Effect of composition on the reactivity of Al-rich alloys with water

Fe-bearing Al–Ga–In–Sn alloys were prepared by using arc melting under high purity argon atmosphere. Their microstructures were investigated by means of XRD, SEM/EDX, and the eutectic reaction of Al with grain boundary phase Ga–In–Sn (GIS) was measured using DSC. Fe dendrites were found to present on columnar Al grain surfaces. As the amount of low melting point metals (Ga, In and Sn) is 6 wt.% with a ratio of In:Sn of 15:7, these alloys just consist of Al(Ga) and In₃Sn two phases. InSn₄ was found in an alloy as its weight ratio of In:Sn approaches 1:1 with an extra addition of Sn (1 wt.%). The reactions of Al alloys with water were performed at different water temperatures ranging from 0.5 to 50 °C. Al reacted with water at a lower water temperature of 0.5 °C, but the reaction suspended within tens of minutes. Once water was heated to a higher temperature of about 15 °C, Al reacted with water again. The H₂ generation rates measured at a water temperature of 50 °C depend on the compositions of alloys. Reasons concerning the reactivity of Al–water at different temperatures are discussed.     

Microstructure and hydrogen storage properties of V48Fe12Ti15-xCr25Alx (x=0, 1) alloys

The microstructure and hydrogen storage characteristics of V₄₈Fe₁₂Ti_15-xCr₂₅Al_x (x = 0, 1) alloys prepared by vacuum arc melting were studied by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and pressure–composition isotherm measurements. It was confirmed that all of the alloys comprise a BCC phase, a Ti-rich phase, and a TiFe phase. Al as a substitute for part of the Ti content caused an increase of lattice parameters of the BCC phase and of the equilibrium pressures of hydrogen desorption, but decrease of the hydrogen storage capacities. The kinetic mechanism of the hydrogenation and dehydrogenation of the alloys was investigated by the classical Johnson–Mehl–Avrami equation. The reaction enthalpies (ΔH) for the dehydrogenation of alloys without and with Al were calculated by the Van't Hoff equation based on the PCI measurement data, which are 30.12 ± 0.14 kJ/mol and 28.02 ± 0.46 kJ/mol, respectively. The thermal stability of the metal hydride was measured by differential scanning calorimetry. The hydrogen desorption activation energies were calculated using the Kissinger method as 79.41 kJ/mol and 83.56 kJ/mol for x = 0 and 1, respectively. The results suggest that the substitution of titanium with aluminum improves the thermodynamic properties of hydrogen storage and reduces the kinetic performance of hydrogen desorption.     

Insight into the effect of In addition on hydrogen generation behavior and hydrolysis mechanism of Al‐based ternary alloys in distilled water—A new active Al‐Ga‐In hydrolysis hydrogen generation alloy

(Al2Ga)‐xIn (x = 0, 2, 4, 6, 8 wt%) ternary aluminum (Al) alloys with different weight ratio of In for hydrolysis H₂ generation were prepared by melting‐casting technique. The phase compositions and microstructures of Al‐rich alloys were investigated by X‐ray diffraction (XRD) and high resolution scanning electron microscope (HR‐SEM) equipped with an energy dispersive spectrometer (EDS). The effect of In addition ratio on microstructures and H₂ generation performance were investigated, and the hydrolysis mechanism for Al‐Ga‐In ternary Al‐based alloys has been proposed. Al phase as matrix phase in the Al‐Ga‐In ternary alloy mainly determines the hydrolysis behavior, and the second phase In strongly promotes the hydrolysis process. The increase of In content can accelerate the H₂ generation rate as well as the final capacity and generation yield in neutral water. The generation yields for (Al2Ga)‐x In (x = 2, 4, 6, 8 wt%) alloys at 50°C are 0.56, 0.59, 0.62, and 0.66, respectively. The raising hydrolysis temperature can elevate the initial hydrolysis rate, final H₂ generation capacity, and yield. The H₂ generation capacities of (Al2Ga)‐8In alloy at 50°C, 60°C, and 70°C are 262, 290, and 779 mL·g^?1, respectively.     

