Mg2Ni Alloy Research Articles

A First-Principles Study of the Structural, Elastic, and Mechanical Characteristics of Mg2Ni Subjected to Pressure Conditions

This study employs first-principles calculations to examine structural, elastic, and mechanistic relationships of Mg2Ni alloys under varying conditions of pressure. The investigation encompasses Young’s modulus, bulk modulus, shear modulus, Poisson’s ratio, and anisotropy index, as well as sound velocity, Debye temperature, and related properties. Our findings indicate that the lattice parameters of Mg2Ni in its ground state are in agreement with values obtained experimentally and from the literature, confirming the reliability of the calculated results. Furthermore, a gradual decrease in the values of the lattice parameters a/a0 and c/c0 is observed with increasing pressure. Specifically, the values for C13 and C33 decrease at a hydrostatic pressure of 5 GPa, while C11 and C13 increase when the external hydrostatic pressure exceeds 5 GPa. All other elastic constants exhibit a consistent increasing trend with increasing pressure between 0 and 30 GPa, with C11 and C12 increasing at a faster rate than C44 and C66. In the 0–30 GPa pressure range, Mg2Ni satisfies the mechanical stability criterion, indicating its stable existence under these conditions. Additionally, the Poisson’s ratio of Mg2Ni consistently exceeds 0.26 over a range of pressures from 0 to 30 GPa, signifying ductility and demonstrating consistency with the value of B/G. The hardness of Mg2Ni increases within the pressure range of 0–5 GPa, but decreases above 5 GPa. Notably, the shear anisotropy of Mg2Ni exhibits greater significance than the compressive anisotropy, with its anisotropy intensifying under higher pressures. Both the sound anisotropy and the Debye temperature of Mg2Ni demonstrate an increasing trend with rising pressure.

All-Solid-State Infrared Electrochromic Devices Based on Thin Metal Films.

Infrared electrochromic devices (IR-ECDs) are pivotal for dynamic thermal regulation. However, the quest for all-solid-state IR-ECDs with high stability and a broadly tunable range of emissivity remains a challenge. This study presents the development of an all-solid-state infrared electrochromic device (IR-ECD) with the structure of ITO/HxWO3/Ta2O5/Pd/Mg3Ni based on the hydrogen-induced metal-insulator transition of Mg-Ni alloy films. The emissivity modulation is improved by film stack optimization, with changes of 0.32 and 0.47 in the 3-5 and 7.5-14 μm bands, respectively. The introduction of an ultrathin Ti isolation layer between the catalytic and electrolyte layers enhances the cyclic stability. Our findings offer a novel strategy for the design and fabrication of all-solid-state IR electrochromic devices and highlight the potential of Mg-Ni alloy-based all-solid-state IR-ECDs in advanced energy and information fields.

Experimental and numerical study of temperature evolution and hydrogen desorption process on an amorphous alloy Mg50Ni50

In the present study, we explored the temperature evolution and hydrogen desorption properties of the Mg50Ni50 alloy through both numerical simulation and experimental analyses. Desorption kinetics characterization was carried out using the volumetric method, specifically employing a Sievert's-type apparatus to investigate solid-gas reactions. The experiments covered a temperature range from 313 K to 353 K, with an initial hydrogen pressure of 12 bar. Simultaneously, a mathematical approach was employed to numerically investigate the temperature evolution within the hydride bed. Using COMSOL Multiphysics as a simulator, a numerical simulation was conducted based on experimental data. The study examined the impact of cooling temperature on hydride temperature evolution. Results revealed that hydrogen desorption kinetics of the amorphous Mg50Ni50 alloy are more significant compared to those of Mg2Ni compounds. Moreover, the effect of the warming temperature on the equilibrium pressure can also be observed in the hydrogen desorption isotherm curves. The experimental study of the Mg50Ni50 alloy provided activation energy data, along with determination of hydride formation enthalpy and entropy. On the other hand, we showed that the hydride temperature is maximum at the hydride-hydrogen interface within the hydride center.

