Study On Synthesis And Hydrogen De/Absorption Properties Of Mg-based Hydrogen Storage Materials

MgH₂ is considered to be one of the most potential hydrogen storage materials due to its high hydrogen storage capacity,good reversibility,low cost,abundant reserves,and environmental friendliness.However,MgH₂ has its own shortcomings such as high desorption temperature and poor hydrogen absorption/desorption kinetics which hinders the practical application of MgH₂.In view of the above problems,the research progress of magnesium-based hydrogen storage materials at home and abroad is reviewed in this paper,and the route for improving the hydrogen storage performance of MgH₂ was designed by using catalyst additives.CeB₆/CeF₃@CNTs,CeF₃@Gn and MnO₂ were prepared and its effects and mechanisms were systematically studied.First,CeB₆/CeF₃@CNTs were prepared and milled with MgH₂ for the purpose of enhancing the hydrogen storage performance.The experimental results show that,the addition of CeF₃@CNTs has eminent effects on the initial hydrogen release temperature and the peak hydrogen release temperature,and the kinetic performance of MgH₂.The MgH₂ without catallyst additive releases only 0.2wt%H₂ at 270?within 36 minutes,while the MgH₂+CeB₆@CNTs sample shows eminent improvement in hydrogen release rate,it releases 3.64wt%H₂ under the same conditions.MgH₂+CeF₃@CNTs shows the fastest hydrogen desorption rate,which reaches 6.04wt%under the same conditions.The microstructures and hydrogen storage performance of CeF₃@Gn-catalyzed MgH₂ system were investigated,and the results indicated that CeF₃@Gn synergistic catalysis can significantly reduce the thermal stability of MgH₂ and improve its thermodynamic properties.The initial hydrogen release temperature of MgH₂+CeF₃@Gn was lower than that of other contrast samples.And MgH₂+CeF₃@Gn has the best hydrogen absorption and desorption kinetics performance.At 275?,the MgH₂+CeF₃@Gn can release 6.35wt%hydrogen within45 minutes.Under the conditions of 150?and 3 MPa,the hydrogen absorption capacity of MgH₂+CeF₃@Gn within 50 s reaches 5.71wt%.SEM and XRD analysis show that CeF₃@Gn synergistic catalysis makes more MgH₂ generated during the sample preparation process,which helps to reduce the particle size,thus provides a fast channel for H atom diffusion,and the element F has a larger electronegativity,which can increase the dissociation and recombination rate of H₂ on the surface of the hydrogen storage material.In addition,the formation of byproducts CeH_2-3 and MgF₂provides catalytic active centers for H atoms and reduces the diffusion barrier of H atoms,therefore effectively improves the hydrogen storage performance of MgH₂.Te effects of MnO₂ addition and wet ball milling on the microstructure and hydrogen storage performance of MgH₂ were investigated,and the experimental results show that MgH₂+MnO₂ has excellent hydrogen absorption and desorption kinetics properties.At 270?,the hydrogen desorption capacity reaches 5.98wt%within 10 minutes.And under conditions of 150?and 3 MPa,the hydrogen absorption capacity reaches up to 5.6wt%within 30 s.It is found that both wet ball milling and MnO₂ addition are beneficial to reduce the reaction barrier of hydrogen desorption,thereby improving the kinetics of hydrogen evolution of magnesium-based hydrogen storage materials,and due to the multivalent existence of Mn element.In the process of reaction,"electron effect"is caused by the change of valence state,and excess electrons are transferred from the catalyst to MgH₂,which lead to the improvement of the hydrogen storage performance of MgH₂.