Effect of the supporting-electrolyte cation on the chloroplatinite ion reduction at a dropping mercury electrode

The effect of nature and concentration of supporting-electrolyte cations (L i+, Na+, Cs+, (CH3)(4)N+, Ca2+, Ba2+) on electroreduction kinetics of PtCl4 2- at a dropping mercury electrode is studied. The electroreduction wave fo r PtCl42- is complicated by a polarographic maximum of first kind followed by a pronounced plateau of limiting current, after which the current passes through a minimum. The electroreduction occurs probably via two different mechanisms and presumably involves the same species, because the charge z(i ) of discharging species, determined by the Frumkin-Petrii method, remains virtually constant (z(i) congruent to -1) on both descending (E = -0.6 to - 1.0 V vs. SCE) and ascending (-1.3 to -1.6 V) branches of polarization curv es and is independent of the nature of the supporting-electrolyte cation. T he mechanism is presumably changed by a changed orientation of discharging species relative to the electrode surface.