Enhanced hydrogen entry into iron from 0.1 M NaOH at definite potentials

This work aimed at explaining the enhancement of hydrogen entry into iron from alkaline solution occurring at definite potentials. Hydrogen permeation rate (HPR) through a 35-mu m thick iron membrane was measured with the electrochemical technique in 0.1 M NaOH at 25 degrees C during cathodic and anodic polarizations. Enhanced HPR was observed at potentials of oxide reduction or iron oxidation, and potentials more cathodic than about -1.65 V-NHE during prolonged galvanostatic polarization. XPS analysis showed that after the polarization, surface layers contained hydrated iron oxides and that amount of these products increased with the polarization time. It is suggested that the enhanced hydrogen entry can be explained by acidification of the near-metal solution due to iron oxidation and/or oxide reduction, and probably by a promoting effect of some Fe-O species. It is proposed that these effects are associated with surface layers. They can affect hydrogen entry as a source of protons in the oxide reduction, as a diffusion barrier making the near-metal acidification possible, and as a resistance causing an IR drop. Strong enhancement of HPR after prolonged galvanostatic polarizations can be associated with the formation of thick surface layers with IR drop enabling anodic oxidation of iron under these layers. (C) 2007 Elsevier Ltd. All rights reserved.