Effect of Ti on the microstructure and Al–water reactivity of Al-rich alloy

Ti-bearing Al alloys (0.1–1 wt.%) were prepared using arc melting techniques. Their microstructures were investigated using XRD and SEM/EDX, and found to depend strongly on Ti contents. Al grains are columnar as Ti contents are lower, but they are refined and turn into equiaxed ones when Ti contents are higher. The particle sizes of Ga–In–Sn phase decrease with Al grain refinement. Al–water reactivities were also investigated under different water temperatures. Kinetic measurements found that Ti prohibits Al–water reaction and reduces hydrogen yields when alloys contain little Ti. However, Al reacts with water fast and hydrogen yields rise with the increase of Ti contents of alloys. Reasons concerning the variations of microstructures and Al–water reactivities with Ti additions are discussed.     

Insight into the reactivity of Al–Ga–In–Sn alloy with water

An Al alloy ribbon with finer Al grains was prepared using a rapid spinning technique, and then was annealed at different temperatures to modify its microstructures, such as: Al grain size, size and number of Ga–In–Sn phase. The microstructures and phase compositions of the as-prepared and those annealed ribbons were investigated by means of XRD and SEM/EDX. The reaction of Al and the grain boundary phase was measured using DSC. Based on DSC analysis and other experiments, the formation of Al–Ga–In–Sn eutectic was suggested the origin of the alloy being capable of splitting water. Kinetic measurements found that the H₂ generation rate depends strongly on the microstructures of ribbons. An analytical expression was established to calculate the H₂ generation rates of ribbons with the measured microstructure parameters, and the calculated results agreed well with measurements.     

Study on hydrogen storage properties of LaNi3.8Al1.2−xMnx alloys

Effects of the Mn substitution on microstructures and hydrogen absorption/desorption properties of LaNi_3.8Al_1.2−xMn_x (x = 0.2, 0.4, 0.6) hydrogen storage alloys were investigated. The pressure-composition (PC) isotherms and absorption kinetics were measured in a temperature range of 433 K ≤ T ≤ 473 K by the volumetric method. XRD analyses showed that with the increase of the Mn content in the LaNi_3.8Al_1.2−xMn_x alloys, the lattice parameter a was decreased, c increased and the unit cell volume V reduced. It was found that the absorption/desorption plateau pressure was increased and the hydrogen storage capacity was enhanced with the increase of Mn content. The absorption/desorption plateau pressure of the alloys was linearly changed with the Mn content x and the lattice parameter a, while the hydrogen storage capacity was linearly increased with the increase of c/a ratio. It was also found that the slope factor S_f was closely correlated with the lattice strain of the alloys.     

Study on the hydrogen generation performance and hydrolyzates of active aluminum composites

In this paper, aluminum (Al) composites with low melting point metal bismuth (Bi) and bismuth oxide (Bi₂O₃) are prepared to realize great hydrogen generation capacity by the ball milling method. The hydrogen generation of Al–Bi composite reacts with water (the initial temperature is 35 °C) can reach 1120 mL/g. The Al–Bi–Bi₂O₃ produces 1140 mL hydrogen within 2 min by simply raising the initial water temperature to 55 °C. The hydrolyzates of the Al composites are collected and characterized. It indicates that the hydrolyzate of Al–Bi composite mainly includes AlOOH (boehmite), while for the Al–Bi₂O₃ the hydrolyzate is Al(OH)₃ (gibbsite). The scanning electron microscope (SEM) images suggest that the AlOOH particles have more pores than Al(OH)₃ particles, which benefit for hydrogen escaping from the hydrolyzate particles surface and for inner Al contacting with water. The Al(OH)₃ particles easily accumulate and form a dense layer on the surface of Al particles, which inhibits the hydrogen generation.     

