Configurations Of Ti Modified C₆H₆,C₄B₂H₆ And C₃B₃H₆ And Their Interaction With Hydrogen Molecules

Transition metals modified small molecular organic complexes have been studied in theory and experiment and need to be widely used in actual hydrogen storage.However,in the process of studying the adsorption of hydrogen molecules,the researchers only pay attention to the behavior of their physical adsorption of hydrogen molecules,and the possible chemical reaction process have received little attention.In fact,the dissociation and migration of adsorbed hydrogen molecules and the formation of C-H bonds are important for further understanding of hydrogen storage mechanisms.The physical adsorption of C₆H₆Ti shows that C₆H₆Ti can effectively adsorb 3 H₂ at temperatures below 210 K and completely desorb at 935 K.The relative Gibbs free energy and the minimum energy path of the continuous hydrogenation step of the C₆H₆Ti-nH₂（n=1-4）isomer indicate that the hydrogen molecules will continue to dissociate into hydrogen atoms after being adsorbed by the metal sites,and some hydrogen atoms will occur.The migration formed a stable CH bond,and C₆H₁₁Ti-3H was the final stable adsorption product,and its total reaction exotherm was 11.07 kcal/mol.The energy barrier of the forward reaction is 1.71 kcal/mol,and the energy barrier of the reverse process is 16.20 kcal/mol,which indicates that hydrogen can be quickly added and released by increasing/decreasing the hydrogen pressure.Up to 6.02 wt%,consistent with the experimental results of AB Phillips.Therefore,it is speculated that the hydrogen storage mechanism of C₆H₆Ti at room temperature is chemical adsorption rather than physical adsorption.The physical adsorption performance of C₄B₂H₆Ti indicates that the adjacent o-,m-, and para-C₄B₂H₆Ti can effectively adsorb four H₂,among which the single-state m-doped C₄B₂H₆Ti is the most stable,and the four H₂ are all released at 510 K,and the reversible hydrogen storage capacity reaches 6.08 wt%.The minimum energy path of C₄B₂H₆Ti-nH₂（n=1-5）hydride intermediates indicates that the H₂ adsorbed by metal Ti will gradually migrate,and the final hydrogenation product is C₄B₂H₁₂Ti-2H,and the total reaction exotherm is 19.69kcal/mol.The final step of chemical adsorption is the hydrogen migration of the third H₂,the energy barrier is 21.96 kcal/mol,and the reverse reaction energy barrier is as high as 42.58kcal/mol,indicating that the chemisorption process is difficult to reversibly at room temperature.It is speculated that the physical adsorption mechanism of C₄B₂H₆Ti is more suitable for practical hydrogen storage.The physical adsorption of C₃B₃H₆Ti shows that the meta-B doping of the doublet is the most advantageous.The formed C₃B₃H₆Ti can effectively adsorb 3H₂ at a temperature below 214 K,but due to the strong adsorption of the first H₂,H₂ can only be at 1881 K.Desorption completely,it is difficult to reversibly store hydrogen by physical adsorption at room temperature.The minimum energy path and total reaction potential energy surface diagram of hydrogenation of C₃B₃H₆Ti-nH₂（n=1-3）indicate that hydrogen molecules will migrate,and the final hydrogenation product is C₃B₃H₁₂Ti-H₂,and the total reaction exotherm is 18.37 kcal/mol.The positive reaction step is 15.49 kcal/mol.During the reverse reaction,the hydrogen migration of the second H2 and the hydrogen migration of the third H₂,the energy barriers are as high as 23.23 and 27.92 kcal/mol,respectively,and it is difficult to reversibly store H₂ at room temperature.Compared with C₆H₆Ti and C₄B₂H₆Ti,C₃B₃H₆Ti is not suitable for hydrogen storage materials.