Molecular and surface transformations governing hydrogen generation in thermally treated organic-rich mudrocks

Hydrogen is increasingly recognized as a key clean energy carrier, motivating the search for alternative and sustainable geologic sources beyond conventional electrolysis and reforming methods. While most studies focus on inorganic processes, the role of organic matter remains largely unexplored. This study examines hydrogen production during the thermal treatment of organic-rich carbonate mudrocks and evaluates the molecular, chemical, and microstructural transformations associated with gas release. An integrated analytical workflow combining gas chromatography (GC), time-of-flight secondary ion mass spectrometry (TOF - SIMS), X-ray photoelectron spectroscopy (XPS), Fourier-transform infrared spectroscopy (FTIR), and scanning electron microscopy (SEM-EDS) was employed to systematically characterize evolved gases and rock alterations. Results reveal significant hydrogen production accompanied by light hydrocarbons and carbon oxides, reflecting concurrent dehydrogenation, cracking, and decarboxylation reactions. TOF - SIMS and XPS analyses show progressive aromatic enrichment and depletion of aliphatic and oxygen-bearing functional groups, while FTIR spectra confirm the loss of aliphatic C–H and carbonyl bands. Microstructural imaging indicates enhanced porosity and mineral reorganization, facilitating gas migration. These results demonstrate that hydrogen generation in organic-rich rocks is predominantly controlled by thermal dehydrogenation, structural reorganization, and mineral-organic interactions that may provide catalytic effects during pyrolysis. The study provides experimental evidence that sedimentary organic matter can serve as a viable natural or thermally stimulated hydrogen source, expanding the understanding of geologic hydrogen systems in the context of future clean energy strategies.