Using Ball Milling for Modification of the Hydrogenation/Dehydrogenation Process in Magnesium-Based Hydrogen Storage Materials: An Overview

High-load Mg2Ni nanoparticle-carbon nanofiber composites for hydrogen storage

Herein, a simple synthesis method for Mg2Ni composites with carbon nanofibers capable of hydrogen storage is presented. Specifically, n-butyl-sec-butyl-magnesium solution in hexane (C8H18Mg, 0.7 M) and bis-cyclopentadienyl nickel(II) (nickelocene or NiCp2) were used as precursors for the Mg2Ni nanoparticles. Subsequently, the nanoparticles were composited with carbon nanofibers (CNF) with high loading of Mg2Ni of 50 wt%, 75 wt%, 90 wt%, and 100 wt%. The physicochemical characterization of the materials indicated that the size of the as-prepared Mg2Ni nanoparticles was less than 5 nm and they were highly agglomerated due to a carbon-based binder. The best hydrogen storage values were determined to be 2.6-2.7 wt%. Among the tested materials, the composite with 75 wt% of Mg2Ni in CNF presented the best hydrogen uptake. The pressure-composition-temperature curves indicated changes in the hydriding equilibrium pressures of the Mg2Ni nanoparticles compared to the material with a similar composition produced using ball-milling and thermodynamic calculations. Thus, the results presented herein indicate the beneficial effect of nanosizing on hydriding reactions.

Ferromagnetic-Antiferromagnetic Coupling in Gas-Phase Synthesized M(Fe, Co, and Ni)-Cr Nanoparticles for Next-Generation Magnetic Applications

Combining ferromagnetic-antiferromagnetic materials in nanoalloys (i.e., nanoparticles, NPs, containing more than one element) can create a diverse landscape of potential electronic structures. As a result, a number of their magnetic properties can be manipulated, such as the exchange bias between NP core and shell, the Curie temperature of nanoparticulated samples, or their magnetocaloric effect. In this work, such a family of materials (namely M-Cr NPs where M is Fe, Co, Ni, or some combination of them) is reviewed with respect to the tunability of their magnetic properties via optimized doping with Cr up to its solubility limit. To this end, gas-phase synthesis has proven a most effective method, allowing excellent control over the physical structure, composition, and chemical ordering of fabricated NPs by appropriately selecting various deposition parameters. Recent advances in this field (both experimental and computational) are distilled to provide a better understanding of the underlying physical laws and point toward new directions for cutting-edge technological applications. For each property, a relevant potential application is associated, such as memory cells and recording heads, induced hyperthermia treatment, and magnetic cooling, respectively, aspiring to help connect the output of fundamental and applied research with current real-world challenges.

Theoretical and Experimental Studies of Al-Impurity Effect on the Hydrogenation Behavior of Mg

In this paper, we study the influence of hydrogen concentration on the binding energies in magnesium hydrides. The impact of aluminum atom addition on the hydrogenation behavior of magnesium was theoretically and experimentally defined. Doping Al into the Mg lattice allows the uniform hydrogen distribution in both the fcc and bcc Mg lattice at a low hydrogen concentration (H:Mg < 0.875) to be more energetically favorable. In addition, this leads to bcc Mg lattice formation with a uniform hydrogen distribution, which is more energetically favorable than the fcc Mg lattice when the atomic ratio H:Mg is near 0.875. In addition, compared with the pure Mg, in the Al-doped Mg, the phase transition from the hcp to the fcc structure with a uniform distribution of H atoms induces less elastic strain. Thus, the uniform hydrogen distribution is more favorable, leading to faster hydrogen absorption. Pure magnesium is characterized by cluster-like hydrogen distribution, which decreases the hydrogen diffusion rate. This leads to the accumulation of a higher hydrogen concentration in magnesium with aluminum compared with pure magnesium under the same hydrogenation regimes, which is confirmed experimentally.

Theoretical and Experimental Research of Hydrogen Solid Solution in Mg and Mg-Al System

The study of hydrogen storage properties of Mg-based thin films is of interest due to their unique composition, interface, crystallinity, and high potential for use in hydrogen-storage systems. Alloying Mg with Al leads to the destabilization of the magnesium hydride reducing the heat of reaction, increases the nucleation rate, and decreases the dehydriding temperature. The purpose of our study is to reveal the role of the aluminum atom addition in hydrogen adsorption and accumulation in the Mg-H solid solution. Ab initio calculations of aluminum and hydrogen binding energies in magnesium were carried out in the framework of density functional theory. Hydrogen distribution and accumulation in Mg and Mg-10%Al thin films were experimentally studied by the method of glow-discharge optical emission spectroscopy and using a hydrogen analyzer, respectively. It was found that a hydrogen distribution gradient is observed in the Mg-10%Al coating, with more hydrogen on the surface and less in the bulk. Moreover, the hydrogen concentration in the Mg-10%Al is lower compared to Mg. This can be explained by the lower hydrogen binding energy in the magnesium-aluminum system compared with pure magnesium.

