Enhanced hydrogen storage capacity and kinetics in AZ61 alloy with nickel and cobalt additives: Insights into reaction mechanisms and activation energy

Abstract

This study explores the synthesis of AZ61 alloy composite powders with Co-Ni additives using high-energy ball milling (HEBM). The powders are extensively characterized using scanning electron microscopy (SEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS) to analyze their morphology, composition, structure, and bonding. The hydrogen storage capacity of the powders is measured using a Sievert's-type system revealing diverse capacities. For AZ61 alloy with Ni additive (2 µm), it absorbs 90% of the capacity in 410 s, showing an activation energy of 91.46 kJmol−1 and displays Mg2NiH4 as an intermediate. On the other hand, AZ61 alloy with Co additive requires 576 s to absorb 90% of the capacity, showing an activation energy of 117.23 kJmol−1 and Mg2CoH5 as an intermediate. When a mixture of Ni and Co is added to AZ61 alloy, it achieves 90% capacity absorption in 300 s. In the absence of additives, AZ61 alloy (15 µm) reaches 90% capacity absorption in 1600 s. The incorporation of additives significantly reduces the activation energy. A correlation between longer absorption times and larger activation energies provides valuable insights into the storage kinetics and activation energy associated with the hydrogen absorption/desorption process.