In-situ synchrotron X-ray diffraction (SR-XRD) combined with transmission electron microscope (TEM) and first-principle calculations was employed to reveal the mechanism of hydrogen-induced decomposition of 18R-type long period stacking ordered (LPSO) structure. 80 wt.% of the structure was decomposed by 0.05 MPa H2 at 280 °C in 90 min, producing 6 wt.% Mg, 50 wt.% MgH2, 15 wt.% YH2, 9 wt.% Mg2Ni, and 3 wt.% Mg2NiH4. The formation of YH2 nanoparticles is the fastest process due to the strong interaction between hydrogen atoms and dispersive L12-Ni6Y8 clusters. Furthermore, the metastable Mg6Ni nanocrystals, which transformed to Mg2Ni and Mg nanoparticles, was detected.Download high-res image (386KB)Download full-size image

In order to provide an efficient tool to explore alloy composition and processing conditions for Mg-based alloys with good hydriding/dehydriding (H/D) properties, investigation of the Mg–Ni–Nd–H quaternary system was carried out by experimental measurements and CALPHAD thermodynamic analysis combined with first-principles calculations. A new stable compound Nd16Mg96Ni12 with the space group of Cmc21 was identified in the Mg–Ni–Nd system by synchrotron powder X-ray diffraction (SR-PXRD). The phase equilibria and phase transformation related to Nd4Mg80Ni8, Nd16Mg96Ni12, NdMg5Ni and NdMg2Ni were studied by scanning electron microscopy (SEM), X-ray diffraction (XRD) and differential scanning calorimetry (DSC). The formation enthalpies of these ternary compounds were calculated by the density functional theory. The existence of the quaternary hydrides NdMgNi4H4 and NdMg2Ni9H12 was taken into consideration. Based on the obtained thermodynamic description of the Mg–Ni–Nd–H system, the hydrogen storage capacities and pressure–composition–temperature (P–C–T) curves were predicted and two new ternary compounds Nd4Mg80Ni8 and Nd16Mg96Ni12 were designed as hydrogen storage alloys with excellent properties. Meanwhile, the H/D mechanism of the Mg–Ni–Nd alloy was revealed.

Long cycling life is one prerequisite for the commercial application of hydrogen storage materials. The cycling stability of a promising Mg + Mg2Ni + YH2 hydrogen storage nanocomposite made by hydrogen-induced decomposition of the 18R-type long period stacking ordered (LPSO) structure is investigated. At 300 °C, it absorbs maximum ∼5.2 wt% H at the 40th de/hydrogenation cycle and still has 4.3 wt% H even after 620 cycles. Both activation and passivation occur during the 40th–620th cycles, where the absorption rate within 0–15 s becomes faster but the rate after 15 s gradually slows down. Characterizations by synchrotron X-ray powder diffraction and transmission electron microscopy reveal that this phenomenon is closely related to the pulverization of particles and the aggregation of YH2 nanocatalysts. From the first-principles calculations, the catalytic effect of YH2 is ascribed to the relatively high interfacial energy of YH2/Mg, the low diffusion energy barrier for H at the YH2/Mg interface, and the high affinity between YH2 and H. 17% loss of hydrogen capacity is attributed to the formation of kinetically inactive Mg/MgH2 phases, the aggregation of YH2 and the oxidation of Mg. Minimizing the separation between the Mg/MgH2 matrix and YH2 nanocatalysts is crucial to maintain the high effective capacity of this nanocomposite.

•Galvanic corrosion accelerates the consumption of remnant Al-rich phase.•MgZn2 phase exists in the interdendritic Zn-rich region of Al–Zn–Si–3Mg coating.•The presence of MgZn2 phase contributes to generate Zn–Al LDH.•The Al-rich phase with a bit of Mg corroded more uniformly.The corrosion behaviour of hot-dip Al–Zn–Si and Al–Zn–Si–3Mg coatings on steel sheets in NaCl solution were investigated by microstructural characterization, weight loss tests, and electrochemical methods Localized corrosion of the Al-rich phase in the Al–Zn–Si coating was observed. The exposure of the intermetallic layer was supposed to present galvanic corrosion and remarkably accelerate the consumption of remnant Al-rich phase. The MgZn2 phase was detected in the interdendritic Zn-rich region of the Al–Zn–Si–3Mg coating. The presence of the MgZn2 and Mg2Si phases contributed to delaying the occurrence of localized corrosion.

•The Al-Ti-V system was experimentally investigated using equilibrated alloys.•The phase transitions in the alloys of Al-rich region were determined.•A thermodynamic description of Al-Ti-V system was developed using CALPHAD approach.Vanadium was added into Al-Ti based alloys to improve the intermediate temperature ductility and refine the grains. However, the change of phase relations and phase transitions resulted from the V addition has not been fully understood. In this study, the phase equilibria in the Al-rich corner of Al-Ti-V system were investigated using X-ray diffraction, scanning electron microscopy, energy dispersive spectrometer and differential scanning calorimeter. To validate the phase relations, five Al-rich key alloys were prepared and annealed at 600 °C and 700 °C for 360 h respectively. The results indicated that two three-phase regions and three two-phase regions exist in the Al-rich corner at 600 °C. And one three-phase region and four two-phase regions are stable at 700 °C. The EDS results showed that the solubility of V in TiAl3 can vary from 2.8 at.% to 27.0 at.%, which results in a solid solution phase (Ti, V)Al3. Based on the isothermal phase equilibria at 600 °C and 700 °C and the invariant reactions determined in this work, the model parameters of (Ti, V)Al3 were optimized and a new thermodynamic description of Al-Ti-V system was obtained. Comparing the calculated results with the experimental data, a good agreement was reached.Download high-res image (303KB)Download full-size image

