Natural hydrogen: Generation mechanisms, occurrence, challenges and future prospects

Natural hydrogen has emerged as a promising low-carbon energy source that could play a crucial role in the global energy transition. This comprehensive review explores the generation mechanisms, occurrence, challenges and future prospects of natural hydrogen, emphasizing its potential as an economically viable and environmentally friendly alternative to conventional hydrogen production. Unlike hydrogen derived from fossil fuels, natural hydrogen extraction processes, such as serpentinization, radiolysis, and mantle degassing, offer a pathway to reduce greenhouse gas emissions and contribute to energy security. Geological settings such as ultramafic complexes, sedimentary basins, and fault zones are highlighted as key environments for natural hydrogen generation and accumulation. Prominent pilot projects, including the one in Mali, demonstrate the feasibility of natural hydrogen exploitation, although challenges remain in exploration, detection, and reservoir characterization. Technological innovations, geochemical analyses, and geophysical methods are essential for advancing the exploration and exploitation of this renewable resource. This review highlights that continued research and development are critical to unlocking the full potential of natural hydrogen as a key player in the clean energy landscape. • Natural hydrogen offers a low-carbon, potentially large-scale energy source • Key generation processes: serpentinization, radiolysis, mantle degassing • Occurs in ultramafic complexes, sedimentary basins, and active fault zones • Pilot projects in Mali, Oman, Brazil, France, and Australia show feasibility • Challenges include detection, reservoir characterization, leakage, and regulation