Structural, morphological, and electrochemical properties of AB₅ hydrogen storage alloy by mechanical alloying

Abstract

Mechanical alloying (MA) is one of the most promising methods in the development of intermetallic alloys and their scientific research. In this paper, elemental powder mixtures of Ca, Ni, and Mn of nominal composition CaNi5‐xMnx (with x = 0.3, 0.5, and 1) were elaborated by MA technique during different milling times (2–60 h). Structural, morphological, and electrochemical changes were investigated by X‐ray diffraction (XRD), scanning electron microscopy, and Ec‐Lab galvanostat, respectively. The XRD test indicated that each alloy has Ni and CaNi3 or CaNi5 phases. In addition, the particle size of the ground powders is decreased with increasing milling time. Furthermore, all alloys have a very high activation capacity, whereby the activation capacity can be fully realized during the first cycle. The results showed that the most significant value of discharge capacity for all alloys was 40 h.

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

“…There is an agreement between the variation of the diffusion coefficient after cycling as a function of the milling time and the evolution of some previously determined parameters ( C pmax,disch , ΔE 1∕2 ). The highest value of the diffusion coefficient, D H , is reached for a weight ratio 8:1 [32,34].…”

“…The electrochemical measurements were performed at ambient temperature using a three-electrode cell consisting of a NiOOH/Ni(OH) 2 counter electrode, an Hg/HgO reference electrode, and a M/MHx negative or working electrode immersed in an electrolyte of optimum concentration of 6 M and coupled directly with an EC-Lab V10.44 system constituted of a potentiostat/galvanostat [33,34].…”

“…This poor affinity explains the formation of pure Ca-Ni alloys, as the Mn part must then be dissolved mainly in Ni. Furthermore, the formation of the CaNi 3 phase depends on the increase of temperature during milling and on the melting temperature of each element, and according to the Ca-Ni phase diagram, at each temperature, one phase is transformed [34].…”

“…In a second previous work [33,34], we have exhaustively examined the effects of Ni substitution by Mn on the structures and electrochemical characterization of CaNi 5 − x Mn x alloys (x = 0.2, 0.3, 0.5, 1) prepared by mechanical synthesis for 40 h with a bead-to-powder ratio of 8:1. The evolution of the kinetic and redox parameters for the different Mn substitution rates is in agreement with the evolution of the discharge capacities.…”

“…In the present work, we will study the CaNi 4.7 Mn 0.3 compound for the optimal 40-h milling time and for different ball-to-powder weight ratios to demonstrate the reason for choosing the 8:1 ratio in previous work [32][33][34].…”