  The understanding of geochemical interactions between H2 and geofluids is of
great importance for underground H2 storage but requires further study. We
report the first investigation on the three-phase fluid mixture containing H2,
H2O, and n-C10H22. Molecular dynamics simulation and PC-SAFT density gradient
theory are employed to estimate the interfacial properties under various
conditions (temperature ranges from 298 to 373 K and pressure is up to around
100 MPa). Our results demonstrate that interfacial tensions (IFTs) of the
H2-H2O interface in the H2+H2O+C10H22 three-phase mixture are smaller than IFTs
in the H2+H2O two-phase mixture. This decrement of IFT can be attributed to
C10H22 adsorption in the interface. Importantly, H2 accumulates in the
H2O-C10H22 interface in the three-phase systems, which leads to weaker
increments of IFT with increasing pressure compared to IFTs in the water+C10H22
two-phase mixture. In addition, the IFTs of the H2-C10H22 interface are hardly
influenced by H2O due to the limited amount of H2O dissolved in bulk phases.
Nevertheless, relatively strong enrichments and positive surface excesses of
H2O are seen in the H2-C10H22 interfacial region. Furthermore, the values of
the spreading coefficient are mostly negative revealing the presence of the
three-phase contact for the H2+H2O+C10H22 mixture under studied conditions.
