Oscillations of pH at the Fe│H2SO4 interface during anodic dissolution

Abstract An unmodified Pt microelectrode and a Pt microelectrode coated with polyaniline were used in conjunction with a scanning electrochemical microscope (SECM) to study anodic dissolution in the Fe│H 2 SO 4 system. The concentrations of Fe 2 + ( c Fe2 + ) measured with the unmodified microelectrode and the pH values measured with the polyaniline-modified microelectrode were recorded in situ during current oscillations in the Fe│H 2 SO 4 system and were found to change periodically at the Fe│H 2 SO 4 interface. The changes in c Fe2 + may be caused by the periodic formation and dissolution of surface film(s), which could be salt films and/or oxide films. If a salt film is formed, it is unlikely to affect the pH. Since the pH changes periodically during the current oscillations, it can be deduced that the surface film is mainly composed of oxide, and that the formation and dissolution of the oxide film play a key role in the current oscillations of the system.