A new strategy for remarkably improving anti-disproportionation performance and cycling stabilities of ZrCo-based hydrogen isotope storage alloys by Cu substitution and controlling cutoff desorption pressure

ZrCo_1-xCu_x (x = 0–0.3) alloys for hydrogen isotope storage were prepared via induction levitation melting. The effects of partial substitution of Cu for Co on the microstructure, hydrogen storage properties including hydriding-dehydriding kinetics, thermodynamic characteristics, cycling stability and related mechanism have been systematically investigated. It is found that all synthesized alloy ingots consist of ZrCo main phase, the grain size is further refined but the segregation of Cu element at grain boundary is more serious with the increase of Cu content. The pressure-composition isotherms for dehydrogenation show that both ZrCoH₃ and ZrCo_0.9Cu_0.1H₃ hydrides undergo one-step desorption, while ZrCo_0.8Cu_0.2H₃ and ZrCo_0.7Cu_0.3H₃ hydrides experience two-step desorption since a new middle hydride phase of ZrCoH_0.8 with CrB-type orthorhombic structure is discovered during their dehydrogenation. This result is proposed to be linked with the changed electronic structure and lattice distortion induced by Cu substitution. To compare their dehydriding kinetics, the apparent activation energies for hydrogen desorption of different hydride phases in the alloys are also calculated systematically, and the value of E_a for hydrogen desorption of ZrCoH₃ phase is decreased from 118.02 kJ/mol to 95.90 kJ/mol, 77.98 kJ/mol and 78.65 kJ/mol, respectively. Prominent cycling stabilities of the Cu-substituted alloys are obtained and follow the trend: ZrCo_0.8Cu_0.2 > ZrCo_0.7Cu_0.3 > ZrCo_0.9Cu_0.1 > ZrCo. Specifically, the optimum cycling stable capacity of ZrCo-based alloy is increased from 0.4 wt % to 1.21 wt %. Furthermore, the ZrCo_0.8Cu_0.2 alloy exhibits further enhanced cycling stability during the cycle by controlling cutoff desorption pressure at 0.253 bar, where only the first-step dehydrogenation happens. Therefore, a new strategy for improving anti-disproportionation performance of ZrCo-based alloys by controlling cutoff desorption pressure is also proposed, which is in favor of the enhanced cycling stability and further application of Cu-substituted ZrCo-based alloys for hydrogen isotope storage and delivery in the International Thermonuclear Experimental Reactor (ITER).     

Thermal decomposition of titanium hydrides in electrochemically hydrogenated electron beam melting (EBM) and wrought Ti–6Al–4V alloys using in situ high-temperature X-Ray diffraction

Thermal decomposition of titanium hydrides in electrochemically hydrogenated electron beam melting (EBM) and wrought Ti–6Al–4V alloys containing 6 wt% β is compared. Differential scanning calorimetry (DSC) is used to identify phase transitions. High-temperature X-ray diffraction (HTXRD) is used to identify phases and determine their contents and crystallographic parameters. Both alloys are found to contain α_H (hcp) and β_H (bcc) solid solutions, as well as δ_a (fcc) and δ_b (fcc) hydrides after hydrogenation. δ_a is found to decompose between room temperature and 350 °C to α_H (in both alloys) plus either β_H and δ_b (wrought alloy) or δ_b only (EBM alloy). δ_b fully decomposes at either 450 °C (wrought alloy) or 600 °C (EBM alloy) to α_H plus H₂ desorption (which starts at 300 and 350 °C in the wrought and EBM alloys, respectively). In the case of the wrought alloy, β_H is also formed in this decomposition reaction due to faster diffusion of hydrogen. The non-continuous, finer needle-like morphology of the β-phase in the as-printed EBM alloy combined with its smaller lattice constants seem to inhibit hydrogen diffusion into the bulk alloy through the β-phase, thus triggering δ_a dissociation into δ_b (rather than to β_H+δ_b) and δ_b decomposition into α_H (rather than to α_H + β_H). Hydrogen incorporation in the α_H phase results in its expansion in the c direction in both alloys. HTXRD allows to conclude that both δ_a and δ_b hydrides decompose up to 600 °C. Hydrogen peaks measured at higher temperatures are due to hydrogen desorption from the hydride that is decomposed from the sample's bulk and/or hydrogen desorption from β_H and/or α_H during heating. These findings indicate that the EBM Ti–6Al–4V alloy might be more prone to hydrogen damage at elevated temperatures than its wrought counterpart when both have a similar β-phase content.     

