Since the mid-1960s, research on metal hydride as hydrogen storage medium has been started at home and abroad. The ultimate goal is to solve the problem of hydrogen energy storage. The main goal of research is to find hydrogen storage materials with small specific gravity, large hydrogen storage capacity, long service life, hydrogen absorption and desorption at room temperature and low price. Hydrogen storage materials have important application value in fields such as energy and environmental protection, such as Ni-MH batteries and fuel cells.

At present, metal hydride is still the most studied hydrogen storage material, and it develops rapidly. There are mainly AB5 type rare earth hydrogen storage materials represented by LaNi5, AB2 type Laves phase hydrogen storage materials represented by ZrM2, TiM2 (M=Mn, Ni, V, etc.), titanium AB type hydrogen storage materials represented by Ti Fe, and magnesium A2B type hydrogen storage materials represented by Mg2Ni.

Recently, many researchers have focused their research on magnesium based hydrogen storage materials, mainly because magnesium is one of the most abundant elements in the crust, ranking eighth, accounting for approximately 2.35% of the weight of the crust. China has one of the largest reserves of magnesium containing minerals, providing a solid material guarantee for the large-scale application of hydrogen storage materials; Secondly, magnesium has a large hydrogen storage capacity, theoretically reaching 7.6 mass% H. Magnesium based hydrogen storage materials are based on the absorption and release of hydrogen from Mg and MgH2. They have a slow reaction rate with hydrogen, a high decomposition temperature of hydrides (560K at 0.1MPa), and the surface of magnesium is often covered with an oxide film, which seriously hinders the adsorption of hydrogen atoms and is difficult to activate, greatly limiting its practical application. To solve this problem, a more effective method is to nanocomposite magnesium based alloys.

In terms of the preparation technology of hydrogen storage materials, there are currently many methods, such as molten salt protection method, metal melting method, displacement diffusion method, coating method, mechanical alloying method, high-pressure gas atomization method, hydrogenation combustion method, vacuum rapid quenching method, etc. Recently, mechanical alloying has attracted much attention due to its ability to effectively improve the hydrogen absorption and desorption properties of materials. However, it is time-consuming and energy consuming, and impurities are introduced into the products, resulting in high costs, low production, and small scale. There are not many reports on the use of physical fields to prepare hydrogen storage alloys, and there is even less research on the preparation of magnesium based hydrogen storage alloys.

In fact, when using external physical field processing technology to prepare alloy materials, the interaction between metal and physical field can improve their performance. This technology has the advantages of being environmentally friendly and easy to operate. At present, the research hotspots in this field mainly focus on the following three aspects: 1) allowing current to pass through the metal melt, i.e. current processing; 2) Allow the metal melt to solidify in a magnetic field, i.e. magnetic field treatment; 3) Perform ultrasonic treatment on metal melts. How to successfully apply these technologies to the preparation of hydrogen storage alloys is a new topic that needs to be studied.

Canadian researchers used nanometer magnesium powder plus zirconium nickel (1.6) chromium (0.4) nanometer powder for high-energy mechanical grinding to prepare amorphous magnesium zirconium nickel chromium alloy. Compared with crystalline alloy, hydrogen desorption kinetics performance is better, hydrogen desorption speed is much faster, and the quality of hydrogen released within 30 minutes at 573K is large (4.3mass% H). X-ray diffraction shows that there is no reaction between magnesium and zirconium nickel chromium alloy during ball milling, activation, and cycling processes. This indicates that amorphous zirconium nickel chromium is an effective hydrogen absorbing alloy.

The magnesium nickel alloy developed by Sung Kyun Kwan University in Japan is relatively economical. Mechanical grinding was carried out under a 2MPa hydrogen atmosphere, and after 72 hours of grinding, the maximum hydrogen absorption reached 3.9 mass% H. It seems that the co existence of nanocrystals and non nanocrystalline phases in the composite phase is the reason for the improved desorption kinetics performance. The magnesium alloy developed by the university has a particle size less than 10nm.

K. Tanaka et al. from Nagoya University of Science and Technology are developing magnesium nickel rare earth (LaNd) alloys with particle sizes ranging from 50-100nm, which exhibit excellent hydrogen absorption kinetics. The alloys developed by the school include Mg17Ni3, Mg3Ni, and Mg16Ni3La. According to reports, the nano crystal structure obtained by mechanical grinding method has improved hydrogen storage capacity. Activation is not required below 473K. After absorbing hydrogen for 1 hour, the hydrogen storage capacity reaches 3.4 mass% H. If it is rich in nanoscale Mg2Ni alloy powder, it can reach a hydrogen storage capacity of 3.53 mass% H after hydrogen absorption.

Japanese researcher Yama Moku believes that the preparation of nanocrystalline amorphous alloys using magnesium nickel alloy and nickel powder ball milling is achieved through ball milling of magnesium nickel materials. The second step is to make Mg2Ni and Ni adhere to each other in the powder particles. The third process is the formation of amorphous nano MgNi phases at grain boundaries as the mechanical alloying time prolongs. The alloy hydride with the maximum hydrogen storage capacity of amorphous nano phase obtained by ball milling is MgNiH1.9.

