Discharge characteristics of CMD, EMD, RHO and synthetic birnessite in concentrated alkaline electrolyte

Different manganese dioxide polymorphs were synthesized, chemically analysed, and characterized by X-ray diffraction (XRD) and infrared (IR) spectroscopy. The MnO 2 samples were discharged in 9 M KOH at a constant current of 1 mA 0.1 g −1. One of the samples, chemically precipitated MnO 2 (CMD-2), was also discharged at 2 mA and 5 mA 0.1 g −1. The discharge was interrupted at specific depths of discharge and the products were removed from the test cell and characterized by XRD and IR spectroscopy as in the case of virgin samples. The oxidation state of the discharged products was MnO 1.75, MnO 1.68 and MnO 1.52, corresponding to r = 0.5, r = 0.75 and r = 1.0, respectively, where r is the reduction parameter. The final reduction products of 2 mA 0.1 g −1 and 5 mA 0.1 g −1 were also removed and characterized, as mentioned earlier. These products correspond to the compositions MnO 1.28 and MnO 0.87, respectively. An attempt was made to correlate the structures of these reduction products with their potentials. These results were also compared with the earlier results of Sugimori and Holton and Tye. A tentative discharge mechanism is proposed taking into consideration the different hypotheses suggested by McBreen, Sugimori, and Tye and co-workers.