Hydrogen Storage Property Study Of H₂Molecule Adsorption On LaFeO₃（100） Surfaces

Alkaline solution of ABO₃oxide as electrode materials not only with the higherelectrochemical reaction activity and the discharge capacity, but also the electrochemicalstorage hydrogen phenomenon has certain catholicity. So use the ABO₃oxides asnickel-metal hydride batteries anode material has the feasibility, with low cost, easyactivation, high discharge capacity and good chemical stability, ABO₃oxides can be appliedin the high energy nickel-metal hydride battery in the future.As Ni-M-H battery cathode material, people have different issues on hydrogen with aproton or atomic state form absorb on the rare earth perovskite-type complex oxides LaFeO₃,and after absorption of hydrogen element valence variation problem. So the adsorption of H₂on LaFeO₃（100） crystal surface and LaFeO₃（100） crystal surface with O vacant defect werestudied by first-principles based on the density functional theory （DFT）.In chapter3, the adsorption of H₂on two kinds of LaFeO₃（100） crystal surface arestudied by first principles. Preferred adsorption sites, adsorption energy, dissociation energyand electronic structure of the LaFeO₃（100）/H₂systems are calculated separately. It is foundthat H₂is adsorbed on the hollow site of LaFeO₃（100） surface which contains Fe atoms and Oatoms more favorably than on the other sites, while two—OH are formed on the LaFeO₃（100） crystal surface. The adsorption energy on the hollow site is2.139eV, belonging tostrong chemical adsorption; The interaction between H₂and LaFeO₃（100） surface is mainlydue the overlapping among H1s, O2s and O2p states, through which covalent bonds areformed between O and H atoms, the bond length is0.971. H₂O is formed after theoptimization of H₂adsorbed on the O top sites on two kinds of LaFeO₃（100） crystal surfaces,The adsorption energy on the Model Ⅰ O top site is negative. In other words, this adsorptionis unstable, it is easy to form a O vacant site after evaporation of H₂O molecule.In chapter4, the adsorption of H₂on two kinds of LaFeO₃（100） crystal surface with Ovacant defect are studied by first principles. Preferred adsorption sites, adsorption energy,dissociation energy and electronic structure of the LaFeO₃（100）/H₂systems are calculatedseparately. It is found that H₂is adsorbed on the hollow site of LaFeO₃（100） surface whichcontains Fe atoms and O atoms more favorably than on the other sites, while two—OH are formed on the LaFeO₃（100） crystal surface. The adsorption energy on the hollow site is2.206eV, belonging to strong chemical adsorption; The interaction between H₂and LaFeO₃（100）surface is mainly due the overlapping among H1s, O2s and O2p states, through whichcovalent bonds are formed between O and H atoms, the bond length is0.971. H₂O isformed after the optimization of H₂adsorbed on the O top sites on two kinds of LaFeO₃（100）crystal surfaces, The adsorption energy on the Model Ⅰ O top site is negative. In other words,this adsorption is unstable, it is easy to form a O vacant site after evaporation of H₂Omolecule. Compared with no O vacancy adsorption results, adsorption energy on the moststable structure is increased, it is easy to adsorb on the hollow site; adsorption energy on theO top sites on two kinds of LaFeO₃（100） crystal surfaces is decreased, so H₂is easy to adsorbon the O vacancy defect LaFeO₃（100） and formed–OH with O atomic from crystal surface.