Fabrication Of High Efficiency Ti-based Oxide Composite Photoanodes And Their Photoelectrochemical Properties Studies

Nowadays,non-renewable fossil fuels account for nearly 80%of the current energy structure.With the consequent problems of energy failure and environmental pollution,it is urgent to develop and utilize renewable energy.Photoelectrochemical（PEC）water splitting is intended to convert the abundant solar energy into storable hydrogen energy,making it become a promising development direction in the new energy field.The processes of PEC water splitting involve solar absorption,the separation and transport of photo-induced chagre,and their collection.The key to achieve high efficiency of PEC water splitting is to develop excellent photoanodes.TiO₂ has been regarded as one of the most promising materials as photoanode by virtue of its favorable band edge position,high stability,strong optical absorption,and inexpensive cost.Nevertheless,TiO₂ is a typical wide band gap semiconductor which limits its activity to only UV radiation.Besides,its low electron mobility and carrier concentration lead to poor charge separation and transport.Therefore,some modified methods are needed to be applied to TiO₂ to enhanced its light absorption,charge separation and transmission,finally achieving efficient TiO₂ based photoanode.At the same time,it can combine with efficient visible light absorption materials,BiVO₄,to construct heterostructure photoanodes,further enhancing their PEC performance.Based on these,the main achievements of this paper are as follows:Based on the model for the structure-property relationship of photo-catalytic materials,the least dense polymorph of TiO₂,TiO₂-B,is chosen as photoanode to be investigated.TiO₂-B nanowires are prapered to construct ordered charge transport channel and its structure analysis indicates its possesses efficient electron mobility along the axis of the nanowire.Oxygen deficient black TiO₂-B nanowires are prapered through hydrohen plasma reduction.Black TiO₂-B nanowires are the first time used as photoanodes for PEC water-splitting and achieve 0.85 mA cm^-22 photocurrent density at1.23 V_RHE.The enhanced PEC performace is due to its increased light absorption,good conductivity induced by oxygen vacancies and efficient surface hole extraction.In order to further increase the PEC performance of TiO₂-B photoanode,anatase,which possesses efficient hole transport and extraction,is used to construct TiO₂-B/Anatase type II heterojunction photoanode.By further reduction treatment,the final reduced TiO₂-B/Anatase photoanode is fabricated.This photoanode simultaneously obtains efficient charge separation,excellent electron and hole transport,and prominent surface hole transfer.Hence,all its PEC processes are optimized,achieving unlimited electron and hole collection even at low applied potential.Finally,this photoanode achieves 1.59 m A cm^-22 photocurrent density at 1.23 VRHE.Although the reduced TiO₂ can absorb a lagre portion of visible light,its photoelectric conversion efficiency is such low.In order to efficient utilize visible light,BiVO₄ is used to construct TiO₂-BiVO₄ heterostructure photoanode.In consideration of band structure matching and efficient electron transport,Nb doping rutile TiO₂ is chosen as electron conductor to support BiVO₄.Through charge dynamics studies,it is found that the low charge injection efficiency accounts for the main limiting PEC perfoamcne.By gradient W doping in the BiVO₄ guest,the band structure of BiVO₄ is properly modified,obtaining simultaneous enhancements in charge collection and charge injection.The final photoanode achieves 4.43 mA cm^-22 photocurrent density at1.23 V_RHE.Note that the introduction of oxygen vacancies can improve light absorption and charge transport,reduction modified method is applied to BiVO₄ to further enhance its light absorption and charge transport.In consideration of that oxygen deificent TiO₂overlayer possesses high activity of oxygen evolution reation,amorphous TiO_2-x-x coating reduced BiVO₄ photoanode is designed to achieve stable and efficient PEC water splitting.The designed photoanode not noly retains high light absorption efficiency,efficient charge separation and transport of reduced BiVO₄,but also realizes long term stability and prompt surface hole transfer,finally achieving 5.62 mA cm^-2photocurrent density at 1.23 VRHE.