MECHANISTIC STUDY OF CATHODIC ELECTRODEPOSITION OF ZINC-OXIDE AND ZINC HYDROXYCHLORIDE FILMS FROM OXYGENATED AQUEOUS ZINC-CHLORIDE SOLUTIONS

Films of zinc oxide and related compounds [ZnO, ZnOx(OH)(y), Zn(OH)(x) Cl-y] are electrodeposited cathodically in aqueous zinc chloride solut ions using dissolved oxygen as a precursor. The influence of the precu rsor concentrations, pH, and deposition temperature on the growth, com position, an properties of the films are investigated by means of in s itu techniques: voltammetry, electrochemical quartz-crystal microgravi metry, surface pH, and ex situ techniques: X-ray diffraction, infrared spectroscopy, scanning electron microscopy, and energy dispersive spe ctroscopy. The deposition mechanism is analyzed in terms of electroche mically induced surface precipitation due to an increase of local pH r esulting from the oxygen reduction reaction. This approach allows us t o explain the formation of either zinc hydroxychloride compounds or zi nc oxide from their calculated solubility diagrams. In conditions of t he formation of ZnO, a dramatic effect of tem temperature is observed, with a transition between amorphous insulating zinc oxyhydroxide to w ell-crystallized and conducting zinc oxide when the temperature increa ses (T-transition approximate to 50 degrees C).