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The Study On Electrochemical Preparation And Photoelectrochemical Properties Of Cu2O/TiO2 Heterojunction Films

Posted on:2019-05-22Degree:MasterType:Thesis
Country:ChinaCandidate:M Z ShaoFull Text:PDF
GTID:2321330569979475Subject:Materials Science and Engineering
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As a two-dimensional material,anatase TiO2 nanosheet is widely used in photocatalytic and optoelectronic devices due to its advantages such as non-toxicity,good light stability,strong oxidizing ability,and high activity?001?surface.However,TiO2 is a wide bandgap semiconductor with a bandgap width of 3.2 eV and can only absorb the ultraviolet light which is 5%in the solar spectrum.Further the photoinduced electron-hole pairs are easily recombined on the surface,which limiting the improvement of the photoelectric conversion efficiency.The TiO2 nanosheets were modified to broaden their optical absorption range,to increase separation and transportion efficiency of photoelectron-hole pairs,and thus,to expand their application in the field of photocatalysis and optoelectronics.In this dissertation,narrow bandgap Cu2O nanocrystals were loaded on anatase TiO2 nanosheets by different electrochemical methods,which allowed TiO2 to have photoresponse in the visible light range and increase the separation and transportion efficiency of photogenerated electron-hole pairs,to improve the photoelectric conversion efficiency and enhance its photochemical properties.The specific research contents are as follows:?1?Anatase TiO2 nanosheet arrays were prepared on FTO by using a hydrothermal method.The thickness of TiO2 nanosheets is 200300 nm,the length is 2.22.6?m,and the photocurrent density is 0.40?A/cm2.?2?Pure-phase Cu2O nanocrystals were loaded on TiO2 nanosheets employing potentiostatic method?I-t?at-0.4 V?vs.SCE?to fabricate Cu2O/TiO2heterojunction films.The results indicate that the photoelectrochemical performance of the specimen prepared in pH=8 electrolyte is excellent,and its photocurrent density is 8.41?A/cm2,which is 21.0 times that of pure TiO2nanosheet arrays.In the pH=7,8,9 electrolytes,the photoelectrochemical performance of the sepcimens obtained after 5 times deposition are optimum,and their photocurrent densities is 4.30,8.41 and 2.07?A/cm2,respectively.?3?Through cyclic voltammetry?CV?at potentials of-0.5+0.25 V?vs.SCE?,pure phase Cu2O nanocrystals were loaded onto TiO2 nanosheets to compose Cu2O/TiO2 heterojunction films.The results illustrate that the photoelectronchemical performance of the sample prepared in pH=8 electrolyte is excellent,and the photocurrent density is 15.87?A/cm2,which is 39.7 times that of TiO2 nanosheet arrays.In the pH=7,8,9 electrolytes,the photoelectron-chemical performance of samples gained after 3 times deposition are optimum,and their photocurrent densities is 11.02,15.87 and 5.55?A/cm2,respectively.?4?Pure-phase Cu2O nanocrystals were loaded onto TiO2 nanosheets by employing chronopotentiometry?CP?method at 0.050.40 mA/cm2 to prepare Cu2O/TiO2 heterojunction films.The results indicate that the photoelectron-chemical performance of the sample prepared at pH=8 is excellent,and its photocurrent density is 27.40?A/cm2,which is 68.5 times that of the TiO2nanosheet arrays.In the pH=7,8,9 electrolytes,the photoelectrochemical performance of the samples achieved at the current density of 0.25 mA/cm2 are optimum,and their photocurrent densities is 21.15,27.40 and 4.39?A/cm2,respectively.?5?Through chronoamperometry?CA?at a negative potential of-0.5 V and a positive potential of+0.25 V?vs.SCE?,pure-phase Cu2O nanocrystals were loaded on TiO2 nanosheets to constitute Cu2O/TiO2 heterojunction films.The results indicate that the photoelectronchemical performance of sample prepared in pH=8 electrolyte is the best,and its photocurrent density is 31.60?A/cm2,which is 79 times that of the pure TiO2 nanosheet arrays.In the pH=7,8,9electrolytes,the photoelectronchemical properties of the specimens prepared after 5,4 and 3 depositions are optimized,respectively,and their photocurrent densities is 16.83,31.60 and 9.59?A/cm2,respectively.?6?By comparing the above four electrochemical methods,it is found that Cu2O nanocrystals deposited by chronoamperometry?CA?were used to modify the TiO2 nanosheets to obtain the optimal photoelectrochemical performance.The optimum photocurrent density of samples prepared by four electrochemical methods is 8.41,15.87,27.40,31.60?A/cm2,respectively.In addition,it is also found that if Cu2O nanocrystalline completely cover the crystal plane?101?of anatase TiO2 nanosheets,and have moderate nucleation,small size,and uniform distribution on the crystal plane?001?of anatase TiO2 nanosheets,the photoelectronchemical properties of Cu2O/TiO2 heterojunction films is excellent.This is because that the synergistic effect of space charge layer between Cu2O and TiO2 and best adsorption ability of TiO2?001?crystal plane will increase the separation and transportation efficiency of photogenerated charge and accelerate the photocatalytic reaction of photogenerated charge on TiO2 surface.Therefore the photoelectron-chemical properties of Cu2O/TiO2 heterojunction will be improved.
Keywords/Search Tags:anatase TiO2 nanosheets, electrochemical method, Cu2O/TiO2 heterojunction, photoelectrochemical properties
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