The study of La and Mg elements on the improved structure and hydrogen storage performance of Ca2MgNi9 alloy

In order to improve the comprehensive hydrogen storage performance of AB3-type (RE/Ca)-Mg-Ni alloys, a new series of Ca(Ca0.75La0.25)2-xMgxNi9 (x = 0.8, 0.9, 1.0, 1.1, 1.2) alloys is designed and prepared. Based on the as-cast Ca2MgNi9 alloy, La is introduced, and the ratio of rare earth (RE) to Mg is adjusted using the induction melting method. This alteration modifies the microstructure of the alloy and significantly enhances its hydrogen storage performance. The effects of microstructure on hydrogen storage performance and mechanism are analyzed. The phase composition and lattice parameters of the main phase are regularly regulated by appropriate element substitution. The lattice parameter of the main phase is increased, the capacity and kinetics of hydrogen storage are significantly improved. The initial hydrogen absorption capacity of the alloy increases from 1.744 wt% for Ca2MgNi9 to 1.975 wt% for Ca(Ca0.75La0.25)1.2Mg0.8Ni9 alloy. Furthermore, the synergistic regulation of La and Mg elements can increase the hydrogen desorption ratio and crystal structure stability of the alloy. This leads to the concurrent enhancement of effective hydrogen storage and cycle performance of the Ca2MgNi9 hydrogen storage alloy. The retention rate of hydrogen absorption capacity for the 50th cycle is increased from 77.13% for Ca2MgNi9 to 84.26% for Ca(Ca0.75La0.25)0.8Mg1.2Ni9. At the same time, owing to the adjustment of the cell volume and phase composition, the platform pressures of hydrogen absorption and desorption of the alloy have also experienced a multi-fold increase between 0.002 and 0.5 MPa at 303 K. This enhancement is advantageous for expanding the potential applications of this type of alloy. This work presents new ideas for enhancing the hydrogen storage performance of Ca2MgNi9 hydrogen storage alloys.

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

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

EFFECT OF Sc ON THE HYDROGEN-STORAGE PERFORMANCE OF Mg2Ni: A FIRST-PRINCIPLES STUDY

The effect of metal scandium (Sc) on the hydrogen-storage properties of the magnesium-nickel (Mg2Ni) alloy has been explored using the ultrasoft pseudopotential approach, rooted in the principles of Density Functional Theory (DFT). The binding energy, lattice constant, enthalpy of formation, standard enthalpy of reaction, charge density, density of states and bond order for the Mg2-xScxNi (x = 0, 0.25, 0.5, 1) alloys and their hydrides were calculated. Furthermore, the analysis of the atomic bonding and the structural stability of Mg2-xScxNi and hydrides were also facilitated. The results show that the preference site of the Sc atom in Mg2-xScxNi (x = 0, 0.25, 0.5, 1) alloys is Mg (6i) under the condition of a Sc doping concentration of 0.25. This causes a decrease in the stability of the Mg1.75Sc0.25Ni alloy. Moreover, the addition of Sc to Mg2-xScxNiH4 weakens the interaction of H-Ni and H-Mg, thereby facilitating the hydrogen-release reaction and effectively enhancing the hydrogen-release capability of Mg2-xScxNiH4.

Wettability, reactivity, and interface structure in Mg/Ni system

The sessile drop method was applied to the experimental investigation of the wetting and spreading behaviors of liquid Mg drops on pure Ni substrates. For comparison, the experiments were performed in two variants: (1) using the Capillary Purification (CP) procedure, which allows the non-contact heating and squeezing of a pure oxide-free Mg drop; (2) by classical Contact Heating (CH) procedure. The high-temperature tests were performed under isothermal conditions (CP: 760 °C for 30 s; CH: 715 °C for 300 s) using Ar + 5 wt% H2 atmosphere. During the sessile drop tests, images of the Mg/Ni couples were recorded by CCD cameras (57 fps), which were then applied to calculate the contact angles of metal/substrate couples. Scanning and transmission electron microscopy analyses, both coupled with energy-dispersive X-ray spectroscopy, were used for detailed structural characterization of the solidified couples.It was found that an oxide-free Mg drop obtained by the CP procedure showed a wetting phenomenon on the Ni substrate (an average contact angle θ < 90° in < 1 s), followed by fast spreading and good wetting over the Ni substrate (θ(CP) ∼ 20° in 5 s) to form a final contact angle of θf(CP) ∼ 18°. In contrast, a different wetting behavior was observed for the CH procedure, where the unavoidable primary oxide film on the Mg surface blocked the spreading of liquid Mg showing apparently non-wetting behavior after 300 s contact at the test temperature.However, in both cases, the deep craters formed in the Ni substrates under the Mg drops and significant change in the structure of initially pure Mg drops to Mg-Ni alloys suggest a strong dissolution of Ni in liquid Mg and apparent values of the final contact angles measured for the Mg/Ni system.

