Analysis of hydrogen absorption under competitive adsorption conditions - Effect of hexamethylenetetramine

The original Iyer, Pickering, and Zamanzadeh (IPZ) analysis is extended to determine the coverage of a second adsorbate using only the hydrogen permeation data. Good agreement was obtained with the coverage determined by two other independent methods. The effect of hexamethylenetetramine (HMTA) as the second adsorbate was studied on iron. HMTA has an inhibiting effect on the hydrogen evolution reaction at all concentrations, whereas it has a mixed effect on the hydrogen absorption reaction (HAR). HMTA enhances the HAR at low concentrations, and it inhibits the HAR at concentrations of more than 100 mM. This analysis is referred to as the IPZA analysis which considers also the surface coverage of the HMTA (theta(HMTA)) was used to determine theta(HMTA) in addition to the usual parameters: hydrogen discharge (k(1)) and recombination (k(2)) rate constants, the hydrogen kinetic-diffusion constant (k), the hydrogen surface coverage (theta(H)) and its concentration in the metal at the charging surface (C-o). (C) 2003 The Electrochemical Society.