Two Dimensional Material As Efficient Cocatalyst For Oxygen Evolution Reaction(OER) In Photocatalytic Water Splitting

Photocatalysis,which drives a series of important chemical reactions with light has great potential in solving energy shortage and environmental problems.Water splitting is an important process of artificial photosynthesis,and water oxidation is recognized as the rate-determining step of water splitting.Semiconductors like WO3possess oxidative potentials for photocatalytic water oxidation.However,the efficiencies are generally low because of multiple electron transfer and fast charge recombination or other factors.Cocatalyst can effectively promote the separation of photoexcited charge carriers,reduce the over-potential of many reactions,and improve the catalytic activity of the semiconductor,which plays an important role in the photocatalytic process.Some semiconductor catalyst has been applied in photocatalytic water oxidation,such as WO₃ and BiVO₄.Because of the high stability and no obvious light corrosion,WO₃ has been widely used in photocatalytic water oxidation.In addition,RuO₂,IrO₂,etc.are common cocatalyst for photocatalytic water oxidation,but their scarcity and high cost limits their large scale application.Furthermore,their enhancement in photocatalytic water oxidation is still limited.So it is of great significance to develop cheaper and more efficient cocatalyst for improving the oxygen evolution of the semiconductor.With the discovery and development of graphene and other two-dimensional materials,more and more interesting properties of two-dimensional materials have been discovered.Monolayer of Ti_1-xO₂ nanosheet is a material that thickness is about nanometer,length is some micron with high crystallinity.Most importantly,its special two-dimensional structure makes it have many unique properties different from the bulk.The low dimension of the material makes band gap widen,leading to the optical and electronic properties have a certain change.It deserves further study in the field of photocatalysis.In this work,the two-dimensional lamellar Ti_1-xO₂ is prepared by stripping the lamellar titanate.After solid phase synthesis,proton exchange,swelling and centrifugation,the suspension of two-dimensional lamellar Ti_1-xO₂ is obtained.AFM tests show that the thickness of the obtained two-dimensional lamellar Ti_1-x O₂ is about1nm,which indicate it should be monolayer Ti_1-xO₂.The composite photocatalyst was obtained by combining WO₃ and the two-dimensional Ti_1-xO₂ layer.The composite photocatalyst significantly increased photocatalytic activity of water oxidation of WO₃.In addition,the two-dimensional lamellar Ti_1-xO₂ is more efficient in enhancing the catalytic activity of WO₃ than that of commonly RuO₂,IrO₂ cocatalyst.As the thickness decrease,the composite catalyst has a higher activity of photocatalytic water oxidation.Through the optimization of cocatalyst loading,heat treatment temperature and other parameters,optimal catalytic activity is obtained.Through the study of the light absorption,electron-hole separation and surface reaction,the mechanism of the photocatalytic of the composite material is explored.Furthermore,the dynamic test was carried out on the samples of WO₃ and the composite,and explains the effect of the cocatalyst on the activation energy of the system from the perspective of reaction kinetics.The research about two-dimensional lamellar Ti_1-xO₂ cocatalyst is of high efficiency and low-cost,which has long-term research value and application significance.