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

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 vertical bar H2SO4 system. The concentrations of Fe2+ (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 vertical bar H2SO4 system and were found to change periodically at the Fe vertical bar H2SO4 interface. The changes in cFe(2+) 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.