Jianxin Zou

Mechanisms of reversible hydrogen storage in NaBH4 through NdF3 addition

In this work, a reversible hydrogen storage composite, 3NaBH4/NdF3, has been prepared using a mechanical milling method. The de-/rehydrogenation properties as well as the mechanisms of reversible hydrogen sorption in the composite were carefully investigated. Based on the pressure–temperature–composition measurements, the de-/rehydrogenation enthalpies of the 3NaBH4/NdF3 composite are determined to be 86.4 kJ mol−1 H2 and −13.2 kJ mol−1 H2, respectively. The onset dehydriding temperature of the composite is determined to be 413 °C in 0.1 MPa Ar atmosphere and can be as low as 80 °C under vacuum conditions. Analyses revealed that NdB6, Nd2H5 and NaF were formed after the decomposition of the composite, which can be hydrogenated to produce NaBH4 and NaNdF4. The formation of NaNdF4 instead of NdF3 in the hydrogenated products is believed to be responsible for the reduced hydrogen storage capacity, while the intermediate formation of B, Nd and NdB4 during dehydrogenation accounts for the asymmetric hydriding/dehydriding behaviors in the 3NaBH4/NdF3 composite.

NaBH4 in “Graphene Wrapper:” Significantly Enhanced Hydrogen Storage Capacity and Regenerability through Nanoencapsulation

A new high-capacity reversible hydrogen-storage material synthesized by the encapsulation of NaBH4 nanoparticles in graphene is reported. This approach effectively prevents phase agglomeration or separation during successive H2 discharge/recharge processes and enables rapid H2 uptake and release in NaBH4 under mild conditions. The strategy advanced here paves a new way for application in energy generation and storage.

Synthesis of Y2O3 particle enhanced Ni/TiC composite on TC4 Ti alloy by laser cladding

Abstract A Y 2 O 3 particle enhanced Ni/TiC composite coating was fabricated in-situ on a TC4 Ti alloy by laser surface cladding. The phase component, microstructure, composition distribution and properties of the composite layer were investigated. The composite layer has graded microstructures and compositions, due to the fast melting followed by rapid solidification and cooling during laser cladding. The TiC powders are completely dissolved into the melted layer during melting and segregated as fine dendrites when solidified. The size of TiC dendrites decreases with increasing depth. Y 2 O 3 fine particles distribute in the whole clad layer. The Y 2 O 3 particle enhanced Ni/TiC composite layer has a quite uniform hardness along depth with a maximum value of HV1380, which is 4 times higher than the initial hardness. The wear resistance of the Ti alloy is significantly improved after laser cladding due to the high hardness of the composite coating.

Study on hydrogen storage properties of Mg–X (X = Fe, Co, V) nano-composites co-precipitated from solution

A systematic investigation has been performed on the hydrogen sorption properties of the Mg–X (X = Fe, Co, V) nano-composites co-precipitated from solution through an adapted Rieke method. It is found that the co-precipitated Fe, V or Co has high catalytic efficiency in enhancing the hydrogen sorption kinetics of nano-sized Mg. The Mg–V nano-composite shows faster hydrogen absorption kinetics than the Mg–Fe and Mg–Co nano-composites at lower temperatures. For instance, the hydrogen capacity within 2 h at 50 °C is 4.4 wt% for the Mg–V nano-composite, while for the Mg–Fe nano-composite it is 2.6 wt% and for the Mg–Co nano-composite it is 3.9 wt%. However, the hydrogenated Mg–Fe and Mg–Co nano-composites display significantly lower hydrogen desorption temperatures compared with the hydrogenated Mg–V nano-composite. The hydrogen desorption activation energies of the hydrogenated Mg–Fe and Mg–Co nano-composites are 118.1 and 110.1 kJ mol−1 H2, much lower than that of the Mg–V nano-composite (147.7 kJ mol−1 H2). High catalytic effectiveness of the co-precipitated Fe, Co or V depends not only on its intrinsic activity, but also on its distribution state, which may be entirely different from previous composites prepared through physical routes.

