Hydrogen storage thermodynamics and kinetics of the as-cast and milled Ce-Mg-Ni-based alloy

Abstract

Aiming at investigating the improvement of hydrogen storage performance of the ternary Ce5Mg85Ni10 alloy after mechanical ball milling, the phase transformation and microstructure evolution of the milled alloys are observed by XRD, SEM and TEM. After ball milling, the alloys mainly exhibit nanocrystalline and amorphous structures and consist of Mg, Mg2Ni and CeMg12 phases. After hydrogen absorption, the milled alloys consist of MgH2, Mg2NiH4 and CeH2.73 phases. Isothermal and non-isothermal reaction curves of hydrogen absorption and desorption of the milled alloys are characterized by an Sievert apparatus, DSC and TGA. The Arrhenius and Kissinger equations are used to calculate the hydrogen desorption activation energy. For the Ce5Mg85Ni10 alloy, its structure and thermodynamics and kinetics performance of hydrogen storage strongly depend on the ball milling time. The results shows that ball milling for 5 h can achieve the optimal activation and kinetics performances but further prolonging the ball milling time lead to the impairment of hydrogen storage performance. Besides, ball milling time has little effect on thermodynamic property. Experiments results show that the 5 h-milled alloy after activation can absorb 4 wt% H2 in 18 s at 473 K and 3 MPa, and can desorb 3 wt% H2 in 906 s at 533 K and 1 × 10−4 MPa. In addition, the hydrogen desorption enthalpy change of the 5 h-milled alloy is 75.28 kJ/mol and the hydrogen desorption apparent activation energy of this alloy is 62.69 kJ/mol.