Mechanism of hydrogen formation during the corrosion of Mg17Al12

Abstract

Previous investigations (DFT calculations) showed that hydrogen atoms adsorption and H2 desorption can occur on MgO and Al2O3 and that H atoms can diffuse on Mg and Al surfaces. However, these three simultaneous actions, i.e. H adsorption, H diffusion and H2 desorption, have not been experimentally proved. In this paper, we propose a mechanism of formation of H2 during the corrosion of an intermetallic compound Mg17Al12 in 3.5 wt.% NaCl aqueous solution based on in situ Raman spectroscopy analysis. We found that, through the passivation zone (e.g. E varying from the open circuit potential (OCP) to +100 mV/OCP), the oxide layer is destroyed in favor of the appearance of Mg and H atoms. Moreover, the formed H atoms are adsorbed on the oxide surface and then diffuse on either the oxide surface or the unreacted metal surface where they recombine forming H2. In situ Raman measurements during anodic polarization experimentally prove, for the first time, the formation of a reaction intermediate which weakens the H–H bond. The obtained results explain the mechanism of hydrogen production under anodic polarization of the intermetallic compound at normal conditions of temperature and pressure.