Zn dissolution−passivation behavior with ZnO formation via in-situ characterizations

Abstract. In this study, ZnO formation during the dissolution−passivation process of Zn anodes is observed via in-situ Raman and optical characterization. The Zn passivation during galvanostatic anodization merely follows the dissolution−precipitation model, whereas that of potentiodynamic polarization exhibits different behaviors in different potential ranges. Initially, the Zn electrode is gradually covered by a ZnO precipitation film and then undergoes solid-state oxidation at approximately 255 mV. The starting point of solid-state oxidation is well indicated by the abrupt current drop and yellow coloration of the electrode surface. During the pseudo passivation, an intense current oscillation is observed. Further, blink-like color changes between yellow and dark blue are revealed for the first time, implying that the oscillation is caused by the dynamic adsorption and desorption of OH groups. The as-formed ZnOs then experience a dissolution−reformation evolution, during which the crystallinity of the primary ZnO film is improved but the solid-state-formed ZnO layer becomes rich in oxygen vacancies. Eventually, oxide densification is realized, contributing to the Zn passivation. This study provides new insights into the Zn dissolution−passivation behavior, which is critical for the future optimization of Zn batteries.