate at low engine speeds (under the critical speed of 1750 rpm for this experimental study), turned advantages of HHO system into disadvantages for engine torque, carbon monoxide (CO), hydrocarbon (HC) emissions and specific fuel consumption (SFC). Investigations demonstrated that HHO flow rate had to be diminished in relation to engine speed below 1750 rpm due to the long opening time of intake manifolds at low speeds. This caused excessive volume occupation of hydroxy in cylinders which prevented correct air to be taken into the combustion chambers and consequently, decreased volumetric efficiency was inevitable. Decreased volumetric efficiency influenced combustion efficiency which had negative effects on engine torque and exhaust emissions. Therefore, a hydroxy electronic control unit (HECU) was designed and manufactured to decrease HHO flow rate by decreasing voltage and current automatically by programming the data logger to compensate disadvantages of HHO gas on SFC, engine torque and exhaust emissions under engine speed of 1750 rpm. The flow rate of HHO gas was measured by using various amounts of KOH, NaOH, NaCl (catalysts). These catalysts were added into the water to diminish hydrogen and oxygen bonds and NaOH was specified as the most appropriate catalyst. It was observed that if the molality of NaOH in solution exceeded 1% by mass, electrical current supplied from the battery increased dramatically due to the too much reduction of electrical resistance. HHO system addition to the engine without any modification resulted in increasing engine torque output by an average of 19.1%, reducing CO emissions by an average of 13.5%, HC emissions by an average of 5% and SFC by an average of 14%.

In this work, hydrogen storage properties and reaction mechanism of NaAlH4-Mg(BH4)2 (2:1) composites system with and without additive have been investigated. The secondary hydride system was found to initiate a transformation of the NaAlH4/Mg(BH4)2 to Mg(AlH4)2/NaBH4 during ball milling, and there was a mutual destabilization among the hydrides. Three major dehydrogenation steps were observed in the systems, which corresponded to the decomposition of Mg(AlH4)2, MgH2, and NaBH4. Temperature programmed desorption results showed that the TiF3-doped NaAlH4-Mg(BH4)2 (2:1) composite sample started to release hydrogen at about 75
C, which was 60
C lower than that of undoped NaAlH4-Mg(BH4)2 (2:1) composite sample. In addition, the reaction pathway of
the NaAlH4-Mg(BH4)2 (2:1) composite system, and the mechanisms that worked in this composite during the de/rehydrogenation process were determined by X-ray diffraction. The Kissinger analysis has shown that the apparent activation energy, EA, for decomposition of NaBH4 in the NaAlH4-Mg(BH4)2-TiF3 composite reduced to 139.85 kJ/mol
compared with 155.73 kJ/mol in NaAlH4-Mg(BH4)2 composite. It is believed that the enhancement of the de/rehydrogenation properties of undoped NaAlH4/Mg(BH4)2 was attributed to the formation of intermediate compounds, including Mg-Al and Mg-AleB alloys, upon dehydrogenation, which changed the thermodynamics of the reactions by altering the de/rehydrogenation pathway. Meanwhile, as for the doped sample, the TiF3 component played a catalytic role through the formation of Ti-containing and F-containing catalytic species, which might have promoted the interaction of Mg(AlH4)2 and NaBH4, and thus, further improved the dehydrogenation of the NaAlH4-Mg(BH4)2 (2:1) system.

This study reports the synthesis of NaAlH 4 by ball milling of NaH and Al mixture along with 3 mol % Mischmetal (Mm) nanocatalyst under hydrogen atmosphere. It is observed that synthesis of the intermediate phase Na 3 AlH 6 can be achieved by ball milling even under 1 atm hydrogen at room temperature. Ball milling of the NaH þ Al with 3 mol % Mm with 3 atm hydrogen in excess of 40 h time did not lead to the formation of NaAlH 4 but charging of the milled material at 100 atm hydrogen pressure at 120 C lead to formation of NaAlH 4 phase. Direct synthesis of NaAlH 4 was achieved by milling of NaH þ Al with 3 mol % Mm under 100 atm hydrogen pressure. Direct synthesis is possible even without any catalyst by high pressure milling. However catalyst is required to improve the hydrogen sorption characteristics of the synthesized material. The as-prepared Mm catalyzed NaAlH 4 is also found to reversibly store hydrogen up to 4.2 wt% hydrogen. Catalytic activity is attributed to defects promoted by ball milling and catalysts. (O.N. Srivastava).

