A promising low-carbon energy source

Deep underground, natural hydrogen can form when water reacts with iron-rich rocks from the Earth’s mantle. During this natural process, known as serpentinization, molecular hydrogen (H₂) is continuously released—unlike green hydrogen, which requires electricity to produce, or grey hydrogen, which relies on fossil fuels. Seeps of natural hydrogen have already been measured at the surface at numerous locations worldwide. In some places, such as Mali and the Philippines, communities have even used it as a local energy source.

Study areas: Western Pyrenees and Northern California

The challenge for science has been to understand how much is truly available and on what timescales it can be tapped. To address these questions, researchers in geophysics, geology, geochemistry and physics from the LIAG Institute for Applied Geophysics, the Federal Institute for Geosciences and Natural Resources, the Czech Academy of Sciences, the Universities of Montpellier and Toulouse, the United States Geological Survey and MARUM - Center for Marine Environmental Sciences at the University of Bremen worked together.

The team investigated two geologically well-documented regions: the Western Pyrenees and Northern California. In both areas, two different ultramafic rocks from the upper mantle react with water at great depth. In the Western Pyrenees, these are fertile lherzolites that were brought to comparatively shallow depths during earlier rifting processes. In Northern California, the team examined depleted harzburgites of the Coast Range Ophiolite. Hydrogen is detectable at the surface at both sites.

Geophysics makes production-rate estimates more robust

Because serpentinisation takes place deep underground, it cannot be observed directly. This is where geophysics comes in: using gravity, magnetic and seismic data, the team reconstructed the distribution, volume, temperature and degree of alteration of the mantle rocks in three dimensions. The geophysical models were then coupled with thermodynamic and kinetic calculations of fluid-rock reactions. Rather than estimating theoretical maximum potential, the study therefore models the actual rates at which hydrogen is generated under real geological conditions, while accounting for physical and chemical constraints that previous studies largely overlooked. The result is a more realistic and actionable picture of natural hydrogen as a resource.

Several hundred tonnes per year - less than expected

For the Western Pyrenees, the study estimates production of around 308 tonnes of hydrogen per year, compared with around 515 tonnes per year for Northern California. These values are substantially lower than earlier theoretical estimates, which projected hundreds of thousands to millions of tonnes per year. At the same time, they are consistent with measurements of natural hydrogen fluxes from comparable geological systems worldwide. This increases confidence that the model captures the true order of magnitude of the process.

"Our results provide a realistic baseline that tells us where to look, which conditions favour accumulation and what timescales need to be considered. That is exactly what responsible exploration of any new energy resource requires," explains Dr Rodolfo Christiansen, lead author of the study, which was carried out as part of his scientific work at the LIAG Institute for Applied Geophysics.

The lower production rates arise mainly because earlier approaches focused predominantly on the available rock volumes. The new modelling also accounts for processes that limit natural hydrogen release. These include the saturation of dissolved hydrogen in pore fluids, which slows formation once the fluid reaches its solubility limit, and the rate at which rock surfaces come into contact with water. Once these factors are incorporated into the model, production rates fall significantly.

More realistic estimates create new opportunities for exploration

At the same time, the study regards the more realistic determination of production rates as an opportunity: it enables exploration programmes to be targeted more effectively.

"Large accumulations of hydrogen remain possible, but they require time and the right geology. With this knowledge and the open-source tool PoNHy, scientists and the exploration industry can investigate more systematically where favourable generation and storage conditions coincide," Christiansen emphasises.

Newly developed PoNHy tool enables global exploration

As part of the study, the team developed the open-source tool PoNHy, short for Potential for Natural Hydrogen. The modelling tool integrates three-dimensional geophysical inversion with the thermodynamics and kinetics of fluid-rock reactions.

PoNHy is freely available on GitHub and Zenodo and can be applied to any serpentinising geological system worldwide. It provides the scientific community and the exploration industry with a shared basis for further development, enabling geological settings to be compared, regional potential to be assessed more realistically and particularly promising study areas to be selected more systematically.

Publication:

Christiansen, R., Sobh, M., Ostertag-Henning, C. et al. Controls on natural hydrogen generation during serpentinization of mantle rocks. Nat Commun 17, 5211 (2026). https://doi.org/10.1038/s41467-026-73920-5

Background information

Code and Data:

• PoNHy source code and data: https://doi.org/10.5281/zenodo.18733249
• Latest version on GitHub: https://github.com/RodolfoChristiansen/PoNHy

Funding:

The development of PoNHy was supported by the European Union's Horizon 2020 Research and Innovation Programme and the German Federal Ministry of Research, Technology and Space (BMFTR)  under the HyAfrica Project, part of the Long-term Europe-Africa Partnership on Renewable Energy (LEAP-RE). Additional support was provided by the German Research Foundation (DFG) under Germany's Excellence Strategy "The Ocean Floor, Earth's Uncharted Interface".

Scientific contact
Dr Rodolfo Christiansen (lead author)
r.christiansen(at)mantle8.com

Public Relations LIAG
Greta Clasen
presse(at)liag-institut.de