THE INFLUENCE OF POTASSIUM-ION ON THE ELECTRODEPOSITION AND ELECTROCHEMISTRY OF ELECTROLYTIC MANGANESE-DIOXIDE

Electrolytic manganese dioxide (EMD) has been prepared with varying levels of incorporated K+, in the range 54 to 5150 ppm K, by varying the amount of K+ in the electrolyte. Higher acid concentrations or higher current densities decrease the amount of incorporated K+. X-ray diffraction patterns reveal the presence of an alpha-MnO2 phase (containing potassium) as a minor component along with the usual gamma-MnO2. Cyclic voltammograms in 9.0 mol dm-3 KOH (nu = 0.5 mV s-1) show that the Mn(IV) reduction peaks shift to more negative potentials while the peak currents decrease with increasing K+, reflecting the increased levels of alpha-MnO2 in the EMD. Chronopotentiometry reveals that voltages (corrected for iR loss) measured during reduction at 0.02 A g-1 are lower for EMDs containing > 590 ppm K, consistent with the presence of alpha-MnO2 in the EMDs. Potassium levels less-than-or-equal-to 590 ppm K do not prima facie effect the electrochemical behavior of EMD under the conditions of this study.