Investigation on hydrogen production using multicomponent aluminum alloys at mild conditions and its mechanism

A series of Al alloys with low melting point metals Ga, In, Sn as alloy elements were fabricated using mechanical alloying method. The phase compositions and morphologies of different Al alloys were characterized by XRD and SEM techniques. The reaction of the Al alloys with water for hydrogen evolving at mild conditions (at room temperature in neutral water) was studied. The results showed that there were no hydrogen yields for binary Al–Ga, Al–In, Al–Sn and the ternary Al–Ga–Sn alloys. The hydrogen yields were observed for Al–Ga–In and Al–In–Sn ternary alloys. The Al–In–Sn alloys showed an even faster hydrogen generation rate and higher yields than Al–Ga–In alloys. Based on the ternary Al–Ga–In and Al–In–Sn system, the hydrogen production property of quaternary Al–Ga–In–Sn was greatly improved. The hydrogen conversion efficiency of the optimized Al–3%Ga–3%In–5%Sn alloy was nearly 100% in tap water. The highest hydrogen generation rate reached 1560 mL/g min in distilled water or deionized water. It was suggested that both the embrittlement of Al by liquid Ga–In–Sn eutectic and the active points formed by intermetallic compounds In₃Sn and InSn₄ may be attributed to the high activity of Al–Ga–In–Sn alloys at room temperature.     

Liquid phase-enabled reaction of Al-Ga and Al-Ga-In-Sn alloys with water

The water-reactivity of Al-Ga and Al-Ga-In-Sn alloys is investigated as a means to utilize the chemical potential energy of Al to split water for the production of H₂. Al in bulk quantities of these alloys participates in a heterogeneous reaction with water to produce H₂ and α-Al(OH)₃ (bayerite). Low melting point phases in these alloys are believed to enable the observed reaction upon liquefaction by providing a means of transport for Al in the alloys to reach a reaction site. In the Al-Ga binary system, this reaction-enabling phase is shown to form at a temperature corresponding to the system’s eutectic melting point. In the Al-Ga-In-Sn quaternary system this reaction-enabling phase liquefies at 9.38 °C, as shown using differential scanning calorimetry (DSC). Alloys with the composition 50 wt% Al-34 wt% Ga-11 wt% In-5 wt% Sn are reacted with distilled water in a series of controlled experiments, and H₂ yield from these reactions is measured as a function of time and temperature. Applying kinetic analysis to the yield data shows the apparent activation energy for the reaction process to be 43.8 kJ/mol. A physicochemical model for the alloy-water reaction is presented in the context of the observed experimental results and relevant scientific literature.     

Microstructures and electrochemical characteristics of Mm0.3Ml0.7Ni3.55Co0.75Mn0.4Al0.3 hydrogen storage alloys prepared by mechanical alloying

The as-cast alloy with the composition of Mm_0.3Ml_0.7Ni_3.55Co_0.75Mn_0.4Al_0.3 prepared by induction melting was milled for 6, 15, 40 and 50 h in this work. The microstructures of alloys were analyzed by XRD and DSC. Two broadening effects of XRD peak caused by crystallite and microstrain were separated by approximate function method and least square method. Crystallite sizes and microstrains of the alloys were calculated. The results show that alloys milled for 6 h or 15 h consist of nanocrystalline and polycrystalline phase. Lattice parameters (a, c) and volumes of alloy increase with the increasing milling time, whereas the ratio of c/a keep constant. Moreover, the crystallite sizes decrease and the microstrains in the alloys increase first and then decrease with the increase of milling time. The alloys milled for 40 h or 50 h transform partly into amorphous structures. The maximum discharge capacities of alloys decrease with the increase of milling time. The cycle stabilities of the milled alloys are better than those of the as-cast. And they increase with the increasing milling time.     

