Hydrostatic pressure effects on the kinetic parameters of hydrogen evolution and permeation in Armco iron

Highlights: •Hydrostatic pressure increases the corrosion potential. •Hydrostatic pressure induces ionization of H₂O. •Hydrostatic pressure inhibits recombination of adsorbed hydrogen atoms to molecules. •Pressure induces hydrogen diffusion from surface to subsurface tetrahedral sites. •Hydrogen coverage at the sample surface increases with hydrostatic pressure -- Abstract: Armco iron samples are exposed to pressures of 0.1–30 MPa to study hydrogen permeation during potentiostatic charging. Elecrochemical impedance spectroscopy (EIS) is performed to analyze the electrode/electrolyte interface reaction. According to EIS and first-principles calculations, the hydrostatic pressure decreases the distance between the adsorbed hydrogen atoms and the sample surface, which induces hydrogen atom diffusion into the subsurface by decreasing the diffusion barrier energy. Under high pressure, hydrogen molecules gather at the sample entry side and inhibit the hydrogen recombination reaction. Thus, the amount of adsorbed hydrogen and the hydrogen subsurface coverage increase.