Liquid-solid phase separation and recycling of permalloys in liquid Mg

Liquid-solid phase separation of permalloy in liquid Mg results in selectively dissolved Ni, which provides a unique opportunity for the design of immiscible heterogeneous composite materials and the comprehensive metal recycling of permalloy scraps. A guideline of the alloy design for the liquid-solid phase separation system was proposed. The effects of immersion temperature and time on the Ni extraction were studied by an experimental method. The diffusion behavior of Ni from the permalloy to liquid Mg and the microstructure evolution in the permalloy during the liquid-solid phase separation were discussed. The results show that the Ni in the permalloy was quickly extracted into the liquid Mg and formed an Mg-Ni alloy, while the other components such as Fe, Co, and Mn were held back in the phase-separated permalloy. The phase-separated permalloy with the solidified Mg exhibits a three-dimensional (3D) Fe/Mg bicontinuous composite structure. Furthermore, simple treatments were carried out for the reaction products such as the Fe/Mg bicontinuous composite and the Mg-Ni alloy, and the recycling strategies for functionalization of these treated reaction products were provided. A 3D porous Fe-based alloy with electromagnetic interference (EMI) shielding efficiency of 52 dB can be obtained if Mg is removed from the Fe/Mg bicontinuous composite. Instead of the complete separation of pure Ni from the recycled Mg-Ni alloy by vacuum distilling, the Mg-Ni alloy can be enriched into Mg2Ni as an initial hydrogen storage material.

Effects of Cu on the microstructure and hydrogen storage properties of Mg-20Ni alloy

In order to improve the hydrogen storage capacity of hypereutectic Mg-Ni alloy, the Mg40Ni10 and Mg40Ni8Cu2 alloys were prepared by metallurgy method. The effects of Cu on the alloys’ phase composition, microstructure were studied systematically. The volumetric Sieverts’ method was used to test and analyze the activation performance and hydrogen absorption and desorption kinetic performance of the alloys. It was found that the partial substation of Ni in the Mg2Ni-riched matrix alloy with Cu can change the primary Mg2Ni and eutectic Mg-Mg2Ni morphology of the alloy. With the doping of Cu content, although the activation property of the alloy decreases, the hydrogen storage capacity as well as the kinetic of hydrogen absorption and desorption are improved significantly.

Hydrogen generation by hydrolysis of ultrafine microstructure Mg[sbnd]10Ni alloy wire

This work presents a MgNi alloy wire prepared by a combination of extrusion and multi-pass hot drawing for fast hydrogen generation from aqueous NaCl solution. The results showed that the hydrogen generation rates of the wire were significantly improved compared to the as-cast alloy. The hydrolysis of the MgNi alloy wire produced 820 ml g−1 hydrogen in 16 min and the maximum hydrogen generation rates reached 67.86 ml g−1 min−1 in 3.5 % NaCl solution and at 25 °C. The improved hydrogen production properties can be attributed to the increase in specific surface area and the ultrafine microstructure with highly dispersed submicron Mg2Ni particles of the MgNi alloy wire.

High energy ball milling composite modification of Mg2Ni hydrogen storage alloy by graphene and MWCNTs

This study focuses on the preparation of a Mg2Ni hydrogen storage alloy through high-energy ball milling, further enhanced by composite graphene and multi-walled carbon nanotubes (MWCNTs) modification. It is evident that high-energy ball milling successfully incorporates graphene and MWCNTs onto the surface of Mg2Ni particles. This process not only creates surface defects but also establishes hydrogen pathways, facilitating the absorption and desorption of hydrogen. This improvement enhances the performance of hydrogen storage. With an increase in the composite quantity of graphene and MWCNTs, a more noticeable lubrication and grinding aid effect become evident during the ball milling process. This effect promotes more efficient grain refinement and minimizes agglomeration and welding phenomena. A comparative analysis with the Mg2Ni alloy reveals that the activation duration for the composite hydrogen storage alloy material significantly decreases. Concurrently, the kinetic performance sees substantial enhancement, and the temperature needed for hydrogen absorption and discharge is correspondingly reduced.

