In Situ High-Speed AFM Observation of Layer Growth and Redeposition during Anodic Dissolution of Zinc Deposits

Abstract

Zinc (Zn) provides sacrificial protection to steel and is, therefore, widely used as a corrosion protection coating such as through galvanizing. Because of its high theoretical capacity, Zn is also attractive as the anode for aqueous rechargeable Zn batteries. In these applications, Zn electrodeposition and dissolution should proceed uniformly and reversibly, but in practice they occur non-uniformly, and the resulting morphological changes strongly affect the reversibility of the electrode reaction and the corrosion resistance. Here, combining electrochemical measurements within situ high-speed atomic force microscopy (HS-AFM), we tracked in real time the local morphological evolution of individual Zn deposits on highly oriented pyrolytic graphite (HOPG). Chronoamperometric current—time transients compared with the Scharifker—Hills model indicated predominantly instantaneous nucleation. HS-AFM revealed that plate-like deposits grow in-plane on HOPG, with atomic layers successively stacked through layer-by-layer growth. Under repeated potential sweeping, the deposits did not dissolve completely but partly persisted, and local dissolution and redeposition proceeded simultaneously within the same field of view. Scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM—EDX) analysis showed that the residual spherical deposits were rich in oxygen, indicating corrosion products consisting mainly of zinc hydroxide or basic zinc chloride rather than metallic Zn.