Research On The Intrinsic Degradation Mechanism Of Hydrogen Storage Performance Of LaNi_5-xCo_x Alloy Based On Synchrotron Radiation Technology

Energy is an important material basis with the development of today's economic society.For the development of economic society energy consumption continues to grow.The and use of traditional fossil energy has led to too many environmental problems.Hydrogen energy has many attractive advantages,such as high energy density,rich reserves and using without pollution.As a new energy,hydrogen had been applied in various living aspects of human beings and there will be more aspects.However,with the ab-/desorbing hydrogen cycle,the hydrogen 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 dismissed to the engineering application.LaNi5-xCox(0.25,0.5)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 LaNi5_xCox hydrogen ab-/desorption properties,thermodynamic and dynamics properties,and the fine structure around Ni atoms,mainly 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 LaNi5-xCox alloy shows that LaNi5-xCox alloy is composed of single phase CaCu5 structure.With the increase of Co 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 LaNi5-xCox alloy is the disproportionation reaction or crystal structure defect.The disproportionation reaction plays a major role in the process of hydrogen absorption and desorption.And the rate of disproportionation reaction increases first,then decreases with the increase of circulation.Through the analysis of the atom spacing between Ni-Ni and Ni-La of simulation results of LaNi5,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.