Doping Effects On Hydrogenation And Dehydrogenation Properties Of Complex Compound And MOF-5:Multiful Simulation Studies

Using DFT and GCMC methods,we performed mutiful simulation studies on typical hydrogen storage materials.This paper is mainly divided into two parts.Part one studies the effects of different additives on the dehydrogenation properties of largely studied metal complex LiBH4 and NaAlH4.Part two mainly studies the hydrogenation properties of MOF-5,this will give a helping hand to experimental preparations.For dehydrogenation of LiBH4,Nb doped its(010)surface has been studied.The most stable adsorption position of Nb on the surface is the top of the B atom,followed by the bridge position of the two B atoms.NbH2 and NbB2 phase are generated.The Nb atom has an electron "giving" effect to the B atoms,which makes the B negative polarity decrease.This benefit to the removal of H atoms.For dehydrogenation of NaAlH4,the catalysis of Ti and Nb on the bulk and(001)surface has been studied.Ti and Nb occupy at Al sites in bulk.The presence of H vacancies plays an important role in Ti(Nb)doping systems.Ti and Nb in surface occupy at the internal site below subsurface layer.In Ti-doped NaAlH4,both TiAl,and TiHx phases are generated.In Nb-doped NaAlH4,there are also NbAlx and NbHx phases exist.Li2Ti and K2Ti co-doped NaAlH4 are then studied.In Li2Ti doping system,the formed Ti-H phase is stronger than that in K2Ti doping,whilst the formed Ti-Al phase is weaker than that in K2Ti doping.For hydrogenation of MOF-5,at 77 and 297 K,the ADC-doped systems is better than pure MOF-5 for hydrogenation when the pressure exceeds a certain value.Comparied with the original BDC linker in MOF-5,the ADC chains hold more active electrons,which can polarize the surrounding hydrogen.The length of the chain is longer and the larger aperture is introduced,which reduces the steric resistance effect during the hydrogenation process.The doping of Ni or Ca exerts no obvious effect on promoting H2 absorption.