Hydrogen is a fuel with a high specific energy or energy per unit mass, but it has a low energy density or energy per
mass, but has a low energy density or energy per unit volume compared to other fuels.
other fuels. As a result, huge volumes of hydrogen are required under standard conditions to provide energy for high-demand processes. This problem is particularly relevant for its application in the transport sector.
Therefore, three alternatives have been proposed to store the largest amount of hydrogen in the smallest possible volume:
Hydrogen in a liquid state.
Hydrogen as part of a solid compound.
In any case, it should be borne in mind that hydrogen is the least dense gas and the substance known to have the second lowest boiling point after helium, which makes it very difficult to store.
Hydrogen is a fuel that provides a large amount of thermal energy when burned in air, which makes it very difficult to store. when burned in air, since its reaction with oxygen is highly exothermic. The hydrogen can also combine with oxygen in the air in a fuel cell to provide electricity as well as heat. Both the combustion of hydrogen and its oxidation in fuel cells are clean processes that generate almost no emissions of pollutant gases or particulate matter harmful to health.
Although hydrogen can also be used as a fuel in internal combustion engines or gas turbines with a significant reduction in associated emissions, fuel cells are the main technology for its energy use.
Hydrogen is an excellent energy carrier, but the development of lightweight solid-state materials for compact, low-pressure storage is an enormous challenge.
Complex metal hydrides are a promising class of hydrogen storage materials, but their feasibility is usually limited by hydrogen absorption and slow release. Nanoconfinement (infiltrating the metal hydride into a matrix of another material such as carbon) can, in certain cases, help make this process faster by shortening hydrogen diffusion paths or changing the thermodynamic stability of the material.
However, nanoconfinement can have another potentially more important consequence since the presence of internal “nanointerfaces” within nanoconfined hydrides can alter the phases that appear when the material is cycled.
By analyzing high-capacity lithium nitride (Li 3 N) under nanoconfinement, using a combination of theoretical and experimental techniques, we demonstrated that the pathways for hydrogen adsorption and release were fundamentally changed by the presence of nanointerfaces, leading dramatically to faster yield and reversibility.
Hydrogenation forms a mixture of lithium amide and hydride (light blue) as an outer shell around a carbon nanoconfined lithium nitride particle (dark blue). The nanoconfinement suppresses all other intermediate phases to avoid interface formation, which has the effect of greatly improving hydrogen storage performance.
On the other hand, hydrogen has been used for many years as a raw material in the chemical, petrochemical, pharmaceutical, pharmaceutical and other industries.
chemical, petrochemical, pharmaceutical, electronics, metallurgical and aerospace industries. Two of the most important chemical processes in which hydrogen is used as a reagent are the production of ammonia and the production of methanol. Both ammonia and methanol are two highly valued products in the chemical industry for the production of fertilizers and many other compounds. In the synthesis of ammonia, hydrogen reacts with nitrogen and in the synthesis of methanol, hydrogen reacts with carbon monoxide:
3 H2 + N2 -! 2 NH3 2 H2 + CO -! CH3OH
In both cases, a catalyst is required to carry out the reaction since the H-H bond of the hydrogen molecule is strong (436 kJ/mol). In addition, it is necessary to pressures, since in both processes there are more reactant molecules than product molecules products. In the petrochemical industry, hydrogen is used in many operations, for example in the removal of sulfur from petroleum and renders the catalysts used in its cracking and transformation into lighter fractions useless. In the metallurgical industry, hydrogen is used because of its ability to reduce metal oxides and prevent oxidation of metals and alloys in certain treatments at elevated temperatures. In the aerospace industry, hydrogen is used as rocket fuel, where it utilizes the energy released during its oxidation with oxygen or fluorine. In the electronics industry, hydrogen is used as a carrier for trace compounds (arsine, phosphine, etc.) in the manufacture of semiconductor layers.
When comparing the different storage technologies available, it is not sufficient to quantify the amount of hydrogen storage from the gravimetric capacity or mass percent that it is capable of storing gravimetric capacity or percentage by mass that it is capable of storing. In the case of a material’s hydrogen storage In the case of the hydrogen storage capacity of a material, this percentage usually refers to the mass of hydrogen stored divided by the mass of hydrogen stored plus the mass of the material storing it storing the hydrogen. However, the hydrogen storage capacity of a system represents the mass of hydrogen stored in the system represents the mass of stored hydrogen divided by the amount resulting from adding the mass of the hydrogen in the storage material, the mass of the storage material, and the mass of the storage vessel. Obviously, in the latter case the storage capacity values are much lower. Another useful parameter, especially in mobile and portable applications, is the volumetric capacity, defined as the mass of hydrogen stored per unit volume of the storage material or system under consideration.
The ideal storage method should have high density values and be fully reversible, as well as economical and safe.
The storage of solid hydrogen in the form of metallic or non-metallic hydrides represents an intermediate situation between storing liquefied or compressed hydrogen. If the hydrogen is stored at higher pressure, the tank volume will be smaller, but much heavier. The determining factor for hydrogen storage in tanks is the wall thickness. In the case of liquid hydrogen storage tanks, the wall must provide consistency and structural strength, as well as thermal insulation, which complicates their manufacture and maintenance.
Although in terms of gravimetric and volumetric capacity values, liquefied hydrogen and some hydrides may be the most advantageous at present, there are several limitations that significantly reduce the performance of these technologies. In addition to the gravimetric and volumetric capacity of the storage systems, the filling and emptying time of the storage vessel must be taken into account, as well as other additional requirements during the filling and emptying process, such as temperature and/or pressure control, energy efficiency in both loading and unloading, leakage losses, the ability to adapt to different shapes and spaces, economic and safety aspects, etc.