The present investigation focuses on a new synthesis route of NaBH4 starting from the 2NaH + MgB2 system subjected to mechanochemical activation under reactive hydrogen atmosphere. The milling process was carried out under two different hydrogen pressures (1 and 120 bar) with two different rotation speeds (300 and 550 rpm). The reaction products were characterized by ex-situ solid state magic angle spinning (MAS) nuclear magnetic resonance (NMR), ex-situ X-ray powder diffraction (XRPD) and Infrared Spectroscopy (IR). From the results of these analyses, it can be concluded that milling in all the considered conditions led to the formation of NaBH4 (cubic-Fm-3m). In particular, a reaction yield of 5 and 14 wt% is obtained after 20 h of milling at 120 bar of H2 for the tests performed at 300 rpm and 550 rpm, respectively. The presence of MgH2 is also detected among the final products on the as milled powders. The influence of the milling conditions and the evaluation of the parameters related the mechanochemical process are here discussed.► New synthesis route of NaBH4 starting from the 2NaH + MgB2 system is presented. ► NaBH4 formation is induced by mechanochemical activation under hydrogen atmosphere. ► The NaBH4 conversion yield depend on the hydrogen pressure used during the milling. ► MgH2 is also detected among the final products on the as milled powders.

In this study, the effect of LaCl3 on the hydrogen storage properties of MgH2 prepared by ball milling was investigated for the first time. It was found that the MgH2 + 10 wt.% LaCl3 sample started to decompose at around 300 C, which was 50 C lower than in as-milled MgH2. For desorption kinetics, the LaCl3-doped MgH2 composite sample released about 4.2 wt.% hydrogen at 320 C after 5 min dehydrogenation, while the as-milled MgH2 only released about 0.2 wt.% hydrogen for the same temperature and time. Meanwhile, a hydrogen absorption capacity of 5.1 wt.% was reached at 300 C in 2 min for the LaCl3-doped MgH2 sample. In contrast, the ball-milled MgH2 only absorbed 3.8 wt.% hydrogen at 300 C in 2 min. The activation energy of dehydrogenation was 166.0 kJ/mol for the as-milled MgH2 and 143.0 kJ/mol for the 10 wt.% LaCl3-added MgH2, indicating that the LaCl3 additive decreased the activation energy for the hydrogen desorption of the MgH2. The improved hydrogen storage properties of the MgH2 in the presence of LaCl3 is believed to be due to the catalytic effects of the LaeMg alloy and MgCl2 that were formed in situ during the heating process.

Reactive Hydride Composites (RHCs), ball-milled composites of two or more different hydrides, are suggested as an alternative for solid state hydrogen storage. In this work, dehydrogenation of 2NaBH4 + MgH2 system under vacuum was investigated using complementary characterization techniques. At first, thermal programmed desorption of as-milled composite and single compounds was used to identify the temperature range of hydrogen release. RHC samples annealed at various temperatures up to 500 °C were characterized by X-ray diffraction, infrared spectroscopy and scanning electron microscopy. It was found that the dehydrogenation reaction under vacuum is likely to proceed as follows: 2NaBH4 + MgH2 (>250 °C) → 2NaBH4 + 1/2MgH2 + 1/2Mg + 1/2H2 (>350 °C) ↔ 3/2NaBH4 + 1/4MgB2 + 1/2NaH + 3/4Mg + 7/4H2 (>450 °C) → 2Na + B + 1/2Mg + 1/2MgB2 + 5H2. In addition, presence of NaMgH3 phase suggests the occurrence of secondary reactions.

