Improved hydrogen storage thermodynamics and kinetics of La-Ce-Mg-Ni alloy by ball milling

Reducing particle size and modifying surface state by ball milling are recognized as a useful method to improve the hydrogen absorption kinetics of Mg-based alloys. In order to obtain amorphous and nanocrystalline structures, ball milling was used to process the as-cast La7Ce3Mg80Ni10 alloy ingot. The effects of ball milling time (5-30 h) on the structures and the thermodynamics and kinetics of hydrogen absorption/desorption of the asmilled alloys were studied. The XRD, SEM and TEM were applied to investigate the structure of the alloys. The Sievert apparatus, DSC and TGA were applied to study the isothermal and non-isothermal properties of hydrogen absorption/desorption. The Arrhenius and Kissinger methods were used to calculate the activation energy of hydrogen desorption. The results indicate that the 10 h-milled alloy has the optimal activation performance and hydrogen absorption/desorption kinetics. Prolonging or shortening the ball milling time results in the impaired hydrogen storage properties. The 10 h-milled alloy in fully activation state can absorb 4 wt% H2 in 80 s at 473 K and 3 MPa, and it can desorb 3 wt% H2 in 191 s at 573 K and 1 x 10-4 MPa. The hydrogen desorption enthalpy (& UDelta;H) of the 10 h-milled alloy is 74.21 kJ/mol. Moreover, the 10 h-milled alloy has the smallest apparent activation energy for hydrogen desorption (62.9 kJ/mol), which is the reason why it has the optimal hydrogen storage properties.