We investigated an experiment to observe the reduction reaction of the cathode during discharge in a nickel-metal hydride battery based on color changes from dark green NiOOH to light green Ni (OH)
2. The cathode NiOOH was prepared as follows. Two types of Ni (OH)
2 obtained by reacting [Ni (NH
3)
6]Cl
2 aq. and Ni (NO
3)
2 aq. with KOH aq. and the reagent Ni (OH)
2 were oxidized with NaClO. Using Al foil as the anode and KOH as the electrolyte, discharge was performed for 60 minutes. The color change of the cathode due to the discharge reduction reaction was clearly confirmed when Ni (OH)
2 obtained from [Ni (NH
3)
6]Cl
2 was used. Also, when the reagent Ni (OH)
2 was used, a color change was sufficiently confirmed. After changing the anode to a Zn plate, we also conducted a discharge experiment using NiOOH prepared from[Ni (NH
3)
6]Cl
2 for the cathode and KOH for the electrolyte. Almost the same color change as to that observed when using Al foil was confirmed.
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