El análisis de un sistema de almacenamiento de energía renovable en forma de hidrógeno es fundamental para detectar aquellas variables físicas que rigen el comportamiento real del sistema e identificar estrategias que permitan incrementar la eficacia y eficiencia del sistema. Con la adquisición y análisis de datos en diversas condiciones de operación del sistema se pueden generar modelos que puedan predecir y caracterizar el desempeño real para retroalimentar su mejor implementación. Este trabajo de investigación consistió en detectar oportunidades de optimización del sistema de generación y almacenamiento de hidrógeno, utilizando como técnicas: la medición y captura de datos de operación, la reducción y simplificación de información con métodos matemáticos, y el análisis e interpretación de resultados. Se evaluó un sistema compuesto por un electrolizador de celdas de membrana de intercambio protónico y dos tanques de hidruros metálicos, los cuales, fueron sometidos a diversas condiciones de operación: 1) el sistema produjo y almacenó hidrógeno en un tanque de almacenamiento a condiciones ambientales en los puntos de control de presión de 0.5 bar, 1.5 bar, 2.5 bar, 4.0 bar, 6.5 y 9.0 bar. 2) Simultáneamente se sometió la producción y carga de hidrógeno en 2 tanques de almacenamiento a 9.0 bar de presión. Los resultados de esta investigación ayudaron a conocer las capacidades y limitantes de un sistema de producción y almacenamiento de hidrógeno bajo ciertas condiciones de operación, enriqueciendo los criterios para la implementación de estos sistemas.

"The thermodynamics of structural phase transformations in thin films depends on the mechanical stress that can be released by
plastic deformation. For thin films below a critical film thickness, plastic deformation is energetically unfavourable: thus, the system
stays coherent and stress remains. For PdHc films less than 22 nm thick, a new situation emerges: while the interfaces between matrix
and hydride precipitates remain coherent throughout the complete phase transition, misfit dislocations form between the hydride
phase and the substrate."

We report a study of the hydrogen storage properties of materials that result from ball milling Ca(BH 4) 2 and MNH 2 (M = Li or Na) in a 1:1 molar ratio. The reaction products were examined experimentally by powder X-ray diffraction, thermogravimetric analysis and differential scanning calorimetry (TGA/DSC), simultaneous thermogravimetric modulated beam mass spectrometry (STMBMS), and temperature-programmed desorption (TPD). The Ca(BH 4)/LiNH 2 system produces a single crystalline compound assigned to LiCa-(BH 4) 2 (NH 2). In contrast, ball milling of the Ca(BH 4)/NaNH 2 system leads to a mixture of NaBH 4 and Ca(NH 2) 2 produced by a metathesis reaction and another phase we assign to NaCa(BH 4) 2 (NH 2). Hydrogen desorption from the LiCa(BH 4) 2 (NH 2) compound starts around 150 °C, which is more than 160 °C lower than that from pure Ca(BH 4) 2. Hydrogen is the major gaseous species released from these materials; however various amounts of ammonia form as well. A comparison of the TGA/DSC, STMBMS, and TPD data suggests that the amount of NH 3 released is lower when the desorption reaction is performed in a closed vessel. There is no evidence for diborane (B 2 H 6) release from LiCa(BH 4) 2 (NH 2), but traces of other volatile boron−nitrogen species (B 2 N 2 H 4 and BN 3 H 3) are observed at 0.3 mol % of hydrogen released. Theoretical investigations of the possible crystal structures and detailed phase diagrams of the Li−Ca−B−N−H system were conducted using the prototype electrostatic ground state (PEGS) method and multiple gas canonical linear programming (MGCLP) approaches. The theory is in qualitative agreement with the experiments and explains how ammonia desorption in a closed volume can be suppressed. The reduced hydrogen desorption temperature of LiCa(BH 4) 2 (NH 2) relative to Ca(BH 4) 2 is believed to originate from intramolecular destabilization.

