Microstructure And Performance Control Of Magnesium-based Hydrogen Storage Alloys

Energy crisis and environmental pollution are two major crises for mankind.The development of new energy sources and the low-carbon economy have become an urgent task in the 21st century.Hydrogen is considered to be the ultimate form of energy in the future world because of its advantages such as high calorific value,pollution-free,and wide sources.Magnesium is one of the hydrogen storage materials with the best application prospects due to its high hydrogen storage density(7.6wt.%),wide sources of raw materials,low cost,and environmental friendliness.However,magnesium has poor kinetic and thermodynamic properties,so it has not been widely used.In view of the above problems,the kinetic and thermodynamic properties of magnesium have been improved through alloying,system nano-metering,and doping modification methods.At the same time,its hydrogen absorption and desorption behavior and modification mechanism have been explored.This article provides theoretical data basis for further study of hydrogen storage alloys in this system.First of all,this article uses induction melting and mechanical ball milling to prepare Mg-x Ni-(20-x)Y(x=0,5,15,20)hydrogen storage alloys,and research the law of changes in the structure and properties of the alloys.The Mg-5Ni-15Y alloy contains a large amount of?-Mg phase,lath-shaped 18R-LPSO phase and a small amount of ternary eutectic structure(Mg+Mg₂₄Y₅+18R-LPSO phase),so the alloy has a large structure;The structure of Mg-x Ni-(20-x)Y(x=0,15,20)is composed of Mg phase and eutectic structure.Among them,the eutectic structure in Mg-15Ni-5Y alloy is a ternary eutectic structure composed of Mg+Mg₂Ni+14H-LPSO phase.Therefore,the alloy has a fine structure,many phase interfaces,a large amount of nano-scale14H-LPSO phase,and a large number of nano-scale powder particles after hydrogen absorption and desorption,so its hydrogen storage performance is the best.The hydrides in these four alloys grow up in a diffusion-controlled one-dimensional growth mode after nucleation.Therefore,the diffusion rate of H atoms determines the hydrogen absorption rate of the alloy.In addition,the reaction enthalpy and hydrogen desorption activation energy of the four alloys are lower than Mg H₂.In particular,the Mg-15Ni-5Y alloy has a hydrogen absorption and desorption reaction enthalpy,hydrogen desorption activation energy and initial hydrogen desorption temperature of 60.61k J/mol,56.91k J/mol,87.69k J/mol and 210^oC respectively.Moreover,the Mg-15Ni-5Y alloy absorbs 5.55wt.%of hydrogen within 1 min at 350^oC and 3MPa,and the total hydrogen absorption is 6.44wt.%,which is almost equal to the theoretical hydrogen absorption of the alloy.Secondly,the influence of the addition of MWCNTs on the structure and properties of Mg-x Ni-(20-x)Y(x=0,15,20)magnesium-based hydrogen storage alloys was studied.After TEM analysis,it can be seen that MWCNTs is evenly wrapped on the surface of the alloy particles,so that the powder particles of the magnesium-based hydrogen storage alloy are significantly refined and dispersed,and the thermodynamic and dynamic properties of the magnesium-based hydrogen storage alloy are significantly improved.Reduce the hydrogen absorption and desorption reaction enthalpy of Mg-15Ni-5Y alloy from 60.61k J/mol and 56.91k J/mol to 57.69 k J/mol and48.49 k J/mol,and increase the hydrogen absorption rate,so that the alloy can absorb5.72wt.%of hydrogen within 1 min at 350^oC and 3MPa.