In-situ precipitation of ultrafine Mg2Ni particles in Mg-Ni-Ag metal fibers and their hydrogen storage properties

The intermetallic compound Mg2Ni shows improved hydrogen de-/absorption kinetics and a lower desorption temperature compared to pure Mg. However, the coarse Mg2Ni phase and its limited hydrogenation capacity restrict the application of the Mg2Ni alloy. In this study, an attempt was made to prepare Mg-Ni alloy fibers with a higher Mg content and a well-distributed Mg2Ni catalytic phase using the melt extraction (ME) method, and a unique metallic glass fiber was formed. With pre-annealing at 350 °C in a vacuum, uniformly dispersed Mg2Ni nanoparticles are in-situ formed, the phase transition is revealed to be metallic glass → Mg6Ni → Mg2Ni + Mg. About 1.5 wt% of hydrogen can be absorbed by the Mg-Ni fibers at 50 °C, and it is completely released in 8.8 min at 225 °C. Both the JMA and Kissinger models were utilized to accurately characterize the dehydrogenation activation energy, and the values of 90.4 and 95.8 kJ/mol were obtained, respectively. The hydrogen desorption process involves two distinct processes, the decomposition of Mg2NiH4 nanoparticles and MgH2 hydride in sequence, with dehydrogenation enthalpy changes of 64.5 and 78.2 kJ/mol, respectively. After hydrogen absorption and desorption cycles, a loose structure forms around the Mg2Ni nanoparticles. This structure serves as an efficient nucleation site for hydrides and provides diffusion paths for H atoms.

Corrosion behavior of Zn in electrolyte during the charge and discharge process and its influence on the electrochemical performance of zinc doped Mg2Ni1-xZnx rapidly quenched alloys

In the electrochemical process, a continuous passivation layer of Mg(OH)2 is formed on the surface of Mg2Ni alloy particles and prevents the penetration of hydrogen atoms, which have a negative impact on the discharge capacity. In this work, Mg2Ni1-xZnx (x = 0, 0.17, or 0.33) rapid quenching alloys were prepared by partially replacing Ni with Zn in order to modify the surface of the alloy with the corrosiveness of Zn in alkaline solution. The microstructure results indicate that Zn doping promotes the corrosion of Mg2Ni alloy in the electrolyte, and many corrosion holes are formed on the surface after the electrochemical process. With the increase of Zn, the charge-transfer reaction resistance (Rct) and polarization resistance (Rp) of the alloy electrode increase from 306.24 and 366.41 mΩ to 508.76 and 526.57 mΩ, respectively, and the corrosion current density (Io) decreases from 70.08 to 48.77 mA/g. The appropriate amount of Zn atoms increases the discharge capacity, and the highest value can reach 92.94 mAh/g at x = 0.33. This reveals that corrosion holes are formed on the surface of Zn-doped alloys during the electrochemical process and destroy the continuity of the passivation layer on the Mg2Ni surface, which facilitate the penetration of hydrogen atoms.

Microstructure and properties study of Mg2-xYxNi0.9Co0.1 (x = 0, 0.1, 0.2, 0.3) hydrogen storage alloys

To enhance the hydrogen storage performance of Mg-Ni system alloys, multi-elemental alloys incorporating Y element, namely Mg2-xYxNi0.9Co0.1 (x = 0, 0.1, 0.2, 0.3), were synthesized through ball milling and sintering. The microstructures of Mg2-xYxNi0.9Co0.1 (x = 0, 0.1, 0.2, 0.3) alloys were characterized using XRD and SEM/EDS techniques, and the hydrogen storage properties of Mg2Ni0.9Co0.1 and Mg1.7Y0.3Ni0.9Co0.1 alloys were evaluated via the Sieverts method. At a sintering temperature of 500 °C, the Y element existed in the form of Y/Y2O3 phases and displayed no reactivity with other alloy constituents. The addition of Y enhanced the activation performance of Mg-Ni system alloys, because it takes 2 times for Mg1.7Y0.3Ni0.9Co0.1 alloy to complete activation, while Mg2Ni0.9Co0.1 needs 3, albeit causing a slight reduction from 3.6 wt% to 3.2 wt% in the hydrogen storage capacity when Y replaced Mg. The enthalpy of hydrogen desorption of Mg1.7Y0.3Ni0.9Co0.1 alloy was 57.4 kJ mol−1 H2, which was significantly lower than that of Mg2Ni0.9Co0.1 (68.0 kJ mol−1 H2) and Mg2Ni alloy (64.4 kJ mol−1 H2), indicating improved thermodynamic properties. Moreover, the apparent activation energy of Mg2Ni0.9Co0.1 (71.48 kJ mol−1 H2) was lower than that of Mg1.7Y0.3Ni0.9Co0.1 (83.62 kJ mol−1 H2), implying that the addition of Y reduced the kinetic properties.

