Natural hydrogen: Advances in genesis mechanisms, global distribution, and geophysical exploration

Natural hydrogen, as a zero-carbon clean energy source, is of great significance for the global energy transition to low-carbon development through its efficient exploration and exploitation. Clarifying the genesis mechanisms, key controlling factors, and distribution patterns of hydrogen is fundamental to achieving large-scale utilization of natural hydrogen resources. Recent advances in hydrogen genesis research are systematically reviewed, a comprehensive genesis classification system is established, and global hydrogen reservoir data with lithological maps, active faults, and basin types are integrated. Summarized are the key controlling factors and spatial distribution patterns of hydrogen reservoirs of different origins, yielding the following insights: (1) Hydrogen genesis can be categorized into three major types: inorganic, organic, and mixed. Inorganic genesis encompasses water-rock reactions such as serpentinization, fault activity, and trapped hydrogen in the Precambrian basement; ionizing radiation effects on water and organic matter; and primary and secondary deep degassing. Organic genesis involves organic matter pyrolysis through the thermal evolution of sedimentary organic matter and methane cracking for hydrogen production, and microbial processes mediated by hydrogenases/nitrogenases. Mixed genesis results from the coupling of multiple mechanisms. (2) Hydrogen enrichment is controlled by faults, lithological assemblages, and basin types. Faults provide triple functions as hydrogen generation sites, migration pathways, and storage conditions, facilitating hydrogen generation, accumulation, and preservation. Metamorphic rocks, plutonic intrusions, and volcanic rocks form favorable lithological backgrounds for hydrogen enrichment. Natural hydrogen predominantly develops within various petroliferous basins. (3) Spatially, inorganic hydrogen is predominantly distributed in tectonically active belts and Precambrian stable zones; organic hydrogen is concentrated in organic-rich sedimentary areas; while mixed-origin hydrogen is commonly found in tectonically complex regions with multiple source superimpositions. China has extensive natural hydrogen resources, though their distribution remains relatively dispersed. Current research on natural hydrogen faces challenges in precisely distinguishing contributions from multiple sources and systematically predicting global resource potential. Future efforts should deepen hydrogen genesis theories, advance deep detection technologies, and develop predictive models to support the evaluation of large-scale natural hydrogen resources and exploration breakthroughs. The study provides a systematic theoretical basis for natural hydrogen genesis mechanisms and enrichment patterns, facilitating the prediction of hydrogen-rich zones and the optimization of exploration targets. These findings hold significant scientific importance for advancing energy transition and achieving the dual carbon goals.