Preparation of LaMgNi4-xCox alloys and hydrogen storage properties

Abstract The LaMgNi 4- x Co x ( x =0, 0.3, 0.5) compounds were prepared by the method of levitation melting and a subsequent heat treatment at 1073 K for 10 h. XRD analysis shows that the obtained LaMgNi 4- x Co x alloys consist of a single phase with the structure of cubic SnMgCu 4 (AuBe 5 type). The hydrogen absorption/desorption properties of LaMgNi 4 were investigated by PCI measurement at various temperatures ( T =373, 398, 423 K) and the results show that the maximum absorbed hydrogen capacity reaches 1.45% (5.79H/M) under a hydrogen pressure of 4.3 MPa at 373 K. The XRD patterns during absorbing procedure at 373 K indicate the phase structure changing from cubic ( α -LaMgNi 4 ) to orthorhombic ( β -LaMgNi 4 H 3.41 ) and after hydrogenation finally back to cubic ( γ -LaMgNi 4 H 4.87 ), and a partial desorption was also observed under this condition. With increasing temperature, a slight decrease of the absorbed hydrogen content was observed and the number of plateaus reduces from two to one, but the hydrogen absorption kinetics improves. The electrochemical properties of the LaMgNi 4- x Co x were measured by simulated battery test, which shows that the discharge capacity of the alloys significantly improves with the increase of Co content.

Reversible hydrogen sorption in NaBH4 at lower temperatures

In the present study, a new hydrogen storage system, being able to reversibly absorb/desorb hydrogen at fairly low temperatures, was developed based on a 3NaBH4–PrF3 composite. It is shown that 3 wt% of reversible hydrogen sorption can be achieved in the 3NaBH4–PrF3 composite at 400 °C with fast kinetics. After the addition of 5 mol% VF3, the dehydrogenation kinetics of the 3NaBH4–PrF3 composite can be significantly improved. The onset dehydriding temperature is lowered down to 46 °C in vacuum, and the dehydrogenation finishes in 2 min at 400 °C. Both the dehydrogenation enthalpy and activation energy of 3NaBH4–PrF3 can be lowered down through the addition of VF3. In particular, the dehydrogenation products of the 3NaBH4–PrF3–5 mol% VF3 composite can be rehydrogenated at a temperature as low as 48 °C with the regeneration of NaBH4. At 84 °C, a reversible hydrogen sorption of about 1.2 wt% can be achieved in the 3NaBH4–PrF3–5 mol% VF3 composite. The improvement in hydrogen sorption properties can be mainly attributed to the formation of the VB2 phase during dehydrogenation as an efficient catalyst, which maintains well its catalytic effect in the re-/dehydrogenation cycles. Based on a series of controlled experiments and phase analyses, the de-/rehydrogenation mechanisms of the 3NaBH4–PrF3 composite without and with VF3 addition are proposed and discussed in detail.

Effects of La fluoride and La hydride on the reversible hydrogen sorption behaviors of NaBH4: a comparative study

In the present work, two new reversible hydrogen storage composites, NaBH4 + LaF3 and NaBH4 + LaH2, have been prepared through a mechanical milling method with the aim of comparatively studying the effects of La fluoride and La hydride on the hydrogen sorption behaviors of NaBH4. Experimental investigations have shown that both La fluoride and La hydride enable reversible hydrogen sorption in NaBH4. In particular, LaF3 exhibits a superior promoting effect than LaH2, which agrees well with theoretical predictions. Surprisingly, better hydrogen sorption properties can be achieved in both systems through undergoing de-/rehydriding cycles. The reversible hydrogen storage capacity reaches up to 3.0 wt% at 238 °C and 2.9 wt% at 326 °C in NaBH4 + LaF3 and NaBH4 + LaH2 systems after the 6th dehydrogenation, respectively. In both cases, the formation of La boride plays the major role in the reversible hydrogen sorption in NaBH4. The superior promoting effect of La fluoride than La hydride upon modifications of thermodynamics and kinetics of NaBH4 should be ascribed to the following factors: (i) the formation of a thermodynamically more stable compound NaF instead of NaH reduces the overall enthalpy changes of re/de-hydriding reactions in NaBH4 + LaF3 to −31.8 kJ mol−1 H2 and 72.5 kJ mol−1 H2, respectively; (ii) the ion exchange of F− for H− leads to the reduction of the onset dehydrogenation temperature of NaBH4 to 160 °C in the NaBH4 + LaF3 composite; (iii) the F− anion favors the formation of LaB6 while H− favors the formation of LaB4. The role of functional anions and cations, de-/rehydrogenation mechanisms and nucleation modes in the two reversible hydrogen storage composites have been proposed based on experimental and theoretical analyses. The comparison study carried out in this work helps to design and search for new metal borohydride based composites for reversible hydrogen storage.

