Hydrogen is the simplest chemical element : its nucleus consists of a single proton and its atom has only one electron. The molecule of dihydrogen (H2) is made up of two hydrogen atoms.
Hydrogen is commonly used to refer to dihydrogen.

Burning 1 kg of hydrogen releases almost 4 times more energy than 1 kg of gasoline and produces only water :

2H2 + O2 -> 2H2O

Hydrogen is very abundant on the Earth's surface but does not exist in its pure state. It is always bound to other chemical elements, in molecules such as water and hydrocarbons. Living organisms (animal or plant) are also composed of hydrogen.
Biomass is therefore another potential source of hydrogen.

Extracting hydrogen from these primary resources such as hydrocarbons, biomass and water requires an energy input.
Hydrogen could be almost inexhaustible, provided that it can be produced in sufficient quantities at a competitive cost and from low-carbon energy (nuclear

Operation of a nuclear power plant

The components of a nuclear power plant. The main components of a nuclear power plant : Nuclear reactor : The nuclear reactor is the heart of the plant where the nuclear fission reactions take place. It contains nuclear fuel, such as enriched uranium or plutonium, as well as moderators and reactor controls to regulate nuclear reactions.
Steam Generator :

and renewables).
Hydrogen technologies are the set of technologies studied to produce hydrogen, store it and convert it for energy purposes.

There are several current ways to produce hydrogen, each with its own advantages and disadvantages in terms of cost, energy efficiency, environmental impact :

Water electrolysis :
Water electrolysis is a process that uses electricity to break down water (H2O) into hydrogen (H2) and oxygen (O2). There are two main types of electrolysis : alkaline electrolysis and proton exchange membrane (PEM) electrolysis. Water electrolysis can be powered by electricity from renewable sources such as solar or wind power, making it an environmentally friendly method of hydrogen production.

Methane steam reforming :
Steam methane reforming is a chemical process that uses methane (CH4), usually in the form of natural gas, to produce hydrogen and carbon dioxide (CO2). This process is commonly used on a large scale in the chemical industry to produce hydrogen. However, it also emits CO2, making it a less environmentally friendly method of hydrogen production compared to water electrolysis.

Biomass gasification :
Biomass gasification is a process that converts organic matter into syngas, which can then be converted into hydrogen. This method uses agricultural, forestry or urban waste as a feedstock, thus offering the possibility of producing hydrogen from renewable and sustainable sources.

Water pyrolysis :
Water pyrolysis is a thermochemical process that uses heat to break down water into hydrogen and oxygen. While this method can be efficient in terms of energy efficiency, it requires high temperatures and specific conditions, which can make it more complex to implement.

Solar photoelectrolysis :
Solar photoelectrolysis is a method of producing hydrogen that uses solar cells to convert sunlight into electricity, which is then used to power the water electrolysis process. This method uses solar energy as a renewable source of electricity, but it can be limited by the efficiency of the solar cells and the associated costs.

Hydrogen storage is an active area of research and development due to its potential as a clean and versatile energy carrier. Here are some of the current ways to store hydrogen :

Gas compression :
Hydrogen can be stored in gaseous form compressed at high pressure in reinforced cylindrical tanks. High-pressure storage tanks can be made of steel or composite materials to withstand high pressures. However, compressing hydrogen at high pressures requires specific infrastructure and can lead to energy losses.

Liquefaction :
Hydrogen can be cooled and liquefied to very low temperatures (below -253 degrees Celsius) for high-energy density storage. Storage in liquid form reduces the volume occupied by hydrogen, but requires expensive cooling equipment and significant energy losses during the liquefaction process.

Adsorption on solid materials :
Hydrogen can be adsorbed onto solid materials with a porous structure, such as activated carbons, zeolites, porous organic metals (MOFs), or organic-inorganic hybrid materials. These materials have a large specific surface area and can adsorb hydrogen at moderate pressures and ambient temperatures. However, hydrogen adsorption can be reversible but requires high pressures for desorption.

Chemical storage :
Hydrogen can be stored in the form of chemical compounds that release it when they are broken down. For example, hydrogen can be stored in the form of metal hydrides or organic compounds such as organic hydrides. The release of hydrogen can be triggered by heating, catalysis, or other methods. However, chemical storage systems may have specific requirements in terms of temperature, pressure, and material regeneration.

Underground storage :
Hydrogen can be stored underground in suitable geological formations such as saline aquifers, natural cavities, or porous reservoirs. Underground storage offers a large storage capacity and can reduce security and infrastructure risks. However, this requires suitable geological sites and safe and reliable storage techniques.

Hydrogen has a wide range of potential applications in various sectors due to its unique characteristics, including its versatility, cleanliness when produced from renewable energy sources, and its potential to reduce greenhouse gas emissions. Some of the potential applications of hydrogen include :

Clean mobility :
Hydrogen vehicles, such as fuel cell cars, buses, trucks, and trains, offer a clean alternative to internal combustion engine vehicles. They generate electricity by combining hydrogen with oxygen from the air, generating only water and heat as by-products, reducing emissions of air pollutants and greenhouse gases.

Energy storage :
Hydrogen can be used as a means of large-scale energy storage, including to store energy produced by intermittent renewable sources such as solar and wind power. Excess electricity can be used to produce hydrogen by electrolysis of water and then stored for later use as a fuel or energy source.

Industrial production :
Hydrogen is widely used in the chemical industry for the production of ammonia, used in the manufacture of fertilizers, as well as in the production of various chemicals, including methanol, chlorinated hydrogen, and hydrocarbon. It can also be used as a reducing agent in the production of steel and other metals.

Electricity production :
Hydrogen fuel cells can be used to generate electricity in a clean and efficient way, for both stationary and mobile applications. They are used in commercial and residential buildings as a backup source of electricity or as a primary source of power. They can also be used to supply electricity to power grids during peak demand periods.

CResidential and commercial heating :
Hydrogen can be used as a fuel for residential and commercial heating, replacing natural gas or fuel oil. Hydrogen boilers are being developed and could offer a low-carbon alternative for heating buildings.

Space applications :
In the space industry, hydrogen is used as a fuel to propel space launch vehicles, especially in the upper stages of rockets. Liquid hydrogen is often used as a propellant due to its high energy density and clean combustion.