Channel role of nano-Mg2Ni in enhancing hydrogen absorption and desorption performances in Mg/Mg2Ni system

Abstract

Mg2Ni is considered as a promising material for both storage hydrogen and catalyze MgH2 decomposition. Using Mg2Ni–Mg as a matrix material may achieve the combination of both advantages. Herein, hypoeutectic and hypereutectic Mg100-xNix (x = 11, 15, 22) alloys are prepared in this work to investigate the relationship between Mg2Ni in different microstructures and hydrogen storage performances. The results indicate that Mg2Ni connected Mg–Mg2Ni eutectics are formed besides the lamellar eutectic in Mg85Ni15 and Mg78Ni22 alloys because Mg2Ni precipitates firstly in eutectics, which are different from the α-Mg connected Mg–Mg2Ni eutectics in Mg89Ni11 alloy. Mg100-xNix alloys show rapid hydrogen absorption rates at ranges of both 125–175 °C and 275–325 °C because the presents of abundant interfaces generated by nano-Mg2Ni particles. Mg89Ni11 alloy with hydrogenation capacities of 3.6 wt% at 125 °C due to the large hydrogenation driving force of α-Mg. The Mg78Ni22 hydride with the highest proportion nano-Mg2Ni phase presents the fastest dehydrogenation rates. Two independent decomposition peaks are observed in the DSC curves of Mg100-xNix hydrides and the desorption temperature of Mg2NiH4 becomes lower with increasing Mg2Ni content due to Mg2Ni nanoparticles providing channels for the rapid diffusion of H atoms, and the reduced H concentration is conducive to the decomposition of MgH2.