Two specific phenomena were observed during electrochemical charging and discharging processes for Mg2Ni alloy electrode at the first cycle, i.e., the decrease of the absorbed hydrogen content (difference between the charged quantity of electricity and the hydrogen gas volume converted to the quantity of electricity) in an alloy during charging process and the discharge capacity larger than the absorbed hydrogen content. In order to investigate these phenomena, the electrochemical behavior of Mg2Ni alloy powders prepared by casting and bulk mechanical alloying(BMA) was studied in 6M KOH solution and water. It was consequently found that Mg(OH)2 was formed and at the same time atomic hydrogen was also formed in the solution so that the hydrogen was absorbed into Mg2Ni alloy. Hydrogen gas was also generated from the alloy surface after hydrogen absorbed was almost saturated in the alloy. Consequently, it was clearly concluded that the specific phenomenon of the former is due to the generation of gaseous hydrogen when Mg2Ni alloy reacted with H2O. The latter is also because of the discharge of the hydrogen absorbed into Mg2Ni by forming Mg(OH)2, except for discharge of the hydrogen absorbed electrochemically.
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