Orange hydrogen? We already knew about grey, blue and green hydrogen. Here is the orange version, named after a process developed by the CNRS (the French National Centre for Scientific Research).

Some geological formations have the property to generate hydrogen naturally, by oxidation-reduction between the iron contained in their minerals and water. It turns out that iron – which makes up about 5% of the earth’s mass crust – could become a huge hydrogen factory. A research team including scientists from CNRS-INSU* has developed a technique, called “orange hydrogen“, to accelerate this natural production in order to exploit it for the energy transition.

This hydrogen, whose name refers to the orange colour of the iron oxides produced, combines hydrogen generation with CO₂ sequestration. The advantage is that the targeted geological formations can also be used as a repository to trap CO₂. When they come into contact with water enriched with carbon dioxide, a second chemical reaction occurs that precipitates carbonates, i.e. CO₂ in solid form, thus preventing it from contributing to the greenhouse effect and global warming.

The exploitation of orange hydrogen is based on injection and extraction wells, similar to geothermal power plants. The water, previously charged with CO₂, is injected into the target rock formation through a well. The water then percolates into the rock, reacts, gets rid of its CO₂, enriches with hydrogen, and is eventually recovered by extraction wells. This technique has worked on a rock core a few centimetres thick, but now it has to be scaled up.

The scientists’ calculations show that there are several million years’ worth of hydrogen sleeping under our feet.

*National Institute for the Sciences of the Universe

Article written by Laurent Meillaud, translated by Logan King and reviewed by Marina Leite.