A recent review in Energy & Environmental Science highlights geologic hydrogen as a promising alternative to conventional hydrogen production, offering a potential path to meet global decarbonization goals while addressing key cost and scalability challenges.
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Why Rethink Hydrogen Production?
Hydrogen plays a central role in industrial operations, energy storage, and the broader shift toward carbon-neutral systems. However, current production methods - such as steam methane reforming and electrolysis using renewable energy - face notable obstacles. These include high costs, environmental impacts, and scalability issues.
To address these limitations, the review introduces geologic hydrogen - hydrogen that occurs naturally or can be stimulated within the Earth's subsurface - as a promising low-emission solution.
The study assesses its resource potential, examines the geological mechanisms of hydrogen generation, reviews exploration and extraction techniques, and outlines the research required to advance the field.
Where Does Geologic Hydrogen Come From?
A key focus of the review is understanding the origin and distribution of geologic hydrogen. Using data from the Global Lithological Map (GLiM), researchers found that sedimentary rocks - typically known for hydrocarbon storage - are not major contributors to natural hydrogen production. Instead, the most significant sources are ultramafic and mafic rocks, rich in magnesium and iron, which produce hydrogen through a process known as serpentinization.
Additional hydrogen generation pathways include:
- Radiolysis of water: This occurs in continental cratons, where radioactive decay triggers radiochemical reactions that release hydrogen.
- Magmatic degassing: Hydrogen emitted from magmatic sources can move through porous rocks or become trapped, making it accessible for extraction.
Exploring Underground Hydrogen
The review details several exploration strategies used to detect and assess hydrogen-rich zones. These fall into two categories:
- Surface methods: Techniques such as geochemical sampling and remote sensing help detect hydrogen seepage and diffuse emissions at the Earth’s surface.
- Subsurface methods: Seismic, magnetic, and gravity surveys, along with well-logging, are used to map geological structures and locate potential reservoirs.
Notably, the integration of machine learning and data analytics is helping researchers improve the accuracy and efficiency of these techniques, enabling real-time insights during exploration and potential production.
How Hydrogen Accumulates Underground
Understanding how hydrogen migrates and accumulates is essential for effective extraction. The review highlights three primary migration mechanisms: diffusion, advection, and buoyant flow. Subsurface properties, such as porosity and permeability, influence these processes.
The formation and stability of underground hydrogen reservoirs depend on:
- Caprock integrity, which prevents hydrogen from escaping
- Structural traps and stratigraphic features, which help concentrate the gas
- Capillary trapping, which holds hydrogen in place within porous formations
A detailed geomechanical analysis is crucial for evaluating these features and guiding successful extraction strategies.
Stimulated Hydrogen Production: A Technological Outlook
Beyond natural hydrogen, the review examines ways to stimulate production artificially. Techniques like hydraulic fracturing can enhance serpentinization by increasing rock permeability, potentially boosting hydrogen yields. Making use of natural seismic activity could help release trapped hydrogen.
These methods, however, demand advanced engineering approaches to balance efficiency with environmental safety, particularly in managing byproducts and minimizing seismic risks.
Challenges and Opportunities in the Field
While the potential of geologic hydrogen is considerable, the review underscores several scientific and technological hurdles:
- Scientific gaps: Key uncertainties remain, including the rate at which hydrogen is generated in different geological settings and how to estimate resource volumes accurately.
- Underexplored regions: Many areas have yet to be assessed for geologic hydrogen potential, limiting our understanding of global availability.
- Technology needs: Cost-effective, scalable, and environmentally responsible extraction methods are still under development.
- Environmental and safety concerns: These include managing wastewater, preventing contamination, and addressing induced seismicity.
Infrastructure and Market Considerations
Infrastructure development is another critical factor. While underground pipelines and storage systems offer viable options, they require adaptation to safely and efficiently handle hydrogen’s unique properties.
The economic landscape also influences progress. Market volatility, demand creation, and policy incentives all play a role in shaping the pace of development. Establishing clear regulatory frameworks and financial incentives will be key to encouraging investment and launching pilot projects.
Conclusion: A Promising Addition to the Hydrogen Supply Chain
Geologic hydrogen presents a compelling opportunity to supplement and diversify the global hydrogen portfolio. Its natural occurrence, potential renewability, and compatibility with existing subsurface exploration technologies make it an attractive, low-emission alternative - particularly in geologically favorable regions.
Moving forward, advancing scientific research, improving exploration and stimulation technologies, and building supportive policy and market frameworks are essential. Field demonstrations and pilot projects will play a pivotal role in validating geologic hydrogen’s feasibility and encouraging broader adoption.
Journal Reference
Mao S., Yu S., et al. (2025). Geologic hydrogen: a review of resource potential, subsurface dynamics, exploration, production, transportation, and research opportunities. Energy & Environmental Science. DOI: 10.1039/d5ee02910d, https://pubs.rsc.org/en/content/articlelanding/2025/ee/d5ee02910d