Nanoconfining hydrogen storage material inside nanopores has emerged as an intriguing strategy to influence the material characteristics but also sacrifices part of system gravimetric and volumetric hydrogen capacity. Herein, we tackle these two challenges by nanoconfining LiBH4 into a new scaffold, zeolite-templated carbon (ZTC), with high porosity and excellent mechanical stability to form a densified nanoconfinement system. After nanoconfinement of LiBH4 and 750 MPa densification, the nanocomposite begins to release hydrogen at 194 °C, 181 °C lower than that of the bulk LiBH4. The rehydrogenation of LiBH4 achieves under mild conditions with improved cycle stability. Moreover, the activation energy of hydrogen desorption is dramatically reduced by 60.4 kJ mol−1, coupled with the foaming effect of desorption almost eliminated. More importantly, the over-infiltrated LiBH4@ZTC systems are capable of maintaining their good hydrogen storage performances, which is attributed to the interface/surface effect between hydrides and scaffolds. With ultra-high pressure densification and high uploading amount of LiBH4, the nanoconfined composite achieves an exceptional gravimetric capacity of 6.92 wt% and volumetric capacity of 75.43 g L−1. These findings add new insights in the development of nanoconfinement systems with enhanced hydrogen storage capacity.

Hydrogen storage Synergistic effect Activation energy a b s t r a c t This paper reports the catalytic effects of mischmetal (Mm) and mischmetal oxide (Mm-oxide) on improving the dehydrogenation and rehydrogenation behaviour of magnesium hydride (MgH 2 ). It has been found that 5 wt.% is the optimum catalyst (Mm/Mm-oxide) concentration for MgH 2 . The Mm and Mm-oxide catalyzed MgH 2 exhibits hydrogen desorption at significantly lower temperature and also fast rehydrogenation kinetics compared to ball-milled MgH 2 under identical conditions of temperature and pressure. The onset desorption temperature for MgH 2 catalyzed with Mm and Mm-oxide are 323 C and 305 C, respectively.

2LiBH(4)-MgH2 is an attractive system for hydrogen storage. However, its dehydriding and rehydriding kinetics have to be further improved for practical applications. To solve these problems, three transition metal chlorides (FeCl2, CoCl2 and NiCl2) were introduced into the 2LiBH(4)-MgH2 system and their catalytic roles in the dehydrogenation-rehydrogenation properties were investigated systematically. The results show that all three chlorides can significantly enhance the dehydriding and rehydriding kinetics of the 2LiBH(4)-MgH2 system with/without hydrogen back pressure, and NiCl2 is the best modifier among them. The NiCl2-doped sample exhibits no incubation period for generating MgB2 during dehydrogenation. X-Ray diffraction and scanning electron microscopy analyses clearly reveal the phase formation of MgNi3B2, which may act as the nucleation site for MgB2 formation, and thus the incubation period shrinks. A highly homogeneous distribution of the in situ formed MgNi3B2 nanoclusters can significantly improve the dehydriding-rehydriding kinetics. Single-phase MgNi3B2 was successfully synthesized and a similar catalytic effect is obtained by directly doping identical MgNi3B2 into the 2LiBH(4)-MgH2 system, which results in a higher hydrogen storage capacity of 9.4 wt%

El análisis de un sistema de almacenamiento de energía renovable en forma de hidrógeno es fundamental para detectar aquellas variables físicas que rigen el comportamiento real del sistema e identificar estrategias que permitan incrementar la eficacia y eficiencia del sistema. Con la adquisición y análisis de datos en diversas condiciones de operación del sistema se pueden generar modelos que puedan predecir y caracterizar el desempeño real para retroalimentar su mejor implementación. Este trabajo de investigación consistió en detectar oportunidades de optimización del sistema de generación y almacenamiento de hidrógeno, utilizando como técnicas: la medición y captura de datos de operación, la reducción y simplificación de información con métodos matemáticos, y el análisis e interpretación de resultados. Se evaluó un sistema compuesto por un electrolizador de celdas de membrana de intercambio protónico y dos tanques de hidruros metálicos, los cuales, fueron sometidos a diversas condiciones de operación: 1) el sistema produjo y almacenó hidrógeno en un tanque de almacenamiento a condiciones ambientales en los puntos de control de presión de 0.5 bar, 1.5 bar, 2.5 bar, 4.0 bar, 6.5 y 9.0 bar. 2) Simultáneamente se sometió la producción y carga de hidrógeno en 2 tanques de almacenamiento a 9.0 bar de presión. Los resultados de esta investigación ayudaron a conocer las capacidades y limitantes de un sistema de producción y almacenamiento de hidrógeno bajo ciertas condiciones de operación, enriqueciendo los criterios para la implementación de estos sistemas.

