OVERCHARGE PROTECTION OF MNO2 CATHODES

A test cell has been developed to examine some metal oxides for their possible application as active oxygen-evolving materials. The tests were run with doped MnO2 electrodes in 9 M KOH and applying current densities Up to 10 mA/cm2. The most effective additives were vanadium pentoxide (V2O5) (if applied in higher concentrations), nickel cobaltites (NiO.Co2O3 and NiO.2CoO) and the cobalt-spinel Co3O4. These compounds were able to convert electrical charges to oxygen with an efficiency close to 100%. The promoted oxygen evolution prevents the oxidation of the MnO2 electrode to soluble manganates subsequently disproportionating to Mn(IV) and Mn(II) causing a loss of active material because the latter will not be re-oxidized to Mn(IV) on charge.