HYDROGEN-SULFIDE EFFECT ON HYDROGEN ENTRY INTO IRON - A MECHANISTIC STUDY

The recently developed I-P-Z model is modified in order to analyze the enhanced permeation of hydrogen that occurs in the presence of hydrogen sulfide during cathodic hydrogen charging of iron. The modification accounts for the fact that the energy of adsorption becomes coverage-dependent at the higher coverages and affects the hydrogen evolution reaction in the presence of H2S. Charging experiments were performed on Ferrovac E-iron membranes 0.5 mm thick using a Devanathan-Stachurski cell in deaerated, pre-electrolyzed solutions made from 0.1 M HClO4 and 0.1 M NaClO4 with pH values of 1 and 2. The transfer coefficient, α, exchange current density io, thickness-dependent absorption--adsorption rate constant, k″, recombination rate constant, k3, surface hydrogen coverage, ΘH, and discharge rate constant, k10, were obtained by application of the model to the experimental results. An important relationship has been derived that will enable the calculation of the absorption, kabs, and adsorption, kads, rate constants from the electrochemical permeation results for different membrane thicknesses.