Effect Of Nickel And Lanthanum Catalysis On The Hydrogen Storage Performance Of Magnesium

Magnesium are attractive for hydrogen storage materials because of its abundant resources,low cost and high hydrogen capacity(7.6 wt.%).However,pure magnesium as the hydrogen storage material can not be widely applied due to the high thermodynamic stability and slow kinetics of hydrogen absorption and desorption.Therefore,doping catalyst is an effective approach to improve the performance of magnesium-based hydrogen storage materials.In this paper,Ni/Mg and La2O3/Mg hydrogen storage materials were regarded as the research objects.The morphology and structure of the materials were characterized by X-ray diffraction(XRD),scanning electron microscope(SEM),transmission electron microscope(TEM).The properties of materials were tested by p-c-T curves,hydrogen sorption kinetics curves.and differential scanning calorimetry(DSC)curves.In this paper,it mainly studied the effect of Ni and La2O3 on the thermodynamic and kinetics of magnesium by the rate of hydrogen absorption/desorption and the calculation of the enthalpy change and activation energy.In the process of ball milling,Ni and La2O3 particles with high hardness can help to grind Mg particles with small hardness,which can rapidly reduce Mg grain to nano-scale,and it is consistent with the calculated results after refined fitting of XRD test data.This is conducive to improving the hydrogen absorption and desorption rates of Mg in the process of hydrogen sorption.From TEM images and XRD patterns,it can be seen that Mg still exists after hydrogen absorption at 350?,which indicates that Mg has not been completely hydrogenated at 350?.During ball milling,Ni does not react with Mg,which only acts as a grinding aid.During the process of hydrogen absorption and desorption,Ni reacts with Mg and H2 to form Mg2NiH4.It is also found that Ni catalysis can reduce the hydrogen desorption temperature of MgH2 by 23?.Like Ni,La2O3 also does not react with Mg during ball milling,which only acts as grinding aid.La2O3 does not react with H2 during hydrogen absorption and desorption,only catalyzes hydrogen absorption and dehydrogenation of Mg,which is different from Ni.The p-c-T curves show that adding Ni or La2O3 can increase the hydrogen absorption activity of Mg and reduce the hydrogen sorption plateau.Kinetic curves show that the hydrogen absorption and desorption rate of Mg have increased significantly with the addition of Ni or La2O3.DSC curves show that the hydrogen desorption rate of MgH2 have decreased with the addition of Ni or La2O3.With the addition of Ni,the activated energy of hydrogen absorption decreases by 58.9 kJ/mol,and the activated energy of hydrogen desorption decreases by 45.34 kJ/mol.With the addition of La2O3,the activated energy of hydrogen absorption decreases by 49.8 kJ/mol,and the activated energy of hydrogen desorption decreases by 23.1 kJ/mol.So,the kinetic performance of hydrogen sorption of Mg is substantially improved with the addition of Ni and La2O3.In addition,the catalytic effect of Ni is better than that of La2O3.