Anodic Polarization Behavior of Copper in Concentrated Aqueous Lithium Bromide Solutions and Comparison with Pourbaix Diagrams Available to Purchase

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°C and 40°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°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 (CuBr₂·3Cu[OH]₂) passive films. Finally, the increase in anodic current density was attributed to oxygen evolution.