Hydrogen production via hydrolysis of Mg-oxide composites

Mg is an attractive candidate for hydrogen generation due to its low cost and high availability as well as its high theoretical H-2 yield and the formation of environmentally friendly byproducts during hydrolysis. On the other hand, the hydrolysis reaction of Mg is rapidly interrupted by the formation of a passive magnesium hydroxide layer. Hydrogen generation via the reaction of ball milled Mg-oxide composites with 3.5% NaCl solution at room temperature was investigated in this paper. Several cheap metal oxides (Fe2O3, CaO, MoO3, Fe3O4, Nb2O5 and TiO2) were used to assess the effects of hydrolysis on the magnesium powder. The results show that Mg-5 wt% MoO3 and Fe2O3 demonstrate the best hydrolysis performance (above 888 mL/g and 95.2% of theoretical hydrogen generation yield in 10 min) in comparison to Mg-Fe3O4, Mg-TiO2, Mg-Nb2O5 and Mg-CaO composites. In addition, the effects of different Mg contents and milling times on the hydrolysis property of the Mg powder were also studied and it was concluded that the addition of 5 wt% oxide and a milling time of 1 h are the optimal parameters for the production of the Mg-MoO3 composite. Moreover, the valence state of metal ions was found to have an important influence on the hydrolysis reaction for the first time. The effect of valence state has been studied for Mg-Fex+ and Mg-Mox+ composites and the results show that a higher valence value of the transition metal ions leads to a better hydrolysis property of Mg. (C) 2016 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.