Hydrogen Storage Properties Of La₂Mg₁₇-X Wt.%Ni-y Wt.%CeO₂Composites Via Ball Milling

Matrix La2Mg17alloy obtaind via melting method. And different amount of Ni and nano-CeO2added successively by mechanically alloying method. The effect of ball milling parameters on maximum hydrogen capacity have been discussed by L9(34) orthogonal experiment. The optimal combination of ball milling parameters is80h ball milling time,350rpm ball milling speed, ball to powder is40:1, in Ar atomosphere have been determined.And then, the effects of addition of different amount of Ni powder to La2Mg17on phase structure, microstructure, gas hydrogen storage properties and electrochemical kinetics have been investigated. The mechanisum research of nano-CeO2to La2Mg17-50,200wt.%Ni composite on maximum hydrogen capacity, kinetics of hydrogen absorption, dehydrogenation temperature and activation energy of dehydriding process. In addition, the effect of nano-CeO2on electrochemical kinetics properties of La2Mg17-200wt.%Ni composites have been analyzed.Different amount of Ni powder both refined the grain size of alloy and gradually transformed into amorphous and nanocrystals. Under optimum condition of La2Mg17-50wt.%Ni composites at300℃and3MPa, the maximum hydrogen capacity reached to5.130wt.%and finished the88.30%of hydrogen capacity in1min. Ni powder not only improve the maximum hydrogen capacity, also fasten the hydrogen absorption kinetics of La2Mg17alloy. PCT measurement show that addition of50wt.%Ni, reduced the formation enthalpy of La2Mg17from-26.2to-21.08kJ/mol. Characterization of DSC and calculation of Kissinger equation reveal that the addition of Ni decline the dehydrogenation temperature from337.39℃to242.39℃, a drop of95℃; the activation energy is reduce from370.26kJ/mol to93.28kJ/mol. The addition amount of200wt.%Ni to La2Mg17obtained the maximum increament from18.10mAh/g to980.70mAh/g, which is54times increasement. A series of kinetics measurement demonstrated that the electrochemical process controlled by hydrogen diffusion step on alloy bulk (x=50,100) to by both the hydrogen diffusion process and alloy surface electrochemical reaction process (x=150,200). The hydriding experiments exhibited that the addition of nano CeO2reduced the optimum hydrogenation temperature from300℃to200℃and moreover, improved the maximum hydrogen capacity of La2Mg17-50wt.%Ni composite from5.130wt.%to5.409wt.%. The dehydriding experiments show that the dehydrogenation temperature reduce10℃and the activation energy decline nearly5kJ/mol. The different addition amount of CeO2illustrated that La2Mg17-50wt.%Ni-1.0wt.%owns the best hydrogen storage properies due to the active catalystic effect of nano CeO2The1.0wt.%amount of nano CeO2to La2Mg17-200wt.%Ni improve the maximum discharge capacity from980.7to1182.0mAh/g, with a fast diffusion speed on both alloy surface and bulk.