Assessment of H2 diffusivity in water and brine for underground storage: A molecular dynamics approach

Abstract

Hydrogen (H 2 ) is poised to play a key role in the future energy landscape, but its efficient storage remains a challenge due to its small size and high mobility. Underground hydrogen storage in aquifers offers potential, yet risks arise from H 2 diffusivity in brine, which can lead to migration or chemical reactions. In this study, H 2 diffusivity in water and NaCl brine is studied using Equilibrium and Non-Equilibrium Molecular Dynamics simulations. A detailed benchmarking of force fields for H 2 , water, and Na + /Cl − ions is performed to ensure accuracy and reliability. These results provide diffusivity data for H 2 across a broad range of underground conditions (298 K–473 K, 1–1000 bar, 0–6 mol/kg NaCl), analyzed within an excess entropy framework and modeled using the Stokes-Einstein relationship and an Arrhenius-type equation, offering a framework for predicting H 2 diffusion behavior in water and brine in various conditions.