•Equilateral triangle Mg2Si phases appear on the surface of Al–Zn–Si–xMg coatings.•Mg-rich phase can obviously improve the corrosion resistance of Al–Zn–Si–xMg coatings.•Zn–Al LDH more easily precipitates on the Al–Zn–Si–xMg coatings with Mg2+.•Mg2Si has better anti-corrosion effects than MgZn2.•De-alloying stage of Mg2Si contributes to prolong the cathodic protection effect.The effects of alloyed magnesium on the corrosion behavior of hot-dip Al–Zn–Si–xMg (x = 0, 1.25, 3 and 4 wt.%) coatings were investigated by analysis of the phase composition, long-term immersion test and electrochemical measurements. Mg2Si phase appeared in the Al–Zn–Si–1.25Mg and Al–Zn–Si–3Mg coatings but only MgZn2 phase existed on the surface of Al–Zn–Si–4Mg coating. The alloyed magnesium improves the corrosion resistance of the Mg-containing coatings and the Al–Zn–Si–3Mg coating shows the highest protective properties in the investigation.

An extended Jonhson–Mehl–Avrami–Kolomogorov model with analytical solutions is developed to achieve the comprehensive determination of kinetic parameters in solid-state phase transitions. A new subexpression is given for the case of adequately small activation energy of nucleation, which is ignored in previous works. Exact or approximate analytical solutions to the expressions in this model for isothermal and non-isothermal conditions are improved by introducing the Euler integral of the first kind, which are proved to be valid, accurate, and simple for possible parameters. On the basis of this model, five kinetic parameters (pre-exponential factor, activation energy of nucleation, activation energy of growth, nucleation index, and growth index) can be comprehensively determined by simultaneous analysis of isothermal and non-isothermal experimental data. Three practical examples, including two simulated examples and one experimental example, are then presented to illustrate and validate the comprehensive determination in detail, in which the kinetic parameters determined by this approach are confirmed to be highly plausible. This is of great importance for in-depth understanding the kinetic mechanisms and taking full advantage of the solid-state phase transitions.

•Phase equilibria of Ce–Mg–Ni system at 673 K was constructed by CALPHAD method.•The hydrogen storage properties of the Ce2.92Mg91.84Ni5.24 alloy were studied.•The mechanism of α-to-β phase transformation was detected by in situ SR-PXRD.The isothermal section of Ce–Mg–Ni ternary system at 673 K was constructed through thermodynamic calculation coupled with experimental verification. Under guidance of the phase diagram in Mg-rich corner, Ce2.92Mg91.84Ni5.24 was designed to investigate its hydrogen storage properties. Moreover, the mechanism of α-to-β (α: diluted phase and β: hydride) phase transformation in the Ce2.92Mg91.84Ni5.24–H2 system was elucidated by in situ synchrotron powder X-ray diffraction (SR-PXRD). The alloy showed a good activated ability and displayed two plateaus in the pressure–composition–temperature curves. The kinetic mechanisms of hydriding and dehydriding reactions were analyzed by Chou model. The rate-controlling steps were the diffusion for the initial stage in hydriding reaction and the surface penetration for dehydriding reaction. SR-PXRD patterns indicated that the activated Ce2.92Mg91.84Ni5.24 gradually transformed into CeH2.51, (Mg) (with solid solution of H atoms) and Mg2NiH0.3, finally transformed into CeH2.51, MgH2 and Mg2NiH4 during the first hydriding process.

•The Chou model with considering PBR is proposed and applied to the kinetic mechanisms of La–Mg–Ni alloys.•The rate-controlling step is determined by the modified Chou model in different alloys under different influence factors.•The comparison between the original Chou model and the modified Chou model is also discussed.The phenomenon of volume change is very important in the hydriding and dehydriding reactions to clarify their kinetic mechanisms. However, few of the theoretical models take this factor into account in the study of kinetic mechanisms. In the present work, the modified Chou model with considering the volume change by Pilling-Bedworth Ratio (PBR) β is applied to interpret the kinetic mechanisms of hydriding and dehydriding reactions in La–Mg–Ni ternary hydrogen storage alloys. The calculation results agree well with the experimental data, indicating that the modified Chou model can well describe the kinetic behaviors of La–Mg–Ni alloys. Diffusion is determined to be the rate-controlling step of hydriding and dehydriding for the examples in this work. The activation energies are calculated to be 39.4 kJ/mol for hydriding reaction (β = 1.29) and 93.1 kJ/mol for dehydriding reaction (β = 0.78) of Mg–10.6La–3.5Ni nanoparticles at 453–623 K. For the hydrogen absorption kinetics of La2Mg16Ni alloy under 0.5–3 MPa at 598 K, β is 1.25 and the equilibrium hydrogen pressure is calculated to be 0.332 MPa. For the hydrogen desorption kinetics of Mgx(LaNi3)100−x alloys at 623 K, the characteristic times increase in the order of tc(x = 70,β= 0.79) < tc(x= 60, β= 0.79) < tc(x= 40, β= 0.97) < tc(x= 50, β = 0.85). The value of β is 0.77 and the hydrogen desorption rate of Mg–5La–10Ni alloy prepared by the ultrahigh pressure (UHP) method is faster than that of the alloy prepared by the as-cast method, whose characteristic times are 7428 s and 4651 s, respectively. Furthermore, the calculation accuracy can also be improved by the modified Chou model compared with the original Chou model after taking PBR into consideration.