Improved H-Storage Performance of Novel Mg-Based Nanocomposites Prepared by High-Energy Ball Milling: A Review

Hydrogen storage in magnesium-based composites has been an outstanding research area including a remarkable improvement of the H-sorption properties of this system in the last 5 years. Numerous additives of various morphologies have been applied with great success to accelerate the absorption/desorption reactions. Different combinations of catalysts and preparation conditions have also been explored to synthesize better hydrogen storing materials. At the same time, ball milling is still commonly and effectively applied for the fabrication of Mg-based alloys and composites in order to reduce the grain size to nanometric dimensions and to disperse the catalyst particles over the surface of the host material. In this review, we present the very recent progress, from 2016 to 2021, on catalyzing the hydrogen sorption of Mg-based materials by ball milling. The various catalyzing routes enhancing the hydrogenation performance, including in situ formation of catalysts and synergistic improvement achieved by using multiple additives, will also be summarized. At the end of this work, some thoughts on the prospects for future research will be highlighted.

The Effect of High-Energy Ball Milling Conditions on Microstructure and Hydrogen Desorption Properties of Magnesium Hydride and Single-Walled Carbon Nanotubes

Magnesium hydride is considered to be one of the most promising hydrogen storage materials, although it nevertheless has some problems, such as the high value of the activation energy of hydrogen desorption. To solve this problem, some scientists have proposed adding nanocarbon materials, in particular carbon nanotubes, to magnesium hydride. Currently, a detailed understanding of the mechanisms of obtaining composites based on magnesium hydride and carbon nanotubes is lacking, as is our understanding of the effect of nanocarbon additives on the activation energy and temperature of hydrogen desorption depending on the parameters of the composite synthesis. In addition, the data obtained at various values of milling parameters are very different, and in some works the effect of carbon nanomaterials on the hydrogen properties of magnesium hydride was not confirmed at all. Thus, it is important to determine the effect of nanocarbon additives on the properties of hydrogen storage of magnesium hydride under various milling parameters. This work is devoted to the study of the effect of nanocarbon additives on magnesium hydride and the determination of the dependences of the hydrogen desorption temperature and activation energy on the synthesis parameters. Composite powders containing MgH2 with 5 wt.% single-walled carbon nanotubes (SWCNT) were prepared using a planetary ball mill. The milling was carried out at various milling speeds, namely 300, 660, and 900 rpm. Results suggested that the structure of the nanotubes is preserved with prolonged grinding of magnesium hydride and SWCNT in a ball mill for 180 min at a relatively low grinding speed of 300 rpm. The composite obtained with these parameters has the lowest temperature of hydrogen desorption and an activation energy of H2 desorption of 162 ± 1 kJ/mol H2, which is 15% lower than that of the magnesium hydride MgH2 (189 ± 1 kJ/mol H2).

Artificial Intelligence Application in Solid State Mg-Based Hydrogen Energy Storage

The use of Mg-based compounds in solid-state hydrogen energy storage has a very high prospect due to its high potential, low-cost, and ease of availability. Today, solid-state hydrogen storage science is concerned with understanding the material behavior of different compositions and structure when interacting with hydrogen. Finding a suitable material has remained an elusive idea, and therefore, this review summarizes works by various groups, the milestones they have achieved, and the roadmap to be taken on the study of hydrogen storage using low-cost magnesium composites. Mg-based compounds are further examined from the perspective of artificial intelligence studies, which helps to improve prediction of their properties and hydrogen storage performance. There exist several techniques to improve the performance of Mg-based compounds: microstructure modification, use of catalytic additives, and composition regulation. Microstructure modification is usually achieved by employing different synthetic techniques like severe plastic deformation, high energy ball milling, and cold rolling, among others. These synthetic approaches are discussed herein. In this review, a discussion of key parameters and operating conditions are highlighted in a view to finding high storage capacity and faster kinetics. Furthermore, recent approaches like machine learning have found application in guiding the experimental design. Hence, this review paper also explores how machine learning techniques have been utilized to fasten the materials research. It is however noted that this study is not exhaustive in itself.

