Theoretical Research On Hydrogen Storage Properties Of Organic Small Molecules And Lithium Atomic Modified Inorganic Cluster Units And Their Porous Materials

The development of technology and times require energy as driving force.However,the widely used traditional energy resources cause serious environmental pollution problems.At present,many countries have been concentrated on the development of hydrogen energy.However,the problem of hydrogen storage has greatly limited the development of hydrogen energy,the realization of safe and efficient hydrogen storage is imminent.The application of porous materials in hydrogen storage has attracted much attention,especially Metal-Organic Frameworks?MOFs?.MOFs exhibit satisfactory hydrogen storage performance at low temperature,however the hydrogen uptake shrinks sharply at ambient temperature and only reaches about 1%of that at low temperature.In order to break through the bottleneck of hydrogen storage of MOFs materials at room temperature,the metal oxides in MOFs structure are supposed to be replaced by stable inorganic clusters with higher hydrogen adsorption efficiency for hydrogen storage at ambient temperature.For this reason,using density functional theory?DFT?,we first designed hydrogen-adsorbing cluster units Si₁₂C₁₂H₁₂?CONHLi?₁₂ and Si₁₂C₁₂H₁₂?CONLi₂?₁₂ with large surface area,using stable Si₁₂C₁₂H₂₄ clusters modified by organic small molecules and lithium atoms.Their maximum hydrogen-adsorbing and storage mass densities were 13.18 wt%and 12.6 wt%,respectively.The average binding energies of Si₁₂C₁₂H₁₂?CONHLi?₁₂·82H₂ and Si₁₂C₁₂H₁₂?CONLi₂?₁₂·84H₂ for each hydrogen molecule are 0.135 eV and 0.134 eV,respectively.On this basis,a MOF-like structure is constructed by using the functional cluster units mentioned above and connecting them with organic linkers.The hydrogen storage performance of the MOF-like structure is predicted by using the Grant Canonical Monte Carlo simulation?GCMC?.In order to simplify the calculation,we have tried to construct and study a new two-dimensional porous material consisting of lightweight clusters Si₂₀H₁₀?CN₂HLi₂?₁₀,Si₂₀H₁₀?CN₂H₂Li?₁₀and organic ligand 2,2'-dimethyl benzene[bc,kl],which have similar structures to metal-organic frameworks,called SMOF-1,SMOF-2 and Li@SMOF-1,respectively.The atomic force fields of the structure were obtained by fitting the potential energy curve calculated based on the first principle.Based on the fitting force field,GCMC simulated and predicted the hydrogen storage performance of the structure at low temperature and near room temperature.Specifically,the excess amount of hydrogen adsorption mass percentages of SMOF-1,SMOF-2 and Li@SMOF-1 at 77K&40bar were 12.11 wt%,10.49 wt%and 13.87 wt%,respectively.While,the hydrogen uptake excess amount of SMOF-1 and SMOF-2 at 243K&50bar were 4.91 wt%?34.52 g/L?and 3.38 wt%?24 g/L?.In particular,Li@SMOF-1 has excess amount of hydrogen storage 4.77 wt%under the condition of 300K&30bar.According to the theoretical calculation,the hydrogen uptake capacity of our structures achieved the target set by U.S.department of energy-4.5 wt%?30 g/L?.This study provides some new research ideas for hydrogen storage of MOFs porous materials at ambient temperature.