Enhanced de-/hydrogenation kinetics of a hyper-eutectic Mg85Ni15-xAgx alloy facilitated by Ag dissolving in Mg2Ni

In order to accelerate the hydrogen absorption and desorption rates of hyper-eutectic Mg-Ni alloy, Mg85Ni15-xAgx (x = 0, 0.2, 0.4, 0.6) alloys were prepared and the results show that fishbone eutectic was formed without change of phase composition. It was found that Ag atoms were dissolved in fishbone eutectic Mg2Ni and the average cell parameters of Mg2Ni increase with the increase of Ag content. Owing to adjusting lattice parameters, the hydrogen absorption and desorption rates of Mg85Ni14.8Ag0.2 alloy are significantly improved. About 4.47 wt% hydrogen is absorbed at 275 degrees C only in 1 min, with the maximum capacity of 5.84 wt% in 60 min. The Mg85Ni15-xAgx (x = 0.2, 0.4, 0.6) hydrides can be completely dehydrogenated within 10 min at 275.. The corresponding activation energies for dehydrogenation are determined to be 80.4, 97.1 and 97.8 kJ/mol, respectively, which are lower than 117.8 kJ/mol of Mg85Ni15. The onset dehydrogenation temperature of Mg85Ni14.8Ag0.2 hydride is reduced to 201 degrees C, which is much lower than 220 degrees C of the Mg85Ni15 hydride. The dissolving of Ag in Mg2Ni leads to a lattice expansion, which facilitates the diffusion for hydrogen atoms and decrease the energy barrier required for nucleation of Mg/Mg2Ni. As a result, the hydrogen de-/absorption rates were obvious accelerated and the onset dehydrogenation temperature was decreased. (c) 2022 Elsevier B.V. All rights reserved.

Automated summary

By dissolving Ag in hyper-eutectic Mg-Ni alloy, a fishbone eutectic structure is formed, and adjusting lattice parameters can significantly improve the hydrogen absorption and desorption rates while reducing the dehydrogenation temperature.