| Photocatalytic/photoelectrochemical water splitting for hydrogen is one of promising way to develop clean energy.Titanium dioxide(TiO2),one of the most widely studied catalysts for water splitting,has attracted much attention.It is of great significance to study the intrinsic role of titanium dioxide in photoelectrochemical water splitting.Photoelectrochemical water splitting of TiO2 occurs at the interface of TiO2 and solution.Understanding interface changes can guide us in regulating interface reaction and controlling the reaction from the nature of the materials and helping us know better of the interface reaction mechanism.We studied the anatase TiO2 monocrystalline thin film(001)face.The photoelectrochemical properties of TiO2 were studied by adjusting the pH of solution.The key points were the influence of pH on photocurrent and the relationship between flat-band potential(Efb)of TiO2 and pH.In the final,the films were subjected to specific doping regulation,and the change of material properties were explored by combining the change of electronic structure.It pointed out the train of thought for studying the structure-activity relationship of materialsLSV curves under different pH solution were tested,and it was found that the photocurrent under different pH values was different at 1.23 V(vs.RHE).There was a minimum point appearing at pH of 8.95,and then the photocurrent increased with the increase of pH.At this time,the phase transition of surface water may occur.When pH was greater than 12,photocurrent basically did not increase with the increase of pH owing to the high concentration of hydroxide,and the oxidation of hydroxide dominated.We also found that the change of the Etb with the pH of solution did not conform to the Nernst relationship completely,known as-59mV/pH,by Mott-Schottky testing.It is suggested that the band edge energies are not controlled solely via surface protonation and deprotonation reactions,but also affected by surface states and proton intercalation.Electrochemical reduction treatment and vacuum annealing treatment of TiO2 film would make the Efb positive shift.However.Nb doping could negatively shift the Etb,and the higher the doping concentration,the more negative shiftAfter some doping treatment,we found that electrochemical reduction,vacuum annealing and low concentration Nb doping had little influence on the crystal structure and surface morphology of TiO2 single crystal films by XRD and AFM characterization.XPS characterization showed that electrochemical reduction and vacuum annealing shifted the binding energy of Ti2p and O1s toward the direction of low binding energy,while Nb doping shifted the binding energy of Ti2p and O1s toward the direction of high binding energy.And electrochemical reduction and vacuum annealing did not affect the valence band composition and the band gap did not change,while doping with Nb made the valence band changed and widen the band gap.The change of electronic structure caused the change of electrochemical properties of thin films.We found that photocurrent was increased by electrochemical reduction and vacuum annealing,and the photocurrent doped with 0.05%(molar content)Nb was higher than that without doping,but Nb doping with 0.5%(molar content)decreased the photocurrent.This indicated that a little amount of low valence Ti is effective to photocurrent,although doping could increase carrier concentration and conductivity,the amount of doping owned an optimal value.Carrier concentration was not the only factor affecting photocurrent,photocurrent may also be related to absorption wavelength,band position and reaction kinetics. |
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