Geologic hydrogen is discovered in a chromite mine

For all the promise of hydrogen as an alternative energy source, not all of it is created equal. Most commercially produced H₂ is a byproduct of fossil-fuel processing, which pollutes the atmosphere with carbon dioxide. So-called green H₂ is made by splitting water with energy from solar panels or wind turbines, but that method is expensive .

A much cheaper possibility is extracting naturally occurring H₂ from deep underground reservoirs. One well-known site in Mali was discovered in 1987 when well diggers were drilling for water—and others are likely in Oman and Turkey, based on observations of H₂ seeps at the surface. As long as the light, reactive element is contained by salt layers or other rock formations that trap gas, it could be burned to produce carbon-free energy. The Malian H₂ was of sufficient purity and flowed fast enough to power a 30-kilowatt generator.

Now Laurent Truche of Grenoble Alpes University in France and his colleagues have characterized another source of geologic H₂ located in a chromite mine 620 m below Bulqizë, Albania. The flow rate of the H₂ deposit is an order of magnitude higher than at similar outgassing sites in Oman and Turkey, and the purity of the flow, about 84% H₂ by volume, means that the H₂ could readily fuel a gas turbine to produce energy. The company that owns the Bulqizë mine, Albania-based AlbChrome, gave the researchers access to the mine. Working for six years using a network of 38 boreholes, they measured a relatively constant H₂ flow rate of some 200 tons annually.

The Bulqizë mine consists predominantly of uplifted oceanic crust, which geologists call an ophiolite. Truche and colleagues identified several types of rocks and minerals in the Bulqizë ophiolite. When exposed to the high pressures and temperatures in the subsurface, the minerals can react with water to form other minerals, methane, and H₂. That process appears to be happening now in the mine, but the researchers say that some of the H₂, which is leaking from a deep fault zone, may have formed from previous chemical reactions between 160 million to 165 million years ago.

Ophiolites elsewhere may also have H₂, but Truche cautions that “one must consider the drawbacks of H₂ exploitation. These geological environments harbor a fragile deep biosphere that relies on H₂ as an energy source.” Safety is a concern too: Three major gas explosions, the most recent one last year, have rocked the mine since seeping H₂ was discovered there in 1992. Although safety precautions have improved, says Truche, “the risk is still there.” (L. Truche et al., Science 383, 618, 2024 .)