Theory Study Of Hydrogen Storage Performance Of TM-doped(TM=Scandium, Titanium And Vanadium) Covalent Organic Frame

A number of research efforts have been made to design and find new hydrogen storage materials because of the high energy density,environmentally clean nature of hydrogen which is an alternative to our fossil fuels.Framework materials including metal organic framework?MOF?and covalent organic framework?COF?have attracted vast research attentions for the unique advantages such as large surface area,high porosity,good thermal stability,small crystal density and so on.A large number of papers have shown that boron substitution and metal doping could strengthen the interaction between not only metal and the substrate but also metal and hydrogen.Inspired by it,we designed a kind of boron-substituted two-dimensional COF structure-C₂₄B₆H₁₈.In the hexagonal cell of C₂₄B₆H₁₈,benzene molecule connects three B₂C₄H₄ units as a pivot.Metal atoms prefer to combine with B₂C₄H₄ unit rather than benzene molecule to form the active site for hydrogen storage.We expect to enhance the hydrogen storage performance of the framework structure by metal decoration.Firstly,the hydrogen storage behaviors of the Sc,Ti and V atoms decorated C₄B₂H₆ blocks were investigated by the density functional theory?DFT?calculations with the Gaussian 09 program.In these calculations,zero-point energy correction and basis set overlapping error correction were fully considered.The results show that Sc,Ti and V atoms in the decorated blocks bind to hydrogen molecules by the Kubas interaction.Each Sc,V atom in the decorated blocks can absorb four and three H₂ molecules at most,with the average binding energy 0.17 e V/H₂ and 0.36 eV/H₂,respectively.As for Ti,in C₄B₂H₆Ti₂:2nH₂?n=1,2,3?,one hydrogen molecule dissociated to hydrogen atoms.At the same time,the hydrogen average binding energy of C₄B₂H₆Ti₂:4H₂ and C₄B₂H₆Ti₂:6H₂ are only 0.04 e V/H₂ and 0.05 e V/H₂.Moreover,the hydrogen absorption process corresponding to n = 1 to n = 2 can't happen on account of the negative continuous adsorption energy of-0.16 e V.So in the following works,only Sc and V doped C₄B₂H₆ were considered further.The Sc and V doped C₄B₂H₆ were designed as the Sc and V doped C₂₄B₆H₁₈ COF and their structures and hydrogen storage properties were further investigated with DFT calculations by MS DMOL³ package.We confirmed that each Sc,V atom in C₂₄B₆H₁₈ can absorb four and three H₂ molecules at most,with hydrogen storage density 7.02 wt%,5.09 wt%,respectively.In general,Sc or V doped C₂₄B₆H₁₈ covalent organic frameworks are potential hydrogen storage materials,which are worthy of further study on the experiment synthesis.