The Kinetics of Hydrogen Absorption into Iron during Cathodic Hydrogen Evolution

Abstract

An electrochemical technique has been developed with which the steady‐state concentration of adsorbed hydrogen on an iron surface, θ, can be determined. By using values of θ determined by electrochemical techniques, a method of evaluating the specific rate constant for hydrogen absorption into iron, k_abs, has been developed. Values of θ determined on a cathodically polarized iron surface in 0.0001N sodium hydroxide + 0.1M sodium sulfate were between 5 and 12% of the total monolayer coverage, over the current‐density range . This current‐density range represents a hydrogen generation rate equivalent to a corrosion rate of 5–150 mils penetration per year. The variation of θ with cathodic overpotential was in close agreement with theory; values of δη/δ log₁₀ θ were 3.5 V/decade measured experimentally and 4.2 V/decade theoretically. Experimental values of θ permit, for the first time, determination of the specific rate constant for the absorption reaction.