Investigation on the improved hydrolysis of aluminum–calcium hydride-salt mixture elaborated by ball milling

• Novel effects of salts addition on hydrolysis of Mg–CaH2 system have been studied.
• NiCl2 shows the best performance among the salts added.
• Different milling time and sample composition affect the hydrolysis differently.
• Ca2Al(OH)6Cl(H2O)2 is newly found to be beneficial for the hydrolysis.

A novel Al based hydrogen production material is prepared by high energy ball milling using Al, CaH2 and different salts as the starting materials. The parameters affecting the Al–H2O reaction are investigated and discussed. Among the salts added, NiCl2 shows the best activation capability. The addition amount of both CaH2 and NiCl2 is found to be an important factor affecting the hydrolysis process during which a kind of hydrocalumite, Ca2Al(OH)6Cl(H2O)2, is generated and facilitates the removal of the by-product layer. Milling time can also generate significant impacts on the hydrogen generation performances of the mixture and 3 h proves to be the optimum choice in this work. The 3 h milled Al-10 mol% CaH2-10 mol% NiCl2 sample shows a hydrogen yield of 92.1% and mHGR (maximum hydrogen generation rate) of 1566.3 ml min−1 g−1. A preliminary study is carried out to understand the optimization mechanisms.