Zinc sulfide surface formation on Hg electrode during cyclic voltammetric scan: an implication for previous and future research studies on metal sulfide systems

Cyclic voltammetry on the Hg electrode was used to investigate the electrochemical behavior of NaCl/NaHCO₃ electrolyte solutions supersaturated with respect to Zn sulfide phases. The voltammetric results clearly show how an Hg electrode, due to exchange between Hg²⁺ from an HgS_adlayer and Zn²⁺ from solution, becomes the site for surface ZnS_adlayer formation in the potential range ?0.45 to ?0.6?V. The exchange reaction is reversible, and the surface-formed ZnS_adlayer persists at the Hg electrode surface until ?1.3?V during cathodic scans. Near ?1.3?V, it is reduced. In the same solution, evidence for reduction of bulk Zn sulfide species including nanoparticles was not obtained. The approach emphasized here can be readily extended to any other system consisting of metal electrode and chalcogenide anions, pointing to the importance of choosing experimental conditions (i.e., deposition potential, stirring, and accumulation times) to avoid artifacts and wrong interpretation of data due to surface formation of metal sulfide species.