Interfacial Control Mechanisms of Hydrogen Injection and Transport Behavior in Aquifers under Nanoscale Confinement

Abstract The structure of the gas–water interface within the pores of nanoscale aquifers directly influences the injection and transport behavior of hydrogen within the aquifer pores, thereby determining the overall efficiency and storage stability of underground hydrogen storage. In this study, a hydroxylated quartz pore model is developed, and nonequilibrium molecular dynamics simulations are used to systematically investigate the effects of pore size, driving pressure drop, and salt type on the gas–water interface structure, interfacial properties, and hydrogen transport behavior. At 5 nm and 60 MPa, storage efficiency reaches 93%. Salt ions exert dual regulation: low salinity promotes injection while high salinity inhibits it. The NaCl system delivers the most pronounced promotion effect at low concentrations, yet complete injection cannot be achieved at high salinity (30 wt %). For divalent MgCl2 and CaCl2 with stronger hydration capacities, hydrogen can be fully injected only within a salinity range of 10–15 wt %. At 30 wt % salinity, CaCl2 markedly increases gas–water interfacial tension, raising capillary resistance by 44% relative to pure water, to 79.2 MPa, versus 70.3 MPa for the MgCl2 system. Notably, the Na2SO4 system exhibits the strongest inhibition, as SO42– tends to form ion clusters in the pore center, introducing additional steric hindrance, thereby enhancing the inhibitory effect. These results confirm capillary resistance as the primary barrier and the key factor regulated by salts , revealing the microscopic mechanisms by which salt ions and driving pressure drop influence the gas–water interface, providing molecular-level insights into underground hydrogen storage systems.