•Analysis of kinetic behaviors for hydrogen storage materials reveals mechanisms.•The assumptions and derivation steps of the kinetic models are illustrated.•The analysis methods on the basis of the kinetic models are summarized.•Some new proposed models and analysis methods are introduced.Analysis of the hydrogenation and dehydrogenation behaviors by kinetic models is an efficient approach to the in-depth understanding of the kinetic mechanism for hydrogen storage materials. A large number of kinetic models as well as analysis methods based on these models have been extensively applied in hydrogen storage materials, and kinetic parameters with physical interpretations are determined to reveal the kinetic mechanism of hydrogenation and dehydrogenation reactions. However, the assumptions and derivation steps of these models are usually difficult to find, and the selection of analysis methods is sometimes confusing. Moreover, some recently proposed models and analysis methods have not been introduced to investigate the kinetic mechanism of hydrogen storage materials yet. These problems significantly prevent the kinetic models as well as analysis methods from further revealing the kinetic mechanism for hydrogen storage materials. Therefore, this review mainly focuses on the illustration of the assumptions and derivation steps of the kinetic models, summarization of corresponding analysis methods, and introduction of some recently proposed kinetic models and analysis methods for hydrogen storage materials.

We report the structure of an aluminum borohydride ethylenediamine complex, Al(EDA)3·3BH4·EDA. This structure was successfully determined using X-ray powder diffraction and was supported by first-principles calculations. The complex can be described as a mononuclear complex exhibiting three-dimensional supramolecular structure, built from units of Al[C2N2H8]3, BH4, and ethylenediamine (EDA) molecules. Examination of the chemical bonding indicates that this arrangement is stabilized via dihydrogen bonding between the NH2 ligand in EDA and the surrounding BH4. The partial ionic bonding between the Al and N atoms in EDA forms a five-member ring (5MR), an Al[NCCN] unit. The calculated H2 removal energies confirm that it is energetically favorable to remove the loosely bonded EDA and H atoms with N–H···H–B dihydrogen bonds upon heating. Our results suggest that the NH2 terminal ligand in the EDA molecule combines with a H atom in the BH4 group to release H2 at elevated temperature, and our results confirm that the experimental result Al(EDA)3·3BH4·EDA can release 8.4 wt % hydrogen above 149 °C with detectable EDA molecules. This work provides insights into the dehydrogenation behavior of Al(EDA)3·3BH4·EDA and has implications for future development of promising high-performance metal borohydride ethylenediamine complexes.

Poor selectivity for gasoline products is a critical issue for the Fischer–Tropsch synthesis (FTS). Herein, we report that the introduction of a polyoxometalate Cs2.5H0.5PW12O40 (CsPW) into a conventional FTS catalyst (Co/Al2O3) can create a highly efficient bifunctional catalyst, leading to 118% increase in the selectivity of gasoline. Furthermore, it was found that such a significant improvement is due to the effective hydrocracking of heavier hydrocarbon products at CsPW sites.

•The Nd–H system is assessed based on the experimental data in literature.•The Nd–Ni–H system is optimized with considering NdNi5H3 and NdNi5H6.•The hydriding and dehydriding temperatures of NdNi5 are determined by HP-DSC.•The predicted PCT curves of NdNi5 are in good agreement with experimental data.A coupled experimental investigation and thermodynamic study of the Nd–Ni–H system have been carried out and the self-consistent thermodynamic database on this system has been obtained. High pressure differential scanning calorimetry (HP-DSC) is used to determine the temperature of reaction NdNi5H3↔NdNi5+1.5H2 in the pressure range of 3.01–11.01 MPa H2. The thermodynamic functions for Nd–H system are developed based on the critical assessment of the equilibrium pressure PH2 over sample at 600–800 °C, invariant reaction temperatures and hydrogen solubilities in Nd. Two sets of thermodynamic functions for Nd–Ni–H system are provided because two sets of models for NdNi5, NdNi5H3 and NdNi5H6 are adopted. The NdNi5, NdNi5H3 and NdNi5H6 are modeled as separated phases in parameter set 1 and described as a single phase in parameter set 2. The calculated decomposition temperatures of NdNi5H3 and NdNi5Ni6 at different pressures agree well with the experimental data. However, the thermodynamic description of parameter set 1 is recommended through comparing the calculated pressure–temperature–composition (PCT) curves with the experimental results. In addition, the obtained thermodynamic database of Nd–Ni–H system is applied to analyze the hydriding process of Nd–Ni alloys.

