Experimental Investigation of Hydrogen Generation and Mineralogical Changes in Basaltic Rocks

The conversion of ferrous iron to ferric iron during water-rock interaction generates molecular hydrogen, a process well-documented in the serpentinization of ultramafic rocks. However, the hydrogen production potential of basaltic rocks remains underexplored, despite their wide distribution and high iron and magnesium content. This study evaluated the hydrogen generation capacity of basaltic rocks through laboratory-scale water-rock interaction experiments using basaltic specimens from the Korean Peninsula. Experiments were conducted in a titanium autoclave at 280°C for up to 14 days. Molecular hydrogen production was measured using gas chromatography equipped with thermal conductivity detector (GC-TCD, FOCUS GC, Thermo Fisher Scientific), and whole-rock chemistry was analyzed using inductively coupled plasma optical emission spectroscopy (ICP-OES, Optima 7000DV, PerkinElmer), both installed at the Integrated Analytical Center for Earth and Environmental Sciences of Pukyong National University, while mineralogical changes were examined using scanning electron microscopy with energy-dispersive spectroscopy (SEM-EDS). Hydrogen production varied significantly across samples. OSB-1A showed delayed hydrogen generation, reaching 51.22 mmol/kg_rock at 336 hours. In contrast, OSB-1B exhibited rapid and sustained hydrogen production, peaking at 115.04 mmol/kg_rock. ULD-2 demonstrated the highest hydrogen yield (182.54 mmol/kg_rock at 336 hours), while other samples such as YI-1 and EI-1 produced lower amounts with delayed onset. SEM-EDS analysis confirmed the dissolution of Fe-bearing minerals associated with abiotic hydrogen production, but no secondary Fe-bearing minerals like magnetite or brucite were detected. Instead, nanoscale amorphous precipitates were observed, likely due to the preferential involvement of fine-grained particles with high surface areas in hydrogen production. These findings enhance our understanding of abiotic hydrogen production in basaltic rocks and its implications for geochemical processes and potential energy resources.