Hydrogen Storage Performances Of Alloys Research Articles

Comprehensive improvement of AB2 hydrogen storage alloy: Substitution of rare earth elements for different A-side alloys

Rare earth substitution enhances the activation, absorption/desorption properties of hydrogen storage alloys, a crucial research area. Despite the extensive variety of A-site elements in multicomponent alloys, there remains a scarcity of reports on how to enhance the hydrogen storage capacity of alloys by substituting different elements with rare earth elements at the A-site, which needs to be further explored. In this study, the AB2 type Ti-Mn based hydrogen storage alloy was selected as the research object, and the effect of replacing different elements in the A-position by rare earth elements with equal atomic ratios was systematically analyzed by replacing the hydrogen absorption elements Ti/Zr with the rare earth metal Ce. The result reveals that Ce substitution significantly enhances the hydrogen storage and cyclic performance of the alloys, with Ce substituting for Ti showing superior performance. Theoretical calculations indicate that Ce substitution for Ti in alloys leads to lower formation energy and easier hydrogen absorption than Ce substitution for Zr. Beyond the influence of the Lundin’s theory, this work proposes for the first time that the difference in electronegativity between substituent elements may one of the crucial factors affecting the hydrogen storage performance of alloys. The greater difference in electronegativity may lead to a higher hydrogen storage capacity of the hydrogen storage alloy. This opens a new avenue for research into doping/substitution modifications of hydrogen storage alloy elements. These findings not only enrich the knowledge on element doping modification but offer valuable insights for future research on rare earth-doped modification of hydrogen storage alloys.

Hydrogen storage properties of MgH2 + Mg2NiH4–Co/C ternary nanocomposite

The application of ternary nanocomposite synergetic catalysis has proven to be an effective modification strategy for enhancing MgH2 hydrogen storage performance. The ternary magnesium-based hydrogen storage alloy, composed of MgH2+Mg2NiH4–Co/C, is successfully prepared and characterized. Through the optimized preparation process and the optimal ratio, it is observed that the catalyst Mg2NiH4–Co/C significantly reduces the reaction activation energy, resulting in a the initial hydrogen desorption temperature is approximately 60 °C lower than that of pure MgH2. The enhanced hydrogen storage properties are attributed to the synergistic catalytic effect of carbon (C) combined with the formation of Mg2Ni and Mg2Co facilitated by Ni and Co elements. Furthermore, the reversible phase transitions of Mg2Co/Mg2CoH5 and Mg2Ni/Mg2NiH4 serve as "hydrogen pumps" further aiding in hydrogen storage. This study extends the investigation of the synergistic catalytic effect of ternary nanocomposites to enhance the hydrogen storage performance of alloys.

Microstructures and hydrogen storage properties of Mg-Y-Zn rare earth magnesium alloys with different Zn content: Experimental and first-principles studies

In this work, as-cast Mg-9.1Y-1.0Zn, Mg-9.1Y-1.8Zn and Mg-9.2Y-3.1Zn (wt%) alloys with different Zn content are prepared by the semi-continuous casting method. The microstructures and hydrogen storage properties are systematically investigated by experimental and first-principles calculations approaches. The results show that more LPSO phases form with increasing Zn content and they mainly distribute at the grain boundaries of alloys. The LPSO phases decompose and in-situ form YH2/YH3 hydrides upon hydrogenation. These YH2/YH3 hydrides are more likely to be concentrated at the grain boundaries with increasing Zn content, which leads to the non-uniform distribution of YH2/YH3 hydrides in these alloys. The more non-uniform distribution of these YH2/YH3 hydrides on the Mg matrix will lead to the worse hydrogen storage performance of alloys. Comparatively, the three alloys exhibit similar hydrogen absorption kinetics, while the as-cast Mg-9.1Y-1.0Zn (wt%) shows the best hydrogen desorption kinetics. First-principles calculations show that the H removal energies Erom and H2 recombination energies Erecom from MgH2(110) surface both decrease upon the role of YH2, which further validates the catalytic effect of YH2 on hydrogen sorption kinetics of Mg-Y-Zn alloys.

Improving the hydrogenation properties of AZ31-Mg alloys with different carbonaceous additives by high energy ball milling (HEBM) and equal channel angular pressing (ECAP)

In this study, the hydrogen storage performance of commercial AZ31-Mg alloys combined with various allotropes of carbon was investigated and the microstructural modifications with respect to plastic deformation and high energy milling techniques investigated, with the aim of obtaining enhanced hydrogen storage efficiency. The hydrogen storage performance of alloys prepared with different weight ratios of carbonaceous materials as a catalyst was monitored in order to explore the effective improvement in hydrogen storage performance through microstructural modification. Additionally, the effects of different processing methods such as equal channel angular pressing (ECAP) and high energy ball milling (HEBM) were also observed. AZ31 Mg based composites with various carbon additives were produced through gravity resistance casting and their micrographic structures examined through optical Microscopy (OM), X-ray diffraction (XRD) and scanning electron microscopy (SEM) with energy dispersive spectroscopy (EDS). The average particle size distributions of the sample powders were also measured. The rate of hydrogenation kinetics was calculated by a Sievert's type apparatus. Significant enhancement of the hydrogenation performance was obtained with the addition of carbonaceous materials. Overall, the hydrogen storage performance after ECAP deformation of the AZ31-3CB (carbon Black) composite showed a gain in the maximum capacity of 6.72 ± 0.05 wt%. Similar, after milling of the AZ31-3G (Graphene) composite materials, a maximum potential capacity of 6.83 ± 0.04 wt% was attained within 792 ± 144.34 s, with desorption of the entire H2 content in 143.2 ± 26.09 s. The obtained results revealed significant improvement in the hydrogen storage capacity of AZ31-Mg alloys with the addition of carbon materials and with respect to plastic deformation and milling techniques.