•Effect of LiH on the H-sorption properties of MgH2 was investigated.•The addition of LiH can deteriorate the desorption kinetics/thermodynamics of MgH2.•H–H exchange was observed between LiH and MgH2.•The negative effect of LiH might be due to H–H exchange between LiH and MgH2.Recent works showed that the addition of LiBH4 significantly improves the sorption kinetics of MgH2, and LiH decomposed from LiBH4 was supposed to play the catalytic effect on MgH2. In order to clarify this mechanism, the effect of LiH on the hydriding/dehydriding kinetics and thermodynamics of MgH2 was systematically investigated. The hydrogenation kinetics of LiH-doped samples, as well as the morphology after several cycles, was similar to those of pure MgH2, which indicate that Li+ had no catalytic effect on the hydrogenation of Mg. Moreover, the addition of LiH strongly retarded the hydrogen desorption of MgH2 doped with/without Nb2O5, and resulted in higher starting temperature of desorption, larger activation energy and larger pressure hysteresis of PCI curves of MgH2. H2, HD and D2 were observed in the desorption products of MgH2-2LiD, which confirms that H–H exchange indeed occurs between MgH2 and LiH, hence deteriorate desorption kinetics/thermodynamics of MgH2. The results implied that the additives containing H− could retard the hydrogen desorption of MgH2 by H–H exchange effect.

•NiCl2 enhanced dehydrogenation of hydrazine bisborane (HBB) was reported.•By adding NiCl2, the desorption rate and the hydrogen purity were improved.•A possible explanation was proposed to understand NiCl2 enhanced desorption of HBB.NiCl2 and CoCl2 were adopted to enhance the dehydrogenation of hydrazine bisborane (HBB), respectively, of which NiCl2 showed better performance. By adding 2.0 mol. % NiCl2, the dehydrogenation property of HBB was significantly improved, for example, the impurity of NH3 during the dehydrogenation of HBB was totally suppressed with more than 13.0 wt. % of pure hydrogen evolved. By Kissinger method, the apparent activation energies of the first step for HBB and Ni-doped HBB were calculated to be 143.2 and 60.7 kJ mol−1, respectively. DSC result showed that the addition of NiCl2 did not change the enthalpy change of HBB dehydrogenation. Based on theoretical analysis and literature review, the improved dehydrogenation property of HBB was potentially ascribed to the solid state interaction of Ni2+ with the electronegative N in the NH2 group of HBB.

Two new derivatives of ammonia borane (AB), 1,2/1,3-di-aminopropane borane (1,2/1,3-TMDAB), were prepared through the coordination reaction between 1,2/1,3-di-aminopropane and BH3–THF, which were then characterized by HR-XRD, FT-IR, 13C and 11B NMR. The crystal structure of 1,3-TMDAB was obtained with a combined technique of HR-XRD data and DFT calculations. 1,3-TMDAB crystallizes in the space group of P212121 (no. 19) with an orthorhombic crystal system and lattice constants of a = 12.6439(8) Å, b = 8.6289(3) Å, c = 7.2322(2) Å, and V = 789.05(3) Å3. Both samples, with a theoretical hydrogen content of 9.8 wt%, were shown to release pure H2 during thermal dehydrogenation, presenting great advantages over AB which releases large amounts of impurities (such as NH3, B2H6 or borazine). Moreover, 1,2/1,3-TMDAB did not foam and showed a faster dehydrogenation rate compared with AB. Our newly synthesized 1,2/1,3-TMDAB may serve as a superior alternative to AB for hydrogen storage and enrich the research field of B–N–H hydrogen storage materials.

•Cobalt-based ammine borohydrides were synthesized via a simple ball milling process.•5.2 wt.% pure hydrogen can be evolved within 45 min at 80 °C from CoCl3·3NH3/3LiBH4.•CoCl2·3NH3/2LiBH4 shows certain advantage over CoCl2/2LiBH4 as hydrogen storage material.Two new cobalt-based ammine borohydrides were prepared via ball milling of LiBH4 and CoCln·3NH3 (n = 3, 2) with molar ratios of 3:1 and 2:1, respectively. X-ray diffraction (XRD) results revealed the as-prepared composites having amorphous state. Thermogravimetric analysis-mass spectrometry (TG-MS) measurements showed that the two composites mainly release H2, concurrent with the evolution of a small amount of NH3. Further results showed that the excessive addition of LiBH4 can suppress the liberation of NH3, resulting in the release of H2 with a high purity (>99 mol.%). By combination with the temperature-programmed-desorption (TPD) results, the CoCl3·3NH3/4LiBH4 and CoCl2·3NH3/3LiBH4composites can release 7.3 wt.% (4.2 wt.% including LiCl) and 4.2 wt.% (2.0 wt.% including LiCl) pure hydrogen, respectively, in the temperature range of 25–300 °C. Isothermal dehydrogenation results reveal that CoCl3·3NH3/3LiBH4 shows favorable dehydrogenation rate at low temperatures, releasing about 5.2 wt.% (2.9 wt.% including LiCl) of hydrogen within 45 min at 80 °C.

