During the anodic oxidation of magnesium in aqueous electrolytes, particularly those containing halide anions, marked disintegration of the electrode is observed accompanied by an increase in the rate of hydrogen evolution above that observed under open circuit conditions (Negative Difference Effect). This phenomenon of electrode disintegration leads to the observation that the apparent valency of magnesium ions going into solution is approximately unity.
Several researchers 1-6 have suggested that the apparent valency can best be explained by postulating the initial formation of unipositive magnesium which then later undergoes further anodic oxidation or is oxidized by reducible species in the electrolyte. Kleinberg 2 strongly endorses this view and has provided substantial experimental evidence that the anolyte when removed from the dissolving magnesium anode contains a reducing species in addition to that of hydrogen. This species he believes to be unipositive magnesium, Uhlig and Krutenat 7 measured the half life of the reducing species formed at anodically polarized magnesium electrodes in buffered H2-deaerated 0.1 M NaC1 and obtained a value of approximately 6 min. This they attributed to the presence of the species H(aq) rather than to Mg Γ·. Earlier, Straumanis s-11, Greenblatt12, King~3 and Hoey and Cohen ~4 had also disputed the existence of Mg Γ· and had suggested that the cause of current inefficiency with magnesium anodes can be attributed to such causes as film damage by anions 13 , the formation of colloidal magnesium or the species Mg 2 Γ·Mg 14
The purpose of this communication is to present evidence from rotating ring-disc studies that no solution soluble reducing species other than that of dissolved molecular hydrogen is produced at an anodically polarized magnesium disc electrode in aqueous NaBr.
The rotating ring-disc electrode (RRDE) consisted of a magnesium disc (99.99%) surrounded by a platinum ring and had the dimensions rl = 0.178 cm, r2 = 0.229 cm and ra = 0.279 cm (N = 0.313) ~s .Galvanostatic steps up to 20 mAcm -2 were applied to the magnesium disc and the resulting potential-time trace was recorded. Concurrently the current-time response of the platinum ring was recorded for various fixed ring potentials. The electrolyte employed was 1 M NaBr and was continuously saturated with high purity nitrogen.