VOLTAMMETRY OF METALS AT MERCURY FILM MICROELECTRODES IN THE ABSENCE AND THE PRESENCE OF VARYING CONCENTRATIONS OF SUPPORTING ELECTROLYTE

The steady-state limiting current for reduction of mono- and divalent metal cations to amalgam in solution without supporting electrolyte depends on both the charge of the cation and the charge of the associated anion. The ratio of limiting current in the absence of supporting electrolyte (i(l) degrees) to diffusional current (i(d)) was found to agree well. with theoretical predictions (for reduction of M(+), 2 and 3/2 for X(-) and X(2-), respectively, and for M(2+), 3 and 2 for X(-) and X(2-), respectively). The reduction current of metal cation depends on the type and concentration of supporting electrolyte. The diffusional current is reached at a lower electrolyte ratio when the cation of the electrolyte is divalent than when it is monovalent. In solutions without supporting electrolyte, the limiting current for reduction of a cation having a large negative reduction potential was found to increase in the presence of a cation reducing at a less negative potential. This phenomenon was observed for thallium ion with hydrogen ion and for lead ion with hydrogen ion. The increase of the current is due to the increased rate of transport of the more easily reduced cation at potentials where both reductions are transport-controlled.