Surface oxide reduction by hydrogen permeation through iron foil detected using a scanning Kelvin probe

The interaction of atomic hydrogen with the air-formed surface oxide film of an iron foil, following cathodic hydrogen evolution on the reverse face, is shown to produce significant Volta potential changes which can be mapped using a scanning Kelvin probe (SKP). The magnitude of the Volta potential depression decreases with holding time following hydrogen charging and exhibits a dependence upon the oxygen partial pressure of the holding environment. It is proposed that the Volta potential depression observed in the area of hydrogen emergence results from a change in the ratio of Fe-III/Fe-II states within the surface oxide. (C) 2012 Elsevier B.V. All rights reserved.