Study On Water Splitting Of Strontium Titanate-based Heterojunction

The consumption of fossil energy causes global warming and energy shortage.Hence,the world is in an energy revolution to rid dependence on fossil energy.Hydrogen energy has the characteristics of green carbon free,highly energy density,high calorific value and renewable,which has attracted extensive attention and research.Photocatalysis technology has attracted attention because it can generate hydrogen energy or effectively degrade environmental pollutants with using solar energy,and the major challenge is to find an efficient,stable and economic catalyst.Perovskite oxides have attracted widespread interest due to their rich elemental composition and electronic structure.Among them,SrTiO₃ has a typical perovskite structureis.Furthermore,the SrTiO₃,with the suitable band edge position,low-cost,high photostability,and high carrier mobility,which is a promising photocatalytic material.However,SrTiO₃ has the disadvantages of poor visible light absorption and high photogenerated carrier recombination rate,which leads to the low catalytic activity of SrTiO₃.Therefore,this paper was based on the basic properties and research status of SrTiO₃,other materials were selected to construct heterojunction with SrTiO₃to enhance water splitting activity,and we proposed the possible reaction mechanism.The specific research contents were as follows:1.SrTiO₃/Ti₃C₂ Schottky heterojunction photocatalyst was prepared for photocatalytic H₂ evolution reaction（HER）.Ti₃C₂-MXene has the advantages of excellent metal conductivity,unique optical properties,large surface area,low hydrogen evolution reaction barrier and tunable hydrophilic functional groups.However,Ti₃C₂ cannot be used directly as a photocatalyst because it does not have the properties of semiconductor,so it was chosen to construct a heterojunction co-catalyst with SrTiO₃.Firstly,the SrTiO₃/Ti₃C₂T_X Schottky junction was constructed using hydrothermal method,and SrTiO₃ nanoparticles were deposited on the surface and between interlayers of 2D Ti₃C₂ nanosheets via SEM characterization.This unique structure facilitates the construction of fast charge transfer channels,which promotes the separation and migration of photogenerated charges and thus improves its photocatalytic performance.The SrTiO₃/Ti₃C₂ Schottky junction showed excellent photocatalytic HER performance,and optimal co-catalyst SM-3 exhibited a great hydrogen evolution reaction rate of 3.43 mmol g^-1h^-1,which was almost 6 times that of the SrTiO₃(0.57 mmol g^-1h^-1).The main reasons for the increased photocatalytic hydrogen production performance of SrTiO₃/Ti₃C₂ composites were:（1）Schottky junction was formed by SrTiO₃ and Ti₃C₂T_x,and the electrons were migrated rapidly from SrTiO₃ to metallic-like Ti₃C₂ under illumination,and the built-in electric field formed at the interface accelerates electron-hole separation and more efficient charge transport.Furthermore,the existence of the Schottky-barrier hinders the backflow of electrons from Ti₃C₂to SrTiO₃.Thus,the effective separation between photogenerated carriers is promoted and the photocatalytic activity of photocatalyst is improved.（2）The O-terminal and F-terminal functional groups of Ti₃C₂ reduce the charge transfer resistance and enhance the reactivity of the active site.（3）The absorption ability of the SrTiO₃/Ti₃C₂ composite material in the visible light range was improved.This work demonstrates a bright prospect to construct highly active,low-cost,and stable earth-abundant photocatalysts with 2D MXene and great application potential in energy conversion fields.2.SrTiO₃/Cd Se type-I heterojunction photocatalyst was prepared for photocatalytic HER.Cd Se is a narrow-bandgap semiconductor,which has strong visible light absorption,abundant surface binding properties,and tunable bandgap.However,it has the problems of fast photogenerated carrier recombination rate and photocorrosion.Therefore,the Cd Se/SrTiO₃ heterojunction was prepared via reflux condenser method in this paper.The Cd Se nanoparticles with smaller particle size were more uniformly grown on the surface of SrTiO₃ via the SEM,TEM and EDS characterization,it is beneficial to expose more reactive sites.The light absorption capacity of the SrTiO₃/Cd Se composite is significantly improved than that of SrTiO₃ via the UV-vis characterization.In addition,PL spectra,i-t curves,and EIS curves indicate that the interfacial contact of the heterojunction can shorten the transport path of photogenerated electrons,increase the separation of interface charges,reduce the recombination rate of photogenerated electrons and holes,and effectively improve the the separation and movement of interfacial charge carriers,which promoting the water splitting performance of SrTiO₃/Cd Se for hydrogen production.Similarly,the SrTiO₃/Cd Se heterojunction showed good photocatalytic water splitting hydrogen production performance via test results of the samples.Optimal SC-20 exhibited a great hydrogen evolution reaction rate of 856.1μmolg^-1h^-1,which is 2 times that of SrTiO₃(403.8μmolg^-1h^-1).