In Situ Scanning Electrochemical Microscopy (SECM) Detection of Metal Dissolution during Zinc Corrosion by Means of Mercury Sphere-Cap Microelectrode Tips

We present a study of the corrosion of zinc samples to illustrate the potential of coupling mercury tips and Scanning electrochemical microscopy in corrosion science under typical metal-corroding conditions

Ricardo M. Souto

2011

Scholarcy highlights

  • Scanning electrochemical microscopy is gaining increasing application in corrosion science for the in situ investigation of localized corrosion processes with high spatial resolution. SECM is a scanning probe microscopy technique that is based on the amperometric signal generated at a microelectrode by redox-active species in solution, which can perform quantitative local electrochemical experiments at interfaces to gather information on the topography or reactivity of substrates
  • Monitoring Zn2+ ions at mercury microelectrodes: Firstly, the potential ranges for the reduction and the oxidation of zinc species at a mercury microelectrode were tested by cyclic voltammetry in an aerated ZnACHTUNGRE(NO3)2 + NaCl solution
  • The observation of various peaks during the cathodic scan in the Cyclic voltammetry can be related to the stepwise reduction of oxygen to hydrogen peroxide, the subsequent reduction of hydrogen peroxide to hydroxide anions, and the reduction of ZnII species, the process of which is complicated by the formation of sparingly soluble zinc hydroxide or oxide species at the electrode surface
  • The anodic sites on the zinc specimen give rise to enhanced cathodic currents at the microelectrode compared to the steady-state limiting current, and the SECM tip was monitoring the flow of ZnII species from the dissolving surface of zinc
  • Indirect detection of the cathodic reaction was achieved from those areas at the zinc surface that originated depleted currents at the tip compared to the steady-state limiting current. They were found in the proximity of the anodic areas, because the tip effectively detected lower concentrations of the dissolved oxygen in the solution close to those sites. Both the anodic and cathodic reactions responsible for the corrosion process were located over the same metal
  • Concentration profiles of dissolved zinc species that originate from the corroding metal could be determined by using simple CVs at the Hg-microelectrode tip for different tip– substrate distances

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