A Voltammetric Study of the Reduction of Chromic Acid on Bright Platinum

The reduction of chromic acid catalyzed and uncatalyzed with was studied on Pt microelectrodes by steady‐state (galvanostatic and potentiostatic voltammetry) and nonsteady‐state (cyclic voltammetry) polarization techniques. The rest potential of Pt in chromic acid is a mixed potential. Although the reduction of hexavalent Cr to trivalent occurs readily at Pt cathodes, the reverse process does not take place at Pt anodes due to the high overvoltage for ion oxidation. It is for this reason that anodes are used in commercial Cr plating practice since the overvoltage for evolution is much higher on than on Pt, thus allowing the current to be used in the oxidation of ion instead of evolution. The reduction of an oxidized Pt surface occurs with more difficulty in chromic acid than in . Metallic Cr is deposited in catalyzed chromic acid at the expense of the reduction of Cr VI to Cr III and evolution.