The present investigation focuses on a new synthesis route of NaBH4 starting from the 2NaH + MgB2 system subjected to mechanochemical activation under reactive hydrogen atmosphere. The milling process was carried out under two different hydrogen pressures (1 and 120 bar) with two different rotation speeds (300 and 550 rpm). The reaction products were characterized by ex-situ solid state magic angle spinning (MAS) nuclear magnetic resonance (NMR), ex-situ X-ray powder diffraction (XRPD) and Infrared Spectroscopy (IR). From the results of these analyses, it can be concluded that milling in all the considered conditions led to the formation of NaBH4 (cubic-Fm-3m). In particular, a reaction yield of 5 and 14 wt% is obtained after 20 h of milling at 120 bar of H2 for the tests performed at 300 rpm and 550 rpm, respectively. The presence of MgH2 is also detected among the final products on the as milled powders. The influence of the milling conditions and the evaluation of the parameters ...

This paper reports mischmetal (Mm) as an effective catalyst for fast desorption kinetics (3.7 wt% in 60 min in which ∼3.3 wt% observed in 30 min and ∼5 wt% in 180 min at the desorption temperature of 150 • C for the 2 mol% Mm-doped material) and rehydrogenation (up to 35 cycles) of the light weight hydrogen storage material NaAlH 4 . In fact this catalyst Mm has been shown to be better than the presently known catalyst Ti. For Mm, its presence when admixed in NaAlH 4 is discernible. Also the higher reversible hydrogen storage capacity (4.77 wt% which is 86% of the total reversible storage capacity) of the total is achievable in the 12th cycle. The possible modes of catalyst Mm for fast desorption kinetics has been outlined and the most feasible mechanism in terms of weakening of Na and AlH 4 bonding has been put forward.

The present paper reports the catalytic effect of carbon nanomaterials, particularly carbon nanotubes (CNTs) and graphitic nanofibres (GNFs) with two different structure
morphology, namely planar GNFs (PGNFs) and helical GNFs (HGNFs) as the catalyst for
improving the dehydrogenation and rehydrogenation behavior of sodium aluminum hydride (NaAlH4). It has been observed that HGNFs posses superior catalytic activity than other carbon nanoforms in improving the desorption kinetics and decreasing the desorption temperature of NaAlH4. Temperature programmed desorption (TPD) reveals that HGNFs admixed NaAlH4 undergo hydrogen desorption at a much lower temperature than PGNFs and CNTs (SWCNTs and MWCNTs) admixed NaAlH4. Thus for the heating rate of 2
C/min, the peak desorption temperature corresponds to initial step decomposition of NaAlH4 admixed with 2 wt.% HGNFs and 2 wt.% PGNFs has been lowered to 143.6
C and 152.6
C, respectively (for pristine NaAlH4, it is w170
C). In addition to the enhancement in desorption kinetics, the HGNFs admixed NaAlH4 undergoes fast rehydrogenation at the moderate condition. Microstructural investigation reveals that the HGNFs were present on the surface of NaAlH4 grains, whereas CNTs were tunneled into the grains of NaAlH4 suggesting a distinct catalytic behavior of different carbon nanovariants.

The study of phonons describes the thermodynamic properties behavior of compounds with small atoms because phonons have an important influence on its properties. Lithium borohydride, LiBH 4 , is one of the suitable materials for hydrogen storage solid state. Although the transformations of Lithium borohydride LiBH 4 were repeatedly studied by experiments and fundamental side, these transformations are still under discussion. In the present work, the mode vibrational analysis of orthorhombic and hexagonal LiBH 4 structures were considered with ab initio lattice-dynamics based on the quasi-harmonic approximation approach as implemented in Phonopy code. The results show that the orthorhombic structure is thermodynamically stable, while the hexagonal structure is unstable owing to the presence of negative mode frequency. The thermal expansion behavior and various thermodynamic properties stability like heat capacity, entropy and Helmholtz energy were also studied and the obtained results are in good agreement with experiments. This shows a deep connection between stability and strength and helps researchers to estimate accurately the thermodynamic performance of LiBH 4 materials.

