Study On The Photogenerated Charge Behavior And PEC Water Oxidation Performance Of Hematite Based Photocatalyst: Insights From Surface And Interface

The quick development of the modern society raises new requirement and the traditional fossil energy face to dry up.Therefore,it is necessary to seek new energy to replace the traditional fossil energy.The photocatalytic hydrogen production using solar,a potential topic has been studied by the researchers.The photocatalytic reaction on a semiconductor contains three main steps:?1?the transition of electrons from valence band to conduction band and generation of photogenerated carriers;?2?the separation and transfer of the photogenerated carriers;?3?the participation in redox reaction for the photogenerated charges in the surface of semiconductors.The first process is the solar absorption for a semiconductor.The light absorption efficiency is related to its light absorption coefficient,which is the inherent property of a semiconductor material.In order to improve the photocatalytic efficiency and the utilization of sunlight,it is important to choose the narrow semiconductor with suitable conduction and valence band.The second process is the separation of the photogenerated charges.In order to enhance the separation efficiency,the construction of interface structure is often used to form the interface electric field.The third process is the injection of the photogenerated charges into electrolyte,then participating in the redox reaction.In this process,the common strategy is surface modification for photocatalysts to heighten the injection efficiency of photogenerated charges,including modification of cocatalyst and passivation of surface state.The anode reaction convert H₂O to O₂.It's gibbs free energy is greater than zero.So this reaction can't occur spontaneously in the thermodynamics.While the hydrogen evolution reaction is that the process of gibbs free energy is equal to zero.Therefore,it is of great importance to study the anodic reaction process for water splitting into hydrogen.This paper focuses on three process in photocatalytic reaction,choosing Fe₂O₃with narrow band gap as photoanode material.The photogenerated charges transfer behavior in interface between photoanode and FTO,and the relation with photochemical water oxidation were researched,using the method of the surface photovoltage spectra,the transient surface photovoltage and electrochemical methods.This paper contains two parts:1.The schottky barrier in Fe₂O₃/FTO interface hinders the photogenerated electrons transfer to FTO,because the work function of FTO substrate is higher than that of Fe₂O₃.Our work focused on the influence of the photogenerated electrons behavior in Fe₂O₃/FTO interface for oxidation performance of photoanode water by doping Ti⁴⁺?Cu²⁺to control the work function of Fe₂O₃.The experimental results show doping Cu²⁺can lower the work function of Fe₂O₃,which facilitates the photogenerated electrons transfer to the FTO substrate.However,the transfer resistance for photogenerated holes in Fe₂O₃ is also enlarged,and the injection efficiency of holes is reduced.Ti⁴⁺doping improves the work function of Fe₂O₃ and impedes the transfer of photogenerated electrons to FTO substrate.Moreover,the transfer resistance of photogenerated holes in Fe₂O₃ is reduced and the injection efficiency of holes is improved.Above all,Ti⁴⁺doping improves the water oxidation activity of Fe₂O₃photoanode,while,Cu²⁺doping reduces the water oxidation activity of Fe₂O₃photoanode.The optimal experiment of Ti⁴⁺doping Fe₂O₃ photoanode demonstrates the presence of the optimal amount of Ti⁴⁺doping,considering both the photogenerated electrons migration in Fe₂O₃/FTO interface and transmission of photogenerated holes in Fe₂O₃,which can improve the water oxidation performance for Fe₂O₃ photoanode.2.Fe₂O₃ serves as the recombination center with rich surface states increase the recombination of photogenerated charges on the surface of Fe₂O₃ photoanode.In order to reduce the recombination of photogenerated charges on the surface of Fe₂O₃ and improve the injection efficiency of holes,we passivated the surface states of Fe₂O₃through acetic acid corrosion.The results of the photovoltage show that acceptor surface states were passivated by acetic acid and the separation efficiency of photogenerated charges was improved.The results of the photoelectrochemistry indicate the acceptor surface states enhance the separation and the injection efficiency of photogenerated charges in Fe₂O₃ photoanode.The results of the experimental datas demonstrate the acceptor surface states enhance the water oxidation performance in Fe₂O₃ photoanode.