Preparation And Hydrogen Evolution Performance Of Ru-Co Modified Nb-Ta₃N₅-based Nanocomposite Photocatalyst

With the increasing demand for resources,human beings are facing the problem of energy shortage,at the same time,the combustion of fossil energy releases greenhouse gases,causing climate change and sea level rise,and the emission of harmful gases will cause environmental pollution.Therefore,the development of new clean energy has become a national development strategy.Hydrogen energy is a kind of clean secondary energy,with the advantages of high energy density,high calorific value of combustion,storability,zero pollution and zero carbon emission.It helps to solve the problems of energy crisis and environmental pollution,and is known as the"the cleanest energy"in the 21st century.Photocatalytic water-splitting for H₂ is regarded as a green technology to alleviate the energy crisis.To efficiently utilize the visible light occupying the main part of solar spectrum,the development of visible-light-driven photocatalysts is one of the most promising ways.Ta₃N₅-based materials with valence band position straddling the redox potential of water and proper bandgap（～2.1 e V）,has high theoretical solar-to-hydrogen（STH）energy conversion efficiency（about 15.9%）.However,its practical application is seriously limited due to its low charge carrier migration rate,easy recombination of carriers,easy to light corrosion and poor stability.The morphology controlled synthesis process of precursor Ta₂O₅ was studied by using mixed molten salt assisted technology.Hexagonal Ta₂O₅and tetragonal Ta₂O₅ were prepared by adjusting hydrothermal time,type of molten salt,ratio of mixed molten salt and mass ratio of Ta₂O₅to mixed molten salt.The results show that when the hydrothermal time is 3 h,the ratio of KCl to KBr is 4:1,and the mass ratio of tantalum oxide to mixed molten salt is 1:2,the hexagonal Ta₂O₅has clear edges and good dispersibility.With the increase of the mass ratio of Ta₂O₅to mixed molten salt,the morphology changes from hexagonal to hexagonal.When the mass ratio of Ta₂O₅to mixed molten salt is 1:4,the tetragonal sample has the best dispersion.By using bulk doping and surface modification technology,the multi-heterostructure Ta₃N₅ based photocatalyst was constructed,and the regulation rules and related mechanisms of material structure and performance were studied.Tetragonal Nb-Ta₂O₅@Ta₃N₅ was prepared by high temperature nitridation of Nb in situ doped Ta₂O₅;then,NbN/Ta₃N₅/Ta₂O₅,RuO₂/Ta₃N₅/Ta₂O₅,Co₂N/Ta₃N₅/Ta₂O₅multiple heterostructures were selectively constructed on the surface of Ta₃N₅using Ru³⁺,Co²⁺/Co³⁺as modifiers by photooxidation deposition and high temperature nitridation reduction technology.The results show that the carrier separation efficiency of Ta₂O₅@Ta₃N₅is significantly improved by Nb-Ru-Co co-modification,and the photocurrent is 4.15μA·cm^-2,which is significantly higher than that of Nb-Ta₂O₅@Ta₃N₅(1.6μA·cm^-2)and Ta₂O₅@Ta₃N₅(0.9μA·cm^-2);The formation of multiple heterojunctions synergistically reduced HER overpotential of 46 m V and OER overpotential of 397 MV,providing active sites for hydrogen and oxygen production;the formation of Co₂N/Ta₃N₅heterogeneous interface significantly reduces the increased charge transfer resistance at the interface between NbN/Ta₃N₅and RuO₂/Ta₃N₅;the formation of Nb-N,Ru-O and Co-N bonds further confirmed the existence of multiple heterostructures;the increase of microporous pores is helpful to provide more active sites;the activity of visible light photocatalytic hydrogen evolution is 1343.02μmol·g^-1·h^-1,which is 2.46 times of Ta₂O₅@Ta₃N₅.Under the irradiation of 420 nm monochromatic light,the apparent quantization efficiency（AQE）is 5.54%,and the STH is 2.30%.It provides a new way to design high-performance Ta₃N₅ based photocatalyst with multiple heterostructures for hydrogen production.