Potentiometric scanning electrochemical microscopy for the local characterization of the electrochemical behaviour of magnesium-based materials

The applicability of scanning electrochemical microscopy for the local detection and quantification of relevant species participating in the corrosion of magnesium-based materials is presented. The iron–magnesium galvanic pair exposed to aqueous NaCl solution was adopted as model system for this purpose. Mg2+ ion concentration and pH profiles were investigated using ion selective electrodes, containing a liquid membrane and Sb/Sb2O3 as sensor elements, respectively. Oxygen consumption at the substrate related to the cathodic reaction was also monitored with the antimony-based electrode though operated amperometrically. Data show a major production of hydroxyl anions at the cathodic sites as result of the oxygen reduction half-reaction, whereas in the vicinity of the magnesium surface pH is greatly affected by the anodic dissolution process instead. The later produces the release of metal cations accompanied by hydrogen evolution.

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► New method for the local detection and quantification of species in the corrosion of magnesium-based materials by SECM.
► Mg2+ ion concentration and pH profiles were investigated using ion selective electrodes.
► Ion selective electrodes employed either a liquid membrane or Sb/Sb2O3 as sensor elements.
► Oxygen consumption at the substrate was monitored amperometrically with the antimony-based electrode.