Zinc dissolution in ammonium chloride electrolytes

The anodic dissolution of zinc RDE in NH₄Cl and NH₄Cl + ZnCl₂ electrolytes at pH 5.5 was studied. XPS and SEM data indicate that the zinc electrode is covered by a porous film composed of a mixture of metallic zinc and zinc hydroxide. The thickness of the film and the zinc hydroxide content is much higher in zinc-containing electrolytes than in NH₄Cl and, although the thickness and Zn(OH)₂ amount decrease with anodic polarization, the electrode is never free from oxidized compounds. Electrochemical results indicate that at low overpotentials the rate of zinc dissolution is determined by the removal of the oxidized blocking particles, while at high overpotentials Zn dissolution takes place through the porous layer.