Work

Dynamic Ni–Fe Interfaces Regulate Stimulated Geological Hydrogen Production

Year: 2026

Type: preprint

Abstract: Geological hydrogen (Geo-H2) generated by water-rock redox reactions could expand low-carbon hydrogen resources by tapping reducing equivalents stored in subsurface minerals. Stimulated Geo-H2 production remains difficult to engineer because the reaction sequence connecting rockhosted Fe2+ release to H2 evolution is incompletely constrained. Here, we support an interfacial sequence linking olivine Fe2+ release, an Fe(II)-bearing hydroxide intermediate state, Fe3O4bearing product growth, and Ni redistribution at evolving Fe-rich interfaces. Across olivine-rich rocks, basalt, and Fe(OH)2 model systems, trace dissolved Ni2+ enhanced H2 evolution over the examined temperatures, reaching rates more than two orders of magnitude above previously reported Geo-H2 systems at comparable temperatures, and dissolved Ni2+ outperformed solid Ni additives under matched additive-form comparisons. Fe-normalized controls show that dissolved Fe2+ alone produced far less H2 than Fe2+ converted to Fe(OH)2, supporting Fe(II)-hydroxide chemistry as a productive gateway to the magnetite-forming pathway. Electron microscopy, spectroscopy, and cross-sectional EDS connected olivine Fe redistribution with Fe-rich alteration products and Ni recruitment, whereas first-principles calculations indicated that adsorbed Ni-Fe sites stabilize dissociated H more strongly. The Ni response was finite, with excess loading suppressing H2 evolution through competing Ni2+ reduction and other high-Ni interfacial inhibitory pathways. These results connect Fe release, hydroxide-associated Fe(II) chemistry, magnetite-bearing product growth, and Ni loading and accessibility, providing an interfacial framework for promoting water reduction in stimulated Geo-H2 systems.

Source: ChemRxiv

DOI: 10.26434/chemrxiv.15009395/v1