Effects of transition metal oxide and Ni addition on the hydrogen-storage properties of Mg

Abstract

Mg-based hydrogen-storage materials with the compositions of Mg–10 wt%oxide (oxide = Cr2O3, Fe2O3, MnO, and SiO2) and Mg–xFe2O3–yNi were prepared by reactive mechanical grinding (RMG). Taking into consideration the hydriding and dehydriding rates and the cost of materials, Fe2O3 prepared by spray conversion is an appropriate oxide additive to Mg. Mg–5 wt%Fe2O3–15 wt%Ni exhibited the best hydrogen-storage performance among the Mg–xFe2O3–yNi hydrogen materials. It stored 5.47 wt%H under 1.2 MPa H2 for 60 min and released 5.42 wt%H under 0.1 MPa H2 for 15 min at 593 K. The addition of Fe2O3 and Ni to Mg by the RMG shortens the diffusion distances through the reduction of the particle size of Mg. These additives are also considered to facilitate nucleation by creating many defects on the surface and in the interior of Mg. The added Fe2O3 and Ni themselves may also act as active sites for the nucleation. Ni forms the Mg2Ni phase by a reaction with Mg, and Fe appears from the reduction of Fe2O3 by hydrogen after hydriding–dehydriding cycling.