Hydrogen permeation in a high strength ferritic steel was shown to depend on the passivity of the surface and the presence of . In the case where is not present, an oxide on the surface of the steel reduced the kinetics of the proton discharge rate and, even more so, the kinetics of the molecular hydrogen evolution rate. Thus, a high percentage of hydrogen permeated the steel. After the oxide was removed, there was an increased proton discharge rate and an equally increased hydrogen evolution rate, thus resulting in very low percentage of hydrogen permeation. When was present, the hydrogen discharge reaction remained high but the recombination reaction was suppressed so the percent of permeation was very high. Thus, plays a multiple role in increasing hydrogen permeation of passivated steel in slightly acidic environments. It increases the rates of iron corrosion and proton discharge and poisons the hydrogen evolution reaction on the depassivated surface, thereby permitting a large fraction of hydrogen atoms to enter the metal.