Nanocrystalline Mg80Y4Ni8Cu8 alloy with sub-10 nm microstructure and excellent hydrogen storage cycling stability prepared by nanocrystallization

Abstract

Nanostructure is effective for improvement of the sluggish hydrogenation kinetics of Mg-based hydrogen storage alloys. However, preparation of homogeneous and fine nanocrystalline alloys is still difficult especially using the traditional physical-metallurgy methods. The present work reports that homogeneous and ultra-fine microstructure in which spherical Mg2Cu and Mg2Ni grains with size smaller than 10 nm can be prepared by nanocrystallization of an amorphous Mg80Y4Ni8Cu8 alloy. Formation of the ultra-fine microstructure is attributed to the simultaneous nucleation of Mg2Cu, Mg2Ni and Y2MgNi2 at quite low temperature and usual existence of well-matched boundary characters. The crystallized Mg80Y4Ni8Cu8 alloy absorbs 4 wt % H2 with fast hydrogen absorption kinetics and presents excellent cycling stability that the capacity retention reaches to 92% after 100 gas-solid cycles. The result enlightens the possibility that further refinement and stabilization of Mg-based nanocrystalline alloys by optimization of the crystallization kinetics, phase constitution and boundary arrangement.