A kinetic model explaining the enhanced rates of hydrogen evolution on anodically polarized magnesium in aqueous environments

•A kinetic model for anomalous hydrogen evolution on Mg is presented.•Actively dissolving anodes assumed as the source of anomalous hydrogen evolution.•Mg oxidation charge transfer coefficient needs to be greater than that for the HER.•Analysis of reproducible experimental data validates the model.

A model to explain the increasing rates associated with hydrogen evolution (HE) originating at the dissolving regions of Mg under anodic polarization is presented. The actively dissolving anodes have been shown experimentally to be the primary source of anomalous evolution of hydrogen. In this model, standard electrochemical laws are used to account for this phenomenon. The fractional coverage of active Mg sites is introduced to localize the cathodic contribution of HE during anodic polarization. A kinetic equation is derived showing that the rate of HE will increase with increasing potential if the charge transfer coefficient associated with the Mg oxidation reaction is greater than the charge transfer coefficient for the HE reaction. Experimental data obtained on high purity Mg galvanodynamically polarized at potentials above and below its Ecorr in 0.1 M NaCl solution are presented to validate the model.