OXYGEN REGENERATION OF DISCHARGED MANGANESE-DIOXIDE ELECTRODE .2. GENERAL PHENOMENA OBSERVED ON ELECTRODEPOSITED LAYER ELECTRODES AND MEMBRANE ELECTRODES

The diffusion of oxygen molecules in both external and interstitial electrolyte solutions and the low solubility of this gas in the concentrated KOH solutions are the processes that limit the kinetics of oxygen regeneration of discharged gamma-MnO2 electrode. Consequently, to increase the kinetics of regeneration it is necessary: (i) to shorten the length of oxygen diffusion pathway. In practice, this involves placing the oxygen source near the surface of the discharged manganese dioxide particles. The most favorable arrangement is surrounding the particles with a thin electrolyte film allowing quick oxygen dissolution up to saturation; (ii) to increase the interface between particles and electrolyte so as to get the largest area where oxidation reactions by oxygen can occur, (iii) to decrease the diffusion path of the oxygen in the interstitial and external electrolyte. To improve the oxygen regeneration, it is better to optimize the electrode device rather than to look for new materials having improved oxygen reoxidation constants. Particularly, the most important improvements would be the formation of a large area thin electrode device. With a membrane electrode device the oxygen-regeneration capacity reaches 2.9 e/Mn, i.e., an increase of about 450%, compared to the case without regeneration. By comparison a thick electrode device shows an increase of 250%.