Portable hydrogen generation from activated Al–Li–Bi alloys in water

A new process to obtain hydrogen from highly activated Al–Li–Bi alloys in water is described. The alloys had good hydrolytic properties at 298 K, and the optimized composite yielded 1340 mL hydrogen/g Al with 100% efficiency and achieved a maximum hydrogen generation rate of 988 mL/min g Al. These values are much higher than those obtained from hydrogen production with pure Al under the same conditions. The improvements were brought about by the increased amount of Li in the alloys; Al alloys with higher Li contents have larger surface areas and smaller grain sizes, allowing more hydrogen to be generated from Li hydrolysis in water. XRD and SEM analyses showed that the formation of BiLi₃ was helpful in improving the hydrolytic properties of the alloys via the work of the micro galvanic cell between Al and Bi, which was stimulated by the LiOH solution obtained from Li hydrolysis in water. Other effects, such as Bi content, global temperature, and annealing conditions, were also discussed. Al–Li–Bi alloys show promise as potential materials for supplying portable hydrogen to fuel cells.     

Comparative study of Ga and Al alloying with ZrFe2 for high-pressure hydrogen storage

ZrFe₂ reacts reversibly with hydrogen under extremely high hydrogen pressure and shows potential for high-pressure hydrogen compression and storage. Alloying is indispensable to tune its hydrogen storage properties for practical applications. Previous works indicated that the Al substitution for Fe would drastically decrease hydrogen storage capacity. This work used the quenching process to prepare the ZrFe_2-xAl_x and ZrFe_2-xGa_x (0.1 ≤ x ≤ 0.2) alloys with a single C15 Laves phase structure. It was found that the presence of the second phase Zr₂Fe in as-cast alloys is responsible for the capacity reduction. The quenched ZrFe_1.9Al_0.1 alloy delivers a maximum hydrogen storage capacity of 1.79 wt%, much higher than as-cast alloys. The comparative study further shows that ZrFe_2-xGa_x alloys have a relatively higher equilibrium pressure than ZrFe_2-xAl_x alloys due to a higher bulk modulus for ZrFe_2-xGa_x alloys by the theoretical calculations. The hydrogen storage performance test indicates that the hydrogen dissociation pressure of ZrFe_1.9Ga_0.1 and ZrFe_1.9Al_0.1 is 164.0 atm and 130.7 atm at 298 K, respectively. Our work demonstrates that ZrFe₂-based alloys with a small Ga or Al substitution are suitable for high-pressure hydrogen storage applications.     

Enhanced hydrogen generation behaviors and hydrolysis thermodynamics of as-cast Mg–Ni–Ce magnesium-rich alloys in simulate seawater

In this study, we developed as-cast (Mg10Ni)_1-xCe_x (x = 0, 5, 10, 15 wt%) ternary alloys by using a flux protection melting method and investigated their hydrolysis hydrogen generation behaviour in simulate seawater. The phase compositions and microstructures of as-cast (Mg10Ni)_1-xCe_x ternary alloys are characterized by X-ray diffraction (XRD), scanning electron microscope (SEM) equipped with electron energy dispersion spectrum (EDS) and transition electron microscope (TEM). Their kinetics, thermodynamics, rate-limiting steps and apparent activation energies are investigated by fitting the hydrogen generation curves at different temperatures. With increasing Ce content, the (Mg10Ni)_1-xCe_x ternary alloys show increased electrochemical activities and decreased eutectic. When 10 wt% and 15 wt% Ce added, the active intermediate phase of Mg₁₂Ce has been observed. The hydrogen generation capacity of (Mg10Ni)₉₅Ce₅ is as high as 887 mLg⁻¹ with a hydrolysis conversion yield of 92%, which is higher than that of Mg₁₀Ni alloys (678 mLg⁻¹) with a yield only 75% at 291 K. The initial hydrolysis reaction kinetics of Mg–Ni–Ce alloys is mainly controlled by the electrochemical activity and the mass transfer channels formed in the alloys. Such a structure-property relationship will provide a possible strategy to prepare Mg-based alloys with high hydrogen conversion yield and controlled hydrolysis kinetics/thermodynamics.     

