In-situ influence of TiF3 catalyst on the hydrogen storage behavior of Mg-Ni-Y based alloy

Abstract

Solid-state magnesium-based hydrogen storage encounters challenges associated with sluggish hydrogen absorption and desorption kinetics. The incorporation of catalysts is considered a promising means to improve the hydrogen absorption and desorption kinetics of these alloys. In this experiment, we prepared the Mg80Ni15Y5 alloy via vacuum melting and incorporated TiF3 in varying weight percentages of 1, 3, 5, and 7 wt% through ball milling. The phase composition and microstructure of the samples were analyzed and measured using X-ray diffraction meter (XRD), Transmission Electron Microscope (TEM), Selected Area Electron Diffraction (SAED), and Scanning Electron Microscope (SEM) techniques. The results revealed that the TiF3 introduced two catalytically phases, MgF and TiF2. And TiF2 transforms into TiH2 after hydrogen absorption, which covers the surface of MgH2 and prolongs the nucleation time of MgH2.Furthermore, the addition of TiF3 made the surface of alloy markedly coarser and more irregular and few cracks, providing channels for hydrogen diffusion. This behavior optimized the kinetic performance of the alloy. It was observed that the samples containing 7 wt%TiF3 achieved 99.2 % hydrogen saturation even in low-temperature. It's worth mentioning that the addition of 7 wt% TiF3 to the Mg80Ni15Y5 alloy significantly reduced the dehydrogenation activation energy to 58.5 kJ/mol, as opposed to pure magnesium with an activation energy of 158.2 kJ/mol. This substantial reduction has effectively accelerated the hydrogen absorption and desorption rates of the alloy. However, it had only a negligible impact on the thermodynamic properties of the sample with 7 wt%TiF3.