S. Rodrigues et al., A cyclic voltammetric study of the kinetics and mechanism of electrodeposition of manganese dioxide, J APPL ELEC, 28(11), 1998, pp. 1235-1241
The kinetics and mechanism of electrooxidation of Mn2+ ions to MnO2 (EMD) h
as been studied in electrolytes comprising MnSO4 and H2SO4 by cyclic voltam
metry at 80 degrees C. The voltammogram of a Pt electrode cycled between 0.
6 and 1.6 V vs SCE exhibits an anodic current peak at about 1.3 V vs SCE re
sulting in the deposition of MnO2 on the electrode, while a cathodic peak a
ppears at 0.8 V vs SCE. It is shown that the pair of peaks do not correspon
d to a single reversible reaction but represent two separate irreversible e
lectrode processes. The cyclic voltammetric peak current for the deposition
of EMD is found to be proportional to the square root of Mn2+ ion concentr
ation in the electrolyte and independent of acid concentration. Based on th
ese results, a mechanism for the formation of EMD involving diffusion of Mn
2+ ions to the electrode surface,oxidation of Mn-surface(2+) to Mn-ads(3+),
and H2O to OHads as the primary oxidation steps is invoked. Mn-ads(3+) ions
dissociate disproportionately into Mn-ads(2+) and Mn-ads(4+) ions at the e
lectrode surface. The Mn-ads(2+) and Mn-ads(4+) ions, respectively, react w
ith OHads and H2O resulting in the formation of EMD.