Kinetics of galvanostatic anodic polarization of Zn in NaOH solutions and characterization of the resulting layers

The kinetics of film formation on zinc in water solutions of sodium hydroxide was investigated. The concentrations of the forming electrolyte were varied between 0.001 and 0.08 mol dm−3. The anodic polarization was carried out in galvanostatic regime with current densities between 5 and 35 mA cm−2. A point at which the rate of film formation changes was found on the kinetic curves. The dependencies of the slopes of the kinetic curves before and after this point, the position of this point, as well as the breakdown voltage on the concentration of the forming electrolyte, on the applied current density and on the temperature were investigated. By means of X-ray diffractometry and Raman spectrometry was found, that the formed film consists of polycrystalline zinc oxide. Further investigations using ATR-FTIR and XPS confirmed these observations and suggested the possible presence of small quantities of impurities in the layers. SEM and AFM studies show that in the initial stages of anodic polarization a film is formed, which fills the concavities of the metal surface and afterwards the electrode is covered with hexagonal plate-like crystals. Subsequently the surface becomes smoother again. Some thermodynamic considerations, as well as some additional experiments with sandwich structures formed on the electrode surface suggest that the shift in the kinetic curves is caused by a change in the specific resistivity of the layer, occurring at a temperature of about 305 K.