Inhibition of the hydrogen evolution reaction on aluminium covered by ‘spontaneous’ oxide

Abstract

The electrochemical behaviour of aluminium covered by a thin ‘spontaneous’ oxide film was studied as a function of temperature and electrolyte composition at pH 1.3 The rectification mechanism of the charge transfer reactions is discussed on the basis of E/I characteristics. Tafel plots for the hydrogen evolution reaction showed anomalous slopes between 2.3 × 3RT/F and 2.3 × 4RT/F, depending on temperature. The inhibiting effects of 1 and 2-naphthylamines on the corrosion kinetics of aluminium in acid media (HClO₄ and NaCl + HCl) were determined using electrochemical methods. Consideration of the protonation of amines and the effects of the positively charged surface suggest that the observed excellent inhibition is due to the planar orientation (with π-electron bonds) of the adsorbed inhibitor molecules and the existence of synergetic effects. The degree of surface coverage was found to increase with temperature up to 40°C. At approximately 40°C the adsorbed molecules probably change their orientation becoming vertically adsorbed on the surface with strong lateral repulsion.