Anodic polarization behavior of copper in concentrated aqueous lithium bromide solutions and comparison with pourbaix diagrams

The anodic polarization behavior of copper was studied in 400-g/L and 700 g/L (4.61 M and 8.06 M) lithium bromide (LiBr) solutions between 25 degrees C and 40 degrees C. In all cases, an initial active region of copper dissolution was followed by a decrease in current density. In the 400-g/L LiBr solutions, four anodic current peaks were observed, whereas in the 700-g/L LiBr solutions, only two well-defined peaks were observed. The low-activation energy values obtained for the copper dissolution process in the 400-g/L and 700-g/L LiBr solutions were consistent with the formation of poorly structured thin passive layers via a diffusion-controlled metal electrodissolution process. The anodic polarization behavior of copper in the 400-g/L and 700-g/L LiBr solutions at 25 degrees C was compared with the respective Pourbaix diagrams (potential-pH diagrams). In the 400-g/L LiBr solution (pH = 6.80), the initial anodic dissolution region exhibited Tafel behavior attributed to the formation of CuBr2- complexes. At higher potentials, passivation was observed, associated with the formation of copper(I) bromide (CuBr) and copper(II) oxide-copper(II) hydroxide (CuO-Cu[OH](2)) films. Lastly, a new active region appeared, initially associated with the oxidation of CuBr2- to Cu2+, and then with the oxidation of water to oxygen. In the 700-g/L LiBr solution (pH = 5.65), the initial active region of formation of CuBr2- was followed by the formation of CuBr and copper trioxybromide (CuBr2 center dot 3Cu[OH](2)) passive films. Finally, the increase in anodic current density was attributed to oxygen evolution.