The Mg17Ni1.5Ce0.5 hydrogen storage composites with different contents of graphite were prepared by a new method of mechanical milling and subsequent microwave sintering. The small particle size (~25 μm) and the low echo ratio of power indicate that graphite plays an important role not only as a lubricant during mechanical milling but also as a supplementary heating material during microwave sintering. As a catalyst in the hydriding/dehydriding (H/D) reaction, graphite also improved the hydrogen storage properties of the composites. The hydrogen absorption and desorption capacities of Mg17Ni1.5Ce0.5 with 5 wt pct graphite were 5.34 and 5.30 wt pct H2 at 573 K (300 °C), its onset temperature of dehydriding reaction was 511 K (238 °C), and its activation energies of H/D reaction were 40.9 and 54.5 kJ/mol H2, respectively. The kinetic mechanisms of the H/D reaction are also discussed.

The significantly enhanced dehydrogenation performance of binary complex system, NH3BH3/LiBH4·NH3, were achieved through a chemical modification of LiH to form ternary composites of x (LiH–NH3BH3)/LiBH4·NH3. Among the studied composites, 3LiH–3NH3BH3/LiBH4·NH3 released ca. 10 wt. % high-pure hydrogen (>99.9 mol%) below 100 °C with fast kinetics, while less than 8 wt. % hydrogen, accompanied with a fair number of volatile byproducts, were released from 3NH3BH3/LiBH4·NH3 at the same conditions. Further investigations revealed that the hydrogen emission from x (LiH–NH3BH3)/LiBH4·NH3 composites is based on the combination mechanism of Hδ+ and Hδ− through the interaction between LiH–NH3BH3 and NH3 group in LiBH4·NH3, in which the controllable protic hydrogen source from the stabilized NH3 group played a crucial role in providing optimal stoichiometric ratio of Hδ+ and Hδ−, and thus leading to the significant improvement of dehydrogenation capacity and purity.Highlights► LiH was introduced to enhance the dehydrogenation of the NH3BH3/LiBH4·NH3 composites. ► The 3LiH–3AB/3LiBH4·NH3 composite can release 10 wt. % pure hydrogen below 100 °C ► The hydrogen release in x (LiH–AB)/LiBH4·NH3 started with the formation of LiAB.

Phase equilibria and thermodynamic properties in the La–Ni–Cu ternary system were studied by coupling thermodynamic modeling and experimental validation. A set of self-consistent thermodynamic descriptions for phases in the La–Ni–Cu system were obtained on the basis of those three constituent binary and ternary experimental data in the literature. The isothermal section at 673 K and the mixing enthalpy of liquid calculated from the currently constructed ternary thermodynamic description were favorably compared with available experimental data. Three key alloy samples were then selected, synthesized and annealed at 673 K in order to further validate the calculated phase equilibria. These alloys were analyzed by means of inductively coupled plasma (ICP), X-ray diffraction (XRD), scanning electron microscopy (SEM)/back-scattered electrons (BSE) and energy disperse spectroscopy (EDS), and the experimental results were in reasonable agreement with the calculated phase equilibrium relationships.Highlights► The enthalpy of mixing of liquid was thermodynamically assessed using the Calphad method. ► The isothermal section at 673 K is thermodynamically calculated and experimentally validated. ► The LaNi and LaCu2 two-phase field was larger than that reported in the literature.

Metal-catalyzed hydrolysis and methanolysis of guanidinium borohydride (C(NH2)3BH4 or GBH) for hydrogen generation are reported. GBH is comparatively stable in water with only 0.3 equiv of H2 liberated in 24 h at 25 °C while it reacts vigorously with methanol, releasing more than 3.2 equiv of H2 within only 17 min. Even at 0 °C, there was still nearly 2.0 equiv of H2 released after 2 h, but no H2 liberation was observed for hydrolysis under the same conditions. Various metal chlorides were adopted to enhance the reaction kinetics of the hydrolysis and methanolysis, of which CoCl2 exhibits the highest activity in both cases. With the addition of 2.0 mol % CoCl2 at 25 °C, the methanolysis of GBH could generate 4 equiv of H2 within 10 min with a maximum hydrogen generation rate of 9961.5 mL·min–1·g–1 while only 1.8 equiv of H2 was obtained under the same conditions at a maximum hydrogen generation rate of 692.3 mL·min–1·g–1 for hydrolysis. Compared with hydrolysis, methanolysis of GBH possesses much faster reaction kinetics, rendering it an advantage for hydrogen generation, especially at subzero areas. It was proposed that the faster reaction kinetics of methanolysis of BH4– containing compounds is ascribed to the more electron donating methoxy group than that of hydroxyl group. Moreover, a comparison between hydrolysis and methanolysis of GBH indicates that the loss of the first H from BH4– controls the hydrolysis kinetics instead of the cleavage of the O–H bond.