In the present work we report the desorption pathway of the 2NaBH4 + MgH2 system. Ex-situ X-ray powder diffraction (XRPD) and solid state magic angle spinning (MAS) nuclear magnetic resonance (NMR) measurements have been performed on samples heat treated up to 450 °C for different times. Ex-situ X-ray powder diffraction experiments conducted on fully desorbed samples allowed us to identify nanocrystalline MgB2 and metallic Na as dehydrogenation products. 11B and 23Na NMR analyses have been also carried out in order to evaluate the structural evolution of decomposed materials. Our measurements show that the local structure of MgB2 is influenced by replacement of Mg with Na atoms in the Mg sites. Moreover, amorphous Na2[B12H12] was detected in the partially desorbed sample and in the final products of the decomposition reaction. The presence of the [B12H12]2– anion was confirmed by both direct comparison with the 11B{1H} NMR spectrum of pure Na2[B12H12] and dynamic cross-polarization experiments.

Observing solute hydrogen (H) in matter is a formidable challenge, yet, enabling quantitative imaging of H at the atomic-scale is critical to understand its deleterious influence on the mechanical strength of many metallic alloys that has resulted in many catastrophic failures of engineering parts and structures. Here, we report on the APT analysis of hydrogen (H) and deuterium (D) within the nanostructure of an ultra-high strength steel with high resistance to hydrogen embrittlement. Cold drawn, severely deformed pearlitic steel wires (FeÀ0.98CÀ0.31MnÀ0.20SiÀ0.20CrÀ0.01CuÀ0.006PÀ0.007S wt%, e ¼ 3:1) contains cementite decomposed during the pre-deformation of the alloy and ferrite. We find H and D within the decomposed cementite, and at some interfaces with the surrounding ferrite. To ascertain the origin of the H/D signal obtained in APT, we explored a series of experimental workflows including cryogenic specimen preparation and cryogenic-vacuum transfer from the preparation into a state-of-the-art atom probe. Our study points to the critical role of the preparation, i.e. the possible saturation of H-trapping sites during electrochemical polishing, how these can be alleviated by the use of an outgassing treatment, cryogenic preparation and transfer prior to charging. Accommodation of large amounts of H in the under-stoichiometric carbide likely explains the resistance of pearlite against hydrogen embrittlement.

El análisis de un sistema de almacenamiento de energía renovable en forma de hidrógeno es fundamental para detectar aquellas variables físicas que rigen el comportamiento real del sistema e identificar estrategias que permitan incrementar la eficacia y eficiencia del sistema. Con la adquisición y análisis de datos en diversas condiciones de operación del sistema se pueden generar modelos que puedan predecir y caracterizar el desempeño real para retroalimentar su mejor implementación. Este trabajo de investigación consistió en detectar oportunidades de optimización del sistema de generación y almacenamiento de hidrógeno, utilizando como técnicas: la medición y captura de datos de operación, la reducción y simplificación de información con métodos matemáticos, y el análisis e interpretación de resultados. Se evaluó un sistema compuesto por un electrolizador de celdas de membrana de intercambio protónico y dos tanques de hidruros metálicos, los cuales, fueron sometidos a diversas condiciones de operación: 1) el sistema produjo y almacenó hidrógeno en un tanque de almacenamiento a condiciones ambientales en los puntos de control de presión de 0.5 bar, 1.5 bar, 2.5 bar, 4.0 bar, 6.5 y 9.0 bar. 2) Simultáneamente se sometió la producción y carga de hidrógeno en 2 tanques de almacenamiento a 9.0 bar de presión. Los resultados de esta investigación ayudaron a conocer las capacidades y limitantes de un sistema de producción y almacenamiento de hidrógeno bajo ciertas condiciones de operación, enriqueciendo los criterios para la implementación de estos sistemas.