The existing magnesium based alloys are Mg2Ni, Mg2Cu, and MgLa. Magnesium based alloys are generally compounded with three types, namely Mg/AB, Mg/AB2, and Mg/AB5. Zalusk et al. recently reported that ball milling of magnesium and nickel powder can directly form chemically equivalent Mg2Ni, with an average grain size of 20-30nm and much better hydrogen absorption performance than ordinary polycrystalline materials. Ordinary polycrystalline Mg2Ni can only absorb hydrogen at high temperatures (if the hydrogen pressure is less than 20Pa, the temperature must be higher than 523K), while nanocrystalline Mg2Ni can absorb hydrogen below 473K without activation treatment. After the first hydrogenation cycle of 573K, the hydrogen content can reach about 3.4 mass% H. In the subsequent cycling process, the hydrogen absorption rate is four times faster than that of ordinary polycrystalline materials. Zhejiang University uses mechanical grinding to produce alloy ZrCr2Mg2Ni, which is then heat treated to obtain a nanocrystalline C14 structure. The discharge capacity is similar to that of argon melted alloys, but activation is much easier.

AB2 type hydrogen storage materials are divided into two categories: zirconium based and titanium based. Their binary alloys have high hydrogen storage capacity, easy activation, and good kinetic performance. By adding alloying elements, better comprehensive properties can be obtained. At present, there are two problems in the large-scale application of hydrogen storage metal materials: one is how to reduce the cost of materials, and the other is how to save precious metal resources.

TiMn2 hydrogen storage material has a lower cost and is a nickel free hydrogen storage material suitable for large-scale engineering applications. Moreover, China is a country rich in titanium production. When the chemical ratio of Ti to Mn significantly deviates from TiMn2, it still exhibits a single Laves phase characteristic. After replacing some Ti or Mn in TiMn2 with other transition alloy elements such as Zr, V, Cr, Cu, and Mo, the hydrogen absorption and desorption performance of the material can be significantly improved. Pu Shengxiao et al. studied Ti-Mn quaternary alloys: Ti1-xZrxMn2-yBy (x=0-0.5, y=0-1.5, B=Mo, Cu, Co, Ni, Cr, Fe, V, etc.). Representative alloys are the Ti1-xZrxMn2-yMoy (x=0.1-0.3, y=0.1-0.3) and Ti1-xZrxMn2-yCuy (x=0.2-0.5, y=0.1-0.5) alloy series.

X-ray diffraction shows that these pseudo binary alloys all have a single-phase C14 type crystal structure, with lattice constants located between TiMn2 and ZrMn2. In these two series, as the Zr content increases or the elements replacing Mn decrease, corresponding to changes in their lattice constants, the platform pressure decreases. This is consistent with the law of the Ti Mn binary system, that is, the larger the lattice constant, the greater the hydrogen absorption amount, and the lower the platform pressure.

The Panasonic Institute of Technology in Japan found that Ti0.8Zr0.2Mn1.2Cr0.8 has good hydrogen storage properties in the Ti Zr Mn Cr quaternary system. The Metal Materials Research Laboratory of Zhejiang University found that Ti0.8Zr0.2Mn1.8Nd0.2 absorbs 180cm3/g hydrogen and releases 140cm3/g hydrogen at 323K, with good platform characteristics and almost no lag, making it a promising material for application.

Hydrogen storage containers made of metal hydrides can easily provide hydrogen sources for fuel cells, which is also an important application field of hydrogen storage materials, especially for high-capacity magnesium based hydrogen storage materials. Currently, we are actively developing large-scale hydrogen storage containers.

For example, Kawasaki Heavy Industries in Japan uses 1000 kg of lanthanum rich mixed rare earth nickel aluminum alloy to make a 175m3 hydrogen storage container. Compared with high-pressure gas cylinders with the same volume, the weight of the container is reduced by 30% and the volume is reduced by 80%. The Japanese Institute of Chemical Technology used 1200kg of MmNi5 series alloy to make a 240m3 hydrogen storage device. Zhejiang University in China has also developed a hydrogen storage device with a capacity of 240m3, mainly used for hydrogen recovery and purification.

At present, only Toyota of Japan has developed a hydrogen storage device using metal hydride to store hydrogen for fuel cell vehicles in the world. In addition, the United States is conducting tests on a golf cart powered by fuel cells using metal hydride to supply hydrogen.

In terms of fuel cell miniaturization applications, the American Hydrogen Energy Company has developed a fuel cell powered wheelchair for the disabled and a 40 watt portable fuel cell power supply, which can be used for laptops, portable radios or other portable devices, by providing hydrogen with metal hydride;

A Japanese company has developed a small fuel cell lighting power supply using metal hydride to provide hydrogen; Canadian Ballard Company has developed a titanium series metal hydride hydrogen storage device matched with the fuel cell in the notebook computer; At present, the development of practical fuel cells in China is still in its infancy. However, with the growth of social demand and the progress of science and technology, the application of fuel cells will become more and more widespread. Therefore, it is imperative to carry out industrial production research on hydrogen storage materials for fuel cell hydrogen sources.

In recent years, with the increasing research and development of fuel cells, the application of hydrogen storage materials as hydrogen storage media has once again attracted people's attention. While improving traditional hydrogen storage methods (mainly high-pressure tank hydrogen storage and liquid hydrogen storage), people place greater hopes on metal hydride hydrogen storage. The key problem is to find a new type of hydrogen storage material with large hydrogen storage capacity and moderate working conditions.

The research on magnesium based hydrogen storage composite materials has only emerged in the past decade, and its basic research and application prospects are very broad. Although some researchers have conducted preliminary research in this field, a large amount of work still needs to be systematically and deeply carried out. At present, due to the use of a single system of hydrogen storage alloys alone, they cannot meet the needs of practical applications well.