Roles of Ti-Based Catalysts on Magnesium Hydride and Its Hydrogen Storage Properties

Magnesium-based hydrides are considered as promising candidates for solid-state hydrogen storage and thermal energy storage, due to their high hydrogen capacity, reversibility, and elemental abundance of Mg. To improve the sluggish kinetics of MgH2, catalytic doping using Ti-based catalysts is regarded as an effective approach to enhance Mg-based materials. In the past decades, Ti-based additives, as one of the important groups of catalysts, have received intensive endeavors towards the understanding of the fundamental principle of catalysis for the Mg-H2 reaction. In this review, we start with the introduction of fundamental features of magnesium hydride and then summarize the recent advances of Ti-based additive doped MgH2 materials. The roles of Ti-based catalysts in various categories of elemental metals, hydrides, oxides, halides, and intermetallic compounds were overviewed. Particularly, the kinetic mechanisms are discussed in detail. Moreover, the remaining challenges and future perspectives of Mg-based hydrides are discussed.

Multielement synergetic effect of NiFe2O4 and h-BN for improving the dehydrogenation properties of LiAlH4

NiFe₂O₄@h-BN composites significantly improved the dehydrogenation and rehydrogenation properties of LiAlH₄. The Al₄Ni₃ and LiFeO₂ found in doped LiAlH₄, and Al_1.1Ni_0.9 in the process of heating, improved the dehydrogenation properties of LiAlH₄.

Hydrogen Accumulation and Distribution in Titanium Coatings at Gas-Phase Hydrogenation

This work is devoted to studying the accumulation of hydrogen in titanium coatings to use a completely new concept of hydrogen accumulators based on a system of easily replaceable cartridges. Modern hydrogen accumulators based on magnesium powder have several problems associated with uneven heating during hydrogen desorption. Increasing the efficiency of hydrogen accumulators and the possibility of their reuse and/or repair remains a topical problem. For the analysis of the microstructure of the received titanium coatings, scanning electron microscopy (SEM) was used, the structural-phase state was studied using x-ray diffraction (XRD) analysis. The coatings were hydrogenation by gas-phase saturation at 450–550 °C. Increased film thickness reduced the storage capacity of coatings. Besides hydrogenation at 450 °C, 20 µm of titanium coatings accumulated 3.96 wt.%, while 80 µm of coatings accumulated 3.98 wt.%. The chemical composition of the coatings before and after the hydrogenation was controlled using glow-discharge optical emission spectroscopy.

Ammonia Borane: An Extensively Studied, Though Not Yet Implemented, Hydrogen Carrier

Ammonia borane H3N−BH3 (AB) was re-discovered, in the 2000s, to play an important role in the developing hydrogen economy, but it has seemingly failed; at best it has lagged behind. The present review aims at analyzing, in the context of more than 300 articles, the reasons why AB gives a sense that it has failed as an anodic fuel, a liquid-state hydrogen carrier and a solid hydrogen carrier. The key issues AB faces and the key challenges ahead it has to address (i.e., those hindering its technological deployment) have been identified and itemized. The reality is that preventable errors have been made. First, some critical issues have been underestimated and thereby understudied, whereas others have been disproportionally considered. Second, the potential of AB has been overestimated, and there has been an undoubted lack of realistic and practical vision of it. Third, the competition in the field is severe, with more promising and cheaper hydrides in front of AB. Fourth, AB has been confined to lab benches, and consequently its technological readiness level has remained low. This is discussed in detail herein.

An Overview of the Recent Progress in Modifications of Carbon Nanotubes for Hydrogen Adsorption

Many researchers have carried out experimental research and theoretical analysis on hydrogen storage in carbon nanotubes (CNTs), but the results are very inconsistent. The present paper reviewed recent progress in improving the hydrogen storage properties of CNTs by various modifications and analyzed the hydrogen storage mechanism of CNTs. It is certain that the hydrogen storage in CNTs is the result of the combined action of physisorption and chemisorption. However, H2 adsorption on metal-functionalized CNTs still lacks a consistent theory. In the future, the research of CNTs for hydrogen adsorption should be developed in the following three directions: (1) A detailed study of the optimum number of metal atoms without aggregation on CNT should be performed, at the same time suitable preparation methods for realizing controllable doping site and doped configurations should be devised; (2) The material synthesis, purification, and activation methods have to be optimized; (3) Active sites, molecular configurations, effectively accessible surface area, pore size, surface topology, chemical composition of the surface, applied pressure and temperature, defects and dopant, which are some of the important factors that strongly affect the hydrogen adsorption in CNTs, should be better understood.