Theoretical Study On The Hydrogen-releasing Mechanism Of Li-Mg-N-H Hydrogen Storage System

Because of the higher hydrogen storage quality percentage density and certain reversible, In recent years, the M-N-H (M means the metal elements of I-IV)of metal complexes hydrogen storage materials have much more attentioned. Currently, about the study on Storage of hydrogen reaction mechanism of the M-N-H is very limited. In this paper, the reaction mechanism between (LiNH2)n(n=1,2) and LiH, the reaction mechanism between Mg(NH2)2and LiH and the reaction mechanism between NH3and MH(M=Li,Na) have been investigated by a B3LYP method of density functional theory. The reaction pathways and reaction mechanism has been studied.In chapter2, the reaction mechanism between (LiNH2)n(n=1,2) and LiH has been investigated by a B3LYP method of density functional theory, while the geometries and harmonic vibration frequencies of reactants, intermediates, transition states and products have been calculated at the B3LYP/6-311G(d,p) level, Vibration analysis and intrinsic Reaction Coordinates (IRC) calculation at the same level have been applied to validate the connection of the stationary points. To get a more accurate energy information, single point energy of stationary points in the reaction channel have been calculated at the MP2/6-311G(d,p) level, given the relative energy and the energy level diagram of the reaction process. The results indicate that the reaction between LiNH2and LiH has two stages; the reaction between (LiNH2)2and LiH has fore stages, and every stage has the similarity process of the reaction between LiNH2and LiH. In the process of the reaction between (LiNH2)n(n=1,2) and LiH, substitution of the H atom in-NH is easier than in-NH2. The released of two hydrogen atoms in H2are from (LiNH2)n(n=1,2) and LiH.In chapter3, the reaction mechanism between Mg(NH2)2and LiH has been investigated by a B3LYP method of density functional theory, while the geometries and harmonic vibration frequencies of reactants, intermediates, transition states and products have been calculated at the B3LYP/6-311G(d,p) level, Vibration analysis and intrinsic Reaction Coordinates (IRC) calculation at the same level have been applied to validate the connection of the stationary points. To get a more accurate energy information, single point energy of stationary points in the reaction channel have been calculated at the QCISD/6-311G(d,p) level, given the relative energy and the energy level diagram of the reaction process. The results indicate that the reaction has three stages, the first step of hydrogen substitution, the second step of hydrogen substitution and Isomerization after the removal of hydrogen. There are two pathways, in which corresponding to the channel of the second step of alignment hydrogen substitution reaction is the main channel. The released of two hydrogen atoms in H2are from Mg (NH2)2and LiH.In chapter4, the reaction mechanism between NH3and LiH(NaH) has been investigated by a B3LYP method of density functional theory, while the geometries and harmonic vibration frequencies of reactants, intermediates, transition states and products have been calculated at the B3LYP/6-311G(2d,2p) level, Vibration analysis and intrinsic Reaction Coordinates (IRC) calculation at the same level have been applied to validate the connection of the stationary points. To get a more accurate energy information, single point energy of stationary points in the reaction channel have been calculated at the QCISD/6-311G(2d,2p) level, given the relative energy and the energy level diagram of the reaction process. The results indicate that the reaction between NH3and LiH(NaH) are single-channel hydrogen substitution reaction, the reaction products are LiNH2(NaNH2) and H2.