Natural Hydrogen Opportunities: The role of geo(bio)chemistry in controlling source/sink constraints

Natural hydrogen here refers to H₂ produced abiotically by water-rock reactions such as serpentinization and radiolysis at naturally occurring rates. Decades of research have focussed towards understanding the spectrum of hydrogen producing reactions, the role of hydrochemistry, mineralogy and rock types, and recently, mapping the accumulations of such natural hydrogen around the world – particularly in continental systems [1]. The Precambrian continents are of particular interest as they host the largest extent of ultramafic rocks on the planet – including the so-called “greenstone belts”. To date, this research into natural hydrogen has largely been done by geochemists, microbiologists, astrobiologists and planetary scientists focused on the search for life in the Earth’s subsurface biosphere, or on other planets and moons in the solar system. Under this lens, microbial ecosystems have been broadly identified in the subsurface, sustained by hydrogen producing water-rock interactions in the continental crust and at the deep ocean vents and seafloor. Only recently have human populations begun to consider competing with their microbial cousins for this subsurface resource on a global scale. As a result, detailed integration of geo(microbio)chemistry into quantitative evaluation of sources and sinks for natural hydrogen has arguably been neglected by many programs investigating the economic potential for this natural resource.

Based on ground-based and subsurface measurements, Sherwood Lollar et al. (2014) and subsequent papers [1,2] demonstrated that saline fracture waters in the Precambrian continental subsurface are as rich in hydrogen as hydrothermal vents and seafloor spreading centres, and similarly produce hydrogen by a combination of hydration of mafic and ultramafic minerals and by radiolysis [3-5]. Here we provide the long-term (>10 year) monitoring data of hydrogen concentrations, volumes, and discharge rates collected from a site located in a major regional industry hub, with this location representative of many additional potential sites in close proximity in a Precambrian continental setting where natural hydrogen may likewise be available. The analysis demonstrates the hydrogen related to an active mine such as previously described in Albania [6] is not a unique phenomenon and may be more widespread and more volumetrically significant than previously identified. This raises the possibility of readily available natural hydrogen being tapped for local use in regional industry hubs where other extraction activities are already underway, and energy supply remains a critical concern. Co-investigation of microbiological communities and sinks for hydrogen are an important component of this evaluation.

[1] Sherwood Lollar et al., 2014 Nature 516 (7531): 379-382

[2] Warr et al., 2019 Chemical Geology 530:11932

[3] Lin et al., 2005 GCA 69(4):893-903

[4] Li et al., 2016 Nature Communications 7:13252

[5] Sherwood Lollar et al., 2021 GCA 294:295-314

[6] Truche et al., 2024 Science 383:618-621