Hydrogen is the simplest (consisting only of one proton and one electron) and most abundant chemical element in the universe. It is found mainly in the form of hydrogen gas (H2) in stars and gaseous planets, and is also found together with other elements to form a wide variety of chemical compounds, such as water (H2O) and most organic compounds.
Hydrogen gas is, under normal conditions of pressure and temperature, colorless, odorless, non-toxic and flammable, with a boiling point of -252.77ºC and a melting point of -259.13ºC. It can react with oxygen (O2) giving off energy and forming water. This reaction is known as combustion and in it hydrogen is the fuel (1).
There are other combustible materials, such as coal, natural gas, gasoline (petroleum), which are known as fossil fuels because they come from compounds formed by the activity of living beings millions of years ago. All of them can also react with oxygen and produce energy. For example, for methane (natural gas) it would be (2).
Our energy system is based on the use of these fuels. We therefore live in what has been called the "fossil fuel society." A large part of the activities carried out by the human being are possible thanks to the energy of these fuels; for example for transport (cars, planes, ships), heating buildings, machine work, in industry, etc.
There are two main reasons why it is desirable to replace fossil fuels with hydrogen:
- The combustion of hydrogen does not pollute, it only produces water as a by-product (reaction 1), while fossil fuels produce CO2 (reaction 2) that remains in the atmosphere as a pollutant and is one of the main causes of what is called the "greenhouse effect". ".
- Fossil fuel reserves will run out sooner or later, while hydrogen will remain inexhaustible.
However, this substitution is complicated at the present time. In the first place, because, unlike fossil fuels, hydrogen is not found in a free state on our planet, but in the form of compounds such as water or most organic compounds; therefore, it is necessary to develop systems capable of producing it efficiently. On the other hand, it would be necessary to enable new infrastructures for the supply of hydrogen; In other words, a complete network of hydrogen service stations or “hydrogenerators” would have to be built, which implies a heavy investment.
Hydrogen, therefore, cannot be considered a primary source of energy -like fossil fuels-, but rather a means of transporting energy, which is why it is called an energy vector. In this way, hydrogen will be transformed into energy and heat in an efficient and clean way, through a chemical process achieved in equipment called a "fuel cell".