Hydrogen migration in olivine based on first principles study: Implications for underground hydrogen storage

Understanding the diffusion behavior of hydrogen in subsurface olivine can elucidate the kinetic processes governing H₂ migration, enrichment, and depletion, thereby establishing a theoretical foundation for deciphering underground hydrogen storage (UHS) mechanisms in geological formations and advancing the exploration, development, and utilization of subsurface H₂ resources. This study investigates H₂ diffusion in olivine using climbing image nudged elastic band (CI-NEB) method based on density functional theory (DFT). Our results reveal pronounced anisotropy in H₂ diffusion activation energies for both fayalite (Fe₂SiO₄) and forsterite (Mg₂SiO₄) under ambient pressure, with the [010] direction exhibiting the highest barriers, and fayalite demonstrates higher activation energies than forsterite. Expanding the pressure range to encompass the entire upper mantle, our calculations for pressure-dependent H₂ diffusion in forsterite show excellent agreement with prior ab initio molecular dynamics (AIMD) studies, validating the reliability of our methodology. To assess hydrogen storage capacity, we calculated H₂ diffusion distances in olivine over Earth's geological timescale. The results demonstrate meter-scale confinement of H₂ migration, confirming olivine's exceptional hydrogen retention capability. Notably, fayalite exhibits far shorter diffusion distances than forsterite, indicating superior storage capacity in Fe-rich olivine. For H₂ extraction, thermal extraction simulations for 100 μm–2000 μm crystals under three heating rates reveal temperature thresholds: under moderate heating (10 °C/Ma), initial H₂ release requires heating to 135 °C (fayalite) and 112 °C (forsterite) for 100 μm crystals, while complete extraction necessitates 190 °C and 162 °C, respectively. These findings establish olivine, particularly fayalite, as a natural hydrogen reservoir and provide critical parameters for evaluating hydrogen storage and recovery in geologic systems.