Research On Degradation Mechanism Of LaNi_5-xAl_x Hydrogen Storage Alloy By EXAFS

Energy is an important material basis for the development of today's economic society.With the development of economic society energy consumption continues to grow.The development and use of traditional fossil energy has led to many environmental problems.Hydrogen energy has many attractive advantages,such as high energy density,rich reserves and almost no pollution.As a new energy,hydrogen will be applied in various living aspects of human beings.However,with the ab-/desorbing hydrogen cycle,the hydro gen storage properties of the alloy will decline,mainly reflects that the reducing of reversible hydrogen storage capacity and increasing of ab-/desorption hydrogen plateau slope,and the alloy will gradually convert into particles with micron metres sizes.These are unfavorable to the engineering application.LaNi_5-xAl_x?x=0.25,0.5,0.75,1?alloy were chosen as studing subject in present work.Synchrotron radiation extended X-ray absorption fine structure?EXAFS?,hydrogen storage performance integrated test system were used to systematically study the LaNi_5-xAl_x hydrogen ab-/desorption properties,thermodynamic and dynamics properties,and the fine structure around N i/La atoms,including coordination number,bond length and the degree of thermal disorder.The main results of the study on the intrinsic degrading mechanism of hydrogen storage properties of alloys are as follows.The study on the long-term cycle of hydrogen absorption and desorption of LaNi_5-xAl_x alloy shows that LaNi_5-xAl_x alloy is composed of single phase CaCu5 structure.With the increase of Al content in the alloy,the lattice parameters and the cell volume increase,the absolute value of the enthalpy of the reaction increases,the plateau pressure of the absorption and desorption hydrogen decreases,and the hydrogen absorption kinetic performance is improved.The main reason for the performance degradation of LaNi_5-xAl_x alloy is the crystal structure defect or disproportionation reaction.The disproportionation reaction plays a major role in the process of hydrogen absorption and desorption.The rate of disproportionation reaction increases first and then decreases with the increase of circulation.Through the analysis of the atom spacing between N i-N i and N i-La of simulation results of LaN i4 Al,the stress has been released in the activation process of the sample,the internal stress of the sample decreases gradually until it reaches the best,and promoting hydrogen ab-/desorbing of alloy at the same time,so that the cell volume expansion,the distance between atoms increase.However,with the cycles continuing,hydrogen absorption and desorption capacity of the sample decrease,the volume of the cell does not expand with the hydrogen absorption and desorption.The increase of the internal stress leads to the destruction of the lattice and the increase of the crystal defects,thus the thermal disorder increases.Therefore,the experimental results show that the properties of LaN i4 Al hydrogen storage alloys are mainly affected by structural defects.