Phase structure and electrochemical characteristics of CaNi4.7Mn0.3 hydrogen storage alloy by mechanical alloying

Abstract

In this paper, we study systematically the effect of ball/powder weight ratio on the morphological, structural, and electrochemical properties of CaNi 4.7 Mn 0.3 powder alloy by mechanical milling. The CaNi 4.7 Mn 0.3 alloy powder is elaborated for an optimal milling time of 40 h with 8:1 and 12:1 ball/powder weight ratios. The X-ray diffraction (XRD) characterization shows that the CaNi 4.7 Mn 0.3 alloy powder is characterized by a nanocrystalline/amorphous crystallographic state and exhibits two major Ni and CaNi 3 phases irrespective of the ball/powder weight ratio. The CaNi 4.7 Mn 0.3 electrode activates rapidly in the first cycle regardless of the ball/powder weight ratio, and the best value of maximum discharge capacity is obtained for an 8:1 ratio (125 mAh g −1 ). The values of diffusion coefficient/mean grain size squared ratio D H a 2 , Nernst's potential E 0 , and exchange current density I 0 at the first activation cycle are the best for 8:1 ball/powder weight ratio. After activation, the discharge capacity decreases exponentially regardless of the ball/powder weight ratio. Indeed, the capacity loss and the degradation rate after 50th cycle are about 71%, 10.71 cycle −1 and 53%, 2.95 cycle −1 for 8:1 and 12:1, respectively. The evolution of the D H a 2 ratio, E 0 , and I 0 during the cycling is in good agreement with that of the discharge capacity. The highest values of the diffusion coefficient D H , Nernst's potential E 0 , and exchange current density I 0 after 50th cycle are observed for 8:1 ball/powder weight ratio. KeywordsCaNi 4.7 Mn 0.3 hydrogen storage alloy • Mechanical alloying • Morphological and structural properties • Electrochemical properties

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Electrochemical study of LaGaO3 as novel electrode material of hydrogen battery (Ni/MH)

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