Linear sweep voltammetry of manganate(VII), manganate(VI), and manganate(V) in alkaline media

Abstract

Electrochemical reactions were assigned to the voltammetric waves obtained in alkaline KMnO 4 and K 2MnO 4 solutions. Plots of i p (AC°ν 1 2 ) −1 and i ap i cp −1 ν s log ν indicate that at slow potential scan rates in MnO − 4 solutions ranging from 0·07 to 0·19 F in NaOH the first step in MnO − 4 reduction is a l-electron reversible charge transfer with no coupled chemical reaction; at fast scan rates (⩾ V s −1 the process becomes quasi-reversible. The standard rate constant and the activation energy for the MnO − 4/MnO 2− 4 charge transfer step were estimated. Plots of i p (AC°ν 1 2 ) −1 and i ap i cp −1 ν s log ν indicate that in 4·O F KOH and at potential scan rates between 0·005 and 2·V s −1 the reduction of MNO 2− 4 to MnO 3− 4 is a reversible charge transfer with no coupled chemical reaction. The diffusion coefficients of MnO − 4 and MnO 2− 4 in alkaline solutions are reported.