A novel eutectic hydrogen storage system, LiBH4·NH3–nNH3BH3, which exists in a liquid state at room temperature, was synthesized through a simple mixing of LiBH4·NH3 and NH3BH3 (AB). In the temperature range of 90–110 °C, the eutectic system showed significantly improved dehydrogenation properties compared to the neat AB and LiBH4·NH3 alone. For example, in the case of the LiBH4·NH3/AB with a mole ratio of 1:3, over 8 wt.% hydrogen could be released at 90 °C within 4 h, while only 5 wt.% hydrogen released from the neat AB at the same conditions. Through a series of experiments it has been demonstrated that the hydrogen release of the new system is resulted from an interaction of AB and the NH3 group in the LiBH4·NH3, in which LiBH4 works as a carrier of ammonia and plays a crucial role in promoting the interaction between the NH3 group and AB. The enhanced dehydrogenation of LiBH4·NH3/AB may result from the polar liquid state reaction environments and the initially promoted formation of the diammoniate of diborane, which will facilitate the B–H⋯H–N interaction between LiBH4·NH3 and AB. Kinetics analysis revealed that the rate-controlling steps of the dehydrogenation process are three-dimensional diffusion of hydrogen at temperatures ranging from 90 to 110 °C.

Chou model was used to analyze the influences of LaNi5 content, preparation method, temperature and initial hydrogen pressure on the hydriding kinetics of Mg–LaNi5 composites. Higher LaNi5 content could improve hydriding kinetics of Mg but not change hydrogen diffusion as the rate-controlling step, which was validated by characteristic reaction time tc. The rate-controlling step was hydrogen diffusion in the hydriding reaction of Mg–30 wt.% LaNi5 prepared by microwave sintering (MS) and hydriding combustion synthesis (HCS), and surface penetration was the rate-controlling step of sample prepared by mechanical milling (MM). Rising temperature and initial hydrogen pressure could accelerate the absorption rate. The rate-controlling step of Mg–30 wt.% LaNi5 remained hydrogen diffusion at temperatures ranging from 302 to 573 K, while that of Mg–50 wt.% LaNi5 changed from surface penetration to hydrogen diffusion with increasing initial hydrogen pressure ranging from 0.2 to 1.5 MPa. Apparent activation energies of absorption for Mg–30 wt.% LaNi5 prepared by MS and MM were respectively 25.2 and 28.0 kJ/mol H2 calculated by Chou model. Kinetic curves fitted and predicted by Chou model using temperature and hydrogen pressure were well exhibited.Highlights► A comparative study on the experimental data and theoretical analysis by Chou model. ► Effects of LaNi5, preparation way, temperature and hydrogen pressure were studied. ► Apparent activation energy was calculated by Chou model. ► We analyzed the hydriding kinetics by the calculated characteristic reaction time.

Two kinds of kinetic models, which are Jander model and Chou model, were applied to investigate the hydriding kinetic behavior of Mg–Ni based alloys. By comparing the calculated values with experimental data, it can be seen that both models were successfully used in the diffusion-controlled hydrogen absorption process of Mg–Ni system. However, Chou model was not only convenient for use but also gave a set of physical meaningful explicit analytic expressions. Chou model should be preferentially recommended to deal with the calculation at multi-temperatures and multi-pressures without multistep calculation. The application of Chou model to Mg20Ni8Cu2 and Mg20Ni8Co2 alloys shows that the calculated results agreed well with the experimental data and it is reasonable to expect that this model will also suitable for other Mg–Ni based alloys if the mechanism is similar.

The phase equilibrium of the Al–Zn–Mg–Si quaternary system containing (Al), (Si), MgZn2 and Mg2Si phases has been studied by means of scanning electron microscopy (SEM), electron dispersive spectrometry (EDS), X-ray diffraction (XRD) and differential scanning calorimeter (DSC) as well as calculation of phase diagram based on PANDAT software. Two three-phase fields and one four-phase field among the 15 wt% Al–Zn–Mg–6 wt% Si alloys in the concentration of Zn ranging from 57 wt% to 67 wt% have been confirmed at 573 K. The result showed non-existence of quaternary compound in this region. Based on the experimental results, the appropriate thermodynamic description of Mg–Si system was chosen. The ternary interactions in the liquid phase of Al–Mg–Si and Mg–Zn–Si systems have been assessed and the calculated ternary phase diagrams agreed well with the experimental data. Combining with the related ternary systems, the thermodynamic description of the Al–Zn–Mg–Si system was presented, and the good agreement between the calculated results and the experimental results was obtained.

The hydrogen storage samples of Nd–Mg–Ni–Fe3O4 alloy were prepared by microwave sintering (MS) and conventional sintering (CS) methods, respectively. Their phase structures, morphologies, hydrogen storage properties were intensively studied by X-ray diffraction (XRD), scanning electron microscopy (SEM) and pressure–composition–temperature (PCT). XRD and SEM analysis results show that the microwave sintered Nd–Mg–Ni–Fe3O4 alloy has multiphase structure involving Mg and homogeneous grains, whereas the alloy prepared by CS has Mg41Nd5 phase and coarse grains. The alloy prepared by MS can release 85% of the saturated hydrogen capacity at 573 K in 600 s and its characteristic reaction time (tc) is less than 2900 s, while the alloy prepared by CS releases less than 70% of the absorbed hydrogen at 573 K within 1300 s and its tc is more than 3000 s. It is found that the alloy prepared by MS not only has high hydrogen capacity, but also better dehydriding kinetic property than the alloy prepared by CS.