Effect of interlayer and deposition temperature on the hydrogen storage properties of amorphous Mg-based thin films

In this work, the effect of different interlayers (including Mo, Nb, and Ti) and deposition temperatures (including 25 °C, 75 °C, 150 °C and 200 °C) on the hydrogen storage performance of MgNi amorphous alloy films are studied. On the one hand, the MgNi amorphous alloy films remain undestroyed after hydrogen absorption and desorption cycles with the help of Mo, Nb and Ti interlayers. However, the onset desorption temperature and peak desorption temperature of the MgNi amorphous alloy films are almost unchanged after inserting the interlayers. On the other hand, as the deposition temperature increases from 25 °C to 200 °C, there are nanocrystalline Mg2Ni and Mg phases formed in the amorphous MgNi alloy matrix. The crystalline-amorphous structure provides abundant nucleation sites for hydride formation, and accelerate the diffusion and dissociation of hydrogen.

Highly reactive hydrogen storage Mg2Ni alloy prepared by mechanochemistry and H-cycling

Hydrogen in a solid form is a promising energy carrier for clean energy applications. Therefore, solid-state hydrogen storage technologies using nanostructured materials is an important field of study. High gravimetric capacity and low cost make Magnesium (Mg)-based alloys exclusive hydrogen storage materials, especially in stationary or electrochemical applications. Mg2Ni has been extensively studied because of its relatively low enthalpy of formation. For the Mg2Ni alloy, fast hydrogen absorption kinetics at temperatures ≤300 °C are usually obtained through complex routes, such as hydriding combustion synthesis or production of nanoparticles. In this study, we obtained Mg2NiH4 hydrides by reactive milling, annealing heat treatments and previous hydrogen absorption cycles at 350 °C. Through this process route, we obtained highly reactive hydrogen storage Mg2Ni alloy, able to absorb and desorb hydrogen at temperatures ≤300 °C, with desorption kinetics similar to those of alloys obtained by nanoparticle production or hydriding combustion synthesis and even better optimized absorption capacities. For example, a storage Mg2Ni sample obtained by one of the routes investigated here, showed hydrogen absorption capacity of 3.0 wt% at 250 °C, with very fast kinects, because the first 2.5 wt% was absorbed in less than 50 s.

Preparation of Mg2Ni Hydrogen Storage Alloy Materials with Mg-Coated Structure by Mechanical Alloying

In this paper, a hydrogen storage alloy material with good hydrogen storage performance, high preparation efficiency and a partially amorphous magnesium-coated Mg2Ni structure was prepared by high-energy ball milling mechanical alloying. The effects of different Mg and Ni mass ratios and ball milling speed on their synthesis were investigated. The results show that compared with the Mg2Ni alloy, the thermodynamic and kinetic properties of the hydrogen storage alloy material change less, but the hydrogen storage capacity increases significantly. In the case of different Mg and Ni mass ratios, the formation time of Mg2Ni alloys is not much different, the obtained particle sizes are all about 5 μm, and the hydrogen storage capacity increases with the increase of mass ratio. However, the formation of Mg2Ni alloy varies greatly at different rotational speeds. At low rotational speed, the formation of Mg2Ni alloy is incomplete or not, and the rotational speed for complete formation of Mg2Ni alloy is 1000/1100 rpm. Through SEM and XRD analysis, it is found that the particle size of the alloy after ball milling is small, and the alloy composition is uniform, which is one of the reasons for the better hydrogen storage performance of the alloy. And it can be seen that the alloy with extremely high phase purity can be obtained by ball milling for 5 h. Through TEM, Mapping and PCT curves combined with XRD analysis, it is found that the particles after ball milling have a structure of partially amorphous Mg-coated Mg2Ni alloy, and the hydrogen storage capacity of the alloy reaches 5 wt%. This is another reason for the two-stage plateau pressure and better hydrogen storage performance. Therefore, the Mg2Ni alloy obtained by the high-energy ball milling mechanical alloying method in this paper has a 90% increase in efficiency compared with the traditional mechanical alloying method; and compared with the melting method, the hydrogen storage performance is also improved.

