Investigation of anomalous hydrogen evolution from anodized magnesium using a polarization routine for scanning electrochemical microscopy

Abstract

• SECM investigation of anomalous hydrogen evolution on 99.9% Mg and AZ63 alloy. • Three-stage anodization procedure for the monitoring the rates of hydrogen evolution reaction (HER) • Separation of the effects of noble impurities from the reactivity of the oxy-hydroxide layer on Mg. • Enhanced H 2 evolution by facilitating the formation of the oxy-hydroxide layer on either pure Mg and AZ63 alloy. • Greater H 2 evolution on pre-polarized surfaces compared to the non-polarized ones. With the goal to facilitate a new experimental procedure for the monitoring of anomalous hydrogen evolution from anodically-polarized magnesium-based materials, this paper presents the application of the three-step (off-on-off) anodization operation sequence for amperometric scanning electrochemical microscopy (SECM) recently proposed by our group to the characterization of 99.9% magnesium in aqueous saline solution. The SECM measurements done above prepolarized and nonpolarized magnesium provided new information on the hydrogen evolution reaction (HER) on this metal, whereas other experiments are presented that enable to monitor the effect of the oxy-hydroxide layer formed on the metal under anodic polarization. In addition, direct comparison of the data obtained for 99.9% magnesium with those previously obtained for AZ63 magnesium alloy contributed to separate the effect of noble impurities from the catalytic effect of the oxy-hydroxide layer formed on magnesium for the hydrogen-evolution reaction.