Effect of milling duration on hydrogen storage thermodynamics and kinetics of ball-milled Ce–Mg–Ni-based alloy powders

To improve the hydrogen storage performance of CeMg12-type alloys, partially substituting Mg with Ni in the alloy was conducted. The way to synthesize the target alloy powders was the mechanical milling method, by which the CeMg11Ni + x wt% Ni (x = 100, 200) alloy powders with nanocrystalline and amorphous structure were obtained. The influence of the milling time and Ni content on the hydrogen storage properties of the alloys was discussed. The X-ray diffractometer and high-resolution transmission electron microscope were used to investigate the microstructures of the ball-milled alloys. The hydrogenation/dehydrogenation dynamics were studied using a Sievert instrument and a differential scanning calorimeter which was linked with a H2 detector. The hydrogen desorption activation energies of the alloy hydrides were evaluated by Arrhenius and Kissinger equations. From the results point of views, there is a little decline in the thermodynamic parameters (enthalpy and entropy changes) with the increase in Ni content. However, the alloys desorption and absorption dynamics are improved distinctly. What is more, the variation of milling time results in a dramatic influence on the hydrogen storage performances of alloys. Various maximum values of the hydrogen capacities correspond to different milling time, which are 5.805 and 6.016 wt% for the CeMg11Ni + x wt% Ni (x = 100, 200) alloys, respectively. The kinetics tests suggest that the hydrogen absorption rates increase firstly and then decrease with prolonging the milling time. The improvement of the gaseous hydrogen storage kinetics results from the decrease in the activation energy caused by the increase in Ni content and milling time.

Phase transformation and electrochemical hydrogen storage performances of La3RMgNi19 (R = La, Pr, Nd, Sm, Gd and Y) alloys

Adjusting the rare earth (RE) compositions in the RE–Mg–Ni alloys can effectively improve the electrochemical hydrogen storage performances of the alloy electrodes. Herein, A5B19 type hydrogen storage alloys with the elemental composition of La3RMgNi19 (R = La, Pr, Nd, Sm, Gd and Y) were prepared by induction melting and subsequent annealing. The phase transformation and electrochemical hydrogen storage performances of La3RMgNi19 alloys were investigated in detail. X-ray diffraction analysis shows that La3RMgNi19 alloys contains AB5, A2B7 (Ce2Ni7 and Gd2Co7) and A5B19 (Pr5Co19 and Ce5Co19) phases, and the increase of annealing temperature obviously reduces the phase abundance of LaNi5 phase. Sm, Gd and Y contribute to the formation of A5B19 phase, especially Ce5Co19, and Pr and Nd promote the formation of A2B7 phase for La3RMgNi19 alloys. With increasing annealing temperature, the maximum discharge capacity (Cmax) of La3RMgNi19 alloy electrodes first increases and then decreases, and the highest value of Cmax is achieved as the annealing temperature is 1223 K. This evolution trend of the Cmax is inversely proportional to that of LaNi5 phase abundance. The substation of La by Pr, Nd, Sm, Gd or Y causes the decrease of Cmax, which is mainly ascribed to the decrease of cell volume. Due to the decrement of LaNi5 phase, the cycling stability increases at first when the annealing temperature is below 1223 K. However, when annealing temperate further increases to 1273 K, the cycling stability decreases, which is caused by the increment of LaNi5 phase. It is worth noting that the phase composition (LaNi5 phase abundance) plays more important role than other factor. The slight decrement of high-rate dischargeability resulted from the substitution of La by Pr, Nd, Sm, Gd or Y should be attributed to the combined effect of advantageous and disadvantageous factors.

Gaseous and Electrochemical Hydrogen Storage Properties of Nanocrystalline Mg<sub>2</sub>Ni-Type Alloys Prepared by Melt Spinning

A partial substitution of Ni by Cu has been carried out in order to improve the hydrogen storage characteristics of the Mg2Ni-type alloys. The nanocrystalline Mg20Ni10-xCux (x = 0, 1, 2, 3, 4) alloys are synthesized by the melt-spinning technique. The structures of the as-cast and spun alloys have been characterized by X-ray diffraction (XRD), scanning electron microscope (SEM) and high resolution transmission electron microscope (HRTEM). The electrochemical performances were evaluated by an automatic galvanostatic system. The hydrogen absorption and desorption kinetics of the alloys were determined by using an automatically controlled Sieverts apparatus. The results indicate that the substitution of Cu for Ni does not alter the major phase Mg2Ni. The Cu substitution significantly ameliorates the electrochemical hydrogen storage performances of alloys, involving both the discharge capacity and the cycle stability. The hydrogen absorption capacity of alloys has been observed to be first increase and then decrease with an increase in the Cu contents. However, the hydrogen desorption capacity of the alloys exhibit a monotonous growth with an increase in the Cu contents.