A new model has been successfully used to investigate the hydrogen absorption kinetics mechanism of La2Mg17-based composites. The results indicate that different preparation conditions lead to different rate-controlling steps during hydrogen absorption process. For La2Mg17–LaNi5 composite synthesized by the method of melting, the rate-controlling step is the surface penetration of hydrogen atoms, which does not change by addition agent (LaNi5). However, mechanical milling can change the rate-limiting steps of hydriding reaction in the La2Mg17–LaNi5 composite from surface penetration to diffusion of hydrogen in the hydride layer. With the enhancement of milling intensity, the rate-controlling step in La1.8Ca0.2Mg14Ni3 alloy changes from surface penetration to diffusion. In addition, the activation energies of hydrogen absorption for La2Mg17−20 wt%LaNi5 and La1.8Ca0.2Mg14Ni3 are obtained by this model.

In this paper, the phase microstructures and electrochemical performances of La0.67Mg0.33Ni3.0 and La0.67Mg0.33Ni2.5Co0.5 hydrogen storage alloys treated by casting, heat treatment and magnetic-heat treatment were studied. The influence of the partial substitution of Co for Ni and heat treatment with and without an external magnetic field on the microstructures and electrochemical performances of La0.67Mg0.33Ni2.5Co0.5 alloys was investigated in detail. The microstructures and morphology of alloys analyzed by XRD and optical microscopy and SEM and EDX showed that the as-cast La0.67Mg0.33Ni3.0 and La0.67Mg0.33Ni2.5Co0.5 alloys in different states had a multiphase structure which is composed of two major phases (La,Mg)2Ni7 and LaNi5 as well as a residual phase (La,Mg)Ni3. The partial substitution of Co for Ni dose not change the phase compositions, but the magnetic-heat treatment is helpful to a transformation of (La,Mg)Ni3 phase to (La,Mg)2Ni7 main phase, and enlarges the cell volumes of alloys. The electrochemical measurements showed that the La0.67Mg0.33Ni2.5Co0.5 alloys obtained by magnetic-heat treatment exhibited the best discharge capacity of 324.8 mAh/g with a good activation property and a large capacity retention of 83.07% after 50 charge–discharge cycles.

The effects of the step size and the cut-off limit of the residual liquid amount on the solidification simulation with Scheil model have been analyzed. A non-zero cut-off limit may terminate the solidification simulation with a larger simulation step size before a eutectic reaction is reached. Although a larger temperature step size can increase the simulation efficiency, it could significantly reduce the accuracy of the simulation modeling such as the amounts of solidified phases. Al–Mg–Zn ternary system is taken as an example to demonstrate the effects.

Two kinetic models (Jander model and Chou model) are used to investigate the hydrogen absorption kinetic mechanism of Zr-based AB2 type Laves phase alloys (Ti0.1Zr0.9Mn0.9V0.1Fe0.5Co0.5, Ti0.1Zr0.9(Mn0.9V0.1)1.1Fe0.5Ni0.5 and Ti0.1Zr0.9Mn0.9V0.1Fe0.55Ni0.55). The analysis shows that the rate-controlling step is the diffusion process at high temperatures in the range from 673 K to 923 K with a low hydrogen concentration (solid solution phase). Both models can well describe the experimental data but Chou model is preferred. Chou model is simpler and easier to use for analyzing the experimental results. The activation energies calculated using Chou model with the least square method are 29.3 kJ/mol H2 for Ti0.1Zr0.9Mn0.9V0.1Fe0.5Co0.5, 43.8 kJ/mol H2 for Ti0.1Zr0.9(Mn0.9V0.1)1.1Fe0.5Ni0.5 and 48.5 kJ/mol H2 for Ti0.1Zr0.9Mn0.9V0.1Fe0.55Ni0.55, which are close to the values reported in the literature (28.3 kJ/mol H2 for Ti0.1Zr0.9Mn0.9V0.1Fe0.5Co0.5 and 40.3 ± 1.5 kJ/mol H2 for both Ti0.1Zr0.9(Mn0.9V0.1)1.1Fe0.5Ni0.5 and Ti0.1Zr0.9Mn0.9V0.1Fe0.55Ni0.55).

Hydrogen diffusion in the solid solution is significant for the hydriding reaction kinetics of hydrogen storage materials. In this paper, Chou model was firstly used to investigate the kinetic mechanism of hydriding reaction in α phase (solid solution) region at the temperature ranging from 773 to 1073 K and the pressure range of 65–190 mbar for cubic Laves Ho1−xMmxCo2 (x = 0, 0.2 and 0.4, Mm = mischmetal) alloys. The results indicate that the hydrogen absorption kinetics in α phase region is controlled by hydrogen diffusion into the bulk. The activation energies calculated using Chou model with the least square method are in the range of 29.4–53.5 kJ/mol H2, which are close to the values reported in the original literature. Meanwhile, the characteristic absorption time can be used to characterize the reaction rate directly. In this way, influence of temperature, initial pressure and Mm concentration on the hydriding reaction kinetics was analyzed and discussed. It was found that the reaction rate can be accelerated with the increase of temperature, initial pressure and Mm concentration, and the diffusivity greatly depended on the Mm concentration.

