| Hydrogen energy is an efficient and clean energy,which is hopefully able to fundamentally solve the ecological and environmental crises and the exhaustion of fossil energy that human beings are facing.As a solid hydrogen storage material,Mg H2 is potential for development due to its advantages of high hydrogen storage capacity,high purity of hydrogen release,simple reaction steps,and abundant reserves of earth resources.In the present dissertation,targeting to kinetic and thermodynamic issues relevant with slow hydrogen absorption and desorption rate and reaction temperature of Mg H2,the following works have been carried out:（1）A polyol reduction method was used to prepare nickel nano-particles with an average size of 2.14 nm.Furthermore,bimetallic core-shell particles of Ni@Pt Ni3@Pt were designed and prepared.The specific composition and structures of the core-shell particles were revealed by TEM,XRD,XPS,ICP-MS and other analytical methods.It was found that the Ni nano-particles are dispersed within the nearly amorphous Pt Ni3 phase to form the core.The Pt clusters constitute the shell.（2）The mixture of nano-Ni and Mg H2 was mechanically milled.It shows that adding 3wt.%of nano-Ni can reduce the initial dehydrogenation temperature of the system to 531K,which is 70K lower than the pristine Mg H2（601K）.The initial dehydrogenation temperature of the Mg H2-10 wt.%nano-Ni sample can be further reduced to 515K,and complete dehydrogenation can be achieved at 598K,with a capacity of 6.2 wt.%H2.The kinetics performance has been significantly improved.In-situ XRD and HRTEM analyses from room temperature to 673K showed that nickel nanoparticles participated in the dehydrogenation reaction of Mg H2 to form Mg2Ni phase.By means of PCI curves and van’t Hoff equation,it was found that the enthalpy change of dehydrogenation reaction of Mg H2-10 wt.%nano-Ni system was reduced by 4.4 k J/mol-H2,which further verifies that the nano-Ni additive not only plays a catalytic role,but also reduce the thermal stability of the system.（3）The Ni@Pt Ni3@Pt nano-particles was combined with Mg H2 and their mixture was mechanically milled.Tthe effect of the additive on the hydrogen storage performance of Mg H2and the catalytic mechanism were discussed.It was found that the initial dehydrogenation temperature of Mg H2-10 wt.%Ni@Pt Ni3@Pt sample can be reduced to 493K,and complete dehydrogenation can be achieved at 573K,with a capacity of 6.2 wt.%H2.At a temperature of475K and under a hydrogen pressure of 1.5 MPa,the sample can quickly absorb 5.7 wt.%of hydrogen within 1000s.It is worth mentioning that even under a pressure of 1.5 MPa,the reversible hydrogen absorption of the sample at 383 K can reach 3.9 wt.%.The in-situ XRD test from room temperature to 673K found that Mg6Ni and Mg3Pt phases appeared in the dehydrogenation reaction,and by observing the HRTEM image of the sample after the reversible hydrogen absorption treatment,the alloy phase in the reversible hydrogen absorption product disappeared.It shows that Ni and Pt metal nanoparticles induce the decomposition of Mg H2 at the microscopic level and react with it to form Mg6Ni phase and Mg3Pt phase,respectively.The calculations by PCI curve and van’t Hoff equation show that the desorption of Mg H2-10 wt.%Ni@Pt Ni3@Pt system.The hydrogen reaction enthalpy change decreased by6.8 k J/mol-H2,which further verified that both Ni and Pt in the Ni@Pt Ni3@Pt additive actively assisted the dehydrogenation process of Mg H2. |
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