Study on in Situ Modification Mechanism of Mg-Ce-Y Based Hydrogen Storage Alloy by Znf2

Abstract

The Mg90Ce5Y5 + x wt. % ZnF2 (x = 3, 6, 10, 15) composites were prepared by mechanical ball-milling. The effects of ZnF2 contents on the hydrogen absorption and desorption properties of Mg90Ce5Y5 alloy were investigated by XRD, ICP-OES, TEM, PCT and DSC. The excellent hydriding-dehydriding characteristics of the samples after activation were attributed to the catalytic effect of the MgF2 and MgZn2 phases introduced in situ by the addition of ZnF2. The Mg90Ce5Y5 + 6 wt. % ZnF2 composites exhibit the fastest hydrogen adsorption/desorption kinetics and lower decomposition temperatures. At 360 °C, 4.12 wt. % H2 can be absorbed within 180 s, and completely dehydrogenated within 740 s. In addition, the activation energy of dehydrogenation is reduced to 89.5 kJ/ mol, the optimal dehydrogenation temperature is reduced to 318 oC. It is due to the generation of in situ catalysts that weaken the Mg-H bond energy, refine the grain sizes, expand specific surface area and increase hydrogen diffusion paths. However, the improvement of the thermodynamics of the composites is limited, the enthalpy is 75.9 kJ/mol H2.

Keywords: Hydrogen storage materials, catalysts, microstructure, kinetics, thermodynamics