Investigations On Stability And Mechanical Properties Of Hydrogen Storage Materias Palladium-rhodium Dihydride Alloys

Hydrogen storage material is a hot issue in recent decades.In 2011,the RhH₂ was synthesized with high pressure compressing.Driven by this discovery,researchers are interested on the hydrogen storage investigation of platinum group metals.As is known,the properties of materials decide their applications.Therefore,the study of mechanical properties of materials helps to guide their engineering applications.In this thesis,the formation possibility,stability,electronic structures of palladium and palladium-rhodium dihydride alloys(Pd_xRh_1-xH₂,x=0,0.25,0.5,0.75,1)have been studied by applying density functional theory of ab initio method under higher pressure.After determination of formation possibility,the mechanical properties and Debye temperature were further investigated.The Pd concentration influence on the properties of Pd_xRh_1-xH₂ was further discussed.Firstly,based on the crystal structure of RhH₂,the Pd_xRh_1-xH₂ were modeled by partial substituting Rh atoms with Pd atoms.The structures were optimized and the total energy were obtained.In order to analysis the formation possibility of Pd_xRh_1-xH₂,the formation enthalpy under high pressure were calculated.It is found that PdH₂,Pd_0.25Rh_0.75H₂,Pd_0.5Rh_0.5H₂ and Pd_0.75Rh_0.25H₂ can be formed under high pressure.Based on experiments,the formation reaction process of Pd/Rh dihydride alloys were further investigated.The formation pressure of Pd/Rh dihydride alloys were obtained by our calculations.The electronic properties of Pd_xRh_1-xH₂ also have been studied by calculating their density states.Based on the obtained equivalent structures,the elastic constants of RhH₂ were studied under high pressure.The mechanical stability and dynamical stability of RhH₂under various pressures have been investigated.The structure,elastic constants,elastic modulus,Poisson's ratio,elastic isotropy,plastic/brittle,sound velocity,Debye temperature of RhH₂ as a function of pressure have been further studied.The ideal strength of RhH₂ have also been studied.This work has reported the mechanical stable pressure of RhH₂.The obtained mechanical parameters of RhH₂ for various pressures can support necessary theoretical guiding for its engineering applications.The mechanical stability and dynamical stability of PdH₂ have been studied under higher pressure.The structure,elastic constants,elastic modulus,Poisson's ratio,elastic isotropy,plastic/brittle,sound velocity,Debye temperature of PdH₂ as a function of pressure have been investigated.The ideal strength of PdH₂ also have been studied.The necessary mechanical parameters are also obtained.The Pd/Rh dihydride alloys system is the high light of this thesis.The mechanical stability of Pd_0.25Rh_0.75H₂,Pd_0.5Rh_0.5H₂ and Pd_0.75Rh_0.25H₂ were studied by first principal theory under high pressure.The mechanical stable pressure of three compounds have been reported.The structure,elastic constants,elastic modulus,Poisson's ratio,elastic isotropy,plastic/brittle,sound velocity,Debye temperature of PdH₂ as a function of pressure have been investigated.Combining with the results of RhH₂ and PdH₂,the relation of Pd concentration of Pd_xRh_1-xH₂ with mechanical and thermal properties have been further discussed.This thesis have guided the formation of Pd_xRh_1-xH₂ system on experiments.And the relevant theoretical parameters of Pd_xRh_1-xH₂ system are supported for their engineering applications.