Key Takeaways & Executive Findings
- •• Ag substitution reduces the formation enthalpy of Mg2NiH4, weakening M–H bonds and lowering hydrogen desorption temperatures. • The Mg1.95Ag0.05Ni alloy was successfully produced by vacuum arc melting and melt spinning, yielding ribbons with fast hydrogen exchange and high storage capacity. • DFT and uMLIP simulations confirmed that Ag doping destabilizes the hydride phase, consistent with experimental observations. • Multi-technique characterization (XRD, XPS, SEM, TEM, DTA, TGA, Sievert and electrochemical) links the structural modifications to improved hydrogen storage performance.
Abstract
In this study, the hydrogen storage properties of Mg1.95Ag0.05Ni alloy and its melt-spun ribbons were systematically investigated. The alloy was synthesized by vacuum arc melting followed by melt spinning to produce micro/nanostructured ribbons. Comprehensive characterization using XRD, XPS, SEM, TEM, DTA, TGA, and electrochemical measurements revealed that Ag substitution alters the electronic environment and reduces the formation enthalpy of the Mg2NiH4 hydride, thereby weakening metal-hydrogen bonds and enabling hydrogen desorption at lower temperatures. Density functional theory (DFT) and universal machine learning interatomic potentials (uMLIP) calculations further confirmed the thermodynamic destabilization of the hydride phase. The combination of experimental and computational approaches provides a comprehensive understanding of the beneficial effects of Ag on Mg-Ni-based hydrogen storage materials, contributing to the development of high-performance hydrogen storage alloys.
1. Introduction
Mg-based alloys are considered promising materials for hydrogen storage due to their high gravimetric capacity, but their practical application is limited by slow kinetics and high thermodynamic stability of the hydride phase. Among various Mg-based alloys, Mg2Ni has attracted attention because of its faster hydrogen absorption/desorption capabilities compared to pure Mg and its role in reducing kinetic barriers, which is a major disadvantage of Mg [18]. In particular, micro and nanostructured Mg2Ni alloys are preferred in energy storage systems due to their fast hydrogen exchange and high storage capacity. In an extensive effort to further improve the properties of Mg2Ni, there are widespread studies dedicated to alloying with other transition metals [19].
The primary thermodynamic impact of Ag substitution is the destabilization of the hydride phase. The differences in electronegativity and atomic radius of Ag alter the electronic environment within the lattice, effectively reducing the formation enthalpy (ΔH) of the Mg2NiH4 hydride. This thermodynamic alteration weakens the metal–hydrogen (M–H) bonds, consequently lowering the energy required for bond breaking and facilitating hydrogen desorption at lower temperatures. This study aims to investigate the hydrogen storage properties of Mg1.95Ag0.05Ni alloy. The research focuses on the structural (XRD, XPS), microstructural (SEM, TEM), thermal (DTA, TGA), and hydrogen storage properties (Sievert-type, electrochemical) of the Mg1.95Ag0.05Ni alloy and ribbons.
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S.E. Sünbül et al. (2025). Comprehensive structural and hydrogenation analysis of arc-melted and melt-spun Mg1.95Ag0.05Ni alloy. Journal of Mineral Metallurgy and Materials Science. https://doi.org/10.1007/s12613-026-3434-5
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Frequently Asked Questions
Why is silver added to Mg2Ni hydrogen storage alloys?
Silver substitution reduces the formation enthalpy of the Mg2NiH4 hydride, weakening metal-hydrogen bonds and facilitating hydrogen desorption at lower temperatures.
What synthesis methods were used in this study?
The Mg1.95Ag0.05Ni alloy was prepared by vacuum arc melting and then rapidly solidified into ribbons using the melt-spinning technique.
What computational methods were applied?
Density functional theory (DFT) with the APW+lo method and universal machine learning interatomic potentials (uMLIP) were used to study phase stability and electronic structure.
What characterization techniques were employed?
The alloy and ribbons were characterized by XRD, XPS, SEM, TEM, DTA, TGA, and both Sievert-type and electrochemical hydrogen storage measurements.
What are the main benefits of Ag substitution?
Ag doping destabilizes the hydride phase, reducing the energy required for hydrogen desorption and improving hydrogen storage kinetics.
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