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 de pends on both the charge of the cation and the charge of the associate d anion. The ratio of limiting current in the absence of supporting el ectrolyte (i(l) degrees) to diffusional current (i(d)) was found to ag ree 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(-) a nd X(2-), respectively). The reduction current of metal cation depends on the type and concentration of supporting electrolyte. The diffusio nal 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 incr ease 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 p otentials where both reductions are transport-controlled.