The Underpotential Adsorption/Deposition and Stripping of Mercury on Gold in Dilute Sulfuric Acid

Abstract

The underpotential deposition of mercury on gold was studied by potentiostatic techniques at a rotating gold ring-disc electrode. Underpotential mercury deposition occurred at potentials more positive than 680 mV (against a dynamic hydrogen electrode). Anodic stripping voltammetry at the disc with ring collection showed that a monolayer coverage of underpotential mercury was equivalent to approximately 370pc/cm². The stripping process yielded several anodic peaks and produced largely Hg^II, at least 16% of which remained adsorbed on the bare gold electrode. Potential-step experiments at the disc and ring-shielding data indicated that the underpotential shift was about 500 mV and that the deposition process involved both adsorbed (35-47% of the theoretical monolayer coverage) and soluble mercury(II) species. The adsorbed mercury had a formal positive charge of 0.40-0.46. The most anodic stripping peak (at 1200 mV) of underpotential mercury may be used to determine nanomolar levels of mercury by anodic stripping voltammetry, by using an overvoltage of less than 100 mV for preelectrolysis.