Hydrogen Storage Properties Of CaMg₂ Based Alloys And Hydrolysis Performances Of Corresponding Hydrides

The hydrolysis of hydrides is one of the most attractive ways to produce hydrogen in lots of hydrogen generation methods with the advantages for the plenty of sources, the massive hydrogen production, high purity and environment friendly. The hydrolysis of Mg H2 has hydrogen production as far as 15.2wt.% in a mild reaction condition. But the byproduct, Mg(OH)2 will form a passive film around the Mg H2 particle and the reaction is interrupted due to the separation of H2 O from Mg H2. In addition, the high temperature was necessary for the synthsis of Mg H2 which increases the cost and energy consuming.A series of Ca Mg2 based alloy have been prepared by introduction me lting and hydrogen storage properties and hydrolysis performance of its hydrides had also been measured. The result shows that the introducing of N i into Ca Mg2 greatly improved the hydrogen absorption property and reduced activation energy of Ca Mg1.9Ni0.1 alloy compare with that of Ca Mg2. Ca Mg1.9Ni0.1 could absorb hydrogen at room temperature without any activation treatment. The hydrogen storage capacity is up to 4.5 wt.% after 15 hours at 25°C under 5MPa hydrogen pressure. The PCI curves are also measured to get the basic thermodynamics datas in hydrogenation and dehydrogenation processes. The main phase of Ca Mg2 in Ca Mg1.9Ni0.1 alloy absorbs hydrogen and transform into a unknown phase. The hydrogenation kinetic curves of Ca Mg1.9Ni0.1 in 25°C, 40°C, 60°C, 80°C were measured and fitted with JMAK equation. The activation energy is calculated to be 39.7k J/mol H2 while the enthalthapy change and entropy through Van’t Hoff equation were calculated to be-96.7k J·mol-1 and-167.2 J·mol-1·K-1.The hydrogenated Ca Mg1.9Ni0.1 alloy(Ca Mg1.9Ni0.1Hx) shows excellent hydrolysis performance. Ca Mg1.9Ni0.1H3.72 can produce 1053 m L/g hydrogen in 12 minutes at room temperature in deionized water, which is 94.6% hydrogen of its theoretical capacity. The rate of hydrogen generation of Ca Mg1.9Ni0.1H3.72 is 53 m L·min-1·g-1hydrogen in first 20 min. Ca Mg1.9Ni0.1H4.97 can yield 1036 m L/g hydrogen in 12 minutes, which is 87.3% hydrogen of its theoretical capacity.