First-principle Study On The Effect Of Oxygen Vacancy On The Electronic Structure And Hydrogen Production Properties Of Anatase TiO₂

With the increasing consumption of fossil energy,environmental pollution and energy shortage have attracted widespread attention.As a kind of green energy with high calorific value,hydrogen energy has become the focus of research.The key of its future development is to seek an efficient and economical preparation method.Researchers have made continuous efforts to develop a variety of highly efficient photocatalysts,and the semiconductor based photocatalytic water splitting technology using solar energy has been rapidly developed.Among them,TiO₂semiconductor photocatalyst is widely used because of its stable chemical properties and high photocatalytic activity.In view of the shortcomings of TiO₂,some researchers adjusted the electronic structure characteristics and photocatalytic reaction performance of TiO₂by introducing oxygen vacancies.However,it is difficult to explore the effects of oxygen vacancies on the structure,properties and chemical reaction process of the catalyst from the microscopic electronic level.Therefore,the effect of oxygen vacancy on the electronic structure of different surfaces of anatase TiO₂and the mechanism of photocatalytic hydrolysis for hydrogen production were studied mainly through first-principles calculation.（1）The CASTEP software package was used to study the electronic properties of the surface of intact and defective anatase TiO₂（001）and（101）,and the reaction mechanism of hydrolysis to hydrogen.The geometric structure,electronic structure and optical properties of anatase TiO₂（101）and（001）surfaces were calculated,and the effect of oxygen vacancies on the photocatalytic properties of the two surfaces was analyzed and discussed.The results show that after introducing oxygen vacancies on the surface,the valence band and conduction band positions of the TiO₂（001）-OV surface are higher than those of the TiO₂（101）-OV surface,indicating that the photogenerated electrons on the TiO₂（001）-OV surface have a stronger reducing ability.While the photo-generated holes on the surface of TiO₂（101）-OV have a stronger oxidizing ability.At the same time,the stable adsorption configurations of a single water molecule on the four surfaces of intact and defective anatase TiO₂（001）and（101）were determined.Through the analysis of charge density and density of states,the relationship between water molecules and different surfaces was discussed.Based on the stable adsorption configuration of a single water molecule,the different hydrogen production reaction paths for water molecules on the above four surfaces were designed to obtain the activation energy of different steps in the reaction process.The reaction mechanism of hydrogen production by water splitting on different surfaces and the relationship between surface properties and reactivity are analyzed.The research results show that the introduction of surface oxygen vacancies can effectively reduce the activation energy of the rate control step,and the activation energy of the hydrogen production reaction on the TiO₂（001）-OV surface is lower than that of the TiO₂（101）-OV surface.（2）The effect of oxygen vacancy concentration on the electronic structure and catalytic performance of anatase TiO₂（101）surface was studied experimentally and theoretically.Black TiO₂nanotube arrays were prepared by anodic oxidation and aluminium reduction.The experimental XRD patterns of TiO₂samples and the simulated XRD patterns of TiO₂crystals were analyzed and compared.The results show that the existence of oxygen vacancies will cause the changes of the crystal structure of TiO₂,and it is also proved that it is feasible to simulate the TiO₂samples obtained by using the TiO₂surface model with different oxygen vacancy concentration.In addition,by analyzing the band structure,density of states and charge density,the effect of different oxygen vacancy concentration on the properties of anatase TiO₂（101）was investigated.The results show that moderate oxygen vacancies can impr OVe the ability of electronic transitions.In particular,the transition states of disintegration of H₂O on different surfaces are simulated.The analysis of the reaction activation energy show that the existence of oxygen vacancy can indeed promote the hydrolysis reaction,but too high concentration of oxygen vacancy will weaken its promotion effect.