Synergistic effects of multiwalled carbon nanotubes and Al on the electrochemical hydrogen storage properties of Mg2Ni-type alloy prepared by mechanical alloying

Mg_2−xAl_xNi (x = 0, 0.25) electrode alloys with and without multiwalled carbon nanotubes (MWCNTs) have been prepared by mechanical alloying (MA) under argon atmosphere at room temperature using a planetary high-energy ball mill. The microstructures of synthesized alloys are characterized by XRD, SEM and TEM. XRD analysis results indicate that Al substitution results in the formation of AlNi-type solid solution that can interstitially dissolve hydrogen atoms. In contrast, the addition of MWCNTs hardly affects the XRD patterns. SEM observations show that after co-milling with 5 wt. % MWCNTs, the particle sizes of both Mg₂Ni and Mg_1.75Al_0.25Ni milled alloys are decreased explicitly. The TEM images reveal that ball milling is a good method to cut long MWCNTs into short ones. These MWCNTs aggregate along the boundaries and surfaces of milled alloy particles and play a role of lubricant to weaken the adhesion of alloy particles. The majority of MWCNTs retain their tubular structure after ball milling except a few MWCNTs whose tubular structure is destroyed. Electrochemical measurements indicate that all milled alloys have excellent activation properties. The Mg_1.75Al_0.25Ni-MWCNTs composite shows the highest discharge capacity due to the synergistic effects of MWCNTs and Al on the electrochemical hydrogen storage properties of Mg₂Ni-type alloy. However, the improvement on the electrode cycle stability by adding MWCNTs is unsatisfactory.     

Effect of Sn and Zn alloying with Al on its electrochemical performance in an alkaline media containing CO2 for Al-air batteries application

Aluminum alloyed with other metals, such as Sn and Zn, was synthesized via fusion to trace the impact of alloying elements on the electrochemical characteristics of Al anodes. The corrosion inhibition and electrochemical tests were performed in a 5 M KOH medium in the absence and presence of CO₂ for the Al–Sn, and Al–Zn anodes and compared to the commercial aluminum. Tafel polarization exhibited that the anodic and cathodic branches display lower current densities than Al metal in pure KOH. The steady state of the open circuit voltage (E_corr.) for the studied alloys was shifted to a more negative magnitude than for Al. The corrosion current is sharply decreased, and potential is significantly shifted to less negative values in the presence of CO₂. This is due to forming of a protective layer from the carbonate of Al, Sn, and Zn on the surface. Amazing results were obtained and discussed in the case of CO₂. Electrochemical impedance spectroscopy (EIS) results exhibited that charge transfer resistance (R_ct) values rise with alloying elements. The data of Tafel plots are consistent with those of EIS. The alloying of Al with Sn and Zn elements significantly affects capacitance, hydrogen evolution process suppression, and charge-discharge efficiency. This reveals that the highest potential value in the presence of CO₂ in the charging process is obtained for Al–Zn alloy, while the most negative potential is obtained for Al in the discharging process with CO₂. Moreover, the discharge time is higher in the alloys than in commercial Al in the absence and more in the presence of CO₂. The produced alloys are thought to provide good anodes for long-life rechargeable batteries.     

