OXYGEN-REGENERATION OF DISCHARGED MANGANESE-DIOXIDE ELECTRODE .1. GENERAL PHENOMENA OBSERVED ON THICK POWDER ELECTRODES

The results are obtained in the following conditions: The rate of discharge of the manganese dioxide has been chosen by analogy with the I.E.C. standard for the tape recorder discharge test of LR6 (AA size) alkaline cells. A reduction drain of 25 mA/g of MnO2 was passed through the electrode for 4000s. The circuit was open for 23h and the electrode is exposed to a pure oxygen atmosphere. The electrode device contains 40 mg of MnO2 and 160 mg of graphite. Nine industrial samples are studied. Thick manganese dioxide electrode discharged above 0 V/ENH (>1.2 V/Zn/Zn++) can be regenerated by oxygen. The best results are obtained for EMD MnO2, with high compacting pressure of pellet, small size of manganese dioxide particles, short diffusion path of oxygen, and large contact surface with gaseous oxygen. When such conditions are fulfilled, the total capacity reaches 1.2 e/Mn. Without oxygen-regeneration, the capacity measured at 0 V/NHE under argon is about 0.48–0.50 e/Mn. This corresponds to a relative increase of about 250% of its initial capacity. Indeed, these data are related to the described experimental conditions. They must be improved by the use of optimized conditions such as a lower graphite/MnO2 ratio. Above 0.09 V/NHE, there is no significant oxygen-reoxidation kinetics. This potential is identical to the potential of manganese dioxide during the catalyst decomposition of hydrogen peroxide. © 1990, The Electrochemical Society, Inc. All rights reserved.