Iodide surface coverage and its effect on the rate constants during hydrogen charging and permeation in iron

• Published in: Electrochimica acta 2003-04, Vol.48 (10), p.1331-1337
• Main Authors: Al-Faqeer, F.M., Weil, K.G., Pickering, H.W.
• Format: Article
• Language: English
• Subjects: Chemistry; Electrochemistry; Exact sciences and technology; General and physical chemistry; Hydrogen evolution; Hydrogen permeation; Inhibitors; Kinetics and mechanism of reactions; Surface coverage
• ISSN: 0013-4686; 1873-3859
• DOI: 10.1016/S0013-4686(02)00820-4

This paper demonstrates the use of the new Iyer/Pickering/Zamanzadeh/Al-Faqeer (IPZA) analysis to determine the effect of the iodide surface coverage ( θ I − ) on the hydrogen surface coverage ( θ H) and the rate constants of the hydrogen evolution reaction (HER) and hydrogen absorption reaction (HAR). Iodide ions have an inhibiting effect on the HER but they enhance the HAR. The IPZA analysis was used to determine θ I − in addition to the usual parameters: hydrogen discharge ( k 1) and recombination ( k 2) rate constants, hydrogen kinetic-diffusion constant ( k) and θ H. Inclusion of the iodide coverage is important as shown by a comparison with literature values that were obtained using the original IPZ analysis, which does not include the θ I − parameter. The θ I − values from the IPZA analysis were within reasonable agreement with θ I − values measured using the electrochemical quartz crystal microbalance (EQCM) and θ I − values calculated from the measured corrosion current densities before and after adding iodide to the electrolyte.