Hydrogen generation via hydrolysis of Mg2Si

A convenient, high-density and low-cost hydrogen supply technology is essential to hydrogen energy system by providing hydrogen to fuel cell component. Magnesium silicide (Mg2Si) can be a good hydrolysis candidate due to its low cost and ability of releasing hydrogen gas during hydrolysis process. However, previous studies have demonstrated that Mg2Si could easily produce large amount of silanes during hydrolysis reaction, which may cause serious problem of explosive danger when in contact with air. Here it is the first time that Mg2Si was used for generation of hydrogen by a simple and convenient one-step hydrolysis reaction. In this study, hydrolysis kinetics and mechanisms of Mg2Si in NH4Cl and NH4F solutions were investigated. The silanes could be almost completely turned into hydrogen by introduction of fluorine ion during the hydrolysis reaction of Mg2Si, leading to very low silanes content in the produced hydrogen. The kinetic studies indicated that when the concentration of the NH4F solution increased to 13.0%, the hydrogen generation rate and the reaction yield were improved significantly and reached the best performance, producing 466 mL g−1 H2 in 10 min and 616 mL g−1 H2 in 30 min at 25 °C. The activation energy was calculated to be 37.3 ± 0.8 kJ mol−1. Furthermore, the hydrogen yield and the hydrolysis rate of Mg2Si can be further improved by high-energy ball milling. After ball milling for 2 and 5 h, the hydrogen generation yield in 30 min increased to 698 and 771 mL g−1, respectively, and the activation energy was decreased to 23.9 ± 0.6 kJ mol−1 and 12.9 ± 0.1 kJ mol−1, respectively. The results revealed that NH4F can be a promising reagent for promoting the hydrolysis of Mg2Si for onsite hydrogen supply.