Mechanism of cathodic electrodeposition of zinc oxide thin films from aqueous zinc nitrate baths

Mechanism of electrodeposition of zinc oxide (ZnO) thin films from aqueous solution of zinc nitrate has been studied under controlled mass transport by using a rotating disk electrode. The current associated with the electroreduction of nitrate ion has not been affected by the rotation speed due to slow electron transfer kinetics. Rate constant and transfer coefficient have been determined as 5.98×10 −10 cm s −1 and 0.159, respectively, for the electrolysis in a 0.1 M Zn(NO 3) 2 aqueous solution. The current, however, is increased by increasing Zn 2+ concentration in the bath. The improvement of the electron transfer kinetics has been interpreted as the catalytic role of Zn 2+ ion to the reduction of nitrate. The current in the presence of Zn 2+ at various concentrations has been nicely described by Langmuir type adsorption of Zn 2+ catalysts to the surface sites of ZnO, for which an equilibrium constant of 1.23×10 5 cm 3 mol −1 (70 °C) has been determined.