Hydrogen storage alloy refers to an intermetallic compound that can reversibly absorb, store and release hydrogen in large quantities under a certain temperature and hydrogen pressure.

Hydrogen storage alloys are composed of two parts. One part is a hydrogen-absorbing element or an element (A) that has a strong affinity with hydrogen. It controls the amount of hydrogen storage and is a key element in the composition of hydrogen storage alloys. It is mainly from groups IA~VB.

Metals, such as Ti, Zr, Ca, Mg, V, Nb, Re (rare earth elements); the other part is the element (B) that absorbs little hydrogen or does not absorb hydrogen at all, which controls the reversible hydrogen absorption/desorption

Properties, play a role in regulating the heat of generation and decomposition pressure, such as Fe, Co, Ni, Cr, Cu, Al, etc.

Figure 1 lists the hydrogen storage capabilities of some metal hydrides.

At present, a variety of hydrogen storage alloys have been developed in the world. According to the number of metal constituent elements of hydrogen storage alloys, they can be divided into: binary system, ternary system and multicomponent system; according to the main metal elements of hydrogen storage alloy materials, they can be divided into

Divided into: rare earth series, magnesium series, titanium series, vanadium-based solid solution, zirconium series, etc.; and the metals that make up hydrogen storage alloys can be divided into hydrogen-absorbing types (indicated by A) and non-hydrogen-absorbing types (indicated by B). According to

Hydrogen storage alloys can be divided into: AB5 type, AB2 type, AB type, and A2B type.

?Inorganic and organic hydrogen storage materials. Some inorganic substances (such as N2, CO, CO2) can react with H2. The products can be used as fuel and can be decomposed to obtain H2. It is a new hydrogen storage technology currently being studied.

For example, the hydrogen storage reaction of the mutual conversion between bicarbonate and formate uses Pd or PdO as the catalyst, highly hygroscopic activated carbon as the carrier, and KHCO3 or NaHCO3 as the hydrogen storage agent. The hydrogen storage capacity can reach 2wt%.

The main advantages of this method are that it is easy to store and transport in large quantities and has good safety, but the hydrogen storage capacity and reversibility are not very good.

Some metals can react with water to produce hydrogen gas.

For example, NaOH is generated after the reaction, and the mass storage density of hydrogen is 3wt%.

Although this reaction is irreversible, NaOH can be reduced to metallic Na via a solar furnace.

Similarly, Li also has this process, and its mass storage density of hydrogen is 6.3wt%.

The main difficulties with this hydrogen storage method are reversibility and controlling the reduction of the metal.

At present, the application of Zn is relatively successful.

The theoretical hydrogen absorption capacity of Li3N is 11.5wt%. When kept in a hydrogen atmosphere at 255°C for half an hour, the total hydrogen absorption capacity can reach 9.3wt%.

At 200 ℃, given enough time, absorption will occur.

Under 200 ℃ vacuum (1 mPa), 6.3wt% of hydrogen is released, and the remaining hydrogen can only be released at high temperature (higher than 320 ℃).

Unlike other metal hydrides, Li3N has two plateaus in the PCT curve: the first has a lower plateau pressure, and the second is a slope.

Organic hydrogen storage technology began in the 1980s.

Hydrogen storage in organic matter is achieved by using a pair of reversible reactions between unsaturated liquid organic matter and hydrogen, that is, using the reversible reactions of catalytic hydrogenation and dehydrogenation.

The hydrogenation reaction realizes the storage of hydrogen (chemical bonding), and the dehydrogenation reaction realizes the release of hydrogen.

As a new hydrogen storage technology, organic liquid hydride hydrogen storage has many advantages: large hydrogen storage capacity, such as the theoretical hydrogen storage capacity of benzene and toluene are 7.19wt% and 6.18wt% respectively; the properties of hydrogen storage agent and hydrogen carrier are similar to

It is similar to gasoline, so it is safe and convenient to store, transport, maintain and maintain, making it easy to utilize existing oil storage and transportation facilities; unsaturated organic liquid compounds can be used as hydrogen storage agents multiple times, with a lifespan of up to 20 years.

However, this type of method has relatively harsh conditions during hydrogenation and dehydrogenation, and the catalyst used is easy to deactivate, so further research is still being conducted.

?Nano hydrogen storage materials Nanomaterials exhibit many unique physical and chemical properties due to their quantum size effect, small size effect and surface effect, and have become the forefront of research in physics, chemistry, materials and other disciplines.

After the hydrogen storage alloy is nanosized, many new thermodynamic and kinetic properties also appear, such as significantly improved activation performance, higher hydrogen diffusion coefficient and excellent hydrogen absorption and release kinetic properties.

Nanohydrogen storage materials usually have better performance than ordinary hydrogen storage materials in terms of hydrogen storage capacity, cycle life and hydrogenation-dehydrogenation rate. The increase in specific surface area and surface atomic number causes changes in metal properties and becomes a bulk material.

properties that it does not have.

Due to the small particle size, hydrogen is more likely to diffuse into the interior of the metal to form interstitial solid solutions, and the surface adsorption phenomenon is also more significant. Therefore, the nanometerization of hydrogen storage materials has become a hot topic in current research on hydrogen storage materials.

Nanotechnology of hydrogen storage alloys provides new research directions and ideas for the research of hydrogen storage materials with high hydrogen storage capacity.

Tanaka et al. summarized the reasons for the excellent dynamic properties of nano-hydrogen storage alloys: (1) A large number of nano-grain boundaries make it easy for hydrogen atoms to diffuse; (2) Nano-crystals have extremely high specific surface areas, making it easy for hydrogen atoms to penetrate into hydrogen storage materials.

Internal; (3) Nano-hydrogen storage materials avoid long-distance diffusion of hydrogen atoms through the hydride layer, and the diffusion of hydrogen atoms in the hydride is the most important factor controlling the dynamic performance.