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

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.