Voltammetry in weakly supported media: The stripping of thallium from a hemispherical amalgam drop. theory and experiment

A theoretical model for electrochemical processes in resistive media is applied to interpret the current measured for the stripping of thallium from a Tl/Hg amalgam. Chronoamperometry is presented for a potential step experiment at a 12.5 μm radius hemispherical mercury drop in which thallium is first deposited and then stripped. Unusual features are observed in the transient stripping current, and it is proposed that these occur when the concentration of thallium(I) cations in solution is so great that the inert electrolyte salt is no longer in excess and the system is only partially supported. The theoretical model uses the Nernst-Planck-Poisson equations, which take into account the effects of the electrical potential in the aqueous phase, and avoids making the approximation of electroneutrality. The numerically simulated current accurately predicts the unusual experimental behavior.