•Doping La2O3 nanoparticles improved the corrosion resistance of SAMs in 0.2 M NaCl.•The compactness of silane film was enhanced by doping La2O3 nanoparticles.•La2O3 nanoparticles changed to be La compounds which covered on the cathode site.•PropS-SH/La2O3 composite film offered better long time protection to brass.Self-assembled monolayers (SAMs) of 3-mercaptopropyltrimethoxysilane (PropS-SH) modified with La2O3 nanoparticles were investigated to evaluate the doping effect of La2O3 nanoparticles on PropS-SH silane film towards brass corrosion protection in NaCl solution. The results indicated that SAMs of PropS-SH modified with La2O3 nanoparticles presented improved barrier properties because La2O3 nanoparticles filled the holes of silane film, which in turn improved the density of silane film, thus enhanced the barrier properties of silane-metal interface. Further, part of La2O3 nanoparticles was transformed to lanthanum oxide hydroxide (LaOOH) by hydrolysis reaction, and the formed La compounds covered the cathode sites, giving rise to a blocking effect.

Poor selectivity for gasoline products is a critical issue for the Fischer–Tropsch synthesis (FTS). Herein, we report that the introduction of a polyoxometalate Cs2.5H0.5PW12O40 (CsPW) into a conventional FTS catalyst (Co/Al2O3) can create a highly efficient bifunctional catalyst, leading to 118% increase in the selectivity of gasoline. Furthermore, it was found that such a significant improvement is due to the effective hydrocracking of heavier hydrocarbon products at CsPW sites.

A novel eutectic hydrogen storage system, LiBH4·NH3–nNH3BH3, which exists in a liquid state at room temperature, was synthesized through a simple mixing of LiBH4·NH3 and NH3BH3 (AB). In the temperature range of 90–110 °C, the eutectic system showed significantly improved dehydrogenation properties compared to the neat AB and LiBH4·NH3 alone. For example, in the case of the LiBH4·NH3/AB with a mole ratio of 1:3, over 8 wt.% hydrogen could be released at 90 °C within 4 h, while only 5 wt.% hydrogen released from the neat AB at the same conditions. Through a series of experiments it has been demonstrated that the hydrogen release of the new system is resulted from an interaction of AB and the NH3 group in the LiBH4·NH3, in which LiBH4 works as a carrier of ammonia and plays a crucial role in promoting the interaction between the NH3 group and AB. The enhanced dehydrogenation of LiBH4·NH3/AB may result from the polar liquid state reaction environments and the initially promoted formation of the diammoniate of diborane, which will facilitate the B–H⋯H–N interaction between LiBH4·NH3 and AB. Kinetics analysis revealed that the rate-controlling steps of the dehydrogenation process are three-dimensional diffusion of hydrogen at temperatures ranging from 90 to 110 °C.

Two new derivatives of ammonia borane (AB), 1,2/1,3-di-aminopropane borane (1,2/1,3-TMDAB), were prepared through the coordination reaction between 1,2/1,3-di-aminopropane and BH3–THF, which were then characterized by HR-XRD, FT-IR, 13C and 11B NMR. The crystal structure of 1,3-TMDAB was obtained with a combined technique of HR-XRD data and DFT calculations. 1,3-TMDAB crystallizes in the space group of P212121 (no. 19) with an orthorhombic crystal system and lattice constants of a = 12.6439(8) Å, b = 8.6289(3) Å, c = 7.2322(2) Å, and V = 789.05(3) Å3. Both samples, with a theoretical hydrogen content of 9.8 wt%, were shown to release pure H2 during thermal dehydrogenation, presenting great advantages over AB which releases large amounts of impurities (such as NH3, B2H6 or borazine). Moreover, 1,2/1,3-TMDAB did not foam and showed a faster dehydrogenation rate compared with AB. Our newly synthesized 1,2/1,3-TMDAB may serve as a superior alternative to AB for hydrogen storage and enrich the research field of B–N–H hydrogen storage materials.

In order to provide an efficient tool to explore alloy composition and processing conditions for Mg-based alloys with good hydriding/dehydriding (H/D) properties, investigation of the Mg–Ni–Nd–H quaternary system was carried out by experimental measurements and CALPHAD thermodynamic analysis combined with first-principles calculations. A new stable compound Nd16Mg96Ni12 with the space group of Cmc21 was identified in the Mg–Ni–Nd system by synchrotron powder X-ray diffraction (SR-PXRD). The phase equilibria and phase transformation related to Nd4Mg80Ni8, Nd16Mg96Ni12, NdMg5Ni and NdMg2Ni were studied by scanning electron microscopy (SEM), X-ray diffraction (XRD) and differential scanning calorimetry (DSC). The formation enthalpies of these ternary compounds were calculated by the density functional theory. The existence of the quaternary hydrides NdMgNi4H4 and NdMg2Ni9H12 was taken into consideration. Based on the obtained thermodynamic description of the Mg–Ni–Nd–H system, the hydrogen storage capacities and pressure–composition–temperature (P–C–T) curves were predicted and two new ternary compounds Nd4Mg80Ni8 and Nd16Mg96Ni12 were designed as hydrogen storage alloys with excellent properties. Meanwhile, the H/D mechanism of the Mg–Ni–Nd alloy was revealed.