Present in abundance in the Sun, hydrogen gas is nearly absent from our own atmosphere. So it has to be extracted from the molecules that contain it, such as water and organic compounds.
Today, several technological fields produce hydrogen from various sources.
The principal field uses organic compounds principally composed of hydrogen and carbon, such as natural gas, coal, and biomass. It currently accounts for over 90% of the total production of hydrogen.
The second field produces hydrogen through the decomposition of water. It uses either an electric current for electrolysis or a series of chemical reactions for the thermochemical cycles that break down the water molecules to obtain hydrogen.
A third field uses the light of the Sun. This method for producing hydrogen is still in the research phase: laboratory experiments are being conducted that seek to produce hydrogen with microscopic algae or bacteria.