Electrochemistry coupled with spectroscopy was used to study the mechanism of oxidn. of Mn2+ to MnO2 at a reticulated vitreous carbon-optically transparent electrode (RVC-OTE) in 0.5 M H2SO4 + 0.5 M MnSO4 soln. Absorbance was followed over 400-600 nm. At 400-700 mV, at a polarization rate of 1 mV/s, absorbance was unchanged. Upwards of 750 mV, Mn3+ aqua-complexes were formed, and above 1000 mV, MnO2 was formed. The Mn3+ ions could diffuse away from the electrode to become disproportionated (-> Mn2+ + Mn4+) or hydrolyzed to yield Mn(III) oxyhydroxide and MnO2, which remained in the RVC pores.