Abstract
Anodic metal dissolution produces hydrated metal salt concentrated at the anode interface and modifies the ion transport in the interfacial diffusion layer to be anion-selective or cation-selective. The anion-selective diffusion layer formed with monovalent chloride or hydroxide contributes to the formation of a chloride film, giving rise to either the chloride-film-induced passivation if the chloride is insoluble (e.g. Ag/AgCl) or the transition from the active state to the polishing state dissolution if it is soluble (e.g. Fe/FeCl2). The cation-selective diffusion layer formed with multivalent phosphate or sulfate gives rise to the formation of an oxide film, and thus to the oxide-film-induced passivation of metal anode (e.g. Ni/NiO). Furthermore, the transformation from a salt film to an oxide film on metal anodes occurs only if the salt film is cation-selective, and does not if it is anion-selective.
