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.

► H2 generation rate at dissolving Mg surface increases with Mg dissolution rate.
► Total H2 volume for given net anodic charge decreases as current density increases.
► Findings are not consistent with univalent Mg ion mechanism of H2 generation.
► New model presented for increased generation of H2 with increased potential.
► Surface catalytic activity and i0,HER presumed to increase with Mg dissolution rate.