The passivation of dilute Cu(Hg) in alkaline solutions

Abstract

The anodic oxidation of dilute Cu(Hg)-pool electrodes (maximum mole fraction of Cu = 0.031) in aqueous solutions of Na 3PO 4 and NaOH pH range 10.5–12.2, yielded a series of potential-time transients that are found to correspond to the formation of Cu 2O, CuO and Cu(OH) 2 at the higher pH value, and Cu 2O and two soluble species, believed to be CuO 2- and HCuO 2-, at the lower pH value. No sign of processes involving Hg appeared even at a mole fraction of Cu as low as 10 −4. Theoretical calculation based on a model of competition between species of Cu and Hg for the available OH- predicts that the electrode should behave electrochemically as pure Cu down to a Cu activity of ca. 10 −12. For both anodic and cathodic processes i-τ −1 2 plots are found linear, proposing the applicability of the law τ = ai − n , with n = 2.