A novel method towards improving the hydrogen storage properties of hypoeutectic Mg-Ni alloy via ultrasonic treatment

Ultrasonic treatment has great contributions on modifying the morphology, dimension and distribution of constituent phases during solidification, which serve as dominate factors influencing the hydrogen storage performance of Mg-based alloys. In this research, ultrasonic treatment is utilized as a novel method to enhance the de-/hydriding properties of Mg-2Ni (at.%) alloy. Due to ultrasonic treatment, the microstructure of as-cast alloy is significantly refined and homogenized. Ascribing to the increased eutectic boundaries and shortened distance inside α-Mg for hydrogen atoms diffusion, the hydrogen uptake capacities and isothermal de-/hydriding rates improve effectively, especially at lower temperature. The peak desorption temperature reduces from 392.99 °C to 345.56 °C, and the dehydriding activation energy decreases from 101.93 kJ mol−1 to 88.65 kJ mol−1. Weakened hysteresis of plateau pressures and slightly optimized thermodynamics are determined from the pressure-composition isotherms. Owing to the refined primary Mg, a larger amount of hydrogen with the higher hydriding proportion is absorbed in the first stage when hydrides nucleate in eutectic region and grow on primary Mg periphery subsequently before MgH2 colonies impinging, resulting in the enhancement of hydrogenation rates and capacities.

Theoretical and experimental study of the titanium substituted Mg2-xTixNi alloys and Mg2-xTixNiH4 hydrides

The formation of the Ti substituted Mg2Ni alloys, a promising hydrogen storage material for various applications is studied in detail. Mg1.95Ti0.05Ni alloy and ribbons are successfully prepared by vacuum arc melting and melt spinning methods. The phases, microstructures, and thermal behavior of the alloys and ribbons are characterized by XRD, SEM, TEM, DTA/TG. Sievert-type apparatus is used to study hydrogen sorption properties. Apart from the dominant Mg2Ni phase, the formation of MgNi2, Mg, and Ni3Ti phases is seen in both Mg1·95Ti0·05Ni alloy and ribbons. During the initial three cycles, Mg1·95Ti0·05Ni ribbons showed 2 wt % hydrogen storage capacity. To explain the atomic-scale influence of Ti dopant in the studied alloys and hydrides, FP(L)APW + lo method based on Density Functional Theory (DFT) is applied to Mg2-xTixNi (x = 0.25 and 0.5) alloys and Mg2-xTixNiH4 (x = 0.25 and 0.5) hydrides. An increase in the Ti dopant on the Mg site leads to the hydrides destabilization. Bader's charge density topology analysis provides insight into the charge transfer and bonding between the constituent atoms.

Hydrogen storage behaviour of Cr- and Mn-doped Mg2Ni alloys fabricated via high-energy ball milling

This paper describes the efficient preparation of an Mg2Ni alloy for hydrogen storage via high-energy ball milling mechanical alloying for 2 h. The degree of alloy amorphisation increases with increasing ball-milling time. Ball milling for 4 h affords partially amorphous alloys exhibiting the best hydrogen storage performance. Partial substitution of Ni with Cr and Mn improves the hydrogen absorption/desorption thermodynamics, kinetics and cycling performance of the alloy. Specifically, partial Mn substitution improves the cycling performance and reduces the activation energy of the hydrogen desorption reaction, effectively improving the hydrogen desorption kinetic performance. Mg2Ni0.8Mn0.2 shows the best cycling and hydrogen absorption/desorption kinetic performances. Partial Cr substitution reduces the entropy and enthalpy changes of the hydrogen absorption/desorption reaction and effectively reduces the temperature of the initial hydrogen absorption/desorption reaction. In particular, Mg2Ni0.9Cr0.1 shows the best thermodynamic performance.