Study On Photocatalytic Hydrogen Production Performance Of Strontium Titanate Promoted By Surface Oxygen Vacancies

As a typical perovskite structure（ABO₃）semiconductor material,SrTiO₃ is a promising photocatalyst for hydrogen production due to its high catalytic efficiency,excellent light corrosion resistance,stable chemical structure,low cost and environmental friendliness.However,because of the fast recombination of the photogenerated electron-hole,photocatalytic efficiency of SrTiO₃ is limited.The crystal structure of SrTiO₃is very stable because of high oxygen binding energy.Thus,the formation of oxygen vacancy for SrTiO₃ is difficult and the condition for oxygen vacancy generation in/at SrTiO₃ is very harsh,such as high temperature（more than 800℃）and high vacuum,Ar⁺ion beam sputtering,which limits the practical application.Therefore,it is necessary to develop low cost and mild reaction conditions for SrTiO₃oxygen vacancy formation.In this work,the SrTiO₃ nanosheets were prepared by the mixed solvothermal method（ethylene glycol-water）.The oxygen vacancies were generated on the surface of SrTiO₃ with the effect the hydrogen spillover,which promoted the transfer of photoelectron to the surface of the catalyst.And Surface oxygen vacancies effectively improved the separation of the photogenerated electron-hole and enhanced the photocatalytic hydrogen production performance of SrTiO₃.The research works are divided into following two parts:The first part:Pt was loaded on the surface of SrTiO₃ by photodeposition to obtained Pt/STO samples.And Pt/STO was calcined in N₂-H₂ mix gas.With the hydrogen spillover effect of Pt,hydrogen moleculars were splitted via dissociative chemisorption into hydrogen atoms with higher reducibility,and the oxygen vacancy was obtained on the Pt/STO surface at low temperature.The study shows that the surface oxygen vacancies of Pt/STO formed by calcining at 150℃for 3 h;the surface oxygen vacancis of Pt/STO rised,and a thin disorder overlayer appeared on the surface of SrTiO₃ at 400℃;and some of surface oxygen vacancies transferred to the interior of the crystal lattice to form bulk defects.With the increasing of hydrogenation temperature,the activity of Pt/STO enhances,and reaches the maximum at 400℃.The produced H₂ amount of Pt/STO-400-3 is about 3 times as high as that of Pt/STO.The activity of Pt/STO-600-3 is significantly lower than that at 400℃.It shows that the surface oxygen vacancies are responsible for the enhanced activity;while the bulk ones decreases the activity.The second part:Ni was loaded on the surface of SrTiO₃ by dip-molding and reduced via hydrogen reduction to obtained Ni/STO samples.The oxygen vacancy can be also generated by the hydrogen spillover effect of Ni,and improve the photocatalytic activity of SrTiO₃.It is found that the value of loaded Ni can also affect the activity,the optimum value of loaded Ni is 1 wt%,high or low value will decrease the photocatalytic activity.In addition,the pH of the reaction system is an important factor affecting the photocatalytic process.Under alkaline conditions,it is beneficial to the ionization of glucose to C₆H₁₁O₆^-,which can capture the photogenerated holes（h⁺）more effectively.And favor the photocatalytic hydrogen production.The optimum pH value is 12 in this reaction system.