Hydrogen storage materials

Hydrogen is a fuel with a very high calorific value. The hydrogen-oxygen combustible combustion product is the cleanest substance and has no pollution. The most promising fuel cells in the future are also mainly hydrogen.
The source of hydrogen is very abundant. If hydrogen can be produced from water, it can be said to be inexhaustible and inexhaustible. There are two traditional hydrogen storage methods. One method is to use high-pressure cylinders (hydrogen cylinders) to store hydrogen. However, the volume of hydrogen gas stored in cylinders is small, and there is the risk of explosion; the other method is to store liquid hydrogen, but the liquid storage The box is very large and requires excellent insulation to insulate it. In recent years, a new type of simple hydrogen storage method has emerged, namely the use of hydrogen storage alloys (metal hydrides) to store hydrogen.
Studies have shown that under certain temperature and pressure conditions, some metals can "absorb" hydrogen in large quantities, react to produce metal hydrides, and at the same time release heat. Thereafter, these metal hydrides are heated and they decompose again, releasing the hydrogen stored therein. These metals, which "take up" hydrogen, are called hydrogen storage alloys. Its hydrogen storage capacity is very strong. The density of hydrogen stored in a unit volume is 1000 times that of gaseous hydrogen under the same temperature and pressure conditions, that is, equivalent to a high pressure of hydrogen where 1000 atmospheres are stored. Hydrogen storage alloys are all solids and require hydrogen to be released through heating or decompression when hydrogen is used. Therefore, hydrogen storage alloys are an extremely easy and convenient hydrogen storage method. At present, hydrogen storage alloys under research and development mainly include titanium-based hydrogen storage alloys, zirconium-based hydrogen storage alloys, iron-based hydrogen storage alloys, and rare earth hydrogen storage alloys.
Hydrogen storage alloys also have the energy conversion function of converting the chemical energy in hydrogen storage into mechanical energy or thermal energy. The hydrogen-absorbing alloy emits heat when absorbing hydrogen and absorbs heat when desorbing hydrogen. This heat-absorbing and heat-recycling cycle can be used to store and transmit heat, and to produce refrigeration or heating equipment. It can also be used to purify and recover hydrogen, which can purify hydrogen to very high purity. For example, using a hydrogen storage alloy, ultrapure hydrogen with a purity of more than 99.9999% can be obtained at a very low cost.
The rapid development of hydrogen storage alloys has opened up a broad path for the use of hydrogen. At present, China has successfully developed a hydrogen-powered vehicle that uses 90 kg of hydrogen storage material and can travel 40 kilometers at a speed of over 50 kilometers per hour. In the future, not only will vehicles use fuel cells, but also aircraft, naval vessels, and space vehicles will use fuel cells as their primary or auxiliary energy sources. In addition, cadmium in the nickel-cadmium battery (Ni-Cd) used in a large amount is toxic, so that the waste battery is complicated in processing and the environment is contaminated. Nickel-metal hydride batteries have the advantages of large capacity, safety, non-toxicity, and long service life compared with nickel-cadmium batteries. The development of nickel-hydrogen batteries (Ni-MH) made from hydrogen-absorbing alloys is another important area for the future use of hydrogen storage materials.