Research On The Enhanced Mechanism Of Carrier Transport At The Surface And Interface Of Polar Materials And Their Photo/Photoelectrochemical Performance

Research on the development of photoelectric conversion materials is one of the effective ways to tackle prevailing issues of energy shortage and environmental pollution.Among numerous photoelectric conversion materials,one of them,polar materials,which have an intrinsic dipole moment and lack a center of inversion symmetry,have a rich variety of physical effects and have occupied the spotlight in the study of catalytic systems.Polar materials have been found to promote the separation and transport of carriers at the surface and interface of the material in the catalytic process by the built-in electric field stimulated by external physical fields,thus enhancing the photoelectric conversion efficiency,and therefore researchers consider the development and utilization of polar materials as an ideal way to improve the catalytic performance.However,since the photoelectric conversion efficiency and stability of polar materials are not yet sufficient for practical production applications,which severely limits their application in commercial catalysis.Hence,it is imperative to develop polar photovoltaic materials with high performance.In this thesis,we aim to construct efficient photocatalysts based on polar materials（ferroelectrics and piezoelectrics）and adopt methods including surface modification engineering,heterostructure construction and external physical field introduction to achieve enhanced carrier separation and transport efficiency at the surface and interface of polar catalysts.The main studies in this thesis are as follows:（1）"Interfacial coupling effect-constructed heterojunction"strategy to synergistically regulate separation and transport of carrier at the surface and interface of photoelectrodesIn this work,FTO/La Fe O₃ and FTO/La Fe O₃/Nafion photoelectrodes were prepared by spin-coating and immersion-drying methods.And were applied to photoelectrochemical water reduction,respectively.After the surface modification of La Fe O₃ photoelectrodes by introducing Nafion organics,the photocurrent density of the photoelectrodes was increased to-23.9μA cm^-2（0.47 V vs.RHE）.In addition,its conduction band position was closer to the proton reduction potential of H⁺to H₂,and the maximum incident photon to current conversion efficiency value is also significantly increased by a factor of 5.The primary reason for the enhanced performance of photochemical water reduction is attributed to the interfacial coupling effect.The coupling of inorganic and organic materials can effectively modulate the electronic bonding between organic and inorganic units to form a homogeneous bonding interface.Meanwhile,the organic modification layer with can also passivate the structural defects at semiconductor/electrolyte interface and act as a charge transfer channel to promote charge separation and transfer.Thus,the photoelectrochemical water reduction performance and stability of the FTO/La Fe O₃/Nafion photoelectrode are enhanced compared to the FTO/La Fe O₃ photoelectrode.Our study provides new insights into the modification of inorganic semiconductor photoelectrodes with organic materials and promotes charge dynamics.（2）"Piezoelectric effect-constructed heterojunction"strategy to synergistically regulate separation and transport of carrier at the surface and interface of bi-piezoelectric materialsIn this work,Ba Ti O₃/Cd S bi-piezoelectric homogeneous heterojunction was grown using hydrothermal method and chemical bath deposition method.And this heterojunction was used to carry out degradation experiments of methyl orange organic dye solution under light,ultrasound and light plus ultrasound conditions using the piezo/photocatalytic effect.The results showed that the Ba Ti O₃/Cd S heterojunction exhibited significantly higher piezo/photocatalytic degradation activity（95.2%）within70 min compared to pure Ba Ti O₃ and pure Cd S.The main reason for the degradation performance enhancement is the dynamic piezoelectric built-in electric field due to the periodic ultrasonic field,which can effectively circumvent the problem of limited carrier separation and transport efficiency at the surface and interface due to the charge shielding effect.In addition,the dual piezoelectric coupling generates large energy band offset and enhances the piezoelectricity.A non-destructive external drive can be used to induce a strong built-in electric field.In this work,the significant advantages of bi-piezoelectric polar materials for photocatalytic degradation are highlighted.（3）"Piezoelectric effect-constructed flexible heterojunction"strategy to synergistically regulate separation and transport of carrier at the surface and interface of bi-piezoelectric materialsIn this work,a Bi₃Ti Nb O₉/PVDF flexible porous dual piezoelectric photocatalytic block with fluid-induced generation of piezoelectric fields was prepared by the molten salt method and the frozen phase change method.The piezo/photocatalytic performance of the catalyst was evaluated by the degradation experiments of the heterojunction on methyl orange organic dye solution.The prepared Bi₃Ti Nb O₉/PVDF dual piezoelectric heterojunction bulk（size 16.69 cm²）degraded methyl orange with an efficiency of 77%within one hour under light plus stirring conditions,which was 65%more efficient than that of the Bi₃Ti Nb O₉ powder sample with the same mass.The contact angle test showed that the flexible porous bi-piezoelectric bulk prepared by the frozen phase transformation method has good water affinity.Hysteresis loop and open-circuit potential tests provide direct evidence for the existence of fluid-induced piezoelectric fields on the Bi₃Ti Nb O₉/PVDF bulk.During the stirring process,the different deformation directions or degrees of the bi-piezoelectric bulk will lead to different initial times of piezoelectric potential generation,and the bi-piezoelectric fields will alternately break the charge shielding effect,thus accelerating carriers separation and transport.Meanwhile,considering the problems of subsequent recycling difficulties and easy agglomeration of powder to lose activity in practical applications,the photocatalyst powder is loaded on a flexible substrate,which is of great practical significance for the application of photocatalytic systems in practical commercial production and environmental purification.