The present paper explores the enhancement in hydrogen sorption behavior of MgH 2 with TiO 2 nanoparticles. The catalytic effect of TiO 2 nanoparticles with different sizes (7, 25, 50, 100 and 250 nm) were used for improving the sorption characteristics of MgH 2 . The MgH 2 catalyzed with 50 nm of TiO 2 exhibited the optimum catalytic effect for hydrogen sorption behavior. The desorption temperature of MgH 2 catalyzed through 50 nm TiO 2 was found to be 310 C. This is 80 C lower as compared to MgH 2 having a desorption temperature of 390 C. It was noticed that the dehydrogenated MgH 2 catalyzed with 50 nm TiO 2 reabsorbed 5.1 wt% of H 2 within 6 minutes at temperature and pressure of 250 C and 50 atm, respectively. The 50 nm TiO 2 catalyst lowered the absorption activation energy of MgH 2 from ∼ 92 to ∼ 52.7 kJ mol −1 .

Hydrogen storage XRD Rietveld X-ray diffraction a b s t r a c t In this work, Mg doped zinc oxide (Mg x Zn 1Àx O, x ¼ 5, 10 and 20 at. %) nanowires were successfully prepared by two step process. Initially, ZnO nanowires were grown by thermal evaporation of Zn powder under oxygen atmosphere. Mg powder was doped in as grown ZnO through solid state diffusion at low temperature. Energy dispersive x-ray spectroscopy (EDAX), transmission electron microscopy (TEM), X-ray diffraction (XRD) and UVeVisible absorption spectra analysis reveals that the Mg doping on ZnO nanowires induces lattice strain in ZnO. Rietveld analysis of XRD data confirms the wurtzite structure and a continuous compaction of the lattice (in particular, the c-axis parameter) as x increases. The hydrogenation properties of ZnO nanowires and Mg doped ZnO (Mg x Zn 1Àx O, x ¼ 0, 5, 10 and 20 at. %) nanowires were studied. The hydrogenated samples were further investigated through XRD and Fourier transform infrared spectroscopy (FTIR). The hydrogen storage capacity of as grown ZnO nanowires has been estimated to be 0.57 wt. % H 2 at room temperature. However, the hydrogen storage capacity gets increased to w1 wt. % upon doping ZnO with 10 at. % Mg. Further increase in Mg concentration decreases the hydrogen storage capacity of ZnO nanowires. Thus for 20 at. % Mg doped ZnO; the hydrogen absorption capacity gets decreased from w1 wt. % to 0.74 wt. %. The mechanism of hydrogen storage in ZnO nanowires and Mg doped samples of ZnO has been discussed. (O.N. Srivastava).

By employing the state of art first principles approaches, comprehensive investigations of a very promising hydrogen storage material, Mg2FeH6 hydride, is presented. To expose its hydrogen storage capabilities, detailed structural, elastic, electronic, optical and dielectric aspects have been deeply analysed. The electronic band structure calculations demonstrate that Mg2FeH6 is semiconducting material. The obtained results of the optical bandgap (4.19 eV) also indicate that it is a transparent material for ultraviolet light, thus demonstrating its potential for optoelectronics application. The calculated elastic properties reveal that Mg2FeH6 is highly stiff and stable hydride. Finally, the calculated hydrogen (H2) storage capacity (5.47 wt.%) within a reasonable formation energy of −78 kJ mol−1, at room temperature, can be easily achievable, thus making Mg2FeH6 as potential material for practical H2 storage applications.

The influence of different high energy milling times and of the addition of catalysts such as Nb2O5, TiCl3 and graphite on the hydrogen absorption/desorption (A/D) kinetics of a mixture of 2LiNH2 + 1.1MgH2 has been studied in the temperature range 220–240 °C. It is found that a prolonged milling time is effective in improving the A/D kinetics, irrespective of the presence or not of any kind of tested additive. The enthalpy of decomposition reaction results to be about 40.4 kJ/mol, as derived from van’t Hoff plot using the values of the plateau pressures measured in desorption mode. This thermodynamic parameter fits well with the current literature data.