Effects of Bi composition on microstructure and Al-water reactivity of Al-rich alloys with low-In

Bi-bearing Al-Ga-In-Sn quinary alloys were prepared by a high-temperature melting technique. The alloys primarily consist of Al(Ga) matrix and Ga, In, Sn, Bi (GISB) grain boundary phase, mainly in the form of Ga-InSn₄-InBi. The microstructure of GISB particles was obviously equiaxed with the increasing Bi dosage. Al-water reaction was tested at 40 °C. Owing to the Bi-doping, the hydrogen generation yields of alloys with InSn₄ intermetallic compound are obviously improved and hydrogen release rates gradually tend to be stable, which show great potential in applications. At the dosage of 2.53 wt% Bi, the hydrogen generation performance of alloys was more prominent in Al-water reaction, including a theoretical hydrogen generation yield and hydrogen released extremum rate to ～0.076 L/min·g Al alloy. Furthermore, the Al-water reaction mechanism of Bi-bearing Al-rich low-In quinary alloys has been put forward.     

Effect of element substitution and surface treatment on low temperature properties of AB3.42-type La–Y–Ni based hydrogen storage alloy

The low-temperature performance (LTP) of AB_3.42-type La–Y–Ni hydrogen storage alloy was studied by methods of element substitution and surface treatment. The effect of Mn-additive on LTP of La_1·3Ce_0·5Y_4·2Ni_19.5-xMn_xAl (x = 0, 0.2, 0.5) was systematically investigated. Electrochemical studies showed that Mn-additive deteriorated the LTP of the alloy by reducing platform pressure, deteriorating kinetic performance and forming more oxides on the alloy surface. RE-substitution and hot alkali-ultrasonic treatment of La_1.3RE_0.5Y_4·2Ni_19·5Al (RE = Ce, Sm, Nd) alloys were applied to further optimize the LTP. The maximum discharge capacity and capacity retention at the 100th cycle of La_1·3Ce_0·5Y_4·2Ni_19·5Al alloy were 252.1 mA h/g and 87.1% at 243 K, respectively. Furthermore, the LTP of RE-substitution alloys at 243 K was conspicuously improved by surface treatment, which were raised from 214.7 mA h/g to 301.1 mA h/g by Sm-substitute, from 220.9 mA h/g to 303.9 mA h/g by Nd-substitute and from 252.1 mA h/g to 254.8 mA h/g by Ce-substitute.     

Effects of adding nano-CeO2 powder on microstructure and hydrogen storage performances of mechanical alloyed Mg90Al10 alloy

For pushing Mg-based alloys developing to the practical applications, nano-CeO₂ powders were added into the mechanical alloyed (MA) Mg₉₀Al₁₀ alloy. The aim of it is to improve the thermodynamics and kinetics through generating new intermetallic compound, reducing the grain size and increasing the solid solubility of Al in Mg. XRD analysis showed that adding nano-CeO₂ powder causes the generation of Mg₁₇Al₁₂ phase and grain refinement of the MA Mg₉₀Al₁₀ + x wt% CeO₂ (x = 1, 3, 5 and 8) composites. It also increases the solid solubility of Al in Mg, while results in the reduction of Mg lattice volume. The dehydrogenation enthalpy (ΔH_de), calculated from Van't Hoff equation, is reduced from 75.43 kJ mol⁻¹ H₂ for the MA Mg₉₀Al₁₀ alloy to 74.22, 72.70, 70.28 and 73.71 kJ mol⁻¹ H₂ for the MA Mg₉₀Al₁₀ + x wt% CeO₂ (x = 1, 3, 5 and 8) composites, respectively. The increased grain boundaries, caused by the grain refinement and formation of the mutilphase structure, are beneficial to reduce the dehydrogenation activation energy (E^de(a)). It is obtained through Johnson-Mehl-Avrami-Kolmogorov model, which is 162.06, 121.86, 103.73, 101.83 and 109.08 kJ mol⁻¹ H₂ for the MA Mg₉₀Al₁₀ + x wt% CeO₂ (x = 0, 1, 3, 5 and 8) composites, respectively.