In situ formed Mg(BH4)2 for improving hydrolysis properties of MgH2

The hydrolysis of MgH 2 delivers high hydrogen capacity (15.2 wt%), which is very attractive for real-time hydrogen supply. However, the formation of a surface passivation Mg(OH) 2 layer and the large excess of H 2 O required to ensure complete hydrolysis are two key challenges for the MgH 2 hydrolysis systems. Now, a low-cost method is reported to synthesize MgH 2 @Mg(BH 4 ) 2 composite via ball-milling MgH 2 with cheap and widely available B 2 O 3 (or B(OH) 3 ). By adding small amounts of B 2 O 3 , the in-situ formed Mg(BH 4 ) 2 could significantly promote the hydrolysis of MgH 2 . In particular, the MgH 2 –10 wt% B 2 O 3 composite releases 1330.7 mL·g −1 H 2 (close to 80% theoretical hydrogen generation H 2 ) in H 2 O and 1520.4 mL·g −1 H 2 (about 95%) in 0.5 M MgCl 2 in 60 min at 26 °C with hydrolysis rate of 736.9 mL·g −1 ·min −1 and 960.9 mL·g −1 ·min −1 H 2 during the first minute of the hydrolysis, respectively. In addition, the MgCl 2 solution allows repeated use by filtering and exhibits high cycle stability (20 cycles), therefore leading to much reduced capacity loss caused by the excess H 2 O. We show that by introducing B 2 O 3 and recycling the 0.5 M MgCl 2 solution, the system hydrogen capacity can approach 5.9 wt%, providing a promising hydrogen generation scheme to supply hydrogen to the fuel cells.