In this study, the hydrogen storage properties and reaction mechanism of 4MgH2-LiAlH4 destabilized system with K2TiF6 additive were studied for the first time. It was found that the addition of K2TiF6 resulted in both decreased decomposition temperature, and enhanced sorption kinetics, compared to undoped 4MgH2 + LiAlH4. The onset dehydrogenation temperature of the 10 wt% K2TiF6-doped 4MgH2 + LiAlH4 sample was reduced by about 50 C compared to the as-milled undoped 4MgH2 + LiAlH4, and the saturation of dehydrogenation process for the K2TiF6-added 4MgH2 + LiAlH4 sample was achieved within 25 min compared with 45 min for the undoped sample. From the Kissinger plot, the activation energy for the MgH2-relevent decomposition was reduced from 126 kJ/mol for 4MgH2-LiAlH4 composite to 107 kJ/mol after addition of K2TiF6. The differential scanning calorimetry measurements indicated that the enthalpy change in the 4MgH2 + LiAlH4 composite system was unaffected by the addition of K2TiF6. It was believed that the formation of Ti-containing and Al-containing species together with a small amount of Li-containing species during the ball milling or the dehydrogenation process might be actually responsible for the catalytic effects, and thus, further improved the dehydrogenation of the K2TiF6-added 4MgH2 + LiAlH4 composite system.

A system of 2LiH-MgB2 and its hydrogenated 2LiBH4-MgH2 is an attractive candidate for hydrogen storage. However, its hydriding-dehydriding kinetics have to be further improved for practical application. In the present work, three kinds of Ni-B nanoparticles with different crystalline states and particle sizes were prepared by wet-chemical reduction and mechanochemical methods, and then introduced into a 2LiH-MgB2 composite for catalytic enhancement. The catalytic roles of Ni-B nanoparticles on the hydriding-dehydriding properties were investigated systematically. The results show that all of the Ni-B nanoparticles can significantly enhance the hydriding-dehydriding kinetics of the 2LiH-MgB2 composite, resulting in no incubation period for the formation of MgB2 during dehydrogenation. The more disordered the amorphous structure and the smaller sized the Ni-B particles are, the better the catalytic effect that is obtained. Microstructure analyses clearly reveal the formation of the MgNi3B2 phase in the dehydriding process, which acts as the nucleation agent for MgB2 formation determined by an edge-to-edge model. Directly doping with Ni-B nanoparticles in the 2LiH-MgB2 system shows a higher hydrogen desorption capacity of 9.4 wt% and obtains a better catalytic efficiency than doping with NiCl2.
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Based on ab-initio molecular dynamics simulations, we investigate the low temperature crystal structure of Li2NH which in spite of its great interest as H-storage material is still matter of debate. The dynamical simulations reveal a precise correlation in the fractional occupation of Li sites which leads average atomic positions in excellent agreement with diffraction data and solves inconsistencies of previous proposals.

Difference of hydrogen solid solution limits in zirconium alloys for hydride formation and dissolution (solubility hysteresis) has been estimated based on general physical assumptions, and sensitivity to model parameters was investigated. Five energy dissipation mechanisms during the phase transition responsible for the hysteresis value were identified. Comparison of experimental data and the estimation demonstrates satisfactory agreement under the model assumptions.

Ti and its alloys have a high affinity for hydrogen and are typical hydride formers. Ti-hydride are brittle phases which probably cause premature failure of Ti-alloys. Here, we used atom probe tomography and electron microscopy to investigate the hydrogen distribution in a set of specimens of commercially pure Ti, model and commercial Ti-alloys. Although likely partly introduced during specimen preparation with the focused-ion beam, we show formation of Ti-hydrides along a grain boundaries and a/b phase boundaries in commercial pure Ti and aþb binary model alloys. No hydrides are observed in the a phase in alloys with Al addition or quenched-in Mo supersaturation.