Electrodeposition amalgam electrodes

Electrodeposited negative electrodes are manufactured by plating zinc in tanks onto metallic grids. The plates must then be amalgamated and pressed or rolled to the desired thickness and density, followed by drying. 

Electrodes of this sort have many different chemical properties from pure mercury electrodes, because of the formation of a gold or platinum amalgam [18]. Normally, a drop is suspended just prior to an experiment, so this problem will be of no serious consequence. Nevertheless, since the solubility of these noble metals in mercury is about 0.05 M at room temperature [19], the concentration of gold or platinum in mercury may be quite significant on a longer time scale. In such cases, gold or platinum may form intermetallic compounds with several metals that are electrodeposited into the mercury [18]. 

Anodic stripping voltammetry (ASV) is the oldest, and still the most widely used version of stripping analysis [3]. The technique is applicable to metal ions that can be readily deposited at the working electrode, and particularly for those metals that dissolve in mercury. In this case, the metals are being preconcentrated by electrodeposition into a small-volume mercury electrode (a thin mercury film or a hanging mercury drop). The preconcentration is done by cathodic deposition at a controlled potential and time. The deposition potential is usually ca. 0.3 Y more negative than E° for the least easily reduced metal ion to be determined. The metal ions reach the mercury electrode by diffusion and convection, where they are reduced and concentrated as amalgams ... 

The preconcentration of trace metals by electrodeposition is an integral part of anodic-stripping voltammetry. The method consists of the preelectrolysis of the stirred solution with a small mercury drop or solid electrode as the cathode (112-114). The metals, which are deposited and dissolve in the mercury, are then stripped from the amalgam after a suitable rest period by a reversal of the electrode potential. The resulting current-polarization curve is characteristic of the metal and its concentration. Concentrations as low as 10 M of metal ions require a preelectrolysis of about 60 min or longer. Other electrodes such as mercury films, platinum, gold, silver, and various forms of carbon have been used (77 ). 

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