Effects of Element Substitution and Magnetic-Heat Treatment on Hydrogen Storage Properties of La0.67Mg0.33Ni3-xMx(M=Co,Cu)(x=0,0.5) Alloys

Abstract:

The effects of the substitution of Co and Cu for Ni and magnetic-heat treatment on the thermodynamics and kinetics properties of hydriding/dehydriding reaction for La0.67Mg0.33Ni3-xMx (M=Co,Cu)(x=0,0.5) hydrogen storage alloys were studied. Results show that after the partial substitution of Co and Cu for Ni, the hydrogen absorption/desorption capacity of the alloys is increased, and the temperature of endothermic peak, characteristic time (tc) of hydriding/dehydriding reaction and the activation energy are decreased. The magnetic-heat treatment improves performances of La-Mg-Ni type alloys, including hydrogen absorption capacity, the hydriding/dehydriding platform width and the hydriding/dehydriding kinetics. The thermodynamic and kinetic property of magnetic-heated La0.67Mg0.33Ni2.5Co0.5 alloy is excellent. It can absorb 1.40 wt% H and desorb 1.32wt% H. Its DSC measurement shows endothermic peak of 77.8 oC. The characteristic time (tc) of hydriding/dehydriding reaction is 91.4 and 379.3 s. The hydriding/dehydriding activation energy is calculated to be 16.3 and 23.3 kJ/mol by the Chou model.

Key words:La-Mg-Ni hydrogen storage alloys; element substitution; magnetic-heat treatment; thermodynamics; kinetics