Evolution of hydrogen at dissolving magnesium surfaces

The origin of hydrogen evolved at dissolving magnesium surfaces, including those subjected to anodic polarisation, remains a topical issue. In this work, a critical appraisal of existing theories is presented, along with data from simultaneous polarisation and hydrogen collection tests. The observations invalidate mechanisms invoking the presence of univalent Mg+. A combined experimental and thermodynamic analysis suggests that the ability of magnesium to support the cathodic reaction is enhanced during dissolution as the result of an increase in the exchange current density for the hydrogen evolution reaction, This mechanism can also explain high rates of hydrogen evolution in aluminium pits. (C) 2013 Elsevier Ltd. All rights reserved.