The effect of benzotriazole (BTAH) and tolytriazole (TTAH) on the electrochemical behaviour of the Fe/0.5 mol L-1 H2SO4 interface at 25 degrees C was studied using cronopotentiometry, anodic and cathodic polarization curves and electrochemical impedance spectroscopy. BTAH and TTAH are inhibitors of anodic iron dissolution and the subsequent hydrogen evolution in 0.5 mol L-1 H2SO4 medium. Mass transport is an important step in the anodic process of inhibitive film formation. Electrochemical impedance spectroscopy was used to investigate the iron dissolution mechanism in the presence of the inhibitors and showed that BTAH and TTAH are adsorbed on the iron surface, thereby changing its dissolution mechanism in sulfate media. Starting from an iron dissolution model, it was possible to suggest two different mechanisms for iron dissolution in 0.5 mol L-1 H2SO4 containing BTAH or TTAH that involve a complex Fe(II)-inhibitor. (C) 2009 Elsevier B.V. All rights reserved