Effects of LnF3 on reversible and cyclic hydrogen sorption behaviors in NaBH4: electronic nature of Ln versus crystallographic factors

In the present work, hydrogen sorption behaviors of some of the 3NaBH4–LnF3 (Ln = Ce, Sm, Gd and Yb) composites were investigated and the mechanisms associated with different effects of LnF3 (Ln = La, Ce, Pr, Nd, Sm, Gd, Ho, Er and Yb) on reversible hydrogen sorption in NaBH4 were proposed based on careful comparisons. The key factors controlling the properties of 3NaBH4–LnF3 can be summarized as follows: (i) electronegativity χp of Ln3+ determines the thermodynamic stability of 3NaBH4–LnF3 composites with their χp in the range of 1.23–1.54 being suitable for reversible hydrogen storage; (ii) the electronic configuration of Ln3+ influences rehydrogenation behaviors: more stable the oxidation state of the Ln3+ is, the better is the rehydrogenation performance of NaBH4; (iii) the unique crystal structure of the Ln–B phase formed during dehydrogenation, and geometrical configuration of B in Ln–B, provide dangling bonds for hydrogen atoms to embed in, consequently modifying the rehydrogenation kinetics. Because Gd3+ possesses a combination of suitable electronegativity, stable oxidation state and favorable geometric structure in GdB4, the 3NaBH4–GdF3 composite exhibits the best overall hydrogen storage properties among all the studied 3NaBH4–LnF3 composites, with high cycling stability up to 51 cycles along with fast kinetics. This understanding provides us with criterions to design new borohydride-based hydrogen storage systems and to optimize their hydrogen storage properties.

The Hot Workability of SiCp/2024 Al Composite by Stir Casting

The hot workability of SiCp/2024 Al composite was explored by conducting hot compression simulation experiments on Gleeble-3500 under temperatures of 300–500 °C and strain rates of 10−3–1 s−1. Constitutive equation was developed through hyperbolic sine function, and the activation energy was calculated to be 151 kJ mol−1. The hot processing maps referring to dynamic material model were drawn in a true strain range from −0.2 to −0.8. At the strain of −0.8, the recommended regions in processing map contained two domains: superplastic domain (500 °C, 10−3 s−1) with an efficiency of about 0.72 and DRX domain (500°C, 1 s−1) with an efficiency of about 0.45. Together with macrostructure and microstructure observations, it was suggested to remove the DRX region.

Hydrogen storage properties of Mg–TiO2 composite powder prepared by arc plasma method

Abstract Mg-based Mg–TiO2 composite powder was prepared by arc plasma evaporation of the Mg+5%TiO2 mixture followed by passivation in air. ICP, XRD and SEM techniques were used to characterize the composition, phase components and microstructure of the composite powder. The hydrogen sorption properties of the composite powder were investigated by DSC and PCT techniques. According to the data from PCT measurements, the hydrogenation enthalpy and entropy changes of the composite powder are calculated to be −71.5 kJ/mol and −130.1 J/(K·mol), respectively. Besides, the hydrogenation activation energy is determined to be 77.2 kJ/mol. The results indicate that TiO2 added into Mg by arc plasma method can act as a catalyst to improve the hydrogen sorption kinetic properties of Mg.