Faradaic Reactions and Their Effect on the Dissolution of Natural Oxide Film on Pure Aluminum during Cathodic Polarization in Aqueous Solutions

Abstract

Faradaic reactions and their effects on dissolution of the natural oxide film on pure aluminum during cathodic polarization were investigated in aqueous 0.5 M sulfuric acid (H2SO4) and 0.5 M sodium sulfate (Na2SO4) solutions using the potentiodynamic polarization, rotating disk electrode (RDE), open-circuit potential (OCP) transient, and potentiostatic current transient methods. Potentiodynamic polarization curves for natural oxide-covered pure aluminum showed two Tafel slopes arising from the change in the faradaic reaction from oxygen reduction to water reduction with decreasing applied potential. The bare surface of pure aluminum was scarcely exposed to the electrolyte despite dissolution of the natural oxide film as a result of chemical attack by hydroxide ions during cathodic polarization. Chemical dissolution of the natural oxide film decreased the instantaneous value of OCP and was enhanced more by hydroxide ions resulting from water reduction than by hydroxide ions from oxygen reduction.