Electrochemical Studies on the Ca-Based Hydrogen Storage Alloy for Different Milling Times

The CaNi4.8Mn0.2 powder was synthesized by mechanical alloying, under an atmosphere of argon at room temperature, at different milling times (2, 10, 20, 30, 40, 50 and 60 h) with ball to powder weight ratio of 8:1. The structural and morphological characterizations of the CaNi4.8Mn0.2 powder were carried, respectively, by scanning electron microscopy and X-ray diffraction. After 2 h, all the alloys had a biphasic structure, two major phases, Ni and Ca2Ni7, remained virtually unchanged when a small amount of Mn was added. After more than 40 h of milling, the same peaks of the Ni and Ca2Ni7 phases appeared, while the intensity of the peaks decreased, indicating an additional amorphization process. After 50 h of milling, this damping was followed by the crystallization amorphization. The electrochemical properties of CaNi4.8Mn0.2 electrodes were studied at different milling times (10, 20, 30, 40, 50 and 60 h) and in KOH electrolyte concentrations (1 M and 6 M) at ambient temperature, as anodes in the Ni-MH battery. Different techniques were used, such as galvanostatic polarization, potentiostatic polarization and potentiodynamic polarization.